Selective removal of copper or nickel from complexing agents in aqueous solution

A method is provided for selectively separating and removing complexed heavy metal ions, preferably copper or nickel, from complexing agents in aqueous solution and removing substantially all heavy metal ions while leaving complexing agent in said solution. In preferred embodiments, complexed copper or complexed nickel is selectively removed from aqueous effluent from electroless plating systems by passage through a bed of chelating ion-exchange resin having an iminodiacetic acid functionality. Substantially all copper or nickel will be removed from solution and retained in the resin bed and the complexing agent will pass through for conventional waste treatment or disposal. The copper or nickel is recovered by elution from the resin bed with an acid solution and may, if desired, be precipitated by addition of sodium hydroxide or the like and subsequently separated for recovery or disposal. An improved process for electroless disposition of copper, or nickel, which facilitates waste treatment or recovery of residual complexed copper or nickel ions from plating or effluent solutions is likewise provided in accordance with the invention.

FIELD OF THE INVENTION 
The invention pertains primarily to the art of electroless deposition of 
heavy metals, particularly copper or nickel, wherein aqueous baths and 
solutions containing complexed heavy metal ions and complexing agents are 
utilized. However, the processes of the invention can also be 
advantageously utilized in various other applications wherein aqueous 
solutions which contain complexed heavy metal ions and their complexing 
agents are utilized. 
More particularly, the invention provides processes for selectively 
separating and removing complexed heavy metal ions from their complexing 
agents in aqueous effluent solutions. This facilitates recovery and/or 
waste treatment, not only of the complexing agents, but also of the 
complexed heavy metal ions. 
BACKGROUND OF THE INVENTION 
Aqueous baths and solutions containing complexed heavy metal ions and 
complexing agents have been advantageously utilized in the electroless 
deposition of heavy metals, such as copper and nickel, as well as in metal 
etchant applications. Complexing agents, such as alkanolamines, ammonia or 
carboxylic acids and their salts form strong bonds or chelates with heavy 
metal ions, such as copper or nickel, and are used in electroless 
deposition baths. However, the strong bonding between the heavy metal ions 
and complexing agents which are advantageously utilized in such 
applications, present a problem with regard to recovery and/or waste 
treatment of such plating solutions and the effluents which emanate from 
processes employing these solutions. 
Typically, waste treatment of plating solutions containing heavy metal ions 
has employed precipitation of the metals, as hydroxides, mainly by 
addition of lime. Hydroxide formation, however, is prevented by the 
presence of complexing agents. In situations where complexing agents were 
present, various precipitation techniques have been employed, such as use 
of starch xanthate, ferrous sulfate, cellulose xanthate, hydrogen 
peroxide, sodium hydrosulfate, sodium borohydride, and the like. However, 
these prior art techniques at best only provided incomplete removal of 
complexed heavy metal ions and frequently fail to provide acceptable 
removal of the heavy metals when applied in the field. Also, these 
materials are expensive, and they produce sludge, which itself requires 
disposal and does not facilitate reclamation of pure heavy metals. 
Thus, an effective and reliable method for selective removal of complexed 
heavy metal ions from complexing agents has been lacking in the prior art. 
It has been suggested that ion exchange resins could be utilized to remove 
both complexed heavy metal ions and their complexing agents from 
electroless copper plating solutions, in order to extend the functional 
life thereof. U.S. Pat. No. 4,076,618 discloses a process utilizing ion 
exchange resins, primarily cation-exchange resins containing sulfonic acid 
functional groups. In this prior art process, an electroless copper 
solution is continuously passed through a series of cation-exchange resins 
beds, which retain both the complexed copper and its complexing agent 
together, with the effluent from the bed being discarded. The complexed 
copper-complexing agent mixture is then removed from the ion exchange 
resin. Trace amounts of complexed copper and complexing agent which remain 
after passage through the cation-exchange resin beds are both removed 
together, by passage through a bed of chelating resin. The complexed 
copper and complexing agent mixture which is removed from the chelating 
resin is either returned for use in the electroless copper bath or 
recovered for subsequent reuse. However, such treatment does not 
facilitate waste treatment or recovery of pure heavy metal, since the 
complexed copper and complexing agent are not separated, but remain 
strongly chelated. 
