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

The feasibility of using electrodialysis to extract metal ions such as cobalt and nickel from spent electroplating baths employing. citrate salts was examined. Modeling of metal-citrate speciation in electrolytes was initially used to identify conditions under which such a separation process might be possible. The most promising separation scheme identified in these studies required acidification of the electrolyte to de-complex the metal ions from citrate, followed by extraction of the metal ions through a cation exchange 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 117 was found to be the most suitable membrane material for metal ion recovery from citrate electrolytes. The rates of transfer of anionic metal citrate complexes through various anion exchange membranes were found to be low compared with other anions and the extraction of metal ions in this manner therefore does not appear feasible. Typically, metal ion separation factors of near unity were observed for both the Cu-Ni and Cu-Co citrate baths, indicating that is it generally not possible to achieve significant separation of divalent metal ions using commercially available cation exchange membranes. (C) 2001 Elsevier Science B.V. All rights reserved.