A. & L. ferrooxidans Generally forming ATP by ferrous iron oxidation Reduced Fe2+ Oxidised e- source Fe3+ e- source O2 Oxidised e- acceptor H2OReduced e-e- acceptor e- H+H+ ADP Precursor H+ H+ ATP Temp. energy storage e-Energy releasing Low pH & 2 Fe2+ + 0.5O2 + 2H+ 2Fe3+ + H2O redox reaction:
These microorganisms actually gainenergy by breaking down mineralsinto their constituent elements. Bioleaching by microorganismstakes place owing to destruction of acrystal lattice of minerals, composingsolid. Microorganisms take elementsnecessary for feeding andconstruction of a cell from a crystallattice. This shakes of a lattice are causesthe destruction of a mineral.
SURFACE OF CRYSTAL PRIOR TO SURFACE OF CRYSTAL AFTER EXPOSUREEXPOSURE TO BACTERIA TO BACTERIA.Experiment conducted by Schaeffer, Holbert And Umbreit in 1962 to demonstrate thenature of attachment of bacteria to the crystals.
SURFACE OF ANOTHER CRYSTAL OF SULFUR AFTER SURFACE OF SULFUR CRYSTAL AFTER INCUBATIONINCUBATION WITH LOW INNOCULUM OF WITH HIGH INNOCULUM OF THIOBACILLUSTHIOBACILLUS THIOOXIDANS. THIOOXIDANS.Comparison of crystal with high and low innoculum of bacteria .
Organisms involved can be conveniently classified into: Mesophiles -(Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and species of Ferroplasma) Moderately thermophilic bacteria-(Sulfobacillus and Acidithiobacillus cladus) Extremophiles- ( Acidianusbrierleyi, Sulfolobus metallicus and Metallosphaera sedula.)
Scanning electron micrographCork screw shaped Leptospirllium and mesophilic rod shaped bacteriaembedded in biofilm on ore particle.
Scanning electron micrograph of moderately thermopilebacteria Bacterial cells are 2-5 micrometer long and 0.5-1 micrometer in diameter
Scanning electron micrograph of Acidianus brierly; an extremophilicthermophilesGrowing on molybdenite
COMMON FEATURES OF ORGANISMS INVOLVED Single-celled organisms. Chemosynthetic metabolism. Derive carbon dio-oxide, oxygen from atmosphere. Requires acidic pH.
Identifying Characteristics Strictly aerobic. Gram-negative. Polarly flagellated. Rod shaped. Motile. Cells are 0.3 to1- 3mm in size. Non-spore forming. Best growth at 25-35 C Able to oxidize sulfide, elemental S, thiosulfate, and polythionate.
CONT… Obligate autotrophs (cannot grow with organic carbon as an electron and carbon source). A few species grow on organic compounds. Grow best at neutral pH. Some spp. are able to live in highly acidic environments. Responsible for acid mine drainage due to the metabolism of coal spoil piles causing the production of sulfuric acid. Some spp. are able to utilize iron as an energy source. Some spp. are able to carry out denitrification.
Yellow and red zones below a hot spring in yellowstone national park,.Where large populations of thermal-tolerant thiobacilli have grown byoxidizing reduced sulfur and iron in the water.
FACTORS EFFECTING BIOMINING: Success of biomining and efficiency in recovery of minerals depends on various factors some of which are discussed below. (a) Choice of Bacteria - This is the most important factor that determines the success of bioleaching. Suitable bacteria that can survive at high temperatures, acid concentrations, high concentrations of heavy metals, remaining active under such circumstances, are to be selected to ensure successful bioleaching. (b) Crystal Lattice Energy - This determines the mechanical stability and degree of solubility of the sulfides. The sulfide ores with lower crystal lattice energy have higher solubility, hence, are easily extracted into solution by the action of bacteria. (c) Surface Area - Rate of oxidation by the bacteria depends on the particle size of the ore. The rate increases with reduction in size of the ore and vice- versa.
CONT… (d)Ore Composition – Composition of ore such as concentration of sulfides, amount of mineral present, and the extent of contamination, has direct effect on the rate of bio-oxidation being selected. The rate of biooxidation is reduced significantly if the temperature is above or below the optimum temperature. (e) Acidity - Biooxidation requires a pH of 2.5-3 for maximum results. The rate of biooxidation decreases significantly if the pH is not in this range since the activity of acidophilic bacteria is reduced. (f) Temperature - The bacteria used in biomining are either mesophilic or thermophilic. Optimum temperature is required for biooxidation to proceed at a fast rate. Optimum temperature range for a given bacteria is between 25-35 C depending on the type of ore
(g) Aeration - The bacteria used in biomining are aerobic thus require an abundant supply of oxygen for survival and growth. Oxygen can be provided by aerators and pipes. Mechanical agitation is also an effective method to provide continuous air supply uniformly and also to mix the contents.(h) Solid-liquid Ratio - The ratio of ore/sulfide to the leach solution (water + acid solution + bacteria inoculum) should be maintained at optimum level to ensure that biooxidation proceeds at maximum speed. The leach solution containing leached minerals should be removed periodically and replaced with new solution.(i) Surfactants - Adding small amounts of surfactants like Tween 20 to the leaching process increases the rate of biooxidation of minerals from sulfide ores. The surfactants decrease the surface tension of the leach solution, thus, wetting the ore and resulting in increased bacterial contact which ultimately increases the rate of biooxidation.
Copper dump bioleach operation atBingham Canyon mine near salt lake city, Utah.
