Kinetics of gold loading from bromide solution onto an anion exchange resin

Abstract

The kinetics of loading of gold from bromide solution onto an anion exchange resin, PAZ-4, was investigated in a batch stirred reactor. The initial loading rate was described mathematically by a first-order reaction rate equation. The effect of such variables as agitation speed, temperature, resin particle size, resin concentration, initial concentration of gold and bromine in solution on the rate was investigated. The model described fairly accurately the loading process in terms of the variables investigated. The rate constant for the initial loading ranged from 0.5 to 1.3×10 −3 sec −1 and the half-time was 9.3 to 56 minutes. The initial rate constant increased with increasing temperature under the conditions investigated with an activation energy of 15.7 kJ/mole (3.8 kcal/mole). The rate constant was directly proportional to the concentration of the resin in solution. The subsequent reduction reaction was also modeled by the first-order rate equation and the apparent rate constant was estimated to be 3.0×10 −6 sec −1 with a half-time of about 44 hours. The loading kinetics involve two major processes: (i) the initial rapid loading dominated by ion exchange-type adsorption, and (ii) the slow electron exchange reduction reaction which becomes dominant only after the completion of the ion exchange process.