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Abstract

An overview is given of source reduction opportunities, organized under three categories: Material substitution, process modification, and modification of operating practices. Problems and benefits are discussed, as well as the place of each in an overall source reduction effort. Options are ranked in order of simplicity and potential impact, and a starting point given for exploring source reduction in a plating operation.

Introduction

Over the past decade, many "opportunities" for source reduction of waste generation in the plating industry have been identified. In fact, what has been documented most often are possibilities, which in the point of view of plating plant operators become opportunities only with application and testing in the field. It is a peculiarity of the plating industry that many possibilities exist for source reduction, and yet implementation has remained limited. Why might this be so?

In partial answer to this question, this paper will report and discuss a selection of techniques and technologies currently in use which reduce the volume and/or toxicity of metal-bearing wastestreams generated by the plating industry. While intended as an overview, the hope is nonetheless that by presenting pitfalls as well as advantages, more possibilities will in fact become reality. Before proceeding, however, the phrase "source reduction" merits some definition as it applies to the challenges presented by this industry and its processes.

For the purposes of this discussion, source reduction in the plating industry will include the following:

- Material substitution

- Process modification

- Modified operating practices

Material substitution can be considered "pure" source reduction, in the sense that it can reduce or eliminate the generation of a waste. However, as will be seen, this purity is nearly always alloyed with the reality of implementation difficulties and continued, though altered, waste generation. Process modification, principally of rinsing systems, holds considerable promise for the plating industry, a promise as yet largely unrecognized. Modified operating practices, including such activities as chemical control of process solutions and process timing, will overlap to some extent with process modification. In fact, there is no intent here to list these three categories of source reduction in order of priority. Source reduction activities in a given plant may begin in any of these categories and proceed through the others in a loop as each change drives another, complementary change.

It is also important to note here that these choices of categories are driven at least in part by the organization of this conference and these proceedings. Separation technologies (e.g., reverse osmosis, ion exchange, electrolytic metal recovery, and evaporation) which facilitate in-plant and in-process recycling are often included in discussions of source reduction in the plating industry,[1][2] but are covered elsewhere in this conference.

Finally, source reduction should not be taken as any more than an important component in a wel1-conceived waste management plan. Field experience and the literature show clearly that source reduction, while ripe for exploitation as a preferred method of waste management by the electroplating industry, cannot eliminate waste generation. As the following discussion will show, implementation of source reduction, whatever is included in its definition, involves site-specific testing of possibilities which are often nothing more than good ideas. This chicken-and-egg dilemma is most obvious in the literature available to plating plant operators, where documentation is often limited to obvious successes and guidance to "try it, you'll like it!"

Plating Mastestream Sources and Characteristics

While seemingly elementary, this section is included in this paper to illustrate the diversity of the challenges facing this industry. In addition, it will serve as a graphic reminder that not all metal-bearing wastestreams in a plating operation can name plating process solutions as their source. While it may be true that the rinsing steps after a plating operation and the batch disposal of unusable plating process solutions are significant contributors to the metals in a plating operations effluent, other contributors, less amenable to source reduction, also exist. In fact, in some operations, such wastes as bottom sludge from carbon treatment of nickel plating solution or hydrochloric acid loaded with zinc stripped from plating racks and plating barrel dangers may constitute the largest wastestreams.[3]

Process Stream

System Constituents

Wastestream Constituent

Cleaning

(other than organic solvents)

Acid solutions Alkaline solutions Abrasives Organic compounds Chelating agents

Low or high pH Dissolved metals Complexed metals Metal chips and fines

Rinsing

Water

Low or high pH

Dissolved metals Organic compounds Waste chemicals Chelating agents

Process Stream System Constituents Wastestream Constituent

Process Stream System Constituents Wastestream Constituent

Plating

Acid metal solutions Alkaline metal solutions Chelating agents Reducing agents Organic compounds

Low or high pH Dissolved metals Complexed metals Waste chemicals

Etching

Acid solutions Alkaline solutions Organic compounds

Low or high pH Dissolved metals Complexed metals Waste chemicals

Control Filtration

Analytical chemistry Activated carbon Diatomaceous earth Filter media—paper, polypropylene, cotton

Low or high pH Organic compounds Dissolved metals Complexed metals Solid metals SIudge

Waste chemicals Waste filter media

Inventory

Concentrated process chemistry

Low or high pH Organic compounds Dissolved metals Complexed metals Chelating agents Reducing

