Reduction of sulfate

Sulfur comes mainly from the decomposition of organic matter, and one observes that with the passage of time and of gradual settling of material into strata, the crude oils lose their sulfur in the form of H2S that appears in the associated gas, a small portion stays with the liquid. Another possible origin of H2S is the reduction of sulfates by hydrogen by bacterial action of the type desulforibrio desulfuricans (Equation 8.1) ... 

A relatively high degree of corrosion arises from microbial reduction of sulfates in anaerobic soils [20]. Here an anodic partial reaction is stimulated and the formation of electrically conductive iron sulfide deposits also favors the cathodic partial reaction. 

Cathodic protection with impressed current, aluminum or magnesium anodes does not lead to any promotion of germs in the water. There is also no multiplication of bacteria and fungi in the anode slime [32,33]. Unhygienic contamination of the water only arises if anaerobic conditions develop in the slurry deposits, giving rise to bacterial reduction of sulfate. If this is the case, HjS can be detected by smell in amounts which cannot be detected analytically or by taste. Remedial measures are dealt with in Section 20.4.2. 

The great evaporite basin deposits of elemental sulfur in Poland were discovered only in 1953 but have since had a dramatic impact on the economy of that country which, by 1985, was one of the world s leading producers (p. 649). The sulfur occurs in association with secondary limestone, gypsum and anhydrite, and is believed Ui be derived from hydrocarbon reduction of sulfates assisted 1 bacterial action. The H2S so formed is consumed by other bacteria to produce sulfur as waste — this accumulates in the bodies of the bacteria until death, when the sulfur remains. 

The case of bacterial reduction of sulfate to sulfide described by Berner (1984) provides a useful example. The dependence of sulfate reduction on sulfate concentration is shown in Fig. 5-4. Here we see that for [SO ] < 5 mM the rate is a linear function of sulfate concentration but for [SO4 ] > 10 itiM the rate is reasonably independent of sulfate concentration. The sulfate concentration in the ocean is about 28 mM and thus in shallow marine sediments the reduction rate does not depend on sulfate concentration. (The rate does depend on the concentration of organisms and the concentration of other necessary reactants - organic carbon in this case.) In freshwaters the sulfate concentration is... 

In the context of diagenesis in recent anoxic sediments, reduced carotenoids, steroids, and hopanoids have been identified, and it has been suggested that reduction by sulhde, produced for example, by the reduction of sulfate could play an important part (Hebting et al. 2006). The partial reduction of carotenoids by sulfide has been observed as a result of the addition of sulfide to selected allylic double bonds, followed by reductive desulfurization. This is supported by the finding that the thiol in allylic thiols could be reductively removed by sulhde to produce unsaturated products from free-radical reactions (Hebting et al. 2003). 

Determinations of 8 " S have been extensively used in studies on the sulfur cycle, including reactions involving microbial anaerobic reduction of sulfate and thiosulfate (Smock et al. 

Biochemical waste transformation occurred at low waste concentrations, resulting in the production of methane. Additional microbial degradation of the waste resulted in the reduction of sulfates to sulfides and ferric ions to ferrous ions. 

As a safer alternative to digestion of vegetable matter with perchloric acid, alkaline oxidation of sulfur compounds to sulfate by sodium hypobromite, and reduction of sulfate to hydrogen sulfide by hydriodic acid/formaldehyde/phosphinic acid is recommended. 

Columbia designed and operated by Nature Works for Teck Metals Limited. The system was constructed in 1997 and rebuilt in 2002 to operate year-round. It treats effluent from historic capped landfills. It is capable of treating effluent with high concentrations of metals Zn (up to 3800 ppm) and As (up to 3600 ppm). However, mean concentrations over a five-year period are lower (Zn 267.6 As 167.6). The system was designed to treat Zn, Cd, Pb and other metals based on bacterial reduction of sulfate. Bacterial processes for removal of Zn and some other cations were known to occur when the system was designed, but unexpectedly high concentrations of As were also removed. The mechanism for As removal is not yet clearly understood. 

