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Analysis of elemental distributions in minerals and rocks by microwave-assisted continuous leaching on-line with inductively coupled plasma mass spectrometry

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Analysis of elemental distributions in minerals and rocks
by microwave-assisted continuous leaching on-line with
inductively coupled plasma mass spectrometry
By
Milithza O. Silva M.
A thesis submitted to the Department of Chemistry
in conformity with the requirements for
the degree of Master of Science
Queen's University
Kingston, Ontario, Canada
November 2004
Copyright © Milithza O. Silva ML, November 2004
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Abstract
Continuous on-line leaching with Inductively Coupled Plasma Mass Spectrometry
(CL-ICP-MS) is a novel technique that can quickly assess the mobility and
fractionation of elements in soils. It involves pumping different reagents sequentially
through a micro-column containing the soil sample while continuously monitoring the
released analytes by ICP-MS.
Previous studies of CL-ICP-MS employed a high
resolution ICP-MS (ICP-HRMS) instrument equipped with a micronebulizer to
demonstrate its application to the analysis of minerals in ore samples. However, the
long sample analysis time, from the slow mass scanning rate of HRMS, hinders its
feasibility in exploration geochemistry.
Focused-microwave
heating
was
used
in
combination
with
simultaneous
multielemental detection through ICP-TOFMS (ICP-time-of-flight mass spectrometry)
at a higher flow rate to speed up the continuous leaching of soils. Heating the micro­
column to 90°C using focused-microwave energy significantly enhanced the release
of analytes, by up to an order of magnitude. This was achieved without any increase
in the time needed for the whole fractionation study, which is about 16 minutes and
is substantially shorter than the several hours that are required for typical procedures
using CL-ICP-HRMS.
Analysis of single minerals as well as a complex sample showed that the flow rate of
reagents through the sample had an effect on the leaching profile, but the
simultaneous application of microwave energy, which speeded up the kinetics of
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dissolution, essentially compensated for the shorter residence time, yielding profiles
fairly similar to those obtained at low flow rate with a micronebulizer and 1CP-HRMS.
iii
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Co-Authorship
All work contained in this thesis was carried out by the author in the Department of
Chemistry at Queen’s University under the supervision of Dr. Diane Beauchemin and
Dr. T. Kurt Kyser.
iv
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Acknowledgments
1 would like to express my sincere gratitude and appreciation to Dr. Diane
Beauchemin for her expertise, guidance and patience throughout the course of this
project.
Many thanks are also extended to Dr. T. Kurt Kyser and his group for their advice
and support, and for providing all the samples used in this research. In particular, I
owe special thanks to April Vuletich, Dr. Don Chipley and William MacFarlane for
their assistance in the operation of the ICP-TOFMS instrument and valuable input
regarding continuous leaching.
I would like to thank CEM Corp. for generously lending the microwave
instrumentation.
The financial support from the School of Graduate Studies and Research of Queen's
University, Anglo American pic and the Natural Sciences and Engineering Research
Council of Canada is gratefully acknowledged as well.
Finally, I would like to thank my fellow colleagues of the Analytical Chemistry Group,
friends, relatives and my husband, Justin, for their continual encouragement and
patience during the writing of this thesis.
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Table of Contents
Abstract
............
.ii
Co-Authorship........................................
iv
Acknowledgments..........................
v
.......
..vi
Table of Content
List of Tables
.....
..ix
List of Figures...................
x
Chapter 1: In tro d u c tio n ...,..,..,......,,......,,..,...........,,.,.........,....,,.........
1
1.1 Leaching and sequential extractions...............
1
1.1.1 Introduction to leaching analysis of soils..............
1
1.1.2 Sequential extractions...........................
2
1.1.3 Chemical speciation and chemical fractionation
.........
1.1.4 Sequential extractions schemes..
3
.......
1.1.5 Limitations in the use of sequential extractions .......
4
9
1.1.6 Continuous on-line leaching................
12
14
1.2 Microwave-Assisted Extraction........................................
1.2.1 introduction..................................
14
1.2.2 Basic principles.......................
15
1.2.3 Parameters influencing the extraction process.
...........
1.3 Inductively coupled plasma mass spectroscopy as detection method
17
19
1.3.1 Introduction.....................
19
1.3.2 Instrument Description and T heory..............................................
20
1.3.2.1 Sample Introduction.....................
21
vi
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1.3.2.2 Argon Plasma/Sample ionization.......................... ................. .
21
1.3.2.3 ICP-MS interface...................................
22
1.3.2.4 Mass Separation................................................................
22
1.3.2.5 TOF mass analyzer..
23
......
1.3.2.5.1 TOF advantages..................................
24
1.3.2.5.2 TOF disadvantages........................
25
1.3.2.6 Detector System ......................................................................
26
1.3.3 ICP-MS Advantages and Limitations
27
1.3.4 Flow injection use in ICP-MS.....................
27
............
1.4 Thesis Objectives.......
Chapter 2: Experimental
.........................
2.1 Instrumentation...................................
2.1.1 Renaissance ICP-TOFMS
28
..
29
29
..................
29
2.1.2 UltraMass 700 ICP-QMS.......................................
29
2.1.3 Star 2 Microwave System............................
31
2.1.4 Continuous Leaching Set-up...........................
32
2.1.5 Flow injection Set-up
33
2.2 Reagents..
........
........................
2.3 Standard P rocedures..............................................................
2.3.1 Optimization
......
35
37
37
2.3.2 Total Digestion................
39
2.3.3 Data Collection and Analysis......................
39
vii
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Chapter 3; Analysis o f single m in e ra ls .,.,..,,.............,.,...,..,.....,..,.......
42
3.1 Effect of microwave heating on the leaching profiles for single minerals....
42
3.1.1 Leaching of malachite.
..........
3.1.2 Leaching of pyrotusite.....
42
....
3.1.3 Leaching of hematite.......
48
....
53
3.1.4 Leaching of a 1:1:1 mixture of malachite, pyrolusite and hematite
58
3.2 Comparison with results obtained at low flow rate and ICP-HRMS
.................
instrumentation
71
3.2.1 RT ICP-HRMS vs. RT ICP-TOFMS.......................
71
3.2.2 RT ICP-HRMS vs. MW ICP-TOFMS.
......
76
3.3 Verification of mass balance.................................
78
Chapter 4: Qualitative analysis of a Sandstone sample from Cigar Lake.
84
4.1 Sample overview.....................
84
4.2 Effect of heat on leaching..............
85
4.3 Area comparison
89
...............
4.4 Reproducibility.
.....
90
4.5 Lead ratios....................
96
4.6 Comparison with results obtained at low flow and ICP-HRMS
instrumentation
........
.................................................
4.6.1 RT ICP-HRMS vs. RT ICP-TOFMS
....
4.6.2 RT ICP-HRMS vs. MW ICP-TOFMS....................
Chapter 5: C onclusions..
............................
R eferences.,..,.....,...,.......... ...........................................
99
99
102
104
106
viii
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List of Tables
Table 1.1 Selected examples of batch leaching techniques
.......
6
Table 1.2 Selected examples of accelerated batch teaching techniques
10
Table 1.3 Selected examples of on-line leaching techniques..........................
13
Table 2.1 Operating Conditions for ICP-TOFMS.......
30
Table 2.2 Operating Conditions for ICP-QMS
Table 2.3 Ion Deflections for ICP-TOFMS
.........
...............................
31
........................................
38
Table 3.1 Quantification and mass balance for hem atite............................
79
ix
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List of Figures
Figure 1.1 Schematic of an inductively coupled plasma mass spectrometer
20
Figure 1.2 Schematic diagram of LEGO Renaissance axial ICP-TOFMS.....
23
Figure 2.1 Diagram of continuous leaching apparatus...................
32
Figure 2.2 Flow injection manifold for eluents going into the microcolumn..........
34
Figure 2.3 Flow injection manifold for external calibration......................
34
Figure 3.1a Leaching profile with microwave heating for malachite......................
43
Figure 3.1 b Leaching profile at room temperature for malachite.......................
43
Figure 3.2a Leaching profile with microwave heating for malachite. ..................
44
Figure 3.2b Leaching profile at room temperature for malachite...........................
44
Figure 3.3a Leaching profile with microwave heating for malachite
45
Figure 3.3b Leaching profile at room temperature for malachite
45
Figure 3.4 Microwave vs. room temperature plot for 55Mn in malachite................
47
Figure 3.5 Microwave vs. room temperature plot for 121Sb in malachite.............
47
Figure 3.6a Leaching profile with microwave heating for pyrolusite..
49
......
Figure 3.6b Leaching profile at room temperature for pyrolusite...
49
Figure 3.7a Leaching profile with microwave heating for pyrolusite......................
50
Figure 3.7b Leaching profile at room temperature for pyrolusite...................
50
Figure 3.8a Leaching profile with microwave heating for pyrolusite.....
51
Figure 3.8b Leaching profile at room temperature for pyrolusite
.......
51
Figure 3.9 Microwave vs. room temperature plot for 121Cd in pyrolusite...............
52
Figure 3.10 Microwave vs. room temperature plot for 232I h in pyrolusite............
52
Figure 3.11a Leaching profile with microwave heating for hematite..................
54
Figure 3.11b Leaching profile at room temperature for hematite.
54
..........
x
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Figure 3.12a Leaching profile with microwave heating for hematite. ...........
55
Figure 3.12b Leaching profile at room temperature for hematite...................... .
55
Figure 3.13a Leaching profile with microwave heating for hematite
56
......
Figure 3.13b Leaching profile at room temperature for hematite.................
56
Figure 3.14 Microwave vs. room temperature plot for 59Co in hematite.
57
.....
Figure 3.15 Microwave vs. room temperature plot for 121Sb in hematite
57
Figure 3.16a Leaching profile with microwave heating for 1:1:1 mixture
59
Figure 3.16b Leaching profile at room temperature for 1:1:1 mixture.
.............
59
Figure 3.16c Sum of individual leaching profiles for microwave heating............
60
Figure 3.16d Sum of individual leaching profiles at room temperature
60
Figure 3.17a Leaching profile with microwave heating for 1:1:1 mixture.............
61
Figure 3.17b Leaching profile at room temperature for 1:1:1 mixture...............
61
Figure 3.17c Sum of individual leaching profiles for microwave heating............. 62
Figure 3.17d Sum of individual leaching profiles at room temperature.
...........
62
Figure 3.18a Leaching profile with microwave heating for 1:1:1 mixture.............
63
Figure 3.18b Leaching profile at room temperature for 1:1:1 mixture
63
Figure 3.18c Sum of individual leaching profiles for microwave heating.....
64
Figure 3.18d Sum of individual leaching profiles at room temperature.....
64
Figure 3.19a Correlation of Mn and Co for minerals with microwave heating......
67
Figure 3.19b Correlation of Mn and Co for minerals at room temperature
67
Figure 3.20a Correlation of Sr and Ce for minerals with microwave heating
68
Figure 3.20b Correlation of Sr and Ce for minerals at room temperature.
68
Figure 3.21 a Measured vs. calculated plot with microwave for Sr in mixture.......
69
Figure 3,21 b Measured vs. calculated plot at room temperature for Sr in mixture
69
xi
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Figure 3.22a Measured vs. calculated plot with microwave for Sb in mixture.
70
Figure 3.22b Measured vs calculated plot at room temperature for Sb in mixture
70
Figure 3.23a iCP-HRMS Leaching profile at room temperature for pyrolusite
73
Figure 3.23b ICP-TOFMS Leaching profile at room temperature for pyrolusite....
73
Figure 3.24a ICP-HRMS Leaching profile at room temperature for hematite
74
Figure 3.24b ICP-TOFMS Leaching profile at room temperature for hematite
74
Figure 3.25a ICP-HRMS Leaching profile at room temperature for hematite......
75
Figure 3.25b ICP-TOFMS Leaching profile at room temperature for hematite
75
Figure 3.26 ICP-TOFMS Leaching profile with microwave heating for pyrolusite.
77
Figure 3.27 ICP-TOFMS Leaching profile with microwave heating for hematite...
77
Figure 3.28a Quantification of major elements with microwave heating ............
82
Figure 3.28b Quantification of major elements at room temperature....,.............
82
Figure 3.29a Quantification of minor elements with microwave heating.
83
Figure 3.29b Quantification of minor elements at room temperature................
83
Figure 4.1a Leaching profile with microwave energy applied for Pb and U
86
...................
86
Figure 4.2a Leaching profile with microwave energy applied for Fe and Mn.......
87
Figure 4.2b Leaching profile at room temperature for Fe and Mn.....................
87
Figure 4.3 Microwave vs. room temperature plot for 137Ba in sandstone..............
88
Figure 4.4 Microwave vs. room temperature plot for 232Th in sandstone ............
88
Figure 4.5 Area comparison for eluent to total area ratio................
89
Figure 4.6a Leaching profile with microwave energy applied for Co..................
91
Figure 4.6b Leaching profile at room temperature for C o.....................
91
Figure 4.7a Leaching profile with microwave energy applied for Mn................
92
Figure 4.1b Leaching profile at room temperature for Pb and U
xii
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Figure 4.7b Leaching profile at room temperature for Mn
........
92
Figure 4.8a Leaching profile with microwave energy applied for Pb
93
Figure 4.8b Leaching profile at room temperature for Pb............
93
Figure 4.9a Leaching profile with microwave energy applied for Sr...................
94
Figure 4.9b Leaching profile at room temperature for S r.....................
94
Figure 4.10a Leaching profile with microwave energy applied for Ba..........
95
Figure 4.10b Leaching profile at room temperature for Ba................
95
Figure 4.11a Lead ratios for leaching performed with microwave heating
......
Figure 4.11b Lead ratios for leaching performed at room temperature.
97
97
Figure 4.12 Comparison of 207Pb/ 206Pb ratios for leaching performed with (MW)
and without microwave heating (R T).................................................
98
Figure 4.13a ICP-HRMS Leaching profile at room temperature for sandstone...
100
Figure 4.13b ICP-TOFMS Leaching profile at room temperature for sandstone.
100
Figure 4,14a ICP-HRMS Leaching profile at room temperature for sandstone...
101
Figure 4.14b ICP-TOFMS Leaching profile at room temperature for sandstone.
101
Figure 4.15 ICP-TOFMS Leaching profile with microwave applied for
sandstone
..............................
Figure 4.16 ICP-TOFMS Leaching profile with microwave applied for
sandstone
...................................................
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103
Chapter 1: Introduction
1.1 Leaching and sequential extractions
1.1.1 introduction to leaching analysis o f soils
Although the mineral constituents of soils are normally related to the parent rock and
various weathering processes, chemical speciation of elements in soils is related to
both mineral constituents and metal binding sites. High concentrations of metals in
soils can be associated with naturally occurring ore deposits, however they can also
be the result of human activities. Moreover, elements may originate from minerals
that were weathered and produced the mineral soil, but this may be complex
because many soils have been transported from other locations to their present site
by water, wind, or ice.
An additional source of metals in soils that further
complicates their distribution is through deposition from aerosols.
In many cases, compositional data are not particularly helpful, as they do not
indicate whether the elements are found as components of the mineral lattice or are
"mobile”, being associated with surface adsorption phenomena. Elements in mineral
lattices tend to be ‘insoluble’ except over geological time, and have minimal effects
on plant growth or most environmental process. In contrast, those elements that are
weakly adsorbed or that occupy ion-exchange sites on mineral surfaces will be more
available for chemical and biological activity. Thus, the prediction of the mobility of
the metals in soil systems is of great interest, since this determines their transport in
hydrobiological systems.
1
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There are difficulties in carrying out these measurements as metals can have
different chemical-physical associations including: (a) simple or complex ions in soil
solution; (b) exchangeable ions; (c) linked to organic substances; (d) occluded or co­
precipitated with oxides, carbonates and phosphates, or other secondary minerals;
and (e) ions in the crystalline lattices of primary minerals1. Thus, evaluation of
environmental risks from toxic metals requires not only determining the total amount
of elements in the soils, but also the amounts of elements in each form.
1.1.2 Sequential extractions
The terms ‘available’ and ‘extractable’ are to some extent synonyms, but there are
operational definitions and analytical procedures for determining these fractions.
A commonly used method for the identification and evaluation of the availability of
heavy metals in soils is leaching of soils by means of chemical extractants, including
both single extraction2-4 and sequential extraction5-9. Initially some of the sequential
protocols were developed for sediment analysis5,6, but they have been applied to the
analysis of soils, sewage sludges, and solid residues10.
Generally, sequential extraction schemes (SES) employ 3-8 extractants to leach soil
samples in a sequence in which the earlier ones are the least aggressive and the
most specific, and subsequent extractants are progressively more destructive and
less specific.
As a result, most mobile fractions are obtained first, followed by
increasingly absorbed fractions and finally those fractions that are strongly attached
to the soil matrix. This approach confers detailed information about the different
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availabilities of the heavy metals, allowing differentiation among exchangeable,
carbonate, oxide, organic and residual forms5.
An assortment of methods have been utilized using different reagents, different
sequencing of reagents, and different experimental conditions.
Extraction media
may be electrolytes (CaCl2 or MgCl2 solutions), pH buffers of weak acids (acetic or
oxalic acid), chelating agents (EDTA or DTPA), reducing agents (NH2OH), oxidizing
agents (HC1, HN03, HCI04, or HF) or basic reagents (NaOH, Na2C 03). The metal
partitioning depends on the extraction conditions, such as the reagent selected,
temperature, extraction time, shaking and mineral crystallinity and grain sizes. The
aim of these speciation studies is to operationally define the fractionation of
elements and to characterize the degree to which they are potentially labile or bioavailable.
1.1,3 Chemical speciation and chemical fractionation
There is a difference between chemical speciation and chemical fractionation. The
International Union of Pure and Applied Chemistry (IUPAC) has defined chemical
species as “the specific form of a chemical element defined according to its
molecular, complex, electronic or nuclear structure” .
Thus, chemical speciation
refers to the distribution of defined chemical species of an element in a system. In
contrast, the term Fractionation describes the process of classification of an analyte
or a group of analytes from a certain sample according to physical (e.g., size,
solubility) or chemical (e.g., bonding, reactivity) properties11.
3
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Speciation analysis Is defined as the analytical process of Identifying and measuring
species. This term includes appropriate sampling, quantification, and qualitycontrolled
analytical
methods.
The
analytical
procedures
that
provide
characterization of species groups but do not lead to an identification of chemical
species are not considered chemical speciation analysis. They are distinguished as
operationally or functionally defined species characterization. Operationally defined
procedures characterize molecule groups, dependent on the selected analytical
operation. The species identity is not considered. The functionally defined species
characterization provides information about the function of species groups in
biochemical paths12,13.
1.1.4 Sequential extractions schemes
In an effort to harmonize the different fractionation schemes, the European
Community Bureau of Reference, BCR, (now known as the European Community
(EC) Standards, Measurement, and Testing Program, SM&T) proposed a threestage sequential extraction protocol14, which is a compromise between the analysis
time and the amount of information obtained.
Marin and coworkers15 examined the BCR method and demonstrated its
reproducibility for the fractionation of trace metals in environmental impact studies.
This scheme involves leaching the sample with CH3COOH (0.11 mol I'1) for 16 h at
20°C to attain the exchangeable, water and acid soluble fraction. The next fraction is
the reducible (e.g. iron/manganese (hydroxides) obtained by treating the residue of
the first step with NH2OH-HCI (0,1 mol I'1) at pH 2 for 16 h at 20°C. Afterward,
4
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treatment with H2 0 2 (8 . 8 mol I'1) followed by CH3 COONH4 (1 mol S"1) at pH 2 for 1h
at room temperature and then for 2 h at 85°C will render the oxidisable portion (e.g.
organic matter and sulfides).
Finally, the residual fraction is the result of the
digestion with HNO3-HF. A complete sequential extraction by this procedure can
take up to two weeks.
