Separation of Pt(IV), Pd(II), Ru(III), and Rh(III) from chloride medium using liquid-liquid extraction with mixed imidazolium-based ionic liquids

A reasonable project was presented for the extraction and separation of Pt(IV), Pd(II), Ru(III), and Rh(III) from the mixed imidazolium-based ionic liquids (ILs) [C(6)mim]Cl, [C(6)mim][NTf2], and [C(6)mim][DDTC]. Pt(IV) was first separated from other three platinum group metals with a mixture of [C(6)mim]Cl and [C(6)mim][NTf2]. Then, separation of Pd(II) and Ru(III) from Rh(III) was realized by changing the concentration of [C(6)mim][DDTC]. Back-extraction of Pt(IV), Pd(II), and Ru(III) from loaded hydrophobic phase and the recovery of Rh(III) in aqueous phase were also investigated. Mechanisms between Pd(II)/Ru(III) and [C(6)mim][DDTC] were further explored using ultraviolet spectrophotometry (UV-Vis), infrared spectrophotometry (FTIR), the method of continuous variations, ab initio quantum chemical studies, and X-ray crystallographic analysis. The results afford more directions for extracting and separating metals by introducing devisable functionalized group into ILs.