biomining

Biomining, or biohydrometallurgy, is the use of microorganisms to extract metals from ores, concentrates, or waste materials. In biomining, microbes oxidize mineral components so that metals become soluble, forming leachates from which metals can be recovered by conventional metal recovery methods. The approach can lower energy use and enable extraction from low-grade ores that are uneconomic to process by traditional techniques.

The principal methods are bioleaching and biooxidation. Bioleaching employs acidophilic bacteria and archaea, such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, to oxidize ferrous iron and sulfide minerals, generating ferric iron and sulfuric acid that dissolve metal-bearing minerals. Biooxidation pretreats refractory gold ores, using similar microbes to break down sulfide coatings and release gold.

Operations typically occur in heaps, vats, or stirred tanks, using warm, acidic conditions and circulating leachates. Metals are recovered from solution by solvent extraction and electrowinning, precipitation, or other hydrometallurgical steps. Biomining is applied to copper sulfide ores, nickel and cobalt laterites, zinc, uranium, and to recover metals from mine tailings or electronic waste.

Advantages include lower energy demand, reduced CO2 emissions, and the ability to exploit low-grade ores and waste streams. Limitations include slow dissolution rates, sensitivity to temperature and oxygen, slow metal recovery, risk of acid mine drainage if unmanaged, and higher capital costs for some operations. Ongoing research seeks to expand metal scope, improve rate and selectivity, and reduce costs.

Biomining has been developed since the late 20th century and is widely used for copper and refractory gold ore processing, as well as recovery of metals from mining wastes and electronic scrap. It intersects with environmental remediation and sustainable mining, but requires careful management of microbial communities and process conditions.