Bioleaching Of Chalcopyrite And Marmatite Using A Mixed Culture Of Extremely Thermophilic Archaea

Bioleaching is an economical method for the recovery of metals from minerals, especially from low grade ores, overburden and waste from current mining operations, which requires moderate capital investment with low operating cost. Furthermore, bioleaching is generally more environmentally friendly than conventional metal recovery processes such as concentration and smelting. In this study, a mixed culture of extremely thermophilic archaea, which consisted of Sulfolobus metallicus JCM 9184, Metallosphaera sedula JCM 9185 and Acidianus manzaensis YN25, was used to bioleach chalcopyrite and marmatite ore. The effects of temperature and pH on the leaching of chalcopyrite were investigated, as well as the succession of the archaea community during the leaching process. And the leaching of marmatite by the same mixed culture was also studied.In the preliminary work, it was found that the optimal growth pHs of the three strains in 9K medium or iron-free 9K medium with elemental sulfur were 1.5 and 2.5, respectively, while in the temperature range from 65℃to 75℃all the strains grew well. Therefore we performed the experiments at different initial pHs (1.5 and 2.5) and temperatures (65℃and 75℃) to investigate the effects of these two factors on the chalcopyrite bioleaching. The results showed that the mixed culture had a high chalcopyrite-oxidizing ability:more than 90% copper extraction was achieved under 65℃at initial pH 1.5 within 24 days. We found that a lower pH favored the copper extraction. Unexpectedly, the copper extraction at 75℃was lower than that at 65℃, but the lower copper extraction at 75℃was not due to the inhibition of the higher temperature.The succession of microbial community during leaching process was analysed by Restriction Fragment Length Polymorphism (RFLP). The results showed that Sulfolobus metallicus was dominant in microbial community at the early stage of leaching, whereas Acidianus manzaensis thrived at the latter stage.In addition, we studied the bioleaching of marmatite ore with a mixture of extremely thermophilic archaea. The results showed that extremely thermophilic archaea displayed a more efficient zinc extraction ability than mesophilic bacteria. The addition of ferric ion could accelerate the bioleaching rate of zinc from marmatite ore, especially at the initial stage. At the beginning of leaching tests, the leaching rate was very high in the bioleaching system with the addition of ferric ion. And the zinc extraction rate achieved 40% within 8 hours. Besides, the pulp density influenced the extraction rate significantly. A better extraction rate was obtained at a lower pulp density, but the extraction rate was low at high pulp density due to the inhibition of microbial growth by high pulp density. The retention time and the pulp density played an important role in the indirect bioleaching tests of marmatite ore by extremely thermophilic archaea. The longer the retention time was, the better the extraction rate was. A higher pulp density caused a lower zinc extraction. The low oxidation rate of ferrous ion was the cause of low extraction rates.