Electrodeposition recovery method for metals in polymer chelates

The process of the present invention for the recovery of metal ions from a polymeric chelating agent stream or solution comprises the circulation of a loaded polymeric chelating agent stream or solution through an electrolytic recovery cell. The chelating agent is loaded with metal ions or complexes of the species to be recovered which have been extracted from a feed stream or solution. These metal ions or complexes will be reduced and recovered from the chelating polymer by an electrodeposition method. If the chelating agent is used in a continuous flow-type system, the lean polymeric chelating agent can optionally be recycled for further use in extraction of the desired metal species. The addition of scrub and regeneration stages to such a system is optional, depending on feed stream composition.

FIELD OF THE INVENTION 
This disclosure is a continuation-in-part of U.S. patent application Ser. 
No. 862,880 filed May 13, 1986. The subject invention is directed toward a 
unique process which employs an electrolytic recovery cell for the direct 
recovery of a desired metal species from a polymeric chelating agent 
solution. Generally, any flow stream which contains a desirable metal ion 
or a contaminant metal ion for which a known adsorbent exists can be 
treated with this process for separation and removal. Applications for 
this process include the direct recovery of metals from streams such as 
plating wastes, photographic processes, and liquors from mining 
operations. 
BACKGROUND OF THE INVENTION 
Electroplating is the electrodeposition of a metallic coating on an 
electrode in order to form a surface with properties or dimensions 
different from those of the electrode material. The properties which may 
be conferred by electroplating include improved corrosion resistance, 
enhanced appearance, frictional characteristics, wear resistance and 
hardness, solderability, and specific electrical properties. 
The thickness of the deposit formed by electroplating varies with the 
application. Where the deposit is applied for decorative purposes as 
little as 0.025 micrometers may be applied. Conversely, nickel-chromium 
deposits on automotive hardware might be as thick as 25-50 micrometers, 
and 1 millimeter deposits may be laid down on electroforms. 
Electrowinning, an electroplating technique in which the metal ions are 
removed in bulk amounts, may deposit as thick as two inches. 
Generally, electrodeposition and electroplating have been used as surface 
treatment. Deposition and plating solutions are usually aqueous. Known 
exceptions to the use of aqueous solutions include plating of aluminum, 
which may be plated from organic electrolytes, and plating of tungsten, 
molybdenum, tantalum, aluminum, and niobium, which may be plated from 
fused electrolytes. The solutions usually contain additives to perform any 
one of several different functions such as providing a source of ions for 
the metal species to be deposited; providing conductivity; stabilizing the 
solution; buffering the pH of the solution; and aiding and modifying other 
properties particular to the invoIved solution. Many viable compounds 
accomplish more than one of the above functions. 
Polymeric chelating agents, conventionally used to enhance physical 
characteristics of the metal being deposited, are examples of solution 
additive. The art is replete with patents documenting the use of polymeric 
additives for the purpose of brightening a plated metal species. This task 
was previously accomplished by post-plating methods, such as buffing, but 
more recently is being achieved during the plating process by addition of 
polymeric chelating agents. The brightening agents used are most often 
organic compounds and are added in small amounts, usually less than about 
one percent of the electroplating solution or bath. 
U.S. Pat. No. 3,864,222 discloses the incorporation of polyethylene imines 
into gold and gold alloy plating baths as agents for the general 
improvement of brightness of the electroplate and of other physical 
properties of the deposit obtained, as well as the operating conditions of 
the bath. 
U.S. Pat. No. 4,425,198 discloses the use of a polyacrylamide polymer as a 
brightener in a zinc alloy electroplating bath. Acrylamide was also used 
as a primary brightener for a zinc electroplating bath in U.S. Pat. No. 
4,176,017. 
Other brightening agents known in the art are used commonly in zinc and 
zinc alloy plating baths, examples of which include beta-amino-propionic 
acid, disclosed in U.S. Pat. Nos. 4,401,526; quarternary ammonium 
silicates, disclosed in 3,993,548; polypropoxy and polypropoxy-ethoxy, 
claimed in 3,928,149; and epihalohydrin-alkylene amine polycondensates, 
used in 3,869,358. 
