Separation of cobalt from nickel in ammonia-ammonium carbonate solutions using pressurized ion exchange

Abstract

High resolution pressurized ion exchange has been used successfully to study and separate the various cobalt and nickel complexes present in commercial ammonia-ammonium carbonate solutions produced by the Caron process. Using chromatographic elution from Dowex 50W-X8 (15–25 micron) resin with ammonium carbonate solutions, three cobalt species, identified as the purple carbonato tetrammine complex, [Co(NH 3) 4CO 3] +, the red carbonato pentammine complex, [Co(NH 3) 5CO 3] +, and the yellow hexammine complex [Co(NH 3) 6] 3+, were separated from a single nickel species. Nickel sorption was found to be a strong function of pH, whereas sorption of the cobalt complexes was essentially independent of pH over a rather wide range, extending from ∼pH 7.8 to 10. Distribution ratios for all species increased significantly with decreasing ammonium carbonate concentration. With ammonium carbonate solution at pH 9.5, the complexes were eluted in the following order: [Co(NH 3) 4CO 3] +, [Co(NH 3) 5CO 3] +, [Ni(NH 3) 6-x(H 2O) x] 2+, and [Co(NH 3) 6] 3+. From 4 M (NH 4) 2CO 3, distribution ratios were 5.0, 7.5, 18, and 75 for the respective complexes identified in the order above. This study points out some of the difficulties and opportunities in developing a viable ion exchange process for the recovery and separation of these metal ions.