National Metal Finishing Resource Center (NMFRC)

Pollution Prevention and Control Technologies for Plating Operations

Section 3 - Chemical Recovery

3.4 ION EXCHANGE

3.4.7 Operational and Maintenance Experience
3.4.7.1 Nickel Plating O&M Experiences
3.4.7.2 Chromium Solutions O&M Experiences
3.4.7.3 Non-Cyanide Zinc Plating O&M Experiences
3.4.7.4 Cadmium Cyanide Plating O&M Experiences
3.4.7.5 Gold Cyanide Plating O&M Experiences

3.4.7 Operational and Maintenance Experience

Of the 27 shops providing data, 17 (or 63%) were still operating their ion exchange equipment at the time of the survey. The average age of the operating systems was 7.0 years (only 4.2 years excluding gold plating applications). The average percentage of downtime experienced by the respondents was 20% (only 8.7% excluding PS 124, PS 080 and PS 061).

The following summarizes the respondents operating labor information. Details on O&M experiences are discussed for each type of application in Sections 3.4.7.1 through 3.4.7.5

Fourteen shops provided operating labor data. For these shops, the average number of annual operating hours per ion exchange system were: 553 hrs/yr. The skill requirement commonly needed for operating this technology is a trained technician or a wastewater treatment plant operator. The following is a breakdown of the responses for skill requirements:
          Environmental Engineer:.................5
          Process/Chemical Engineer:..............5
          Chemist:................................4
          Consultant:.............................3
          Plumber/Pipe Fitter:....................4
          Electrician:............................4
          Vendor:.................................1
          Senior-Level Plater:....................6
          Junior Level Plater:....................4
          Trained Technician:....................14
          Wastewater Treatment Plant Operator:...13
          Common Labor:...........................3
          Other:..................................0
      
3.4.7.1 Nickel Plating O&M Experiences

Reported O&M problems for nickel plating ion exchange applications relate to equipment failure and process chemistry concerns. Of the 11 shops providing data, six (or 63%) were still operating their ion exchange equipment at the time of the survey. The average age of the operating systems was 4.4 years. The average percentage of downtime experienced by the respondents was 17% (only 4% excluding PS 124).

The following O&M experiences were reported by respondents:

PS 124 was the earliest installation (1977). Considering the cost ($60,849 total installation cost), this was apparently a major recycling project for the shop. The shop provided the following responses concerning the equipment and the process: "Continuous and repeated failure of cheap valves used in design caused unit to plug up". "Return of calcium sulfate to plating tank clogged pipes and anode bags."

PS 212 reported that: "(The ion exchange system) was used for a short period of time. It never did the job it was intended to do."

PS 263 reported that their equipment, which they refer to as "prototype", "worked well, but created plating problems." This was a 4 gpm unit that recycled rinse water from the final rinse of a muti-stage counterflow rinse system. The shop believes that their plating problem was caused by the water in the final rinse (i.e., that which is recycled to the ion exchange column) because it was too clean and resulted in passivation of the nickel plated parts before chrome plating (i.e., the subsequent process).

PS 261 was the only shop that reported that they had no significant O&M problems.

PS 063 reported O&M problems with probe indicators and the balancing of chemicals.

3.4.7.2 Chromium Solutions O&M Experiences

Reported O&M problems for chromium ion exchange applications relate to resin fouling and equipment failure. Of the four respondents providing data for this application, two were still in operation at the time of the survey. The average age of operating systems was 3.5 years. The percentage of downtime experienced by the respondents was 27% (only 3% excluding PS 080).

The following summarizes the respondent's O&M experiences:

PS 080 indicated that their ion exchange system failed due to resin fouling. A discussion of this shop's system is presented in section 3.4.6.2.1.

PS 052 indicated that their ion exchange regeneration process was very time consuming. They also indicated that only dilute rinse waters can be effectively processed by the unit and that their rinse waters are occasionally too concentrated for the unit.

PS 001 indicated that their ion exchange system was also sensitive to the chromium concentration of the rinse water (i.e., feed to the ion exchange unit) and that to prevent overloading of the resin they initially rinse over the plating bath before using the rinse tanks.

PS 305 indicated that they cannot process the contents of their drag-out tank with ion exchange, without oxidizing the resin. (Note: The recovery of chemicals from concentrated solutions is not a good application for ion exchange. This technology is best applied to dilute solutions.)

3.4.7.3 Non-Cyanide Zinc Plating O&M Experiences

Reported O&M problems for non-cyanide zinc plating ion exchange applications relate to equipment failure and resin contamination with oil. Of the two respondents providing data for this application, none were still in operation at the time of the survey. One was purchased in December, 1989 (PS 061) and the other in January, 1990 (PS 130). PS 130 indicated that they intend to use their system in the future, although no specific plans were discussed in their survey form.

The following summarizes the respondents O&M experiences:

PS 061 provided the following information that relates to O&M problems: "Never believe an engineer again! This technology should be never used to treat zinc wastewater from a job shop. Way to touchy-system, must be simple-discontinued July 4, 1990." "Pump failure, resin fouled, computer failure, float switch failure, heater failure, and on and on and on-" "Nothing worked for this project." This same shop offered the following regarding technical restrictions of the technology that they have encountered: "Chemical concentration & flow rates are critical! Failure of any one part can shut down the whole system without warning-[sic]"

PS 130 indicated that the reason they are no longer using their zinc ion exchange system was a problem with oil in the rinse water feed to the unit that fouled the resin. They indicated that they plan on using the system in the future, after making changes to their cleaning process. This shop indicated the ion exchange system was not working 50% of the time as a result of the oil problem.

3.4.7.4 Cadmium Cyanide Plating O&M Experiences

Reported O&M problems for cadmium cyanide plating ion exchange applications relate to equipment failure, frequency of regeneration, excess regenerant production and bath contamination. Of the four shops providing data, two systems were operational at the time of the survey. The average age of the operating systems was 5.5 years. The average percentage of downtime reported by the respondents was 8%.

The following summarizes the respondents O&M experiences:

PS 229 reported that their ion exchange units were overloaded due to high drag-out rates and improper rinsing practices by their operators (discussed in Section 3.4.6.4.1). They also indicated that they felt their O&M problems were related to the manufacturer going out of business.

PS 245 reported that their ion exchange columns loaded quickly and that the frequency of regeneration was very high.

PS 254 eliminated their ion exchange process because it was returning ferrocyanides to the plating bath.

3.4.7.5 Gold Cyanide Plating O&M Experiences

Generally, the ion exchange units used for this purpose are small (< 0.5 ft3 of resin) and are free of complex regeneration and control systems. As a result, the operational and maintenance problems are minimal and the units that are purchased remain in use. In fact, all of the gold cyanide ion exchange installations identified in the Users Survey were in operation at the time of the survey. The average age of the units was 14 years. The only specific problem identified by a respondent was flow blockage caused by algae growth. The average percentage of downtime experienced by the respondents was 5%.

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