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Bioleaching is a biotechnological process that uses microorganisms to extract valuable metals from ores or industrial wastes through biochemical reactions. Instead of applying high temperatures or strong chemical reagents, bioleaching relies on the metabolic activities of bacteria or archaea, which oxidize metal sulfides or other minerals to solubilize metals in an aqueous phase. This eco-friendly alternative to conventional metallurgy minimizes air pollution, reduces energy demand, and allows treatment of low-grade ores that are uneconomical by traditional smelting. The organisms involved in bioleaching derive energy by oxidizing sulfur or ferrous iron, producing acids or oxidants that attack the mineral lattice, liberating metal ions into solution. The most studied bioleaching mechanism is the dissolution of sulfide minerals such as chalcopyrite (CuFeS₂), sphalerite (ZnS), and pyrite (FeS₂) through the activity of chemolithotrophic microorganisms. Species like *Acidithiobacillus ferrooxidans*, *Acidithiobacillus thiooxidans*, *Leptospirillum ferrooxidans*, and some archaea such as *Sulfolobus metallicus* thrive in acidic environments and catalyze oxidation reactions. In the indirect mechanism, these microbes oxidize ferrous iron (Fe²⁺) to ferric iron (Fe³⁺) or oxidize reduced sulfur to sulfuric acid. Ferric iron, acting as an oxidant, attacks the metal sulfide lattice, forming soluble metal sulfates and elemental sulfur or sulfuric acid. The direct mechanism involves adhesion of microbial cells to the mineral surface and enzymatic attack, accelerating sulfide oxidation. Copper bioleaching exemplifies the process on an industrial scale. Low-grade copper ores, especially chalcopyrite, are heaped on impermeable pads and irrigated with acidic solutions containing bacterial ___ _______ _______ ____ ________ __________ __________.
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