Bio-Mining

Biominingis an approach to the extraction of desired mineralsfrom ores. Microorganismsare used to leach out the minerals, rather than the traditional methods of extreme heat or toxic chemicals, which have a deleterious effect on the environment. Overview The development of industrial mineral processing has been established now in several countries including South Africa, Braziland Australia. Iron-and sulfur-oxidizing microorganisms are used to release occluded copper, goldand uraniumfrom mineral sulfides. Most industrial plants for biooxidation of gold-bearing concentrates have been operated at 40 °C with mixed cultures of mesophilicbacteria of the genera Acidithiobacillusor Leptospirillum ferrooxidans. In subsequent studies the dissimulatory iron-reducing archaea Pyrococcus furiosusand Pyrobaculum islandicumwere shown to reduce gold chloride to insoluble gold. UsingBacteriasuch as Acidithiobacillus ferrooxidansto leach copperfrom mine tailingshas improved recovery rates and reduced operating costs. Moreover, it permits extraction from low grade ores - an important consideration in the face of the depletion of high grade ores. The potential applications of biotechnology to mining and processing are countless. Some examples of past projects in biotechnology include a biologically assisted in situmining program, biodegradation methods, passive bioremediation of acid rock drainage, and bioleaching of ores and concentrates. This research often results in technology implementation for greater efficiency and productivity or novel solutions to complex problems. Additional capabilities include the bioleaching of metals from sulfide materials, phosphate ore bioprocessing, and the bioconcentration of metals from solutions. One project recently under investigation is the use of biological methods for the reduction of sulfur in coal-cleaning applications. From in situ mining to mineral processing and treatment technology, biotechnology provides innovative and cost-effective industry solutions. The potential of thermophilicsulfide-oxidizing archaea in copper extraction has attracted interest due to the efficient extraction of metals from sulfide ores that are recalcitrant to dissolution. Microbial leachingis especially useful for copper ores because copper sulfate, formed during the oxidation of copper sulfide ores is very water-soluble. Approximately 25% of all copper mined worldwide is now obtained from leaching processes. The acidophilicarchaea Sulfolobus metallicusand Metallosphaera sedulatolerate up to 4% of copper and have been exploited for mineral biomining. Between 40 and 60% copper extraction was achieved in primary reactors and more than 90% extraction in secondary reactors with overall residence times of about 6 days. The oxidation of the ferrous ion (Fe2+) to the ferric ion (Fe3+) is an energy producing reaction for some microorganisms. As only a small amount of energy is obtained, large amounts of (Fe2+) have to be oxidized. Furthermore, (Fe3+) forms the insolubleFe(OH) 3precipitate in H2O. Many Fe2+oxidizing microorganisms also oxidize sulfur and are thus obligate acidophiles that further acidify the environment by the production of H2SO4. This is due in part to the fact that at neutral pH Fe2+is rapidly oxidizedchemically in contact with the air. In these conditions there is not enough Fe2+to allow significant growth. At low pH, however, Fe2+is much more stable. This explains why most of the Fe2+oxidizing microorganisms are only found in acidic environments and are obligate acidophiles. The best studied Fe2+oxidizing bacterium is Acidithiobacillus ferrooxidans, an acidophililic chemolithotroph.