The bio-assisted leaching of flotation concentrate, produced in a copper mining in Brazil, was initiate with the use of micro-organisms present in the acid mining drainage collected directly in the aforementioned copper mine, besides an strain of Acidithio-bacillus ferrooxidans bacteria. That strain came from a primary copper ore of Surubim mine in Bahia state. The concentrate under consideration, after being technologically characterized, was constituted, mainly, of chalcopyrite (CuFeS_2) and bornite (Cu_5FeS_4) at 70 and 30 percent, respectively. The high chalcopyrite content in this refractory concentrate caused a huge difficulty of extracting copper from such sulphide using only the above-mentioned microorganism, which was verified, once getting the analytical results for copper, ferrous and ferric ions concentrations and monitoring the pH and Eh values, along the bio-leaching tests, as being due to no sulphuric acid generation, when such mineral is solubilized, demanding a constant monitoring of those parameters to avoid, mainly, the pH rising, which otherwise would cause the precipitation of iron salts (hydroxides and jarosite). That phenomenon was verified, in some tests, due, certainly, to a sudden pH rising and confirmed, through X-ray diffraction analysis, as being a jarosite precipitate, which contains, in its composition, ferric ions decreasing, in a detrimental way, the oxidizing power of reaction system. Independent of these inconveniences, bearing in mind the operational adjustments, a copper extraction of nearly 67 percent was reached within 62 days.
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