Simple Amides and Amines for the Synergistic Recovery of Rhodium from Hydrochloric Acid by Solvent Extraction

Andrew I. Carrick, Euan D. Doidge, Alexander Bouch, Gary S. Nichol, Jane Patrick, Emma R. Schofield, Carole A. Morrison, Jason B. Love

Research output: Contribution to journalArticlepeer-review

Abstract

The separation and isolation of many of the platinum group metals (PGMs) is currently achieved commercially using solvent extraction processes. The extraction of rhodium is problematic however, as a variety of complexes of the form [RhCln(H2O)6-n](n−3)− are found in hydrochloric acid, making it difficult to design a reagent that can extract all the rhodium. In this work, the synergistic combination of a primary amine (2-ethylhexylamine, LA) with a primary amide (3,5,5-trimethylhexanamide, L1) is shown to extract over 85 % of rhodium from 4 M hydrochloric acid. Two rhodium complexes are shown to reside in the organic phase, the ion-pair [HLA]3[RhCl6] and the amide complex [HLA]2[RhCl5(L1)]; in the latter complex, the amide is tautomerized to its enol form and coordinated to the rhodium centre through the nitrogen atom. This insight highlights the need for ligands that target specific metal complexes in the aqueous phase and provides an efficient synergistic solution for the solvent extraction of rhodium.
Original languageEnglish
JournalChemistry - A European Journal
Early online date24 May 2021
DOIs
Publication statusE-pub ahead of print - 24 May 2021

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