Kinetic analysis of the reactive liquid–liquid test system ZnSO4/D2EHPA/n-heptane

The kinetics of zinc extraction and stripping have been investigated for the ZnSO4/D2EHPA/diluent system (D2EHPA=di(2-ethylhexyl) phosphoric acid), which is under consideration as a proposed reactive extraction liquid–liquid test system by the European Federation of Chemical Engineering. Data in low and high concentration domains have been fitted to chemical kinetic and kinetic–diffusive models in order to discern the mechanism of zinc extraction and stripping for practical operational conditions. The existence of the correlation between the estimated parameters and the contributions to the overall flux of the reactive species through the interface has been determined by statistical analysis. The study has concluded that both extraction and stripping rate processes are described by the same reaction mechanism scheme as suggested by Ajawin et al. [Chem. Eng. Res. Des. 61 (1983) 62] but with the stoichiometry and complexes proposed by Mansur et al. [Hydrometallurgy (2002)]. Flux equations lead to the calculation of the individual resistance terms for mass transfer and chemical reaction using simple equations with activity coefficients equal to unity. The extraction process shows mixed controlled kinetics, whereas the mass transfer of the zinc complex was found to be rate-determining for stripping conditions. The model satisfactorily explains the data with a relative error lower than 10%.