National Metal Finishing Resource Center (NMFRC)

Pollution Prevention and Control Technologies for Plating Operations

Section 4 - Chemical Solution Maintenance

4.6 ION TRANSFER

4.6.6 Performance Experience

A partial summary of the Users Survey data relative to ion transfer technology is presented in Exhibit 4-26. There are a number of observations that can be made from these data, other data contained in the database and from the literature.

In general, shops using ion transfer for chromic acid bath maintenance gave the technology a high rating. The average satisfaction level for ion transfer applied to bath maintenance is 3.8 (on a scale of 1 to 5, with 5 being most satisfactory). Seventy percent of the shops 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:
         To meet of help meet effluent regulations:        2
         To reduce plating chemical purchases:             8
         To reduce the quantity of waste shipped off-site: 2
         To reduce wastewater treatment costs:             1
         To improve product quantity:                      5
      
The use of ion transfer for bath maintenance generally improved the production quality but did not impact the rate of production. The following responses were provided:
                    Product Quality   Production Rate
           Improved         6               2
           No Change        2               4
           Decreased        0               1
      
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:     8
          Purchase the same technology from a different vendor:  1 
          Purchase a different technology:                       2
          Do nothing:                                            0
      
The major savings from the operation of ion transfer for bath maintenance was the result of reductions in bath chemical use. The reported savings were in the range of $500 to $2,000 per year.

The ion transfer process is relatively slow with respect to removal of dissolved metals. For example, a PPS2 was tested on a 50 gal solution of chromic acid contaminated with 13.05 g/l of copper, iron and nickel (i.e., combined concentration). The contaminant level was decreased to 4.08 g/l in 192 hours (8 days). The maximum tank volume applicable to the PPS2 is 700 gal (ref. 371). For this size tank the time needed for purification would be 112 days. If the tank were used for production while purification was conducted, the time for purification could be much longer and possibly unachievable (e.g., if the introduction rate of contaminants exceeded the removal rate).

One survey respondent has used three different types of chromic acid bath maintenance techniques since 1980 (ref. PS 234). This shop did not provide the data requested in the survey form, but attached the following useful insight:

Over the years, we have tried three different technologies in order to solve this problem. We moved into new offices 2 years ago, and I have been unable to locate my files relating to the specifics of each system. Therefore, the following information is based on my recollection.

Short-bed ion exchange. Purchased from Eco-Tec (Canada) in 1983 - 1985 at a cost of $17,000 plus. Of the three systems, this technology provided the best results as far as removing impurities. The major problem, which resulted in our selling the equipment, was the overloading of our waste treatment facilities with hex chrome - producing large quantities of F006 sludge.

Porous Pot. Purchased from Cosmos (California) somewhere around 1980 - 1981. Purchase price unknown. This experiment was a disaster. The cleaning of the system was an incredibly messy operation which took 4 to 5 hours to complete. This system also produced abundant amounts of hex cr. waste, and the porous pots were susceptible to breakage. This system gave only marginal results for purification of the bath, although it did a good job of removing trivalent chromium.

Membrane. Unable to recall name of company. They were out of the Atlanta, GA area. The cost of the unit was around $8,000. This system was similar to the porous pot technology with the substitution of a membrane for the porous pots. Like its predecessor, however, it was dreadful to clean out the collected material. It also generated tremendous amounts of hex cr. and seemed limited to the removal trivalent chromium only. The other impurities such as cu. and iron were largely unaffected.

All of these systems were sold, and we are in the market for suitable (proven) technology [sic].

[The third technology discussed by the respondent was actually a membrane electrolysis technology (Section 4.7). The particular system they purchased is no longer being sold. As indicated in Section 4.7, some membrane electrolysis technology applications have been successful.]

There was very little performance experience documented in the survey forms with respect to the polyfluorocarbon membrane units. Of the two shops providing data, one was satisfied with its performance, but discontinued its use due to maintenance problems (PS 134) and the other respondent was dissatisfied with the performance of the unit (PS 194).

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