Thus, the process of U.S. Pat. No. 4,076,618 yields substantial amounts of 
complexed copper and complexing agent mixture which must be processed 
further for recovery or waste disposal of copper. In addition, the cation 
exchange resins used have an extremely low efficiency, due to the presence 
of large quantities of sodium byproducts in the plating solutions or 
effluents passed therethrough. This results from the greater affinity of 
cation exchange resins having sulfonic acid functionality groups for 
alkali or alkaline earth cations, such as sodium, over transition metals, 
such as copper or nickel. The only utilization of a chelating ion exchange 
resin in this prior art process is for passage of very dilute solutions 
containing complexed copper and complexing agents, with the result being 
removal of the complexed heavy metal and complexing agent together, 
without separation. 
In accordance with the invention, applicants have unexpectedly discovered 
that a bed of chelating ion exchange resin having an iminodiacetic acid 
functionality can be utilized to selectively remove complexed heavy metal 
ions from complexing agents in aqueous solution. In accordance with the 
invention, applicants provide a method for removal of complexed heavy 
metal ions from complexing agents, so as to facilitate not only waste 
treatment and disposal of effluents containing the same, but also recovery 
of heavy metal ions and control of maximum concentration levels of heavy 
metal ions in electroless deposition baths containing the same. 
Accordingly, waste treatment and disposal techniques which utilize 
biodegradation can then be utilized, whereas previously such was not 
possible due to the interference with such treatments caused by the 
presence of complexed metal ions in the aqueous effluents being treated. 
In accordance with the invention, applicants provide a simple and 
inexpensive method for removing substantially all complexed heavy metal 
ions from solutions in the presence of complexing agents, whereas prior 
art chemical precipitation methods fail to provide the requisite degree of 
removal. Furthermore, the method of the invention is efficient, 
inexpensive, convenient and yields heavy metal in a more concentrated form 
of high purity, which facilitates easy reclamation or disposal. 
SUMMARY OF THE INVENTION 
The process of the invention for selective removal of heavy metal ions from 
an aqueous solution containing complexed heavy metal ions and complexing 
agent comprises the steps of providing a bed of chelating ion exchange 
resin, having an iminodiacetic acid functionality, and passing the aqueous 
solution containing complexed heavy metal ions and complexing agent 
through the resin bed, preferably until the capacity of the resin bed to 
remove the heavy metal ions from solution is substantially depleted. The 
heavy metal ions are retained in the resin bed, while the effluent passing 
out of the resin bed contains the complexing agent, but is substantially 
free of complexed heavy metal ions. The retained heavy metal ions are 
eluted from the resin by passage of an aqueous acid solution through the 
bed, whereby the eluate contains uncomplexed heavy metal ions and is 
substantially free of complexing agents. 
In preferred embodiments of the invention, selective removal of copper 
complexed with alkanolamines, ammonia or carboxylic acids or their salts, 
or nickel complexed with ammonia or carboxylic acids or their salts, can 
be accomplished. 
The invention also provides a continuous process for maintaining a 
predetermined maximum concentration of complexed heavy metal ions in an 
aqueous rinse solution in which complexed heavy metal ions and complexing 
agents are continuously received or built up. This is accomplished by 
selective removal of complexed heavy metal ions by passage of a portion of 
the aqueous bath through a chelating ion exchange resin bed, with 
retention in the effluent from the bed of substantially all of the 
complexing agent, which is recycled to the bath. 
