Biohydrometallurgy

Biohydrometallurgy is a branch of hydrometallurgy that uses microorganisms to extract metals from ores, concentrates, and wastes through biologically mediated oxidation or reduction reactions. The two main processes are bioleaching and biooxidation. Bioleaching employs acidophilic, chemolithotrophic microorganisms to oxidize sulfide minerals, generating ferric iron and sulfuric acid that solubilize metals such as copper, gold, zinc, and nickel. Biooxidation is used to pretreat refractory oxide and sulfide minerals, removing protective coatings and making the embedded metals more accessible to downstream processing. Biomining is the industrial application that combines bioleaching and biooxidation in systems such as heap leach pads or stirred-tank reactors to recover metals from low-grade ores and mine wastes.

Key organisms include Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, and related archaea and acidophilic bacteria. These microbes oxidize ferrous iron and reduced sulfur compounds under acidic conditions, typically at pH 1-3 and temperatures around 20-40 C.

Applications extend to the recovery of copper and gold from chalcopyrite and other sulfide minerals, as well as zinc, nickel, cobalt, and rare earths, including treatment of tailings and waste materials. The approach enables exploitation of low-grade resources and mine wastes that are unsuitable for traditional mining, often with lower energy consumption and potentially reduced emissions relative to smelting.

Challenges include slow dissolution rates, sensitivity to environmental conditions, inhibitory substances, formation of passivation layers, and management of acidic, metal-rich effluents and arsenic-bearing materials. Ongoing research aims to improve kinetics, microbial consortia, reactor design, and the range of recoverable metals, while mitigating environmental risks.