Optimization of vanadium(V) extraction by 2-ethyl-1-hexanol and the study of extraction reaction mechanism

Abstract The aims of the present work are to investigate the mechanism and thermodynamics of pentavalent vanadium (V(V)) extraction by 2-ethyl-1-hexanol and to optimize the extraction process. The stoichiometry of V(V) extraction reaction and the extraction equilibrium constants at different temperatures were determined using the slope analysis method applied to the experimental data. It was shown that the extracted V(V) was in the form of HVO3(ROH) in the organic phase. The standard enthalpy and the standard entropy of extraction reaction were calculated as 39.56 kJ/mol and 54.38 J/(mol.K), respectively. A statistical experimental design method, including Plackett-Burman design (PBD) followed by a central composite design (CCD), was employed to obtain the regression models for the prediction of extraction percentages and to optimize the recovery of V(V) from a synthetic leach solution containing Fe(III), U(VI), Si(IV), and Al(III). The accuracy of the predictive models was proven by the analysis of variance (ANOVA). The optimum condition for selective separation of V(V) was: initial pH of 1.9, extractant concentration of 70 %v/v, and T=59.3 °C. Under the optimum condition, the extraction percentages for V(V), Fe(III), U(VI), Si(IV), and Al(III) were 91.3%, 1.7%, 6.3%, 10.6%, 2.7%, respectively. Developed models were validated by solvent extraction experiments at optimum conditions.