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Pollution Prevention and Control Technologies for Plating Operations
Section 4 - Chemical Solution Maintenance
4.4 ION EXCHANGE
4.4.6 Performance Experience
Eleven respondents to the Users Survey provided some detailed data on their experience using ion exchange for chromium bath maintenance. All of these applications involved hexavalent baths, except for one, which was applied to a trivalent decorative chromium bath. A summary of the Users Survey data for these applications is presented in Exhibit 4-11.
The following information and data summarize the performance experience of the eleven survey respondents.
- In general, shops using ion exchange for bath maintenance gave the technology a high rating. One exception to the high satisfaction level was PS 244. This shop only operated the process for eight months during 1983 and 1984. Their low level of satisfaction was due to a high residuals generation rate (see Section 4.4.8). Also, they indicated that the supplier stated capacity of the unit was 208 gallons per 12 hours and that the actual capacity was approximately fifty percent of this rate. Another shop that gave this technology a low rating was PS 273. This shop indicated that they discontinued use of the technology shortly after startup for administrative and technical reasons (discussed later in this section). The one shop using ion exchange for trivalent chromium bath maintenance had a satisfaction level of 5. The average satisfaction level for ion exchange applied to bath maintenance is 3.9 (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 (3.2). Seven of the shops (or 64%) indicated that this technology satisfied the need for which it was purchased. The following is a breakdown of the reasons why shops purchased this technology (multiple responses were permitted):
To meet of help meet effluent regulations: 4 To reduce plating chemical purchases: 8 To reduce the quantity of waste shipped off-site: 8 To reduce wastewater treatment costs: 4 To improve product quantity: 9
- The use of ion exchange for bath maintenance generally improved the production quality and to a lesser extent improved the rate of production. The following responses were provided:
Product Quality Production Rate Improved 8 4 No Change 2 6 Decreased 0 0
- Most plating shops indicated, that based on their experience with this technology, 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: 7 Purchase the same technology from a different vendor: 1 Purchase a different technology: 3 Do nothing: 0
- One shop indicated that they are able to recycle spent chromic acid bath as another product and have therefore eliminated the need for the ion exchange system (PS 244).
- The major cost savings from the operation of ion exchange for bath maintenance were due to reductions in bath chemical use and disposal costs.
- One respondent used ion exchange to treat a chromic acid copper strip solution (PS 273). Their efforts have been unsuccessful thus far (project stopped due to change in personnel and other reasons). This facility uses, on an annual basis, 25,900 lbs/yr of chromic acid to strip approximately 3,200 lbs of copper in a 1,158 gallon strip tank. The process is operated at 160°F with a chromic acid concentration of 120 g/l. This shop purchased a water softening ion exchange unit and was told by the manufacturer's representative that they could process the bath at full strength at its operating temperature. The result was that the "copper removal efficiency dropped quickly after start-up." The respondent felt that the hot, concentrated chromic acid had oxidized the resin.
- At different times, one of the respondents used ion exchange, the porous pot technology and membrane electrolysis for chromic acid bath maintenance. This shop indicated that ion exchange provided the best results in terms of impurity removal (PS 234). The complete statement provided by this shop, which provides a great deal of insight to this problem, is presented in Section 4.6.6