The most widely applied fractionation method is that originally proposed by Tessier
et al.5 or modifications of it16. This five-step method yields five different solutions:
1st, exchangeable, from treatment of the sample with 1 mol I"1 MgCl2l (pH 7) for 1 h,
at room temperature and continuous shaking;
2nd, bound to carbonates or specifically adsorbed, from extracting with 1 mol I'1
NaOAc/HOAc, (pH 5) for 5 h, at room temperature, continuous shaking;
3rd, bound to Fe-Mn oxides, from treating with 0.04 mol I"1 NH2OH-HCI in 25% HOAc
for 6 h, at 95°C, intermittent shaking;
4th, bound to organic matter and sulphides resulting from the reaction of the residue
with 0.02 mol I'1 HN03, in 30% H20 2, pH 2, for 2 h, at 85°C and intermittent shaking;
followed by 30% H20 2, pH 2, for 3 h, 85°C, intermittent shaking and 3.2 mol I"1
NH4OAc in 20% (v/v) HNO3 for 30 minutes with continuous stir; and
5th, residual, the leftover is dissolved in HF + HCIO4 overnight at room temperature,
and 2 h heating under reflux. The time required for conducting the first 4 steps (not
including metal determination) was 15 h.
Once each fraction is obtained, analysis of the metal content is determined by a
suitable analytical technique. As shown in Table 1.1, many options have been used
including flame atomic absorption spectrometry (FAAS)7,17'20, electrothermal atomic
5
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absorption spectrometry (ETAAS)9,21,22, inductively coupled plasma-atomic emission
spectrometry (ICP-AES)8,23,24, inductively coupled plasma-mass spectrometry (ICPMS)i5.25-27^ and anodjC stripping voltametry28. ICP-MS is very advantageous when
compared to other methods, as it has multielement capabilities, whereas FAAS and
ETAAS can only detect one element at a time. ICP-AES can also be applied when
multieiemental analysis is required but, unlike ICP-MS, it cannot be used for isotope
ratio determinations and is orders of magnitude less sensitive.
Extensive research has been done on the use of sequential extractions, as they
provide detailed information about the origin, mode of occurrence, biological and
physicochemical availability, mobilization and transport of trace metals.
A
comprehensive review of sequential extraction schemes for metal fractionation in
environmental samples has been published by Filgueiras and colleagues10.
Table 1.1 Selected examples of batch leaching techniques
Sample
Analytes
type
marine
reference
sediment
contaminated
soil
marine
sediments
Sc, Cr, Co,
Ni, Cu, Zn,
Cd, Sn, Cs,
Pb, Th, U
Cd, Cr, Cu,
Fe, Mn, Ni,
Pb, Zn
Cu, Pb, Zn,
Cr, Mn, Fe
Extraction
Detection
method
method
BCR
sequential
extractions
ICP-MS
three-step
Maiz, Tessier,
and Ure
sequential
extractions
ETAAS
Tessier, BCR
and KerstenForstner
sequential
extractions
FAAS
Comments
Ref
The sequential extraction proce­
dure is found to be reproducible
enough
for
environmental
studies of speciation.
A potential order of metal availa­
bility is proposed: Cd > Pb > Zn
* Cu > Mn > Ni > Fe = Cr. The
method proposed was compared
with the other two sequentiai
exfraction
methods
and
substantial time saving was
achieved.
The results showed that the
metai distribution obtained with
the
three
procedures
is
significantly different.
15
7
17
6
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Table 1.1 Selected examples of batch leaching techniques (continued)
Sample
Analytes
type
Extraction
Detection
method
method
industrially
contaminated
soil
Cd, Cr, Cu,
Pb, Mn Ni,
V, Zn
BCR
threestep
sequential
extraction
FAAS,
ETAAS
intertidal
sediment
U-238/U235
BCR
threestep
sequential
extraction
ICP-MS
agricultural
topsoils
Cr, Mn, Fe,
Ni, Cu, Zn,
Ba, Pb
ZeienBriimmer
sequential
extractions
ICP-AES
sediment
Cd, Cr, Cu,
Ni, Pb, Zn
original and
improved BCR
FAAS,
ETAAS,
ICP-AES,
sediment
Cu, Pb, Cd,
Zn
BCR threestep
sequential
extraction
SI-ASV
polluted soils
Cd, Cr, Cu,
Fe, Mn, Ni,
Pb, Zn
Tessier and
two-step Maiz
sequential
extractions
AAS
and
ETAAS
Comments
Ref
Some iarge discrepancies were
apparent, especially for Pb. The
amount of metal extracted in the
sequential procedure did not
generally
agree well with
pseudototal digestion.
No interferences were found
from the extractant matrices.
Recoveries of U by sequential
extraction were generally within
± 10%of pseudototal values.
Used for Environmental Hazard
Assessment. In stage VII, the
original total decomposition by
means of several acids was re­
placed by measuring the entire
content in the original sample by
XRF*. The balance between
this content and extraction steps
I—VI yields a characterization of
the compounds with very low
solubility.
Results of a small-scale inter­
laboratory study, which tested a
revised version of the extraction
schemes by comparing the
original and the
modified
protocols using a CRM sample
showed better reproducibilities
with the modified BCR protocol.
No interferences due to adsorp­
tion of organic matter, colloids or
complexes with slow rate of
dissociation were observed.
Results were in good agreement
with those obtained by ICP-AES.
Factor analysis was used to
check the associations between
the levels of the different
sequential soil fractions and the
total content in grass. Cd, Cu
and Zn labile levels were
correlated with the total content
of these metals in grass,
indicating the suitability of the
short procedure for availability
studies of those elements. The
labile levels obtained with the
Tessier procedure showed for
Cd, Cu, Fe and Ni, a behaviour
intermediate between those
showed by the short procedure
and by the total content.
21
* XRF = X-ray fluorescence analysis
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25
8
22
28
9
Table 1.1 Selected examples of batch leaching techniques (continued)
Sampie
Analytes
type
Extraction
Detection
method
method
Comments
Ref
sewage
sludge,
amended soil,
lake sediment,
road dust and
soil SRMs
freshwater
sediment
Al, Cu, Fe,
Mn, Pb, Zn
optimized
BCR
FAAS
The procedure was found to be
precise for all metals in al!
fractions, with most values <5%.
18
U
BCR
threestep
sequential
extraction
ICP-MS
26
soil and road
deposited
sediment
Al, Co, Cu,
Fe, Mn, Ni,
Pb, Zn
three-step
sequential
extraction and
single
HCI
chemical
digestion
FAAS; ICPAES
contaminated
sediments
Cd, Cu, Fe,
Pb,
single­
extraction with
complexation
FAAS
fly ashes
B, Al,
Ca, Cr,
Fe, Mg,
Ni, Sr,
Zn
Ba,
Cu,
Mn,
V,
four-step
modified
BCR
sequential
extraction
ICP-AES
spoil pile
material
Cr, Cu, Fe,
K, Ni, Zn
four-step
sequential
extraction
FAAS,
GFAAS,
marine
sediments
V, Cr, Mn,
Fe, Co, Ni,
Cu, Zn, Mo,
Sn, Cd, Pb
BCR
threestep
sequential
extraction
ICP-MS
Digestion of the residual fraction
with aqua regia was introduced
as a fourth step to validate the
results and compare with pseu­
dototal digestion values. Inclu­
sion of an ion exchange step
prior to analysis allowed isotopic
ratio determination of U-238/U235.
The precision obtained
was 0.18%.
Results indicate that the diluted
HCI leach was slightly more
aggressive than the sequential
procedure for Al, Cu, Fe, Mn and
Ni,
though
no
significant
differences were observed for
Co, Pb and Zn.
The feasibility of kinetic extrac­
tion studies using EDTA as the
complexing agent is evaluated.
It has been concluded that the
quantities of metal extracted by
EDTA do not depend on the mlV
ratio and that an EDTA concen­
tration of 0.05 M ensures an
excess of extractant.
The BCR extraction protocol has
been modified by the introduc­
tion of leaching with deionized
water as the first step. The effi­
ciency of the extraction process
for each step was examined.
The comparison of sequential
and single extraction showed
strong deviations between the
results of both procedures. The
sequential extraction cannot be
substituted offhand by a single
extraction procedure.
To ascertain the concentration of
the elements associated with the
residual
components
of
sediment matrix, a fourth step
involving digestion of residue
from the third step with mixed
acid (2 ml HNOa and 0.5 ml HF)
was introduced.
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23
19
24
20
27
1.1.5 Lim itations in the use of sequential extractions
One of the main limitations of sequential extraction procedures is that they are
tedious and time consuming. Additionally, not all the available forms are equally
important. Hence, the very stable forms contained in the residual are unlikely to be
released under weathering conditions; whereas soluble, exchangeable and chelated
metal species are quite mobile and thus more available to the food chain29. Other
difficulties, especially for risk assessment studies, are that sequential extraction does
not represent field conditions and that crushing and grinding change the sample
matrix.
Problems
associated
with
the
sequential
extraction
techniques
(extraction
temperature, time of soil-extractant contact, ratio of soil to extracting solution, matrix
effects, etc.) are well known. Moreover, precipitation and readsorption of initiallydissolved heavy metals may further complicate the situation.
Perhaps the major
drawback of sequential extraction techniques, is the low degree of selectivity of the
extraction reagents30. For instance, solutions such as NH4-EDTA not only dissolve
organic substances, but also minor amounts of oxidic components, which are
supposed to be isolated in later stages of the extraction procedure. It follows that
the results achieved using such methods must be treated carefully and are
qualitative at best. Gleyzes and coworkers31 have described some of the criticisms
usually conferred to sequential extraction schemes; however they remain widely
applied and are considered an essential tool in establishing element fractionation in
soils and sediments.
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To make the application of these techniques more amenable to routine analysis,
many researchers have attempted to accelerate conventional sequential extraction
methods.
Decreasing the time required for the BCR and Tessier sequential
extraction schemes for soils, sewage sludge and sediments has been achieved with
ultrasound treatment and microwave heating.
sequential
and single extraction methods have
Other alternative accelerated
also been proposed32'43, as
summarized in Table 1.2.
Table 1.2 Selected examples o f accelerated batch leaching techniques
Sample
Analytes
type
Extraction
Detection
method
method
Comments
Ref
three-step
sequential
extraction with
microwave
Tessier sequential
extraction with
ultrasonic probe
Tessier sequential
extraction, with
shaking and with
microwave
FAAS
The scheme proposed is
considerably faster than
conventional extraction.
35
FAAS
32
Cu, Cr, Ni,
Pb, Zn
Tessier sequential
extraction;
microwave single
extractions
FAAS
sewage
sludgeamended soil
lake sediment
Cu, Fe, Mn,
Zn
BCR three-stage
sequential with
ultrasonic
agitation
FAAS and
ICP-OES
estuarine
SRM
Cd, Cr, Cu,
Ni, Zn
BCR three-step
sequential extrac­
tion with ultrasonic
bath and with a
microwave oven
ICP-MS
Ultrasonic energy was used
to reduce the operation time
in each of the stages.
The
original
Tessier’s
method was modified, for
each stage, using micro­
wave heating to reduce the
long operation time. Extrac­
tion conditions (heating time
and power) were specifically
optimized with the aim of
finding extraction efficien­
cies similar to that of the
original Tessier’s method.
The results were compared
with those established from
direct
microwave
single
extractions, to reduce the
conventional treatment time
and simplify the procedure.
An ultrasonic bath and
ultrasonic probe have been
used to develop rapid
versions of the three-stage
BCR sequential extraction
procedure.
Ultrasonic method gave more
accurate results than the
microwave method.
Both
methods significantly lowered
sample preparation time.
calcareous
soil
Co, Zn, Pb
river
sediments
Cu, Cr, Ni,
Pb, Zn
sewage
sludges
Cu, Cr, Ni,
Pb, Zn
sewage
sludge
FAAS
36
37
33
38
10
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Table 1.2 Selected examples of accelerated batch leaching techniques (continued)
Sample
Analytes
type
Extraction
Detection
method
method
Compost and
lake sediment
SRM
Cr, Mn, Fe,
Co, Ni, Cu,
Zn, As, Cd,
Pb
BCR three-step
sequential
extraction with
ultrasonic probe
ICP-AES,
ICP-MS
Soil and
sediment
SRM
As, Cu, Fe,
Mn, Pb, Zn
ICP-AES
Urban
sewage
sludges, CRM
and Sediment
Cu, Cr, Ni,
Pb, Zn
Kersten-Foerstner
and McLarenCrawford sequen­
tial extraction
accelerated with
rotating coiled
columns (RCC)
EDTA and acetic
acid single
extraction
procedures, using
either
conventional
shaking or
microwave
heating, and the
Tessier sequential
extraction
Lake
sediment
SRM
Cd, Cr, Cu,
Ni, and Pb
single extraction
with ultrasound
ETAAS
Soils
SRM 2710
and
SRM 2711
Ag, As, Cd,
Cu, Pb
single extraction
procedures, using
either ultrasound;
microwave
digestion, or reflux
ICP-AES
River sedi­
ment, indus­
trial sludge,
bituminous
coal, and coal
fly SRMs
Pb, Mn, Cu
single extraction
with pressure
assisted
complexation
AAS
FAAS
Comments
Ref
In most cases the mean
values obtained by the ultra­
sound method are compa­
rable with those obtained by
the conventional shaking
method. The reproducibilities
of the methods were also
comparable.
Proposed procedure is much
faster than traditional batch
methods.
34
Good agreement was found
between the metal contents
released in the first three
fractions of Tessier’s method
and those leached by the
simpler single extraction
procedures for most of the
elements studied. The ex­
traction efficiency of the first
three fractions of Tessier’s
method and that of the
optimised microwave single
extraction procedures were
satisfactory for the elements
studied, except Cr and Pb.
Comparison of the standard
SM&T sequential extraction
method with small-scale
ultrasound-assisted
single
extractions. Although similar
overall extractability was
observed with the SM&T
SES and the two approa­
ches proposed, complete
agreement was not observed
when results from specific
phases were compared,
mainly when ultrasoundassisted extraction was used.
The analysis of the SRMs
showed that the ultrasoundassisted extraction method is
highly comparable with the
other methods used for such
purposes.
Used a programmed se­
quence of temperature, static
time, pressure and thermal
equilibration. Achieved metal
recovery equivalent to that of
wet digestion techniques.
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40
39
41
42
43
While most of the sequential extractions have been carried out in batch systems, a
few continuous-flow extraction techniques have been proposed44"46. Reduction in
errors associated with repeated centrifugation, filtration and washing is one the
features in favor of continuous systems.
Additionally they are faster than batch
extractions and are likely to lessen readsorption problems.
1.1.6 Continuous on-line leaching
Several people have tried to implement extraction techniques on-line with the
detection system. Several examples are summarized in Table 1.3.
The most promising approach of continuous on-line leaching, which was developed
by Beauchemin ef a/.45 and modified by Jimoh et a/.46, involves leaching a micro­
column containing the soil sample with different reagents of increasing acid
concentration while continuously monitoring the released analyte by iCP-MS45. As a
result, it provides real-time data on what metals are released and what phases are
breaking down, and can reliably assign trace elements to host phases. This is a
great advantage compared to batch approaches that suffer from lack of selectivity of
reagents (releasing elements from
stable phases along with
mobile/labile
components), as well as problems of readsorption and redistribution of metals
solubilised during the extraction.
Therefore, continuous on-line leaching has proven to be a great aid in quickly
assessing the mobility and site of specific elements in complex natural materials
such as soils and rocks. It also offers other advantages such as minimal sample
12
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preparation, reduced contamination risk and greater resolution of the various phases
reacting with a specific reagent45.
Thus, this novel technique has promising
geochemical applications including the detection of small anomalies, generation of
pathfinder elements suites and evaluation of contaminant mobility.
Table 1.3 Selected examples o f on-line leaching techniques
Sample
Analytes
type
Extraction
Detection
method
method
polluted soils
and
river
sediments
Cd, Zn, Cu,
Pb
sequential
extraction
ICP-AES
ground plant
material
SRM
Fe
single extrac­
tion with ultra­
sound,
and
subsequent
complexation
Spectrophotometric
solid mussel
samples
Fe
single
acid
continuous
ultrasoundassisted
extraction with
flow injection
FAAS
soil
Ca, Cr, Mn,
Fe, Co, Cu,
Sr, Cd, Ba,
Pb, Th, U
ICP-MS
urban
air
particulate,
pyrrhotine
ore, spinach
leaves, and
soil SRMs
Ni, Cu, Zn,
Cd, Pb, Al
sequential
extractions
either
conti­
nuous or with
flow injection
sequential
extractions
FAAS and
ICP-MS
Comments
Ref
The sum of metals extracted by
each reagent is in agreement
with the total analysis of the
sample.
Comparable with conventional
method using AAS after hot-acid
treatment.
44
The results obtained with the
proposed method were com­
pared with those achieved by a
conventional off-line sample
digestion method using concen­
trated nitric acid with subsequent
iron determination by FAAS and
the agreement between the two
methods is satisfactory.
Continuous monitoring of trace,
major elements and isotopic
ratios to ascertain the phases
being sequentially released by
water, 1%, 10% and 30% HN03
The entire sequential extraction
took less than 1 h and allowed
the study of slow elution kinetics.
The instrumental configuration
used permits ready optimization
of the operational parameters
and also the adaptation of
different
detectors
without
changing the leaching conditions.
48
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47
45
46
1.2 Microwave-Assisted Extraction
1.2.1 In tro d u ctio n
The bulk of trace element analytical techniques cail for the sample to be in solution
form.
There Is no universal dissolution methodology for all types of samples.
Ideally, a dissolution method would have the following features: (a) the ability to
dissolve the sample entirely {no residues); (b) be relatively quick and safe; (c) have
no possible sources of sample loss through adsorption onto the walls of the vessel
or vo la tility; and (d) have no sample contamination from the reagents used in the
dissolution operation.
Most of the dissolution protocols entail dry ashing or wet
digestion using one or a combination of concentrated mineral acids49.
The use of microwave heating for extractions and digestions has the advantage of
providing both a closed system method and shorter digestion times, with the added
benefit of preventing contamination and reducing sample preparation costs.
Additionally, recoveries of analytes increased when using focused-microwave
heating compared to other extraction techniques50. Optimal conditions depend on
the
sample
(composition,
weight,
volume
of
digestion
reagents,
reaction
temperature, pressure, and time), and the digestion system (especially power
ratings).
Microwave heating is quite different from traditional conductive heating methods.
Conventional methods require a finite period of time to heat the container before the
heat is transferred to the solution, whereas microwaves heat the solution directly.
14
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This keeps the temperature gradient to a minimum and increases the rate of heating.
Moreover, microwave use leads to a significant reduction in solvent consumption as
well as the possibility of running multiple samples51,52.
Abu-Samra ei al.53 were the first to use a domestic microwave oven in the
laboratory. They performed trace analysis of metals from biological samples and
since then microwave digestion methods have been proposed for different sample
types such as environmental, geological, and metallic matrices, as well as for fly ash
and coal.
1.2.2 Basic principles
Microwave heating is very efficient and can essentially be explained by the
interaction of an electric field with charged particles and polar molecules in solution
involving two mechanisms of energy absorption: ionic conductance and dipole
rotation. Ionic conduction is the electrophoretic migration of ions when an
electromagnetic field is applied. The solution gets heated as a result of the friction
caused by the resistance of the solution to this flow of ions. Dipole rotation refers to
the realignment of dipoles with the applied field.
At 2450 MHz, which is the
frequency used in commercial microwave systems, the dipoles align and randomize
4.9 x 1Q9 times per second and this forced molecular movement results in heating51.
