Selective recovery of palladium and rhodium by combined extraction and photocatalytic reduction

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 (beta Pd(II)/Pt(IV) and beta Pd(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.

Automated summary

In this study, four novel functionalized ionic liquids were synthesized and used for the selective extraction of Pd(II) from an HCl medium containing Pt(IV), Pd(II), and Rh(III). The optimal system of [C5mim][DDTC]/CHCl3 was selected based on theoretical analysis, resulting in Pd(II) extraction efficiencies higher than 99%. Factors affecting Pd(II) extraction were investigated and optimized, achieving separation factors greater than 104. Overall, a simple hydrometallurgical process was developed to yield nanometer-scale Pd(0) and Rh(0) with high recovery rates from simulated secondary resource leaching solutions.