U.S. Pat. No. 4,396,647 discloses the use of a cobalt, nickel, or indium 
hardener as a chelate with the acid form of a methyl vinyl ether/maleic 
anhydride interpolymer for gold cyanide electroplating baths. 
In each of the above cited patents, and in the known art, polymers of the 
types mentioned function as brightening agents, or agents which impart 
ductility, hardness, and other physical characteristics to a plated metal 
coating. It is noted here that in each instance, the metal plated was 
plated for the purpose of surface coating an existing material to enhance 
specific characteristics. 
Electrowinning is an electrodeposition technique for extracting bulk 
amounts of a metal from its ore in an electrolytic cell. 
Hydrometallurgical processes have been used for electrowinning for the 
recovery of zinc, cobalt, chromium, manganese, nickel, cadmium, gallium, 
thalium, indium, silver, gold, and copper. The process involves subjecting 
the metal salt in solution to electrolysis and electrodepositing the metal 
at the cathode. 
Direct electroplating has been used as a recovery method of sorts to remove 
objectionable pollutants from electroplate feed streams or solutions, as 
pollution is a prevalent proble with electroplating processes. In the 
past, the problem was solved by destruction of the objectionable metal 
species. The metals were precipitated as sludges and disposed of in 
landfills. Metal cyanides, which are among the most dangerous of chemical 
pollutants, are most often dealt with by destruction methods such as 
chlorination, electrolysis, solvent extraction and catalytic methods. 
Emphasis has shifted, however, to the direct recovery of objectionable 
metals for reuse in the plant or for resale to refiners. Proposed recovery 
methods for metals less dangerous than cyanides include reverse osmosis, 
evaporative recovery, ion exchange, and combinations thereof. High cost of 
equipment, among other costs particular to specific methods, such as 
membrane replacement in reverse osmosis, make such methods prohibitive in 
many instances. 
A specific instance where the recovery of desirable metal species may be 
important is in affinity dialysis and other similar soluble affinity 
adsorbent systems. The conventional means for removal of metal species 
from the feed solution of such systems is to bind the metal species to an 
affinity adsorbent in an extraction step and then strip the metal from the 
soluble adsorbent at a later stage of the process. This requires use of a 
strip reagent, which destroys the binding complex and releases the metal 
species to be stripped. The strip reagent comprises an aqueous solution of 
an acid or base, depending on the charge character of the material to be 
stripped. Where the system is a continuous flow system, this addition of 
reagent may then further necessitate regeneration, or adjustment of the 
pH, of the affinity adsorbent by further addition of acid or base solution 
prior to its recirculation through the system. Such processes require 
costly chemicals, extensive pumping equipment, and highly sensitive 
controls for monitoring of system parameters such as temperature, pH, and 
feed flow to affinity adsorbent flow ratio. 
What is lacking in the art is a means for efficient recovery or removal of 
metals in substantially pure bulk form from feed solutions containing a 
polymeric chelating agent which has adsorbed the metal species. Also 
lacking is a bulk metal ion recovery or removal process applicable in 
either single pass or continuous flow systems. 
Therefore, it is an object of the present invention to provide a feasible 
method for the recovery of desirable metals as well as the removal of 
objectionable metals from solutions. 
It is also an object of the present invention to provide a method for the 
recovery of desired metal species in a substantially pure form from a 
polymeric chelating solution. 
It is a further object of the present invention to provide a method for the 
recovery of metal species from affinity adsorbent systems in an efficient 
and simple manner. 
These and additional objects of the present invention will become apparent 
in the description of the invention and examples that follow. 
