Scholarly record
EFFECT OF ORGANIC NUTRIENTS ON BIOOXIDATION OF SULFIDE CONCENTRATE IN BATCH EXPERIMENT AT DIFFERENT TEMPERATURES
Abstract
Biohydrometallurgical technologies based on the oxidation of sulfide minerals by iron- and sulfur-oxidizing acidophilic microorganisms are widely used to extract non-ferrous and noble metals from sulfide ores and concentrates. Acidophilic microorganisms oxidizing sulfide minerals include autotrophs, heterotrophs, and mixotrophs. Therefore, studying of the effect of different carbon sources on biooxidation of sulfide minerals is relevant issue. The goal of the present work was to study the effect of different organic nutrients (yeast extract and molasses) on the biooxidation of pyrite-arsenopyrite concentrate. Representatives of microorganisms predominant in biohydrometallurgical processes (strains Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans SH-1, and Acidiplasma sp. MBA-1) were used for the experiment. Sulfide concentrate containing 48% of pyrite and 9% of arsenopyrite was the subject of the study. The experiments were carried out in flasks with 100 mL of liquid mineral nutrient medium and 2 g of the concentrate on a rotary shaker for 30 days at temperatures of 40 to 55°?. The medium was supplemented with 0.02% of yeast extract or molasses. In control variant, the medium did not contain organic nutrients (autotrophic conditions). Addition of organic nutrients considerably affected bioleaching activity at 55°?. At 55°? under autotrophic conditions, pH was significantly higher, while Eh and Fe3+ and As concentrations were significantly lower than at temperatures of 40 to 50°?. In the experiments with organic nutrients, the increase in the temperature up to 55°? affected bioleaching activity to a lesser degree. It may be explained by the fact that among three strains used in the study, only A. caldus MBC-1 is autotrophic microorganism that capable of sulfur oxidation. Mixo- and heterotrophic strains S. thermosulfidooxidans SH-1 and Acidiplasma sp. MBA-1, which depend on organic carbon sources, are active iron oxidizers and play the most important role in biooxidation of sulfide concentrates. As the strain A. caldus MBC-1 is not active at 55°C, it was not able to provide iron-oxidizing strains with organic carbon source. Under autotrophic conditions, biooxidation activity at 40?50°? was almost as high as in the presence of organic nutrients, while at 55°?, biooxidation activity strongly depended on their presence. The addition of organic nutrients may be promising approach to increase the rate of biooxidation of sulfide minerals and provide opportunity to stabilize the activity of microbial population at high temperatures at which autotrophic microorganisms may not provide mixo- and heterotrophs with organic carbon source. Molasses that is the waste of the food industry may be used as organic nutrient, which provides as high activity as yeast extract that usually used for cultivation of mixo- and heterotrophic acidophiles. Hence, organic wastes may be used to improve the efficiency of biohydrometallurgical processes.
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