Selective recovery of platinum by combining a novel reusable ionic liquid with electrodeposition

In this study, five new imidazolium ionic liquids (ILs) were synthesized, and their efficiencies toward the precipitation of PtCl62− in HCl media were evaluated. The prepared compounds were identified as 1-alkyl-3-propylimidazolium bromide ([CnPIm]Br, n = 12, 14, and 16), 1-tetradecyl-2-aminoethylimidazolium bromide ([C14PImNH2]Br), and 1-tetradecyl-3-butylimidazolium bromide ([C14PIm]Br). FT-IR, 1H NMR, and continuous variation method analysis were used to establish the ion-exchange model of Pt(IV) precipitation. To extract Pt(IV) from mixed metal solutions, and a novel mixed-ILs system was obtained through the dissolution of 1-tetradecyl-3-propylimidazolium bromide ([C14PIm]Br) in hydrophobic ILs ([C8MIm][PF6]). The mixed-ILs ([C14PIm]Br/[C8MIm][PF6]) exhibited excellent extraction efficiency compared to single [C8MIm][PF6]. Also, Pt(IV) ions were selectively separated from mixed metal solutions containing Rh(III), Fe3+, Ni2+, Cu2+, and Zn2+ metal ions. The separation factor βPt/M (M: Fe, Ni, Cu, Zn, or Rh) was above 105 for all systems. The optimal potentiostatic deposition voltage of Pt was estimated to −1.75 V. Direct electrodeposition from ILs containing [C14PIm]Br/[C8MIm][PF6] with Pt(IV), more than 97% of Pt(IV) was reduced to Pt(0) on the copper cathode, while the system could also be regenerated for PtCl62− extraction. Surface characterization techniques like SEM, TEM, and XPS identified the deposited silver-grey films on cathode surfaces as Pt metal with metallic luster.