Reduction of sulfate, nitrate, selenate and chromate Analogous isotopic behavior... 

If the cell is well supplied with nutrients, then the production of activated enzyme is great and this step is relatively fast. If the transport of sulfate into the cell cannot keep up with the reduction of sulfate, the concentration of sulfate within the cell becomes small, and very little of the isotopically fractionated sulfate inside the cell can leak back out of the cell. Thus, the effect of the internal isotopic fractionation on the outside world is minimal and the overall fractionation of the process is small. In a hypothetical extreme case, every sulfate anion entering the cell would be consumed by reduction. This would require a complete lack of isotopic fractionation, because when all S atoms entering are consumed, there can be no selection of light vs. heavy isotopes. The isotopic fractionation of the overall reduction reaction would be equal to that which occurs during the diffusion step only. 

Thode HG, Kleerekoper H, McElcheran DE (1951) Isotope fractionation in the bacterial reduction of sulfate. Research Lond 4 581... 

Calcined LDHs have been investigated as potential materials for the reduction of SOx and NOx emissions from FCCU in oil refineries [75,76]. Corma et al. found that mixed oxides obtained from a Cu/Mg/Al LDH precursor were the most effective at catalyzing both the oxidation of SO2 to S04 in the FCC regenerator and the reduction of sulfates to H2S, which may be recovered, in the reducing atmosphere of the cracking zone [76]. Calcined Cu/Mg/Al LDHs [77] and Co/Mg/Al LDHs [78], subsequently activated by heating under H2, can simultaneously remove SOx and NOx. In both cases, reduced transition metal species have been proposed as the active sites. 

Peck then became interested in sulfate-reducing bacteria, which he had got to know in Gest s laboratory. To study the reduction of sulfate. Peck worked in Fritz Lipmann s laboratory in Massachussetts General Hospital (1956) and with Lipmann at Rockefeller University (1957). Lipmann started work on active sulfate in 1954 with Helmut Hilz as a postdoctoral fellow and studied the activation of sulfate to APS and PAPS. Lipmann had left the active sulfate projects by 1957 and started, at Rockefeller University, the studies on protein synthesis. Peck published one paper on the reduction of sulfate with hydrogen in extracts of Desulfovibrio desul-furicans (1959) and one on APS as an intermediate on the oxidation of thiosulfate by Thiobacillus thioparus (1960). 

Figure 8.1. Redox proteins catalyzing electron transfer from hydrogen to sulfate in Desulfovibrio. The cytoplasmic uptake of protons associated with the reduction of sulfate is not shown. Hyd, hydrogenase cyctcs, cytochrome C3 HmcA, HmcB, HmcC, HmcE, HmcF, components of the Hmc complex IM, inner membrane OM, outer membrane.

Deviations in the SO4 ion ratios have also been observed in coastal areas, particularly in the sediments. This effect is due to bacterial reduction of sulfate to sulfide, which occurs in waters devoid of dissolved oxygen. Environmental conditions that contribute to the depletion of dissolved oxygen include restricted water circulation and high rates of organic matter supply. This subject is discussed in Chapters 8 and 12. 

Chemical/Physical. Although no products were identified, the estimated hydrolysis half-life in water at 25 °C and pH 7 is 44 yr (Mabey and Mill, 1978). Bromochloromethane reacts with bisulfide ion (HS ), produced by microbial reduction of sulfate, forming 1,3,5-trithiane and dithiomethane. Estimated reaction rate constants at 25 and 35 °C were 7.29 x 10 and 2.42 x 10 VM-sec, respectively (Roberts et al, 1992). 