Stripping

Alkaline solutions Acid solutions Chelating agents Organic compounds Abrasives

Low or high pH Dissolved metals Complexed metals Waste chemicals Metal chips, fines

Waste treatment

Process chemistry Treatment chemistry

Metal compounds

Other inorganic compounds

It should be noted that in most cases wastestreams are composed not only of process chemistry but also of by-products of chemical reactions and electrolysis. This fact becomes important when attempting to recover and return those "escaped" solutions (e.g., dilute metal-bearing rinse streams) which are often the focus of process and operation modification. It is usually not sufficient to stop generating waste simply by returning it to its source. Usually some type of purification or separation, themselves sources of waste generation, will eventually be required. This quickly puts the lie to the myth of "closed-loop" operations. While source reduction is powerful, it is only reduction, not elimination.

Material Substitution

Of the three source reduction strategies to be discussed in this paper, material substitution in the plating industry is the most fraught with barriers beyond the control of plating plant operators. This is because, in many operations, the status quo has become nearly codified, either informally through customer acceptance and resistance to change or more formally in specifications which require specific processes. The plating plant operator does not, however, escape the blame for a lack of implementation of alternative processes. Suppliers have often been "ahead of the wave" in devising process chemistries which address current effluent concerns squarely, and yet only a few brave pioneers in the plating industry have changed, and then often under extreme pressure. The following examples will illustrate the perils and promise of material substitution.

Deionized Water

Of all the substitutions possible, the use of deionized water in place of tap or softened water has potentially the greatest impact and widest application in the reduction of waste generation. Strongly supported in the literature [6][7], this option has seen widespread use in industries where water quality is seen to be a critical parameter (e.g., semiconductor manufacture). And yet most plating operations use deionized water only to replace evaporation from plating process solutions, if at all. The results of this choice are significant and far-reaching.

First, any material added to a process solution other than pure water or replenishment chemistry must be considered at least a potential contaminant, requiring later removal through purification or solution disposal. Therefore, adding tap water to a process solution, when replacing evaporative losses with either "fresh" water or captured rinses containing diluted process chemistry, hastens the demise of that solution, thereby increasing waste generation.

Second, rinse water, especially in fully integrated systems which return rinse solution containing process chemistry to the process solution should be as free of contaminants as possible. While a certain level of hardness is tolerable while achieving high-quality rinsing, that level is often exceeded by the tap water in several regions of the country,[8] and at any rate is unpredictable. This can lead to blaming rinsing quality problems, such as spotting, on rinse water which is "dirty", without determining exactly which contaminant is the problem. This in turn leads to higher rinse water volumes (to dilute the contaminants) and higher levels of waste generation.

Finally, any material other than pure water which becomes combined with contaminants which must be removed (e.g., heavy metals mixed with hard water ions) can increase waste volumes substantially.[7] This is especially true with hydroxide precipitation systems and ion exchange systems used for effluent pretreatment. Neither of these technologies discriminate between heavy metals and other inorganic constituents of a wastestream. Therefore, in the case of hydroxide sludge, we can have a hazardous waste which may be composed of as much as 90% (dry weight) precipitated hard water ions and other non-hazardous materials. And in the case of ion exchange, we have an inefficient use of the resins (especially in nonrecirculating systems) resulting in a greater volume of regenerate solutions and associated wastes.

Systems are available to generate sufficient volumes of deionized water for rinsing in a plating operation. However, at the volumes required in most plating facilities, the cost is prohibitive. Here we have another "which comes first?" question: In order to financially justify using deionized water for rinsing, rinse water volumes must be reduced. But to justify the effort involved in rinsing modification, the high costs associated with use of excess deionized water would be most persuasive. In Europe, the plating industry typically uses much less water and is more closely attuned to water quality as a parameter because of the extent of recovery and recycling of effluent which is performed. Using this as a model, it seems that this is one material substitution which must eventually be implemented on a much wider scale.

Non-cyanide Plating Solutions

As a source reduction option, this substitution is viscerally attractive, since it eliminates completely a process chemistry component which not only requires special pretreatment activities, but is also a health and safety hazard and just plain frightening to those not inured to it by daily contact. One type of substitution in particular, non-cyanide zinc plating processes, has received sufficient research and development that there are two competing process chemistries, each with its own attractions and drawbacks. Non-cyanide copper plating, especially acid copper (copper sulfate) plating processes are being used in more applications than once thought possible. Progress is being made in non-cyanide cadmium processes.[9] However, research in this area (non-cyanide plating) still must be done before acceptance of these alternatives is widespread.[10]

While attractive from a cost and liability standpoint when waste disposal is included, this substitution is still thwarted by technical challenges. These are summarized for non-cyanide zinc plating in the following table, along with benefits, projected and realized.

