The NASA Lewis Research Center developed and is patenting a new high capacity ion exchange material (IEM) that removes toxic metals from contaminated water in laboratory tests. The IEM can be made into many forms, such as thin films, coatings, pellets, and fibers. As a result, it can be adapted to many applications to purify contaminated water wherever it is found, be it in waste water treatment systems, lakes, ponds, industrial plants, or in homes. Laboratory tests have been conducted on aqueous solutions containing only one of the following metal cations: lead, copper, mercury, cadmium, silver, chromium (III), nickel, zinc, and yttrium. Tests were also conducted with: (1) calcium present to determine its effects on the uptake of cadmium and copper, and (2) uranium and lanthanides which are stand-ins for other radioactive elements, (3) drinking water for the removal of copper and lead, and (3) others compositions. The results revealed that the IEM removes all these cations, even in the presence of the calcium. Of particular interest are the results of the tests with the drinking water: the lead concentration was reduced from 142 ppb down to 2.8 ppb (well below the accepted EPA standard)

Philipp, Warren H., Jr.

Street, Kenneth W., Jr.

English

NASA Technical Reports Server

J --7
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N94- 30471
A NEW MATERIAL FOR REMOVING HEAVY METALS FROM WATER
Warren H. Philipp, Jr.
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, OH 44135
Kenneth W. Street, Jr.
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, OH 44135
ABSTRACT
The NASA Lewis Research Center developed and is patenting a new high capacity ion exchange material
(IEM) that removes toxic metals from contaminated water in laboratory tests. The IEM can be made into many
forms, such as thin films, coatings, pellets, and fibers. As a result, it can be adapted to many applications to
purify contaminated water wherever it is found, be it in waste water treatment systems, lakes, ponds, industrial
plants, or in homes. Laboratory tests have been conducted on aqueous solutions containing only one of the
following metal cations: lead, copper, mercury, cadmium, silver, chromium (III), nickel, zinc, and yttrium. Tests
were also conducted with: (1) calcium present to determine its effects on the uptake of cadmium and copper,
and (2) uranium and lanthanides which are stand-ins for other radioactive elements, (3) drinking water for the
removal of copper and lead, and (3) others compositions. The Results revealed that the IEM removes all these
cations, even in the presence of the calcium. Of particular interest are the results of the tests with the drinking
water: the lead concentration was reduced form 142 ppb down to 2.8 ppb (well below the accepted EPA
standard).
BACKGROUND
Many industries, such as the electroplating and mining companies, produce large amounts of waste water
that contains hazardous amounts of mercury, lead, cadmium, silver, copper, and zinc ions. They are required by
law to reduce the concentrations of these toxic metals in their waste water before it is discharged into sewers,
lakes and streams. A number of companies we have contacted have told us that existing technology appears to
be too expensive or inadequate for meeting the new lower limits. Also pressure is developing for eliminating the
disposal of the wastes in land fills. For these reasons, industries and some government agencies are looking for
new technology with which to dean the water.
The IEM is a spinoff from research done on space batteries. During the research, it was discovered, quite
by accident, that it had an affinity for heavy metal ions, even when calcium ions are present. This is an
important feature because many commercial ion exchange materials cannot remove heavy metals when the
calcium is present. The calcium saturates the resins, thereby blocking the adsorption of heavy metal ions. This
is not the case for this new IEM. Those commercially available ion exchange resins that do pick up the metal
cations when calcium is present are very expensive. As a result, it was realized that this new IEM may have direct
application to cost effective purification of contaminated water.
Once this potential became apparent, the NASA Lewis Research Center started a program in fall of 1991
to determine if the IEM was indeed an advance over existing technologies and if the IEM could be spun off as
a new commercially viable product. The Cleveland Area Manufacturing Program (CAMP) helped by pointing
out that the local electroplating industry was seeking new technology with which to remove heavy metal cations
from their waste rinse water. The Northeastern Ohio Regional Sewer District also helped by explaining the
nature and magnitude of the heavy metal disposal and cleanup problems facing the electroplaters and other
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industries. Opinions were sought from waste water treatment experts, in particular an expert at the Cleveland
State University. He called the IEM "an exciting new material". With this information, it was decided to proceed
with a modest program to first characterize the key heavy metal adsorption rates, quantity adsorbed per unit
weight, and other important physical properties such as the mechanical strength, tear resistance, resistance to
degradation by chemical attack from a variety of aqueous solutions, etc. Simultaneously, the Lewis Technology