When microwave energy penetrates a sample, the energy is absorbed by the
sample at a rate dependent upon its dissipation factor (tan 8). The dissipation factor
is a ratio of the dielectric loss or “loss” factor (ea) in a sample to its dielectric constant
15
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(s ’); tan S = e 7 e ’. The dielectric constant is a measure of a sample’s ability to
obstruct the microwave energy as it passes through the sample, and the loss factor
measures the sample’s ability to dissipate that energy. The word “loss” is used to
designate the amount of input microwave energy that is lost to the sample by being
dissipated as heat54.
Polar molecules and ionic solutions (usually acids) absorb microwave energy
strongly since they have a permanent dipole moment that is affected by the
microwaves. On the other hand, non-polar solvents such as hexane will not heat up
when exposed to microwaves. For extraction of organic contaminants this will be a
drawback, but increasing the polarity by adding an amount of polar solvent can solve
this problem51.
Different chemical substances absorb microwave energy to different extents, which
implies that the heating conferred to the surrounding media will vary with the
chemical substances used.
Consequently, for samples with non-homogeneous
structural characteristics, or that contain various chemical species with different
dielectric properties dispersed into a homogeneous environment, it is possible to
selectively heat some areas, or components of the sample. This phenomenon Is
sometimes called superheating.
The extraction heating process may occur by one or more of the following
mechanisms:
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•
the sample could be immersed in a single solvent or mixture of solvents that
absorb microwave energy strongly (have high dielectric loss coefficients);
•
the sample could be extracted in a solvent mixture containing solvents with
both high and low dielectric losses mixed in various proportions;
•
a susceptible sample that has a high dielectric loss can be extracted with a
microwave transparent (low dielectric) solvent.
1.2.3 Param eters in fluencing the extraction process
The main factors that affect microwave assisted extraction are solvent composition,
solvent volume, extraction temperature, extraction time and matrix characteristics
including water content and particle size distribution55-60.
The selection of solvent should include consideration of the microwave-absorbing
properties of the solvent, the interaction of the solvent with the matrix, and the
analyte solubility in the solvent.
Preferably, the solvent should have a high
selectivity towards the analyte of interest excluding unwanted matrix components.
Another imperative aspect is the compatibility of the extraction solvent with the
analytical method used for the final analysis step. If the solvent molecule is not able
to absorb microwave energy there will be no heating and therefore no effective
extraction.
The temperature is a key aspect contributing to increased recoveries, not only for
microwave-assisted extractions but for all extraction techniques. Since microwaveassisted extractions are usually conducted in closed vessels (also referred as
17
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focused-microwave systems)61, the temperatures achieved can be greater than the
atmospheric boiling points of the solvents.
These elevated temperatures afford
improved extraction efficiencies, because desorption of analytes from active sites in
the matrix will increase. When using microwave, extraction times are much shorter
than for conventional techniques, often in the range of 3-15 minutes.
Moreover,
solvents have higher capacity to solubilize analytes at higher temperatures, while
surface tension and solvent viscosity decrease with temperature, which will improve
sample wetting and matrix penetration, respectively.
Another factor of great influence on the recoveries of the compounds is the nature of
the matrix in which the analytes of interest are bound. In studies of different sample
preparation techniques, decreasing recoveries were observed to result from aging of
matrices; specifically, native analytes are being more strongly bound to the matrix
than spiked analytes due to longer contact times.
Lopez-Avila and coworkers62 found that method performance was a function of the
matrix for the extraction of organic pollutants. Often the presence of moisture in the
matrix improves the extraction recoveries, as the water added (or naturally occurring
in the sample) will have an effect on the microwave-absorbing ability and hence
facilitate the heating process. The strong absorption of microwave energy by water
dipole molecules increases sample temperature, causing both water evaporation
and rupture of the analyte-matrix bonds58. Additionally, there could be a swelling
effect on the matrix or influence on the analyte-matrix interactions, rendering the
analytes more available to the extracting solvent.
18
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Particle size distribution also affects analyte recoveries and a better contact between
sample and solvent results in an efficient diffusion of the analyte out of the
matrix55,58. Leteliier and Budzinski59 showed that samples with smaller particle sizes
resulted in lower relative standard deviations.
The application of high pressures not only achieves solvent temperatures greater
than their boiling point (at atmospheric pressure), but also promotes better extraction
of analytes trapped in matrix pores, because the solvent is forced into the pores at
higher pressures.
Generally a clean-up step is required after microwave-assisted extractions. These
could involve a simple filtration of the extract using quartz or glass wool, glass
microbore filters or membrane syringe filters.
1.3 Inductively coupled plasma mass spectroscopy (ICP-MS) as detection
method
1.3.1 Introduction
The development of Inductively coupled plasma mass spectroscopy (ICP-MS)
through the late 1980's was achieved to combine the easy sample introduction and
quick analysis of ICP technology with the accuracy and low detection limits of a
mass spectrometer.
The resulting instrument is capable of trace multielement
analysis, often at the part per trillion level. Since its inception by Houk, Gray and
coworkers63, ICP-MS has been used extensively, finding applications in a number of
19
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different fields including Geological and Environmental Sciences, Nuclear and Semi­
conductor Industries, Materials Science, Food and Biological Sciences, and
Medicine.
1.3.2 Instrum ent D escription and Theory
ICP technology was built upon the same principles used in atomic emission
spectrometry.
Samples are sequentially desolvated, vaporized, atomized and
ionized In a high temperature argon plasma, resulting in ions that can be detected
based on their mass-to-charge ratios.
There are four main processes in any
analysis by ICP-MS: sample introduction and aerosol generation, ionization by a
plasma source, mass separation, and detection. The schematic below illustrates a
typical quadrupole-based ICP mass spectrometer.
V a t*
SswffeMine
Torefc
Yaentim pomps
Figure 1.1 Schematic of an inductively coupled plasma mass spectrometer65
20
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1.3.2.1 Sam ple Introduction
With aqueous samples, the conventional method of sample introduction for ICP-MS
is by aspiration via a nebulizer into a spray chamber. The nebulizer, which aspirates
the sample with high velocity argon, forms a fine mist. The aerosol then passes into
a spray chamber where larger droplets are removed via a drain. This process is
necessary to produce droplets small enough (< 10 pm) to be vaporized in the plasma
torch. Approximately 1 m l of sample is required per analytical run, but only 1-2% of
the original mist passes through the spray chamber. Recently, low uptake rate, high
efficiency nebulizers have been employed to combat this problem.
ICP-MS
spectrometers can accept solid as well as liquid samples. Solid samples are usually
introduced into the ICP by way of a laser ablation system. Other approaches for
sample introduction include Electrothermal Vaporization (Graphite Furnace), Flow
Injection (for concentrated solutions), and Hydride generation.
1.3.2.2 Argon Plasma/Sample Ionization
After the sample passes through the nebulizer and is partially desolvated, the
aerosol moves into the torch body.
A coupling coil is used to transmit radio
frequency to the heated argon gas, producing an argon plasma located at the
torch54.
Although Ar is the gas most widely used for plasmas, other alternatives
such as He, N2 or other mixtures have also been used65'72. The hot plasma with
temperatures up to 10 000 K, causes sample desolvation and vaporization followed
by atomization and then ionization.
21
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1.3.2.3 ICP-MS Interface
The interface between the ICP and MS components becomes vital in creating a
vacuum environment for the MS system since atomization/ionization occurs at
atmospheric pressure. Ions flow first through the sampler cone, which has a small
orifice approximately 1 millimeter in diameter; and then they pass through the
smaller orifice (0.4-0.8 mm internal diameter) of the skimmer cone into a pumped
vacuum system. The skimmer is positioned within the Mach disk. A supersonic jet
forms between the sampler and skimmer, and the sample ions are directed through
a series of lenses and then passed into the MS system at high speeds, expanding in
the vacuum system. The entire mass spectrometer must be kept in a vacuum so
that the ions are free to move without collisions with air molecules. Since the ICP is
maintained at atmospheric pressure, a pumping system is needed to continuously
pull a vacuum inside the spectrometer. Commonly, several pumps are used in order
to most efficiently reduce the pressure, which will gradually go to 10"7-1 O'8 torr before
the ion stream reaches the mass analyzer.
1.3.2.4 Mass Separation
The most commonly used type of analyzer is the quadrupole, which permits the
detection of ions at each mass in rapid sequence (typical speed for a full mass scan
~ 100 ms)64, ailowing signals of individual isotopes of an element to be scanned.
Mass discrimination occurs by adjusting the potentials of two pairs of conductive
rods (operating in opposition) such that only one mass is allowed to pass at any
instant. Other analyzers include double focusing (magnetic/electric sector) and time
of flight (TOP), but only the latter will be discussed here as it was used in this work.
22
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1.3.2.5 TO F mass analyzer
Since the 1950’s, with the works of Wiley and McLaren with TOF mass
spectrometry73, there has been extensive research into developing this technique,
especially with the advent of new ionization methods that generate rapid
concentration-variable signals such as ICP-MS, laser desorption and electrospray
ionization.
In TOF-MS analyzers, the ions of different m/z ratios are separated due to different
times of their passing a fixed path in the Instrument.
The ions are formed or
sampled in packets at a definite time. The packet of ions is introduced into a fieldfree region at high vacuum, the flight tube, where the separation occurs. A discrete
ion packet is selected from the ion beam by modulation. Because the ions enter the
flight tube after acceleration to the same kinetic energy (KE = O.Smv2), the velocity
(v) acquired by each ion depends on its mass (m). As a result, the time for the ions
to arrive at the detector depends on their masses.
Flight Tubek,
M
D e te cto r^
I '\
P a r f im lin n
Torch
'T " ’N jOfid<ted ion Mirror
^
"IReflectron Low
1Reflectron High
_
‘^Sampler
".Skimmer
Ion Lens 1
/
/
Elnze’ 1 ,
Accelerator? /
Repeiterf
Modulation.'
flon
I Lens 2 i £3idstage orifice)
i-Lens
Figure 1.2 Schematic diagram of LEGO Renaissance axial ICP-TOFMS82
23
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Most instruments use a device called a reflectron to reduce small variations of the
kinetic energy acquired by ions of the same mass. This is just an ion mirror that
refocuses and reflects the ions back to the detector, effectively doubling the flight
path and hence increasing resolution.
The resultant mass spectrum for a given
packet of ions is a plot of ion signals versus time, calibrated to mass74' 76.
1.3.2.5.1 TOF advantages
Sequentially scanning mass analyzers, such as quadrupole or double sector mass
spectrometers, can only detect one mass at a time, which means that a compromise
always exists between number of elements, detection limits, precision and the
overall measurement time. The TOF-MS technique provides some advantages over
conventional scanning mass analyzers such as extremely high data acquisition
speed, high ion transmission and quasi-simultaneous measurement of all masses for
each ion packet extracted from the ion source. The ion packets can be analyzed at
a rate that is dependent on the flight time (tens-of-microseconds regime) of the
heaviest (slowest) ions through the field-free region.
The system allows the
accumulation of thousands of mass spectra per second.
Quasi-simultaneous
detection of all masses is possible due to the extremely low time difference
(nanoseconds regime) between adjacent masses77.
Myers and Hseftje reported in 1993 the successful combination of an ICP ion source
with TOF-MS for simultaneous muitielementai analysis78. Since then there has been
extensive research on the technique in atomic spectroscopy.
Time-of-flight
analyzers concede a substantial improvement in the detection of rapid transient
24
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signals where high precision of the results are required. The spectral acquisition
speed of TOF-MS analyzers surpasses that of a quadrupole by at least two orders of
magnitude77*79. Besides the enhanced sample throughput and elemental coverage,
other practical advantages include elimination of time (spectral) skew80, unlimited
use of internal standards without performance compromises, the potential for
elimination of the effects of drift and multiplicative (flicker) noise components in the
source, and improved isotope ratio precision capability due to simultaneous
sampling81.
1.3.2.5.2 TOF disadvantages
Despite the many strengths of ICP-TOFMS for transient analysis, there are
performance limitations that hinder certain applications. Since ions of a given mass
to charge ratio reach the detector at virtually the same time, the TOFMS is often
regarded as a low-resolution instrument. The sensitivity of ICP-TOFMS instruments
is as much as an order of magnitude poorer than comparable quadrupole systems,
and the detection limits correspondingly worse by a similar margin81'83. One reason
for this lower sensitivity has to do with the relatively low duty factor of an ICPTOFMS. The duty cycle refers to the percentage of the ions that are measured with
respect to the total number presented to the mass spectrometer, which is usually
about 5-10% for TOF instruments, thus most of the possible signals are lost.
Detection limits depend upon both signal strength and background noise level, and
while the sensitivity of ICP-TOFMS is typically IQ7 counts per second per ppm,
detection limits are compromised by elevated background noise.
Thus, the
sensitivity of ICP-TOFMS is nearly one order of magnitude lower than those reported
25
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for commercial quadrupole systems, when a single mass is monitored under similar
conditions81'82.
Additionally, surveillance of the entire atomic mass range with each extraction event
exerts great demands on the dynamic range of ICP-TOFMS instruments. Sfs been
observed that when peaks occur with greater than a 10® disparity in abundance
within a single spectrum, detector saturation can influence the remainder of the
spectrum. Orse key feature of the axial ICP-TOFMS is the transverse rejection ion
pulse (TRIP). The purpose of this device is to deflect matrix ions such as 0 +, OH+,
NO+, A r\ ArO* and Ara* which otherwise would overload or destroy the detector
since ions of all masses theoretically enter the mass spectrometer regardless of
whether they are of analytical interest or not. In few instances, analyte ions are also
concomitant with matrix ions from the sample. Hence, additional deflection windows
need to be implemented besides the standard deflections for background from the
plasma.
The deflection windows have reproducible side effects on neighboring
isotopes and affect roughly 5 amu seen over the whole mass range. For lower m/z
(<40) the narrowest TRIP settings affects 1-3 amu82,84.
1.3.2.6 Detector System
The detector system uses a Channeltron-type detector, which is essentially a
trumpet shape, and funnels the ion beam Into it by a negative potential. One ton
collision generates - 108 electrons as the ion passes down the detector. Counts are
stored in a Multi-Channel Analyzer (MCA) before transfer to the computer for data
reduction.
26
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Most of the elements from the periodic table can be detected except those with
ionization potential greater than that for Ar, such as He, F and Ne, or too close to the
ionization potential of Ar, like N, H, O, Cl and Kr.
1.3.3 ICP-MS Advantages and Limitations
The most important advantages of ICP-MS include multi-element capability, high
sensitivity, fast analysis, extensive analytical range (ppt - ppm for solution ICP-MS)
and the possibility to obtain isotopic information on the elements determined.
Limitations inherent to the ICP-MS system include difficulties due to matrix effects
(also called effect of concomitant elements), strong dependence of signal on plasma
parameters, clogging by dissolved solids and isobaric interferences produced by
polyatomic species arising from the plasma gas or sample matrix.
1.3.4 Flow injection use in ICP-MS
Aside from continuous sample aspiration, flow injection and discrete sampling can
also be applied, both of which deliver transient signals.
In 1975 Ruzicka and
Hansen85 were the first to describe the flow injection technique (FI), in which a
known volume of the analyte solution is injected into a carrier flow with the aid of a
valve provided with a loop, prior to determination with the detector of choice. The
basic apparatus for FI consists of a peristaltic pump, micro-bore tubing and a sample
injection valve64. FI has proved to be a helpful tool for continuous monitoring and
process control, for linking chemistry procedures and instruments86, as well as
making
numerous
on-line
techniques
possible
such
as
on-line
27
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separation/preconcentration and on-iine calibration strategies, particularly when a
range of calibration standards is needed, standard additions are compulsory or
where variations in solution properties (e.g. viscosity) may affect continuous
nebulization64, According to Simonsen and colleagues87, quantitation using peak
area is independent of viscosity differences between standards and samples.
1.4 Thesis O bjectives
Continuous on-line leaching with ICP-MS is a novel technique that was first
described by Beauchemsn and coworkers45.
Chipfey and his colleagues88
demonstrated its application to the analysis of minerals in ore samples while
MacFarSane89 further studied its potential usefulness for exploration geochemistry.
However, because high resolution ICP-MS was used for on-line monitoring, the
teaching flow rate had to be maintained at 100 pl/m in to allow multieiemeotal
sequential scanning.
This resulted in long analysis time, which would hinder its
feasibility in exploration and environmental geochemistry.
The purpose of this
project was to speed up the continuous teaching of materials using focusedmicrowave heating while maximizing the fractionation information obtained by using
simultaneous multielemental detection by ICP time-of-flight MS (ICP-TOFMS). In an
attempt to ascertain if microwave heating significantly changed the teaching profiles,
such as inducing the release of analytes in weaker reagents, the results obtained
were compared with data from samples previously analyzed with a high resolution
instrument (tCP-HRMS)89.
28
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Chapter 2: Experimental
2.1 Instrumentation
Most of the experiments were done using an ICP-TOFMS instrument (Renaissance,
Leco Corp., St-Joseph, Ml, USA), although the quantification section employed a
quadrupole instrument, ICP-QMS (UftraMass 700, Variart Australia Pty Ltd.,
Mulgrave, VIC, Australia).
2.1.1 Renaissance ICP-TOFMS
Continuous monitoring of elements released from the sample, with and without
focused-microwave heating, was done with the ICP-TOFMS instrument fitted with a
concentric nebulizer and a Smitb-Hieftje spray chamber. The operating conditions
are indicated In Table 2.1. The measurement time was 994.5 ms and is Independent
of the number of elements monitored as a result of the simultaneous scanning
property of ICP-TOFMS.
2.1.2 UftraMass 700 ICP-QHS
The quantification analysis in section 3.3 was done using an ICP-QMS instrument
with a standard concentric nebulizer and a Sturman-Masters spray chamber. The
operating conditions are Indicated In Table 2.2. The measurement time was 399 ms.
Data were acquired using WinMass software by peak hopping in the time-resolved
acquisition mode with a 1-ms dwell time at each mass (except for masses 25 and
204-207 where 10-ms was used), 3 point/peak, 1 scan/replicate, and 0.025 amu
spacing. Some bulk analysis was done with the steady state mode, also by peak
29
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hopping with the same dwell time indicated above, 3 points/peak, 5 scans/replicate,
10 repficafes/sampfe, 2 sec replicate time and 0.025 amu spacing.
Table 2.1 Operating Conditions fo r ICP-TOFMS
ICP Source
Ar plasma gas flow rate (L/min)
15
Ar auxiliary gas flow rate (L/min)
0 .8 0 -1 .0 2
Ar nebulizer gas flow rate (L/min)
0.76 - 0.98
RF power (kW)
1.3
RF frequency (MHz)
40.68
Sample uptake rate (mL/msn)
0 .6 -0 .9
interface and Mass Spectrometer Settings
Ni sampler cone orifice diameter (mm)
0.9
Ni skimmer cone orifice diameter (mm)
0.5
Flight Tube (V)
-1500
Reflectron low (V)
200
Reflectron high (V)
1537
X Steering (V)
(-1503) - (-1507)
Y Steering (V)
(-1560) - (-1575)
Einzel lens 1 (V)
(-1220)-(-1400)
Einzel tens 2 (V)
(-925) - (-1005)
Ion lens 1 (V)
(-550) - (-625)
ion lens 2 (V)
(-425) - (-500)
Modulation negative
(-100) - (-115)
Discriminator threshold
(-65) - (-95)
Repeller pulse (V)
1000
Repeller bias (V)
0
Detector (V)
(-1750)-(-2400)
30
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Table 2.2 Operating Conditions fo r ICP-QMS
Plasma
Ar plasma gas flow rate (L/min)
15
Ar auxiliary gas flow rate (L/min)
1.05
Ar nebulizer gas flow rate (L/min)
0.91
Sampling depth (mm)
6.5 - 7
< 0
0
Sample uptake rate (mt/m in)
1
o
1.2
0 0
RF power (kW)
Interface and Ion O ptics
Ni sampler cone orifice diameter (mm)
1.0
Ni skimmer cone orifice diameter (mm)
0.5
Extraction tens (V)
(-595) - (-600)
-221
First lens (V)
<q
I
CO
Third Sens (V)
I
to
i
Second iens (V)
0.0
Fourth lens (V)
(-49) - (-69)
Photon stop (V)
-13.2
Entrance plate (V)
0
Exit plate (V)
0
2.1.3 S tar 2 M icrow ave System
The focused-microwave heating was carried out with an open vessel microwave
digestion system (Star 2 Microwave Digestion System, GEM Corp., Matthews, NC,
USA) that has two individual microwave cavities and a temperature feedback control
it
features
pre-programmable
“Time-to-temperature”
parameters
for
rapid
optimization of methods.
