Transfer of cobalt and nickel from sulphate solutions to spent electrolyte through solvent extraction and stripping

Abstract

We report in this paper studies carried out on the separation and recovery of cobalt and nickel from sulphate solutions through solvent extraction using acid form of PC 88A and D2EHPA diluted in kerosene and stripping of metals from loaded organic phase with synthetic spent electrolyte solutions to generate respective pregnant electrolyte solutions. The typical composition of sulphate solution used for the present study contains Co: 1.91 g/L and Ni: 14.83 g/L. Variation of aqueous phase equilibrium pH in the range from about 3.1 to 6.5 using 0.15, 0.2 and 0.25 M PC 88A indicated increase of cobalt extraction and reaches maximum (∼92–95%) around 5.5 pH with co-extraction of nickel from 0.1 to 5.7%. Comparison of cobalt extraction behavior with the three extractant concentrations showed 0.2 M PC 88A as the best with highest separation factor of about 730 and about 3% co-extraction of nickel only. Using 0.2 M extractant concentration, almost quantitative extraction of cobalt in two counter-current (CC) stages at an aqueous to organic (A:O) phase ratio of 1.5:1 and stripping of metal from loaded organic (LO) in two CC stages at A/O ratio of 1.7 with synthetic spent electrolyte (SE) solution was achieved, generating a pregnant electrolyte solution of pH around 3 suitable for electrowinning. Similar optimum conditions for the treatment of cobalt raffinate to recover nickel using 0.7 M D2EHPA (pH 6.6, unit phase ratio, two stages) and stripping of metal from LO (O/A: 1.7, two stages) with synthetic nickel SE solution were established. Finally, complete process flowsheet for the separation and recovery of cobalt and nickel is demonstrated.