Transfer Office began to search for the potential applications for the IEM and to determine the status of the
existing technology being used to remove the heavy metals from waste and potable water.
THE ION EXCHANGE MATERIAL - IEM FILM PREPARATION
The IEM is composed of a crosslinked copolymer of polyvinyl alcohol and polyacrylic acid (Patent
Pending). The IEM is made, in sheet form, by casting an aqueous solution of the two polymers on a fiat surface
to the desired thickness and allowing the water to evaporate. The water soluble sheet is crosslinked at elevated
temperature in an aqueous solution containing a salting-out agent, the crosslinking agent and an acid catalyst.
The resulting water insoluble film, in the acid form, is then converted to the desired salt form which is usually
the calcium form.
LABORATORY TESTS AND EXPERIMENTS
The following adsorption characterization tests have been completed on:
(1) Single ion aqueous solutions contaminated with one of the following ions: lead, copper, mercury, cadmium,
silver, chromium(Ill), nickel, zinc, yttrium, and mercury.
(2) Hard water solutions containing cadmium or copper to determine the effects of the hard water on the
adsorption.
(3) An electroplater's rinse water containing primarily zinc, some other heavy metal ions, and some unknown
contaminants, e.g. brighteners and chelating agents.
(4) Solutions of uranium and lanthanides, which are stand-ins for other radioactive elements.
(5) Drinking water containing copper and lead at levels exceeding those recommended in the new drinking
water standards. These tests were conducted in a flow system. The lead ladened water was passed through
an annulus whose inner surface was coated with the IEM. The calcium content of the water was
approximately 40 ppm.
(6) Copper and lanthanides to determine if superior spectroscopic chemical analysis methods could be
developed.
TEST RESULTS
This report contains some of the significant results from the tests conducted to date. They are described
below and supported by tabular and graphical illustrations. A study of those results show that the adsorption
rates and the mass adsorbed per gram of the IEM vary with the pH of the solutions and on the initial con-
centrations. The most noteworthy findings are:
O) The adsorption of an ion is not affected by the presence of other ions (including calcium) in the mixture
so long as there is sufficient ion exchange material in the solution to absorb all ions. For example, it is
seen in Figure 1 that the rate and amount of copper adsorbed is the same whether it is in a mixture
containing other ions (listed in Table 2) or it is the only ion in a solution.
267
(2) The amount of an element adsorbed varies with the pH of the solution. This is shown in Figure 2 for
cadmium, mercury, copper and zinc. For most metals the lower pH limit for effective uptake of metal
is governed by the acid exchange constant for the film, and the upper pH limit is governed by the affinity
of the particular metal to form insoluble or anionic hydroxy species. Using the zinc curve, for example,
the lower limit is at approximately pH=5, and the upper limit is approximately pH=7.
(3) Acid and base titrations of the IEM indicate the capacity for metal uptake to be in the range of 3.5 to 5.0
milliequivalents/gramn, depending on the form of the IEM film. These uptakes are comparable to
commercial high capacity ion exchangers. In Table 1 are the calculated maximum uptakes of various
metals based on the titration capacity. For comparison, the experimentally determined IEM saturation
for zinc occurred at 170 grams zinc per kilogram IEM in a system containing a limited amount of IEM
and excessive amounts of zinc ions.
(4) Table 2 gives the IEM recoveries from an actual electroplaters waste solution which contained all of the
ions listed in the table plus others not measured.
(5) The final concentration of most of the elements tested are below the EPA discharge limits for those ions.
(6) Table 3 indicates the ability of the IEM to recover uranium and other elements used to model the
behavior of various radioactive elements.
(7) The results presented in Table 4 indicate that the IEM, when used in a flowing system, removes copper
and lead in drinking water from an order of magnitude above the recommended concentration levels down
to levels an order of magnitude below the recommended value.
(8) A simple colorimetric test was developed for use in the field or in homes to determine the concentration
of copper in water. This test is done by simple eye comparison similar to a color chart. More sophisticated
methods of spectroscopic analysis have also been developed based on the superior optical properties of
the IEM film.
Other tests have shown that the ion exchange polymer is:
* Easy to use and inexpensive to make.
* Strong_ flexible, and cannot be easily torn.
* Chemically stable in storage, in aqueous solutions, and in acidic or basic solution.
* Although no toxicity tests have been performed, it is anticipated that this IEM is safe and non-toxic
to handle.
DISPOSAL
Another important feature of the material is that the adsorbed metals can be easily reclaimed by either
a destructive or a non-destructive process. With the destructive process, the spent IEM is burned, thereby
producing carbon dioxide, water vapor, and oxides of the adsorbed metals which can be recycled. With the non-