31
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2,1.4 Continuous Leaching Set-up
The approach involves the preparation of a micro-column by loosely packing 200 mg
of sample in a 6.3-cm long, 3/16 in. o.d, 1/8 in. i.d. FEP (fluorinated ethylene
propylene) tube, between quartz wool plugs (total weight for both wool plugs used
was 10-13 mg for the sandstone columns and 20-30 mg for the single minerals
ones). The micro-column was placed in line between the peristaltic pump and the
nebulizer of an ICP-MS instrument (Figure 2.1).
Microwave
flow rate sample column
0.6mL/min,
to ICPTOFMS
I
quartz
200 mg w° 0 !
of sample
peristaltic eluent
pump________
Figure 2.1 Diagram of continuous leaching apparatus
A bypass valve (Rheodyne, Inc., Cotati, CA, USA) was used to rinse the nebulizer
during the insertion of micro-columns and prevent the possible extinction of the
plasma that could result from the aspiration of air.
Eluents were degassed by placing them in an ultrasound bath for 3-5 minutes prior
to leaching to avoid bubble formation during the analysis. Leaching was carried out
by sequentially pumping doubly deionized water (DDW), then 1% HNOs, 10% HN03
and finally 30% HN03 through the sample at a rate of 0.8-0.8 mL/min for up to 5
minutes each. The micro-column was placed in the microwave cavity of a focused
32
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microwave digestion system (Star 2 Microwave Digestion System, GEM Corp.,
Matthews, NC, USA), which was filled with water. The temperature of this water was
maintained at about 902G. PER Teflon tubings of 1/ i6 in. o.d., 0.03 in. I.d., 88.3 cm
and 82.5 cm respectively were used to connect the micro-column to the valve on one
side and the nebulizer on the other. For the leaching done at room temperature,
which was heid at 20-212C, the micro-column was simply taken out of the
microwave cavity and placed on the counter of the ICP-TOFMS.
2.1.5 Flow in je ctio n Set-up
A manual flow injection system was utilized for all eluent injections for the
quantitative part because it allows quantification of a transient signal by means of
area comparison.
This consisted of a flow injection (FI) valve (model 5020,
Rheodyne Inc., Cotati, CA, USA) controlled by a switching module (Universal
module, Anachem, Luton, England). The sample injection valve was connected to
the bypass valve (used in the Leaching Set up described above), which would direct
the flow to either the nebulizer or the micro-column.
Position zero on the FI actuator allowed passage of air as carrier through a 250 pL
injection loop. The sample injection valves were filled manually by suction into a
syringe directly from a polypropylene sample bottle to minimize contamination from
the syringe. Once the FI valves were filled with eluent, the loading position “0” was
manually switched into injection position “1”, for eluent passage to the micro-column
(Figure 2.2).
33
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sample column
Eluents
to ICPQMS
Air
per staltic
pump
valve
Figure 2.2 Flow injection manifold for eluents going into the micro-column
A peristaltic pump was used to maintain constant sample uptake during acquisitions
at a rate of 0.8 - 0.9 mL/min. The peristaltic pump tubing was made of Tygon and
had an internal diameter of 0.76 mm. The eluents going towards the micro-column
were injected in air after injecting the proper set of standards going directly to the
nebulizer; thus, the bypass valve was set to direct the flow to the nebulizer instead of
the micro-column (Figure 2.3). The injections were carried out starting with a blank
(the eluent itself, to allow for blank-subtraction of the standard solution), followed by
the least concentrated standard solution to the highest concentrated standard
solution. Six to eight repeat injections of all standard solutions were done.
Microwave
sample column]
Standards
Air
to ICPQMS
or -
DDW
peristaltic
pump
valve
Figure 2.3 Flow injection manifold for external calibration
34
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This quantification part was done with the Ultramass quadrupole instrument rather
than with the Renaissance TOF for two reasons. First, the Renaissance TOF could
not be used since its plasma is not robust enough to withstand nebulized air, unlike
the UftraMass. Second, the hematite sample had a high content of certain elements
(Fe, Mn, Ba, Ce and Pb), so that deflections had to be placed in certain mass areas
to avoid detector overload (see Table 2.3). This would affect not only the masses
deflected but also the adjacent ones, impairing the quantification of these isotopes
(as described in section 1.3.2.5.2).
2.2 Reagents
All apparatus that was used to prepared and store solutions, such as volumetric
flasks, graduated cylinders, polypropylene bottles, etc., was soaked in 10% (v/v)
nitric acid (HN03) overnight, and rinsed with DDW (18 M£2 cm '1, Millipore, Bedford,
MA, USA) before use. All solutions were stored in polypropylene bottles.
Reagents were prepared with DDW and concentrated HN03 (Trace Metal Grade,
Fisher Scientific, Nepean, Ontario, Canada). Leaching eluent solutions (1%, 10%,
and 30% HN03) were prepared by placing the proper volume of concentrated HN03
in a volumetric flask and diluting with DDW to the mark. The multielement standard
solutions (10, 100, and 500 pg/L) were prepared by serial dilution of a 10 mg/L stock
solution in each eluent matrix. The stock solution was prepared by placing in a 100mL volumetric flask, 2 m l of concentrated HNQ3 and 1 mL of each of the 1000 mg/L
monoelement (Co, Cr, Cu, Mg, Mn, Mo, Ni, Pb, Sb, V and Zn) ICP-MS standards
35
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solutions of the analyte nitrate (PlasmaCAL purchased from SCP Science, Baie
d’Urfe, GC, Canada and Plasma Standard from SPEX Industries, Inc., Edison, NJ,
USA) and diluting with DDW to the mark.
Samples were obtained from the Department of Geological Sciences and Geological
Engineering. A sandstone sample having a grain size of 0.5 - 1 . 4 mm was taken
230 m from a U-mineralized drill hole near the Cigar Lake uranium deposit in the
Athabasca Basin, northern Saskatchewan, Canada. This sample consists of quartz,
iliite, kaolinite, and hematite as major minerals.
Some mono-mineralic samples were selected from the collection of the Miller
Geological Museum at Queen's University.
They had being previously crushed,
powdered, and analyzed by X-ray diffraction to confirm their mono-mineralic
composition, and by Continuous Leaching ICP-MS (CL-ICP-MS) to estimate the
major and trace element release patterns for individual phases. The single minerals
studied were Malachite [Cu2C 03(0H)23, Pyrolusite [MnQ2], and Hematite [Fe20 3]. A
mixture 1:1:1 of these single minerals was also prepared to check if incongruent
dissolution or back reactions would occur with microwave heating.
38
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2.3 Standard Procedures
2.3.1 O ptim ization
To achieve maximum sensitivity and precision and to minimize certain interference
effects in the SCP-MS, careful optimization of the instrument operating conditions is
needed.
This process is particularly important for multielement determinations
where optimal performance for one analyte may not be most favorable for another,
requiring a compromise of conditions.
The plasma and instrumental settings for the ICP-TOFMS, are indicated in Table
2.1.
basis.
Slight modifications to these parameters are usually required on a regular
Right after plasma ignition and preceding the optimization, it is crucial to
ensure that deflection settings are valid, to repel matrix ions such as 0 +, OH+, NO+,
Ar+, ArO+ and Ar2+, as well as other undesirable isotopes and prevent overload or
damage of the detector (see Table 2.3). Following deflection checks and instrument
warm up, optimization can be carried out. This procedure is done with a 5 fjg/L
mass calibration solution containing Li, Mg, Sc, Co, Y, In, Ce, Ba, Pb and Bi
(prepared from a 10 pg/mL stock solution supplied by LECO). The signal intensity of
115ln+ is maximized by adjusting the torch position X, Y and Z (the latter is also called
sampling depth), nebulizer gas flow rate and ion lens 1.
A mass calibration is
necessary after all optimization events and prior to data collection, especially if
parameters in the mass spectrometer have been changed.
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Other mass spectrometer parameters that have a significant effect on sensitivity can
be adjusted less frequently as they do not change much in day-to-day operations.
These include the potentials on ion lens 2, Einzel lenses 1 and 2 and X- and Ysteering.
Table 2.3 Ion Deflections for SCP-TOFMS
Start Time/ps
W idth/ps
Deflected ions
0.897
0.158
12-16 amu: C+, N+, 0 +,
1.320
0.136
28-36 amu: N2\ NO*, 0 2+,0 2H \ 36Ar*
1.497
0.100
40 amu: ^Ar*. 40Ca*
2.046
0.050
80 amu: Ar2+,
1.738
0.050
56 amu: ArO\ CaO*
1.636
0.056
40-42 amu: ^ArH*
1.097
0.078
17-23 amu: H20 +, H30 +, Na+
1.246
0.034
27-29 amu: AT, Si+, N2H+,
2.131*
0.028
87 amu: Mn02+
1.860*
0.068
63-65 amu: Cu+
3.227*
0.039
208 amu: Pb+
2.660*
0.048
138-140 amu: Ba+
1.968*
0.034
71 amu: MnO+
3.067*
0.050
191 amu: lr+
* Deflections added for the single mineral analysis only
For the UitraMass system, optimization was performed while nebulizing a 100 pg/L
multi-element solution of Ba, Be, Ce, Co, In, Pb, Mg, and Th (prepared from a 10
pg/m l stock solution provided by Varian). First, the torch position and nebulizer gas
38
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flow rate were optimized so as to maximize 59Co* signal. Following this, the ion lens
settings were adjusted, if necessary.
2.3.2 Total D igestion
For quantitative analysis, a sample of 50 mg of hematite was dissolved by digestion
with 12 ml_ of aqua regia (1:3 mixture of high purity HN03 and HCl) at medium heat
on a hot plate with stirring. When most of the liquid had evaporated (--1-2 m l acid
left), another 6 m l of HCl was added and the stirring was maintained (with a glass
rod) until all the solid had dissolved. The liquid was then allowed to evaporate to
dryness. Ten m l of HN03 were added to redissolve the product at the bottom of the
beaker.
The resulting solution was transferred to a 100-mL volumetric flask and
filled to volume with DDW, and later placed in a labeled polypropylene bottle in the
refrigerator until determination by ICP-QMS.
A blank solution was also prepared
following the same procedure but without the hematite in order to do blank
subtraction.
This same procedure was applied to the residue of the hematite-filled micro-columns
leached at room temperature and with microwave heating, to verify mass balance.
2.3.3 Data C ollection and A nalysis
Qualitative analysis, with the ICP-TOFMS, involved monitoring the following
isotopes: 25Mg, 35CI, 44Ca, 51V, 52Cr, 55Mn, ^Fe, 57Fe, 59Co, 62Ni, 63Cu, 65Cu, ^Zn, 68Zn,
69Ga, 75As, 78Se, 79Br, 88Sr, 98Mo, 103Rh, 1Q5Pd, 107Ag, 114Cd, 121Sb, 127l, 137Ba, 140Ce,
193ir,
195Pt,
197A u ,
202Hg, 204Pb, 2Q6Pb, 207Pb, 208Pb, 232Th and 238U.
39
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All raw data files were imported into Excel (Windows 2000 Professional) for
processing and graphing.
With the iCP-QMS, isotopes monitored were 24Mg, 25Mg, 51V, 52Cr, 55Mn, s9Co, 62Ni,
63Cu, 65Cu, ^Zn, "Z n , "M o, 121Sb, 204Pb, 206Pb, ^ P b
and 208Pb. For the
quantification section, data files containing raw count rate versus time were
smoothed with in-house QBASIC software (using a seven-point Savitzky-Golay
polynomial moving window).
Peak area was used for quantification and was
obtained using in-house QBASIC software as well.
Significant matrix effects were noticed when the entire matrix was present, so the
method of standard additions was used as a calibration strategy for quantification of
the total digestion of the raw hematite and the residue from the leached micro­
columns.
Because this method was not possible with continuous leaching, an
external calibration using standards prepared in each of the reagents was used to
quantify analytes in the leachates from the micro-column. This procedure consisted
of injecting 250 pL volumes of each of the standards prepared in DDW matrix (0,10,
100, and 500 jjg/L) for 5 min. using the flow injection set up Indicated in Figure 2.3,
and then proceeding with the continuous leaching with DDW (see Figure 2.2) for 15
minutes. These injections were done in air as carrier. The next set of standards
would then be injected (0, 10, 100, and 500 pg/L in 1% HNOs matrix), followed by
the micro-column leaching with that eluent, until all eluents were used. Chu and
Beaucfiemin90 used a similar calibration approach, which was successful for the
analysis of solid food.
40
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For quantification of the total digestion of the hematite and the residue from the
leached micro-columns, external calibration was used to get a rough estimate of the
analyte concentrations to properly cafcuiate the standard volume additions to be
used.
Using 4-mL aliquots, small volume additions of the multielement stock
solution were made to prepare solutions in which the end known concentration
would be 0.5, 1, 3, 5, 10, 30, 60, 75, 100, 140, 200, 300 and 600 pg/l.
The Ultramass 700 ICP-QMS instrument gives the readings in counts/s only, while in
the Renaissance ICP-TOFMS design, ion counting and analog signals are obtained
simultaneously. The ion counting mode is used for the most sensitive work near the
detection limit, whereas the analog mode (units of millivolts) is used to extend the
dynamic range, since the signal from the ion counting mode is not linear at
intensities higher than 2000 cts/s.
Therefore both modes were used in the
qualitative analysis. For example, elements with low concentration in the samples
such as Mo and Sb were measured in the counting mode, and high abundance
elements such as Sr and Pb were measured in the analog mode. In some of the
graphs that include several elements, the analytes measured in millivolts were
converted to counts by multiplying the analog signal by 2000 for the sake of having
them on the same scale (in the ICP-TOFMS, 1 mV * 2000 cts/s).
Additionally,
multiplication factors are applied to bring elements to a common scale, for ease of
comparison and to simplify the interpretation process. The moving average trend
(with periods of 10 in most cases) was applied to the graphs of single minerals to
smooth out fluctuations in the data and show the trend more clearly.
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Chapter 3: Analysis of single minerals
3.1 E ffect o f m icrow ave heating on the leaching p ro file s fo r sin g le m inerals
To determine how different phases are dissolved when applying microwave energy
during continuous leaching, single minerals were evaluated.
A previous study
conducted at room temperature by MacFariane89 revealed that the samples supplied
were not pure single minerals, but rather dominantly one phase.
The “mono-
mineralic” phases examined were Malachite [Cu2C 03(0H)2j, Pyrolusite [Mn02], and
Hematite [Fe20 3].
3.1.1 Leaching of malachite
For malachite, analytes such as Mg, Mn, Co, Cu, Ba, Ce, Pb, Th and U had similar
release profiles at both microwave and room temperature but with a more significant
release when microwave energy was applied (see Figures 3.1a - 3.3b).
Other
minor elements such as Sb and Hg, which were not extracted at room temperature,
were released with microwave heating. Sr and Cd exhibited similar profiles for both
leaches with the first eluents, but when the more acidic ones were used, the release
increased significantly with the microwave-assisted experiment. The application of
microwave heating appeared to enhance the extraction kinetics of some analytes as
suggested by the narrower peaks in the Fe and Ag microwave profiles. This could
not be a spurious physical effect of gas since all elements did not exhibit narrower
peaks in this region.
homogeneous.
Dissolution was not congruent, because the sample is not
This was noted as the profile for Co follows the one for Mn, Cd
follows Sb, and Fe follows Pb.
42
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6.E+05
— 10 per. Mov. Avg. (Mg x5Q)
.- 10 per. Mov. Avg. (Sr x150)
— 10 per. Mov. Avg. (Cd x50)
— 20 per. Mov. .Avg. (Co x100)
— 20 per. Mov. Avg. (Mn x3E3)
HNOS 10%
5.E+05
- S r x 150
HNOS 30% I
> .
I
I H N O S 1%
4.E+05
Co x 100
'[ 9<J x 50
fl
/
V
In x 3E3
2.E+05
i
v a V I iP
I I M
1.E+05
!'■■
, _
®
Q.E+00
8
Time,
1.E+05
a
V iii
A ir
$4^
t
V to 1
^ 1l
C~\
'f r>j v
Mg x 50
12
16
m in .
Figure 3.1a Leaching profile with microwave heating for malachite
The trend used was the moving average with a period of 10 (10 per. mov. avg.)
Multiplication factors are applied to bring elements to a common scale
(e.g. Mn x 3E3 means that the Mn signal was multiplied by 3 x 103)
6.E+05
— 10 per. Mov. Avg. (Mg x120)
10 per. Mov. Avg. (Sr x10Q)
— 10 per. Mov. Avg. (Cd x150)
— 20 per. Mov. Avg. (Co x90)
— 20 per. Mov. Avg. (Mn x5E3)
H N 031%
water
HN03 10%
5.E+05
S rx 100
4.E+05
Cox 90
x 150
iI w
m
3.E+05 -
HN03 30%
*:L
~rr
f
A Mn x 5 E 3 1
L
It
Mg x 120
C 2.E +05
w
m
1.E+05
fy -
v -f-;
0.E+00
-1.E+05
n ™ rw
12
Time, min.
Figure 3.1b Leaching profile at room temperature for malachite
43
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
— 10 per. Mov. Avg. (Fe x2.6)
— 20 per. Mov. Avg. (Cu x100)
8.E+05
5.E+05
...10 per. Mov. Avg. (Ag x38}
-..10 per. Mov. Avg. (Sb x25Q)
— 10 per. Mov. Avg. (Hg x40)
H N 031%
Fe x 2.6
HN03 10%
HNOS 30%
Sb x 250
.Hg x 40
4.E+05
Cu X 100
iv
ts
2.E+05
Ag x 38
iLA
.A , v
1.E+05
,
rt
irJ
O.E+OO
T im e , m m .
-1.E+05
Figure 3.2a Leaching profile with microwave heating for malachite
6.E+05 t
5.E+05
HNOs1%
water
HNOS 30%
HN03 10%
Fe x 2.7
0
1
per. Mov. Avg. (Fe x2.7)
— 20 per. Mov. Avg. (Cux 160)
....10 per. Mov. Avg. (Ag x120)
— 10 per. Mov. Avg. (Sb x550)
— 10 per. Mov. Avg. {Hg x5Q0)
Cu x 160
4.E+05 m
X
3.E+05 -
Ag x 120
Sb x 55r
d
\
Mi
"5
j£ 2.E+05 J- -------------------------V - I-,-1
OJ
Hg x 500
m
!______
1.E+05
?
} ^ r 'A
A, 4:
V1
1:
4if*k? .
0.E+00
-1.E+05 -J-
nr
4
____
8
tf*7 5 f_
yr
I
- ~
12
Time, min.
Figure 3.2b Leaching profile at room temperature for malachite
44
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
-10 per. Mov. Avg. (Ce x180)
-10 per. Mov. Avg. (Ba xi .4)
-10 per. Mov. Avg. (Pb xQ.13)
-15 per. Mov. Avg. (Th x1200)
15 per. Mov. Avg. (U x30)
HNOS1%
6. E+05
water
HNOS 30%
5. E+05
Pb x0.13
m
m X1200
/
I
Ux30
—X
4. E+05
3.E+05
Cex 180
= 2. E+05
to
1.E+05
Ik l
Ba x 1.4
0.E+00
8
Time, min.
