Pilot-scale tank biooxidation of gold bearing arsenopyrite concentrates
This article shows the results of experimental tests of bacterial oxidation of arsenopyrite gold concentrate that contains gold (60 g/t), sulfides (23 %), iron (26 %) and arsenic (11 %). A consortium, consisting of the mesophilic strain Acidithiobacillus ferrooxidans AF-2 and moderately thermophilic strains of Sulfobacillus thermosulfidooxidans OT-1 and Sulfobacillus thermosulfidooxidans SK-4, was used in the test. The tests were carried out on the equipment, consisting of 6 reactors with a volume of 1.5 m<sup>3</sup> each. The concentration of solids in the pulp was maintained at 20 % (w/w). In the process of optimizing the parameters of the bacterial oxidation plant, the retention time of the concentrate was reduced from 12 to 6 days. During the test, the destruction of sulfides was over 90 %, which provided gold recovery from biooxidation products by cyanide leaching over 94 %. In addition, the average gold recovery rate reached 95 %. The removal of arsenic from the leaching solutions was carried out by means of two-stage neutralization with calcium carbonate. Due to high oxidation degree maintained throughout the entire operation of the experimental plant, a high ratio of iron to arsenic concentration in the solution was observed, which provided ideal conditions for arsenic precipitation in the form of trivalent iron arsenate. Determination of the stability of precipitate residuals was carried out according to the protocol Toxicity Characteristic Leaching Procedure (TCLP). The precipitate obtained after neutralization of the leaching solution does not require special disposal, since the final concentration of arsenic in the extracts of TCLP tests was 0.14 mg/L.