The equilibrium characteristics of aqueous cobalt and nickel mixtures with the extractant bis-(2-ethylhexyl)-phosphonic acid.

Abstract

In this work, binary solutions of cobalt and nickel in aqueous ammonium sulfate solutions were extracted using a simple shake-out technique with a mixed organic phase consisting of the extractant bis-(2-ethylhexyl)phosphonic acid (PC-88A), the modifier tributyl phosphate, and the diluent Esso Varsol DX3641. It was found that the optimum pH for the separation of cobalt and nickel was 5.0, and that the separation of the ions was a complex function of the porportion of cobalt and nickel in the equilibrium phases. The maximum metal loading of the organic phase, based on the population of dimer extractant complexes was approximately 73%. Two methods, used to describe the equilibrium extraction of two or more metal ions were compared namely, the Delta Y method and the Pseudo-Gamma approach. Each of these methods account for the non-ideal interactions between mixture components. Barclay's Pseudo-Gamma relationship was found to be simpler, and correlated the data very well. (Abstract shortened by UMI.)