Production of Sulfides

This may involve the production of FeS, Fe(OH)2, and so on and aggressive HjS or acidity. Microorganisms may also interact with oxygen or nitrite inhibitor and thus consume chemical species that are important in corrosion reactions. Microorganisms may form a slime or poultice leading to the formation of a differential aeration cell attack or crevice corrosion. Microorganisms may also affect the desirable properties of lubricants or protective coatings (52). 

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Besides adding biocides to wells, another approach seems to be promising— modifying the reservoir ecology. The production of sulfide can be decreased, and its concentration is reduced by the establishment and growth of an indigenous microbial population that replaces the population of sulfate-reducing bacteria. 

M. J. Mclnemey, A. D. Montgomery, and K. L. Sublette. Microbial control of the production of sulfide. In E. C. Donaldson, editor. Microbial enhancement of oil recovery recent advances Proceedings of the 1990 International Conference on Microbial Enhancement of Oil Recovery, volume 31 of Developments in Petroleum Science, pages 441-449. Elsevier Science Ltd, 1991. 

The major metabolic pathway for hydrogen sulfide in the body is the oxidation of sulfide to sulfate, which is excreted in the urine (Beauchamp et al. 1984). The major oxidation product of sulfide is thiosulfate, which is then converted to sulfate the primary location for these reactions is in the liver (Bartholomew et al. 1980). 

Salzsauler, K. A., Sherriff, B.L., Sidenko, N.V. 2005. As mobility in alteration products of sulfide-rich, arsenopyrite-bearing mine wastes, Snow Lake, Manitoba, Canada. Applied Geochemistry, 20, 2303-2314. Simpson, S. 2007 The Source, Attenuation and Potential Mobility of As at New Britannia Gold Mine, Snow Lake, Manitoba. M.Sc Thesis, University of Manitoba. 

The potential production of sulfide depends on the biofilm thickness. If the flow velocity in a pressure main is over 0.8-1 ms-1, the corresponding biofilm is rather thin, typically 100-300 pm. However, high velocities also reduce the thickness of the diffusional boundary layer and the resistance against transport of substrates and products across the biofilm/water interphase. Totally, a high flow velocity will normally reduce the potential for sulfide formation. Furthermore, the flow conditions affect the air-water exchange processes, e.g., the emission of hydrogen sulfide (cf. Chapter 4). 

The expressions shown in Table 6.1 all include constants that have been found good approximate values based on experiments. These values may of course be adjusted to account for specific cases. As an example, different flow conditions in continuously and intermittently pumped mains may affect the transfer of substances and products across the biofilm-water interface, and, thereby, the production of sulfide (Melbourne and Metropolitan Board of Works, 1989). 

Organisms such as Thiobacillus thiooxidans and Clostridium species have been linked to accelerated corrosion of mild steel. Aerobic Thiobacillus oxidizes various sulfur-containing compounds such as sulfides to sulfates. This process promotes a symbiotic relationship between Thiobacillus and sulfate-reducing bacteria. Also, Thiobacillus produces sulfuric acid as a metabolic by-product of sulfide oxidation. 

Recovered sulfur supply predictions depend on explicit assumptions or scenarios concerning the development of specific fuels and the production of sulfide ores. They also depend on a second set of assumptions with respect to sulfur pollution control regulations, the means by which these will be met, and the recursive impact of the controls on the production scenarios. For example, given uncertainties surrounding regenerative flue gas desulfurization (FGD) processes, including the sale of sulfur products and concern over process reliability, utilities have been emphasizing throw-away techniques. As new control standards are implemented the disposal... 

This bacterial production occurs in the pore fluids of sediments and in stagnant basins (seas, lakes, rivers and fiords). At the interface between anoxic and oxic waters the H2S can be oxidized. This oxidation is frequently coupled to changes in the redox state of metals (1.2) and non-metals (2). Another major interest in the H-jS system comes from an attempt to understand the authigenic production of sulfide minerals as a result of biological or submarine hydrothermal activity and the transformation and disappearance of these minerals due to oxidation (4). For example, hydrothermally produced H2S can react with iron to form pyrite, the overall reaction given by... 

K2Feg+(S04)4(0H)12] was commonly observed as an alteration product of sulfides or as mixtures with iron oxyhydroxide and both frequently contained a few weight percent As. An additional As-rich phase was only observed as scattered micrometersized grains, containing only Fe and As ( 0), as identified by SEM-EDS. The atomic ratio of Fe/As is about 1 and the phase is possibly scorodite, FeAsCVdfTO. 

