Pollution Prevention and Control Technologies for Plating
Section 3 - Chemical Recovery
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).
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