SUMMARY OF THE INVENTION 
The present invention relates to a process for the recovery of at least one 
metal species from a polymeric chelating agent stream comprising the steps 
of: 
circulating the polymeric chelating agent stream through an electrolytic 
recovery cell, the polymeric chelating agent being loaded with metal ion 
or complexes of the species to be recovered; 
reducing the metal ions or complexes from the polymeric chelating agent by 
application of voltage and current through the stream of loaded polymeric 
chelating agent; and 
depositing the metal species from the stream at the cathode of said 
electrolytic recovery cell. 
The invention also relates more specifically to a process for the recovery 
of metal species from an affinity adsorbent/polymeric chelating agent 
stream of an affinity dialysis system wherein the lean polymeric chelating 
agent is recycled to the extraction stage of the affinity dialysis system. 
The addition of scrub and regeneration stages to such a system is 
optional, depending on feed stream composition. 
DETAILED DESCRIPTION OF THE INVENTION 
In accordance with this invention, metal ions or metal complexes adsorbed 
by a polymeric chelating agent are recovered by direct electrodeposition. 
Direct electrodeposition of metal ions or complexes is accomplished in an 
electrolytic recovery cell. The cell consists of an anode and a cathode 
disposed in a cell housing. The electrolyte of the cell enters from one 
side of the cell, flows across both electrodes of the cell, and exits the 
cell on another side thereof. A potential is applied across the cell, 
supplied by an exterior power source, which causes the reduction of the 
desired metal species and deposition thereof at the cathode. 
The cathode of the electrolytic recovery cell is a material suitable for 
the deposition of the metal ion or complex of interest, and may be in the 
form of a plate electrode, rotating electrode, or other suitable form. 
Some suitable cathode materials include copper, nickel, stainless steel 
and others known to those skilled in the art. Suitable anodes may include 
DSA, lead-calcium alloy anodes and other conventional anode material known 
in the art such as carbon felt, granular carbon, graphite, and stainless 
steel. 
The electrolyte of the cell is the polymeric chelating agent solution or 
stream, which may or may not contain quantities of other components which 
are not the metal species of interest in the instant electrodeposition 
process. The electrolyte solution comprises the bound polymer, the metal 
ions or complexes to be reduced and deposited or plated out, and these 
other components. The polymeric chelating agent of the present invention 
may be any of a wide variety of adsorbent materials. The agent may be 
soluble, suspended in or otherwise carried along by the solution or stream 
as a stable suspension of microparticles used to circulate the polymer. 
The polymer is selected for its preferred affinity to chelate or otherwise 
combine with the material or materials to be separated from other material 
or materials in a liquid feed stream, i.e. it must demonstrate a 
selectivity for at least one metal species over other metal species 
present in the feed stream or solution. The polymer chosen must also be 
susceptible to being stripped of the desired metal species by a direct 
electrodeposition method. It may affect and bind the metal ion or complex 
such that it concentrates or enriches the desired species. 
Representative adsorbent materials operative in the subject invention 
include most chelating and ion exchange polymers. Exemplary polymers 
include sulfonated polyolefins, polyacrylic acid based compounds, 
polyethylenimine of a weight average molecular weight of about 2,000 or 
greater, hydroxyethylated polyethylenimine of a weight average molecular 
weight of about 2,000 or greater, polyimino acetic acid, polyimino 
diacetic acid, polythiourea, poly(2-acrylamide-2-methyl-l-propanesulfonic 
acid), poly(l,l-dimethyl-3,5-dimethylene-piperidinium chloride), water 
soluble polymers with Schiff base chelates attached, water soluble 
polymers with hydroxy quinolines attached, and other chelating polymers 
known in the art and envisioned based on known chelation behavior and 
known polymer backbones. 
The chelating agent is carried by a solvent which is either water or an 
aqueous media, for example water and alcohols or other water miscible 
organic solvents. The chelating agent is generally dissolved in the 
solvent to a maximum concentration, which concentration will vary as the 
chelating agent and solvent vary, as well as with practical limitations 
due to viscosity. 
