THE KINETICS OF COBALT AND NICKEL EXTRACTION USING HEHEHP

Abstract

ABSTRACT The kinetics of the extraction of cobalt and nickel using purified mono 2-ethyl hexyl phosphonic acid mono 2-ethyl hexyl ester (HEHEHP) were studied using the Rotating Diffusion Cell (RDC) apparatus. The extraction of cobalt was Investigated over a wide range of cobalt concentration, extractant concentration, pH and temperature conditions. Nickel extraction was examined over a wide range of nickel concentrations. The kinetic data were treated according to both interfacial and mass transfer with chemical reaction (MTWCR) models. The MTWCR model adequately described the kinetic data for both the cobalt and nickel extraction experiments. No variation of an interfacial model was adequate to describe the data. In the MTWCR model, the extraction rate was shown to be controlled by a mechanism involving diffusion of the extractant into the aqueous phase boundary layer with subsequent reaction involving the addition of the first ligand to the cobalt or nickel ion. This extraction mechanism was substantiated by supplementary results including the activation energy determination which indicated mixed diffusion and chemical reaction control, the significant measured rate of partition of the extractant to the aqueous phase, and the values of the cobalt and nickel complex formation constants in the aqueous phase.