Separation of Pt(IV), Pd(II), Ru(III) and Rh(III) from model chloride solutions by liquid-liquid extraction with phosphonium ionic liquids

Abstract

The recovery of metals from waste is profitable not only from an economic but also from an ecological point of view. The natural resources of metals (especially platinum group metals – PGM) are limited, while the amount of waste containing the desired metals is still growing. The purpose of the work is the use of quaternary phosphonium salts, i.e. Cyphos IL 101 (trihexyl(tetradecyl)phosphonium chloride), Cyphos IL 102 (trihexyl(tetradecyl)phosphonium bromide) and Cyphos IL 104 (trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate), for the separation of palladium(II), platinum(IV), rhodium(III) and ruthenium(III) from their multi-component model mixtures of composition based on real solutions after leaching of PGM-containing wastes (e.g. automobile catalytic converters). Though, Pd(II) could not be separated from Pt(IV) by one-stage extraction, separation of Pd(II) from Pt(IV) was possible by stripping with 0.1 M thiourea in 0.5 M HCl. The extraction of Rh(III) from the four-component solution practically did not occur (Rh(III) stayed in raffinate), therefore Pt(IV) and Pd(II) could be selectively separated from Rh(III). As a result of the work, a separation procedure of successful separatation of Pd(II), Pt(IV), Ru(III) Rh(III) from four-component solutions has been developed based on two stages of extraction with ionic liquid solution (trihexyl(tetradecyl)phosphonium chloride) and two stages of stripping.