COPPER RECOVERY FROM CHALCOPYRITE CONCENTRATE BY THE THERMOACIDOPHILIC ARCHAEON Acidianus copahuensis

CASTRO C.,; DONATI E.R.

Congreso; SAMIGE 2014; 2014

Bioleaching means the dissolution of metal sulfides (MS), such as pyrite (FeS2) and chalcopyrite (CuFeS2), catalyzed by microbial oxidation processes. Metals like copper, cobalt, zinc and nickel can be recovered from low-grade ores by bioleaching which is less contaminating and less expensive than the traditional alternatives in metallurgy. Chalcopyrite is the most abundant copper sulfide, but due to the refractory nature of this mineral bioleaching using mesophilic microorganisms shows low dissolution rates. This process can be strongly enhanced using thermophilic microorganisms. Acidianus copahuensis is a new species of archaeon recently isolated from Copahue geothermal zone. One of the most striking characteristics of Acidianus copahuensis is its metabolic versatility. It grows on sulfur, tetrathionate, iron(II) and glucose under aerobic conditions, but it can also develop under anaerobic conditions. Due to the extremely metabolic versatility it is interesting to study its potential applications in bioleaching processes especially in the case of refractory sulfides like chalcopyrite. Precisely in this work we have studied the solubilization of metals (mainly copper) from a chalcopyrite concentrate by an Acidianus copahuensis strain. With the aim of study the effects of different energy sources on the mineral bioleaching, several systems varying the culture medium composition were designed. Alternatively, one or more of the following compounds were used as energy source: sulfur, tetrathionate, iron(II), glucose and yeast extract. All cultures contained 2% (w/v) pulp density of mineral and were inoculated with cells of Acidianus copahuensis. Flasks were incubated at 65°C with shaking at 120 rpm during 110 days. Samples from supernatants were taken periodically and pH, copper, ferric and ferrous iron concentrations were determined. All inoculated systems tested in this study successfully leached the copper concentrate. In controls the amount of copper released from the mineral was very low and did not increase significantly over the time of the experiment. An enhanced oxidation activity of these microorganisms over the ore was detected in autotrophic conditions. After 110 days of the experiment, copper recoveries of 100% and 84% were obtained in the cultures without any additional energy source and with the supplement of tetrathionate, respectively.