A STUDY ON SCATCHARD-HILDEBRAND SOLUTION THEORY FOR METAL SOLVENT-EXTRACTION SYSTEMS

In this paper the thermodynamic properties of two important extractants in hydrometallurgy (D2EHPA and EHEHPA) are studied. The activity coefficients of various diluents in D2EHPA-hydrocarbon binary systems are measured by gas chromatographic headspace analysis. The experimental data are regressed by using the Scatchard-Hildebrand solution theory. After revision of the mixing entropy, departures from the geometric mean of the cohesive energy are determined. Some regularities have been found. A new parameter delta //1//2 indicating the interaction energy between unlike molecules has been defined and discussed. The extension of Scatchard-Hildebrand equation from binary systems to multicomponent systems with metal complexes in organic phase (EHEHPA-nC//7H//1//6-CoSO4-CuSO4 extraction system) is also studied. The real 'thermodynamic equilibrium constants' for metal extraction reactions have been determined.