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Pollution Prevention and Control Technologies for Plating Operations
Section 3 - Chemical Recovery
3.6 ELECTRODIALYSIS
3.6.2 Development and Commercialization
Although the phenomenon of electrodialysis was observed in the 1800ís, it did not achieve any commercial application until durable, ion-selective membranes were developed in the 1950ís (ref. 39). The two early applications of this technology, desalination and recovery of edible salt from sea water, still constitute the bulk of membrane utilization. The largest electrodialysis installations are salt recovery systems located in Japan. These systems replaced solar ponds that once occupied large tracts of land (ref. 400).
Large-scale industrial usage of electrodialysis began in the early 1970ís with applications in chemical processing, biotechnology and water pollution control. In 1972, the first attempts were made to use electrodialysis to reclaim plating chemicals from rinse solutions (ref. 32). This early work was performed with unidirectional systems, where the transfer of ions is in one direction only. These efforts were plagued by membrane fouling with scale, slime and undesirable organics (ref. 32). Subsequently, the electrodialysis reversal (EDR) process was utilized, where there is a periodic reversal of direct current flow through the membrane stack and a simultaneous interchange of diluting and concentrating streams. This improvement greatly reduced the occurrence of membrane fouling. By 1984, there were more than 100 recovery units operating in the U.S. on a variety of plating solutions. The major area of application was nickel plating, with most other applications restricted to cyanide baths (e.g., gold, cadmium, silver and zinc). Additional applications at that time, mentioned in the literature, include tin and tin-lead fluoroborate and trivalent chromium (ref. 39). Since approximately 1985, there have not been any major changes to electrodialysis as applied to chemical recovery from rinse waters. However, similar technology applications for bath maintenance have significantly increased. Presently, membrane electrolysis, a related technology, is applied to the maintenance and reformulation of solutions containing chromic acid, nitric acid, sulfuric acid or sodium hydroxide (Section 4).