Recovery of indium based on the combined methods of ionic liquid extraction and electrodeposition

Publication date: 7 August 2018
Source:Separation and Purification Technology, Volume 201
Author(s): Masahiko Matsumiya, Maori Sumi, Yuuki Uchino, Itaru Yanagi
The diluent characteristics and the wide electrochemical window of the ionic liquid (IL), n-hexyl-trimethyl ammonium bis(trifluoromethyl-sulfonyl)amide; [N1116][TFSA], have been exploited for the extraction of In(III) from 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methane sulfonamide (H[TFSA]) aqueous solution using 1.0 M tri-n-butylphosphate (TBP) in [N1116][TFSA], followed by direct electrodeposition as In metal from organic phase. The extraction mechanism of In(III) with TBP/[N1116][TFSA] has been investigated from the slope analysis. As a result, it was revealed that the extraction mechanism of In(III) in IL system was based on the following solvation extraction by TBP and the [N1116⁺] cation exchange extraction; [In(III)]aq + 3[TBP]IL + [N1116][TFSA]IL + 2[TFSA⁻]aq ↔ [In(TBP)3³⁺(TFSA⁻)3]IL + [N1116⁺]aq. Moreover, the selective extraction of In(III) from the aqueous phase including Ni(II) and Zn(II) was performed in the range of pH = 1.5–4.0.The electrochemical behavior of extracted [In(TBP)3³⁺] complex in [N1116][TFSA] on a platinum quartz crystal electrode was investigate by EQCM analysis. The reduction peak at −1.0 V was assigned at the [In(TBP)3³⁺]/In(0) couple on the voltammogram. Potentiostatic electrodeposition of [In(TBP)3³⁺] at −1.0 V allowed us to obtain the blackish electrodeposits, which were identified as most of In metal by EDX and XRD analyses.

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