A further embodiment of the invention provides an improved process for 
electroless deposition of copper, which facilitates waste treatment or 
recovery of complexed copper ions from electroless copper plating or rinse 
solutions, or effluents from processes in which they are employed. A 
workpiece is contacted with an electroless copper plating bath which 
contains complexed copper ions and complexing agent, and is subsequently 
contacted with one or more aqueous rinse solutions in which complexed 
copper ions and complexing agents accumulate. The improvement in the 
process provided in accordance with the invention comprises provision of a 
bed of chelating ion-exchange resin having an iminodiacetic acid 
functionality, passing aqueous solutions containing the complexed copper 
ions and complexing agent through the resin bed, preferably until its 
capacity to remove copper ions from solution is depleted. The copper ions 
are retained in the resin bed, while the effluent passing out of the bed 
contains the complexing agent, but is substantially free of complexed 
copper ions. The resin bed is then eluted with an aqueous acid solution, 
with the eluate containing uncomplexed copper ions and being substantially 
free of complexing agent. 
Likewise, yet a further embodiment of the invention provides an analogously 
improved process for electroless deposition of nickel, which facilitates 
waste treatment or recovery of complexed nickel ions from electroless 
nickel plating or rinse solutions or their effluents from processes in 
which they are employed. 
It is an object of the invention to provide a method for selectively 
separating and removing complexed heavy metal ions, preferably copper or 
nickel, from complexing agents in aqueous solutions, so as to 
substantially remove all of the heavy metal ions, while leaving almost all 
of complexing agent in solution. 
It is also an object of the invention to provide a process for the 
continuous maintenance of a predetermined maximum concentration of 
complexed heavy metal ions in an aqueous rinse solution in which the 
concentrations of such heavy metal ions and complexing agent continuously 
build up. 
It is a further object of the invention to provide improved processes for 
electroless deposition of heavy metals, particularly copper or nickel, 
which facilitate recovery or waste treatment of such complexed heavy metal 
ions in a manner which is both inexpensive and suitably reliable for 
compliance with environmental regulations. 
Other objects and advantages of the various embodiments of the process of 
the invention will be readily apparent to those skilled in the art through 
study of the following description of the preferred embodiments and the 
appended claims. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As will be evident from the various preferred embodiments of the invention 
to be described herein, it has been discovered that chelating ion-exchange 
resins having an iminodiacetic acid functionality can be utilized to 
separate and remove complexed heavy metal ions from the agents used to 
form complexes with them. These specialized ion-exchange resins are highly 
specific to heavy metal cations, most notably for purposes of the 
invention to copper and nickel. In contrast, the cation exchange resins 
utilized in the prior art have an inherent preference for the common 
alkali or alkaline earth cations, most notably sodium, over the heavy 
metal ions or complexing agents. Thus, while the efficiency of the cation 
exchange resins is typically very low with conventional plating solutions, 
which contain high levels of sodium, the chelating resins employed in 
accordance with the invention are extremely efficient. 
In accordance with the invention, it has been unexpectedly discovered that 
the iminodiacetic acid functionality of such chelating resins, which 
possesses a moderate chelating formation constant (K=10.55), will 
completely remove copper from NNN'N'-tetrakis-(2-hydroxypropyl) 
ethylenediamine (K=9.2) or tartaric acid (K=9.9). Typically, removal of 
the metal from complexing agents having such close K values would not be 
expected. 
It has also been unexpectedly discovered that a chelating ion-exchange 
resin of the type utilized in accordance with the invention will take 
nickel away from its complex with ammonium in a neutral or alkaline 
solution (i.e. pH of 7.0 or higher), while it will remove copper from its 
complex with ammonia from a solution at any pH above about 2.2. 
The preferred chelating ion-exchange resin utilized in accordance with the 
invention is commercially available under the trade name "Amberlite 
IRC-718" from Rohm & Haas Company, Philadelphia, Pennsylvania, U.S.A. This 
resin contains an iminodiacetic acid functionality and is preferably 
eluted with a strong acid solution and after rinsing the physically 
retained acid, the resin is ready to be used for another cycle. It may be 
converted to its salt form with sodium or potassium bases, but this is not 
necessary and, in accordance with the invention, is less preferred. 
It is fully within the purview of the invention that equivalent chelating 
ion-exchange resins, having the iminodiacetic acid functionality, can be 
utilized. For example, Zerolit S-1208, commercially available from Zerolit 
Ltd. of London, England, and Chelex 100 available from BIO-RAD 
Laboratories of Richmond, California, U.S.A. and comprising a styrene 
divinylbenzene copolymer containing iminodiacetate functional groups, can 
likewise be utilized. 
