Solvent extraction of tetravalent titanium from chloride solution by di-2-ethylhexyl phosphoric acid in kerosene

The solvent extraction of Ti4+ from chloride solution by di-2-ethylhexyl phosphoric acid (D2EHPA, H(2)A(2)) dissolved in kerosene has been investigated over a wide range of aqueous acidity as a function of phase contact time, Ti4+, H+ and Cl- concentrations in aqueous phase, D2EHPA concentration in organic phase and temperature. The equilibrium is reached within 2 h. The distribution coefficient is found to be independent of Ti4+ concentration at least up to 1 g/l Ti4+ in the aqueous phase. The pH and log extractant concentration dependences are approximately -2 and 2, respectively. The extraction is independent of Cl- concentration. These results suggest that extraction occurs via the following reaction: TiO2+ + 2H(2)A(2(0)) reversible arrow [TiO(HA(2))(2)]((0)) + 2H(+). The temperature dependence data give Delta H values of 30 kJ/mol in the higher temperature region (> 30 degrees C) and 78 kJ/mol in the lower temperature region (similar to 15 degrees C) under investigation. The equilibrium constant, K-ex at lower loading is 1 x 10(3.95) with a standard deviation of log K-ex of 0.023. The loading capacity of D2EHPA for Ti4+ is 7.31 g Ti(IV)/100 g D2EHPA. The loading study suggests that a variation of the extraction equilibrium reaction occurs during the course of loading. At high loading Ti4+ is extracted by the reaction: TiO2+ + H(2)A(2(0)) reversible arrow [TiOA(2)]((0)) + 2H(+). The structure of the solid complex prepared from the high loaded organic phase has been established by determining the Ti/P ratio and using infrared spectroscopy. (C) 1998 Elsevier Science B.V. All rights reserved.