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Flotation of a Copper-Zinc Ore Using p-Nonylcupferron as Collector.

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Dev. Chem. Eng. Mineral Process., 5(3/4),pp.183-193, 1997.
Flotation of a Copper-Zinc Ore Using
p-Nonylcupferron as Collector
R. Natarajan
Department of Chemistry, Campion Higher Secondav School,
Tiruchirapalli-620001, Tamil Nadu, INDIA
and
I. Nirdosh* and S.V. Muthuswami
Department of Chemical Engineering,
Lakehead University, Thunder Bay, Ontario, CANADA P7B 5El
Bench-scale potation tests were done with a chalcopyrite, sphalerite and pyritecontaining ore from Timmins, Canada using p-nonylcupferron as collector. Eflects of
pH and the need for adding copper sulphate for zinc activation and lime as pyritedepressant were studied
The collector floated nearly 94% copper and 94% zinc
without pyritic iron in 30% mass at pH 4 and 5, and 93% Cu and 18% Zn at pH 6 in
30% mass. At higher pH values, metal recoveries were poor. No copper sulphate was
neededfor activating zincflotation. Addition of lime did not d e c t pyrite suppression.
Keywords: Flotation; base metals; cupferron; nonylcupferron; copper; zinc; iron;
chalcopyrite.
~
*Authorfor correspondence.
I 83
R. Natarajan, I. Nirdosh and S. V. Muthuswami
Introduction
Flotation reagents, known as collectors, are classified into two groups, those that work
by physical adsorption and those that work by chemisorption. Sulphonates, alkyl
sulphates and carboxylates belong to the former whereas xanthates and
dithiophosphates to the latter group of collectors'. Chelating agents also belong to the
latter group, and have received attention as potential collectors in froth flotation-.
They are more selective in the flotation of complex mineral systems because they act
by chemisorbing on selected mineral surfaces. Due to the presence of vacant d
orbitals in transition metals, their ions form chelates more readily than the other metal
ions. It may be noted that most valuable minerals contain transition metals, whereas
the gangue minerals such as clay and silica contain non-transition metals. Hence,
chelating agents chemisorb on the valuable minerals more readily than on the gangue.
This results in improved selectivity of the chelating agents.
Some of the chelating agents that have been tested as collectors are 8hydroxyquinoline, dimethylglyoxime,cupferron, p-hydroxy oxime, a-hydroxy oxime,
mercaptobenzothiazole and thiocarbomates.
These attempts have remained a
laboratory curiosity because of their greater cost and higher concentration of the
collector necessary for separation.
Canada has vast reserves of a wide spectrum of base metal sulphide minerals,
the most common amongst them being chalcopyrite (CuFeSJ. chalcocite (CqS),
chalmersite (Cupe,Sd, bornite (Cu,FeS,), sphalerite (ZnS), galena (PbS) and
pentlandite (FeSNiS) with varying amounts of pyrite (FeSJ, pyrrhotite (FexS&,),
arsenopyrite (FeAsS) and maramatite (ZnSFeS)4. These minerals rarely occur alone
in the ore and are invariably found as mixtures in varying proportions. In addition,
precious metals such as gold, silver and platinum group metals are also frequently
present. The ores are usually low-grade and single or multistage flotation is used to
concentrate the minerals. Thus, flotation may produce a single concentrate (primconcentrure), two concentrates (a primary rougher concentrate and a secondconcentmte obtained by flotation of the primary rougher tails), or three concentrates
(an additional tertiary concenhute obtained by flotation of the secondary rougher
184
Flotarion of a copper-zinc ore using p-nonylcupferron as collector
The number of valuable minerals in the ore determines the number of
concentrates produced.
Copper-zinc sulphide ores are usually floated with collectors such as
xanthates or dithiophosphates. Woods6has recently given an extensive review of the
chemisorption of xanthates on metals and metal sulphides. A xanthate collector
renders the sulphide mineral as hydrophobic by forming an insoluble metal xanthate
on the mineral surface'. These collectors are more effective for the flotation of copper
than for zinc because CuS is more stable than ZnS, especially in alkaline medium'.
In order to float sphalerite, therefore, copper sulphate is added to the flotation pulp
as activator. Cuz+ions replace Zn2+in sphalerite and copper xanthate deposits on the
mineral surface* providing a hydrophobic coating on the mineral. The amount of
copper sulphate needed depends on the zinc content of the ore. For instance, up to
90 g of copper sulphate per percent of zinc is needed for processing a tonne of oreg.
