BACKGROUND Recycling of spent platinum group metals (PGMs) has attracted much attention in order to overcome the problems associated with the low natural abundance of these resources. To recycle such metals, efficient hydrometallurgical processes are required. To improve the efficiency of these processes, we have designed a new phosphonium‐based ionic liquid as an extraction solvent. This paper reports on the potential use of the ionic liquid for extraction and separation of PGMs, namely Pt(IV), Pd(II), and Rh(III). RESULTS An ionic liquid, trioctyl(dodecyl)phosphonium chloride, P88812Cl, which was newly synthesized, showed highly efficient extraction for Pt(IV), Pd(II), and Rh(III). P88812Cl features several advantages as an extraction solvent, such as high hydrophobicity and low viscosity compared with those features of a commercial analogue, trihexyl(tetradecyl)phosphonium chloride (P66614Cl). The favorable features of our novel ionic liquid were reflected by its high extraction efficiency and low release of phosphorus from the ionic liquid into the aqueous feed solution. Stripping operations were possible, and the high reusability of the ionic liquid was confirmed. CONCLUSION The novel ionic liquid P88812Cl is potentially useful as an extraction solvent for PGMs. Results highlight the strengths of ionic liquids and the tuneability of their properties through design of their molecular structure. © 2017 Society of Chemical Industry

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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 8,8,8,12 Cl), 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 Na 2 SO 3 . The Pd(II) and Rh(III) were selectively recovered from the IL using 1 mol L −1 CS(NH 2 ) 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.

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