Influence of the structure of chelating resins with guanidyl groups on gold sorption

Abstract

The chemical composition and structure of copolymers determines modification degree, concentration of ligands, their accessibility and hence capacity and selectivity of chelating resins. In order to investigate all such influences, a new series of copolymers have been obtained: one with increased polarity and hydrophilicity of polymer surface has been synthesized from vinyl benzyl chloride (VBC), methyl methacrylate (MM) and divinylbenzene (DVB) mixture, another one with toluene and hexadecane as inert diluents. As was expected copolymers synthesized in the presence of hexadecane, which is thermodynamically poor for the mixture of monomers, are porous with small pores (less than 1.8 nm radius) and with macropores (radius bigger than 17 nm). After modification with aminoguanidine bicarbonate, resins with the ligand concentration in the range 1–2 mmol/g are more hydrophilic but porosity decreases due to the elasticity of networks. The copolymers and resins obtained in the presence of toluene have a gel expanded structure. The ability of resins to remove dicyanoaurate complexes has been tested under the following conditions: an excess of potassium cyanide, 50 mg/l of dicyanoaurate concentration and ratio of aminoguanidine ligands to gold complexes 7.7:1. Under these conditions the sorption for the concentration of ligands of 1.2 mmol/g was about 23 mg/g and for 2.0 mmol/g it was 30 mg/g. Sorption of gold increases with increased ligand content. Sorption of gold at pH 7 is higher than at pH 9.5 and at 13.5 comparable to that at pH 9.5. Lowering dicyanoaurate concentration to 5 mg/l decreases the sorption of gold, but when the ligand to dicyanoaurate anions ratio is 1.1:1 the sorption reaches 30 mg of gold/g, which corresponds to a distribution coefficient of 6900. However, better sorption at low ligand to dicyanoaurate ratio is accompanied by much lower extraction degree and distribution coefficient.