National Metal Finishing Resource Center (NMFRC)

Pollution Prevention and Control Technologies for Plating Operations

Section 3 - Chemical Recovery

3.4 ION EXCHANGE

3.4.6 Performance Experience
3.4.6.1 Nickel Plating Performance Experience
3.4.6.2 Chromium Plating Performance Experience
3.4.6.3 Non-Cyanide Zinc Plating Performance Experience
3.4.6.4 Cadmium Cyanide Plating Performance Experience
3.4.6.5 Gold Cyanide Plating Performance Experience

3.4.6 Performance Experience

A summary of the Users Survey data for ion exchange recovery applications is presented in Exhibit 3-31. Within this exhibit, the response data has been grouped by types of plating solution. These include: nickel, chromium, non-cyanide zinc, cadmium cyanide, and gold cyanide. A general discussion of the ion exchange data is presented, followed by specific information regarding each of the different types of applications.

The following information and data summarizes the performance experience of the survey respondents.

The average satisfaction level for ion exchange recovery is 3.2 (on a scale of 1 to 5, with 5 being most satisfactory), which is lower than the average level rating for chemical recovery in general (weighted average for all chemical recovery applications is 3.4). Fifty-four percent of the shops indicated that this technology satisfied the need for which it was purchased and another 11% indicated that it partially satisfied their need. Thirty-five percent indicated that it did not satisfy the need for which it was purchased. The following is a breakdown of the reasons why shops purchased this technology (not all shops responded and some shops gave multiple reasons):
        To meet or help meet effluent regulations:.........21
        To reduce plating chemical purchases:...............8
             (includes all four gold applications)
        To reduce the quantity of waste shipped off-site:..14
        To reduce wastewater treatment costs:..............13
        To improve product quantity:........................6
        Other:..............................................0
      
The use of ion exchange generally did not impact production quality or the rate of production. The following responses were provided:
                        Product Quality    Production Rate
        Improved               5                 1
        No Change             16                18
        Decreased              3                 4
      
The majority of plating shops indicated, that based on their experience with this technology, if given the chance they would purchase the same type of equipment from the same vendor. The following is a breakdown of their responses:
        Purchase the same technology from the same vendor:.... 18
        Purchase the same technology from a different vendor:...0
        Purchase a different technology:........................8
        Do nothing:.............................................2
      
The major savings from the operation of ion exchange for non-gold applications was due to reduced water use and reduced sludge generation. For gold applications, the major savings was due to the recovered gold.

3.4.6.1 Nickel Plating Performance Experience

Thirteen respondents to the User Survey provided detailed data regarding their experience applying ion exchange to nickel rinse waters. Two of these responses cover systems that were being installed at the time of the survey and therefore, no performance data are available from these shops (PS 105, PS 139). Three shops used the process for a short time period, but abandoned their efforts due to disappointing results (PS 212, PS 317, PS 318). None of the remaining eight shops currently operate the traditional recovery configurations (Exhibit 3-22), where the cation regenerant is subsequently processed by electrowinning to recover the nickel or nickel sulfate is returned to the bath. At one time, PS 124 recycled nickel sulfate regenerant directly to the bath. However, this shop discontinued use of the process due to "continuous and repeated" equipment failure. PS 015 purchased an electrowinning unit for nickel recovery, but the unit did not work and therefore, they selected to treat the regenerant instead. Also, one of the two new installations plans to operate with metal recovery (PS 139). Three shops use off-site recycling for regeneration of their columns (PS 161, PS 196 and PS 063) and another shop regenerates on-site and sends the regenerant to an off-site metals recycling firm (Inmetco) (PS 261).

Although no on-site recovery is presently practiced, the configurations used by the respondents involve the recycle of water. These applications have been included in this recovery section because they process a segregated nickel rinse water with ion exchange. As such, that they most likely experienced many of the same performance and O&M problems as recovery operations.

The following performance details were provided by survey respondents:

The two most successful installations among survey respondents are PS 161 and PS 261. PS 161 sends their used ion exchange columns to off-site services for regeneration, most recently using Dayton Water Systems for regeneration of both nickel and chromium columns. This shop has used this form of off-site recycling since 1972. Originally, their equipment was purchased from Pollutronics and the columns were regenerated in Cleveland (company name not specified). They used Culligan's service in the late 1970's until 1991, when they switched to Dayton Water Systems "because of their recycling ability." After contacting Dayton Water Systems, it was learned that they do not currently provide a regeneration service for heavy metals, but may resume this service in the near future. The ion exchange columns used by PS 161 contain 3.2 ft3 of mixed (anion and cation) resin. During the past year, PS 161 sent 18 nickel columns and 8 chromium columns to Dayton Water Systems. The cost of the service was $336 per column for regeneration plus a $70 per month rental fee for the equipment (therefore, the total annual cost for most recent year is $6,888 for nickel and $3,528 for chromium). According to PS 161, Dayton Water Systems sent the regenerant to Inmetco for recovery of the metal (see Section 7 for information on off-site recycling).

