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Leachability of Lead and Cadmium from Cementitious Wastes.

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Dev.Chem Eng. Mineral Process. 12(3/4),pp. 355-3@,2004.
Leachability of Lead and Cadmium from
Cementitious Wastes
C.E. Halim, R. Amal*, D. Beydoun, and J.A. Scott
Centre for Particle and Catalyst Technologies, School of Chemical
Engineering and Industrial Chemistry, The University of New South
Wales, Sydney, New South Wales 2052, Australia
Gary K.-C. Low
New South Wales Environment Protection Authority, Analytical and
Environmental Chemistry Section, Lidcombe, NS W 2141, Australia
In this paper, the leachability of lead and cadmium from cementitious waste was
investigated to determine the leaching mechanism of these heavy metals from a
cement matrix so that a more appropriate leaching test can be designed. The leaching
studies were carried out using a modified Toxicity Characteristic Leaching Procedure
(TCLP), and variations in leaching parameters such as leachate pH, the duration of
agitation, the particle size, and the liquid to solid ratio were investigated. The main
finding of these studies was that the leachability of Pb and Cd in cementitious waste
was highly dependent on the p H of the leachate. Other findings included: (i) the
leachability of metals initially decreased with increasing leaching duration but
increased after the leachate pH reached equilibrium; (ii) the particle size of the
cementitious waste affected the rate of leaching of alkalinity from cement and hence
the leachability of the heavy metal ions; and (iii) the total metals in the leachate
increased with increasing liquid to solid ratio. Overall, the TCLP was found to be
inappropriate f o r assessing the leachabiliv of heavy metals from cementitious waste
due to the high buflering capacity of the calcium ions in the cement. This maintained
the pH of the leachate at a value where heavy metals are insoluble. The test was
found to underestimate the concentration of heavy metal ions leached from
cementitious waste relative to the concentration in the actual landfill environment.
Introduction
Leaching tests are used to regulate solid waste disposal in landfills, to classify
industrial and municipal wastes for disposal in landfills and to evaluate the stability of
solid waste forms for beneficial reuse of wastes. The procedure currently used in New
South Wales is the Toxicity Characteristic Leaching Procedure (TCLP) as described
* Author for correspondence (r.amal@unsw.edu.au).
355
C.E. Halim, R. Amal, D. Beydoun, J.A. Scott and G.K.C. Low
in the Australian Standard AS4439.1-1997 - 4439.3-1997, and is based on standards
provided by the US Environmental Protection Agency. The Australian TCLP has two
main differences from the US TCLP. The US TCLP uses two leaching fluids (acetic
acid solution pH 2.9 and acetate buffer pH 5.0) and specifies a maximum particle size
of 9.5 mm, whereas the Australian TCLP uses three leaching fluids (the leaching
fluids used in the US TCLP plus 0.1 M sodium tetraborate, pH 9.2) and specifies a
maximum particle size of 2.4 mm.
Although the TCLP has been used widely, many argue that it is not an appropriate
tool to assess the long-term stability of metal ions in landfills. The TCLP adopts the
“one size fits all” approach, meaning all wastes are tested under the same conditions.
The test is based on a co-disposal mismanagement scenario, where industrial waste is
assumed to be codisposed with municipal waste into a sanitary landfill and is
designed to simulate the worst-case scenario in landfills [ 11. However, this may not
always apply. For example, many wastes, such as those from mineral processing
industries, are not codisposed with municipal wastes and do not experience the
aggressive leaching performed during the TCLP. Another example where the TCLP
may not apply is with monolithic wastes which do not experience compaction in
landfills. The aggressive acid leaching and the particle size reduction can
overestimate the extent of leaching, leading to incorrect classification of wastes as
hazardous. Hence, there is a need to critically assess the suitability of t h s test in
examining the potential hazards of wastes.