Preferred embodiments of the invention provide for selective removal of 
heavy metal ions which preferably are either copper or nickel, as utilized 
in solutions for electroless deposition, metal etching or related 
processes. 
When copper is utilized, the preferred complexing agents are alkanolamines, 
particularly NNN'N'-tetrakis-(2-hydroxypropyl) ethylenediamine, 
triethanolamine, tri-isopropanolamine or diethylenetriamine 
penta-substituted with one or more substituents selected from hydroxyethyl 
or hydroxypropyl or combinations thereof, ammonia or carboxylic acids or 
their salts. Preferred carboxylic acid is tartaric acid, with the 
carboxylic acid salt preferably being sodium potassium tartrate. 
In embodiments directed to selective removal of complexed nickel, the 
preferred complexing agents are ammonia or carboxylic acids or their 
salts, which preferably are either citric, malic, succinic, or lactic acid 
or their salts. 
In accordance with one preferred embodiment, a bed of chelating 
ion-exchange resin having an iminodiacetic acid functionality, preferably 
Amberlite IRC 718 resin, is utilized. The aqueous solution from which the 
complexed heavy metal ions are to be selectively removed is passed through 
the resin bed. While it is fully within the purview of the invention that 
passage through the resin bed may be continued or maintained for any 
period of time, as long as the resin bed maintains its capacity to remove 
heavy metal ions from solution, it is preferable to continue passage 
through the resin bed until the capacity thereof to remove heavy metal 
ions from solution is substantially depleted. Depletion of the resin bed 
capacity may be determined by detection of the presence of complexed heavy 
metal ions in the effluent passing from the resin bed, or in any other 
conventional manner. 
The effluent passing from the resin bed contains the complexing agent, but 
is substantially free of complexed heavy metal ions. For purposes of the 
invention, it is to be understood that it is acceptable to have trace 
amounts of complexed heavy metal ions present in the effluent, provided 
that such does not adversely affect or interfere with subsequent recovery 
or waste disposal of the complexing agent. 
In order to regenerate the resin bed, which may be done when its capacity 
to remove heavy metal ions from solution is either partially or fully 
depleted, it is eluted by passage therethrough of an aqueous acid 
solution, preferably a strong acid solution having a pH approaching zero. 
Preferably, a 0.5 to 20% solution of sulfuric or other strong acid is used 
as the eluent. The eluate passing from the resin bed is not allowed to mix 
with the previously collected effluent, but is collected or treated 
separately, since it contains uncomplexed heavy metal ions, free from the 
complexing agent with which it was previously complexed. 
For purposes of the invention, it is to be understood that trace amounts of 
complexing agent may be present in the eluate, provided that it is not 
present in an amount sufficient to adversely affect or interfere with 
subsequent recovery or waste disposal of the heavy metal ions. 
A further, optional step in accordance with the invention involves 
effecting preciptiation of the uncomplexed heavy metal ions from the 
eluate solution. For example, addition of an alkali hydroxide, such as 
sodium or potassium hydroxide, will precipitate the heavy metal ions. The 
precipitate can then be removed from the eluate by conventional 
techniques, for example by filtration or centrifuging, followed by 
decanting of the supernatant eluate solution. 
Following elution, the chelating resin bed can, if desired, be returned to 
its sodium form by passage therethrough of a caustic solution, such as an 
aqueous solution of sodium hydroxide or the like. However, it is preferred 
to omit this step and proceed with reuse of the regenerated resin in its 
acid form, which is believed to extend the life of the resin. 
After regeneration, additional quantities of aqueous solution containing 
complexed heavy metal ions and complexing agents may be passed through the 
regenerated resin bed. 