This large requirement of copper sulphate and its corrosive nature" are matters of
concern for the industry. In addition, about 1 kg lime per tonne of ore is usually used
as pyrite-depressant during the flotation of Cu and Zn oresg.
Cupferron has been used for the flotation of chalcopyrite". Addition of fuel
oil was found necessary to promote flotation. Fuel oil forms a strong bond with x electrons of the benzene ring of cupfernon and presents a hydrophobic end for
attaching to the air bubble. Though addition of fuel oil in a Hallimond tube was
successful, its scale-up would be difficult because the fuel oil introduces another phase
into the system. In order to overcome this, in our previous work'' we introduced long
hydrophobic alkyl chains into the para-position of the benzene ring of cupferron. The
side chain serves the same purpose as fuel oil without introducing another phase.
Among the several alkyl-substituted cupferrons synthesized, p-nonylcupferron was
found to give the best results in the flotation of uranium ores".
The objective of this work was to test the effectiveness of p-nonylcupferron
as collector for a typical
chalcopyrite-sphalerite-pyriteore to determine whether: (i)
zinc could be floated without the need for activation with copper sulphate; and (ii) a
separation between Cu-Zn minerals and pyrite could be effected by producing a single
185
R. Natarajan, I. Nirdosh and S. V. Muthuswami
primlay concentrate containing mainly Cu and Zn, leaving pyrite in the tails without
the need for a pyritedepressant such as lime.
Materials and Methods
Ground Cu-Zn ore was obtained from Kidd Creek Mines, Timmins, Ontario, Canada.
The ore contained an average of 3.5 wt% each of copper and zinc, and about 10-15
wt% iron. The typical mineral composition in the ore were: 11 wt% chalcopyrite; 6
wt% sphalerite; 5 wt% pyrrhotite; 10 wt% pyrite; and varying amounts (usually < 1
wt%) of galena and b~rnite'~.
p-Nonylcupferron was prepared following the procedure
reported in our previous paper".
Flotation tests were done in a laboratory Denver flotation machine at an
impeller speed of 1100 rpm.
All pH adjustments were done with 1 mol/L
hydrochloric acid or with 1 mol/L potassium hydroxide solutions. The pH was
controlled within f 0.05 units.
About 330 g of the ore (500 g of the ore slurry) was used for each flotation
test. The slurry was wet ground for 7 minutes in a 1 litre 'porcelain-fortified-withalumina' ball mill with burundum grinding media, in order to expose fresh unoxidized
surface. The contents were immediately transferred to the 1.5 L flotation cell, 600
mL of water was added, and pH adjusted to the desired value (4-1 1). 20 mL of a
0.01 mom collector stock solution was added and the pulp was agitated for 20
minutes for conditioning. 2 drops of a 1% solution of Aerofroth 73 were added, if
required. It may be noted that usually the collector provided the required stable froth.
Air was then introduced to float the ore. The mineral-rich froth was collected to
exhaustion, i.e. until the slurry stopped foaming. Similarly three more floats were
collected, adding 10 mL of the collector solution, and conditioning for 10 minutes,
each time. The floats and tails were filtered separately, and the solids dried and
weighed. Appropriate amounts of the solid samples were weighed, digested, filtered,
and the filtrates analyzed for elements by Inductively Coupled Argon Plasma
Emission Spectrometery.
186
Flotation of a copper-zinc ore using p-nonylcupferron as collector
To study the effect of lime, about 1 g CaOkg ore was added in the grinding
stage, and the flotation tests were conducted at pH values of 6 to 11. In most tests,
p-nonylcupferron provided a stable froth and addition of any frothing agent was not
needed.
Results and Discussion
(i)
Eflect ofpH
The cumulative percentage mass, and copper, iron and zinc recoveries in all floatconcentrates of each test at different pH values are given in Table 1, and the
percentage metal recoveries are plotted in Figure 1.
Table 1. Results of Flotation Tests of Cu-Zn Ore Using p-Nonylcupferron.
pH
I
Total wt% Recovery in all Floats
I
T -cuWith
out
Lime
With
Lime
Fe
-
With
With
With
With
out
Lime
Lime
out
Lime
out
94
e in Float
I
Zn
With
- -. -
W
Lime
Lime
94
1.6
94
1.6
With
Lime
-
4
32
5
30
6
30
28
92
90
48
46
78
87
1.9
2.0
7
26
28
87
87
43
43
68
74
2.0
2.0
8
22
18
69
58
34
27
58
53
2.0
2.2
9
22
17
63
57
31
24
55
45
2.0
2.4
10
26
22
72
65
37
33
58
47
2.0
2.1
11
29
-
29
68
65
37
37
51
45
1.8
94
58
-
I
1.8
-
These results show that at pH 4 and 5 , recovery of copper and zinc was 94%
each in 30% mass, whereas at pH 6 the Cu recovery was still >93% but the Zn
recovery dropped to 78% (a 16% drop), in 30% mass. The metal recoveries declined
at pH 7 and above. These results are consistent with those reported in literat~re’”’~.
