Recovery of gold by solvent extraction and direct electrodeposition using phosphonium-based ionic liquids

Matsumiya, Masahiko*; Kinoshita, Ryoma*; Sasaki, Yuji  

The phosphonium-based ionic liquids (IL), triethyl--pentyl, triethyl--octyl, and triethyl--dodecyl phosphonium bis (trifluoromethyl-sulfonyl)amide, ([P][NTf), (X = 5, 8, and 12) were investigated for Au(III) extraction. Slope analyses confirmed the anion-exchange mechanism of Au(III) extraction by (P). The enthalpy, entropy, and Gibbs free energy for Au(III) extraction were determined using thermodynamic analysis. Electrochemical analysis revealed that extracted Au(III) can be reduced in two steps: (i) Au(III) + 2e Au(I), (ii) Au(I) + e Au(0)]. Because of the viscosity of the IL medium, the diffusion coefficient of the extracted Au(III) increases with increasing alkyl chain length.