Biomining is a technique used to recover the various types of minerals from ore using microorganism. Biomining method is cheap, reliable, efficient and also environment friendly method of mineral recovery. Using biotechnology efficiency of biomining can be increased by using genetically modified microorganisms. Biomining is done in two steps known as bioleaching and biooxidation. Biomining is also known as microbial leaching or as biooxidation.
Characteristics of Bacteria used in Biomining:
Bacteria are most suitable microorganism for the extraction of minerals from low grade ores.
1. Bacteria which are thermophilic that is bacteria which can survive at high temperature are selected for biomining, as mineral extraction involves the high temperature procedures.
2. Bacteria which are chemophilic, as biomining uses both strong acid and alkalis.
3. Autotropic bacteria are selected for biomining. That is bacteria which has the ability to produce energy from inorganic compounds through photosynthesis pr chemosysnthesis.
4. Bacteria which have the capacity to form biofilms are selected for biomining purpose.
Techniques such as genetic engineering and conjugation are used to produce the bacteria with all the desired characteristics to increase the biomining yield. That is to increase the extraction of minerals from low grade ores.
Identification of Bacteria for Biomining:
Identification of biomining bacteria from colonies of other bacteria are done using techniques such as immunofluoresence, dot immunoassay and dot-blot hybridization.
Immunofluurosence technique is used in identifying specific antibody or antigen, which are present in the biological fluid. Biomining bacteria are identified using fluorescent antibodies.
2. Dot Immunoassay:
Identification of ore adhering bacteria like T. Ferroxidans and T. Thioxidans can be done using dot immunoassay technique. In this technique bacteria are placed as dots in nitrocellulose paper, antigen-antibody reaction is done on the film, and at last secondary antibodies are added to produce visible color. Comparing the sample with test sample can be used to approximate the sample.
3. Dot-blot Hybridization:
Dot-blot hybridization technique can be used to identify biomining bacteria like T. Ferroxidans. Dot-blot hybridization is a DNA based technique. First the bacteria are isolated from the ore. Bacterial cells are then treated with some chemicals, which help in the extraction of DNA. Extracted DNA are then purified and fixed on nitrocellulose membrane via southern blotting technique. DNA or RNA probes are used to identify biomining bacteria.
Minerals are extracted from the ores using microorganisms by two methods or reactions such as direct or indirect oxidation or by reduction of the ore. Three different methods are used in biomining such as stirred tank biomining, bioheaps and in-situ biobleaching. Bioming efficiency or mineral recovery from its ore depends on factors like choice of bacteria, crystal lattice energy, surface area, composition of the ore, acidity, temperature and also surfactants used in biomining. Copper, gold and oil are extracted from its ore or reservoir by biomining method.
Biotechnology or genetic engineering can be used to produce strains of bacteria which are resistant to heavy metals like mercury, cadmium and arsenic. These heavy metals slow the process of biomining. Therefore these heavy metal resistant bacteria can be used in biomining process.
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