Using the TCLP, the pH of the leaching fluid increases over time due to the
release of alkalinity from cement, while in landfills the long-term pH of the leachate
is approximately constant (values between 6 to 8). Many authors have investigated the
influence of leaching parameters on cementitious waste containing heavy metals [2131. However, in most studies the pH of the leaching fluid (during the leaching
process) was not measured or controlled. Hinsenveld suggested that, as the solubility
of many metals is governed by the pH of the system, this is one of the most important
factors that need to be considered in the development of a new leaching test [14].
The aim of this work was to investigate the effects of leaching parameters on the
leachability of the heavy metals, lead and cadmium, from cernentitious wastes. The
parameters investigated included the effect of leachate pH, leaching duration, particle
size, liquid to solid ratio, and the type of leaching fluid. The concentrations of other
cations (Ca, Si, K, Mg, Al, and Fe) present in cement were also measured to help
explain trends in the concentrations of Pb and Cd. Ultimately the results will assist
both in the development of a model that can predict the leachability of heavy metals
from landfills and the design of a leaching test that is more material- and site-specific.
Experimental Procedure
The experimental flowsheet is shown in Figure 1. Stabilisation of cementitious waste
was foIlowed by crushing of waste using three crushers. The crushed waste was
subjected to the leaching test, which was based on the TCLP, and analysis of the
leachate using ICP-AES. A more detailed description is given below.
Materials
Ordinary Portland Cement (OPC) was supplied by Australian Cement. Lead nitrate
(Pb(NO& by Ajax) and cadmium nitrate tetrahydrate (Cd(N03)2.4H20by Fluka)
356
Leachability of Lead and Cadmiumfiom Cementitious Wastes
provided the heavy metal ions for stabilisation by the OPC. Acetic acid of analytical
grade was used as the leachmg fluid. Dilution of the acetic acid was performed using
deionised water. For digestion of samples, 70% €€NO3(Univar), 37% HCl (Univar),
and 30% H202 (Univar) were used.
Stabilisation of
cementitious
waste containing
1-2% Pb and Cd
With 28-day
curing time
-
el+
Leaching of
waste
(TCLP)
Cone Crusher
Roller Crusher
<2.4mm
Analysis of
-+ leachateusing
ICP-AES
-
Figure 1. Experimental jlowsheet.
Preparation of cementitious waste
The wastes studied consisted of cementitious waste containing 2.3% Pb and 1.3% Cd
with water to cement ratios of 0.38 and 0.44 respectively. Initially the metal salt was
dissolved in deionised water, and then blended with cement powder, Additional water
was added slowly while the cement mixture was mechanically stirred for 10-15
minutes. The cementitious waste was then cured for 28 days.
Crushing was performed using three consecutive sets of crushers (jaw crusher,
cone crusher, and roller crusher) to reduce the particle s u e to less than 2.4 mm (in
accordance with the Australian TCLP). Particles having a size between 2.4 mm and
9.5 mm, and greater than 9.5 mm, were collected and stored for investigation into the
effect of particle size. Sieves with mesh sizes of 2.4-mm and 9.5-mm were used to
classify the particles.
Leaching experiments
The leaching procedure used was based on the “Australian Standard for Wastes,
Sediments, and Contaminated Soils; Part 3: Preparation of Leachates - Bottle
Leaching Procedure” [15]. For most samples, forty grams of crushed waste was
mixed with 800 millilitres of leaching fluid (with 20:l w/w liquid to solid ratio) in
1-1itre high density polyethylene (HDPE) square wide-mouth bottles (Crown
Scientific, catalogue no. BGE340P), and tumbled at a speed of 30 rpm for 18 hours.
The solids were settled for a few minutes and the liquid (called “leachate”) was
filtered through a 0.8-micron membrane filter. The pH of the leachate was measured,
and it was analysed for the heavy metal ions as well as Ca, Si, K, Mg, Al, and Fe
using Optima 3000 Inductively Coupled Plasma-Atomic Emission Spectroscopy
(ICP-AES).
