Removal of heavy metal ions using a novel integrated electrolytic-electrodialytic process

Abstract

Wastewater containing toxic metal ions, such as cadmium, copper, gold, lead, nickel, silver, and zinc ions, are generated in large quantities in the mining, metal finishing, microelectronic fabrication, and photographic film processing industries. The heavy metal ions in wastewater can be recovered in their metallic form by electrodeposition at the cathode of an electrolytic cell. The concentration limits for safe discharge of metal ions to waste streams are typically less than 1 ppm. At these low concentrations, the current efficiency for electrodeposition becomes extremely low, which results Into high energy consumption. The electrodialysis method, on the other hand, is able to reduce the metal ion concentrations to a low level by permeating the metal ions through an ion- exchange membrane with low energy requirement. The method, however, produces a by product of concentrated solution containing mixed metal ions and impurities, which requires further purification or treatment with other processes.