The polymeric chelating agent solution has a polymer concentration of about 
0.5 weight percent to about 25 weight percent, more preferably of about 10 
weight percent to about 15 weight percent, wherein the term "weight 
percent" refers to the number of grams of polymer per one hundred grams of 
solution. Polymer concentrations lower than about 0.5 weight percent 
deposit or plate substantially lesser amounts of metal, requiring that the 
electrolytic cell capacity be considerably increased in order for a 
significant amount of metal to be recovered, which causes a corresponding 
decrease in current efficiency, and may require that higher value metals 
be reduced and deposited or plated to justify reduced efficiency. The 
effect of lower concentrations on adsorbent systems similar to affinity 
dialysis systems would be to decrease the efficiency of the extraction 
process. Polymer concentrations much higher than 25 weight percent result 
in a solution of extremely high viscosity in which the polymeric chelating 
agent is not efficiently utilized. 
The polymeric chelating agent solution or stream may contain interfering or 
non-interfering metal ions or complexes. Where the purpose of the system 
is to recover a substantially pure metal deposit or plate, interfering 
metal ion species, which reduce and are released or plate in the same or a 
similar potential range as the desired species, must be removed. The 
desired metal species may be deposited or may plate in a dendritic manner, 
leaving voids which may be occupied by interfering species unless the 
interfering species is removed prior to deposition or plating. However, 
contaminating or interfering ions may be removed from the solution or 
stream prior to the electrodeposition process by passing the solution or 
stream through a scrub stage. Where the interfering ion or complex is 
bound to the polymeric chelating agent, the scrub stage normally 
encompasses the passage of the stream or solution carrying the desired 
metal species and the contaminant through a basic or acidic reagent stage, 
such reagent having an affinity for the interfering species. This causes 
release of the interfering species, leaving only the desired species 
intact. Alternatively, a water stream may be used in the scrub stage to 
remove contaminants not bound to the polymer. 
Non-interfering metal ions are those ions which are picked up by the 
polymeric chelating agent stream or solution, from the feed stream, which 
do not demonstrate an affinity for the potential applied across the cell 
and consequently are not released, but rather remain in the stream. In a 
continuous flow system, a steady state concentration of non-interfering 
metal ions and complexes will be achieved. This results from the 
recirculation of the polymer stream or solution, which has adsorbed the 
ions. During recirculation the ions migrate back and forth across a 
separating membrane or between the feed stream and the polymer stream 
until the concentration of noninterfering ions reaches an equilibrium 
state between the solution from which the ions or complexes originate and 
the polymeric chelating agent stream or solution. These noninterfering 
ions and/or complexes will not be plated out due to the affinity of 
certain ions and complexes to plate out more readily at certain specific 
voltages. 
The potential applied across the cell is related to the metal species being 
deposited or plated. The deposition of metal species follows what is 
effectively a hierarchy of deposition order, wherein different metal 
species reduce at different ranges of electrical potential. Thus, at a 
given potential, some species deposit or plate more readily than others. 
Consequently, controlling the applied electrical potential is one means of 
controlling the deposition or plating process with respect to choice of 
metal species recovered. The current density of a typical electrolytic 
recovery cell for the recovery of metals ranges from about 1 amp/ft.sup.2 
to about 300 amp/ft.sup.2, preferably about 5 to about 100 amp/ft.sup.2. 
When the electrolytic cell is operated at appropriate voltage and current 
density, the circulation of the polymeric chelating agent solution or 
stream through the cell results in the reduction of the metal ion species. 
Once reduced, the metal ions will deposit or plate at the cathode of the 
electrolytic recovery cell. 
The pH of the polymeric chelating stream or solution, which may range from 
greater than 0 to 14, should be maintained within a range sufficient to 
bind the desired metal ion species. Acid is generated in the stream or 
solution by the deposition or plating process and may, therefore, 
depending on the amount generated and the operating pH of the stream, 
require balancing or neutralization of the stream for maintenance of the 
optimal pH. When the metal species to be recovered is a metal cation, the 
pH preferably ranges from greater than 0 to about 5. When the metal 
species to be recovered is in the complexed form, it is usually an anion 
with a pH preferably ranging from about 9 to about 12. 