187
R. Natarajan, I. Nirdosh and S.V. Mulhuswarni
Prabhakar and Khangaonkar” found that maximum adsorption of cupferron OR acid
washed (pyrite-free) chalcopyrite occurred at pH 4.04. F m a n et al.I4 found that
cupferron effectively complexes with the metal ions in aqueous medium in the same
pH range of 4-5. It is interesting to note that Fuerstenau et al.” found that flotation
recovery of sphalerite with xanthate was > 90% at pH 3.5 and relatively less xanthate
was needed with increased hydrocarbon chain length in the collector.
Although iron was also in the float, it appeared to be associated with copper
in the chalcopyrite rather than that with pyrite. The ratios of Cu/Fe in various floats
are given in the last two columns in Table 1. These values vary from 1.6 to 2.4, and
are much higher than the Cu/Fe ratio in chalcopyrite which is 1.16. These results
show that there was less Fe present in the floats than would be expected if
chalcopyrite was the only mineral in the float. This indicates two effects:
(a) In addition to chalcopyrite, Cu-predominant minerals such as chalcocite,Cu,S, or
those containing relatively more Cu than Fe (e.g. bornite, Cu,FeS,, with a Cu/Fe mass
ratio = 5.8) were floated by the collector.
(b)
Fe-predominant minerals such as pyrite and pyrrhotite, or those containing
relatively more Fe than Cu (e.g. chalmersite, Cu$e,S,,
with a Cu/Fe mass ratio =
OX), were not floated by the collector because, otherwise, the Cu/Fe ratio would
have been much lower than that indicated in Table 1.
Thus, p-nonylcupferron floated Cu and Zn minerals (such as chalcopyrite,
bornite and chalcocite, and sphalerite) in preference to the Fe-predominant minerals
(such as pyrite, pyrrhotite or chalmersite).
(ig Effect of Collector Concentration
The results showed that > 90% copper or zinc was floated in 30% mass by 0.25 g pnonylcupferron per kg of ore. The collector requirement was much lower than the
minium cupferron concentration reported in the adsorption of cupferron on
chalcopyrite”. The lower collector requirement may be due to the presence of the
long hydrocarbon chain in the collector molecule used in this study. The presence of
Flotation of a copper-zinc ore using p-nonylcupferron as collector
100 5
I
I
I
1
I
I
I
I
90 -
-
80 -
-
70 -
cu
-
60 -
-
50 -
-
40 -
30 -
20
-'
I
I
I
I
I
I
PH
Figure I . Percentage recovery of Cu,Zn and Fe at dferent pH values.
100
-
I
I
I
I
I
I
I
I
1
I
I
I
4
5
6
7
8
9
10
11
I
I
I
I
90-
80 70 -
?i
600
8
5040
-
20
3
12
PH
Figure 2. Percentage recovery of Cu, Zn and Fe at different pH values afer adding
lime.
189
R. Natarajan, I. Nirdosh and S. V. Muthuswami
a long hydrocarbon chain with nine carbon atoms would cover a greater surface of the
ore than unsubstituted cupferron, and would render it hydrophobic.
(iii) Effect of Lime Addition
Lime is usually added to depress pyrite if present during the flotation of CdZn
sulphide ores with conventional collectors such as xanthates. The added lime forms
mixed films of Fe(OH),, FeO(OH), CaSO, and CaCO, on the pyrite surface, reducing
the adsorption of xanthate on pyrite7. In order to find the effect of adding lime with
p-nonylcupferron as collector, flotation tests were repeated with addition of nearly the
same quantity of lime as is usually added during CdZn flotation with xanthate, i.e.
1 g CaOkg ore, at pH values of 6-1 1. The results are included in Table 1 and are
plotted in Figure 2. These results indicate that addition of lime did not affect the
percentage iron recovery to any sipficant degree. It may be concluded that addition
of lime as a depressant for pyrite is not essential for floating this ore with p nonylcupferron.
