Ion-exchange sorbents for precious metal recovery: Design, mechanisms, and regeneration

Recovery of precious metals (Au, Pd, Pt, Ag) from chloride- and nitrate-containing leachates, electroplating effluents, spent catalyst solutions, and electronic-waste liquors is increasingly shaped by the need for high selectivity at low concentrations, resistance to aggressive media, and sustainable regeneration. Ion-exchange and chelating sorbents bearing soft donor functionalities are particularly effective because noble metal ions commonly exist as stable chloro-complexes (e.g., [AuCl₄]⁻, [PdCl₄]²⁻, [PtCl₆]²⁻) and exhibit strong affinity toward sulfur-containing ligands. This review focuses on thiophosphonate/ thiophosphoryl-derived and (di)thiocarbamate/thiocarbamate-derived functional motifs immobilized on polymer matrices (styrene–divinylbenzene, acrylic, cellulose/chitosan derivatives) and on solvent-impregnated resins (SIRs) incorporating dithio(phosphinate/phosphate) extractants. We critically analyze design principles (matrix morphology, spacer engineering, functional group density), adsorption/ion-exchange mechanisms (outer-sphere ion exchange, inner-sphere S,S-coordination, ligand exchange, reduction–deposition pathways), kinetics/isotherms, selectivity under high chloride strength, and process-relevant regeneration schemes. Key limitations-oxidative aging of sulfur sites, diffusion constraints in macroporous beads, incomplete stripping of strongly bound Pd species, and loss of impregnated carriers-are discussed alongside emerging strategies such as covalent tethering of thiophosphoryl ligands, mixed-donor architectures, redox-tuned regeneration, and column-scale validation.

کلیدواژه ها:

precious metal recovery ، ion-exchange ، thiophosphonate ، thiophosphoryl ، thiocarbamate ، Dithiocarbamate ، Solvent-impregnated resin