Only one of the shops indicated that an ion exchange unit applied to nickel plating was the cause of an effluent compliance excursion (PS 196). This shop stated: "Excursions happen when the mixed bed of resin is saturated with copper and nickel and will no longer polish the water." This shop uses an off-site service for regeneration and is charged by the number of columns used. Therefore, the shop may tend to load the resin beds to their maximum or beyond their breakthrough point.

PS 261 reported a satisfaction level of 4 for ion exchange applied to nickel rinse waters. Their configuration is unusual in that the ion exchange unit is connected to the first rinse tank (i.e., most concentrated). Rinse water from the first rinse is pumped through the ion exchange column and is recycled to the last rinse (four-stage counterflow system). With this configuration, the ion exchange column receives the most concentrated rinse water. The normal configuration (see Exhibit 3-22) makes use of drag-out recovery to reduce the chemical load on the ion exchange system and recycles the final rinse. Using their configuration, PS 261 probably experiences the need for frequent regeneration. Their regenerant is sent to Inmetco for off-site recycle.

PS 317 and PS 318 applied ion exchange to rinse waters from electroless nickel plating. Both shops eventually abandoned their efforts to make the technology work. PS 317 described their use of the technology as a poor experience and indicated that their unit "required more water to restore the resin beads than water being processed." PS 318 indicated that the "process did not meet expectations or effluent guidelines."

3.4.6.2 Chromium Plating Performance Experience

Five respondents to the Users Survey provided some detailed data on their experience using ion exchange for chromium recovery. One of these shops uses an off-site regeneration/recycle service (PS 161) for regenerating columns applied to decorative chromium rinses (chromic acid, fluoride, barium carbonate). This shop also uses the off-site service for nickel recovery, details of which are provided in Section 3.4.6.1. Another respondent (PS 305) regenerates their unit on-site and sends the regenerant (sodium dichromate) to an off-site recycle company (Inmetco). One of the respondents recovers chromium from combined chromic acid anodizing and chromate conversion coating rinse waters and recycles the anion regenerant (dichromate) to the dichromate seal tank (PS 001). This system includes both anion and cation columns. The cation column removes contaminants such as aluminum and the anion column removes hexavalent chromium. Rinse water from the first rinse is filtered and passes through the columns and is returned to the final rinse. The cation column regenerant is treated and the anion column regenerant is transferred to the dichromate tank. Two of the four respondent's systems are not currently in use, but were previously used for chromium recovery from hard chrome plating rinse waters. One of these respondents intends to put their system back into use if the need arises (PS 052). Presently they have zero discharge, which is achieved through drag-out recovery rinsing. Bath contaminants are removed using membrane electrolysis and a porous pot. The other shop tried the ion exchange process for a short time period in 1984 and does not intend to reuse it in the future (PS 080).

The following information and data summarize the performance experience of the five survey respondents.

In one case, performance was hampered by operational and maintenance problems. PS 080 indicated that: "Initial attempts to use ion exchange for removal of impurities from chromic acid rinse water failed. Resins became fouled and could not be regenerated and maintain plating production throughput requirements." It should be noted that this system was relatively inexpensive ($3,025) as compared to the other chromium recovery units. The respondent indicated that the supplier stated capacity was 200 gpd and that the actual capacity was 0 gpd. The respondent provided a diagram in the survey that seems to indicate they were processing rinse water from drag-out tanks. This solution may have been overly concentrated with chromic acid for the apparently small ion exchange unit, causing almost immediate total loading of the resin. Also, their low capital expenditure may indicate that prefiltration was not included with the purchased ion exchange equipment.

PS 001 indicated that the supplier stated capacity and the actual capacity of their ion exchange system was 6 gpm at a feed concentration of 100 mg/l CrO4. At this flow rate the system recovered 98% of the chromium.

None of the shops indicated that an ion exchange unit applied to chromium recovery was the cause of an effluent compliance excursion.

3.4.6.3 Non-Cyanide Zinc Performance Experience

Five respondents to the Users Survey provided data on their experience with ion exchange used with non-cyanide zinc plating. Only two of these respondents provided sufficient detail to be considered useful for this report (PS 061 and PS 130). Both of these systems were manufactured by the same company and were purchased just one month apart. One ion exchange system was applied to acid zinc and the other to alkaline zinc. As will be discussed, the performance of the two systems was reportedly very different. The more successful of the two systems (PS 130) is a combination ion exchange and electrowinning system, similar in configuration to that shown in Exhibit 3-22. The other shop (PS 061) used ion exchange as an end-of-pipe treatment for "zinc bearing rinses and selected bath dumps," with the ion exchange regenerant going to an evaporator for concentration and the concentrated solution being hauled to an off-site recycle firm. The ion exchange processed wastewater was pH adjusted and discharged to a city sewer. This shop does not have a conventional hydroxide precipitation system following the ion exchange process. Originally this shop planned to return the zinc chloride concentrate from the evaporator to the zinc plating tank. As discussed later in this section, this plan did not work.

The following information and data summarize the performance experience of the two survey respondents.

One of the two shops providing detailed data on zinc applications indicated that their ion exchange unit was not the cause of an effluent compliance excursion (PS 130). The other shop indicated that their overall treatment system, which included zinc and chromium ion exchange, evaporation and pH adjustment, caused an effluent limitation excursion. Their treatment system was put into operation in December, 1989. On July 4, 1990, they received a cease and desist order from their control authority.