357
C.E. ffalim,R. Amal, D. Beydoun, J.A. Scot?and G.K.C. Low
The effects of leaching parameters were investigated by varying one parameter
while keeping the other parameters constant. The leachate pH was controlled by
varying the initial concentration of the leaching fluid (acetic acid). The leaching fluid
used was acetic acid at concentrations between 0.1 M and 5.7 M (initial pH values
between 2.88 and 2.0).
Three particle size ranges were studied: less than 2.4 mm (as in the Australian
TCLP); between 2.4 mm and 9.5 mm; and larger than 9.5 mm. The duration of
leaching was vaned from no tumbling to 7 days (168 hours) of tumbling. At 0-hour
(no tumbling), the TCLP bottle containing the waste and the leaching fluid was
shaken for a few seconds, and the leachate was filtered for subsequent ICP-AES
analysis. At other leaching durations, the TCLP bottle was placed inside a tumbler
and tumbled at 30 rpm. The liquid to solid ratios used were 10:1,20:1,40:1, and 60:1.
Digestion of cement and other samples
The composition of the cement and other samples was determined by digesting the
sample with aqua regia solution. Aqua regia digestion involved digesting 1 gram of
dry sample with 5 ml of 70% HN03,15 ml of 37% HCI, and 0.5 ml of 30% H202,and
heating the mixture at 80-90°C for 30 minutes. The heated sample was filtered and
diluted to 100 ml for ICP-AES analysis. The composition of metals in the OPC from
the digestion is shown in Table 1.
54
2.5
Ca
Fe
I
A1
1
2.4
I
1.2
0.72
0.05
0.03
0.02
0.01
0.003
Mg
K
Mn
Na
Ba
Zn
V
I
Ni
0.002
mostly Si and 0.
Results and Discussion
Effect of leachate p H
The effect of leachate pH on the leachability of Ca, Pb, and Cd is shown in Figure
2(a) and (b). It shows that the concentration of metals in the leachate is governed by
the pH of the leachate.
358
Leachability of Lead and Cadmiumfrom Cementitious Wastes
The increase in the pH of the leaching fluid during the leaching process was
predominantly due to the calcium ions from the cementitious waste. Calcium is
considered as “the secondary matrix or matrix filler” of cement due to its readiness to
dissolve when cement is introduced to an acidic leaching medium [ 141. This is
illustrated by the high percentage of calcium that was leached from the cement, even
at high pH (see Figure 2a). According to Hinsenveld [14], calcium can be present as
two forms in cement. Calcium that f o m hydrates is called bound calcium while
calcium (in the form of Ca(OH)2) located within the pores of the cement matrix is
referred to as free calcium. The later provides the acid neutralisation capacity of
hydrated cement, which governs the buffering capacity for acid attack [ 141.
Figure 2(a) also shows that the percentage of Pb and Cd in the leachate decreased
with increasing pH. This may be because Pb and Cd are insoluble at high pH as their
hydroxides. At the high leachate pH values, these metals could precipitate out of the
leachate, and either settle with the unleached solids or be filtered out during the
filtration process for the ICP-AES. However, due to the amphoteric nature of Pb, its
concentration decreased to an undetectable level between pH 9 and 12, but increased
to approximately 12 mg/l above pH 12.
Evidence of hydroxide precipitation was observed for Fe(II1) leached during the
TCLP. The colour of the leachate changed from red to clear after a few hours of
leaching when htgh concentrations of acetic acid were used while the colour of the
solid at the bottom of the TCLP bottle at the end of the leaching was slightly red,
indicating the presence of Fe(OH)3 precipitates. Measuring the concentration of
metals in the leachate with and without filtration revealed that 10% of the metals were
removed during filtration.