-1.E+05
Figure 3.3a Leaching profile with microwave heating for malachite
HNOS1%
6. E+05
water
j'
I /C e x 180
|
T
j
HN03 10%
5.E+05
m
4. E+05
-10 per. Mov. Avg. (Ce x180)
- 10 per. Mov. Avg. (Ba x6)
-10 per. Mov. Avg. (Pb x3)
15 per. Mov. Avg. (Th x2400)
Pb x 3
I \ Bax 6
I iV
i
I
S 2. E+05
Th x 2400
i \
:
V
3. E+05
1
U x75
.
L&
HNOS 30%
U
J
;
:'
^
;
^
m
s'
1.E+05
i
r
V■
' is’-.
■ :/
j \
'j
1
0.E+00
9
-1.E+05 -I.
8
1 2
1
Time, min.
igure 3.3b Leaching profile at room temperature for malachite
45
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Profiles for both microwave heating and room temperature exhibited many irregular
peaks probably because leaching with the more acidic eluents enhanced dissolution
(attested by the green hue of the liquid coming out of the column when 10% HN03
was the eluent) and generated C02 bubbles in the line. Thus, deflections for the
mass range for Cu (63-65 amu) and for Pb (208 amu) were required to avoid
detector overload. Additionally, microwave heating induced the formation of bubbles
in all samples, despite prior degassing of reagents, due to the heating cycle of the
instrument (it reaches a temperature of ~ 93°C and after a few minutes when the
sensor notes the temperature lowered to 89°C, it initiates the heating again).
To better understand the effect of the microwave heating on the release patterns, the
microwave analyte signals in each eluent were plotted against the room temperature
ones. For example, Mn (Figure 3.4) as well as Mg, Co and Cu, seemed to have
roughly similar release in both experiments, as illustrated by points being dispersed
in above and below the 1:1 line. In contrast, Sb was not released in water in either
experiment but then with 1% and 10% HNQ3 the release was approximately the
same and finally the Sb leached out with 30% HNOs appeared to be from a
refractory phase in the malachite (Figure 3.5).
46
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
100
1:1
80
line
1:
60
g
1
40
£ *'
_ * 9 if *
. ■ '*
**>
,VTI
* *ite*
“ -■ ■*
*
♦
s
A
t t .v
water
■ acid 1%
-»
•■- acid 10%
® acid 30%
30
40
50
60
i
80
70
RT 55Mn, cts/s
Figure 3.4 Microwave vs. room temperature plot for 55Mn in malachite
700
♦ water
■ acid 1%
600
acid 10%
J2 500
« acid 30%
ja 400
m
5
g
300
200
1:1
100 -J*
0
«
0
l
line
l■fs±4>
§i
.
20
40
80
©0
RT 121Sb, cts/s
100
120
140
Figure 3.5 Microwave vs. room temperature plot fo r 121Sb in malachite
47
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
3.1.2 Leaching of pyroiusite
Release of elements during leaching of pyroiusite (Figures 3.6a - 3.8b) is interesting
since many elements have nearly matching profiles. Figures 3.6a and 3.6b show
that the signal intensity for Mg, Mn, Co, Sr and Cd increased by almost an order of
magnitude with the application of microwave energy, and progressive decreasing
release with greater acidity.
This is further illustrated in Figure 3.9 where the
increased release of Cd is much higher than the 1:1 ratio. Profiles for Cu, Ag and
Hg somewhat follow this trend {Figures 3.7a and 3.7b), whereas the release trend
for Sb is the opposite. Leaching at room temperature did not seem to release much
Fe, in contrast to the microwave-assisted leaching.
Preliminary tests with pyroiusite showed that Cu overloaded the detector, thus a
deflection had to be placed in that mass range (63-65). However mass 105, which
corresponds to ArCu+ and Pd, the latter being absent in this sample as indicated by
SCP-HRMS, was used as indicative of the copper signal. Other deflections employed
included Mn (55 amu), MnO (71 amu) and MnG2 (87 amu).
Other elements that followed the release trends for Mn (Figures 3.6a and 3.6b) were
Ba, Ce and U (Figures 3.8a and 3.8b). On the other hand, Pb and Th, which did not
seem to be leached much with water, were increasingly released as the eluent
acidity increased, as was Fe (Figures 3.7a and 3.7b). A reason for this could be that
these elements were located in a refractory phase in the mineral (Figures 3.10).
This difference in the release profiles of Fe and Mn seemed to be controlling the
release of the other elements.
48
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
S. E+05
15 per. Mov. Avg. (Mg x16)
10 per. Mov. Avg. (Srx12)
10 per. Mov. Avg. (Cd x14)
10 per. Mov. Avg. (Co x25)
10 per. Mov. Avg. (Mn x30)
HN03 1'
5. E+05
HN03 10%
HN03 30%
4. E+05
«
= 2. E+05
m
Mg x 16
1.E + 05
0 .E + 0 0
T
Time, min.
-1.E+05
Figure 3.6a Leaching profile with microwave heating for pyroiusite
- 15 per. Mov. Avg. (Mg :<200)
10 per. Mov. Avg. (Sr x200)
-10 per. Mov. Avg. (Cd x180)
-10 per. Mov. Avg. (Co x350)
-10 per. Mov. Avg. (Mn x300)
6. E+05 T IL
HNOS1%
water
5. E+05
4. E+05
HNOS 10%
Ui
It
HNOS 30%
) % Mg x 200
r
3. E+05
m 2. E+05
«
1 .E+05
ill
•W
Sr x 200
V
Sa,
.i'M._
U„
\
'
0.E+00
-1.E+05
Mn x 300
Cd x 180
8
V"
—
j—i
12
Time, min.
Figure 3.6b Leaching profile at room temperature for pyroiusite
49
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
— 10 per. Mov. Avg. (Fe x4.5) i
— 10 per. Mov. Avg. (ArCu x12)
10 per. Mov. Avg. (Ag x160)
“ 10 per. Mov. Avg. (Sb x150)
6. E+05
— 10 per. Mov. Avg. (Hg xi .6)
“ HNOS 10%
HNOS1%
i Fe x 4.5
ArCu x 12
4. E+05
Hg x 1.6
HNOS 30%
Sb x 150
3. E+05
Ag x.160
c 2. E+05
u>
1.E+05
/V’-v
0.E+00
Time, min.
-1.E+05
Figure 3.7a Leaching profile with microwave heating for pyroiusite
— 10 per. Mov. Avg. (Fe x5Q) |
— 10 per. Mov. Avg.iArCuxiSO)
•1 0 per. Mov. Avg. (Ag x240)
. . . 1 0 per. Mov. Avg. (Sb x3Q0)
10 per. Mov. Avg. (Hg x8i
HNOS1%
6. E+05
HNOS 10%
5. E+05
HNOS 30%
Sb x 300
ArCu x 150
Ag x 240 ;■|
2. E+05
1.E+05
^
w >^0?i/i' f
0.E+00
1.E+05
8
Time, min
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
HNOS1%
ii
5. E+05
ft
;
water
3. E+05
= 2. E+05
A
HNOS 10%
[ }
a.................. . HNOS 30% j"
I \
Ux 1
4. E+05
m
-10 per. Mov. Avg. (Ce x0.25)
— 10 per. Mov. Avg. (Ba xQ.007)
-10 per. Mov. Avg. (Pb x0.7)
■10 per. Mov. Avg. (Th x20)
10 per. Mov. Avg. (U x i )
Ce x 0.25
f
\
Pb x 0 J
IU V "
M
I \ Ba x 0.007
\k \
I ns 1 / \ /
l ' \ \ Th x 20 1/ \ ’■' t
..V....... , ..\ ...s.. v
\ f\
!
\
\
\
X
0.
%/\J
1 .E+05
O.E+OO
Time, min.
-1.E+05
Figure 3.8a Leaching profile with microwave heating for pyroiusite
— 10 per. Mov. Avg. (Ce x2.8)
— 10 per. Mov. Avg. (Ba xO.06)
— 10 per. Mov. Avg. (Pb x1.7)
6. E+05 t ~
10 per. Mov. Avg. (Th x40)
— 10 per. Mov. Avg. (U x9)
H N 0 3 1%
HNOS 10%
5. E+05
Ce x 2.8
HN03 30%
U.x 9
4. E+05
Ba x 0.08
3. E+05
Th x 40
O.E+OO
Time, min
Figure 3.8b Leaching profile at room temperature for pyroiusite
51
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 3.9 Microwave vs. room temperature plot fo r 121Cd in pyroiusite
i
2
► water
sacid 1%
!
acid 10%
* acid 30%
0.5
1
1.5
2
2.5
3.5
2Th, mV
Figure 3.10 Microwave vs. room temperature plot for 232Th in pyrolui
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
4
3.1.3 Hem atite
The elements Mg, Mn, Co, Sr and Cd appeared to be leached from hematite
together and primarily in the first two eluents (see Figures 3.11a and 3.11b),
although the amounts released increased when microwave energy was applied.
Minor eiements such as Sb and Hg (Figures 3.12a and 3.12b) have very similar
release profiles in both experiments, but the amounts released are enhanced with
microwave heating. A much higher leach with microwave in the more acidic eluents
for Co and Sb (Figure 3.14 and 3.15) implies extraction from a refractory phase. On
the other hand, Fe, which does exhibit an increased release with microwaveassisted leaching, presents opposite trends for the microwave-heated and room
temperature profiles. Other analytes that differ in their profiles are Cu and Ag, where
most of the leaching occurred with the first two eluents at room temperature, while
the microwave-heated experiment released these elements in each of the eluents.
The deflections in place were the same as indicated above for the pyroiusite plus
one more for the mass range of 138-140 amu (Ba and Ce). This would explain their
low signal response in both profiles illustrated in Figures 3.13a and 3.13b.
The minor element Th appeared to have a lower release with microwave heating
than at room temperature. This could only be explained by retrograde solubility,
where heating actually hinders solubility, as well as differences in the packing of the
column, particle size, surface structure or defects on the sample.
For Pb, both
profiles were quite similar with some increased release with microwave heating. In
contrast, the U profile is slightly different.
53
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
6. E+05 n
-15 per. Mov. Avg. (Mg x35)
10 per. Mov. Avg. (Srx120)
10 per. Mov. Avg. (Cd x180)
-10 per. Mov. Avg. (Co x350)
-10 per. Mov. Avg. (Mn x480)
water
HNOS 10%
5.E+05
S rx 120
Mn x 480
4. E+05
m
I /M g x 35
3. E+05 Tvft m
S 2. E+05
HNOS 30%
i Co x 350
" f . T i Cd x 160
1.E+05
v
O.E+OO
Time, min.
-1.E+05
Figure 3.11a Leaching profile with microwave heating for hematite
6. E+05
5. E+05
4. E+05
HN031%
R Mn x 840
HN03 10%
S rx 750
HN03 30%
Cox350
/
3. E+05
15 per. Mov. Avg. (Mg x150)
10 per. Mov. Avg. (Srx750)
10 per. Mov. Avg. (Cd x45Q)
10 per. Mov. Avg. (Co x350)
10 per. Mov. Avg. (Mn x840)
fV*
Cd x 450
Mg x 150
a
£ 2 . E+05
, /V"%;
1.E+05
O.E+OO
-1.E+05 -
8
Time,
m in .
Figure 3.11b Leaching profile at room temperature for hematite
54
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
- 10 per. Mov. Avg. (Fe x1)
6, E+05 i
HNOS 10%
water
|
-10 per. Mov. Avg. (ArCux150)
10 per. Mov. Avg. (Ag x1S)
10 per. Mov. Avg. (Sb x50)
10 per. Mov. Avg. (Hg x50)
HNOS 36%
5. E+05
A gx 15
Sb x 50
ArCu x 150
4.E+0:
( *i
o 3. E+05
«
\
’ »
j)
i
i
v
§,2. E+05
m
1.E+05
I
\
O.E+OO
8
Hgxou
V
12
Time, min.
-1.E+05
Figure 3.12a Leaching profile with microwave heating for hematite
-10 per. Mov. Avg.
-10 per. Mov Avg.
10 per. Mov. Avg.
10 per. Mov. Avg.
■10 per. Mov. Avg.
6. E+05
HNOS1%
5. E+05
ArCu x 175
HNOS 10%
4. E+05
m
(Fe x10)
(ArCuxI 75)
(Ag x300) 1
(Sb x200)
(Hg x320)
HNOS 30%
\n
3. E+05
Hg x 320
§ 2 . E+05
CO
bx200 \
Aq x 300
1.E+05
■■■
...
/
V
A
--
Vv
j
0 E+00
(j
-1.E+05 -I
Time, min.
12
18
Igure 3.12b Leaching profile at room temperature for hematite
55
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
8. E+05
HN O S1%
HNOS 10%
-10 per. Mov. Avg. (Ce x500)
-20 per. Mov. Avg. (Ba x20Q)
-10 per. Mov. Avg. (Pb xO.02)
10 per. Mov. Avg. (Th x65)
10 per. Mov. Avg. (U x50)
HNOS 30%
5. E+05
11x50
l\
Pb x 0.02
f\
4. E+05
Th x65
itCe x 500
2. E+05
B a x 200 i
1.E+05
O.E+OO -!
Time, min.
-1.E+05
Figure 3.13a Leaching profile with microwave heating for hematite
6. E+05
water
-10 per.
-20 per.
-10 per.
10 per.
10 per.
HNOS1%
Mov. Avg. (Ce x200)
Mov. Avg. (Ba x100)
Mov. Avg. (Pb xQ.075)
Mov. Avg. (Th x17)
Mov. Avg. (U x180)
HNOS 10%
5. E+05
Th X 17-
4. E+05
HNOS 30%
Ce x 200
J.------------
s
Pb x 0.075
'T<■%
-* ,
■§
IS3. E+05
V
V
^ K _ _ X
U x 180
B ax 100
1.E+05
0.E+00
1.E+05
Time, min.
Figure 3.13b Leaching profile at room temperature for hematite
56
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
P 500
♦ water
« acid 1%
. acid 10%
« add 30%
1:1 sine
♦
$ ^ ^
§ 300 -
♦
♦
*
S 200
100
iw
0
w
r "
100
—
200
300
400
500
RT 59Co, cts/s
600
700
800
Figure 3.14 Microwave vs. room temperature plot for S9Co in hematite
4000
,
»i
. ;* * *
*
■ acid 1%
acid 10%
* acid 30%
m 3000
?,
u
xT
m 2000
5
2 1000
1:1 me
50
100
150
RT 121Sb, cts/s
200
250
300
Figure 3.15 Microwave vs. room temperature plot for 121Sb in hematite
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
3.1.4 Leaching o f a 1:1:1 m ixture o f m alachite, pyroiusite and hem atite
The analysis of an artificial mixture of the three single minerals indicated a lack of
significant back reactions, as the profiles (Figures 3.16a - 3.18b) are similar to the
ones for each of the individual single minerals.
The analytes have very similar
profiles in both leaches, with microwave heating resulting in enhanced release than
at room temperature, in some cases with up to an order of magnitude increase in
signal intensity (Figures 3.16a and 3.16b as well as 3.18a and 3.18b).
Profiles for each of the analytes depicted in Figures 3.17a and 3.17b are similar to
dissolution of elements from specific minerals in the mixture. For example, Hg and
Ag show similar patterns as exhibited in hematite; Fe follows the pattern displayed
by hematite and pyroiusite, whereas Cu and Sb mirror their trends in malachite,
pyroiusite and hematite.
During leaching of the mixture, many bubbles and some dissolution of the sample
were also noted, especially when the eluent was 10% HN03 (a green hue was
observed In the leachate), which is consistent with leaching of the Cu In malachite.
Evidence of this can be observed in the profiles of Co and Cu. The deflections
employed were the same as the ones used for the hematite leaching, but in this case
the regular mass 63 was used to account for Cu.
Pair of elements were plotted to see if correlations were the same. For Mn and Co
at room temperature every single mineral has its own slope and the mixture trend
falls somewhere in between.
However the application of microwave seemed to
58
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
6. E+05
— 10 per. Mov. Avg. (Mg x 301
10 per. Mov. Avg. t'Sr *c20)
— 10 per. Mov. Avg. (Cd x130)
— 10 per. Mov. Avq. (Co x40;
— 10 per. Mov. Avg. (Mn xJ>)
water
HNOS 30%
HNOS1%
5. E+05
A
4. E+05 4
Mfl x 5
m
\
3. E+05
EL2.E+05
,, Cd x 138
A /v
i i
i
I;V|/ \
!
Jf \f ... Sx ,....... I
\ if 1
Co x 40
pj A 'S r x 20
--- ' -- -------- -- —f l ~wt\\ .—............. 1
11
Mg x 30
-------------- / -------------
1.E+05
Y' 7 V-'
0.E+00
12
Time, min.
1.E+05
Figure 3.16a Leaching profile with microwave heating for 1:1:1 mixture
X
6. E+05
.1
— 10 per. Mov. Avg. (Mg x 70)
... 10 per. Mov. Avq. (Sr x230)
— 10 per. Mov. Avg. (Cd x280)
— 10 per. Mov. Avg. (Co
— 10 per. Mov. Avg. (Mn x60)
HNOS 30%
HN03 10%
5. E+05
Srx J23Q
HNOS1%
4. E+05
1n x 60
Co x 40
3. E+05
Mg x 70
2. E+05
1.E+05
V
v /A
/
7
vt
■ip,
~r
O.E+OO
.E+05
\
Cd x 280
12
16
Time, min.
Figure 3.16b Leaching profile at room temperature for 1:1:1 mixture
59
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
6. E+05
10 per. Mov. Avg. (Mg x50)
10 per. Mov. Avg. (Srx30)
— 10 per. Mov. Avg. (Cd x75)
10 per. Mov. Avg. (Co x60
10 per. Mov. Avg. (Mn x80
H N O S 1%
w a te r
HNOS 10%
5. E+05
\ w C o x 80
HNOS 30%
V
4. E+05
Mgx50
S rx 30
MnxSO
%3. E+05
Cd x 75
i
= 2. E+05
1.E+05
0.E+00
Time, min.
-1.E+05
Figure 3.18c Sum of individual leaching profiles for microwave heating
6. E+05
w a te r
—- 10 per. Mov. Avg. (Mg x100)
10 per. Mov. Avg. (Srx160)
— 10 per. Mov. Avg. (Cd x400)
20 per. Mov. Avg (Co x300)
(Mn x450)
HNOS1%
Cd
HNOS 30% -i
HNOS 10%
5. E+05 - I t - - - - - - - - - - - - —
x 400
S r x 160
4. E+05
Mn x 450
\i h A
H 3. E+05
Mg x 100
---------------
E 2. E+05
A
'
1.E+05
,
k- f*
I
,
--1--
,
8
12
Time, min.
j
-1.E+05
~o—
0.E+00
Co x 300
Figure 3.16d Sum of individual leaching profiles at room temperature
80
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
■— 10 per. Mov. Avg. (Fe x0.5)
— 10 per. Mov. Avg. {Cu x90)
10 per Mov. Avg. (Ag x25)
—10 per. Mov. Avg. (Sb x50)
— 10 per. Mov. Avg. (Hg x30)
8. E+05 i
water
HNOS 30%
HNOS1%
Fe x 0.5.,.
I SbxSOl
4. E+05
3. E+05
Cu x 90.
£, 2. E+05
/ /
0.E+00
T im e ,
-1.E+05
min.
Figure 3.17a Leaching profile with microwave heating for 1:1:1 mixture
— 10 per. Mov. Avg. (Fe x5)
— 10 per. Mov. Avg. (Cu x15Q)
....10 per. Mov. Avg. (Ag x280)
— 10 per. Mov. Avg. (Sb x900)
— 10 per. Mov. Avg. (Hg x200)
6. E+05
HNOS 10%
HNOS1%
5. E+05
Cu x 150
| M ^gx280
Fe x5.