In accordance with another embodiment of the invention, a predetermined 
maximum concentration of complexed heavy metal ions in an aqueous bath or 
solution, such as a rinse, which contains complexed heavy metal ions 
together with complexing agent can be maintained. A continuous process is 
employed, comprising removal of a portion of the bath or solution, 
treatment with a chelating resin in accordance with the invention and 
recycling of the resin bed effluent. The amount and rate at which such 
solution is passed through the bed of chelating ion-exchange in accordance 
with the invention is determined by selection of a rate substantially the 
same as the rate at which complexed heavy metal ions enter, or build up 
in, the bath or rinse being treated. 
The heavy metal ions are retained in the resin bed, and effluent flowing 
from the chelating resin bed is recycled, preferably until the capacity of 
the resin bed to remove heavy metal ions from solution becomes 
substantially depleted. When it is appropriate, or necessary such as upon 
depletion, to regenerate the resin bed, the appropriate portion of the 
aqueous solution is preferably directed to a backup resin bed or beds, and 
the resin to be regenerated is taken off-stream. 
The partially, or fully, exhausted resin bed is eluted with aqueous acid 
solution. The eluate contains uncomplexed heavy metal ions and is 
substantially free of complexing agent. The heavy metal ions in the eluate 
can be recovered or disposed of, as may be desired. The eluted resin bed 
is preferably left in its acid form, but may, if desired, be returned to 
its sodium form in the manner previously disclosed, and then placed back 
on-stream, when the current "on-line" resin is regenerated. 
In yet another embodiment of the invention, an improved process for 
electroless deposition of copper is provided which facilitates waste 
treatment or recovery of complexed copper ions from plating or rinse 
solutions or their effluents. Conventional electroless copper deposition 
baths and solutions are utilized, with the workpiece being contacted with 
a copper plating bath containing complexed copper ions and complexing 
agent. It is fully within the purview of the invention that any 
conventional electroless copper plating solutions which contain complexed 
copper ions and complexing agent, preferably 
NNN'N'-tetrakis-(2-hydroxypropyl) ethylenediamine, triethanaolamine, or 
tri-isopropanolamine or diethylenetriamine penta-substituted with one or 
more substitutents selected from hydroxyethyl or hydroxypropyl, can be 
utilized. 
Subsequent to contacting the workpiece with the copper plating bath, it may 
be contacted with one or more aqueous rinse solutions or other treatment 
solutions, in which complexed copper ions and the complexing agent 
accumulate. These aqueous baths or solutions are passed through a bed of 
chelating ion-exchange resin having an iminodiacetic acid functionality, 
preferably until the capacity of the resin bed to remove copper ions from 
solution is substantially depleted. The copper ions are retained in the 
resin bed, while effluent passing from the resin bed contains complexing 
agent and is substantially free of complexed copper ions. Elution of the 
resin bed yields an eluate which contains uncomplexed copper ions and is 
substantially free of complexing agent. The resin bed is either left in 
its acid form, or if desired may be returned to its sodium form, and 
reutilized. 
In yet a further embodiment of the invention, an improved process for 
electroless deposition of nickel is provided which likewise facilitates 
recovery or waste treatment of the complexed nickel ions contained in 
plating or rinse solutions to their effluents. As with the aforementioned 
embodiment directed to electroless deposition of copper, the workpiece is 
contacted with a conventional electroless nickel plating bath, containing 
complexed nickel ions together with complexing agents. Subsequently it is 
contacted with one or more rinse or treatment solutions, in which said 
complexed nickel ions and complexing agent accumulate. 
As with previously described embodiments, the aqueous solution to be 
treated is passed through a bed of chelating ion exchange resin having an 
iminodiacetic acid functionality, preferably until the capacity of the 
resin bed to remove nickel ions from solution is substantially depleted. 
The nickel ions are retained in the resin bed, and effluent passing from 
the resin bed contains complexing agent for the nickel, but is 
substantially free of complexed nickel ions. The resin bed is then eluted, 
with the eluate containing uncomplexed nickel ions and being substantially 
free of the complexing agent. The eluted resin bed is either left in its 
acid form, or if desired may be returned to its sodium form, and 
reutilized. 
The following examples are illustrative of, but do not limit, the scope and 
application of the invention.

