The solvent extraction of zinc, cadmium and chromium from phosphoric acid solutions by tri-n butyl phosphate in kerosene diluent

In this paper, the solvent extraction of zinc(II), cadmium(II) and chromium(III) from phosphoric acid solutions by tri-n butyl phosphate (TBP) in kerosene as diluent was investigated. The distribution coefficients were determined and the results showed clearly a maximum values at 5.5 mol/L H3PO4 concentration and a minimum values at 1.0 mol/L H3PO4 concentration. The apparent standard molar enthalpies ΔH° for extraction of zinc(II), cadmium(II) and chromium(III) were found to be, respectively, 51.11, 45.43 and 59.87 kJ/mol which indicate the endothermic nature of the extraction process. The apparent standard entropies ΔS° were also determined 1.685 × 10−3, 1.377 × 10−3 and 1.961 × 10−3 kJ/mol K. The apparent standard Gibbs free energies ΔG° of extraction of zinc(II), cadmium(II) and chromium(III) were consequently calculated. Based on the regression analysis of the data, the equations for prediction of the distribution coefficients D of zinc(II), cadmium(II) and chromium(III), respectively were obtained.