Bio-oxidation of refractory gold ores containing stibnite and gudmundite

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

“…As a result the final bacterial population was 10 7 cells mL −1 in the test at 50°C as compared to 10 8 cells mL −1 observed in the case of the At. ferrooxidans strain (32°C) (similar observations were reported by de Carvalho et al 4 ). This justifies the higher arsenic concentrations observed in the test with the latter strain.…”

“…This outcome confirms the refractoriness of the tailings under study, as gold was locked inside the sulfide grains although this metal was not observed in SEM-EDS analyses due to its microscopic size. In previous studies with the same ore, de Carvalho et al 4 also did not detect gold using SEM-EDS in the same flotation tailings (0.64 g t −1 gold) or even in the concentrate (78.0 g t −1 gold). In addition, the effect of the ferrous iron concentration on gold extraction depended on the type of reactor.…”

“…1,2 In the gold industry, biomining is traditionally applied to the processing of refractory ores. These ores are characterized by low gold extractions (<80%) when subjected to direct cyanidation even after fine grinding 3,4 because the gold particles are locked inside sulfide minerals, usually pyrite (FeS 2 ) and arsenopyrite (FeAsS). 2,5,6 In such cases, the term bio-oxidation is applied because the gold particles are not dissolved by the microorganisms, as in other bioleaching processes, and gold is recovered in a subsequent step, usually via cyanidation.…”

“…Regardless, this biotechnology is still the theme of several studies 1,2,4,5,[8][9][10][11] and extractions above 85% are commonly reported. 2,4,5,8,10 For instance, 86% gold extraction was achieved through cyanidation from both a gold-bearing sulfide concentrate and a flotation tailing bio-oxidized by Acidithiobacillus ferrooxidans at 32°C, 10% (w/v) pulp density, pH 1.75, 5.0 g L −1 Fe 2+ with a residence time of 14 days. Besides that, the gold extraction was only 21% for the non-bio-oxidized material samples.…”

“…Besides that, the gold extraction was only 21% for the non-bio-oxidized material samples. 4 Experiments with a higher pulp density (15% w/v) of refractory pyrite-arsenopyrite gold-bearing concentrates were carried out by Hu et al, 2 who attained 94% gold extraction with a residence time of 10 days. The bacterial community was composed of species belonging to the Acidithiobacillus, Leptospirillum, Ferroplasma and Sulfobacillus genera and the temperature was maintained in the range 42-45°C.…”