EXAMPLES 
EXAMPLE 1 
A solution of spent electroless copper plating bath, containing 11.1 g/l 
copper sulfate pentahydrate (CuSO.sub.4.5H.sub.2 O), 25 g/l 
NNN'N'-tetrakis-(2-hydroxypropyl) ethylenediamine complexing agent, 8 g/l 
sodium hydroxide, 14 ml/l of formaldhyde (37% solution) and 60 g/l each of 
sodium sulfate and sodium formate, was treated in accordance with the 
preferred method of the invention for selective removal of copper from the 
NNN'N'-tetrakis-(2-hydroxylpropyl) ethylenediamine complexing agent. The 
pH of the spent electroless plating solution was adjusted to about 2.5 by 
addition of 18 ml of sulfuric acid per liter of spent bath. 
A glass column, 4 cm in diameter, was charged with 292 grams of Amberlite 
IRC-718 wet resin to a height of 30 cm. The acidified spent plating 
solution was passed through the resin at a rate of 12 ml/min. The effluent 
was collected in the following fractions which contained 8.3 to 15.6 g/l 
of the complexing agent, as follows: 
______________________________________ 
Total Volume Atomic Absorption 
of Effluent Passed (ml) 
pH of Effluent 
Analysis (Cu.degree., ppm) 
______________________________________ 
600 1.0 Less than 1 
1200 1.7 Less than 1 
2200 2.0 Less than 1 
3000 1.8 3.4 
______________________________________ 
The column was then rinsed with water and eluted with 4% by volume of 
sulfuric acid, which has passed through the column at a rate of 12 ml/min. 
The eluate was analyzed with the following results: 
______________________________________ 
Analysis of Eluate 
Frac- Volume of Eluate 
Copper Content 
Total 
tion Collected (ml) 
(CuSO.sub.4 . 5H.sub.2 O) 
CuSo.sub.4 . 5H.sub.2 O 
______________________________________ 
1 550 (discarded) 
Less than 1 ppm 
2 100 32.2 g/l 3.2 g 
3 100 85.8 g/l 8.6 g 
4 100 125.0 g/l 12.5 g 
5 100 91.0 g/l 9.1 g 
6 100 2.1 g/l 0.2 g 
______________________________________ 
Total CuSO.sub.4 . 5H.sub.2 O 33.6 grams 
Total CuSO.sub.4 . 5H.sub.2 O passed 33.3 grams 
The pH of each of the eluate fractions was adjusted to between 9 to 10 by 
addition of sodium hydroxide. After overnight settling, the fractions were 
filtered and the filtrates were analyzed for copper. The copper hydroxide 
collected from the filtrates was very pure and could be converted to 
sulfate, nitrate or chloride salts. The copper sulfate reclaimed was found 
to be suitable for formation of additional electroless copper plating 
solutions. 
Fractions No. 4-6 contained less than 1 ppm of copper, while Fraction No. 
2-3 contained a total of 9 ppm of elemental copper in 200 ml of filtrate. 
Thus, first 200 ml of filtrate required further passage through the resin 
in a subsequent cycle for substantially complete removal of copper. 
EXAMPLE 2 
In accordance with the embodiment of the invention directed towards a 
continuous process for maintaining a predetermined maximum concentration 
of complexed heavy metal ions in an aqueous bath, Example 1 was repeated 
with the following modifications. A total of 6 liters of simulated rinse 
water, contaminated with complexed copper and complexing agent, was 
prepared by continuously adding 0.36 ml/min. of electroless copper 
solution, which contained 2,375 ppm of complexed copper. This simulates 
approximately a 1:1000 scale-down of operating conditions in an existing 
plating-on-plastics installation. 