destructive process, the heavy metals are removed from the IEM and reclaimed by an acid stripping process. The
IEM is then reusable and the metal concentrate can be recycled.
The acid stripping procedure uses nominal concentrations of simple mineral acids to strip the IEM of
metals within 5 to 10 minutes. Tests with zinc and other heavy metals indicate that the recovery of metal is in
the range of 95-100% (see footnote Table 3). The trim is then reconverted to the appropriate salt form for reuse
as discussed above in the Film Preparation discussion.
268
PROJECT STATUS
(1) Some of the characterization tests, which were conducted on the thin film form of the IEM, are complete.
(2) The patent covering this IEM has been filed.
(3) A test has been started at a local electroplating firm to determine the effectiveness of the IEM in a zinc
plating process. The test will determine how well the waste zinc ion is removed from the first wash bath
which also contains brighteners, carriers, etc. associated with the plating process.
(4) Work has started to develop the methods for making the IEM into fine pellets for use in packed columns
and to measure their adsorption properties.
CONCLUDING REMARKS
It is the mission of the NASA Lewis Research Center's Technology Utilization Office (TUO) to spin-off
technology developed inside NASA to U.S. industry. When a new NASA technology is developed, usually for an
aerospace application, the TUO tries to determine where in the U.S. market the new technology might be used
and whether there is a market potential for it. We learned through many contacts with industries and government
agencies who are addressing the problems of heavy metal removal from waste water, that there is a need for new
technology because the existing technology is either too expensive or not suitable. Based on the responses we
received from these contacts, we concluded that the IEM appears to be a promising technology that could
contribute to improving the environment. Our contacts told us that the IEM appears to have some unique
characteristics that are not available in ion exchange resins on the market today and that it should be developed
to the point where it can be made available commercially.
The IEM is still in the development stage. Much work remains to be done to fully characterize the
adsorption characteristics of the film and pellet forms. At present, only the film form has been well
characterized in the laboratory. Tests of the film in an industrial setting has started. A number of such tests are
planned in selected applications. The method for making pellets is under development. Once pellets are available
laboratory characterization tests and industrial tests will also be performed. However, if any companies are
interested in licensing the IEM technology at this stage, they are invited to do so.
269
Table 1 - CALCULATED ION EXCHANGE
UPTAKE OF INDIVIDUAL METALS.
METAL ION gins metal/kg IEM
Zinc 168
Cadmium 289
Lead 533
Chromium(Ill) 89
Copper 163
Mercury 516
Nickel 151
Table 2 - ADSORPTION PROPERTIES OF THE IEM IN AN ELECTROPLATERS WASTE MIXTURE 1
pH=5 pH=7
METAL INITIAL PERCENT INITIAL PERCENT
CONCENTRATION RECOVERY CONCENTRATION RECOVERY
(ppm) (ppm)
Zinc 8.38 97.6 8.38 96.4
Cadmium 0.88 > 97.7 z 0.88 > 97.72
Nickel 1.11 82.0 1.11 82.0
Copper _ 0.11 > 90.92 0.07 85.7
Manganese 0.22 95.4 0.22 > 99.62
The mixture contained ions of all of the metals listed in this table.
The following elements are initial concentrations measured at pH 7 which
were not followed during the course of this experiment: Silver, 0.01 ppm;
Sodium, 1415 ppm; Cobalt, 0.01 ppm, Magnesium, 0.9 ppm; Lead, <0.03 ppm;
Chromium (III), 0.03 ppm, Iron, 0.02 ppm.
2 Final concentration at or below limit of instrument detection.
3 Northeast Ohio Regional Sewer District determination.
270
Table 3. Uranyl and lanthanide ion uptake by the IEM from water.
METAL
u (vi)"
Ce (III)
Eu (III)
Gd (III)
Tb (III)
IMTIAL
CONCENTRATION
PERCENT
REMOVED pH
15.2 68 6.3
15.2 78 6.6
1.0 *° 80 6.6
14.2
15.6
13.4
99.6
96.4
99.9
86.716.6
7.0
6.9
7.0
7.0
* UO22+ + dimers, etc.
"* 96% U(VI) recovered by acid stripping of film.
Table 4. Removal of lead and copper from spiked tap water.
Batch Testing Technique for Lead
Test Conditions:
Sample Size: 1 liter with 0.4 grams of IEM film
Sample continuously stirred
Initial Lead Concentration: 56 ppb
Equilibration time: 2.5 hrs.
Results: Final lead concentration: 1.5 ppb
Dynamic Testing Process for Lead and Copper
Test Conditions:
Flow inside an annulus (length 3 ft.)
IEM film wrapped around inner surface of annulus
Residence time: 3 hrs.
a) Lead tests
Initial Lead Concentration: 142 ppb
Results: Final lead concentration: 2.8 ppb
b) Copper tests
Initial copper concentration: 15 ppm
Results: Final copper concentration: 0.004 ppm
271
1
O
100
80
6O
4O
2O
COPPER IN STANDARD
X COPPER IN MIXTURE
0 _ ×
0 300 600 900 1200 1500
Time (Minutes)
Figure 1. The adsorption rate characteristics of the New Ion Exchange Material for
copper alone in a standard solution and in a solution of the rinse water flom a copper
electroplating process.
g_
O
100
8O
60
4O
20
-=-_r .... ZINC ..-
/
.......<>......... CADMIUM .."
----O------ COPPER
MERCURY
0
1 2 3 4 5 6 7 8
pH
Figure 2. Metal Adsorption by the New Ion Exchange Material as a function of the
solution pH.
272


A new material for removing heavy metals from water

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