It has been shown that welds provide unique environments for the colonization of SRB with the subsequent production of sulfides that affect the weld seam surface of the heat-affected zone. Exposure of sulfide-derived surfaces to fresh, aerated seawater resulted in rapid spalling on the downstream side of weld seams. The bared surfaces became anodic to the sulfide-coated weld root, initiating and accelerating localized corrosion. (Dexter)5... 

Microbial-mediated production of sulfides and further oxidation to sulfuric acid ... 

The sulfide minerals are at present the major source of the base metals. Associated with most of the sulfide ores are the minerals pyrite and pyrrhotite. If the hydrometallurgical processing of ores becomes the predominant method of metal extraction, the recovery of elemental sulfur as a by-product is a very promising possibility. The formation of elemental sulfur has been observed by many investigators as a reaction product of sulfide minerals under certain experimental conditions. 

In an effort to systematize differences in the absolute magnitude of benthic phosphate efflux in freshwater versus marine systems, Caraco et al. (1989) argue that more efficient benthic P-release occurs in lake relative to marine sediments as a direct consequence of the presence of higher sulfate in seawater, and that redox conditions exert secondary control. This argument is overly simplistic, however, because redox conditions control production of sulfide from sulfate, and it is the removal of ferrous iron from solution into insoluble ferrous sulfides that decouples the iron and phosphoms cycles (e.g., Golterman, 1995a,b,c Rozen et al., 2002). Thus, the presence of sulfate is a necessary but not sufficient criterion to account for differences in benthic P-cycling in marine versus freshwater systems redox conditions are an equally crucial factor. 

Thiolsulfonates decompose thermally according to first-order kinetics with the production of sulfides, sulfur dioxide, hydrocarbons and other products resulting from secondary decompositon of a thioaldehyde... 

Allman, 1968 Davy, 1975). Transport by water movement of end-products of sulfide oxidation at one site to other locations can influence the development of microbial populations and may facilitate chemical interactions leading to the modification of as yet unoxidized components. For example, a metal interchange reaction of the kind indicated below can lead to a stabilization of the concentration of solubilized copper and a conversion of chalcopyrite to the more readily oxidizable covellite (E. Peters, 1976, personal communication) (eqn (17)) ... 

In aquatic settings, sulfate reducers are intimately associated with various heterotrophs and autotrophs. These include purple and green sulfur bacteria and thiobacUli which affect the availability of organic matter and alter the distribution of sulfur compounds in their various valence states. In the majority of the sites where elemental sulfur is formed (see Chapter 6.2), oxidation to sulfate also occurs and other intermediate oxidation states may also be found. For example, Volkov et al. (1972) reported the presence of thiosulfate in waters of some sediments from the Pacific Ocean east of Japan. These are interpreted as oxidation products of sulfide rather than intermediates of sulfate reduction since their concentration increased with increasing free sulfide ion content. 

Biological factors play many roles in the cycling of sulfur minerals associated with fossil fuels. Sulfate reduction may lead to the solution of eva-porite sulfates while production of sulfide ions at various stages in the formation and degradation of fossil fuels may lead to deposition of sulfide minerals or elemental sulfur (see Chapter 6.2). 

The reaction by-products of sulfide oxidation are distinct thus, evidence of sulfide oxidation can be found in the chemical signatures of ground water. In aquifers where sulfide oxidation occurs, ground water chemistry should show a positive correlation of arsenic with sulfate, iron, and trace metals contained in the sulfide minerals. Increases in total dissolved solids and specific conductance also result from sulfide oxidation, due to an increase of dissolved ions in the impacted waters. Ground water impacted by sulfide oxidation may reveal a negative correlation of arsenic with pH, provided that there is minimal buffering capacity provided by the host rocks. 

This reaction leads to the production of sulfide species, such as H2S (hydrogen sulfide), I IS (bisulfide), and 82 (sulfide ion), which are the most reduced forms of sulfur. Sulfides are toxic most popularly known is H2S, which forms in rotten eggs and gives them their characteristic pungent odor. Sulfides are also important in causing the chemical precipitation of many metals, such as iron, copper, lead, and zinc, which form solids (such as FeS, CuS, PbS, ZnS) on reaction with S2. ... 

Oxidation of reduced sulfur species. Oxidation of reduced sulfur species in the presence of oxygen can occur spontaneously, without bacterial mediation. Bacteria of the family Thiobacteriaceae are probably the most important bacteria involved in sulfur oxidation. Of these, bacteria of the genus Thiobacillus have been most studied (Goldhaber and Kaplan 1974 Cullimore 1991). The first product of sulfide oxidation abiotically or by Thiobaccillus is thought to be elemental sulfur according to... 

COS may also influence metal cycling in the ocean. The hydrolysis of COS in the upper ocean results in the production of sulfide [195], a ligand that can reduce the biological lability of metals by chelation or formation of insoluble metal sulfides. Certain metal sulfide complexes photoreact efficiently when exposed to solar UVR. Other interactions of UV with metals cycling are considered in the next section. 

