Recovering gold from mine tailings: a selection of reactors for bio‐oxidation at high pulp densities

Abstract

AbstractBACKGROUNDBiomining is one of the few cost‐effective technologies that can be applied to low‐grade ores and also mining tailings. In the current work, the bio‐oxidation of a gold sulfide flotation tailing at high pulp densities was investigated and information concerning the high cyanide consumption commonly reported in bio‐oxidative processes is discussed in order to promote less use of this chemical reagent during cyanidation.RESULTSVarious reactors were compared alongside the performance of strains of At. ferrooxidans and S. thermosulfidooxidans. Shaking flask tests performed using 5% (w/v) solids revealed that the mesophiles presented a faster adaptation to the solids and resulted in better tailings oxidation as compared to the moderate thermophile. Rolling bottle (pilot‐scale rotating drum) experiments, carried out afterwards, enabled the adaptation of the At. ferrooxidans strain to 20% (w/v) solids. This adapted strain was thus utilized in a 10 L stirred tank reactor (pilot‐scale stirred tank) experiment at the same pulp density. The concentration of the ferrous iron used in the bio‐oxidation step had a detrimental effect on the cyanide consumption during cyanidation of the bio‐oxidized material. The cyanide consumption varied from 6.9 to 13.7 kg t−1 as the initial Fe2+ concentration increased from 0.0 to 10.0 g L−1 Fe2+, respectively, in the shaking flasks.CONCLUSIONSHigher pulp densities (20% (w/v) solids) resulted in a lower cyanide consumption, which was around 7.0 kg t−1 in the experiments carried out in both rolling bottle and stirred tank reactors when 5.0 g L−1 Fe2+ was used during bio‐oxidation. This cyanide consumption was associated with a gold extraction of around 95%.