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

Abstract

The extraction behavior of Ir(IV) in a phosphonium-based ionic liquid (IL) system, triethyl-n-pentyl phosphonium bis(trifluoromethyl-sulfonyl)amide ([P2225][NTf2]), was investigated using an amine extractant. In addition, the electrochemical behavior of the extracted Ir(IV) species in [P2225][NTf2] during electrodeposition was studied. Voltammetry-based electrochemical analysis revealed that the reduction of Ir(IV) proceeded via an intermediate Ir(III) species in two steps, namely, Ir(IV) + e− → Ir(III) and Ir(III) + 3e− → Ir(0). Diffusion coefficients of the extracted Ir(IV) species in the IL were determined over the temperature range of 298–373 K using semi-integral and semi-differential analyses, and values obtained from the two analyses were consistent with each other. Furthermore, consecutive solvent extraction and electrodeposition of Ir metal in the IL bath were performed for 10 cycles. The entire Ir electrodeposit was in the metallic state, as is evident from the 4f 7/2 spectrum obtained by XPS.