Recovery of platinum by solvent extraction and direct electrodeposition using ionic liquid

• Published in: Separation and purification technology 2019-05, Vol.214, p.162-167
• Main Authors: Matsumiya, Masahiko, Song, Yueqi, Tsuchida, Yusuke, Ota, Hisashi, Tsunashima, Katsuhiko
• Format: Article
• Language: English
• Subjects: Direct electrodeposition; Electrochemistry; Ionic liquids; Platinum; Solvent extraction
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2018.06.018

•Pt(IV) was extracted by anion exchange mechanism with tri-n-octylamine hydrochloride in ionic liquids.•The electrochemical behavior of [R3NH]2[PtCl6], R = (CH2)7CH3 was investigated in ionic liquids.•Pt metal was recovered by direct electrodeposition of the loaded organic phase. The diluent characteristics and the wide electrochemical window of the ionic liquid (IL), triethyl-n-hexyl phosphonium bis(trifluoromethyl-sulfonyl)amide; [P2225][NTf2], has been exploited for the extraction of Pt(IV) using tri-n-octylamine (TOA, R3N, R = (CH2)7CH3) hydrochloride, followed by direct electrodeposition as Pt metal from organic phase. The extraction mechanism of Pt(IV) with [R3N·HCl]/[P2225][NTf2] has been investigated from the slope analysis. As a result, it was revealed that the extraction mechanism of Pt(IV) was based on the following anion exchange extraction; [PtCl62−]aq + 2[R3N·HCl]org ⇔ [R3NH]2[PtCl6]org + 2[Cl−]aq (R = (CH2)7CH3) The viscosity and the ionic conductivity for the [R3NH]2[PtCl6] were satisfied by Vogel-Fulcher-Tamman (VFT) equation and each best-fit parameter can be estimated in this study. The electrochemical behavior for [R3NH]2[PtCl6] in IL was investigated by Electrochemical Quartz Crystal Microbalance (EQCM) at 373 K. It was revealed that the cathodic reaction: Pt(IV) + 2e− → Pt(II) was estimated from 0 V to −0.87 V and Pt(II) + 2e− → Pt(0) was proceeded from −0.87 V to −1.13 V considering from Mapp = 178.5 evaluated by CV/EQCM. Moreover, the alternation of Δηρ (product of viscosity and density) was corresponded to the locally decrease of the viscosity of IL near the electrode. Finally, the potentiostatic electrodeposition of [R3NH]2[PtCl6] allowed us to recover the blackish electrodeposits, which were identified as most of Pt metal by EDX and XRD analyses.