Chemistry Benefits Drawbacks

Zinc chloride

97-100% efficiency

Reduced ductility

(higher production rates)

over .5 mil thickness

(lower energy costs)

reduced plate distribution

bright finish

high capital cost for

accept most chromaters

equipment

low cost chemistry

(corrosion resistance)

tighter chemical control

required

Alkaline zinc

Good throwing power

Reduced ductility over .5

no special equipment required

mil thickness

lower waste treatment costs

does not plate well over

cast iron and heat-treated

steel

tighter chemical control

required

Zinc cyanide has long been a popular plating process because it tolerates impurities and is easy to control. In fact, it is often operated with minimal filtration, agitation, and pre-plate cleaning of parts. This stands in contrast to both of the alternatives, which require careful control and are limited in their application. So the plating plant operator faces adjustment not only to a new process chemistry, but new methods of processing and quite possibly limitations on what sorts of parts may be plated. Closer scrutiny of Table 2 also reveals a key restriction in the area of ductility. Since zinc plating in thicknesses greater than .005" is often done for corrosion protection, and decreased ductility decreases corrosion protection, both non-cyanide zinc plating processes are effectively limited to more cosmetic applications.

It may be possible to improve the operation of zinc cyanide process solutions and effect enormous reductions in waste generation.[12][13] After improving operations, it may be further possible to capture and return "escaped" process solution from the rinsing system. However, even if cyanide plating systems could be "close-looped" and the process solutions successfully maintained using standard purification techniques, the trend is definitely towards the substitutes. It may be necessary to operate several process solutions where one would suffice before, and alloy plating processes (e.g., zinc/nickel and zinc/cobalt) may see wider application for corrosion protection. Whatever the mechanism, treatment and disposal costs and community - and worker-right-to-know activities will ultimately force the cyanide plating systems from the scene.

Trivalent chromium plating and chromating solutions

This is another substitution which appears immediately attractive, since it reduces substantially the health risk associated with hexavalent chromium process solutions. Trivalent chromium plating processes, first commercialized in 1975, are receiving substantial amounts of research and development attention. There are as many as 500 installations performing trivalent chromium plating nationwide.[14] Trivalent chromating solutions are much less prevalent, mostly because of technical barriers such as production times and reduced corrosion protection.[15] Another immediate attraction of this substitution is reduced waste treatment costs. First, since trivalent chromium processes are much more dilute than hexavalent, losses to the rinsing system are greatly reduced, thus reducing treatment needs. In addition, the reduction step required for pretreatment of hexavalent chromium before precipitation can be eliminated.

However, three major issues remain unresolved.[14][15] Since hexavalent chromium is either decorative (a thin plate over a bright surface), functional (a heavy plate, which may later be cut or ground) or protective (chromates), any substitutes must duplicate these capabilities. "Color" is the critical issue for decorative chromium plating. Not easily defined, the perception by customers (and platers) is often that hexavalent and trivalent plates do not have the same appearance. Especially in cases where parts plated by the different processes may be placed in juxtaposition, this can be a significant barrier to implementation. A more serious barrier is encountered in the case of functional (hard chrome) plating. Trivalent solutions usually deposit relatively thin coatings, and even the thickest is not sufficient for functional applications, leaving this market (a large one) to hexavalent process solutions, at least for the time being. And in the case of trivalent chromates, problems with consistent protection have already been mentioned. On the other hand, trivalent processes require less current to deposit an equivalent thickness of plating have better throwing power (plating in recessed areas) and will not deposit a "burned" plate (usually cause for rejection).

Hexavalent chromium plating solutions are proving to be amenable to recover-and-return source reduction techniques, and treatment of aqueous chrome-bearing effluent should continue to decline for this reason. Development of "high-efficiency" and "low-concentration" solutions will continue, in an effort to further reduce these discharges. But the epidemiology of the health effects from exposure to hexavalent chromium, and regulations being written in reaction to these data, are presenting a near-monumental case. The most obvious and pressing is in the area of air emmisions.[16] Even if control devices could reduce emissions to levels specified by regulations, worker exposure at the line level is the ascendant issue which will drive this substitution. More research is clearly needed, and more field experience, but hexavalent chromium processes are on the way out.

