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EFFECT OF ORGANIC NUTRIENTS ON BIOOXIDATION OF GOLD-BEARING REFRACTORY CONCENTRATE
Abstract
Biohydrometallurgical technologies based on the oxidation of sulfide minerals by acidophilic microorganisms oxidizing ferrous iron and sulfur are widely used for the extraction of non-ferrous and precious metals from sulfide ores and concentrates including gold-bearing refractory concentrates. Microorganisms involved in oxidation of sulfide minerals differ in ability to use sources of carbon for constructive metabolism and capable of both CO2 and organic nutrients assimilation. Their activity depends on availability of carbon sources and therefore application of additional organic sources may allow to increase the efficiency of biooxidation of sulfide concentrates. The goal of the present work was to evaluate the possibility to increase the efficiency of tank biooxidation of sulfide gold-bearing concentrate by addition of organic carbon source required for the constructive metabolism of acidophilic microorganisms oxidizing sulfide minerals. The concentrate contained 20.7% of iron, 3.63% of arsenic, 21.1% of sulfide sulfur, and 23.8 g/t of gold. Pyrite and arsenopyrite content comprised 34.7 and 7.9%, respectively. The concentrate was refractory and gold extraction by cyanidation did not exceed 15%. Biooxidation was performed in batch mode in laboratory scale reactors for 30 days. Pulp density was 20% (200 g of the concentrate and 1 L of mineral nutrient medium). Mixed culture of moderately thermophilic microorganisms used for biooxidation included strains Sulfobacillus thermosulfidooxidans VKMV 1269T, Acidithiobacillus caldus MBC-1, and Acidiplasma sp. MBA-1. In the first variant of the experiment, biooxidation was performed at 45°C without additional carbon sources (i.e. under autotrophic conditions). In the second and in the third variants, biooxidation was performed at 45°C and 55°C, respectively, and nutrient medium was supplemented with 0.02% of the yeast extract as organic carbon source. Biooxidation under autotrophic conditions made it possible to oxidize 65% of sulfide sulfur and increase gold extraction by cyanidation up to 73%. Biooxidation at 45°C using the medium supplemented with yeast extract, made it possible to oxidize 87% sulfide sulfur and increase gold extraction by cyanidation up to 81%. In the same time, biooxidation at 55°C made it possible to oxidize only 53% of sulfide sulfur and extract only 59% of gold. Thus, application of organic carbon source made it possible to increase biooxidation efficiency at 45°C, while increase in temperature to 55°C led to decrease in biooxidation rate. Probably, addition of yeast extract led to the increase in activity of acidophilic microorganisms, but high temperature may inhibit some microorganisms of the mixed culture and, therefore, decrease biooxidation rate.
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