Biomining.docx

Biomining is the process of extracting valuable metals from ores and mine tailings with the assistance of microorganisms. It is a very low capital, low operational cost, and a low energy input process. This technology is also environmentally friendly as it generates minimal amount of pollutants. It has the added benefit of mining low grade ore and/or mine tailings. The depletion of high grade ores and the onerous environmental burden inherent in the pyrometallurgical technologies are forcing mining companies to examine alternative metal-extractive procedures. Biomining can undoubtedly provide such a green technology to exploit mineral resources. Physical-chemical processes utilized in conventional mining technologies necessitate large amounts of energy for roasting/smelting and produce harmful gaseous emissions such as sulfur dioxide; biomining will help eliminate these problems. What is Biomining? Biomining is the process of extracting valuable metals from ores and mine tailings with the assistance of microorganisms. It is an effective and green technology to mine metals. Biomining an Effective Mining Technology: 1. Low infrastructure 2. Low-labour input 3. Green Technology, low gaseous emission 4. Low energy demand 5. Low operating cost compared to other mining technologies 6. Cleaner tailings 7. Mine high/low grade ores and economically viable tailings Types of Biomining 1. Stirred Tank Biomining 2. Bioheaps 3. In- situ Bioleaching 1. Stirred Tank Biomining:- This method is used for leaching from substrates with high mineral concentration. Special types of stirred tank bioreactors lined with rubber or corrosion resistant steel and insulated with cooling pipes or cooling jackets are used for this purpose. Thiobacillus is commonly used bacteria. Since it is aerobic the bio reactor is provided with an abundant supply of oxygen throughout the process provided by aerators, pumps and blowers. This is multistage process consisting of large number of bio-reactors connected to each other. The substrates moves from one reactor to another and in the final stage it is washed with water and treated with a variety of chemicals to recover the mineral.

2. Bioheaps :- Bioheaps are large amount of low grade ore and effluents from extraction processes that contain trace amounts of minerals. Such effluents are usually stacked in the large open space heaps and treated with microorganisms to extract the minerals. Bioheaps are also called biopiles, biomounds and biocells. They are also used for biodegradation of petroleum and chemical wastes. 3. In- situ Bioleaching: - In this method the mineral is extracted directly from the mine instead of collecting the ore and transferring to an extracting facility away from the site of the mine. In-situ biomining is usually done to extract trace amounts of minerals present in the ores after a conventional extraction process is completed. The mine is blasted to reduce the ore size and to increase permeability and is then treated with water and acid solution with bacterial inoculums. Microbes useful for biomining operations :- There are wide varieties of bacteria with varying capabilities existing on earth. Therefore, it is essential to identify precisely the types that can perform biooxidation/ bioleaching effectively. Thiobacillus ferrooxidans is a chemophilic, moderately thermophilic bacteria which can produce energy from oxidation of inorganic compounds like sulfur and iron. It is the most commonly used bacteria in biomining. Several other bacteria such as: T. thioxidans, Thermothrix thiopara, Sulfolobus acidocaldarius and S. brierleyi are also widely used to extract various minerals.