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Lead Removal from Synthetic Leachate Matrices by a
Novel Ion-Exchange Material
a
b
c
Kenneth W. Street Jr. , Edward S. Hovanitz & Sulan Chi
a
NASA Glenn Research Center , Cleveland , Ohio , USA
b
Engelhard Corp , Elyria , Ohio , USA
c
Eli Lilly & Co. , Clinton , Indiana , USA
Published online: 27 Dec 2011.
To cite this article: Kenneth W. Street Jr. , Edward S. Hovanitz & Sulan Chi (2002) Lead Removal from Synthetic Leachate
Matrices by a Novel Ion-Exchange Material, Journal of the Air & Waste Management Association, 52:9, 1075-1082, DOI:
10.1080/10473289.2002.10470840
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TECHNICAL PAPER
ISSN 1047-3289 J.
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Copyright 2002 Air & Waste Management Association
Lead Removal from Synthetic Leachate Matrices by a Novel
Ion-Exchange Material
Kenneth W. Street, Jr.
NASA Glenn Research Center, Cleveland, Ohio
Edward S. Hovanitz
Engelhard Corp., Elyria, Ohio
Sulan Chi
Eli Lilly & Co., Clinton, Indiana
ABSTRACT
because of the large quantities of contaminated soil that
would otherwise have to be contained in a waste-storage
This paper discusses the application of a novel
polyacrylate-based ion-exchange material for the removal
of Pb ions from water. Preliminary testing includes the
establishment of the operating pH range, capacity infor-
2
,3
facility. In soil washing, the soil is pretreated to remove
large Pb sources (e.g., bullets). The corroded Pb that has
leached into the soil is stripped with a leachant. Because
the Pb encountered in different washing situations
occurs in different forms, the wash solution must be
tailored to the site. Typical wash solutions that have been
employed range from a simple acidification medium, such
2
+
mation, and the effect of Ca and anions in the matrix.
Batch testing with powder indicates slightly different op-
timal operational conditions from those used for column
testing. The ion-exchanger is excellent for removing Pb
from aqueous solutions.
as dilute HNO or fluosilicic acid, to strong complexing
3
agents, such as ethylenediaminetetraacetic acid (EDTA).
Although EDTA has been shown to solubilize Pb fairly
well, it creates other problems with the soil to be subse-
quently recovered. Weak chelators have been employed
as well, including nitrilotriacetic acid and acetic acid. Ace-
tic acid is attractive because it is inexpensive, has been
demonstrated to be a moderately good leachant, and is
readily biodegradable. The leachate is then stripped by
ion-exchange technology and recycled. This last step in
the loop is often problematic, because a good leachant is
often hard to strip of the solubilized Pb.
INTRODUCTION
Lead in the water supply is an ever-increasing concern.
Common sources include the corrosion of transport sys-
tems and material leached from the environment. The
environmental sources are diverse, ranging from Pb paint
1
,2
in the soil to spillage at battery-cracking facilities. Be-
cause of its extreme toxicity, acceptable concentration
levels of Pb in potable water must be maintained at low
parts per billion. One of the most common techniques
for lowering the concentration of metal ions to suitable
levels in potable water is ion-exchange treatment.
A novel polyacrylate-based ion-exchange material
A proposed method of remediation technology is soil
washing. This treatment appears to be extremely attractive
(
IEM) was developed at NASA after the serendipitous dis-
covery that a marginal battery separator retained Cu ions
from distilled water. The source of the Cu in the distilled
water used to wash the separator was traced to a corrod-
ing line in the still. In earlier versions of the separator,
polyacrylic acid (PAA) was cross-linked with radiation to
produce films. These materials had ion-exchange capac-
ity but were readily fouled before reaching a useful load-
IMPLICATIONS
This work demonstrates the ability of a polyacrylate ion-
exchange material to remove toxic metals from water. The
material has significant affinity for Pb in the presence of
considerable amounts of competing or complexing ions,
and it also works well in the presence of hard water to
readily remove other toxic metals. An important property
of this material is that it can be fabricated in many forms,
such as coatings, films, and conventional beads.
4
-7
ing capacity. In subsequent versions of the material,
polyvinyl alcohol (PVA) was incorporated in the film
8-12
matrix, which solved the fouling problem.