As shown in Figure 2(b), using the leaching fluid specified by the TCLP (0.1 M
acetic acid solution), the pH of the leachate was found to be above 12 and the
concentration of Pb in the leachate was approximately 12 mg/l while Cd was
undetectable. According to these results, Pb did not pass the TCLP test while Cd did
as the threshold values of Pb and Cd are 5 mg/l and 1 mg/l respectively [ 161, At a
leachate pH of 7 (which was performed using 0.6 M of acetic acid as a leaching
fluid), the concentrations of Pb and Cd were found to be approximately 50 mg/l and
300 mg/l, respectively. The test showed that the TCLP incorrectly assessed the
leachability of Cd from cementitious waste due to the stability of Cd as its hydroxide
at h g h pH. The reason that Pb did not pass the TCLP when using 0.1 M acetic acid
was due to the amphoteric nature of Pb. However, as the pH of landfill leachate is
usually between 6 to 8, the TCLP might underestimate the concentration of those
heavy metals in real leachate, and not adequately assess the hazard of cementitious
waste containing these heavy metals [17]. This agrees with the conclusions of Li et al.
[lo].
Effect of leaching duration
The leaching of Pb and Cd from cementitious waste with 0.1 M acetic acid as
leaching fluid over 7 days is plotted in Figure 3. The pH of all batches was above 12.
Figure 3 shows that the leachability of Pb increased from 3 mg/l after 3 hours of
tumbling to 15 mg/l in 7 days (168 hours) using 0.1 M acetic acid while Cd was
undetectable. Janusa et al. [ 181 also found that increasing the contact time between the
samples and leaching fluid prior to or after the tumbling increased the concentration
359
C.E. Halim, R. Amal, D. Beydoun, J.A. Scott and G.K.C. Low
of Pb from cementitious waste containing Pb(NO& under the same conditions used in
this study. Hence, increasing the duration of leaching increases the leaching of
contaminants.
The metal leachability trend as a function of duration of leaching was further
investigated using 0.1 M acetic acid, until the pH of the leachate reached an alkaline
value (see Figure 4a and b). This was performed in order to observe the changes in the
metal concentrations as the pH of the leachate increased from acidic values (as the
waste was firstly mixed with the acidic leachmg fluid) to alkaline.
100
7
-
- -..
-
2m2 9 0 -
5m
- .A
' A
-,.
80-
p 1600 - -
=
1400 -
$
1200 - * P b
~
.
-
.
A-
a,
U
m
2 1000
-
800
0
.c
-
.-C
I
=
c
600 -
i
4
200
00:
A CaxO. 1
rCd
_- -
-
m
~
-*
.
_ _ _
-
__
A
A
'.
\
a,
5
A
c
r"
01
Figure 2. The effect of leachate pH on the leachability of metals from cementitious
waste (leachingjluid was acetic acid with concentration between 0. I M to 5.7 M; the
waste and leachingfluid were tumbledfor 18 hours at 30 rpm).
(a) The percentage of metals in the leachate as a function of leachate pH.
(b) The concentration of metals in the leachate as a function of leachate pH.
360
Leachability of Lead and Cadmium@om Cementitious Wastes
0 '=
0
-
I
50
100
Leaching time (hours)
I
150
200
Figure 3. The effect of leaching duration on the leachability of Pb and Cd from
cementitious waste tumbled with 0.I M acetic acid over 7 days.
The concentrations of Pb and Cd in the leachate before the waste was tumbled
were approximately 40 mg/l, while after 3 minutes the concentrations of the metals
dropped to an undetectable level. This can be explained by the fact that the pH of
leachate increased with time due to the increasing amount of alkalinity leached over
time. The increase in pH might cause precipitation of Pb and Cd as hydroxides, which
resulted in a decrease in the amount of soluble Pb and Cd (Pb and Cd begin forming
their hydroxides at a pH of 7 [18, 191). The increase in the alkalinity is shown by the
increase in the calcium concentration in the leachate as shown in Figure 4(a) and (b),
which contributed to most of the alkalinity in cement. On the other hand, the
concentrations of Fe and A1 in the leachate (not shown) decreased in a similar manner
to Pb and Cd, indicating that they might also be precipitated as hydroxides.