Selecting 43 ppm of complexed copper as the maximum concentration of copper 
to be permitted in the simulated rinse, a rate of recirculation of 20 
ml/min. was calculated, in accordance with the following: 
Since V, the volume of rinse passing through the column per minute, would 
yield all of its complexed copper ions during passage, then, 
##EQU1## 
Accordingly, 20 ml/min. of the simulated rinse solution was passed through 
the resin bed, as in Example 1, and the system operated continuously for 6 
full twenty-four hour days, with the pH of the rinse being maintained 
between 2.5-5.0. During this time, the simulated rinse was analyzed by 
atomic absorption analysis and found to contain between 25-35 ppm of 
copper. The effluent from the resin bed contained less than 1 ppm of 
copper and was returned to the simulated rinse solution. The experiment 
was continued for a 7th day, whereupon the copper level in the rinse rose 
to a final concentration of 52 ppm, with the resin bed effluent being 
returned to the simulated rinse containing 5 ppm of copper. At this point, 
had the experiment been continued, it would have been necessary to place a 
backup resin bed on line, and elute and regenerate the resin bed initially 
utilized. 
EXAMPLE 3 
Example 2 was repeated, except that a column 25 cm in diameter by 180 cm in 
height was packed with 0.092 cubic meters of Amberlite IRC 718 resin. This 
approximated a scale-up of Example 2 to 275:1. 
The volume of simulated rinse water and flow rates were likewise scaled up 
to approximately 275:1. Over four days of continuous operation, the level 
of copper in the rinse water was maintained at between about 25-35 ppm, 
with the effluent leaving the resin bed and being returned to the 
simulated rinse containing less than 1 ppm of copper. 
EXAMPLE 4 
Another scale-down of an existing production installation was repeated, in 
accordance with the method set forth in Example 2. However, the simulated 
rinse solution was contaminated with an electroless copper plating 
solution having the following composition: 
Sodium potassium tartrate: 20 g/l 
Copper sulfate: 21 g/l 
Formaldehyde (37% solution): 50 ml/l 
Free sodium hydroxide: 12 g/l 
pH maintained between 3.0-5.0 
The resin bed utilized was packed in a column 4 cm in diameter, loaded to a 
height of 10 cm. 
A 600 ml portion of simulated rinse water was provided to receive 3.9 ml of 
the above electroless copper solution every hour over four continuous 
24-hour days of operation. The rate of recirculation was 16 ml/min. 
For the first 58 hours of operation, the level of complexed copper in the 
rinse was approximately 26 ppm. By the 82nd hour of operation, the level 
had increased to 55 ppm. 
The effluent flowing from the resin bed and returning to the simulated 
rinse solution contained less than 1 ppm of copper during the first 38 
hours of operation. This level rose to 16 ppm after 58 hours of operation. 
Elution of the copper from the resin bed and subsequent regeneration 
thereof was accomplished as in the previous examples. 
EXAMPLE 5 
A column containing Amberlite IRC-718 resin, as described in Example 1, was 
utilized for selective removal of copper from ammoniacal etch rinse water, 
which contained 13.4 g/l copper sulfate pentahydrate fully complexed with 
ammonia at pH=11.5. The rinse water was acidified to pH 4.0 and passed 
through the resin bed. The eluate fractions passing from the resin bed had 
the following content: 
______________________________________ 
Fraction Volume (ml) Cu ppm 
______________________________________ 
1 710 1.0 
2 350 1.6 
3 390 2.5 
4 720 4.4 
5 130 5.6 
______________________________________ 
A total of 2,388 ml of the rinse solution, containing a total of 32 g of 
copper sulfate pentahydrate was passed through the column. 
The column was eluted using a 4% by volume sulfuric acid solution yielding 
the following: 
______________________________________ 
Fraction Volume (ml) Copper Metal 
______________________________________ 
1 285 0.9 gr/l 
2 230 10.0 gr/l 
3 195 23.9 gr/l 
4 110 11.5 gr/l 
5 205 53.0 ppm 
6 345 18.0 ppm 
7 315 14.0 ppm 
8 330 1.5 ppm 
______________________________________ 
Fractions 1-4 were combined and the pH adjusted to between 10-11, with 
sodium hydroxide. Copper hydroxide was precipitated, filtered, washed and 
dissolved in sulfuric acid and analyzed to contain 30.3 grams of copper 
sulfate pentahydrate. The supernatant solutions remaining from fractions 
1-4 totalled 820 ml and contained 1.7 ppm of copper metal. 