IEM is chemically cross-linked at the PVA, leaving the PAA
loosely trapped in the matrix. This configuration of the
The new
Volume 52 September 2002
Journal of the Air & Waste Management Association 1075

Street, Hovanitz, and Chi
material provides additional flexibility for the PAA sites
to exchange ions.
was collected for AAS and pH analysis. The IEM was
weighed in the acid form, converted to the correct extent
We have characterized the new IEM for removal of
Pb in the presence of various anions that are commonly
found in the environment. Chloride also was tested be-
cause it is ubiquitous and will be of interest in systems
with standard Ca(OH) solution, and loaded into the col-
2
umn. The void volume of the column was monitored by
the injection of a salt spike to generate a signal at a con-
ductivity detector placed at the column effluent. Chal-
lenge solutions were prepared from the Pb salts with the
corresponding anion. To prevent hydrolysis and subse-
quent precipitation of the Pb, the solutions were stabi-
lized with a trace of hexamethylenetetramine (a weak
complexing agent). The pH was then adjusted with HNO3.
For challenge solutions containing excess anion, the
solution was prepared such that an excess of 0.1-molar
anion was generated from 0.09-molar Na salt and
0.005-molar Ca salt. Various challenge solutions, column
geometries, and flow conditions were tested as described
in the subsequent sections and figures.
where noncomplexing leachants such as HNO are used.
3
Acetic acid was investigated as a weak complexing agent
associated with proposed soil-washing scenarios. The study
includes the effects of pH, because it is important when
using weak cation exchangers, and the Ca ion, which of-
ten fouls ion exchangers. For comparison, limited data
on Cu and Zn also are presented.
MATERIALS AND METHODS
The ion-exchange resin was obtained from Southwest
Research Institute. The powder was manufactured by
spray-drying a solution containing 8.4% solids (1:1 mix-
ture of PVA and PAA) and 0.13% glutaraldehyde to cross-
RESULTS
8
,12
link the PVA framework. The ion-exchange beads were
The powder form of the IEM, nominally in the 5–75 µm
range, was used as received. Titration of this material in-
dicated a capacity of 4.81 ± 0.11 meqꢀg IEM. Equilibra-
tion of the Ca form of the IEM with a large excess of Cu
ions in an acetate buffer at pH 5.0 yielded a capacity of
4.8 meqꢀg IEM. Titration of two subsequent lots of pow-
der yielded capacities of 5.29 and 5.36 meqꢀg IEM. By
end point differences in the back titration of these mate-
rials, it is possible to determine the amount of PAA re-
leased from the cross-linked PVA during the reaction with
the NaOH. The leakage numbers correspond to 1.72, 0.86,
and 1.05 meqꢀg, respectively, indicating that the latter
lots of IEM were cross-linked more efficiently and, there-
fore, yielded the higher capacities.
1
3
manufactured by a novel patented process. The aque-
ous phase contained 14% solids (1:1 mixture of PVA and
PAA) and 1.3% glutaraldehyde. This solution was mixed
with mineral oil and fumed silica in a sufficient amount
to cause droplets of resin to remain suspended after stir-
ring stopped. The mixture was heated to 60–70 ºC over-
night. The spheres were strained, washed with hexane,
and air-dried. All IEMs were received in the acid form.
Before use in uptake experiments, they were converted to
the Ca form. Powder was stirred with excess suspended
Ca(OH) , filtered, and washed prior to use. Bead conver-
2
sion is described later in this section.
The capacity of the IEMs was determined by equili-
brating the acid IEM with an excess of standard NaOH for
at least 12 hr. The resin was filtered off and the excess
Figure 1 demonstrates the pH working range for the
powder form of the IEM using Cu and Pb as test ions.
Figure 2 illustrates the rate at which the powder and film
forms of the IEM take up Pb ions in batch testing. For
–
OH was determined by titration with standard HCl. For
batch tests, the IEM (typically 100 mg) was stirred with
the test solution (typically 100 mL), and aliquots were
taken at defined time intervals. An aliquot was taken be-
fore the introduction of the IEM to the test. The amount
taken was such that all aliquots totaled less than 5% of
the original volume. Metal ion concentrations were de-
termined on all aliquots by flame or graphite furnace
atomic absorption spectrophotometry (AAS) using the
1
4
conditions described in SW-846 or as close to that as
possible. The pH was determined at the start and end of
15
each experiment.
Column testing was performed in glass columns with
sintered glass frits at either end. The columns were typi-
cally packed with 1 g of beads 80% converted to the Ca
form. Challenge solutions containing various concentra-
tions of Pb and Pb with excess anions at varying pH were
pumped continuously through the column. The effluent
Figure 1. Fraction of metal removed as a function of pH for Ca form
of IEM powder.