4. E+05
Is. E+05
4- 4-
Hg x 200
/ /
\
-1.E+05
\ ----- ;---:TyU
v
,M
f; US
U U rA A C
1A
1.E+05 TAT
3.£+00
Sb 5<90Q./U
ft
§ 2. E+05
5
HNOS 30%
M.
■
f
■ —
PCX
12
1!6
Time, min.
Figure 3.17b Leaching profile at room temperature for 1:1:1 mixture
61
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
-10 per. Mov. Avg. (Fe x2.5)
-15 per. Mov. Avg. (Cu x100)
6.E+05
10 per. Mov. Avg. (Ag x40)
sr. Mov. Avg. (So x140)
water
B 3.E+05
HN03 30%
Sb x 140
Ag x 40
4.E+05
m
HND3 10%
HN03 1%
5.E+05
, ^Hgx 12
IV'
I
c 2.E+05
r vj
Fe x 2 .5 !
K lU
f _ _ V — —W
*~''n
u_____
■ ^
1.E+05 -j-#——
O.E+OO
in
- J
'ill
........ ...
M
l
HiC/N
>v >v * V
A-*VSw,./U— ~
I
3
m
........
rs
V \
■si - ■.
,
T
\j
8
4
. .. 1 J
v\/\
12
16
Cu x 100
Time, min.
-1.E+05
-t-H
j V iv
Figure 3.17c Sum of individual leaching profiles for microwave heating
6.E+05
10 per.
20 per.
10 per.
10 per.
HN03 1%
water
HN03 10%
5.E+05
Mov. Avg.
Mov. Avg.
Mov. Avg.
Mov. Avg.
(Fe x9)
(Cu x350)
(Ag x320)
(Sb x650)
HN03 30%
Cu x 350
4.E+05
Sb x 650
3.E+Q5
I
V*
Hg x 16
£ 2.E+05
I
1.E+05
0.E+00
-1.E+05
8
1—
12
u
16
Time, min.
Figure 3.17d Sum of individual leaching profiles at room temperatur#
62
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
— 10 per. Mov. Avg. (Ce x150)
— 15 per. Mov. Avg. (Ba x60)
— 10 per. Mov. Avg. (Pb xO.I)
- ..........10 per. Mov. Avg. (Th xlQO)
— 10 per. Mov. Avg. (U x25)
6.E+Q5
H N 03 1i%
5.E+05
warier
HNOS 30%
U x25
Bax 60
HnOS «
4.E+05
Th x 100 s?
3.E+05
Cex 150
= 2.E+05
1.E+05
HeM
0.E+00
Time, min
-1.E+05
Figure 3.18a Leaching profile with microwave heating for 1:1:1 mixture
— 10 per. Mov. Avg. (Ce x5GQ)
— 15 per. Mov. Avg. (Ba x300)
— 10 per. Mov. Avg. (Pb x1)
- -10 per. Mov. Avg. (Th x1000)
■10 per. Mov. Avg. (U x150)
d.E+05
5.E+05
water
HN03 30%
HNOS 10%
U x 150
HNOS 1%
...........................
4.E+05
Tq x 1000
Ce x 500
h H i A/
Pb x 1
a®
3.E+05
.
Vrsrri"
2.E+05
Ba x 300
1.E+05
0.E+00
-1.E+05
Time. min.
Figure 3.18b Leaching profile at room temperature for 1:1:1 mixture
63
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
-10 per. Mov. Avg. (Ce x12)
-10 per. Mov. Avg. (Ba x3)
-10 per. Mov. Avg. (Pb xO.OS)
■10 per. Mov. Avg. (Th x120)
-10 per. Mov. Avg. (U x4)
6. E+05
HN031%
HNCS3 10%
water
5. E+05
HM03 30%
Ux4
ft.X
4.E+05
PbxQ.05
IT
M
m
1
3. E+05
§,1
«
c 2. E+05
Ol
m
1.E+05
\
Ba x 3
\ Th x 120
\ '
I?/
V
h
\
-n
-U
v*
0.E+00
8
Time, min.
-1.E+05
H:
~r
12
Figure 3.18c Sum of individual leaching profiles for microwave heating
— 10 per. Mov. Avg. (Ce x1Q)
— 10 per. Mov. Avg. (Ba x0.1)
— 10 per. Mov. Avg. (Pb x0.02)
8.E+05
1,0 per.. Mov. AvaiTh x80)
H N 031%
5. E+05
HNQ3 10% |— 1| HN03 3 Q % p k2Q*
A
j Y~C e x 10
4.E+05
■'f/ \
m
\
Bax0.1% /
= 2. E+05
iT
5
/
X ,
..
Th x 80 J \
.
.J i
rx
* <
' I
vy/
i f \
1.E+05
-1 .E+05
V\
/
3. E+05
Q.E+00
U x 20 -
Pb x 0.02
.............. .'
■
%
7
8
12
16
Time, min.
Figure 3.18d Sum of individual leaching profiles at room temperature
64
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
release these elements from two different phases in the pyrolusite (Figures 3.19a
and 3.19b).
In the case of Sr and Ce, the room temperature plot indicates three
possible phases for malachite and only one for hematite and pyrolusite, whereas this
is not observed with microwave heating. Here is the pyrolusite that has element
releases in three phases. The mixture however plotted quite similar at both room
temperature and microwave heating (Figures 3.20a and 3.20b).
To further demonstrate the absence of back reactions, the sum of the individual
profiles for each of the single minerals with microwave heating and at room
temperature (Figures 3.16c - 3.18d) were compared to the profile from the mixture.
A perfect match is not expected, given the variation from sample to sample and
changes in sensitivity may induce additional differences between the summed profile
and that of the 1:1:1 mixture.
In Figures 3.16a and 3.16c, Mg has a similar profile whereas the other elements
(Mn, Co, Sr and Cd), all showed a great release with 30% HN03, which differed in
the trend for the first eluents profile. In the case of the room temperature results in
Figures 3.16b and 3.16d, Mn also has a very comparable profile whereas the other
elements (Mg, Co, Sr and Cd) showed little similarity.
Figures 3.17a and 3.17c for the microwave-assisted leaching depict a fairly similar
trend for Fe, Cu and Sb, while the profiles of other elements (Ag and Hg) do not
match, in contrast, the room temperature scenario for this set of elements (Figures
3.17b and 3.17d) exhibits almost parallel profiles for Cu, Ag, Sb and Hg.
65
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
The microwave heating Figures 3.18a and 3.18c did not show much similarities for
any of the analytes profiles. For the room temperature results illustrated in Figures
3.18b and 3.18d, it appeared that only Pb had a matching trend.
Plots of the measured signals against the calculated (the sum profiles) indicated that
the anticipated profiles were overestimated. For example, the calculated release in
Sr was higher for 1% HN03 in both room temperature and microwave. In the case of
Sb, the more acidic eluents had greater estimated release than the actual leach
(Figures 3.21a - 3.22b).
Nonetheless, the similarity observed for several elements between the summed
profile and that of the mixture, despite changes from sample to sample and in
sensitivity, further supports the absence of significant back-reaction, at least for the
elements in this mixture.
66
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
25000
20000
15000
10000
♦ Hmt
■ Pyr
- Mai
5000
Mix
2000
4000
8000
-5000
8000
10000
12000
14000
Co, cts/s
Figure 3.19a Correlation of Mn and Co for minerals with microwave heating
(Hmt, Pyr, Mai and Mix correspond to hematite, pyrolusite, malachite and mixture)
10000
♦ Hmt
■ Pyr
: Mai
m = 3.2216
R2 = 0.8191
8000
Mix
6000
m = 1.6598
R2 = 0.9511
4000
m = 0.955 |
R2 = 0.9573 !
2000
1000
-2000
2000
3000
4000
5000
6QD0
Co, cts/s
Figure 3.19b Correlation of Mn and Co for minerals at room temperature
67
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
25000
m = 5.6212
R2 = 0.8773
20000
15000
m = 0.97
R = 0.7938
(10000 -f-
0
IK #
2000
4000
6000
♦ Hmt
■ Pyr
. Mai
- Mix
8000
10000 12000
14000
16000
-5000
Ce, cts/s
Figure 3.20a Correlation of Sr and Ce for minerals with microwave heating
♦ Hmt
£
m 3000
_1000
.1000.._ 2 0 0 0 _ .... 3000....j4000...... 5000......60Qp_._70p0...._80p0
Ce, cts/s
Figure 3.20b Correlation of Sr and Ce for minerals at room temperature
68
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
12
♦ water
•1:1 line
■ add 1%
10
acid 10%
' add 30%
I
£
3 c
m6
J&4
k>
«s<0
w 2
0
10
25
20
Sr (calculated,m V)
35
30
15
40
Figure 3.21a Measured vs. calculated plot with microwave for Sr in mixture
m = 0.1644
1:1 line
R2 = 0.9546 ^ ^
'
♦
\
\
*
l
«
IS
m
3
♦ water
*
■ acid 1%
s H M K r J i hp * •
Jfkm * ^
■ acid 10%
acid 30%
Sr (calculated, mV)
Figure 3.21b Measured vs. calculated plot at room temperature for Sr in mixture
69
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
0
1000
2000
3000
4000
5000
6000
121Sb (calculated, ctslsj
Figure 3.22a Measured vs. calculated plot with microwave for Sb in mixture
350
,1:1 line
300
250
cf
„
200
150
♦ water
.a 100
. acid 1%
. acid 10%
- acid 30%
0
400
800
121Sb (calculated, cts/s)
1200
1600
Figure 3.22b Measured vs. calculated plot at room temperature for Sb in mixture
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
3.2
Comparison with
results obtained
at low flo w
and
ICP-HRMS
instrum entation
3.2.1 RT ICP-HRMS vs. RT ICP-TOFMS
The results of continuous leaching at room temperature (RT) and detection by ICPTOFMS were compared with the data obtained by MacFarlane89 using ICP-HRMS to
elucidate if increased flow rate significantly changed the leaching profiles. The latter
data were collected using 50 mg of sample, 100 pl/m in sample uptake flow rate and
0.00011ms acquisition time for low resolution or 0.0015 ms for medium resolution; in
contrast 200 mg, 800 pL/min and 994.5 ms were employed for this project. Within
error, analyses at low flow rate and at the higher flow rate were performed at the
same temperature.
Leaching results for pyrolusite are shown in Figures 3.23a and 3.23b. In both cases,
Pb has a similar profile, with increasing release as a result of more aggressive
eluents. Other analytes such as U, Cu (inferred by mass 105 in the SCP-TOFMS
results, as described earlier in section 3.1.2), and Mn have similar profiles in both
types of experiments with a considerable release of U and Cu in the water eluent
and then less release as the eluent increased in acidity. This decrease is, however,
commensurate with the signal suppression induced by the increasing acid
concentration45, in contrast, for Mn and Fe in the low flow rate scenario, it appeared
that the analyte was released significantly with water and then leached in relatively
similar amount with the other eluents. Meanwhile, the higher flow rate experiment
had a low amount of Fe leached with water. The low sensitivity of the ICP-TOFMS
71
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
could explain this.
The isotopes monitored were 54Fe and 57Fe, which have low
abundance (5.8% and 2.2%), whereas the isotope monitored on the ICP-HRMS was
56Fe (91.7% abundance), but this Isotope could not be monitored with the ICPTOFMS since it cannot resolve the interference from 40Ari6O+. Since all the isotopes
of Fe can have polyatomic interferences (40Ar14N+, 38Ar1sO+, 36Ari80 +, 40Ca14N+,
40Ar16OH+, 38Ari8OH+ and 40Ca16OH+) their measurement by ICP-MS is difficult
unless a high resolution instrument is used or an ICP-MS with collision cell.
Nonetheless, the fact that at least in both cases Mn, Fe, Cu, and U matched each
other trends is worthy of mention. Also, analysis with ICP-TOFMS at higher flow rate
required 16 minutes, while the low flow rate leaching required 160 minutes, ten times
longer.
Some analytes in the hematite sample (Figures 3.24a and 3.24b) presented trends
similar to that described above for the pyrolusite. The elements Mn, Fe, and U, in
both flow rates during leaching of hematite have less release as the acidity of the
eluent increased.
Minor analytes such as Mo and Hg have different profiles
depending on flow rate with decreasing release with each eluent for the low flow rate
leaching, but increasing release with more acid eluent in higher flow rate. Both Mo
an Hg have a signal so low, is almost near background. Moreover, they are known
to suffer from interferences. These difficulties may account for the differences in
their profiles. Release of Pb (depicted in Figures 3.25a and 3.25b) was similar for
both flow rates in 1% and 30% HN03, but the higher flow rate released less Pb for
the other two eluents and the low flow rate profile exhibited the maximum release
with 10% HNOs.
72
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
-10 per.
-10 per.
-10 per.
10 per.
Mov. Avg. (Mn X0.7)
Mov. Avg. (Fe XT)
Mov. Avg. tPb X5)
Mov. Avg. (U X80)
-10 pgr. Mov.
" Ayo.
‘ fCu
;cuXiso)
8.E+G?
7.E+07
i_ :
Fex7
|?4.E+Q7
M n x 0 .7
/
f t
Ik ,,
J 3.E+07
£
\
2.E+07
1.E+07
/
/
’’X
I
-
If
|
\\
^
S.
\A
V \
I w
A a.
\ \ X . ' A ||/
■; " " X '
'1
t
:
x.
!
1
1
^
40
/
U\
j
K
O.E+OO
!
p^
/
'i
U xSO
j
'
&
Cu x 160
x
)
X
M
rri \
&>.
1
\
1\
y
f\ \
Si
:\
!
!
t ,
5.E+07
/
8.E+07
m
?■
P frx S i
120
Time (minutes)
Figure 3.23a !CP-HRMS Leaching profile at room temperature for pyrolusite
Sample flow rate = 100 pL/min. (Effluent flux = 3 pL/min-mg.)
6. E+05
— 10 per. Mov. Avg. (Mn x300)
— 15 per. Mov. Avg. (Fe x50)
— 10 per. Mov. Avg. (Pb xl .7)
10 per. Mov. Avg. (Pd x80)
10 per. Mov. Avg. (U x9)
H N031%
HN03 10%
5. E+05
U x9
ArCu x 80
4.E+05
HN03 30%
Pb x 1.7
Mn x 300
3.E+05
2. E+05
1.E+05
0.E+00
-1.E+05
Time, min.
Figure 3.23b ICP-TOFMS Leaching profile at room temperature for pyrolusite
Sample flow rate = 800 pL/min. (Effluent flux = 4 pL/min-mg.)
73
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
!
a
O
•t?
Mov. Avg. (Fe X2.5)
— 10 per. Mov. Avg. (Mn X14)
— 10 per. Mov. Avg. (Mo X2.000)
—-10 per. Mov. Avg. (Hg X1,800)
8.E+G7
7.E+07
M nx 14
6.E+07
5.E+G7
Mo x 2. QQO
e x 2.5
4.E+07
baxxBDQ
Jf 3.E+07
2.E+07
1.E+07
O.E+Ou
Time (minutes)
Figure 3.24a ICP-HRMS Leaching profile at room temperature for hematite
Sample flow rate = 100 pUmin. (Effluent flux = 3 pL/min-mg.)
—
—
—
—
6. E+05
10 per.
10 per.
20 per.
15 per.
Mov. Avg.
Mov. Avg.
Mov. Avg.
Mov. Avg.
(Fe x12)
(Mn x700)
(Mo x1000)
(Hg x30Q)
HN03 1%
5. E+05
HN03 10%
M nx 700
4. E+05
3. E+05
HN03 30%
Mo x 1000
= 2. E+05
1.E+05
O.E+00
Time, m in......
Figure 3.24b ICP-TOFMS Leaching profile at room temperature for hematite
Sampie flow rate = 800 pl/m in. (Effluent flux = 4 pL/min-mg.)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
—
—
—
—
8.E+07
-30 per.
10 per.
10 per.
10 per.
Mov. Avg.
Mov. Avg.
Mov. Avg.
Mov. Avg.
(Pb X0.14)
(Th X9.S00)
(U X5S0)
(Hg X1,800)
7.E+07
U x580
6.E+07
Th x 9,500
5.E+Q
£ 4.E+Q7
3.E+07
P b x0 . 14
1
2.E+07
1.E+07
V
;7
Hg x 1,800
O.E+QO
Time fm ilS tes)
Figure 3.25a ICP-HRMS Leaching profile at room temperature for hematite
Sample flow rate = 100 pL/min. (Effluent flux = 3 pL/min-mg.)
— 10 per. Mov. Avg. (Pb xO.075)
....10 per. Mov. Avg. (Th x17)
— 10 per. Mov. Avg. (U x180)
— 15 per. Mov. Avg. (Hg x450)
____ __ __
6. E+05
H N 031%
w ater
HNOS 10%
HNOS 30% |
5. E+05
T h x 174. E+05
T U x 180
?b---------
P b x 0 .0(5
f
3"
Hg x 450
3. E+05
\
§,2. E+05
_
%
«
5
I ...
1.E+05
0. E+00
-1.E+05
v v -
-/y V
F'Y
Time, min.
Figure 3.25b IGP-TOFMS Leaching profile at room temperature for hematite
Sample flow rate = 800 pl/m in. (Effluent flux = 4 pl/m in-m g.)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Similarly, limited release of Th with 1% HN03 and maximum release with 10% HN03
occurred in the tow flow rate experiment, whereas the higher flow rate extracted
most of the Th with 1% HN03 and a smaller amount in 10% HN03.
ft is possible that the higher flow rate is affecting the release of some elements
through either enhanced reactions or matrix effect. At the lower flow rate, there is a
longer residence time, which allows more time for leaching but also for re­
adsorption.
At the higher flow rate, elements are more effectively removed,
minimizing re-equilibration and enhancing the rate of dissolution, which may or not
compensate for the smaller residence time. For some elements (Fe in particular)
spectroscopic interferences arising from co-eluting elements cannot be ruled out.
Additionally, the presence of colloids could play an adverse role in the release of
analytes from the sample.
3.2.2 RT ICP-HRMS vs. MW ICP-TOFMS
The results of continuous leaching with microwave heating (MW) and detection by
ICP-TOFMS were compared with the data obtained by MacFarlane89 using ICPHRMS to elucidate if the heating plus the increased flow rate significantly changed
the leaching profiles. For the pyrolusite sample (Figures 3.23a and 3.26), Cu, Pb
and U followed the exact pattern in both leaches (namely an apparent lower release
with higher acidity of the eluent). On the other hand, other analytes such as Mn and
Fe had a slightly different trend in the room temperature ICP-HRMS profile where
the amount leached appeared to be similar in all HN03 eluents.
76
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
— 10 per.
— 10 per.
-— 10 per.
....10 per.
..” 10 per.
6.E+Q5
5. E+05
i
4. E+05
ra ra w liras
n ................
11
!
\ Fe x 4.5
^"U x1
%
nx26
3rCu x 12
Mov. Avg.
Mov. Avp.
Mov. Avg.
Mov. Avg.
Mov. Avg.
(FSffnx26)
(Fe x4.5)
(Pb xQ.7)
(Cux12)
(Ux1)
n
M
----------------HNOS 3S% r
j 1
2. E+05
1.E+05
rv s s ..
O.E+OO
8
Time, min.
-1 .E+05
Figure 3.26 ICP-TOFMS Leaching profile with microwave heating for pyrolusite
MW Temp. -90 °C. Sample flow rate = 800 pL/min. (Effluent flux = 4 pL/min-mg.)
—
—
—
—
5. E+05
H N 031%
HN03 10%
Fex 1
10 per.
10 per.
20 per.
10 per.
Mcrv. Avg.
Mov. Avg.
Mov. Avg.
Mov. Avg.
