Thiobacillus sulfide minerals

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). 

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... 

Thiobacillus neapolitanus H2S, sulfide minerals, S(0), S2O3, S4O6... 

These reactions, in particular carbonate solvation, deplete the sulfuric acid content of the extraction solution. Later metal recovery from the solutions, however, returns an equivalent acid strength to the water. Also, Thiobacillus ferro-oxidans in the presence of air converts sulfide minerals to sulfates, which contributes to the acid content of the solvent when metal is recovered from the solution. 

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 ... 

Oxidation of insoluble mineral sulfides to the usually water-soluble sulfates (PbS04 is an exception) can also be carried out in many cases by microbial leaching, that is, by the use of bacteria such as Thiobacillus fer-rooxidans which can use the sulfide-sulfate redox cycle to drive metabolic processes. The overall reaction still consumes oxygen... 

Some microorganisms can catalyze certain oxido-reduction reactions like the oxidation of iron and manganese in water, the oxidation of sulfur compounds, and oxidation-reduction of nitrogen compounds. Aerobic autotrophic bacteria of the type Thiobacillus can release soluble iron, copper, and sulfuric acid as sulphates into water. These organisms can be found everywhere in nature wherever an acidic environment is maintained in the presence of sulfide-containing minerals. 

When acid sulfate soils are flooded, reduced Fe can combine with sulfide and form insoluble compounds, finally resulting in mineral formation (see Chapters 3 and 10 for details). Pyrite formation can also occur in swamp sediments. When oxygen is introduced into these systems by draining, sulfides are oxidized to sulfates biologically. This lowers the pH. The pH of these soils can drop as low as 3.0, where Thiobacillus may not function. These soils are also called cat clays—predominant in most of the coastal areas of the world. 

Sulfur/Sulfide Oxidizing Bacteria This broad family of aerobic bacteria derives energy from the oxidation of sulfide or elemental sulfur to sulfate (Fig. 10.10). Some types of aerobes can oxidize sulfur to sulfuric acid, with pH values as low as one reported. These Thiobacillus strains are most commonly found in mineral deposits, and are largely responsible for acid mine drainage, which has become an environmental concern. They proliferate inside sewer lines and can cause rapid deterioration of concrete mains and the reinforcing steel therein. 

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