The temperature and pressure at which the electrodeposition process is 
conducted is dictated by the materials and conditions of the 
electrodeposition bath. These parameters can be selected to be consistent 
with practices conventional in the art and compatible with the instant 
process materials. The bath temperature is determined by the individual 
bath, as each bath solution is characterized by a range of temperatures 
within which best results may be achieved. Temperature affects such 
parameters as conductivity, current efficiency, nature of deposit and 
stability. The pressure may generally be ambient, however, in some 
instances, recognizable by those skilled in the art, pressure control by 
conventional methods may be necessary. 
Substantially any metal species that can be chelated and electrodeposited, 
anionic or cationic, can be recovered by the method of the subject 
invention. More particularly, substantially any type of anion, such as 
chromates, stannate, and zinc, silver or gold cyanide complexes can be 
recovered through direct electrodeposition; cations which are similarly 
recoverable include transition metal ions, such as copper, nickel or zinc, 
metals in photographic processes, and metals recoverable from the liquor 
of mining operations. Where the metal species to be recovered is 
complexed, the complex is destroyed in order to release the metal 
component which can then be recovered. Exemplary metal ion and complex 
species which may be recovered include Cr, CrO.sub.4.sup.2-, Mn, Fe, Rh, 
Ir, Bi, Sb, Re, Tc, In, Tl, Ga, Te, Po, Co, Ni, Cu, Zn, Zr, Ru, Pt, Pd, 
Ag, Cd, Sn, Hg, Pb, [Zn(CN).sub.4 ].sup.2-, [Ni(CN).sub.5 ].sup.3-, 
Na.sub.2 Sn(OH).sub.6 and K.sub.2 Sn(OH).sub.6. Preferred metal species 
are Cu, Cr, Ni, Zn, Ag, Cd, Sn, Pb, Pd, Pt, Ru, Ir, Zr, CrO.sub.4.sup.2-, 
[Zn(CN).sub.4 ].sup.2- , [Ni(CN).sub.5 ].sup.3-, Na.sub.2 Sn(OH).sub.6 and 
K.sub.2 Sn(CH).sub.6. Most preferred metal species are Cu, Zn, Sn, Ni, 
CrO.sub.4.sup.2-, and Ag. alloy materials such as Cu/Zn, Cu/Sn, Pb/Sn, 
Sn/Ni, Ni/Co, and Ni/Cr, may also be deposited or plated by the process 
disclosed herein.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 depicts an electrolytic recovery cell encompassed by the disclosure 
of the subject invention. The loaded polymeric chelating agent stream or 
solution 19 enters the electrolytic recovery cell 30 at an inlet port 31, 
flows through the cell, and exits the cell at outlet port 33 as a lean 
polymeric chelating agent stream or solution 16. While within the 
electrolytic recovery cell, polymeric chelating agent stream 19 flows over 
the cell's anode 35 and cathode 36. A potential applied across the anode 
35 and cathode 36 from a remote power supply 37 causes reduction of the 
desired metal species, which subsequently deposits at the cathode 36 of 
the cell assembly. Multiple cell assemblies may be connected in sequence, 
separated by a series of baffles 38 to help direct electrolyte flow, to 
increase recovery efficiency per pass of loaded polymeric chelating agent. 
Conversely, a singular cell assembly may be employed. The metal species 
recovered may be removed from the cell by removal of the electrodes, 
mechanical stripping thereof and replacing the electrodes, or other 
methods known in the art, i.e., where the deposited or plated material 
forms directly on the electrode, but is precipitated immediately by 
turbulance, release agent or vibration. 
