Bacteria can wreck havoc in our bodies or help us enrich our soil; spoil our food or help with our digestion. Mining engineers have come up with a new and fascinating use for them in an effort to reduce the environmentally harmful chemicals that are needed to extract metals and minerals from low grade ores. Low grade ores are those that have less concentrated quantities of metals widely scattered throughout the rock.
There are two techniques in which bacteria are used to remove metals from ores. The first is bioleaching. In this process the ores are ground into fine powders and acidic liquids containing specific bacteria such as Thiobacillus ferrooxidans, are added. These bacteria liquefy the metals leaving the rock behind. The metals are then recovered from the liquid solution via chemical processes. Currently 25% of the worlds copper is extracted by this process.
The second technique is bio-oxidation. This is used primarily in the extraction of gold that is scattered in small particles in ores. These so called “refractory ores” are difficult to extract because the gold is often coated with minerals that are difficult to dissolve. Naturally occurring bacteria, including Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans , are able to remove these insoluble minerals making it possible to extract the gold. Currently these techniques are used on a very small number of metals. The process has not been proven efficient for the vast majority of metals that are presently mined.
Geneticists are working to find bacteria that may prove effective for other metals and are considering the possibilities of genetic engineering of bacteria to make the process more efficient. Bio-mining is a way to make the notoriously “dirty” process of mining and extracting ores more environmentally friendly. It can help to prevent the release of harmful chemicals into the air, water and soil.