Synthesis and characterization of a copolymer with pendant weak base groups suitable for the separation of gold(III) from base metals in chloride media

Abstract

A new copolymer has been prepared by reaction of chloromethylated polystyrene (Amberlite XE 305) with 1,3,4-thiadiazole-2-amino-5-thiol so that the pendant group is covalently bound to the polymer through the thiol group. There was no evidence for free thiol groups in the copolymer, which behaves as a weak base resin in which the active amine group is adjacent to the aromatic thiadiazole ring. The copolymer is able to extract gold as [AuCl 4] − from 0.05 to 6 M hydrochloric acid. The base metals cobalt and nickel were rejected over this range. Iron(III) was extracted from strongly acid solutions (greater than 3 M). The capacity of the copolymer for gold and the base metals varied with acid concentration but in 2 M HCl the capacity for gold was 1.9 mmol g −1 and negligible for the above base metals and copper(II). The gold may be quantitatively eluted with acidic thiourea from which it may be recovered using direct chlorination. A cross-sectional elemental scan using an X-ray microprobe indicated that S, Cl and Au were evenly distributed throughout the bead.