REACTIONS INVOLVED IN COPPER BIOLEACHING 4FeSO + O + 2H SO 2Fe (SO4) + 2H O. CuFeS (chalcopyrite)+2Fe (SO4) CuSO +5FeSO + 2S FeS (pyrite) + Fe (SO4) 3FeSO +2S CuO (tenorite) + 2H SO CuSO + H O CuS (covellite) + 2O CuSO
URANIUM MININGAccording to the World Nuclear Association, the largest national share of nuclear reserve was1. Australia (1,243,000 tones, 23%)2. Kazakhstan (817,000 t, 15%)3. Russia (546,000 t, 10%)4. South Africa (435,000 t, 8%)5. Canada (423,000 t, 8%)6. USA (342,000 t, 6%)7. Brazil (278,000 t, 5%)8. Namibia (275,000 t, 5%)9. Niger (274,000 t, 5%)10. Ukraine (200,000 t, 4%)11. Jordan (112,000 t, 2%).
CONT……With current technology, there are three main techniques in use for uraniummining. These are open pit mining, underground mining, and in situ leachmining. In open pit mining, the land above the material is blasted and dug awayto reveal the ore body. After they have found the fuel deposit, it will be blasted,excavated and removed with dump trucks. Underground mining is carried withaccess tunnels, and drilling and blasting. In situ leach mining involves drillingboreholes down into an ore body, pumping a leaching fluid into the ore and thenpumping the resulting solution to the surface to extract the uranium. Theleaching fluid is sometimes a combination of acids or sometimes alkalinesolution. The type of the solution used depends on the type of the ore body.
CONT… Micro-organisms degrading DBTs: Rhodococcus sp. (Gray et al., 1996) Pseudomonas (Kilbane, 1989) Brevibacterium sp. (McEldowney et al., 1993) Aspergillns nigerThe inorganic sulphur in coal can be oxidized by chemolithotrophs : Thiobacillus ferrooxidans, Thiobacillus thiooxidans, Sulfolobus acido-caldarius,Linked to the oxidation of reduced iron, T. ferrooxidans generates energy by the direct oxidation of iron (II) sulphide to iron (I) sulphate 2FeS2 + 7O2 + 2H2O 2FeSO4 + 2H2SO4 Microbial action can also directly convert elemental sulphur to sulphuric acid. 2S + 3O2 + 2H2O 2H2SO4
BIOLEACHING FROM ELECTRONIC SCRAPSOrganism involved : Thermophillic and acidophillic bacteria which includes Sulfobacillus thermosulfooxidans and an unidentified acidophillic heterotroph isolated from local environment.
ULTRASONICATION The irradiation of a liquid sample with ultrasonic (>20 kHz) waves resulting in agitation. Sound waves propagate into the liquid media result in alternating high-pressure (compression) and low-pressure (rarefaction) cycles. During rarefaction, high-intensity sonic waves create small vacuum bubbles or voids in the liquid, which then collapse violently (cavitation) during compression, creating very high local temperatures.
THE FUTURE OF BIOLEACHING Isolate new bacterial strains from extreme environments, such as mine-drainage sites, hot springs, and waste sites, and use these to seed bioleaching processes. Improve isolates by conventional mutation and selection or by genetic engineering. One possibility would be to introduce arsenic resistance into some bioleaching organisms, which could then be used in gold bioleaching. Heterotrophic leaching is a solution for wastes and ores of high pH (5.5) where many of the acidophiles would not grow. Fungi likeTrichoderma horzianum have been shown to solubilize MnO2, Fe O3, Zn, and calcium phosphate minerals. The population dynamics within the bioleaching dumps and the relative importance of various organisms and mechanisms needs to be understood
CONCLUSION The mining industry is constantly seeking new and more practical and environmental friendly technologies. Therefore biogeotechnology occupies an increasingly important place among the available mining technologies. Today it is no longer a promising technology but the actual alternative for solving various mining and geological problems.
REFERENCES Analytical applications of ultrasound By M. D. Luque de Castro, F. Priego Capote;137-140 Microbial Processing of Metal Sulfides By Edgardo R. Donati, Wolfgang Sand;127-132 Textbook Of Environmental Biotechnology PB Pradipta Kumar Mohapatra I. K. International 395-411 Environmental Biotechnology: Basic Concepts and Applications Textbook I.K .International Pvt. Ltd Indu Shekhar Thakur 359-366 Environmental Biotechnology: Fundamentals And Applications Pradeep PariharAgrobios (india)473-483 Microbial Biotechnology - Fundamentals Of Applied MicrobiologyAlexander N. Glazer, Hiroshi Nikaido Cambridge University PressSecond edition 609-610 http://www.rsc.org/publishing/journals/prospect/ontology.asp?id=CMO:0001708&MSID=b903391b Journal ( 1962)Department of Bacteriology, Rutgers, The State University, New Brunswick, New Jersey Biol-CSES 4684 - Thiobacillus.mhtss Biomining%20-CL%20Brierly%203_12_08.pdf http://biomine.skelleftea.se/ html/ BioMine/ The%20overlay%20technique... 2.6Mb http://environnement.u-psud.fr/ %21Biogeotechnology%20maxime.ppt 4.9Mb http://www.biotechnology.uwc.ac.za/ teaching/ BTY227/ Microbial%20appl... 601k Nova Biotechnologica VII-I (2007).pdf Department of Biotechnology, Institute of Geotechnics of the Slovak Academy of Sciences, Watsonova 45, Košice, SK-043 53, Slovak Republic Photomicrograph courtesy ofNewmont Mining Corporation Photos courtesy of compañía quebrada blanca www.ALLAN LISSNERS.net Photo courtesy of Brierley Consultancy LLC.
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