Effect of grain size on the bacterial oxidation of a refractory gold sulfide concentrate and its dissolution by cyanidation

Abstract

Bacterial oxidation was used to pre-treat a refractory gold sulfide concentrate obtained from the flotation of a gold ore from Madagascar. A mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was used to oxidize the sulfides. The major form of sulfide was pyrite, which represented approximately 24.8% of the mineralogical composition of the concentrate. During the bacterial pre-oxidation, three grain sizes (D80: 75 µm, 38 µm, and 12 µm) were considered with two pulp densities (10% and 20% solids). After 14 d of bacterial oxidation, the bioleached residues were treated using the conventional cyanidation method. After 48 h of cyanidation for the residue bioleached with 10% solids and D80 of 75 μm, 38 µm, and 12 µm, the gold dissolution yields were 49%, 64%, and 83%, respectively. Similarly, for the residue with 20% solids, the gold dissolution yields by cyanidation were 48%, 65%, and 91%, respectively. For cyanidation alone, the gold dissolution yields were 51%, 52%, and 68%, respectively. Based on these results, bacterial pre-oxidation with the finer D80 of 12 µm and 20% solids provided a 20% gain in refractory gold dissolution compared to cyanidation alone.