Modification and preparation of polymeric adsorbents for precious-metal extraction in hydrometallurgical processes

Abstract

This paper describes the efforts made to develop polymeric adsorbents that could be applied to the recovery of precious metals (Au, Pt, Pd and Rh) from cyanide leaching solutions. The polymeric adsorbents prepared should fit they following criteria: be compatible with the nature of the leaching solutions concerned; have good selectivity patterns against the other metal cyanides; have good elution properties and be compatible on integrated systems of leaching and extraction (resin-in-pulp (RIP) and resin-in-leach (RIL)). Knowledge of the chemical speciation of the target metals in the leaching solutions to be treated and the nature and structure of the metal complex to be extracted is very important in understanding the metal-extraction reactions and selectivity factors. As selectivity patterns are greatly influenced by the polymer structure, ionic density and hydrophilic/hydrophobic nature of the polymeric supports, the definition of the structure and functionality of the polymeric supports has been based on the chemical speciation as one of the more effective options fbr polymer support selection. Two methods have been used in selecting polymeric adsorbents: commercial ion-exchange resins and ion-exchange impregnated resins prepared by physical immobilisation of selective and specific reagents used, in solvent extraction onto high surface polymeric materials. Both types of material were evaluated in two applications: extraction and recovery of gold cyanide from leaching liquors and recovery of Pt, Pd and Rh from leaching solutions obtained on cyanidation steps of automobile catalytic converters. The introduction of both polymeric materials is directed towards the selective recovery of gold and precious metals (Pt, Pd, Rh) as an alternative to defined processes based on adsorption steps by activated carbon and/or precipitation by thermal processes.