Influence of CO2 and O2 Feeding Rates on the Continuous Bioleaching of a Chalcopyrite Concentrate Using Sulfolobus Metallicus

Abstract

Bioleaching of secondary sulfides is a technical and economical well established bioprocess. However in the case of bioleaching of primary sulfides, like chalcopyrite and enargite, still is necessary to improve the bioprocess kinetic. One alternative that has been proposed to overcome this situation is to use hyperthermophilic bioleaching microorganisms. Nevertheless, higher process temperatures modifies in a different extent operation parameters like CO2 and O2 transfer rates, both gases being essential to the bioprocess. The aim of this work was to establish quantitatively, using a continuous bioreactor operating at steady state conditions, which gas limits the growth and activity of bioleaching microorganisms when air is used as source of both of them. The experiments were run in a 3.3 L agitated continuous bioreactor operated at 70°C, pH 1.8 and 150 g/L of copper concentrate rich in chalcopyrite. Operating at steady state condition with an aeration rate of 1.2 vvm, a copper solubilization volumetric productivity of 1.7 g(Cu2+)(L•day)-1 and a copper extraction of 55% were obtained. Enriching the inflow air with CO2 up to 5% (v/v) showed the maximum values of these indexes, increasing 34% the volumetric productivity of copper solubilization and reaching 74% of copper extraction. On the opposite way, enriching air with oxygen or increasing the aeration rate did not bring about any change either of the volumetric productivity or the percentage of copper extraction. The results allow concluding that the CO2 is the limiting nutrient for cell growth in the continuous bioleaching of a chalcopyrite concentrate using hyperthermophilic microorganisms.