Microkinetics and reaction equilibria in the system ZnSO4/D2EHPA/isododecane

Studies have been made on the kinetic a of zinc extraction for the ZnSO4/D2EHPA/isododecane system which is being considered as a Recommended Liquid-Liquid Extraction Test System by the European Federation of Chemical Engineering (EFCE) Working Party on Distillation, Absorption and Extraction. A constant interfacial cell has been used to determine the chemical rate-controlling parameters at 25 degrees C. Additionally, correlations for the system properties such as density, viscosity and interfacial tension have been developed as well as a correlation for the distribution coefficient. A rigorous equilibrium model based on chemical potential theory serves as a frame for the microkinetic formulation. The heterogeneous mass transfer is controlled at low zinc concentrations by two slow reversible interfacial reactions. The adsorption of the interfacial solutes is considered with the Langmuir law. It could be shown that neither complex stoichiometry, equilibria nor microkinetic constants will depend on a chosen aliphatic diluent, when the model formulation is expressed in activities. (C) 1999 Elsevier Science B.V. All rights reserved.