Au Recovery Using an Activated Carbon Column

Abstract

The feasibility of a process involving the use of activated carbon in a multistage column (NIMCIX contactor) for the recovery of gold from unclarified pregnant solutions was investigated on pilot-plant scale. It was found that satisfactory extractions, corresponding to a recovery of 99.6 percent, can be achieved with an average gold concentration of 0.0077 p.p.m. in the barren solutions from a feed averaging 1.89 p.p.m. The results show that excessive loading of CaCO3 can be prevented by lowering of the pH of the feed to about 7.6. This obviates the need for the carbon to be treated with hydrochloric acid. The gold was eluted from the carbon by the Zadra procedure. The operating conditions of the elution and electrowinning circuits are reported, and the elution of the gold and other metals is discussed. The reactivation of the carbon, which was carried out in a vibrating-deck kiln, is described, and the effects of this reactivation on the activity of the carbon and its microstructure are also discussed. The consumption of reagents in the adsorption and elution circuits is presented in sufficient detail to allow the potential of the activated-carbon process as an alternative to the Merrill-Crowe process for the treatment of high-grade solutions to be evaluated. In addition, the results of parallel small-scale investigations on the effect of pH on the loading of CaCO3, gold, and other metals on activated carbon are presented and discussed briefly.