Figure 5 illustrates the leaching of metals using 0.6 M acetic acid as the leaching
fluid. It is clear that Figure 5 shows a similar trend to Figure 4. The concentrations of
Pb and Cd also decreased with increasing leaching time when 0.6 M acetic acid was
used, while the concentration of Ca increased causing an increase in the leachate pH.
This result confirms the earlier findings, which showed that the metal concentrations
in the leachate decreased with increasing leaching duration, due to the rise in the
alkalinity leaching from cement matrix.
Cheng [2] proposed a mechanism of leaching of Pb and Cd which may explain the
decrease of the concentrations of both metals in the leachate. This consists of two
processes that govern the leaching of metals; diffusion, and adsorptioddesorption to
and from the silica surface in the cement matrix. Cheng suggested that initially Pb and
Cd leaching was due to the concentration difference of acid in the aqueous and solid
phases. The mobilised metal ions form a concentration peak at the leaching boundary,
and diffuse both inwards and outwards. The metals diffusing inward re-precipitate
due to the high pH in the unleached section of the matrix, while the metals diffusing
outward might re-precipitate or be adsorbed the on silica surface. Cheng [2] found
361
C.E. Halim, R. Amal, D. Beydoun. J.A. Scott and G.K.C.Low
that Cd was controlled by diffusion alone, while Pb was more preferentially adsorbed
on the silica surface. Bishop [3] found the adsorption trend also applied for arsenic
and lead. Experiments were also conducted on the levels of Pb and Cd retained in
silica gel formed when mixing cementitious waste with 0.79 M nitric acid. The
amount of Pb retained in the silica gel was 4.2 w/w% while that of Cd was 0.3 w/w%,
showing a greater tendency for Pb to be adsorbed on silica gel in cement than Cd, and
agreeing with Cheng's experiments [2].
5
250
-
-
*
m
m
200
A
-ma,
A
A
A
(1
i
5
22
5 0
2
0
1
A
3
PH
2
1
A
A
I
0.5
0
4 :
Ca x0.1
-
v
8
6
+Pb
A
9
7
m
*
IL
10
v
2
2.5
Leaching time (minutes)
1.5
3
0
3.5
(a)
250
m
c
RI
5
200
RI
a,
I
--t
0.5
0
1
1.5
2
2.5
Leaching time (minutes)
Ca xO.1
3
3.5
(b)
Figure 4, The efect of duration of tumbling on the leachability of metals from
cementitious waste tumbled with 0.I M acetic acid over 3 minutes at 30 rpm; (a)
waste containing Pb; (b) waste containing Cd.
362
Leachability of Lead and Cadmiumfiom Cementitious Wastes
.-C
1200
1000
800
600
400
200
0
0
50
100
150
200
Leaching time (hours)
Figure 5. The effect of leaching duration on the leachability of cementitious lead and
cadmium waste tumbled with 0.6 M acetic acid over 7 days.
The investigations into the effect of leaching duration again shows that pH plays a
dominant role in the leachability of heavy metals from cementitious waste by
controlling the concentration of soluble metals in the leachate. The fact that the
concentrations of Pb and Cd decreased in Figure 4(a and b) and Figure 5 indicates that
the leaching has not reached an equilibrium time in both figures. That is, not all H'
from the acidic leaching fluid has been consumed to neutralise the alkalinity from
cement. Thus, it is important to choose a leachng duration that represents the
equilibrium condition for the leaching.
Effect of particle size of crushed sample
Figure 6 shows that the concentration of Pb in the leachate decreased with increasing
particle size, while Cd (for all particle sizes) was undetectable when 0.1 M acetic acid
was used as leaching fluid. The pH value was above 12 for all mns. This can be
explained by the smaller particles exposing a larger surface area to the leaching fluid,
thus increasing the amounts of metals leached. Cd was not detectable at all particle
sizes because it was present as its hydroxide at high pH.
