How is bioleaching used for metal extraction and what organisms are involved?

Bioleaching (biomining) uses microorganisms to solubilize metals from ores or wastes. Mechanisms: Direct mechanism - bacteria directly oxidize metal sulfides, releasing metals into solution. Indirect mechanism - bacteria oxidize ferrous iron to ferric iron and/or sulfur to sulfuric acid; these chemical agents then dissolve metals. Key reactions for copper: 2Fe2+ + 0.5O2 + 2H+ -> 2Fe3+ + H2O (bacterial); CuFeS2 + 4Fe3+ -> Cu2+ + 5Fe2+ + 2S0 (chemical). Organisms: Acidithiobacillus ferrooxidans (iron and sulfur oxidizer), A. thiooxidans (sulfur oxidizer), Leptospirillum ferrooxidans (iron oxidizer), thermophilic archaea (Sulfolobus, Metallosphaera) for higher temperatures. Process types: Heap leaching - crushed ore piled, irrigated with acidic solution; slow but low cost. Stirred tank reactors - faster, controlled, but higher cost; used for high-value metals or concentrates. Applications: copper (20% of global production), gold (pretreatment of refractory ores), uranium, zinc. Advantages: lower energy, applicable to low-grade ores, reduced emissions.