Once deposition or plating has taken place, the lean polymeric chelating 
agent solution or stream can be recirculated for further use. Depending on 
the ratio of feed flow volume to polymer flow volume, a regeneration stage 
may be necessary. When the ratio is high, the acid that is generated 
during the electrodeposition process will diffuse out of the polymer flow 
and into the feed flow without substantially changing the pH, therefore, 
no regeneration process is necessary. At lower ratios, however, the 
presence of the acid in the polymer stream may shift the pH of the stream 
making the polymer unable to bind the metal species. When the pH range is 
more basic, an acidic reagent solution may be added to the stream to 
enable binding of the metal species. 
The preferred embodiment of the subject application is depicted in FIG. 2 
which is a schematic diagram of a continuous flow affinity dialysis 
system. Such a system is disclosed in pending applications U.S. Ser. Nos. 
742,872 and 802,836. These applications disclose a process for selective 
dialysis using polymeric affinity adsorbents and size selective membranes, 
and a scrubbing unit for high feed concentrations to be used in the 
affinity dialysis process, respectively. 
U.S. Ser. No. 742,872 provides for the use of a porous membrane with pores 
of a sufficient dimension to allow the passage of different materials 
therethrough. An affinity adsorbent stream, comparable to the polymeric 
chelating agent stream of the subject invention, is circulated against a 
first side of this membrane, the dimension of the adsorbent being larger 
than the pores of the membrane. A feed stream containing materials to be 
adsorbed is passed against the second side of the membrane. The materials 
to be adsorbed, being of smaller dimension than the membrane pores, pass 
through the membrane from the second feed stream side to the 
first-affinity adsorbent stream side where they are adsorbed onto the 
affinity adsorbent. 
The loaded polymeric chelating agent stream then passes from the extraction 
stage to an optional scrub stage, which is described in detail in U.S. 
Ser. No. 802,836, where any interfering or objectionable adsorbed species 
can be removed. 
The polymeric chelating agent stream then, according to U.S. Ser. No. 
742,872, must pass through a stripper unit in order for the species 
adsorbed by the polymeric chelating agent to be released and possibly 
recovered. This often requires the addition of a stripping reagent, which 
in turn generates a need for a regeneration unit wherein a second reagent 
solution is added to rebalance the system before recirculation to the 
extraction stage. Thus, an acid/base cycle is undergone. 
The electrolytic recovery cell of the present invention may be substituted 
into the affinity dialysis system of either of the two cited U.S. patent 
applications to replace the strip stage when the species to be recovered 
is a metal ion or metal complex. The incorporation of an electrolytic 
recovery cell into an affinity dialysis system will negate the need for 
the acid/base cycle referred to above in conjunction with 
stripping/regenerating the affinity adsorbent stream. As there will no 
longer be a need for the addition of a stripping reagent, there will also 
no longer be a need for the concomitant addition of a second reagent to 
neutralize or rebalance the system. An optional regeneration stage may 
still be necessary with the electrolytic recovery cell depending on the 
amount of acid generated in the cell during destruction of the metal 
species-chelating agent complex and metal ion reduction at the cell 
electrode. 
The replacement of the stripper/regeneration portions of prior known 
affinity dialysis systems with the electrolytic recovery cell of the 
subject invention will reduce equipment use and needs, and simplify system 
operation and maintenance due to the lack of strip reagent addition, and 
elimination of the membrane strip stage. 
The preferred embodiment of the subject application is depicted in FIG. 2 
comprising an extraction unit 10, optionally followed by a scrubbing unit 
20, an electrolytic recovery cell 30, and an optional regeneration unit 
40. 
In the affinity dialysis system of the preferred embodiment, the extraction 
unit 10 comprises an apparatus for continuous counter current mode work, 
operative for long-term, steady-state work. The apparatus includes a 
membrane unit of stainless steel or other suitable material within which 
are enclosed semipermeable membranes. A feed 12 of different materials, 
including the metal species to be recovered, is circulated against one 
side 13 of the membrane 14. A supply of polymeric chelating agent 16, 
either fresh or regenerated, is circulated against a second side 15 of the 
membrane 14 in a countercurrent mode to feed stream 12. The membrane 14 
has a pore diameter of sufficient size to allow migration of metal ions 
through the membrane pores. These metal ions are then complexed by the 
polymeric chelating agent 16 which is flowing in a counter current mode on 
the second side 15 of the membrane 14. The depleted feed 18 exits the 
extraction unit to be discarded and the loaded polymeric chelating agent 
19 is circulated to electrolytic recovery cell 30. 