1076 Journal of the Air & Waste Management Association
Volume 52 September 2002

Street, Hovanitz, and Chi
Table 2. Capacity and leakage of IEM beads.
Bead Size
µm
Capacity
Leakage
meq/g
Standard
meq/g
Standard
a
a
Deviation
Deviation
<
2
6
250
4.2
—
—
—
b
b
50–600
00–1400
4.3
0.07
0.02
0.4
0.03
0.02
5.4
1.2
a
b
Standard deviation, n = 2; Determined on beads recycled from column testing.
material. Digestion of the beads resulted in a silica con-
tent of ~10% by weight from entrapped silica introduced
during the manufacturing process.
Figure 2. Metal ion concentration remaining in solution as function of
equilibration time for various resins.
For comparison, the beads packed into the columns
were weighed and the column dimensions were recorded
along with the experimentally measured void volumes.
Typically, 1.00 g of the 80% converted beads packed into
a 10-mm inside-diameter (id) column produced a bed
comparison, the Na form of the Biorad cation exchange
resin (AG 50W-X2, 38–75 µm) for uptake of Cu ions is
also presented. Table 1 summarizes the results of 16 sepa-
rate conditions tested and demonstrates the immunity of
the IEM against some common anions for the uptake of
Pb ions when 100 mg of IEM powder is challenged with
60 mm long (4.7 mL) with a void volume of 2.5 mL. The
bulk density of the beads then was calculated to be 0.2 gꢀ
3
cm (dry) and the void volume to be 53%. In most cases,
1
00 mL of test solution under the conditions specified in
the table.
The beads received from Southwest Research Insti-
tute were fractionated into two sizes (600–1400 µm and
600 µm). These were presumably manufactured as one
the length of the bed decreased by 2–3 mm by the end of
the experiment.
Two different experiments compared beads that were
converted to the 20 and 80% Ca forms. Figure 3 is a plot
<
of the Pb concentration of the exit C divided by the
e
lot having a similar composition. The <600-µm lot was
further sized into two fractions, <250 µm and 250–600
µm. The limited quantity of the latter fraction was saved
for testing in column experiments and then was recycled
for capacity testing. The other two fractions were subj-
ected to several batch experiments. Table 2 gives ca-
pacity and leakage values for the limited testing
performed on these materials. It is apparent that the
recycled beads give considerably lower leakage values
and that the capacity is in line with that of the original
initial challenge concentration C versus the volume of
i
Pb solution run through the column. It is apparent that
Table 1. Recovery of Pb from various matrices.
Lead Recovered in IEM
Hydrogen Ion
Concentration
pH
a
%
(std. deviation)
Anion
None
Nitrate
Chloride
Acetate
1
0-ppm Pb with 0.1-Molar Anion
9
9
2.2 (0.4)
.2 (3.6)
92
21
91
81
0
5.0
3.0
5.5 (0.5)
1
00-ppm Pb with 0.1-Molar Anion
15
00-ppm Pb with 0.1-Molar Anion
16.2 11 14
9
.2 (2.4)
8
1
3.0
3.0
5
Figure 3. Fraction of original concentration of PbNO and PbCl in
3
2
1
0.4 (3.9)
column effluent (C /C values × 1000) as function of volume of Pb
e
i
solution through columns for IEM beads 80% and 20% converted to
Ca form. Flow rate through columns, 1.0 mL/min.
a
Standard deviation between replicate experiments.
Volume 52 September 2002
Journal of the Air & Waste Management Association 1077

Street, Hovanitz, and Chi
breakthrough occurs early with the 20% converted beads.
Even at a very low challenge concentration (100 ppm),
the 20% converted beads are not as effective at remov-
ing Pb as is the 80% converted material. The behavior of
the columns is understood by close examination of the
associated pH profile of the effluent during a column
experiment. In Figure 4, the effluent pH is plotted for
the two 500-ppm Pb samples in Figure 3. Figure 4 dem-
onstrates the relationship between percent of bead
conversion to the Ca form and ability to maintain pH as
Pb is removed from the influent solution.
A careful examination of the pH profiles for all col-
umn tests performed with the 80% converted IEM and
Figure 5. pH of column effluent pH as function of pH of column
e
–
–
Pb solutions containing Cl or NO is shown in Figure
influent pH (pH taken as pH of challenge solution) for challenge solutions
3
i
i
containing NO3 and Cl–.