Process Modification

For this paper, process modification for the purpose of source reduction in a plating operation will be defined as changes in equipment which lead to reduced generation of wastes. Purposely excluded are separation and concentration technologies covered elsewhere in this conference. The intent of this section is to list options, in rough order of simplicity of implementation, and provide information about each which should place it in an overall source reduction scheme. However, a few generic comments are in order. First, process modification requires capital investment and, more importantly, requires production downtime. Next, before most of these options can be implemented, considerable background data must be gathered to determine such parameters as rinse water volumes, contamination levels, rinsing efficiencies and effectiveness, dragout rates, and product quality requirements. Without these data, a decision appropriate for a given shop, rather than a generic shop, is very difficult to make. Finally, operating and line management personnel should be involved in the process from conception to implementation to ensure the best possible opportunities and application.

Drain boards

Simple and inexpensive, these devices are still in place in plating operations all too rarely. The intent of a drain board is to catch drips, preventing them reaching the floor and requiring treatment as waste. Construction can be of any compatible material. Care should be taken to orient the board so as to direct drips to the correct solution (e.g., drips of process solution back to the process bath, not into the following rinse). A small dam at either end is also useful in preventing runoff.

Agitation-solution and air

Used in a rinse system, agitation can improve rinsing efficiencies dramatically.[6] This can result in lower rinse water volumes and open the door to further source reduction opportunities. The agitation is introduced at the bottom of the rinse tank through an H-shaped set of pipes (sometimes called a sparger) drilled with sufficient holes to create considerable turbulence. It is this turbulence which enhances process solution removal and enables less water to do more work. Care should be taken to use only clean air, but small diaphragm compressors (<$60) are often sufficient when equipped with a ball valve for throttling the flow.

Flow restrictors

These are effective in dealing with the all-too-human tendency to want to rinse with the cleanest water possible, which is sometimes not necessary in a well-designed rinse system. Placed directly in the inlet to a rinse tank, they restrict the flow to a predetermined level. Once the correct flow is determined, it is a simple matter to keep that flow in place. However, restrictors are non-adjustable, which can be a problem in jobshops with variable work flows.

Conductivity cells

Flow controllers utilizing conductivity cells can address the problem of variable work flows. Water flows only when needed, and only to a set value of contamination (cleanliness) thus reducing the volume of water requiring management or treatment. Calibration to this set value is a critical activity, and can be confounded by rinsing more than one type of process solution in the same rinse system. The equipment also requires diligent maintenance, since the probes can become coated, and must be cleaned regularly. Installation should account for this eventuality.[19]

Spray rinses and air knives

These devices are grouped because of their similarity in application. When mounted on the lip of a process tank, a pipe directing a flow of either water or air at work pieces through appropriate nozzles can reduce the amount of solution carried over the subsequent process steps. Especially when applied to work pieces being removed from a plating solution, this can make it possible to keep solution in the process tank, rather than becoming diluted into a wastestream. Not all solutions can accept this sort of solution removal, and neither system is applicable to barrel plating.

Dragout recovery

Beginning with this option, process modification requires not only capital and downtime, but also floor space. This can be a significant barrier in many plating operations, and therefore this option is most easily implemented in new facilities or where substantial reconstruction of process lines is taking place. The concept is to use a non-flowing rinse, or empty tank, to capture process solution for eventual return to the process tank, with or without further separation or concentration. It has seen wide application with nickel and chrome plating, and seems to function quite well. Some concerns have arisen, however.

The most important problem is that of contamination of process solutions. Just to take one example, that of nickel, sodium and calcium concentrations have been shown to increase when dragout is returned to the process solution, likely sources being the water used for rinsing. These contaminants interfere with the plating process. Organics, chlorides, and heavy metals, from sources including the process solution itself and the work being processed, can also accumulate and pose problems. And finally, nickel metal can rise to undesirable concentrations because of the difference in anode and cathode efficiencies. While these problems may take years to manifest themselves in a low-volume operation, eventually treatment and purification is required.[20]

Therefore, it is important that this option not be implemented hastily. Careful data collection, as advocated early in this section, will help guide the decision-making process. And careful process control, as advocated in the next section, will make problems visible before affecting production. All elements of the process, including cleaning and etching solutions, must be considered as integral to successful dragout recovery.

