Recovery of metal ions from spent solutions used to electrodeposit magnetic materials

The feasibility of using electrodialysis to extract metal ions such as coba lt and nickel from spent electroplating baths employing. citrate salts was examined. Modeling of metal-citrate speciation in electrolytes was initiall y used to identify conditions under which such a separation process might b e possible. The most promising separation scheme identified in these studie s required acidification of the electrolyte to de-complex the metal ions fr om citrate, followed by extraction of the metal ions through a cation excha nge membrane. A number of commercially available cation exchange membranes have been shown to be suitable for the recovery of Co2+, Ni2+ and Cu2+ ions from citrate-based electrolytes. In terms of current efficiency, Nafion 11 7 was found to be the most suitable membrane material for metal ion recover y from citrate electrolytes. The rates of transfer of anionic metal citrate complexes through various anion exchange membranes were found to be low co mpared with other anions and the extraction of metal ions in this manner th erefore does not appear feasible. Typically, metal ion separation factors o f near unity were observed for both the Cu-Ni and Cu-Co citrate baths, indi cating that is it generally not possible to achieve significant separation of divalent metal ions using commercially available cation exchange membran es. (C) 2001 Elsevier Science B.V. All rights reserved.