Precious metal recovery by porous polymers

Abstract

Urban mining of precious metals from electronic waste (e-waste) has been gaining attention these days as profitable and eco-friendly business. Currently, urban mining is conducted by pyrometallurgy and hydrometallurgy techniques. As a more sustainable method than pyrometallurgy, many adsorbents have been developed to recover precious metals from e-waste leachate in hydrometallurgy processes. However, selective recovery of precious metals from e-waste solution is still challenging, since precious metals exist at very low concentrations compared to other common metals. In this study, 10 different covalent organic polymers (COPs) with chelate functionality were newly developed to selectively capture precious metals. Four of phenazine-linked porphyrin polymers and three of alkyl-linked porphyrin polymers exhibited remarkable selectivity toward precious metals, especially gold with fast adsorption and high capacities. Nitrile, amidoxime, and pyrazole-based polymers showed the control of metal adsorption properties by employing different functional groups. The developed polymers were investigated in the aspects of metal selectivity, capacity, chemisorption, reduction mechanism, adsorption kinetics, and desorption. Furthermore, the polymers could recover the gold effectively from actual e-waste eluate, confirming the practical applicability of the developed polymers.