Issue 23, 2020

Separation of precious metals by split-anion extraction using water-saturated ionic liquids

Abstract

A split-anion solvent extraction process was developed for the separation of precious metal ions Au(III), Pt(IV), Pd(II) and Rh(III) from aqueous chloride media using water-saturated ionic liquids. The metal extraction and stripping behavior of the chloride form [A336][Cl], bromide form [A336][Br] and the iodide form [A336][I] of the quaternary ammonium ionic liquid Aliquat 336 were compared. The three ionic liquids extracted Au(III), Pd(II) and Pt(IV) quantitatively in most cases, whereas the co-extraction of Rh(III) was strongly dependent on the acidity and the chloride concentration. Among the studied ionic liquids, [A336][I] achieved the highest separation factors between Pd(II)/Rh(III), Pt(IV)/Rh(III), and Au(III)/Rh(III) at 6 mol L−1 Cl. Additionally, the selective stripping of the individual metal ions Pd(II), Au(III), and Pt(IV) was only possible from loaded [A336][I] using ammonia solution (NH4OH), sodium thiosulfate (Na2S2O3), and thiourea ((NH2)2CS), respectively. A closed-loop flow sheet was designed for the recovery of the precious metals from chloride media using split-anion extraction with [A336][I]. The integrated process was demonstrated to be suitable for the purification of Rh(III), Pt(IV) and Pd(II) from a complex metal feed such as the leachate of spent automotive catalysts. The ionic liquid-based split-anion extraction process is simple, selective and effective for the sustainable separation of the precious metals, using only one green extractant [A336][I], which can be regenerated for consecutive extraction-stripping cycles.

Graphical abstract: Separation of precious metals by split-anion extraction using water-saturated ionic liquids

Supplementary files

Article information

Article type
Paper
Submitted
10 Jul 2020
Accepted
02 Sep 2020
First published
06 Nov 2020
This article is Open Access
Creative Commons BY-NC license

Green Chem., 2020,22, 8375-8388

Separation of precious metals by split-anion extraction using water-saturated ionic liquids

V. T. Nguyen, S. Riaño and K. Binnemans, Green Chem., 2020, 22, 8375 DOI: 10.1039/D0GC02356F

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