(Fe x1)
(Mn x480)
(Mo x360)
(Hg x50)
HNOS 30%
Mo x 360
\
, . /
f\ M l
3. E+05
Mnx 480
« 2- E+05
1.E+05
i
Hg x 5 0
O.E+OO
-1.E+05
Time, min.
Figure 3.27 ICP-TOFMS Leaching profile with microwave heating for hematite
MW Temp. ~90 °C. Sample flow rate = 800 pL/min. (Effluent flux = 4 pL/min-mg.)
77
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
In the case of the hematite (shown in Figures 3.24a and 3.27), Fe, Mo and Hg have
opposite profiles In both cases, but Mn does not follow this pattern: most of the
leaching occurred with the first two eluents in the microwave-assisted scenario while
the trend for the data obtained by ICP-HRMS was progressively lower amount
leached with increased acidity of the eluent. Nevertheless, the microwave leaching
still allows correlating major mineral dissolution with trace mineral release.
The
application of microwave energy compensated to some extent for the lower
residence time at the higher flow rate.
These observations are quite encouraging, indicating continuous leaching with MW
ICP-TOFMS can provide similar results to those obtained with RT ICP-HRMS with
significantly shorter analysis time.
3.3 Verification of mass balance
Verification of mass balance was first attempted using a sediment standard
reference material. However, the high back-pressure that resulted from the small
particle size of this material inhibited leaching.
A sample of hematite was used
instead. The total digest results of the sample of hematite were compared to the
total amount leached, using external calibration with matrix-matched standards for
each reagent, plus the amount in the residue left after leaching. In all cases, 200-mg
aliquots of hematite were used. These results are detailed in Table 3.1 and were
obtained by a single determination.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Good agreement was found for V, Co, Ni, Mo and Pb.
some discrepancies.
Nonetheless there were
For example, for the two Zn isotopes used, the sum of the
amount leached plus residue was less than the total digest. However, Zn has the
highest first Ionization potential and, as a result, is more susceptible to suppression
due to matrix effects. Chu and Beauchemin90 used an internal standard to overcome
this problem, but that was not possible in this work and might explain why the values
are consistently low. Spectroscopic interferences are very unlikely since the same
result was obtained with both isotopes.
Table 3.1 Quantification and mass balance for hematite
Leach
Residue
Residue + Leach
(in ng)
(in ng)
(in ng)
% Leach/
(Res. + L.)
24Mgmw
6305
5.9 x104
6.5 x104
9.61
24Mgrt
7745
4 x104
5 x104
17.02
25Mgmw
7788
5.8 x104
6.6 x104
11.75
25Mgrt
9600
4 x104
5 x104
20.32
51V»mw
41
6 x102
6 x102
6.48
51v rt
37
7.0 x102
7.3 x102
5.08
52Crmw
279
3 x102
6 x102
50.81
52Crrt
195
74.7 x102
76.6 x102
2.54
“ M rw
11587
2.0 X104
3.1 x104
37.14
55Mnrt
9159
2.5 x104
3.4 x104
27.01
s9Comw
19
4 x102
4 x102
4.81
59Cort
27
4.5 x102
4.7x102
5.72
Elem.
Total digestion
(in ng)
5.9 x104
5.8 x104
7 x102
5 x102
2.37 x104
mw: for microwave, rt: for room temperature
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
5 x i 02
Table 3.1 Q uantification and mass balance for hematite (continued)
Residue
Residue + Leach
% Leach/
Total digestion
fin ng)
(in ng)
{in ng)
{Res. 4- L.)
(in ng)
181
1 x102
3 x102
55.23
72
2 x1Q2
3 x102
24.04
63P
i,
vUmw
5930
1.5 x10s
7.4 x10s
79.45
s3Curt
6646
4.5 x103
11.1 x103
59.51
6927
1.4 x10s
8.3 x10s
82.82
“ Curt
6881
5 x10s
11 x103
58.95
^Zrimw
239
3.7 x103
3.9 x103
6.07
^Z flrt
273
4.3 x103
4.6x103
5.99
“ Z rw
402
4.5 x103
4.9 x103
8.15
“ Zrirt
360
4.4 x103
4.8 x103
7.52
98Momw
13
1.5 x102
1.6 x102
8.19
98Mort
65
2.4 x102
3.1 x102
21.08
,21Sbmw
69
3.8 x102
4.5 x102
15.33
121Sbrt
374
7.4 x102
11.1 x102
33.61
^Pbm w
72313
0.2 x104
7.43 x104
97.24
204Pbrt
71326
1.5 x104
8.6 x104
82.60
^Pbmw
60275
0.12 x104
6.14 x104
98.07
^ P b rt
67704
1.9 x104
8.7 x104
77.68
207Pbmw
61176
0.13 x104
6.24 x104
97.98
^Pbrt
68181
1.9 x104
8.7 x104
78.26
208Pbmw
53843
0.13 x104
5.51 x104
97.65
64774
1.9 x104
8.4 x104
77.09
Elem.
02Nimw
62Nirt
Leach
3 x102
8.4 x10s
8.6 x10s
13.0 x103
14.5 x103
1.6 x102
4.5 x102
7.6 x104
7.64 x104
7.29 x104
7.36 x104
mw: for microwave, rt: for room temperature
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Similarly, for both isotopes of Mg, the room temperature teaching values where
consistently lower than the total digest, while the microwave-assisted leaching
values were higher. One reason for this could be a slight difference in the actual
composition of the sample, as the hematite sample was not 100% homogeneous.
It’s also possible that there were small errors in the dissolution of the residues.
For Cr, Cu and Sb, there seemed to be good agreement between the values for
microwave-assisted leaching and the total digest, whereas at room temperature, the
amount from the leach plus residue was higher than the total digest. For Cr and Cu,
a spectroscopic interference is unlikely since the results at room temperature and
with microwave heating would both be biased high. A factor affecting Cr could be
the origin of it in the sample, since chromites are very refractory.
Despite the similarity of the Mn values at room temperature and with the microwave
heating, these results were much higher than the values obtained for the total digest.
Spectroscopic interferences such as 39K160 + or 40Ar14N1H+ could account for this.
The value for residue plus amount leached fell between a range of ± 10% of the total
digest value for most of the elements monitored (Figures 2,28a - 2.29b), which Is
good considering that the hematite sample used is “predominantly” monomineralic.
81
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
80030
T
70000
♦ 24 Mg
m 60000
c
50000
#
ot 40003
1:1 line.
■
,
..
□
*
t
*3
1
30000
25Mg
55Mn
65Cu
65cu
54Zn
68Zn
, 204 pb
£ 20000
, 2 « pb
# 207 pb
. 208pb
10000
20000
80000
40000
60000
Residue + Leach, ng
Figure 3.28a Quantification of major elements with microwave heating
(- - - indicates 10% above and below the 1:1 line; error bars correspond to 1a)
80000
1:1 line,
70000
60000
=jF|p
50000
—
y "
^
3 40005
xt
30000
1
--* fjM fl
■ 25 Mg
.. 55 Mn
®3Cu
Q 65Qy
* 64Zn
6SZn
204 p b
206 Pb
* 207pb
20000
10000
.
2®Pb
0
20000
40000
60000
80000
100000
Residue + Leach, n§
Figure 3.28b Quantification of major elements at room temperature
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
1000 T
1:1 l i n e ^ x '
.
j
800 -
os
sx
i
m
■o
1
♦ 51 V
600 -
« 52 cr
>Co
62 Ni
400 -
U t'-
&
h-
o 98 Mo
• 121Sb
200 0
200
400
600
800
1000
Residue + Leach, ng
Figure 3.29a Quantification of minor elements with microwave heating
1000
V
800
'A
Y y
O
)
c
''"
\
1:1 line
i
♦ 51V
■ 52Cr
59Co
62Ni
o 98Mo
• 121Sb
| 600
a
■5 400
200
-i---H—r
0
0
200
400
600
800
1000
Residue + Leach, ng
1200 7600
7800
Figure 3.29b Quantification of minor elements at room temperature
83
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Chapter 4:
Qualitative analysis of a sandstone sample
from Cigar Lake
4.1 Sample overview
Given the encouraging results obtained with the single minerals, a “real” sample of
quartz arenite sandstone with high clay content (5%) was also used for the
continuous on-line leaching analysis. The major minerals in this sample are quartz
(95%), illite (3%), kaolinlte (2%), and hematite (1%) and it was obtained from a Umineralized drill core near the Cigar Lake uranium deposit in the Athabasca Basin,
northern Saskatchewan, Canada. The Pb isotopic ratios in this sample may be used
to identify different sources of Pb, particularly those derived from the decay of the
proximal uranium ore. This sample has been characterized by Dr. Kyser’s group
from the Department of Geological Sciences and Geological Engineering at Queen's
University. The particle size of 0.5 - 1 . 4 mm was chosen because it releases the
clay matrix without significantly breaking the detrital quartz grains, and this size is
amenable to on-line analysis without inducing too much back-pressure.
The
elements of interest in this sample include Pb and U, that may indicate effects from
the deposit, and Fe and Mn that reflect oxides that are likely traps for the U and Pb
migrating from the deposit91.
Qualitative analysis was done to verify if there was a noticeable effect when applying
heat. Continuous on-line leaching of this sample using a hot bath (at 75°C) and a
hot bath with ultrasound Indicated that heat enhanced the rate of release of most
elements.
84
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4.2 E ffect o f heat on leaching
The results from comparative tests (Figure 4.1a - 4.2b) with and without microwave
heating showed increased release of analytes, by up to an order of magnitude (as
evident from the differences in y-axis scales), with the application of focusedmicrowave energy so as to keep the temperature at ca. 90°C. A similarity in the
profile shape for some of the analytes was also noted (see Section 4.3). The
application of microwave energy increased the leaching process as some analytes
with minimal release in certain eluents at room temperature were released in
significant quantities with microwave-assisted leaching (Figure 4.4a - 4.5b).
To better understand the effect of the microwave heating on the release patterns, the
microwave analyte signals in each eluent were plotted against the room temperature
ones. For example, Ba (Figure 4.3) as well as Sr and Ce, is mobile and released
much more in the microwave experiments, as illustrated by points above the 1:1 line,
but the Ba from a refractory phase can only be released with more acidic eluents
and with heating. In contrast, Th had little release in water and 1% HN03 in either
experiment but then with 10% HNOs there was release and finally the Th leached out
with 30% HNO3 appeared to be from a refractory phase in the sandstone (Figure
4.4).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
25
I
water
MW 208 p b
HNOs1% [
MW 238 U
Signal, mV
20
15
HNOs10%
10
HNOs 30%
5
0
10
Time, min.
-n
-5 1 .
15
igure 4.1a Leaching profile with microwave energy applied for Pb and U
2.5
— PT 208 Dh
........ —..... -..-
water
HNOs 1%
_ _ p-j- 238 y
2
Signal, mV
1.5
1
h
%
jV
I
HNOs10%
HNOs 30% [-
0.5
0
-0.5
........................I ........................ i........ ......... .... .
15
20
10
TiriieLm iii.
Figure 4.1b Leaching profile at room temperature for Pb and U
86
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
16000 H N 0 3 10%
14000
12000
water
HNOs 30%
6000
« 4000
2000
-2000
Figure 4.2a Leaching profile with microwave energy applied for Fe and Mn
1600
HNOs1% - ^
1200
j\
|||
water
*,1000
IS 800
A
||
0
-200
HNO3 30% j
|
\A
1 800
o>
« 400
200
— RT 55 Mn
HNOs1 0 %
1400
|
\
I
I
\
\
\
f
\J K f
1/
!
i
**! A
*
10
-'-Tunei-fnlfii-'
/\^
15
Figure 4.2b Leaching profile at room temperature for Fe and Mn
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
:
;
i
20
5
4
.s
■
1-3
m
1:1 line
2
o
-
* u * r#
I V« ♦M *
l 8p
♦ water
■ acid 1%
- acid 10%
» acid 30%
.
2.5
1.5
0.5
RT 137Ba, mV
Figure 4.3 Microwave vs. room temperature plot for 137Ba in sandstone
14000
♦ Th w
12000
■ Th 1%
. Th 10%
«10000
* Th 30%
8000
4000 4
2000
-
0
500
1000
1500
2000
2500
3000
3500
4000
RT 232Ih , ctsfs
Figure 4.4 Microwave vs. room temperature plot for 232Th in sandstone
88
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4.3 Area comparison
Comparison of the ratio of the area leached by a certain reagent to the total leached
area (Figure 4.5) indicates that microwave heating releases more of the available
analytes in a given reagent without shifting material between reagents. A t-test at a
95% confidence level showed no significant difference between the proportion of
analyte leached with microwave (MW) heating (3 replicates) and at room
temperature (RT) (3 replicates). Note however, that the area does not exactly equal
amount, because the sensitivity is different in the different reagents. Beauchemin
and coworkers45 noticed a decrease in sensitivity with increasing acid concentration,
but the use of a single internal standard would not provide an appropriate correction
because this suppression is mass dependent. However, for results obtained on the
same day, a comparison of relative areas should be valid.
0.9
B MW 57Fe
U RT 57Fe
■ MW 208Pb
0 RT 208Pb
0.8
0.7
0.6
0.4
0.3
0.2
0.1
0.0
-
0.1
water/total
acid 1% /total
acid 10% /total
acid 30% /total
Leaching eluent
Figure 4.5 Area comparison for eluent to total area ratio
(Error expressed as standard deviation, n=3)
89
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4.4 Reproducibility
Leaching of the sandstone sample was carried out on three different days to verify
the reproducibility. The shapes of the profiles are similar and small differences in
intensity can be attributed to variability in the particle size and hence, how much of
the matrix was included, packing of the column and sensitivity of the instrument.
Also, small differences depend on where in the sample the element is held. Figures
4.6a to 4.10b show the results for selected masses for leaching with both microwave
heating and at room temperature.
90
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1000
water
Jan. 14
' tn. 10
Jan. 05
HNOS 1%
800
600
HN03 10%
HNOS 30%
400
Time, mln.
-200
Figure 4.6a Leaching profile with microwave energy applied for 59Co
1IOT
800
Jan. 14
Jan. 10
Jan. 05
HN03 1%
water
600
HNOS 30%
a 400
200
-200
Time, min.
Figure 4.6b Leaching profile at room temperature for 59Co
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
4500
3600
HNOS 10%
water
n
—= Jan. 10
Jan. 05
m w zm ,
2700
m 900
0
Time, min.
-900
Figure 4.7a Leaching profile with microwave energy applied for 55Mn
1500
Jan. 14
Jan. 10
H N 031%
1200
900
Jan. 05
HNOS 10%
HNOS 30%
«=" 600 c
w
« 300 -
-300 J
Time, min.
Figure 4.7b Leaching profile at room temperature for 55Mn
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Jan. 14
I03 1%
Jan. Of
24
«16
c
a
HNOS 30%
Time, min.
Figure 4.8a Leaching profile with microwave energy applied for 208Pb
20
Jan. 14
Jan. 10
Jan. 05
HNOS1%
16
12
HNOS 10%
8
HNOS 30%
4
0
-4
Time, min,
igure 4.8b Leaching profile at room temperature for 208Pb
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
180
water
Jan. 14
Jan. 10
150
Jan. 05
120
HNOS1%
HNOS 30%
60
-30
Figure 4.9a Leaching profile with microwave energy applied for 88Sr
60
Jan. 14
Jan. 10
Jan. 05
HNOS1%
50
water
40
E 30
HNOS 10%
»20
HNOS 30%
10
0
-10
TSroe. m in ...
Figure 4.9b Leaching profile at room temperature for 88Sr
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Jan. 14
Jan. 10
Jan. 05
water
I HNOs 10%
HN03 30%
3 4
2D
Time, min.
Figure 4.10a Leaching profile with microwave energy applied for 13'Ba
HNOS1%
Jan. 14
Jan. 10
Jan. 05
2.5
HNOS 10%
HNOS 30%
0.5
-0.5 J
Time, min.
Figure 4.10b Leaching profile at room temperature for 137Ba
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
4.5 Lead ratios
Lead consists of four naturally occurring stable isotopes with varying amounts of
isotope abundances: 208Pb (52.4%), 207Pb (22.1%), 206Pb (24.1%) and 204Pb (1.4%).
While 204Pb is the only Pb isotope that is not formed by decay, the remaining
isotopes (208Pb, 207Pb and 206Pb) are radiogenic as a result of the radioactive decay
of 232Th, 235U and 238U, respectively. Differences In ages, and Th/Pb and U/Pb ratios
are responsible for substantial variations in Pb isotopic abundance; thus isotopic
ratios for Pb vary in soils samples. Typically Pb isotope ratios are within 1.95 to 2.15
for 208Pb/206Pb, 0.78 to 0.95 for 207Pb/206Pb, and 16.6 to 20.0 for 206Pb/204Pb for most
natural substances92. Hence, the Pb isotope ratios (i.e., 208Pb/206Pb and 207Pb/206Pb)
in a given sample can be used to identify the source of the Pb.
The Pb isotopes 206Pb, 207Pb and 208Pb are free from isobaric overlaps, whereas
204Pb has an isobaric interference from 204Hg. Although the latter can be corrected
through the intensity of an isotope of Hg that is free of interferences in combination
with an assumed isotopic composition of Hg, the low abundance of 204Pb makes its
detection difficult by ICP-MS. Therefore, only the ratios 208Pb/206Pb and 207Pb/206Pb
were used in this study.
Figure 4.11a and 4.11b show the release of Pb isotopic ratios for the sandstone
sample, which were computed using the point-by-point average over the top of each
peak. These confirm that the release pattern did not change upon the application of
microwave energy for this particular sample.
96
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4
2Q 8pb/2 0 6 p b
207pb/208pb
water
3
.2
HNOs 1% |------1HN03 10%
HNOs 30%
2
1
..... --------------
0
i
.........
5
0
10
Time. min.
•i
>
15
f
2f
Figure 4.11a Lead ratios for leaching performed with microwave heating
water
HNOs
1%
—
2 0 8 p b/2 0 6 p b
—
207pb /206pb
HNOs10%
o
33
£
10
Time, min.
15
Figure 4.11b Lead ratios for leaching performed at room temperature
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
20
Average ratios 207Pb /206Pb over 3 separate days were similar for room temperature
(RT) and with microwave (MW) heating for the water and 1% HN03 reagents,
although they are statistically different for 10% and 30% HNQ3 when treated with a ttest at a 95% confidence level (Figure 4.12). This suggests that for this sample a
different source of Pb is being released with microwave heating under very acidic
conditions relative to room temperature.
2 0.4
water
acid 1%
acid 10%
acid 30%
Leaching reagent
Figure 4.12 Comparison of 207Pb/ 206Pb ratios for leaching performed with (MW)
and without microwave heating (RT)
98
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4.6 C om parison
with
results obtained
at low flow
and
ICP-HRMS
instrumentation
Results of continuous leaching using focused-microwave heating and detection by
ICP-TOFMS were compared with the data obtained by Chipiey et a i '88 using ICPHRMS in order to elucidate if microwave heating significantly changed the leaching
profiles.
As mentioned earlier in Section 3.2, these data were collected using a
smaller sample amount, sample uptake flow rate and acquisition time (respectively
50 mg, 100 pL/mfn and 0.00011ms for low resolution or 0.0015 ms for medium
resolution; in contrast 200 mg, 800 pL/min and 994.5 ms were employed for this
project).
4.6.1 RT ICP-HRMS vs. RT ICP-TOFMS
Leaching results at low flow rate and room temperature with the ICP-HRMS and at
higher flow rate and room temperature with the ICP-TOFMS is illustrated in Figures
4.13a and 4.14b. For the elements Mn, Sr, Ba, Pb, and U, the trends in the two
experiments are similar. With the slow flow rate (Figure 4.13a), enhanced release
occurred with the first two eluents and then decreased release with the next two
eluents. With the higher flow rate experiment (Figure 4.13b), there was minimal
release with water, but enhanced leaching with 1% HN03, followed by decreasing
analyte leaching with the next eluents. Other elements such as Fe seemed to be
affected by the flow rate. Low flow rate (in Figure 4.14a) released little Fe with water
and 10% HNOg, followed by a significant release In 1% HN03 and 30% HNOsIn contrast, leaching with higher flow rate (Figure 4.14b) showed similar release with
99
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
_ 40
m
| 35
I
.........................
