Removing Trace Co from NiSO4 Solutions Using Cyanex 272

Although there are many articles about the effective separation of cobalt and nickel, the investigation on separation of trace cobalt and high concentration nickel are still poorly reported. In this paper, the process of extraction and separation of trace cobalt from sulfate solution containing high concentration of nickel was systematically investigated. The commercial product Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid) in kerosence was used. The initial solution used for the present study contained in [Co] 25.45 mg/L and [Ni] 96.00 g/L. A cobalt extraction rate of more than 99% has been achieved under the condition of 10 vol. % Cyanex 272, O/A 1:1, pH 5.5, and 60°C, with cobalt concentration being reduced from 25.45 to below 0.5 mg/L. NiSO4 solution with such a low Co level is required for producing ultra-high 5N-6N purity nickel. In addition, high pH value, high Cyanex 272 concentration in organic phase, high O/A ratio, and adding TBP to the organic phase can lead to increased Ni loss.