A. Warshawsky et al., Ion exchange resins for gold cyanide extraction containing a piperazine functionality, 1 - Synthesis and physico-chemical properties, MACRO MAT E, 283(10), 2000, pp. 103-114
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.