EXAMPLE 6 
Example 5 was repeated, except that the rinse water was passed through the 
column at pH=11.0. The ammoniacal etch rinse used in this experiment 
contained 12.9 g/l of copper sulfate pentahydrate. A total of 3000 ml of 
the solution was passed through the resin bed in the column with the 
following fractions collected: 
______________________________________ 
Fraction Volume (ml) Cu (ppm) 
______________________________________ 
1 240 less than 1 
2 333 less than 1 
3 380 1 
4 355 1.6 
5 380 2.1 
6 390 3.1 
77 405 4.9 
Rinsed with deionized water collected fractions: 
8 385 7.0 
9 330 less than 1 
10 114 less than 1 
______________________________________ 
All of the fractions collected yielded an ammonia odor in alkaline pH, 
indicating that substantial amounts of the complexing agent had passed 
through the resin bed. The column was rinsed with an additional 6 liters 
of water, with the effluent passing from the bed continuing to yield an 
ammonia odor and giving a basic reaction on pH test paper. 
The column was eluted with a 4% by volume solution of sulfuric acid to 
yield copper solutions from which copper was quantitatively precipitated 
with sodium hydroxide at pH 12. The filtrate was colorless, indicating the 
absence of more than 5-6 ppm of copper, and had a faint ammoniacal odor, 
indicating the presence of only residual amount of ammonia. 
EXAMPLE 7 
An electroless nickel solution, containing 9 g/l of nickel, 100 g/l of 
sodium citrate, 50 g/l of ammonium chloride, 10 g/l of sodium 
hypophosphite, at pH 8.3, was passed through the resin column identical to 
that utilized in Example 1. The rate of passage through the resin bed was 
14 ml/min. The initial 600 ml fraction of effluent passing from the bed 
contained less than 1 ppm of nickel (with 5.4 grams of nickel having been 
retained in the resin bed). The next fraction of 200 ml contained 3 ppm of 
nickel, while the third fraction of 250 ml contained 46 ppm of nickel. The 
column was rinsed with water and eluted using a 4% by volume solution of 
sulfuric acid. The initial 245 ml of eluate contained about 20 ppm of 
nickel, with the following fractions which totalled 800 ml, containing the 
bulk of nickel, each of which varied from 4 to 26 g/l. The final eluate 
fraction of about 500 ml contained only a few ppm of nickel. The eluate 
fractions were combined and treated with sodium hydroxide, with nickel 
being quantitatively precipitated, with the filtrate containing only 0.4 
ppm of nickel. 
EXAMPLE 8 
Example 1 was repeated, except that the electroless copper solution 
contained 10.5 g/l copper sulfate pentahydrate, which was passed through 
the resin bed at a pH of 11.0, in order to illustrate the operability of 
the invention with alkaline solutions. 
After two liters of solution was passed through the resin bed, the effluent 
flowing from the column showed the characteristic blue color of copper 
sulfate. 
The column was rinsed with water until the effluent flowing from the bed 
turned colorless. This required approximately 7.5 liters of rinse at a 
high flow rate. Although the effluent flowing from the resin bed was 
acidic until rinsing was begun, it was basic upon completion of the rinse. 
Elution of the resin bed was accomplished using a 4% by volume solution of 
sulfuric acid. The eluate was treated with sodium hydroxide to precipitate 
97.5% of the copper, leaving the remaining 2.5% chelated with 
NNN'N'-tetrakis-(2-hydroxypropyl) ethylenediamine. 
As will be readily apparent to one skilled in the art, various 
modifications can be made in the details of the invention and the various 
embodiments of the method and process thereof to provide for selective 
removal of complexed heavy metal ions from their complexing agents in 
aqueous solution. For example, above a minimum pH of about 2.2 for removal 
of copper and about 7.0 for removal of nickel for aqueous solutions, it 
should be readily apparent that pH is not otherwise a critical factor, 
except to the extent to which utilization of the particular bed of resin 
having iminodiacetic acid functionalities can be maximized or utilized in 
accordance with the particular process or environmental considerations of 
any given application.