[01] Obi Clifford Nkemnaso, Department of Microbiology, College of Natural Sciences, Michael Okpara University of Agriculture, Umudike, Nigeria. [02] Ejukonemu Francis Ejovwokoghene, Department of Science Laboratory Technology, Delta State Polytechnic, Otefe-Oghara, Nigeria. [03] Chiekie Uchenna Innocent, Department of Microbiology, College of Natural Sciences, Michael Okpara University of Agriculture, Umudike, Nigeria.

The use of microbes to extract metals from ores is simply the harnessing of a natural process for commercial purposes. Microbes have participated in the deposition and solubilization of heavy metals in the earth’s crust since geologically ancient times. Most of this activity is linked to the iron and sulfur cycles. Anaerobic sulfate reducing bacteria generate sulfides that can react with a variety of metals to form insoluble metal sulfides. There are two main types of processes for commercial-scale microbially assisted metal recovery. These are irrigation-type and stirred tank-type processes. Bio-mining involves a chemical process called leaching which are actually oxidation reactions and maybe called bio-oxidation. Bio-leaching processes can be carried out at a range of temperatures and as would be expected, the iron and sulfur-oxidizing microbes present differ depending on the temperature ranges. In mineral bio-oxidation processes that operate at 40°C or less, the most important microorganisms are believed to be a consortium of gram-negative bacteria such as Acidithiobacillus ferrooxidans. In continuous-flow stirred tank processes, the steady-state ferric iron concentration is usually high and under such condition, A. ferrooxidans appears to be less important than a combination of Leptospirillum and A. thiooxidans. Microorganisms that dominate bio-leaching at 50°C include A. caldus and some Leptospirillum spp. At temperatures greater than 65°C, bio-mining microbial consortia are dominated by archaea rather than bacteria with species of Sulfolobus and Metallosphaera being most prominent.

Archae, Bacteria, Bio-mining, Metals, Ores

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