–
5
. This figure is a plot of the pH of the first eluent col-
lected (pH ) from the column versus the pH of the influ-
e
It also is evident that the high ionic strength generally
improves the performance of the IEM. In another experi-
ment (not shown), the effect of ionic strength was a dou-
bling of the apparent onset of column breakthrough for
two flow rates. Figure 8 shows the effect of flow rate on
column retention of Pb. Figure 9 is a plot of the Pb in the
IEM at the end of the experiment normalized by the
weight of IEM used in the experiment plotted against the
final reading of C ꢀC for 30 column experiments. The large
ent challenge solution (pH ). The figure reveals that the
i
resin initially attempts to adjust the pH of the solution
in the column to a value coincidentally close to the pKa
of the IEM, ~5.5. A plot of (pH - pH ) versus the pH of
e
i
the challenge solution pH is presented in Figure 6. This
i
plot demonstrates the amount of pH adjustment on the
solution by the column.
Figure 7 shows typical breakthrough curves for col-
–
e
i
umns of varying length and the effect of NO ions.
3
scatter in the data is attributable to varying conditions of
flow rate, column length, pH, anion associated with the
Pb salt, and, in some cases, 0.1 molar excess of the corre-
sponding anion. Extrapolation of the data having C ꢀC >
–
3
Excess NO ions only influence this system by providing a
high ionic strength. In subsequent experiments, the longer
length columns were used, because they provided more
ideal curves. For comparison, the weights of resin used to
vary the column length are included in the figure legend.
e
i
0
.01 (22 data points) to C ꢀC = 0 indicates that Pb load-
e i
ing of ~10% by weight (~20% of the calculated equilib-
rium capacity) leads to breakthrough in unoptimized
conditions. In the most extreme data, at C ꢀC > 0.8, the
e
i
resin has, at best, taken up 28% of its weight as Pb, which
is only 60% of the calculated equilibrium capacity.
–
The effect of Cl was examined because it is ubiqui-
tous, has complexing ability, and forms a sparingly soluble
salt with Pb. Acetate is of interest because acetic acid has
Figure 4. Correlation of fraction of original concentration of Pb in
column effluent C /C as function of volume of Pb solution through
e
i
column to pH of column effluent as function of volume through column
for IEM beads 80% and 20% converted to Ca form. Note: pH of
challenge solution is pH at volume = 0 mL.
Figure 6. Difference in pH between column effluent pH and column
e
influent pH (pH taken as pH of challenge solution) as function of pH.
i
i
i
1078 Journal of the Air & Waste Management Association
Volume 52 September 2002

Street, Hovanitz, and Chi
Figure 9. Weight percent of Pb in IEM vs. ratio of concentration of Pb
in column effluent C for final data point in run divided by concentration
e
of Pb in challenge solution Ci.
DISCUSSION
Preliminary investigations with laboratory samples of the
IEM indicated that it has the following properties: high
Figure 7. Fraction of original concentration of Pb in column effluent
C /C) as function of volume of Pb solution through column for columns
of various lengths challenged with low- and high-ionic-strength Pb
solutions. Flow rate, 2.0 mL/min of 500-ppm lead nitrate through 80%
IEM converted to Ca form.
2+
capacity; mechanical durability; immunity to Ca ; im-
(
e
i
munity to Fe and several other nontoxic metal ions; high
efficiency in the removal of Pb, Cd, and other toxic metal
ions; easy recyclability or disposability; and easy forma-
tion into many shapes (e.g., beads, fibers, film, or coated
8
-12
magnetic beads).
Because of these properties, we de-
been used in soil-washing scenarios. Acetate has moderate
complexing ability and acts as a solution-buffering agent.
Figure 10 presents additional data for column experiments
cided to have the material manufactured by a commer-
cially scalable process for evaluation as a potentially useful
product. Proposed uses include drinking-water purifica-
tion and application in environmental processes such as
soil washing. To date, powder, beads, film (both porous
fiberglass-reinforced and nonporous), and irregular gran-
ules have been produced at the pilot scale. These potential
–
involving Cl and acetate.
Figure 8. Fraction of original concentration of Pb in column effluent
(
C /C) as function of volume of Pb solution through column for various
Figure 10. Fraction of original concentration of Pb in column effluent
(C /C) as function of volume of Pb solution through column for various
anions. Pb concentration, 500 ppm.
e
i
flow rates. Columns contained 0.5 g of 80% Ca-converted IEM
challenged with 500-ppm lead nitrate.
e
i
Volume 52 September 2002
Journal of the Air & Waste Management Association 1079

Street, Hovanitz, and Chi
products indicate that the manufacturing process for this
material is feasible.
lowers the effectiveness of the IEM as discussed in the
section titled Column Performance.