(iv) CoUecror-Mimed i'erocrion
For the flotation of sulphide minerals with a xanthate as collector, there exists a
theoryI6 which is based on Pauling's study" on the structure of transition metal
sulphides, stating that xanthate-sulphide interactions occur through the formation of
an S-S bond (i.e. the collector-mineral sulphur bond). The present results, however,
do not support this theory. If the donor oxygen atoms of the chelating group (-
N(N0)O) of the collector were chemisorbed by bonding through the sulphur atoms,
the sulphide minerals sphalerite, pyrite and chalcopyrite should all have floated. The
fact that Cu and Zn floated equally, and Fe from pyrite did not float, as discussed in
section (i), it indicates that the collector chelated with mineral metal ions on the
surface rather than with the mineral sulphur. The higher recovery of copper and zinc
at low pH reinforces this conclusion because it shows that a possible surface oxidation
of the mineral S to SO: took place, the SO: ions dissolved away, and the Cu2+and
Zn2' sites were exposed and made available for chelation. Pyrite oxidation did not
190
Flotation of a copper-zinc ore using p-nonylcupferron as collector
take place during these conditions because much stronger oxidizing conditions are
needed for the oxidation of pyritel*(e.g. high temperatures, high electromotive force
(EJ, and the presence of an external oxidant such as NaC10, or ferric iron, Fe33.
It may be noted that (a): present flotation was done at room temperature where pyrite
oxidation by air is insignificant” ; (b) no external oxidant was added to the system
during the present investigations; and (c) Fe” ions could not have existed in the
flotation pulp at the pH values (>3) studied in h s work because ferric hydroxide
precipitates at pH values higher than 3”.
Conclusions
Zinc was floated by p-nonylcupferron without the need for activation with copper
sulphate. Chalcopyrite and sphalerite were floated in preference to pyrite without the
addition of lime. Addition of a frothing agent was not needed because the collector
provided a stable froth. Because of the elimination of three reagents required in the
current flotation processes, namely the expensive and corrosive copper sulphate, lime
and a frother, and hence their absence from mill effluents, the use of
p-
nonylcupferron makes the beneficiation process more attractive both economically
and environmentally. A collector usage of 0.25 kgMg ore was required and 94% Cu
and 94% Zn were floated at pH 5, as a p r i m q concentrate, under the conditions
investigated in this work.
Industrial practice is to float the ores at alkaline pH values unless a slightly
acidic pH such as 5 or 6 is the natural value in the mill, or is required by the process
(e.g. maintaining a pH of 6 by bubbling SO, was found desirable in the flotation of
a Ni-Cu-Co ore from LYM Lake, Manitoba’?. The optimum pH can be established
only after extensive optimization studies of operating conditions such as collector
concentration, degree of grind, conditioning time and temperature. It may therefore
be noted that the present results do not in any way suggest that pH 5 is recommended
as optimum for this system. The important inference from this study is that it is
possible to separate the CdZn minerals from pyrite using p-nonylcupferron and
produce a primary concentrate containing =94% Cu and Zn, from which the metals
I91
R. Natarajan, I. Nirdosh and S.V. Muthuswami
may then be separately recovered without the need f o r copper sulphate, lime or a
frother. It is suggested that for an actual milling practice, Cu may be floated first
with a conventional collector to give a primcay concentrate, followed by the flotation
of Zn as a secondary concentrate with a cupfemonderivative such as p nonylcupfemon. This is without adding copper sulphate as activator or lime as pyritedepressant, leaving pyrite behind in the secondary rougher tails.
Acknowledgements
Financial support for this research was provided by the Natural Sciences and
Engineering Research Council of Canada. Thanks are due to Ms Silvana D'Carlo of
Kidd Creek Mines (Falconbridge), Timmins, Ontario, for discussions and ore
mineralogy, to Mr. Kelly Roberts of the same company for samples; and to Mr. R.
Morrow of Inmet Mining, Schreiber, Ontario, for discussions.
Refenmces
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
192
Arbiter, N., Cooper, H.. Fuerstenau, M.C., Harris, C.C., Kuhn, M.C., Miller, J.D., Yap, RF.
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Somasundaran, P. and Nagaraj, P.D. 1984. Chemistty and qplication for chelaring agenfs in
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pp. 209-219. The InstiMion of Mining and Metallurgy, UK.
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in M i n e d Processing, SME, Littleton, Colorado, pp 35-50.
McLachlan, C.G. 1957. The Milling of Cu, Cu-Ni. Cu-Zn and Zn .Ores, In. J. Convey et al.
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Flotation of a copper-zinc ore using p-nonylcupferronas collector
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Received: 15 June 1996; A ccepted ajter mvision: 16 June 1997
193
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