THE KINETICS OF VANADIUM (IV) EXTRACTION IN THE ACIDIC SULFATE-D2EHPA-NORMAL-HEXANE SYSTEM USING THE ROTATING DIFFUSION CELL TECHNIQUE

The kinetics of the extraction of vanadium (IV) from acidic sulphate solutions by di-2-ethylhexyl-phosphoric acid (D2EHPA or H2R2) dissolved in n-hexane have been investigated over a range of vanadium concentrations, extractant concentrations, pH, sulphate concentrations and temperature conditions. The rotating diffusion cell technique was employed. The experimental data have been analysed in terms of a mechanism of mass transfer with chemical reaction (MTWCR) using either the monomer or dimer models for D2EHPA. The data have been fitted to the generalised MTWCR model of Hughes and Rod using the kinetic and equilibrium parameters. The data are best fitted using the model for the monomer of D2EHPA reacting in a thin aqueous film at the interface and the value of the kinetic parameter, THETA-1, (10(4)-mu-m2s-2) indicates that the extraction is under mixed control. The activation energy for the system, in the temperature range 297-309 K, depends slightly on the pH of the aqueous solution and varies within 49-34 kJ mol-1.