Recovery of Pd(II) from Hydrochloric Acid Medium by Solvent Extraction-Direct Electrodeposition Using Hydrophilic/Hydrophobic ILs.

Mixed [Cbet]Br/[Cmim][NTf] ionic liquids were used as a new extraction system to extract Pd(II) from multimetal-ion solutions. The separation factors (M: Cu, Fe, Ni, Zn, Co) are greater than 10. Thiourea was found to be an effective stripping agent. After three cycles, the recovery efficiency was higher than 91.0%. Direct electrodeposition of palladium from the mixed ionic liquid phase was also studied. The Pd(II) complex in [Cbet]Br/[Cmim][NTf] system was studied by cyclic voltammetry at 348 K. The results indicate the existence of three types of Pd(II) complex in the [Cbet]Br/[Cmim][NTf] system, leading to three reductive waves. The reduction of Pd(II) to Pd(0) in this system is irreversible. A uniform black coating was obtained by constant-potential deposition at -1.7 V on a nickel foil, confirmed to be palladium metal by energy-dispersive spectrometry, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy analyses. After three cycles of continuous extraction-electrodeposition, over 90.0% of palladium was recovered.