Most industrial plants for biooxidation of gold-bearing concentrates have been operated at 40 °C with mixed cultures of mesophilic bacteria of the genera "Acidithiobacillus" or "Leptospirillum ferrooxidans". In subsequent studies the dissimulatory iron-reducing archaea "Pyrococcus furiosus" and "Pyrobaculum islandicum" were shown to reduce gold chloride to insoluble gold. Using "Bacteria" such as "Acidithiobacillus ferrooxidans" to leach copper from mine tailings has 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. Some examples of past projects in biotechnology include a biologically assisted in situ mining 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 thermophilic sulfide-oxidizing archaea in copper extraction has attracted interest due to the efficient extraction of metals from sulfide ores that are recalcitrant to dissolution. Microbial leaching is especially useful for copper ores because copper sulfate, as 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 acidophilic archaea "Sulfolobus metallicus" and "Metallosphaera sedula" tolerate 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.