Loading of gold bromo species onto anion exchange resin

Abstract

The loading characteristics of gold-bromo species onto an anion exchange resin were evaluated using a batch system. The observed apparent saturation capacity for gold-bromo species by the resin was found to be 64 meq Au/g dry resin (4000 kg Au/tonne resin), substantially higher than the salt-splitting capacity of 12.5 meq Cl/g. The overall extraction of gold onto the resin continues indefinitely (within the experimental range) so long as there is gold in solution, and it appears to be irreversible. Therefore equilibrium considerations were not of much use, but rate considerations were important. The loading capacity increased with increasing temperature and decreasing initial gold concentration in solution. The apparent saturation capacity was proportional to the ratio of mass of gold in solution to mass of adsorbent used. The correlation between the apparent saturation capacity and the ratio was described by an empirical linear equation. The mechanism for the loading of gold-bromo species onto the resin is postulated to consist of the initial adsorption of Au[Br 4] − species by a simple ion exchange process and the reduction of ionic gold species to elemental Au 0 by an electron exchange reduction reaction. Elution of gold from the loaded resin was feasible provided the resin had not been loaded to high capacity levels. If the gold loading is carried to high levels, complete elution becomes impractical and the gold may be recovered by ashing the loaded resin. The abnormally high loading capacity of the resin for gold may have potential economic benefits for the bromine process for gold recovery.