A significant development in this regard was the correlation of the solubility products of a series of heavy metal-ethyl xanthate salts with the floatability of corresponding sulfide minerals by (Kakovsky, 1980). He found the decrease in the order of the solubility product of sulfide minerals to be in line with the increase in the order of their floatability. From exchange reactions of lead-diethyl xanthate, the well-known Barsky equation can be derived ... 

In contrast to pore-water data, analysis of the solid phase shows extensive and comparable production of sulfide fixed as FeS (acid-volatile sulfide) in all areas. Deep-water stations show extensive loss of solid-phase sulfide either prior to or after conversion of FeS to FeS2 (pyrite). All stations have comparable standing crops of organic matter and all stations are capable of supporting approximately the same rate of sulfate reduction in the upper 10 cm of sediment where most decomposition takes place. 

The pathways of sulfide oxidation in nature are varied, and in fact poorly known, but include (1) the inorganic oxidation of sulfide to sulfate, elemental sulfur, and other intermediate sulfur compounds, (2) the nonphototrophic, biologically-mediated oxidation of sulfide (and elemental sulfur), (3) the phototrophic oxidation of reduced sulfur compounds by a variety of different anoxygenic phototrophic bacteria, and (4) the disproportionation of sulfur compounds with intermediate oxidation states. The first three of these are true sulfide-oxidation pathways requiring either the introduction of an electron acceptor (e g. O2 and NO3 ), or, in the case of phototrophic pathways, the fixation of organic carbon from CO2 to balance the sulfide oxidation. The disproportionation of sulfur intermediate compounds requires no external electron donor or electron acceptor and balances the production of sulfate by the production of sulfide. This process will be taken up in detail in a later section. A cartoon depicting some of the possible steps in the oxidative sulfur cycle is shown in Figure 6. 

According to Chang et al. [6], when some ligneous cellulosic materials are used as the carbon source (such as hay or straw), the reduction of sulfate with further production of sulfide can be improved with the supplementation of electron donors easily accessible by the microbes, such as sucrose, peptone, and lactate. This can explain the marked increase in the efficiency of metal removal observed in run II, where seaweed was mixed with a certain quantity of sugarcane bagasse. 

For run I (seaweed only), in the noninoculated column (B), Cd removal was high, but Zn removal was not so good. In this case, the predominating mechanism was biosorption of metals. On the other hand, in the inoculated column (A), both Cd and Zn removals were very high, confirming the importance of the production of sulfides by SRB cells. 

Although the production of sulfide was not enough to precipitate all zinc and cadmium present in the influent, other mechanisms also acted to improve the treatment process. 

The conversion of serine to cysteine involves some interesting reactions. The source of the sulfur in animals differs from that in plants and bacteria. In plants and bacteria, serine is acetylated to form O-acetylserine. This reaction is catalyzed by serine acyltransferase, with acetyl-GoA as the acyl donor (Figure 23.13). Conversion of O-acetylserine to cysteine requires production of sulfide by a sulfur donor. The sulfur donor for plants and bacteria is 3 -phospho-5 -adenylyl sulfate. The sulfate group is reduced first to sulfite and then to sulfide (Figure 23.14). The sulfide, in the conjugate acid form HS", displaces the acetyl group of the O-acetylserine to produce cysteine. Animals form cysteine from serine by a different pathway because they do not have the enzymes to carry out the sulfate-to-sulfide conversion that we have just seen. The reaction sequence in animals involves the amino acid methionine. 

In sulfate-dominated wetlands, production of sulfide (through biological reduction of sulfate) and formation of ferrous sulfides may preclude phosphorus retention by ferrous iron in regulating phosphorus bioavailability (Caraco et al., 1991). In iron- and calcium-dominated systems, Moore and Reddy (1994) observed that iron oxides likely control the behavior of inorganic phosphorus under aerobic conditions, whereas calcium phosphate mineral precipitation governs the solubility under anaerobic conditions. This difference is in part due to a decrease in pH under aerobic conditions as a result of oxidation of ferrous iron compounds, whereas an increase in pH occurs under anaerobic conditions as a result of reduction of ferric iron compounds. The juxtaposition of aerobic and anaerobic interfaces promotes oxidation-reduction of iron and its regulation of phosphorus solubility. 

The biogenic reduction of sulfate follows two biosynthetic pathways (1) assimilatory incorporation of sulfur into the amino acids e.g. cysteine) with very small sulfur isotope fractionation (2) dissimilatory production of sulfide coupled to oxidation of OM to CO2 (see Scheme 1). If we take, for example, methane as the electron donor, the reaction is... 

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