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In this study, four novel functionalized ionic liquids ([C4mim][DDTC], [C5mim][DDTC], [C6mim][DDTC], and [BMPip][DDTC]) were synthesized and used for the selective extraction of Pd(II) from an HCl medium containing Pt(IV), Pd(II), and Rh(III). The extraction mechanism was investigated using Job’s plots, UV–Vis, SXRD, and MS analysis. A mechanistic investigation revealed the formation of hydrophobic extraction complexes Pd(DDTC)2 and PdClDDTC via coordination between [DDTC]− and Pd(II). In addition, the solubility and polarity of the solutes were investigated using DFT calculations to determine the optimal extractant and diluent. From the results of the theoretical analysis, [C5mim][DDTC]/CHCl3 was selected as the optimum system for the selective extraction of Pd(II). The effects that factors have on Pd(II) extraction, including temperature, [C5mim][DDTC] amount, HCl concentration, and O/A ratio, were investigated and optimized using single-factor and response surface experiments. Under the optimized conditions, Pd(II) extraction efficiencies were higher than 99%, and the separation factors (βPd(II)/Pt(IV) and βPd(II)/Rh(III)) were greater than 104. After extraction, Pd and Rh were directly recovered from the organic and aqueous phases via photocatalytic reduction, respectively. TEM, XPS, and PXRD results revealed that the resulting nanoparticles were Rh(0) or Pd(0). The recovery of Pd and Rh exceeded 95%. Overall, a simple hydrometallurgical process with low reagent consumption was developed to yield nanometer-scale Pd(0) and Rh(0) from simulated secondary resource leaching solutions.

In this study, based on a cyano-functionalized ionic liquid, 1-nitrile-1-octylpyrrole bromide ([C8Y3Pr]Br), a [C8Y3Pr]Br/cyclohexane/tributyl phosphate (TBP)/NaCl microemulsion system was constructed and used for the extraction of Pd(II) and preparation of Pd nanoparticles from multimetal solutions. The key extraction parameters including vibration time, [C8Y3Pr]Br concentration, phase ratio (RW/O), and HCl concentration were evaluated. Compared with other ionic-liquid microemulsion systems, the cyano-functionalized ionic liquid [C8Y3Pr]Br microemulsion system showed excellent extraction performance for Pd(II). Almost all Pd(II) was extracted (>98.0%) from a multimetal solution using the microemulsion system, while the separation factors (βPd/M) of [C8Y3Pr]Br-based microemulsions for Pd(II) with Cu2+, Fe3+, Ni2+, Zn2+, Co2+, and Mg2+ exceeded 1.0 × 103. The mechanism extracting Pd(II) using [C8Y3Pr]Br was confirmed to be an anion-exchange reaction via Job’s method, spectral analysis (UV, FTIR), and DFT calculations. Alcohols and hydrazine hydrate were used as demulsifiers, and Pd nanoparticles were directly obtained from the microemulsion phase. The Pd nanoparticles were identified by TEM, XPS, and XRD analyses. The chemical structures of extracted species based on the microemulsion system and the mechanism of demulsification of alcohols were studied. Thus, an effective new process was developed in this study for the direct preparation of Pd nanoparticles from mixed metal solutions via solvent extraction.

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.