For the extraction of sulfates and total sulfur a suitable acid and reducing agent, such as tin(II)-phosphoric acid (the Kiba solution of Sasaki et al. 1979) is needed. The direct thermal reduction of sulfate to SO2 has been described by Holt and Engelkemeier (1970) and Coleman and Moore (1978). Ueda and Sakai (1984) described a method in which sulfate and sulfide disseminated in rocks are converted to SO2 and H2S simultaneously, but analyzed separately. With the introduction of on-line combustion methods (Giesemann et al. 1994), multistep off-line preparations can be reduced to one single preparation step, namely the combustion in an elemental analyzer. Sample preparations have become less dependent on possibly fractionating wet-chemical extraction steps and less time-consuming. 

Fig. 2.21 Rayfeigh plot for sulphur isotopic fractionations during the reduction of sulfate in a closed system. Assumed fractionation factor. 1.025, assumed starting composition of initial sulfate ...

McKay et al. (1996) furthermore suggested on the basis of morphology that tiny sulfide grains inside the carbonates may have formed by sulfate-reducing bacteria. 5 S-values of sulfides range from 2.0 to 7.3%c (Greenwood et at. 1997), which is similar to values from terrestrial basalts and probably not the result of bacterial reduction of sulfate. 

Characteristics often ascribed to MVT deposits include temperatures generally <200°C and deposition from externally derived fluids, possibly basinal brines. Sulfur isotope valnes from MVT deposits suggest two major sulfide reservoirs, one between -5 and +15%c and one greater than +20%c (Seal 2006). Both sulfide reservoirs can be related, however, to a common sea water sulfate source that has undergone different sulfur fractionation processes. Reduction of sulfate occurs either bacterially or by abiotic thermochemical reduction. High 5 S-values should reflect minimal fractionations associated with thermochemical reduction of sea water sulfate (Jones et al. 1996). 

Cole JE, Fairbanks RG, Shen GT (1993) The spectrum of recent variability in the southern oscillation results from a Tarawa atoll. Science 260 1790-1793 Coleman ML, Moore MP (1978) Direct reduction of sulfates to sulfur dioxide for isotope analysis. Anal Chem 50 1594-1595... 

Kitchen NE, Valley JW (1995) Carbon isotope thermometry in marbles of the Adirondack Mountains, New York. J metamorphic Geol 13 577-594 Kiyosu Y, Krouse HR (1990) The role of organic acid in the abiogenic reduction of sulfate and the sulfur isotope effect. Geochem J 24 21-27... 

Ming T, Anders E, Hoppe P, Zinner E (1989) Meteoritic silicon carbide and its stellar sources, implications for galactic chemical evolution. Nature 339 351-354 Minigawa M, Wada E (1984) Stepwise enrichments of along food chains further evidence and the relation between 5 N and animal age. Geochim Cosmochim Acta 48 1135-1140 Mizutani Y, Rafter TA (1973) Isotopic behavior of sulfate oxygen in the bacterial reduction of sulfate. Geochem J 6 183-191... 

As evaporation proceeded, sodium chloride began to precipitate and later potassium chloride and potassium sulfate. The mother liquor then contained the iodides of sodium and postassium, part of the sodium chloride, sodium sulfate, sodium carbonate, cyanides, polysulfides, and some sulfites and hyposulfites resulting from the reduction of sulfates during calcination. 

Hydrogen sulfide enters natural waters from decay of organic matter (e.g., in swamps), bacterial reduction of sulfate ion, or underground sour natural gas deposits. It can be removed by aeration, anion exchange (Eq. 14.14), or oxidation by chlorine to elemental sulfur ... 

In another definitive study, Lovely et al. (1995) demonstrated the complete mineralization of, 4C-benzene by enrichment cultures from San Diego Bay sediments. Their cultures clearly coupled the reduction of sulfate to the oxidation of benzene with no detectable extracellular intermediates. 

As with nitrate, the anaerobic biodegradation of m- and /-xylene could also be linked with the reduction of sulfate at a rate of about 1 /M/day. Edwards et al. (1992) demonstrated the sulfate-dependent degradation of all three xylene isomers. Interestingly, the xylenes were not degraded until toluene was almost depleted. 

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