The performance of the ion exchange system operated by PS 061 was hampered by operational and maintenance problems. These are discussed in Section 3.4.6.3.2. The supplier stated capacity of this application was 18 gpm and the actual capacity was 10 to 12 gpm.

PS 061 originally planned to recover the zinc chloride regenerant by concentrating it with evaporation and then reusing it in the zinc plating tank. This was not possible due to: (1) Chromium was present in the regenerant, and to remove the chromium would have required redesigning the ion exchange system. (2) The amount of zinc chloride generated by "false regenerations (a constant problem)" was much more volume than could be used in the plating tank, even after evaporation. (3) The low pH of the regenerant kept destroying the heaters in the evaporation unit and the steam from the system was so acidic that it corroded a hole in the shop roof. This shop also tried to recover the zinc using electrowinning. They found that it was too difficult to maintain a chemical balance during the process and that chlorine gas was liberated. Both problems made the process ineffective and the electrowinning unit was never put into full operation.

Although PS 130 gave their system a satisfaction level rating of 3, they indicated that its downtime due to O&M problems was 50%.

Both of the shops indicated, that based on their experience with this technology, they would purchase a different technology if given the opportunity to repeat the process.

3.4.6.4 Cadmium Cyanide Performance Experience

Four respondents indicated that they have used ion exchange for chemical recovery with a cyanide plating solution other than gold cyanide. These four shops included four applications to cadmium cyanide rinse waters and one for zinc cyanide rinse waters (one shop did both).

The shop using both applications (PS 229) installed their equipment in stages during the early to mid-1980's and it was integrated with an HSA electrolytic recovery system. The shop provided insufficient details to draw any conclusions, however, they offered the following as a summary of their experience with the combined system: "Costs in 11 years far outweigh benefits. Would have been much more practical to install conventional precipitation technology."

The other three respondents also provided sketchy information for their applications. One of the units was a pilot system purchased in 1991 that is still being used in 1993 (PS 025). The response from that shop indicate that they are relatively satisfied with the system. PS 245 used a rented ion exchange column for cadmium recovery and found that the resins "loaded very quickly and did not appear to be the right application." They intend to use the equipment following conventional precipitation for water reuse. Since these two applications require different types of resins, it appears that this respondent has not received sufficient technical support to utilize this technology. PS 254 purchased ion exchange equipment in 1985 for cadmium recovery. They later eliminated the ion exchange process because it was recycling ferrocyanides to the plating bath.

The following information and data summarizes the performance experience of the survey respondents.

The major savings from the operation of ion exchange for this application was the result of water use reduction, treatment chemical reduction and sludge volume reduction.

PS 229 reported that the capacities of their ion exchange columns were 50 percent of the supplier stated capacity (2 lb/column vs 4 lb/column). They also indicated that they were unable to reuse either their zinc chloride or cadmium chloride regenerant due to an excess volume problem in the plating tank (i.e., insufficient surface evaporation from the low temperature baths). They evaporate water from the zinc chloride regenerant (500 gpy) and send the concentrated solution to a landfill. They electrowin cadmium from that regenerant (1,000 gpy) and then send the metal-depleted regenerant to off-site disposal. A discussion of cyanide plating applications is presented in Section 3.4.3. Low cation capacity may be due to excess free cyanide. Methods for concentrating the solution and making headroom in the plating tank using evaporation are discussed in Sections 3.2 and 3.3. Electrowinning of the cadmium regenerant is an acceptable method of recovery. The recovered metal can often be used as anode material. It is possible to increase the recovery rate by reusing the cation regenerant following electrowinning (see Exhibit 3-22). PS 229 also indicated that the fact that their equipment manufacturer went out of business within two years of installing their ion exchange equipment hindered the performance of their application.

None of the shops completing the survey indicated that an ion exchange unit applied to cyanide plating rinse waters was the cause of an effluent compliance excursion.

3.4.6.5 Gold Cyanide Performance Experience

Five user survey respondents provided some detailed data on their experience with ion exchange used for gold recovery. All but one of these shops send their used resins to their gold solution suppler for credit toward bath chemicals. The other shop regenerates the resin on-site and uses electrowinning to recover the metal (PS 123). The following information and data summarizes the performance experience of the survey respondents.

The average satisfaction level for ion exchange applied to gold cyanide is 4.0 (on a scale of 1 to 5, with 5 being most satisfactory), which is higher than the average level rating for ion exchange chemical recovery in general. Also, all of the shops indicated that this technology satisfied the need for which it was purchased. In each case the need was identified as reducing plating chemical purchases or other (i.e., reclaim gold). The range of savings from gold recovery for these shops was $1,320 (PS 283) to $134,400 (PS 123) per year.

Only one of the shops provided any capacity data. PS 179 indicated that they experience an average resin loading of 4 troy ounces per cubic foot of resin. They typically use 1 ft3 of resin per year.

In some cases, performance was hampered by operational and maintenance problems. These are discussed in Section 3.4.7.

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