30
» 25
«?
V 20
«s 15
c
J?
« 10
5
5
208Pb x 3
1
238U x 0.5
i
-=■- 87Srx 10
_j,_. 138ggj Xg
1
la
1
Pi
1 ,
fly
0- :W
^__^
0 — ....i..........i ........ f — .......... .
21
41
61
81
101 121
Time (minutes)
141
161
181
Figure 4.13a ICP-HRMS Leaching profile at room temperature for sandstone
Sample flow rate =100 pL/min. (Effluent flux = 3 pt/min-mg.)
100000
80000
water
— RT 208pbx2.5
— RT 238 u x 8
■RT 88Sr x 0.5
— *RT 137 Ba x 5
HN031%
« 60000
»
HNOS 10%
- - 40000
c
e»
«
HNOS 30%
20000
0
I:.,
"
10
-20000 -L
15
20
Time, min.
Figure 4.13b ICP-TOFMS Leaching profile at room temperature for sandstone.
Sample flow rate = 800 pt/m in. (Effluent flux = 4 pL/min-mg.)
100
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1
21
41
61
81
101 121
Time (minutes)
141
161
181
Figure 4.14a ICP-HRMS Leaching profile at room temperature for sandstone.
Sample flow rate = 100 plim in. (Effluent flux = 3 pL/min-mg.)
1600
1400
1200
water
« 400
200
-200
Figure 4.14b ICP-TOFMS Leaching profile at room temperature for sandstone.
Sample flow rate = 800 pl/m in. (Effluent flux = 4 pL/min-mg.)
101
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
the first three eluents and only a smaii amount leached with 30% HM03. Although
this could indicate some shift in the pattern of the leaching, it is more likely a
spurious effect of spectroscopic interferences such as 40Ca16OH+ and 41K160 + on
57Fe+with the higher flow rate and ICP-TOFMS.
4.6.2 RT ICP-HRMS vs. MW ICP-TOFMS
Figures 4.13a and 4.15 as well as 4.14a and 4.16 exhibit relatively similar profile
shapes and significantly shorter analysis time for the sandstone leached with
microwave and ICP-TOFMS. The much closer profiles between the leaching done
at low flow rate with ICP-HRMS and the one done with microwave-assisted heating
at higher flow rate with ICP-TOFMS indicates that microwave heating compensated
for the lower residence time in the latter case. Similar information could therefore be
obtained within 20 min as opposed to 3 hours with ICP-HRMS. Further study to
verify if similar observations can be made for other sample types are warranted.
102
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100000
wafer
MW
MW
MW
MW
80000
208Pb x -i I
288u x 2
88Sr xO.Sf
187Ba x 5 f
60000
HNOS 10%
40000
HNOS 30%
T im e , min,
-20000
Figure 4.15 ICP-TOFMS Leaching profile with microwave applied for sandstone
MW Temp. -90 °C. Sample flow rate = 800 pL/min. (Effluent flux = 4 pL/min-mg.)
16000
HNOs10%
14000
12000
m10000
I
HNOs1%
water
HNOs 30%
8000
6000
» 4000
2000
Figure 4.16 ICP-TOFMS Leaching profile with microwave applied for sandstone MW
Temp. -90 SC, Sample flow rate = 800 pL/min. (Effluent flux = 4 pL/min-mg.)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Chapter 5: Conclusions
Continuous on-line leaching with ICP-HRMS detection was demonstrated to be a
very useful technique for reliably assigning trace elements to host phases45,88,89.
However, the slow mass scanning rate of HRMS and the use of a micronebulizer at
100 pL/min limited the sample throughput. The present study combined three ways
of increasing the sample throughput: quasi-simuitaneous detection with ICP-TOFMS,
a higher flow rate and microwave heating of the reagents and the micro-column of
sample. Detection by ICP-TOFMS allowed the simultaneous monitoring of a greater
number of elements without increasing the analysis time or requiring the use of a
micronebulizer. The greater number of measurements possible may also allow a
better resolution of various phases.
Increasing the flow rate of reagents through the sample had an effect on the
leaching profile, which was unavoidable due to the shorter contact time between the
reagent and the sample.
However, the simultaneous application of microwave
energy, which speeded up the kinetics of dissolution, essentially compensated for
the shorter residence time, yielding profiles fairly similar to those at low flow rate with
a micronebulizer and ICP-HRMS. Although analysis with ICP-TOFMS is plagued by
spectroscopic interferences (most of which can be resolved in ICP-HRMS), which
precludes a definitive conclusion on the release of some elements, the drastically
shorter analysis time could render this technique a valuable tool for screening
multiple samples. Hence, it will further enhance the usefulness of this technique for
exploration geochemistry and other areas such as environmental studies.
For
1 04
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example, it could be used to rapidly assess the potential of soils to act as sources of
certain contaminants.
Compared to batch sequential leaching methods, the proposed approach features
considerably reduced analysis time, much simpler sample preparation, reduced
reagent consumption, reduced contamination (since the leaching is performed within
a closed system) and a greater resolution of the various phases released by a given
reagent.
It also overcomes the reprecipitation or adsorption problems that were
experienced with previous sequential leaching techniques, which are efficiently
prevented by the continuous flow of fresh reagent.
Finally, it allows on-line
monitoring of isotopic compositions, which enables the identification of different
sources of elements (whose isotopic distribution varies in nature) as they are
released.
This information is unavailable to batch methods where the analytes
released from the different phases leached by a given reagent are mixed together.
On the other hand, because no assumption is made about the phases being
dissolved, i.e. both trace and minor elements are monitored, complex spectra result.
Some knowledge of the sample will therefore facilitate data interpretation for
heterogeneous samples.
Future studies should investigate in greater detail the effect of various factors in
order to establish the optimum reagent flow rate, sample size, particle size, and
microwave temperature.
Ultimately, the results obtained for various soil samples
from several known sites should be examined to identify path-finder elements i.e.
that are indicative of ore deposits in their neighborhood.
105
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References
1. J. K. Soon and T. E. Bates, J. Soil Sci., 1982, 33, (3): 477-488.
2. W. L. Lindsay and W. A. Norvell, Soil Set. Soc. Am. J., 1978, 42, (3): 421-428.
3. R. Leschber, R. D. Davis, and P. L’Hermite, Chemical methods for assessing bioavailable metals in sludges and soils, 1985, Elsevier Applied Science Publishers,
London, UK.
4. P. H. T. Beckett, Adv. Soil Sci., 1989, 9, (1): 143-176.
5. A. Tessier, P.G.C. Campbell, and M. Bisson, Anal. Chem., 1979, 51, (7): 844-851.
6. A. M. Ure, Ph. Quevauviller, H. Muntau, and B. Griepink, Int. J. Environ. Anal.
Chem., 1993, 51, (1-4): 135-151.
7. E. Maiz, M. V. Esnaola, and E. Millan, Sci. Total Environ., 1997, 206, (2-3): 107115.
8. M. Manz, L. Weissflog, R. Kuhne, and G. Schuurmann, Ecotoxicol. Environ. Saf.,
1999, 42, (2): 191-201.
9. E. Maiz, I. Arambarri, R. Garcia, and E. Millan, Environ. Poll., 2000, 110, (1): 3-9.
10. A. V. Filgueiras I. Lavilla, and C. Bendicho, J. Environ. Monit., 2002, 4, (6): 823857.
11. D. M. Templeton, F. Ariese, R. Cornelis, L. G. Danielsson, H. Muntau, H. P. Van
Leeuwen, and R. Lobinski, Pure Appl. Chem., 2000, 72, (8): 1453-1470.
12. B. Michalke, Ecotoxicol. Environ. Saf., 2003, 56, (1): 122-139.
13. J. A. Caruso, B. Klaue, B. Michalke, and D. M. Rocke, Ecotoxicol. Environ. Saf.,
2003, 56, (1): 32-44.
106
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
14. Ph. Guevauviller, G. Rauret, and B. Griepink, Int. J. Environ. Ana!. Chem., 1993,
51, (1-4): 231-235.
15. B. Marin, M. Vafiadon, M. Polve, and A. Monaco, Anal. Chim. Ada, 1997, 342,
(2-3): 91-112.
16. M. Kersten and U. Forstner, Water Sci. Techno!., 1986, 18, (4-5): 121-130.
17. J. Usero, M. Gamero, J. Morillo, and I. Gracia, Environ Int., 1998, 24, (4): 487496.
18. R. A. Sutherland and F. M. G. Tack, Anal. Chim. Acta, 2002, 454, (2): 249-57.
19. D. Fangueiro, A. Bermond, E. Santos, H. Carapuca, and A. Duarte, Anal. Chim.
Acta, 2002, 459, (2): 245-256.
20. S. Eichfeld, J. Einax, and G. Knapp, Anal. Bioanal. Chem, 2002, 372, (7-8): 801807.
21. C. M. Davidson, A. L. Duncan, D. Littlejohn, A. M. Ure, and L. M. Garden, Anal.
Chim. Acta, 1998, 363, (1): 45-55.
22. G. Rauret, J. F. Lopez-Sanchez, A. Sahuquillo, R. Rubio, C. Davidson, A. Ure,
and Ph. Quevauviller, J. Environ. Monit, 1999, 1, (1): 57- 61.
23. R. A. Sutherland, Appl. Geochem., 2002, 17, (4): 353-65.
24. A. Smeda and W. Zyrnicki, Microchem. J., 2002, 72, (1): 9-16.
25. S. E. Howe, C. M. Davidson, and M. McCartney, J. Anal. A t Spectrom., 1999,
14, (2): 163-168.
26. S. E. Howe, C. M. Davidson, and M. McCartney, J. Anal. A t Spectrom., 2002, 17
(5): 497-501.
27. C. G. Yuan, J. B. Shi, B. He, J. F. Liu, L. N. Liang, and G. B. Jiang, Environ Int.,
2004, 30, (6): 769-783.
107
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
28. C. L. da Silva and 3. C. Masini, Fresenius J.
A n a !.
Chem., 2000, 367, (3): 2 8 4 -
290.
29. A. Kabata-Pendias, Appl. Geochem., 1993, 2, (1): 3-9.
30. A. Barona and B. Etxebarria, Fresenius Environ. B u l l 1996, 5, (9-10): 604-609.
31. C. Gleyzes, S. Tellier, and M. Astruc, Trends Anal. Chem., 2002, 21, (6-7): 451467.
32. B. Perez Cid, I. Lavilla, and C. Bendicho, Int. J. Environ. An. Ch., 1999, 73, (2):
79-92.
33. C. M. Davidson and G. Delevoye, J. Environ. Monit., 2001, 3, (4): 398-403.
34. G. M. Greenway and Q. J. Song, J. Environ. Monit, 2002, 4, (6): 950-955.
35. E. Campos, E. Barahona, M. Lachica, and M. D. Mingorance, Anal. Chim. Acta,
1998, 369, (3): 235-243.
36. B. Perez Cid, I. Lavilla, and C. Bendicho, Anal. Chim. Acta, 1999, 378, (1-3):
201- 210 .
37. B. Perez Cid, A. F. Albores, E. F. Gomez, and E. F. Lopez, Anal. Chim. Acta,
2001, 431, (2): 209-218.
38. I. ipolyi, C. Brunori, C. Cremislni, P. Fodor, L. Macaluso, and R. Morabito, J.
Environ. Monit, 2002, 4, (4): 541-548.
39. B. Perez-Cid, M. D. Gonzalez, and E. F. Gomez, Analyst, 2002, f27, (5): 881688.
40. P. S. Fedotov, A. G. Zavarzina, B, Y. Spivakov, R. Wennrich, J. Mattusch, K. D.
C. Titze, and V. V. Demin, J. Environ. Monit., 2002, 4, (2): 318-324
41. A. Filgueiras, I. Lavilla, and C. Bendicho, Anal. Bioanai. Chem, 2002, 374,
(1): 103-108
108
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
42. A. Valsanen, R. Suontamo, J. Silvonen, and J. Rintala, Anal.
B lo a n a l.
Chem,
2002, 373, (1-2): 93-97.
43. A. K. Wanekaya, S. Myung, and O. A. Sadik, Analyst, 2002, 127, (9): 12721276.
44. P. O. Scokart,
K.
Meeus-Verdinne, and R. De Borger, Int. J. Environ. Anal.
Chem., 1987, 29, (4): 305-315.
45. D. Beauchemin, K. Kyser, and D. Chipley, Anal. Chem., 2002, 74, (15): 39243928.
46. M. Jimoh, W. Frenzel, V. Muller, H. Stephanowitz, and E. Hoffmann. Anal.
Chem., 2004, 76 (4): 1197-1203.
47. F. Lazaro, M. D. Luque de Castro, and M. Valcarcel, Anal. Chim. Acta, 1991,
242, 283-289.
48. M. C. Yebra and A. Moreno-Cid, J. Anal. A t Spectrom., 2002, 17 (10): 14251428.
49. F. W. Fifield and P. J. Haines (Eds.), Environmental Analytical Chemistry, 1997,
Blackie Academic & Professional, London, UK, pp 342-343, 388.
50. J. Szpunar, V. O. Schmitt, O. F. X. Donard, and R. Lobinski, Trends Anal.
Chem., 1996, 15, (4): 181-187.
51. C. Sparr Eskiisson and E. Bjdrklund, J. Chromatogr. A, 2000, 902, (1): 227-250.
52. R. C. Richter, D. Link, and H. M. Kingston, Anal. Chem., 2001, 73, (1): 30A-37A.
53. A. Abu-Samra, J. S. Morris, and S. R. Koirtyohann, A nal. Chem., 1975, 47, (8):
1475-1477.
54. H. M. Kingston and L. B. Jassie (Eds.), Introduction to microwave sample
preparation: theory and practice, 1988, American Chemical Society, Washington,
DC, pp 9.
109
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
55. B. Kaufmann, P. Christen, and J.-L. Veuthey, Phytochem. AnaL, 2001, 12, (5):
327-331.
56. Y. Y. Shu and T. L. Lai, J. Chromatogr. A, 2001, 927, (1-2): 131-141.
57. H. Budzinski, M. Leteier, P. Garrigues and K. Le Menach, d. Chromatogr. A,
1999, 837, (1-2): 187-200.
58. L. E. Garcia-Ayuso and M. D. Luque de Castro, Anal. Chim. Acta, 1999, 382, (3):
309-316.
59. M. Letellier and H. Budzinski, Analyst, 1999, 124, (1): 5-14.
60. M. Letellier, H. Budzinski, S. Capes, and A. M. Dorthe, Fresenius J. Anal. Chem.,
1999, 364, (3): 228-237.
61. J. A. Nobrega, L. C. Trevizan, G. C. L. Araujo, and A. R. A. Nogueira,
Spectrochim. Acta B, 2002, 57, (12): 1855-1876.
62. V. Lopez-Avila, R. Young, and W. F. Beckert, Anal. Chem., 1994, 66, (7): 10971106.
63. R. S. Houk, V. A. Fassel, G. D. Flesch, H. J. Svec, A. L. Gray, and C. E. Taylor,
Anal. Chem., 1980, 52, (14): 2283-2289.
64. K. E. Jarvis, A. L. Gray, and R. S. Houk, Handbook o f Inductively Coupled
Plasma Mass Spectrometry, 1992, Chapman and Hall, New York, N.Y., pp 10-13, 8,
119.
65. http://www.natur.cuni.cz/~ugmnz/fcplab/icpm 1.htmt
66. J. R. Chirinos, K. Kahen, S. E. O’Brien, and A. Montaser, Anal. Bioanal. Chem.,
2002, 372, (1): 128-135.
67. A. Montaser and H. Zhang, Mass spectrometry with mixed-gas and helium ICPS.
In Inductively Coupled Plasma Mass Spectrometry, A. Montaser (Ed.) Wiley-VCH,
New York, N. Y „ 1998, pp 809-890.
110
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
68. H. Ucfoida and T. Ito, 3. Anal. A t Spectrom., 1997, 12, (9): 913-918.
6 9 .1. Piatzner, J. V. Safa, F. Mousty, P. R. Trincherini, and A. L. Poiettini, J. Anal. At.
Spectrom., 1994, 9, {6): 719-726.
70. L. Ebdon, M. J. Ford, R. C. Hutton, and S. J. Hill, Appl. Spectrosc., 1994, 48, (4):
507-516.
71. S. F. Durrant, Fresen. J. Anal. Chem., 1993, 347, (10-11): 389-392.
72. S. J. Hill, M. J. Ford, and L. Ebdon, J. Anal. At. Spectrom., 1992, 7, (8): 1157—
1165.
73. W. C. Wiley and I. H. McLaren, Rev. Sci. Instrum., 1955, 26, (12): 1150-1157.
74. M. Guilhaus, J. Mass Spectrom., 1995, 30, (11): 1519-1532.
75. M. Guilhaus, V. Mlynski, and D. Selby, Rapid Commun. Mass Spectrom., 1997,
11, (9): 951-962.
76. M. Guilhaus, Spectrochim. Acta B, 2000, 55, (10): 1511-1525.
77. M. Balcerzak, Anal. Sci., 2003, 19, (7): 279-989.
78. D. P. Myers and G. M. Hieftje, Microchem. J., 1993, 48, (3): 259-277.
79. G. M. Hieftje, D. P. Myers, G. Q. Li, P. P. Mahoney, T. W. Burgoyne, S. J. Ray,
and J. P. Guzowski, J. Anal. At. Spectrom., 1997, 12, (3): 287-292.
80. J. F. Holland, C. G. Enke, J. Allison, J. T. Stults, J. D. Pinkston, B. Newcome
and J. T. Watson, Anal. Chem., 1983, 55, (3): 997A-1010A.
81. R. E. Sturgeon, J. W. H. Lam, and A. Saint, J. Anal. At. Spectrom., 2000, 15, (6):
607-616.
82. X. D. Tian, H. Emteborg, and F. C. Adams, J. Anal. At. Spectrom., 1999, 14,
(12): 1807-1814.
83. S. J. Ray and G. M. Hieftje, J. Anal. At. Spectrom., 2001, 16, (10):1206—1216.
111
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
84. H. Emteborg, X. D. Tian and F. C. Adams, d. Anal A t Spectrom., 1999, 14, (10):
1567-1572.
85. J. Ruzicka and E. H. Hansen, Anal Chim. Acta, 1975, 78, (1): 145-157.
86. J. Ruzicka, Fresenius Z. Anal Chem., 1988, 329, (6): 653-655.
87. K. W. Simonsen, B. Nielsen, A. Jensen, and J. R. Andersen, J. Anal. At.
Spectrom., 1986, 1, (6): 453-456.
88. D. Chipley, T. K. Kyser, D. Beauchemin and W. MacFarlane, Can. J. Anal. ScL
Spectrosc., 2003, 48, (5):269-276.
89. W.
MacFarlane,
Continuous Leach Inductively Coupled Plasma Mass
Spectrometry (CL-ICP-MS): Assessment for potential applications in exploration
geochemistry, 2003, M. Sc. Thesis, Queen's University, Kingston, Ontario, Canada.
90. M. Chu and D. Beauchemin, J. Anal At. Spectrom., 2004, 19, (9): 1213-1216.
91. G. J. Hoik, T. K. Kyser, D. Chipley, E. E. Hiatt and J. Marlatt, J. Geochem.
Explor., 2003, 80, (2-3): 297-320.
92. M. Viczian, A. Lasztity, and R. M. Barnes, J. Anal. A t Spectrom., 1990, 5, (4):
293-300.
112
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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