Powder Properties
Bead Properties
The capacity numbers are consistent with the theoretically
calculated value of just under 7 meqꢀg for a material con-
taining 50% PAA. From prior experimentation with bead,
granular, powder, and film IEM, there are a number of rea-
Beads would be expected to have a 10% lower capacity
than the powder because of the silica incorporated dur-
ing manufacturing. The rest of the capacity reduction in
the beads is attributable to a lack of bead porosity and the
resulting mass diffusion problems. For the purpose of com-
parison, the calculated uptake of Pb based on a capacity
of 4.3 meqꢀg IEM is 45% of the weight of the IEM. From
prior comparative studies with the film and with irregu-
lar granular and powder forms of the IEM, the majority
12
sons for the leakage. A small amount of initial leakage
appears to be inherent in the structure of the material, in
that the PVA is cross-linked into a matrix that entangles
the PAA, the only mechanism for retention of the PAA in
the resin. Some small amount of additional PAA leaks dur-
ing the first conversion to the salt form, the active form of
of the performance properties (e.g., pK of the IEM, ca-
a
2
+
the resin. The conversion process with Ca tends to shrink
the resin, which causes the remaining PAA to be more
strongly retained in the resin so that subsequent leakage is
negligible. Consequently, the working version of the IEM
uses the Ca salt, which is immune to leakage and deterio-
ration of mechanical strength. Conversion with NaOH as
in the titrations tends to expand the volume of the resin
pacity, affinity for metal ions, and pH uptake profiles for
various metals) are very similar. The two exceptions are
the kinetic-related properties and the apparent extended
operating pH range for the powder demonstrated in the
single experiment reported herein (see Figure 1).
Column Performance
(
prior unpublished studies indicate by as much as 40%),
Even though the columns prepared with 20% converted
beads do not work well at high-challenge concentrations,
Figure 3 demonstrates that a substantial amount of Pb
can be removed for low-challenge concentrations with a
20% converted material. The key to the behavior of the
columns is that the resin behaves as a pH buffer by alter-
ing the pH of the medium passing through the column,
as seen in Figure 4. For water at a pH of 5 passing through
an 80% converted column (IEM pH of ~6.6), the column
would be expected to pick up hydrogen ions from the
medium and release Ca from the resin. This behavior
should result in a slight increase in the pH of the column
effluent; however, this activity is not what was observed.
For Pb solutions passing through the column, the Pb was
exchanged onto the column, releasing both Ca and hy-
drogen ions. The hydrogen release causes the drop in the
pH of the solution passing down the column.
In columns where the percent conversion to the Ca
form was greater, less hydrogen was released into the sys-
tem to lower the pH of the medium passing through the
remainder of the column (see Figure 4). For the 20% con-
verted beads (IEM pH of ~4.9) in Figure 4, substantial
hydrogen ions are released, dropping the pH of the me-
dium to ~3. For higher Pb concentrations, the effect would
be even more dramatic. From Figure 1, the equilibrium
concentration of Pb in the solution over the IEM at pH 3
should be 60% of the original concentration, which is
what was observed in the effluent. In all other studies,
80% converted beads were used, and the pH of the efflu-
ent was monitored as samples were collected.
causing deterioration of the mechanical strength. Sodium
conversion also may release more PAA than the working
Ca form. Hence, the leakage numbers may be an overesti-
mate and the actual capacities reported may be underesti-
mates. In the formulation process, we have also observed
that too little cross-linking or using a PAA with lower mo-
lecular weight facilitates leakage. This topic will be addressed
further in the section titled Bead Properties.
The IEM is a weak acid cation-exchange resin esti-
mated to have a pK of ~5.5. The operational pH range for
a
the IEM (see Figure 1) is limited at lower pH values be-
cause acid competes heavily for the resin sites. The pow-
der does not appear to suffer the same shortcoming
described in our earlier work, where many metal ions that
exist as neutral precipitates or as anionic hydroxy species
at the higher pH values (typically pH > 7) are not taken
up by the film form of the IEM. In the present work, the
powder IEM clearly effectively removed Cu to a pH ap-
9
proaching 8. In our earlier work with films, the Cu re-
covery had dropped from nearly 100% at pH 6.5 to 50%
at a pH slightly greater than 7. The extended operational
pH range probably is caused by the higher surface area of
the powder, hence the better performance. The slowness
in uptake for the film versus the powder (see Figure 2) is
attributed to mass transfer problems associated with the
film being a single entity in a large volume of solution.
