Bioleaching
Extracting valuable metals such as copper, gold or uranium from their ores can be made easier and more efficient by chemically altering those metals to increase their solubility. Microbes can act biochemically to make these alterations, allowing the minerals to be more easily harvested, a process known as bioleaching. These approaches have seen increasing application, especially in the developing world. Many poorer countries have largely untapped mineral reserves, and the low cost of bioleaching has made the recovery of these mineral resources economically viable.
The Beginning of Bioleaching
Modern microbial mining begins in 1947 with the discovery by Colmer and Hinkle that two previously unidentified bacteria species were able to oxidize ferrous iron to ferric iron, a form of iron more easily extracted from ore. These bacteria were named, in honor of their iron-oxidizing characteristics, Thiobacillus thiooxidans, and Thiobacillus ferrooxidans, later reclassified as Acidithiobacillus ferrooxidans.
Commercial Viability
A copper mine in Minera Pudehuel, Chile, was the site of the first major commercial exploitation of microbes in mining. In the mid-1980s, this operation yielded 14,000 tons of fine copper per year from ore containing 1 to 2 percent copper, demonstrating the commercial viability of this approach and advantages over traditional chemical leaching without microorganisms.
Future of Microbial Mining
Microbial mining has now been well established as a commercially viable and in many ways superior approach to extracting metal from ore. One limitation is that microorganisms thrive at a narrow temperature range, and the optimal range for microbial growth and biochemcial activity is general lower than the temperature typical of mining operations. Current research focuses on identifying new types of microorganisms that flourish at higher temperatures.