Multiple rinse tanks

Designed to flow in a counter-current fashion, the use of more than a single rinse tank has seen unanimous support in the literature. A multitude of arrangements are possible,[3] and whether or not the effect is to allow dragout recovery, the impact on water use can be remarkable.[6] A three-tank system, for example, can rinse as effectively with .1 gpm as a single-tank system can with 10 gpm. Especially when combined with earlier options mentioned in this section, product quality should not be impaired. Unfortunately, this option is very difficult to implement in existing operations because of space restrictions.

Modified Operating Practices

Activities discussed in this section will be defined for this paper as changes which are dependent on human participation to effect a reduction in waste generation. While not a complete list, these changes can be seen as those having the most potential for source reduction in plating operations. The intent of this section is to list options in rough order of importance, and provide information about the significance of each. While not as dependent on data-gathering as process modification, and therefore initially more attractive, these options are nonetheless somewhat difficult to implement because of the human factor which defines them. The most important caveat to be extended is that change is difficult for humans, even under the best of circumstances, and cure must be taken account for the sentiments of and request participation from operating personnel.

Process solution control

Historically, solution maintenance in plating operations has been considered most important in high-value-added situations (e.g., circuit boards or semiconductors). The great majority of plating plant operators allowed, and were able to allow, great variation in process solution parameters and chemical balance. However, the effect of this latitude has been solutions requiring premature disposal, rejected parts, extensive purification and filtering, and a generalized resistance to process solutions requiring careful control. All of these effects can be seen to increase waste generation.

When source reduction options are implemented, however, process solution control becomes critical. As was seen in the discussion of Material Substitutions, most new processes will operate only within "windows" which are much narrower than those which they replace. And fully integrated systems, such as those discussed under Process Modification, require tracking of contaminants heretofore lost to the sewer. Therefore, the plating plant operator who wishes to pursue source reduction must consider familiarity with and control of all processes as crucial.

Training and education

Many times operators are asked only to "operate", that is, to perform certain functions by rote. Whether or not actions have consequences other than completing the workday is not in the scope of work. While expensive and difficult, this option can be seen as a keystone concept in many operations, for no equipment, no process, will be any better than the operator assigned to it. Therefore, at a minimum, operators should understand the consequences of spills, leaks and overflows, the destination, both immediate and eventual of all wastes, and their part in the process of waste generation.

Withdrawal time

The speed with which work is removed from a process solution can have the greatest impact of any single factor on dragout volume.[3][6] While controlling withdrawal speeds is straightforward when processing is automated, manual operations are highly variable. In those operations, the next option becomes more important.

Extended drain times

A drain time of at least 10 seconds has been shown to reduce dragout by 40+% over immediate rinsing.[22] Once again straightforward when processing is automated, the key to implementing this option in manual operations is to provide suitable rests for the work piece while it drains.

Contact time

This refers to the amount of time a work piece is actually in a tank being rinsed. Its effect on rinsing efficiency, and therefore its potential for source reduction, can be nearly as great as that of the previous two options.[21] Taken together, these three options provide a set of rinsing procedures which, when done well, can reduce dragout, and therefore waste requiring treatment by over 50%.

Parts orientation

Only applicable in rack operations, whether or not a part is allowed to "cup" solution and carry it away is an important factor which is sometimes open to adjustment. However, in many operations and for many parts this consideration is overriden by considerations for plating coverage and trapped gas. Another, simpler change is to ensure that parts are racked with points or corners oriented downwards.[21]

Housekeeping

Covering many small changes, this category can be very important or inconsequential, depending on the plating plant. Spills, leaks and overflows should be inspected for once a month using a sheet of white paper slipped under process tanks. Racks should be scrupulously maintained, especially the coating and excess plating, both of which can increase dragout by trapping solution. Barrels should be checked for draining efficiency, since the action of tumbling work can "peen" the openings closed. Finally, inventory should be protected, especially from moisture. Some of the most expensive wastes to dispose are unusable raw materials.

Sunmary

As stated in the introduction, implementing source reduction in a plating operation can be described as a series of loops, touching first on process modification, then on to material substitution, then perhaps to operating practices. If a starting point was to be given, however, it would probably be to gather as much data as possible on what is being done in the operation at a given time, and why it's done that way. Then the possibility is much greater that the pitfalls pointed out in this paper can be avoided.