Electrolytic recovery cell 30 consists of a cathode and anode assembly, 
suitable for recovery of the desired metal species, and a power source 
supplying potential across the cell appropriate for reduction of the metal 
ions that are to be recovered. The specific assembly of the cell is more 
completely illustrated in FIG. 1, described in detail above. 
The loaded polymeric chelating agent stream 19 is circulated through 
electrolytic recovery cell 30, acting as the electrolyte therein. The 
potential across the cell, supplied by a remote power source (not shown) 
causes the loaded polymeric chelating agent to release the metal ions 
complexed thereon. These metal ions are deposited at the cathode as is 
described above in conjunction with the explanation of FIG. 1. The 
deposited metal product is removed from the cell, and the lean polymeric 
chelating agent 16, devoid of metal ions of the desired species is 
circulated out of electrolytic recovery cell 30 and back to extraction 
unit 10 for reuse. 
An optional regeneration unit 40 may be used to return the polymeric 
chelating agent to a pH amenable to complexing of the desired metal 
species. The regeneration unit comprises a vessel 42 to which a regenerant 
stream 44 is fed. The regenerant added will be a base where the acid 
produced during electrodeposition of the metal ions in electrolytic 
recovery cell 30 has caused a significant shift in the pH of polymeric 
chelating agent stream 16. Conversely, if polymeric chelating stream 16 is 
more basic, the regenerant added will be an acid. The necessity of adding 
regeneration unit 40 to the system will most often be determined, however, 
by the feed flow volume to polymer flow volume, as was previously 
explained. 
As a further optional step, either to the dialysis process conducted in 
unit 10 with the electrolytic recovery cell, unit 30, or where 
electrolytic recovery is conducted as a separate process, the scrubbing 
unit 20 can be employed. The scrubbing unit 20 can comprise a cell or 
hollow fiber unit 21 not unlike that of extraction unit 10 referenced 
hereinabove. The cell 21 also employs a membrane 14 that can be the same 
or a different membrane as employed in the other cells. The purpose of the 
scrubbing stage is to remove metal ion species or other species which 
would interfere with the recovery of the desired metal species in the 
electrolytic recovery cell. 
In operation, the loaded polymeric chelating agent stream 19 is fed to a 
first side 22 of the membrane 14 and a stream of water or basic or acidic 
reagent 23 is fed to the second side 24. The purpose of the water feed is 
to remove any extraneous material that is first soluble and second not 
complexed with the adsorbent. The basic or acidic reagent is chosen to 
remove interfering material complexed by the polymeric chelating agent. 
The effluent complex stream 25, once devoid of extraneous materials, can 
be fed directly to electrolytic recovery cell 30. 
EXAMPLES 
In order to further illustrate the present invention, the following 
examples are provided, which examples are not intended to be limitative of 
the invention disclosed herein. 
The examples, examples 1-6, results of which are shown in Table I, were 
conducted according to the procedure set forth herein below. 
Typically, 100 to 200 milliliters of polymeric chelating agent solution was 
placed into a beaker or other suitable container. An anode was submerged 
in the solution at one side of the beaker or container, and a cathode was 
submerged on the opposite side in a substantially parallel position. 
Agitation was provided by the use of a teflon coated magnetic stirrer. All 
experiments were conducted at ambient temperature, except example 6 which 
was done at 65.degree. C. For deposition or plating at elevated 
temperature, a hot plate/stirrer was used. A suitable DC power supply was 
attached to the electrodes and an appropriate amperage and field applied. 
