Effect of process variables on the kinetic and thermodynamic parameters of platinum solvent extraction by cyanex 921

Abstract

Platinum is a precious metal which may be processed under acidic conditions. Accordingly, the extraction of platinum from an acidic chloride media is of immense practical importance. In this study, the extraction of platinum was investigated in a Pt(IV)-HCl-Cyanex 921 matrix in order to establish the effect of temperature, extractant concentration, pH and the initial platinum concentration which had been used in the evaluated solvent extraction (SX) process. The extractant phase contained a mixture of Cyanex 921 and kerosene. In addition, the extraction mechanism of platinum, and the extracted species, are also described in the study, including the determination of the following: extraction ratio, extractant loading, distribution ratio, thermodynamic parameters, and the kinetic mechanism involved in the Pt(IV)-HCl-Cyanex 921 system used. Inductively coupled plasma emission spectroscopy (ICP-ES) was used to measure the platinum concentration in the aqueous phase with a mass balance being used to determine the concentration of platinum in the organic phase.

Using a combination of the variables under investigation, the experiments which were evaluated indicated that it is possible to extract sufficient platinum chlorocomplex under the following conditions: pH of 1, Cyanex 921 concentration of 8% (v/v), temperature of 298 K and an initial platinum concentration of 55.22 mg/L. Under these conditions the maximum organic-phase loading of 253.9 mg/L was achieved as compared to the theoretical loading of 507.24 mg/L. The equilibrium loading of ~50% of the platinum chlorocomplex in the organic phase was achieved after 2400 seconds of reactor operation. In this case, a distribution ratio of 9.4 was achieved. This value was observed to be higher as compared to the other SX conditions evaluated in this study.