Toxicity of metal extraction and flotation chemicals to Sulfolobus metallicus and chalcopyrite bioleaching

The effect of chemicals used in preparation of mineral concentrates and subsequent extraction of metals to the thermophilic, acidophilic microorganism Sulfolobus metallicus has been tested. The chemicals tested included collectors and frothers employed during flotation of the ore to produce a mineral concentrate, solvent extraction reagents used to remove metals after leaching, and thiocyanate produced as a decomposition product during cyanidation for gold recovery. The effect of these chemicals to S. metallicus depends on the conditions and time frame that the experiments were carried out due to their mode of toxicity and stability in acid pH. The metal extraction chemical that had the least effect on bioleaching was potassium amyl xanthate that increased the leaching rate, possibly due to solubilization of sulfur that can form passivation layers on the surface of minerals. The frother Flotanol C-7 decreased the chalcopyrite leaching rate, despite having no effect on Fe2+ oxidation by S. metallicus resting cells. This is probably due to inhibition of oxygen transfer during bioleaching that had little effect on Fe2+ oxidation over 20 min. Solvent extraction chemicals inhibited both Fe2+ oxidation and bioleaching suggesting their mode of inhibition is due to Fe2+ oxidation. The results suggest that relevant concentrations of metal extraction and flotation chemicals can be toxic to chalcopyrite bioleaching by S. metallicus.