Thiobacillus pyrite

F. ferro-oxidants is capable of accelerating the oxidation of pyritic (FeSj) deposits at acid pH values. It is usually found in association with Thio-bacillus and was known as Thiobacillus ferroxidans before the distinction between the two organisms was appreciated. It is responsible for pollution problems arising from acid waters in gold and bituminous coal mines such waters are corrosive to pumping machinery and mining installations (see Fig. 2.20). 

In the leaching process, bacteria such as Thiobacillus ferroxidans and those belonging to the Sulfolobus genera, play a major role in the oxidation reactions at moderate and higher temperatures respectively. The oxidation of sulfides by bacteria is typified by the reactions of pyrite, a common accessory mineral in primary copper ore bodies this reaction can be considered to proceed through two stages ... 

Finally, whereas most laboratory experiments have been conducted in largely abiotic environments, the action of bacteria may control reaction rates in nature (e.g., Chapelle, 2001). In the production of acid drainage (see Chapter 31), for example, bacteria such as Thiobacillus ferrooxidans control the rate at which pyrite (FeS2) oxidizes (Taylor et al., 1984 Okereke and Stevens 1991). Laboratory ob-... 

However chemical methods of mercury detoxification are far from adequate. It has become evident that mercury can be solubilized from HgS under conditions that could be present in a landfill. We have demonstrated chemical solubilization followed by volatilization with Fe2(S04)3, a product of oxidation of FeS04 (pyrite) by Thiobacillus ferrooxidans (data not shown). Other researchers have indicated that T. ferrooxidans can facilitate solubilization and volatilization of Hg° from HgS. Growth of T. ferrooxidans in the presence of cinnabar (mercury ore-contains HgS and some impurities) by Silver and Torma (1984) resulted in dissolved mercury concentration in the bioreactor of 64 mg/L (the form of Hg was not given). In similar experiments with T. ferrooxidans and cinnabar, Baldi and Olson (1987) did not... 

Baldi, F. and G. J. Olson. 1987. Effect of cinnabar pyrite oxidation by Thiobacillus ferrooxidans and cinnabar mobilization by a mercury-resistant strain. Appl. Environ. Microbiol. 53 772-776. 

Rudimentary investigations of microbial desulfurization have received little attention in the literature at this time (2). One successful example of desulfurization is the removal of pyrite from coal by Thiobacillus sp. and Ferrobaccus sp. (3). While studies of the complex hydrocarbon-sulfur systems are of great value, being closer to in situ reality, investigation of a defined system should form the foundation of these more detailed studies. 

Bacteria may catalyze and considerably enhance the oxidation of pyrite and Fe(II) in water, especially under acidic conditions (Welch et al., 2000, 597). Many microbial species actually oxidize only specific elements in sulfides. With pyrite, Acidithiobacillus thiooxidans is important in the oxidation of sulfur, whereas Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans (formerly Thiobacillus fer-rooxidans) oxidize Fe(II) (Gleisner and Herbert, 2002, 140). Acidithiobacillus ferrooxidans obtain energy through Reaction 3.45 (Gleisner and Herbert, 2002, 140). The bacteria are most active at about 30 °C and pH 2-3 (Savage, Bird and Ashley, 2000, 407). Acidithiobacillus sp. and Leptospirillum ferrooxidans have the ability to increase the oxidation of sulfide minerals by about five orders of magnitude (Welch et al., 2000, 597). 

Lizama, H. M. and I. Suzuki. 1989. Rate equation and kinetic parameters of the reactions involved in pyrite oxidation by Thiobacillus ferrooxidans. Appl. Environ. Microbiol. 55 2918-2923. 

Wakao, N., M. Mishina, Y. Sakurai, and H. Shiota. 1982. Bacteria pyrite oxidation. I. The effect of the pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans on release of iron. J. Gen. Appl. Microbiol. 28 331-343. 

SABA [Spherical Agglomeration-Bacterial Adsorption] A microbiological process for leaching iron pyrite from coal. The bacterium Thiobacillus ferrooxidans adsorbs on the surface of the pyrite crystals, oxidizing them with the formation of soluble ferrous sulfate. Developed by the Canadian Center for Mineral and Energy Technology, Ottawa. In 1990, the process had been developed only on the laboratory scale, using coal from eastern Canada. 

