SOLVENT EXTRACTION OF COBALT AND NICKEL IN BIS (2,4,4-TRI-METHYLPENTYL) PHOSPHINIC ACID, “CYANEX -272”

Abstract

A study has been made of the extraction of cobalt and nickel from sulfate solutions into bis(2,4,4 tri-methylpentyl) Phosphinic acid - “Cyanex 272”, diluent Esso solvent DX 3641, for both high and low metal loading in the organic phase. In dilute solution, 0.01 M, extraction constants and enthalpies were determined for both metals. The extraction of cobalt was always favored over that of nickel, increasing with increase in temperature. No structure change with temperature was found for the cobalt-Cyanex complex. Phase modifiers were found to effect the selectivity of “Cyanex 272” for cobalt. At high metal loading, equilibrium curves for cobalt were fitted using semi-empirical curve fitting, while for nickel a straight line variation was observed. Organic phase polymerization was observed for both metals the degree of aggregation increasing with increase in loading. A step change increase in the viscosity of the organic phase was observed at high cobalt loading. Phase modifiers proved to be ineffective In reducing the increase in organic phase viscosity.