However, different trends were observed when 0.6 M acetic acid was the leachng
fluid (see Figure 7). Figure 7 indicates that the concentration of Pb in the leachate
increased with particle size while the concentration of Cd remained approximately
constant until particle size 9.5 mm, where an increase in the leachability was
observed.
363
C.E. Halim, R. Amal, D. Beydoun, J.A. Scott and G.K.C. Low
13
1 2 r - -- 12.5
..._......__
...._
:
t12
11.5
11
C2.4
2.4< Size < 9.5
Particle Size (mm)
In
s
2
0
a
Q)
4-
>9.5
Figure 6. The effect of particle size on the leaching of metals from cementitious waste
tumbled with 0.I Macetic acid at 30 rpm for 18 hours.
It is postulated that for the small particle size, the leaching of the metal hydroxides
that contributed to the alkalinity of the cement (such as calcium) might have occurred
at a faster rate because of the hgher surface area of the particles. The faster alkalinity
leaching rate resulted in a faster increase in the pH of the leachate, leading to faster
precipitation of Pb and Cd as hydroxides. On the other hand, the batch with a larger
particle size was exposed to the acidic leaching fluid for a longer period of time
because the leaching of the alkalinity from the cementitious waste occurred at a
slower rate. As a result of the longer exposure to acidic conditions, in which most
heavy metals are soluble, the particles with a larger size released a higher
concentration of heavy metals to the leachate.
Again, the above results show that leachate pH plays an important role in
determining the leachability of metals for different particle sizes. When the pH was
not constant, that is, the leaching of alkalinity had not reached a maximum for a given
amount of H’ in the leachmg fluid, such as occurred in Figure 7, the pH dominated
the leachability of metal and thus, the “true” effect of particle size could not be
measured. However, when the pH was constant after the alkalinity leaching had
reached its maximum, as shown in Figure 6 , it can be seen that particle size
influenced the leachability of metals. This agrees with experiments conducted by
Brown and Bishop [21] and Bishop [3]. Bishop [3] investigated the leaching of Pb,
Cd, and Cr from cementitious waste. He found that the initial leachate metal
364
Leachabiliv of Lead and Cadmiumfiom Cementitious Wastes
concentration was low for small particles because of the higher pH of the leachate due
to the release of alkalinity from the cement. However, with increasing leaching
duration, the leachability of the smaller sized particles increased ultimately to be
greater than that of the larger sized particles.
450
c
Q)
m
c
0
m
-Q,c
400 -
f .E. 200 8c 150
s
c
300 -
-
>
a,,
350 -
.C
.P = 250
Tij.5
1
'..
/
7
.w
-. ,
/'
Pb
A Ca xO.1
Cd
PH
..*.
1 6.4 5
6.3 2
1
6.2
6.1
t6
I 5.9
,
~2.4
6.7
0)
-.-
o !
i
2 . 4 Size
~
c 9.5
Particle Size (mm)
>9.5
Figure 7. The effect ofparticle size on the leaching of metals from cementitious waste
tumbled with 0.6 A4 acetic acid at 30 rpm for I8 hours.
Effect of liquid to solid ratio
The effect of liquid to solid ratio on the leachability of metals is shown in Figure 8.
The leachability of Pb and Cd increased with increasing liquid to solid ratio (L/S),
reaching a maximum at an L/S of 40. This is because at a low L/S ratio, the leaching
fluid did not have enough alkaline neutralizing capacity to account for the alkalinity
released into the leachate, therefore the pH was high. At higher liquid to solid ratios,
the extra H' from the acid reduced the pH of the leachate into a region where the
metals were more soluble. The higher amount of available H+ in the sample would
increase the concentration gradient of acid between the solution and the solid,
increasing the mass transfer of both acid and metals to and fiom the leaching region in
the cement matrix.
