Graduate School of Environment and Information Sciences, Yokohama National University
Graduate School of Environment and Information Sciences, Yokohama National University
Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency
抄録
In this study, phosphonium-based ionic liquids (IL), i.e., triethyl-n-pentyl, triethyl-n-octyl, and triethyl-n-dodecyl phosphonium bis(trifluoromethyl-sulfonyl)amide, [P222X][NTf2], (X = 5, 8, and 12) were investigated for Au(III) extraction. The IL–Au complex was identified as [P2225][AuCl4] using UV–Vis–NIR and Raman spectroscopic analyses. Slope analyses with the concentration dependence of [P222X+] confirmed the anion-exchange mechanism of Au(III) extraction by [P222X+] (X = 5, 8, and 12). The enthalpy, entropy, and Gibbs free energy for Au(III) extraction were determined using thermodynamic analysis, indicating that lower temperatures had a positive effect on the Au(III) extraction. 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)]. The diffusion coefficients of the extracted Au(III) species in [P222X][NTf2] (X = 5, 8, and 12) were evaluated from 323 to 373 K using semi-integral and semi-differential analyses. Because of the viscosity of the IL medium, the diffusion coefficient of the extracted Au(III) increases with increasing alkyl chain length. The 4f7/2 spectrum based on X-ray photoelectron spectroscopy revealed that the Au electrodeposits obtained after 10 cycles of continuous extraction and electrodeposition were in the metallic state.
Recovery of Gold by Solvent Extraction and Direct Electrodeposition Using Phosphonium-Based Ionic Liquids
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