Deposition or plating was continued until the chelate solutions appeared 
to be free of metal or until several hours had elapsed and a solid bulk of 
the desired metal was apparent at the electrode. Metal recovery was 
determined by the weight increase after air drying of the electrode. 
The results and operating parameters of examples 1-6 are presented in the 
following table, Table I. 
TABLE I 
__________________________________________________________________________ 
Wt/Vol %, 
Polymer in Current 
Plating Feed Solution Density % Metal 
Example 
Solution PPM Metal 
pH Cathode.sup.(c) 
amps/ft.sup.2 
Metal Plated 
Recovery 
__________________________________________________________________________ 
1 5% POLYMIN-P.sup.(a) 
12,750 Cu(II) 
4 Copper 
10 7,700 ppm Cu 
60% 
18.625 Ca(II) (1.95 g) 
8,000 Zn(II) 
2 10% POLYMIN-P.sup.(a) 
15,000 Cu(II) 
4 Copper 
10 9,500 ppm Cu 
63% 
50,000 Ca(II) (2.4 g) 
20,000 Zn(II) 
3 5% hydroxyethylated 
polyethylenimine 
15,000 Cu(II) 
3.2 
Ni 200 
20 15,000 ppm Cu 
100% 
(1.8 g) 
4 2.5% AAMPS.sup.(b) 
5,000 Cu(II) 
3.0 
Ni 200 
40 5,000 ppm Cu 
100% 
(0.64 g) 
5 6% Polystyrene 
sulfonic acid 
10,000 Cu(II) 
3.0 
Ni 200 
40 10,000 ppm Cu 
100% 
(1.062 g) 
6 10% poly(1,1 dimethyl- 
3,5-dimethylene- 
piperidinium 
33,000 Sn as 
13.5 
Copper 
288 8,000 ppm Sn 
24% 
chloride) Na.sub.2 Sn(OH).sub.6 (0.83 g) 
__________________________________________________________________________ 
.sup.(a) trademark of BASF 
.sup.(b) poly(2acrylamide-2-methyl-1-propanesulfonic acid) 
.sup.(c) all used carbon anodes, except Example 6 which used platinum wir 
 
Table I shows the metal recovery values for each of examples 1-6, and 
relates the selectivity of the particular polymeric chelating agent 
employed for the metal plated. 
Examples 1 and 2 show the selectivity of the polymeric chelating agent for 
one metal species over another. In example 1, the polymeric chelating 
agent stream was a 5% concentration by weight/volume of POLYMIN-P. This 
was increased to a 10% concentration by weight/volume of POLYMIN-P in 
example 2. The feed solution in both examples contained Cu(II), Ca(II) and 
Zn(II). Both examples show a recovery of 60% or better of copper, the 
desired metal species. This demonstrates the selective chelation of the 
desired metal species by the polymeric chelating agent in the presence of 
other metal species with good recovery percentage. 
Examples 3-5 each illustrate recovery of the desired metal from a feed 
stream which does not contain substantial amounts of other metal species. 
The percent recovery in each instance was 100%, illustrating the utility 
of the recovery technique in situations such as the clean up of a loaded 
waste or product stream. Examples 3-5 used different polymeric chelating 
agents, at varying concentrations, exemplifying the need to coordinate the 
concentration of a particular polymeric chelating agent stream with the 
metal to be recovered and the amount of metal in the stream, as well as 
with the binding power of the agent. 
Example 6 is illustrative of the recovery of a metal species from an 
anionic complex thereof. The pH of the system was 13.5, corresponding to 
the basicity of the anionic complex. Recovery percentage was somewhat less 
than in previous examples 1-5 due to shorter exposure time to the 
applicable electric field, however, the plate was essentially pure for 
tin. 
While the invention has been explained in relation to a preferred 
embodiment and several examples, it is to be understood that various 
modifications thereof will become apparent to those skilled in the art 
upon reading the Specification. Therefore, it is to be understood that the 
invention disclosed herein is intended to cover such modifications as fall 
within the scope of the appended claims.