Nonetheless, it is equally effective at removing ions, pro-
vided that there is sufficient equilibration time. At the
lower pH values, the anions evaluated in Table 1 are less
problematic than the pH. At higher pH values, the ac-
Examination of the pH profiles for each column ex-
periment is required for the correct interpretation of results.
1
6
etate, which has a high formation constant with Pb,
1080 Journal of the Air & Waste Management Association
Volume 52 September 2002

Street, Hovanitz, and Chi
Interpretations tend to be complicated by a drifting pH
and the inability to maintain the influent pH during runs,
even for the highly acetate-buffered test solutions. Fig-
ures 5 and 6 show the effect of the column on the pH of
the challenge solution. Figure 5 demonstrates that the
column attempts to adjust the pH to a value coinciden-
tally equal to the pKa of the IEM. A good linear correla-
tion of the amount of pH adjustment initially performed
by the column on the challenge solution to adjust the pH
toward 5.6 is shown in Figure 6. Other percent conver-
sions would be expected to produce a similar effect, al-
though the pH value converged upon should be different.
In an unrelated experiment using the large beads to
develop a home test kit for determination of Pb (ppb level)
in drinking water that also contained Cu and Zn (ppm
range), the pH of the challenge solutions was buffered to
values between 3.8 and 4.5. At the lower pH, the majority
of the Pb and a small fraction of the Cu is retained on the
column, whereas no Zn is collected. At the higher pH, Pb
and the majority of the Cu are retained by the column but
only a small fraction of the Zn is removed from the chal-
lenge solution. These experiments further illustrate the
effect of pH on the retention of metal ions on this IEM.
The optimization of column conditions presented in
Figures 7 and 8 are as expected. The larger columns provide
more reasonable-looking curves because flow patterns in the
columns are more homogeneous. Slower flow rates provide
better equilibration, particularly with respect to mass trans-
fer in the ion-exchange media. Based on the results of these
experiments, subsequent experiments used 1 g of IEM and a
flow rate of 2 mLꢀmin. The higher, unoptimized flow rate
was used to expedite breakthrough conditions. The effect of
ionic strength observed in Figure 7 is the result of several
simultaneous processes, an advanced discussion of which is
beyond the scope of this report. Briefly, the processes lead-
ing to the improved performance of the IEM include a com-
bination of the change in activity of the exchanging ions
along with a lowering of the surface tension of the solution.
The ionic strength alters the activity of the exchanging ions
in predictable fashion. The change in surface tension
promotes mass transfer across the interface between the
solution and ion-exchange resin.
if a slower flow rate were used. The problems associated
with mass transfer in the IEM are confirmed in Figure 9,
which indicates that Pb loading of ~10% by weight leads
to breakthrough for unoptimized conditions. To give a
perspective, the 0.5-mLꢀmin data having C ꢀC = 0.0004
e
i
at the end of the run has a loading of 17% by weight
(38% of theoretical). This indicates that optimizing the
conditions allows considerably more Pb to be removed
before breakthrough is approached.
Chloride ion weakly complexes Pb ion, and in addi-
tion, PbCl is sparingly soluble. From equilibrium con-
2
stant calculations, the solubility of the Pb is complete
under all conditions tested, including that in the pres-
–
ence of 0.1 molar excess Cl ion. Furthermore, the con-
+
–
centrations of PbCl and PbCl are negligible at 500-ppm
3
–
16
Pb with 0.1 molar excess Cl ion. In a preliminary ex-
periment at pH 5.5 using 107 ppm PbCl pumped at 2
2
mLꢀmin through a 10-mm id column containing 1 g of
80% converted IEM, the Pb concentration in the column
effluent was lowered to below the limit of instrumental
detection (<2 ppb Pb) throughout the run (total volume
of 240 mL). Effluent Pb concentrations in the low-ppb
range were typical of the IEM performance before column
breakthrough for challenge solutions containing modest
Pb concentrations. Figure 10 illustrates the effect of vari-
ous anions on the retention of Pb. The interpretation of
the figure is complicated by the effect of pH on the sys-
–
tem. Plots for NO3 are complicated by the drift of the pH
to unfavorable absorption values toward the end of the
run. The pH started in the 5.8 range and drifted toward 4
or less for the last data points, demonstrating that Pb
–
preferentially displaces Ca over hydrogen. The Cl curves
have a less pronounced pH effect and exhibit the same
general trend as that for the ionic strength curves pre-
–
sented in Figure 7. The last data points on the Cl curves
–
show that in the presence of 0.1 molar excess Cl , the Pb
is retained more effectively, even with slightly less
favorable pH (pH = 5.5 vs. 5.3 for the excess-anion run).
