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Pollution Prevention and Control Technologies for Plating Operations


Section 4 - Chemical Solution Maintenance

4.7 MEMBRANE ELECTROLYSIS

4.7.6 Performance Experience

Only five membrane electrolysis applications were identified during the Users Survey. These included two applications of in-house units built by PS 275, two applications of Ionsep units and one application of a Pentol CAPS system (manufactured in France). Detailed data were provided for all systems except for the Pentol unit. The user of that system, however, provided a short informative description of their experience. A summary of the Users Survey data are provided in Exhibit 4-33.

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

  • Shops using membrane electrolysis for chromic acid bath maintenance gave the technology mixed ratings, even for the same manufacturer. PS 006 and PS 052, both of which purchased Ionsep units, had general satisfaction levels of 1 and 5, respectively (1= lowest and 5 = highest). The low satisfaction level from PS 006 may have been influenced or otherwise related to the manufacturerís technical support, which they also rated 1. That shop also provided the following: ìTechnical support info very difficult to get from vendor. Process not compatible with our bath, which we had to learn on our own.î PS 052 gave a manufacturerís support rating of 4. The owner of the Pentol unit was displeased with its performance (PS 234). They wrote: Seemed limited to the removal (of) trivalent chromium... other impurities such as Cu and iron were largely unaffected.î
  • The following is a breakdown of the reasons why shops purchased this technology:
          To meet or help meet effluent regulations:        0
          To reduce plating chemical purchases:             1
          To reduce the quantity of waste shipped off-site: 2
          To reduce wastewater treatment costs:             0
          To improve product quantity:                      3
          Other:                                            0
      
  • The use of membrane electrolysis had a variable impact on production quality and the rate of production. The following responses were provided:
                        Product Quality   Production Rate
          Improved (PS 275)    1                1
          No Change (PS 052)   1                1
          Decreased (PS 006)   1                1
      
  • Although PS 052 indicated in the survey form that product quality and the production rate were not impacted, they also stated that purifying their plating solutions ìreduces our reject rates which eliminates the costly need to strip the part and replate.î
  • None of the shops provided any estimates of savings from the operation of membrane electrolysis units.
  • Membrane electrolysis may be more applicable to simple chromic acid bath chemistry (e.g., generic chromic acid/sulfuric acid hard chromium bath) more so than baths with complex chemistry (e.g., dual catalyst plating baths). This is evidenced by the difficulties of PS 006, who operated their unit on a proprietary fluoride bath (M&T CR 110), whereas PS 052, successfully operates their unit on a generic hard chromium bath.
  • Two of the survey respondents have purchased and used alternative technologies for chromic acid bath maintenance. PS 006 previously used the porous pot (an ion transfer technology) and PS 234 previously used the porous pot and ion exchange. PS 006 indicated that the porous pot was ìmoderately successfulî, whereas they were unsatisfied with the membrane electrolysis unit. They indicated that both technologies caused bath chemistry problems with their proprietary plating solution. PS 234 has not been satisfied with any of the chromic acid bath maintenance technologies that they have tried and subsequently sold each of them. However, they indicated that ion exchange provided the best results of the three technologies. A complete discussion of their comments is presented in Section 4.6.8.

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