AMD is probably the most severe environmental problem that occurs on mine sites, It happens where mineral and coal deposits contain sulfide minerals, particularly pyrite (FeS2). When waste rock containing sulfides is exposed fo air, these minerals are oxidized, releasing sulfuric acid, The process is accelerated by bacteria such as Thiobacillus ferrooxidans that obtain energy from the oxidation reaction for their growth. The release of acid can cause the pH of... 

Table 5 Members of the bacteria genera Thiobacillus, Leptospirillum, Sulfobacillus and four additional Archaea spp. that have been observed in acid mine waters and are associated with pyrite oxidation. The species in bold type are...

Fowler T. A. (2001) On the kinetics and mechanism of the dissolution of pyrite in the presence of Thiobacillus ferrooxidans. Hydrometallurgy 59, 257-270. 

Olson G. J. (1991) Rate of pyrite bioleaching by Thiobacillus ferrooxidans-rcsults of an interlaboratory comparison. Appl. Environ. Microbiol. 57, 642-644. 

Sasaki K., Tsunekawa M., Ohtsuka T., and Konno H. (1998) The role of sulfur oxidizing bacteria Thiobacillus thioox-idans in pyrite weathering. Coll. Surf. 133, 269 - 278. 

Microbes can control the local geochemical environment of actinides and alfect their solubility and transport. Francis et al. (1991) report that oxidation is the predominant mechanism of dissolution of UO2 from uranium ores. The dominant oxidant is not molecular oxygen but Fe(III) produced by oxidation of Fe(II) in pyrite in the ore by the bacteria Thiobacillus ferroxidans. The Fe(III) oxidizes the UO2 to UOl. The rate of bacterial catalysis is a function of a number of environmental parameters including temperature, pH, TDS, fo2, and other factors important to microbial ecology. The oxidation rate of pyrite may be increased by five to six orders of magnitude due to the catalytic activity of microbes such as Thiobacillus ferroxidans (Abdelouas et al., 1999). 

This principal environmental problem posed by coal-cleaning waste is that the pyrite and marcasite in the waste are oxidized to sulfuric acid in the presenee of air, water, Ferrobacillus ferrooxidans, and Thiobacillus ferrooxidans. The sulfuric acid is usually sufficiently concentrated to dissolve numerous metallic constituents and large quantities of iron from the pyrite in the leachate. Any ECT intended to prevent sulfuric acid formation must eliminate either the air, the water, or the oxidizable sulfur compounds in the waste, or inactive Ferrobacillus ferrooxidans and Thiobacillus ferrooxidans by maintaining alkaline conditions. Post-treatment of pile drainage comprises ECTs designed to neutralize the acid in the effluent and remove the metal ions by some sort of precipitation, adsorption, flocculation, or ion-exchange phenomenon. 

The principles imderlying this method have been given in Section II. The bacteria oxidize the pyrite present in the ore to give an acidic solution of Fe(III). This oxidizes UO2 to UOl, which dissolves in the acidic leach solution. Thiobacillus ferrooxidans is able to catalyze this reaction directly, but not rapidly enough to compete with oxidation by Fe(III). 

Rusticyanin is a component in the respiratory chain of the bacterium Thiobacillus ferrooxidans (44-46). This bacterium is capable of growth solely on the energy available from the oxidation of aqua Fe(II) to Fe(III) by O2. It is found in acid mine leachings, and is used commercially in the extraction of copper and uranium (see the review by Ewart and Hughes, this volume). Its ability to take into solution iron pyrites is particularly relevant. It has been suggested that an acid-stable cytochrome mediates electron transfer between rusticyanin and Fe (47, 48). The working pH is —2.0. 

Bacterial leaching with thiobacillus thiooxidans is also an acid leaching process. Sulfidic sulfur, e.g. in pyrites, is oxidized to sulfate and iron(II) is oxidized to iron(lll), which itself oxidizes uranium(IV) to uranium(VI). This process has not yet been operated industrially. 

Brierley, J.A. and Le Roux, N.W., 1977. A facultative thermophilic Thiobacillus-Uke bacterium oxidation of iron and pyrite. Conference Bacterial Leaching 1977. GBF Monograph Series, No. 4 (August, 1977), pp. 55—66. 

Magne et al. (1974) made a somewhat similar study, but their emphasis was on the enhancement of the solubility of uranium in granites through the activity of heterotrophic bacteria. In their experiments microbial activity increased the amount of uranium in solution by factors of 2 to 97. Several organisms may have been involved. Bacillus licheniformis being the one species definitely isolated. Species of Thiobacillus were absent, so that the enhancement of solubility observed was probably quite unrelated to leaching processes depending upon the oxidation of pyrite. ... 

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