Ion exchange resins for gold cyanide extraction containing a piperazine functionality, 1 : synthesis and physico-chemical properties

The synthesis of two types of metal-chelating resins incorporating gold-specific piperazine groups is described. PS-PIP is a styrene-divinylbenzene macroporous network. MC-PIP is a (glycidyl methacrylate)-co-(ethylene dimethacrylate) network. The nominal functional group concentrations are 1.84 mmol/g for PS-PIP and 1.14 mmol/g for MC-PIP. The proton exchange capacity is 1.95 mmol/g for PS-PIP and 0.91 mmol/g for MC-PIP. Accurate titration curves were used to determine pKa values (pKH = 7.05 ± 0.12). XPS analyses of PS-PIP resin were followed as a function of pH (cf. Fig. 8) demonstrating that the protonation of the amine is observable by a shift in binding energy of the N (1s) peak (±1.6 eV) moving from tertiary amine form (N (1s) 399.7 eV) to the protonated tertiary amine form (N (1s) 401.3 eV). Additionally, the presence of quaternary ammonium groups was detected at a N (1s) peak at 402.3 eV (cf. Fig. 9). Metal extraction from cyanide solutions, including Brazilian mine leach solution, showed considerable preference for gold (cf. Fig. 11–12). The piperazine resins extract gold via two mechanisms: (a) ligand substitution reactions at pH > 7.05 (pKH(a)) or (b) anion exchange reactions via the quaternary ammonium groups at high pH values. Extraction profiles were S-shaped (cf. Fig. 10) with 50% extraction ability at pH 8.0. Cyclic experiments involving extraction, elution, regeneration and recomplexation (cf. Tab. 6 and 7) showed the ability of MC-PIP to perform consistently at high extraction efficiencies from pH 8.6