Acetate is a complexing anion that neutralizes the
1
6
charge on the Pb, rendering it a neutral species. Ac-
cording to the values of the stepwise formation constants,
+
appreciable amounts of PbAc can be generated as the
2
+
A major drawback of the IEM is that mass diffusion
in the resin is a limiting factor for the breakthrough of
Pb. As the flow rate is slowed, there is more time for Pb at
the surface of the resin to diffuse inwardly. Hence, in Fig-
ure 8, the amount of Pb removed per gram of IEM is dra-
matically improved at a flow rate of 0.5 mLꢀmin. Because
the intent of these experiments was to amplify the differ-
ences in column performance by various conditions in
the challenge solutions, higher flow rates than optimal
were used. The actual performance of the columns used
in the following experiments could be improved greatly
acetate forms the neutral PbAc species. Either the Pb
2
+
or the PbAc ion is capable of immediately adsorbing to
the IEM; however, the equilibrium is probably reestab-
lished rapidly enough to produce substantial cationic
species as the IEM removes the Pb from solution. None-
theless, acetate competes markedly with the IEM for Pb.
For 500-ppm Pb prepared from PbAc , substantial
2
amounts of the Pb are in cationic species at pH 4 where
the IEM is less effective. As the pH rises to 5 and 6, the
amount of cationic species is on the order of two-thirds
and one-half, respectively (exact calculations rely on an
Volume 52 September 2002
Journal of the Air & Waste Management Association 1081

Street, Hovanitz, and Chi
iterative process). In the presence of a large excess of ac-
etate (0.1 molar), the calculations are more exact and the
concentrations of cationic Pb drop markedly from pH 4
Administration (NASA), Lewis Research Center. Trade
names or manufacturer’s names are used in this report
for identification only. This usage does not constitute an
official endorsement, either expressed or implied, by NASA
or EPA.
2
+
+
2+
+
(
2% Pb and 1% PbAc ) to 6 (<0.5% Pb plus PbAc ).
Under these conditions, the rapid establishment of equi-
librium in the solution enables the IEM to remove Pb suc-
cessfully (see Figure 10). The Pb breakthrough correlates
directly with the amount and strength of competing
ligands in solution. In unrelated beaker experiments with
REFERENCES
1
.
Xintaras, C. Analysis Paper: Impact of Lead-Contaminated Soil on Pub-
lic Health; U.S. Department of Health and Human Services: Atlanta,
GA, 1992.
2
.
U.S. Environmental Protection Agency. Literature Review Summary of
Metals Extraction Processes Used to Remove Lead from Soils, Project Sum-
mary; EPAꢀ600ꢀSR-94ꢀ006; National Service Center for Environmen-
tal Publications: Cincinnati, OH, 1994.
1
7
Zn and IEM films, similar results were achieved with
EDTA. None of the Zn was removed from solution by the
IEM because of the complexing strength of the ligand that
3. U.S. Environmental Protection Agency. Remedial Action, Treatment,
and Disposal of Hazardous Waste; EPAꢀ600ꢀ9-91ꢀ002; Risk Reduction
Engineering Laboratory: Cincinnati, OH, 1991.
2
-
creates an anionic complex, ZnEDTA .
A final note regarding the often-detrimental effects
4. Philipp, W.H.; May, C.E. New Ion-Exchange Membranes; NASA TM-
8
1670; NASA Lewis Research Center: Cleveland, OH, 1980.
2
+
of Ca in the matrices is that this resin operates most
effectively in the Ca form for all divalent cations that have
been tested with the IEM to date. This point is further
demonstrated in the excess-anion experiments wherein
the matrix is ~0.005 molar (200 ppm) in Ca. In experi-
ments performed stripping Pb from seawater, the effect
of Na was to eventually displace Ca and expand the resin,
causing deterioration of the IEM and column performance.
To this end, we spiked the matrices with small amounts
of Ca to replenish the resin as the experiment proceeded.
In all experiments using excess, noncomplexing anions,
results were superior to runs without the excess anions.
These results are more likely because of ionic strength
5
.
