Recovery of Gold by Solvent Extraction and Direct Electrodeposition Using Phosphonium-Based Ionic Liquids. Issue 8 (1st August 2022)

• Record Type: Journal Article
• Authors: Matsumiya, Masahiko; Kinoshita, Ryoma; Sasaki, Yuji
• Is Part Of: Journal of the Electrochemical Society. Volume 169:Issue 8(2022)
• Publication Date: 2022-08-01
• Subjects: Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/1945-7111/ac876d
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : 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 4 f 7/2 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.