Equilibrium, thermodynamics and kinetics study on Au(III) extraction by gemini surfactant with different spacer length

The effect of spacer lengths of imidazolium gemini surfactant [C-14-n-C(14)im]Br-2 (n = 2, 4, 6) on the equilibrium, thermodynamics and kinetics of Au(III) extraction from hydrochloric acid medium were investigated in this article. The thermodynamic parameters, including the changes in enthalpy (Delta H*), entropy (Delta S*) and Gibbs free energy (Delta G*) were determined. The values of Delta H* demonstrated that the extraction of Au(III) by [C-14-n-C(14)im]Br-2 was endothermic at first and exothermic at last. The kinetics study found that extraction rate became faster when the spacer lengths were increased. Moreover, kinetics results demonstrated that the diffusion is the controlling step, and the mass transfer coefficients of Au(III) in the investigated systems indicated that the resistance of mass transfer was smaller when the spacer lengths was longer. The studies of interfacial tension further confirmed the better extractability of [C-14-n-C(14)im]Br-2 with longer spacer lengths. Our results reveal efficient and sustainable gold separation.