Sustainable and Selective Modern Methods of Noble Metal Recycling

Abstract

Noble metals exhibit broad arrange of applications in industry and several aspects of human life which are becoming more and more prevalent in modern times. Due to their limited sources and constantly and consistently expanding demand, recycling of secondary and waste materials must accompany the traditional mineral extractions. This Minireview covers the most recent solvometallurgical developments in regeneration of Pd, Pt, Rh, Ru, Ir, Os, Ag and Au with emphasis on sustainability and selectivity. Processing-by selective oxidative dissolution, reductive precipitation, solvent extraction, co-precipitation, membrane transfer and trapping to solid media-of eligible multi-metal substrates for recycling from waste printed circuit boards to end-of-life automotive catalysts are discussed. Outlook for possible future direction for noble metal recycling is proposed with emphasis on sustainable approaches.

Keywords: Circular Economy; Gold; PGM; Recycling; Silver.

Figure 1

Annual production via mining and recycling of gold, silver and platinum group metals compared to annual consumption.[ ³ , ⁷ , ⁸ ]

Figure 2

Opportunities for selectivity and sustainability at different stages in solvometallurgical recycling of noble metals. Multi‐metal separation techniques can be roughly divided to (a) selective dissolution, (b) selective precipitation and (c) selective complexation combined with partitioning in different (liquid/liquid or solid/liquid) media.

Figure 3

Selective oxidative dissolution of PGM (and base metal) mixtures and selective reductive precipitation from dissolved mixture of PGMs (and other metals).

Figure 4

General approaches to separation of PGMs from each other and from base metals by solvent extraction. PGM ions are transported from acidic aqueous solutions to less polar organic solvents by formation of neutral inner‐ or outer‐sphere complexes or to ionic liquids by ion‐exchange reactions.

Figure 5

Selectivity and possibilities of sustainable approaches in solvometallurgical gold recycling. Gold can be dissolved in novel media (a–d) after metals with lower oxidations potential are removed first. Preferential dissolution (e) and time‐dependent dissolution (f) are also applicable. Separation of multi‐metal solutions can be achieved by selective coordination (g–k).

Figure 6

Ion exchange membranes selective separation of specified metal ions, Ag and Au.