Biomining

The possibility of using microorganisms in biomining applications was realized after the 1951 paper by Kenneth Temple and Arthur Colmer. In the paper the authors presented evidence that the bacteria Acidithiobacillus ferrooxidans (basonym Thiobacillus ferrooxidans) is an iron oxidizer that thrive in iron, copper and magnesium-rich environments. Following this experiment, the potential to use fungi to leach metals from their environment and use microorganisms to take up radioactive elements like uranium and thorium have also been explored. In western Europe the practice of extracting copper from metallic iron by placing it into drainage streams, used to be considered an act of alchemy. In China, the use of biomining techniques has been documented as early as 6th-7th century BC. The relationship between water and ore to produce copper was well documented, and during the Tang dynasty and Song dynasty copper was produced using hydrometallurgical techniques. Though the mechanism of oxidation via bacteria was not understood, the unintended use of biomining allowed copper production in China to reach 1000 Tons per year. ==Mechanism==

The processes often involve the use ferric ions (Fe3+) for oxidation of sulfide minerals. The organisms that promote these reactions tolerate high metal concentrations and low pH: :CuFeS2+4H++O2 → Cu2++Fe2++2S0+2H2O :4Fe2++4H++O2 4Fe3++2H2O, :2S0+3O2+2H2O→2SO2−4+4H+, :CuFeS2+4Fe3+→Cu2++2S0+5Fe2+ ==Bioleaching technologies==

Heap or dump leaching Bioleaching was one of the first widely used applications of biomining. It is practiced in two broad venues: • rock is treated with an extractant (lixiviant), which percolates through the solid and the metals are recovered from the leachate. • Dump bioleaching, waste rock is piled into mounds (>100m tall) and saturated with sulfuric acid to encourage mineral oxidation from native bacteria. In-situ mining also shows promise for applications in cost-effective deep subsurface extraction of metals. In situ biomining, is the one current method utilizing bioleaching that serves as an effective and viable replacement for traditional mining. Because in-situ biomining, negates the need for the extraction of the ore bodies, this method stops the need for hauling or smelting of the ore. This would mean there would be no waste rocks or mineral tailings that contaminate the surface. In-situ biomining poses environmental challenges, such as the contamination of ground water. == Applications ==

Gold Biological pre-treatment utilizes the natural oxidation abilities of microorganisms to solubilize minerals that interfere with the extraction of gold. 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. Gold is frequently found in nature associated with arsenopyrite and pyrite. In the microbial leaching process Acidithiobacillus ferrooxidans, etc. dissolve these minerals, exposing trapped gold (Au). :2 FeAsS[Au] + 7 O2 + 2 H2O + H2SO4 → Fe(SO4)3 + 2 H3AsO4 + [Au] Copper One of the largest applications of these leaching methods is in the mining of copper. Acidithiobacillus ferrooxidans has the ability to solubilize copper from its sulfidic ores. The acidophilic archaea Sulfolobus metallicus and Metallosphaera sedula can tolerate up to 4% of copper. The main application is for extraction from low grade ores using Thiobacillus thiooxidans. – an important consideration in the face of the depletion of high grade ores. Similarly to copper, Acidithiobacillus ferrooxidans can oxidize U4+ to U6+ with O2 as electron acceptor. However, it is likely that the uranium leaching process depends more on the chemical oxidation of uranium by Fe3+, with At. ferrooxidans contributing mainly through the reoxidation of Fe2+ to Fe3+. :UO2 + Fe2(SO4)3 → UO2SO4 + 2 FeSO4 Economic feasibility and potential drawbacks Bioleaching can be economical mainly as a complement to traditional mining. It allows for economic extraction of low-grade ore and allows exploitation of abandoned mine tailings. ==Future prospects==

Additional capabilities, of current bioleaching technologies include the bioleaching of metals from sulfide ores, phosphate ores, and concentrating of metals from solution. Coal desulfurization Biological methods have demonstrated some promise for the removal of sulfur from coal, giving a cleaner-burning fuel. This concept has not progressed beyond demonstration phase, however. Biomining in space The concept of space biomining is creating a new field in the world of space exploration. Species of filamentous fungi, specifically those in the genera of Aspergillus and Penicillium have been shown as effective bioleaching agents. Despite the promise of fungal bioleaching, there has been no industrial applications of it as it does not out compete its bacterial counterparts. == See also ==