Philipp, W.H.; May, C.E. Kinetics of Copper Ion Absorption by Cross-
Linked Calcium Polyacrylate Membranes; NASA TM-83052; NASA Lewis
Research Center: Cleveland, OH, 1983.
6. May, C.E.; Philipp, W.H. Ion-Exchange Selectivity for Cross-Linked
Polyacrylic Acid; NASA TM-83427; NASA Lewis Research Center: Cleve-
land, OH, 1983.
7
.
May, C.E. Kinetics of Chromium Ion Absorption by Cross-Linked
Polyacrylate Films; NASA TM-83661; NASA Lewis Research Center:
Cleveland, OH, 1984.
8
.
Philipp, W.H.; Street, K.W., Jr. Ion-Exchange Polymers and Method
for Making. U.S. Patent 5,371,110, December 6, 1994.
9. Hill, C.M.; Street, K.W.; Philipp, W.H.; Tanner, S.P. Determination of
Copper in Tap Water Using Solid-Phase Spectrophotometry; Anal. Lett.
1
994, 27, 2589-2599.
1
0. Uy, O.M.; Ginther, M.J.; Folkerts, J.T.; Street, K.W., Jr. Use of a NASA-
Developed Ion-Exchange Material for Removal of Zinc from Electro-
plating Baths; Johns Hopkins APL Tech. Dig. 1996, 17, 371-376.
1. Tanner, S.P.; Street, K.W., Jr. Solid-Phase Luminescence of Several Rare
Earth Ions on Ion-Exchange Films; Appl. Spect. 2000, 54, 669-675.
2. Hill, C.M.; Street, K.W.; Tanner, S.P.; Philipp, W.H. Preparation of Ion-
Exchange Films for Solid-Phase Spectrophotometry and Solid-Phase
Fluorometry; Anal. Lett. 2000, 33, 2779-2792.
1
1
2
+
considerations than Ca enhancement.
1
3. Schlameus, H.W.; Barlow, D.E. Method for Preparing Polymeric Beads.
U.S. Patent 5,959,073, September 28, 1999.
CONCLUSION
14. U.S. Environmental Protection Agency. Proposed Update Number III:
Physical/Chemical Methods Test Methods for Evaluating Solid Waste;
Method 7471A, Rev. 1, SW-846; Government Printing Office: Wash-
ington, DC, 1994.
The IEM, developed from battery separator technology, is
composed of cross-linked PVA and entrapped PAA and
can be produced in a variety of forms. The current evalu-
ation is designed to demonstrate the ability of the mate-
rial as a replacement for column ion-exchangers where
weak acid exchangers are applicable. Data are presented
for Pb adsorption under a number of physical and chemi-
cal conditions. Physical conditions were several geom-
etries, the quantity of IEM in the test column, and flow
rates. The chemical conditions were Pb concentration, pH,
ionic strength, and effect of weakly competing organic
complexing agents. The IEM removed Pb effectively under
most conditions; however, the breakthrough characteris-
tics for similar columns were greatly affected by pH and
the presence of complexing anions. Under ideal conditions,
this IEM will remove modest amounts of Pb (high-ppm
concentration range) and reduce the Pb concentration to
the low-ppb range.
1
5. Standard Methods for the Examination of Water and Wastewater, 15th
ed.; American Public Health Association: Washington, DC, 1980.
6. Ringbom, A. Complexation in Analytical Chemistry: A Guide for the Criti-
cal Selection of Analytical Methods Based on Complexation Reactions; R.E.
Krieger Publishing: Huntington, NY, 1979.
1
1
7. Gorse, J. Department of Chemistry, Baldwin Wallace College, Berea,
OH. Unpublished results, March 1993.
About the Authors
Kenneth W. Street (corresponding author; e-mail:
kenneth.w.street@grc.nasa.gov) currently performs tribo-
logical research for aerospace applications. The present
work was performed while Sulan Chi and Edward Hovanitz
were on contract to NASA via the Bionetics Corp. Sulan
Chi currently works as a chemist in a quality-control labo-
ratory using spectroscopic and chromatographic tech-
niques to analyze pharmaceutical products. Edward
Hovanitz is a spectroscopic analyst who examines the
metal content of catalysts.
ACKNOWLEDGMENTS
This work was funded wholly by the U.S. Environmental
Protection Agency (EPA) under Contract Number
DW80936188-01-0 to the National Aeronautics and Space
1082 Journal of the Air & Waste Management Association
Volume 52 September 2002