Application of a Novel Phosphonium-Based Ionic Liquid to the Separation of Platinum Group Metals from Automobile Catalyst Leach Liquor

The recovery of platinum group metals (PGMs) from automotive exhaust catalysts is important, and hydrometallurgical extraction is an effective approach. In the present study, a newly designed phosphonium-based ionic liquid (IL) was applied to the separation and recovery of PGMs from an automobile catalyst leach liquor in conjunction with varying pH levels. This IL, trioctyldodecyl phosphonium chloride (P_8,8,8,12Cl), allows quantitative extraction of Pd(II) at any HCl concentration, with almost 80% removal of Rh(III) at 1 mol L^-1 HCl after two extractions. Significant amounts of Fe(III) were extracted into the IL phase, but could be removed using 1 mol L^-1 Na₂SO₃. The Pd(II) and Rh(III) were selectively recovered from the IL using 1 mol L^-1 CS(NH₂)₂ and 5 mol L^-1 HCl, respectively. This work therefore demonstrated the selective recovery of PGMs through optimization of various parameters and shows the significant potential of this IL with regard to recycling PGMs from leach liquor.