However, it can be argued that the increase in the leached amount of Pb and Cd in
Figure 8 was due to the lower pH at higher L/S. Moreover, when the pH of the
leachate was the same (as in L/S of 40 and 60), the amount of leached metal was the
same. Further investigations using a fixed pH will be conducted to clarify this effect.
365
0
03
9
C.E. Halim, R. Amal, D. Beydoun, J.A. Scott and G.K. C. Low
12
10
8
Ip
a
6 g
0
nl
..--.. .........___.____._._
0
Q)
4 J
+Pb
+Cd
2
-+Ca x0.05
..*.pH
0
0
10
20
30
40
50
Liquid to Solid Ratio (US)
60
70
Figure 8. The effect of liquid to solid ratio on the leachability of Pb and Cd using 0.6
M acetic acid as leachingfluid and leachingfor 18 hours.
Conclusions
The leachability of metals from cement was found to be highly dependent on the pH
of the leachate as it governed the metal solubility. Investigations into the effect of pH
on the leachability of Cd from cementitious waste showed that the concentration of
Cd in the leachate decreased to an undetectable level at pH 9 and greater. A similar
effect was observed for Pb. However, at pH 12, Pb was detected in the leachate due to
its amphoteric nature. The investigations indicated that the TCLP cannot measure the
potential hazard of cementitious waste due to the high amount of alkalinity released
fiom the cement, thus buffering the leachate to a high pH where most metals were
insoluble. The leachate pH also affected the results for other leaching parameters and
must be taken into account when designing a leaching test to examine the hazards of
wastes.
The concentration of metals in the leachate decreased with increasing leaching
duration, until the alkalinity from the cement was exhausted. After this point,
increasing the duration of leachng increased the leaching of metals.
The particle size of cement governed the cation leaching rate and thus the rate of
increase in pH, subsequently affecting the leachability of the metals from
cementitious waste. Smaller particles had a greater surface area, which led to a greater
leaching of alkalinity, resulting in a faster increase in pH. This faster increase in pH
led to a lower amount of leaching of metals as the leachate was at low pH values for a
366
Leachability of Lead and Cadmiumfiom Cementitious Wastar
shorter time. However, once the alkalinity leached had reached a maximum, the
leaching of metals decreased with an increasing particle size. This was due to the
smaller surface area of the larger particles.
Finally, increasing the liquid to solid ratio was found to increase the leachability of
metals due to the greater alkaline buffering capacity of the leachate available to
neutralise the alkalinity from cement.
Acknowledgments
The authors would like to thank Julie Cattle, Roy Foley, and Jin Yang of the New
South Wales Environmental Protection Authority for their contribution to the project.
T h s project has been assisted by the New South Wales Government through its
Environmental Trust.
References
Kimmel, T.A. 1999. Original Purpose of the Toxicity Characteristic Leaching Procedure (TCLP) US. EPA 1999 Public Meeting; Development of New Waste Leaching Procedures. U.S.
Environmental Protection Agency.
Cheng, K.Y. 1991. Ph.D. Thesis, University of Cincinnati, USA.
2
Bishop, P.L. 1988. Leaching of inorganic hazardous constituents from stabilized/solidified hazardous
3
wastes, Hazard. Waste Hazard. Muter., 5, 129-143.
4
Cartledge, F.K., Butler, L.G., Chalasani, D., Eaton, H.C., Frey, F.P., Herrera, E., Tittlebaum, M.E.,
and Yang, S.L. 1990. Immobilization mechanisms in solidification/stabilization of Cd and Pb salts
using portland cement fixing agents, Environ. Sci. Technol., 24,867-873.
5
Thomas, N.L., Jameson, D.A., and Double, D.D. 1981. The effect of lead nitrate on the early
hydration ofportland cement, Cement Concr. Rex, / I , 143-153.
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