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

Abstract

Biomining 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 sulphide flotation tailing at high pulp densities was investigated and information for the high cyanide consumption commonly reported in bio-oxidative processes are discussed in order to promote less use of this chemical reagent during cyanidation. RESULTS: Different reactors were compared alongside the performance of strains of At. ferrooxidans and S. thermosulfidooxidans. Shaking flasks tests performed using 5% solids (w/v) revealed that the mesophiles presented a faster adaptation to the solids and resulted in better tailings oxidation as compared to the moderate thermophile. Rolling bottles (pilot scale rotating-drum) experiments, carried out afterwards, enabled the adaptation of the At. ferrooxidans strain to 20% solids (w/v). This adapted strain was thus utilized in a 10 litrestirred 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-oxidised material. The cyanide consumption varied from 6.9kg/t to 13.7kg/t as the initial Fe2+ concentration increased from 0.0g/L to 10.0g/L Fe2+, respectively in the shaking flasks. CONCLUSION: Higher pulp densities (20% solids (w/v)) resulted in a lower cyanide consumption, which was around 7.0kg/t in the experiments carried out in both rolling bottle and stirred tank reactor when 5.0g/L Fe2+ was used during bio-oxidation. This cyanide consumption was associated to a gold extraction around 95%.