Pyrite formation process

The importance of polysulfides in the pyrite formation process was outlined by several studies (37, 38). Schoonen and Barnes (37) showed that no precipitation from homogeneous solution can be observed within a reasonable time scale, even in solutions highly supersaturated with respect to pyrite, unless pyrite seeds are already existing. Therefore future studies should address the role of ferric oxide surfaces in promoting the nucleation of pyrite. 

Wachtcrshauser s prime candidate for a carbon-fixing process driven by pyrite formation is the reductive citrate cycle (RCC) mentioned above. Expressed simply, the RCC is the reversal of the normal Krebs cycle (tricarboxylic acid cycle TCA cycle), which is referred to as the turntable of metabolism because of its vital importance for metabolism in living cells. The Krebs cycle, in simplified form, can be summarized as follows ... 

The strong coupling between sulfur and iron chemistry becomes obvious in this example. Conservation of alkalinity within the system is achieved only if the sulfide formed is prevented from reoxidation, a process that would restore the acidity. Prevention of reoxidation occurs through the ultimate storage of sulfide in sediments, either as organic sulfur or as iron sulfides (12, 13). The overall reaction of pyrite formation proceeds via formation of FeS ... 

In the freshwater peat swamp, bacterial reduction of organic sulfur in plant tissues may be an important process in the formation of pyrite (93). Altschuler et al. (93) proposed that in the Everglades peat, pyrite precipitates directly by the reaction of HS or organic sulfide (produced by reduction of oxysulfur compounds in dissimilatory respiration) with ferrous iron in the degrading tissues. Pyrite formation in low-sulfur coal may be accounted for by this process. 

Metastable Iron Sulfides Organic Sulfur Elemental Sulfur MECHANISM OF PYRITE FORMATION. 4.1 Evidence from Experimental Studies. 4.2 Isotope Effects during Experimental Pyrite Formation. 4.3 Origin of Morphological Variations in Pyrite SULFUR DIAGENETIC PROCESSES IN MARINE SEDIMENTS. 5.1 Depth Distribution of Diagenetic Sulfur Products. 5.2 Rates of Sulfate Reduction... 

Wilkin R. T. and Barnes H. L. (1997) Formation processes of framboidal pyrite. Geochim. Cosmochim. Acta 61(2), 323-339. 

Hydrogen sulfide can be oxidized in less than an hour in seawater. This removal can be through oxidation by oxygen or iodate. There is a possibility of oxidation, by hydrogen peroxide, but it is probably a minor pathway (Radfordknoery and Cutter, 1994). Photo-oxidation is also possible (Pos et ai, 1998), along with oxidation by Fe(III) oxide particles. This latter process is dependent on the way in which the particle forms and on pH with a maximum near 6.5. The Fe(III) oxide route gives mostly elemental sulfur as a product, which may have implications for pyrite formation (Yao and Millero, 1996). 

Secondly, the zone of greatest thiol production occurs at 6-9 cm which is also the interval of optimal pyrite formation in that marsh during the winter season( ). Thus, pyrite is a possible starting material for thiol production because pyrite formation and its eventual oxidation during the growing season are important geochemical processes in most salt marshes(, , ). Pyrite formally contains zero and -2 valent sulfur. In the case of pyrite... 

The discrepancy between the relative rates of sulfate reduction, FeS inventories, and the resulting quantity of pyrite formed at each station may be due to several processes acting alone or in concert (1) the rate of conversion of FeS to FeSj may differ, although this was largely discounted previously (2) FeS may be reoxidized prior to pyrite formation or (3) FeSz may be oxidized after formation. 

As the fractionation associated with pyrite formation from dissolved sulfide is less than 1 %o (Price and Shi eh 1979), the explanation for this discrepancy must rest elsewhere, most likely isotope fractionations imparted during sulfide oxidation. The direct oxidation of sulfide to sulfate, however, even through intermediate compounds, and by a variety of different sulfide oxidation processes (see above), provides only minimum fractionation (Table 3), and is probably insufficient to explain the isotopic composition of sedimentary sulfides. By contrast, considerable fractionation accompanies the disproportionation of sulfur intermediate compounds (Tables 4, 5 and 6) and disproportionation processes probably account for the highly " S-depleted sulfides found in marine sediments (Jorgensen 1990 Canfield and Thamdrup 1994 Canfield and Teske... 

Iron sulfides represent the most important minerals that form in association with both organoclastic and methanotrophic snlfate reduction, or - more precisely - as a resnlt of the hydrogen snlfide prodnced by these processes. The different pathways of pyrite formation via intermediate iron snlfides will be described in more detail in Section 8.4.2. The first step in all pyrite forming seqnences involves a reaction of hydrogen snlfide with either dissolved Fe " or solid-state iron (oxyhydr)oxides. The reactivity of oxidized iron minerals towards snlfide varies... 

Sulfur is involved in a number of biogeochemical processes in wetland, including sulfate reduction, pyrite formation, metal cycling, energy transport, and gaseous emissions to the atmosphere. 

Several other processes for extracting Be from beryl have been patented the most feasible involves the formation of BeCl2 by direct chlorination of beryl under reducing conditions several volatile chlorides are produced by this reaction (BeCl2, AICI3, SiCl4 and FeClj) and are separated by fractional condensation to give the product in a pure state. Other methods involve the fusion of beryl with carbon and pyrites, with calcium carbide and with silicon. 

The great importance of minerals in prebiotic chemical reactions is undisputed. Interactions between mineral surfaces and organic molecules, and their influence on self-organisation processes, have been the subject of much study. New results from Szostak and co-workers show that the formation of vesicles is not limited to one type of mineral, but can involve various types of surfaces. Different minerals were studied in order to find out how particle size, particle shape, composition and charge can influence vesicle formation. Thus, for example, montmorillonite (Na and K10), kaolinite, talc, aluminium silicates, quartz, perlite, pyrite, hydrotalcite and Teflon particles were studied. Vesicle formation was catalysed best by aluminium solicate, followed by hydrotalcite, kaolinite and talcum (Hanczyc et al., 2007). 

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