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-sp ecific piperazine groups is described. PS-PIP is a styrene-divinylbenzene m acroporous network. MC-PIP is a (glycidyl methacrylate)-co-(ethylene dimeth acrylate) network. The nominal functional group concentrations are 1.84 mmo l/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 curve s were used to determine pK(a) values (pK(H) = 7.05 +/- 0.12). XPS analyses of PS-PIP resin were followed as a function of pH (ef. Fig. 8) demonstrati ng that the protonation of the amine is observable by a shift in binding en ergy of the N (1s) peak (+/-1.6 eV) moving from tertiary amine form (N (1s) 401.3 eV). Additionally, the presence of quaternary ammonium groups was de tected at a N (1s) peak at 402.3 eV (cf. Fig 9). Metal extraction from cyan ide solutions, including Brazilian mine leach solution, showed considerable preference for gold (cf. Fig 11-12). The piperazine resins extract gold vi a two mechanisms (a) ligand substitution reactions at pH > 7.05 (pK(H(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% extracti on ability at pH 8.0. Cyclic experiments involving extraction, elution, reg eneration and recomplexation (cf. Tab. 6 and 7) showed the ability of MC-PI P to perform consistently at high extraction efficiencies from pH 8.6.