Recovery of Gold by Solvent Extraction and Direct Electrodeposition Using Phosphonium-Based Ionic Liquids

Abstract

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.

Nitrogen‐Doped Titanium Carbide (Ti3C2Tx) MXene Nanosheet Stack For Long‐Term Stability and Efficacy in Au and Ag Recovery

“…Coexisting metal ions with a positive surface charge, such as Al(III), Ru(III), Pb(II), Ni(II), Fe(II), Cu(II), Mn(II), and Zn(II) in acidic conditions, could not form a stable bond with the positively charged surface of the N‐MXene nanosheet stack due to electrostatic repulsive force (Figure S11, Supporting Information). Although some elements such as Ir(III), Pt(II), and Pd(II) form metal halide complexes such as [IrCl 4 ] 2− , [PtCl 4 ] 2− , and [PdCl 4 ] 2− in acidic solutions, [ 40 ] the [AuCl 4 ] − anion in an acidic solution was selectively reduced on the N‐MXene nanosheet surface because the stack's oxidation potential was appropriate for reducing Au ions. [ 41 ] The reduction potential of the Au ion was the highest value (1.50 V) among metal ions (−1.19–1.18 V) in the acid solution.…”

First Gold Recovery from PCBs through en-thiosulfate Leaching and Selective Adsorption with Carbon

“…This, in turn, could lead to the deposition of gold ions into metallic gold, as shown in Eq. ( 8) (Matsumiya et al, 2022). Furthermore, the decomposition products of thiosulfate would adhere to the surface of the circuit board, forming a 'membrane of passivation' that could protect the gold from oxidation, thereby hindering further leaching of gold.…”

“…( 2), whose key point lies in the inclusion of two substances: Cu 2+ and NH3 , which act as a oxidizer of gold. Even though, this Cu 2+ -NH3-S2O3 2method still faces several challenges: toxic and highly volatile ammonia gas (Erik, 2018, Xueyan, 2023 would be produced from the leaching solution that contains more than 0.6 M NH3•H2O, and intricate gold recovery procedures (Matsumiya et al, 2022), such as various modification or decoration method of activated carbon, which restrict their industrial application (Chen, S. et al, 2020).…”

On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions

“…Considering these various separation technologies, recent published applications of these on gold(III) processing included solvent extraction [ 7 , 8 , 9 , 10 , 11 ], precipitation [ 12 , 13 ], ion exchange [ 14 , 15 , 16 ], adsorption [ 17 , 18 , 19 , 20 , 21 ] and even polymer inclusion membranes [ 22 ].…”