Bioleaching uses bacteria to extract precious metals from low concentration ores in an environmentally friendly way. Special microorganisms act as catalysts to accelerate natural processes in the mineral. Bioleaching produces little air pollution and has a low impact on the environment.
Bioleaching is the use of bacterial microorganisms to extract precious metals, such as gold, from the ore in which it is embedded. As an alternative to smelting or roasting, miners use bioleaching when there are lower concentrations of metal in the ore and they need an efficient and environmentally friendly method of extracting it. The bacteria feed on the nutrients in the ores, thus separating the metal from the ore. Other metals that are commonly mined via bioleaching include silver, zinc, copper, lead and uranium.
Use Special Microorganisms
This process works because of the way special microorganisms act on mineral deposits. These microorganisms are catalysts for accelerating natural processes in the mineral. The types of bacteria most used in this process include Leptospirillum ferrooxidans, Thiobacillus ferrooxidans and some species of Acidianus, Sulfolobus and Sulfobacillus.
Oxidation
Bacteria use a chemical reaction called oxidation to transform metal sulfide crystals into pure metals and sulfates. These constituent parts of the ore are separated into precious metal and residual sulfur and other acidic chemicals. Eventually, enough material builds up in the waste solution to filter it out and concentrate it into recoverable metal.
Feasibility
For some metal types, such as copper, bioleaching is not always economically feasible or fast enough, even with its low cost. In some areas of the world or with other metals, however, this simple, low-cost, effective method is considered a smart choice. For example, developing countries often lack the infrastructure or capital investment to begin smelting, but their land contains enough ore that its extraction can significantly improve their national economies. Many scientists believe that bioleaching could one day be used to mine metals like zinc and nickel on the moon.
Low impact on the environment
At the start of the 21st century, approximately 20% of the copper mined in the world came from bioleaching. Mining companies need to be aware of the pollution that could result from solutions reaching an underground water source. Overall, however, bioleaching produces a relatively small amount of air pollution and little damage to geological formations, because the bacteria occur there naturally. An ideal metal deposit must allow a certain amount of water in the rock to carry the bacteria. It should be surrounded by water-impermeable rock, however, to make sure the groundwater doesn’t get polluted by sulfur.
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