References

[1] Higgins, Thomas E. 1989. Hazardous Waste Minimization Handbook. Lewis Publishers, Inc., Chelsea, Michigan.

[2] Cushnie, George C., Jr. 1985. Electroplating Wastewater Pollution Control Technology. Noyes Publications, Park Ridge, New Jersey.

[3] EPA. January 1982. Control and Treatment Technology for the Metal Finishing Industry—In-Plant Changes. Industrial Environmental Research Laboratory, Cincinnati, Ohio. EPA 625/8-82-008.

[4] Sellers, Veronica R. 1986. "Waste Management Alternatives for Electroplating and Printed Circuit Board Manufacturing Operations." 4th Massachusetts Hazardous Waste Source Reduction Conference Proceedings. Massachusetts Department of Environmental Management, Boston, Massachusetts.

[5] Roy, Clarence. 1980. "In-Plant Conservation." Environmental Compliance and Control Course. American Electroplater's Society, Inc., Winter Park, Florida.

[6] Kushner, Joseph B. 1976. Water and Waste Control for the Plating Shop. Gardner Publications, Cincinnati, Ohio.

[7] Roy, Clarence. 1979. "Methods and Technologies for Reducing the Generation of Electroplating Sludges." 2nd Conference on Advanced Pollution Control for the Metal Finishing Industry. American Electroplater's Society, Inc. and Environmental Protection Agency. EPA 600/8-79-014.

[8] Sperry, Elmer A. and J.B. Möhler. 1978. Rinse Tank Control Handbook. Beckman Instruments, Inc., Cedar Grove, New Jersey.

[9] Humphreys, Paul G. May 1989. "New Line Plates Non-Cyanide Cadmium." Products Finishing, Gardner Publications, Inc., Cincinnati, Ohio.

[10] Vaaler, Luther E. 1986. "Prospects for Developing Substitutes for Cyanide-Containing Electroplating Baths." 4th Massachusetts Hazardous Waste Source Reduction Conference Proceedings. Massachusetts Department of Environmental Management, Boston, Massachusetts.

[11] Poll, Gerard H., Jr. April 1988. "Zinc Plating 188." Products Finishing, Gardner Publications, Inc., Cincinnati, Ohio.

[12] Poll, Gerard H., Jr. April 1987. "The Case for Alkaline Non-Cyanide Zinc." Products Finishing, Gardner Publications, Inc., Cincinnati, Ohio.

[13] Dargis, Raymond D. April 1988. "Zinc Plating-Entrenchments and Trends." Products Finishing, Gardner Publications, Inc., Cincinnati, Ohio.

[14] Snyder, Dr. Donald L. March 1988. "Trivalent: The Second Decade." Products Finishing, Gardner Publications, Inc., Cincinnati, Ohio.

[15] Klos, Dr. Klaus Peter. June 1988. "Clear Chromates: Theory and Practice." Products Finishing, Gardner Publications, Inc., Cincinnati, Ohio.

[16] Zaki, Nabil. 1989. "Complying with Air Quality Standards with New Trivalent Chromium Plating Technology." 10th AESF/EPA Conference on Environmental Control for the Metal Finishing Industry. American Electroplaters and Surface Finishers Society, Inc., Orlando, Florida.

[17] Anonymous. October 1988. "Turn to Trivalent." Products Finishing, Gardener Publications, Inc., Cincinnati, Ohio.

[18] PRC Environmental Management, Inc. 1988. Waste Audit Study—Metal Finishing Industry. United States Environmental Protection Agency and California Department of Health Services, San Francisco, California.

[19] Beall, John F. and Rod McGathen. September 1977. "Guidelines for Waste-Water Treatment." Metal Finishing, Metals and Plastics Publications, Inc., New York, New York.

[20] Kirman, Lyle. 1988. "Some Unsolved Problems in Close Loop Nickel Recovery." 9th AESF-EPA Conference on Environmental Control for the Metal Finishing Industry. American Electroplaters and Surface Finishers Society, Inc., Orlando, Florida.

[21] Meitzer, Michael Paul. 1989. Reducing Environmental Risk: Source Reduction for the Electroplating Industry" Ph.D. dissertation, University of California at Los Angeles.

[22] Bosshardt, Rich. 1987. Reducing Dragout in Cooper and Tin/Lead Plating. Intern report, Minnesota Technical Assistance Program, Minneapolis, Minnesota.

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