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Pollution Prevention and Control Technologies for Plating Operations
Section 4 - Chemical Solution Maintenance
4.5 ACID SORPTION
4.5.8 Residuals Generation
The acid sorption process only recovers a portion of the free or unused acid and it does not recover any of the combined acid (salt). As a result, approximately 35 to 70 percent of the total acid used is incorporated into a by-product. The by-product or waste stream from the process will require treatment. Depending on the metal involved, treatment will range from simple neutralization (pH adjustment with caustic) to metals removal (e.g., precipitation). Eco-Tec also suggests that electrowinning can be used; however, no specific applications were identified. Sludges resulting from waste treatment will be a listed hazardous waste (F006 or F019). PS 167 indicated that treatment of their by-product results in the generation of 2 drums of sludge per year.
Eco-Tec indicates that work is currently under way to recover the by-product streams from the acid sorption system. A demonstration site has been set up for the recovery of nitric and hydrofluoric acid from the metal salt by-product, and work is proceeding on the recovery of a usable by-product from an APU™ system used with an anodizing process (ref. 364).