Environments, sulfur speciation

Sulfur isotopes can effectively be used to examine important geochemical processes associated with redox changes in sedimentary environments. The speciation of sulfur is strongly affected by redox potential, pH, productivity, microbial sulfate reduction, and iron availability (Berner, 1984). More details are provided on the sulfur cycle in chapter 12. In general, during microbial dissimilatory sulfate reduction there is fractionation of sulfur... 

Sulfur Speciations and Redox Processes in Reducing Environments... 

Nuzzio D. B. (2001) Sulfur speciation monitored in situ with solid state gold amalgam voltammetric microelectrodes polysulfides as a special case in sediments, microbial mats and hydrothermal vent waters. J. Environ. Monitor. 3, 61-66. 

Figure 12.15 Distribution of sulfur species versus pH in the system H2S-S(conoid)-H2O-NaCl(0.7 M) for ZS(aq) = 10" M. Reprinted with permission from Am. Chem. Soc. Symp. Ser. 93, J. Boulegue and G. Michard, Sulfur speciations and redox processes in reducing environments. In Chemical modeling in aqueous systems. Copyright 1979 American Chemical Society,...

Hartgers W.A., Lopez J.F, Sinninghe Damste J.S., Reiss C., Maxwell J.R., GrimaltJ.O. (1997) Sulfur-binding in recent environments II. Speciation of sulfur and iron and implications for the occurrence of organo-sulfur compounds. Geochim. Cosmochim.Acta 61, 4769—88. 

Huffman GP, Mitra S, Huggins FE, Shah NS, Vaidya N, Lu F (1991) Quantitative analysis of all major forms of sulfur in coal by X-ray absorption fine structure spectroscopy. Energy Fuels 5 574-581 Huffman GP, Shah NS, Huggins FE, Stock LM, Chatterjee K, Kilbane JJ, Chou M, Buchanan DH (1995) Sulfur speciation of desulfurized coals by XANES spectroscopy. Fuel 74 549-555 Huggins FE, Huffman GP (1995) Chlorine in coal anEXAFS spectroscopic investigation. Fuel 74 556-569 Hundal LS, Carmo AM, Bleam WL, Thompson ML (2000) Sulfur in biosolids-derived fulvic acidic characterization by XANES spectroscopy and selective dissolution approaches. Environ Sci Technol 34 5184-5188... 

Although the abundance of silver in the Earth s crust is comparatively low (0.07 pgg-1), it is considered an environmental contaminant and is toxic at the nanomolar level. As an environmental pollutant it is derived from mining and smelting wastes and, because of its use in the electrical and photographic industries, there are considerable discharges into the aquatic environment. Consequently, there have been studies on the geochemistry and structure of silver-sulfur compounds [31]. Silver, either bound to large molecules or adsorbed on to particles, is found in the colloidal phase in freshwater. In anoxic sediments Ag(I) can bind to amorphous FeS, but dissolved silver compounds are not uncommon. A more detailed study of silver speciation in wastewater effluent, surface and pore waters concluded that 33-35% was colloidal and ca. 15-20% was in the dissolved phases [32]. 

Zaback DA, Pratt LM (1992) Isotopic composition and speciation of sulfur in the Miocene Monterey Formation reevaluation of sulfur reactions during early diagenesis in marine environments. Geochim Cosmochim Acta 56 763-774... 

The solubility of Hg(II) is controlled by chemical speciation in natural waters, and the availability of ligands for complexation shifts dramatically under varying redox conditions (40). Speciation of dissolved Hg(II) in anoxic environments, such as sediments or the hypolimnion, should be strongly influenced by reactions with reduced sulfur (40, 41), whereas organic complexation is potentially important under oxic conditions (42, 43). 

The transformation of contaminants by sulfur species in anaerobic environments can involve both reduction and nucleophilic substitution pathways. These processes have been studied extensively (67-74), but the complex speciation of sulfur makes routine predictions regarding these reactions difficult. 

High sulfur content in coal hinders the use of coal resources because sulfur dioxide emissions from utility and industrial boilers are a cause of acid rain. Thus, research into the nature of sulfur in coal is important for improving coal utilization. Geochemical studies of sulfur in coal provide information about the abundance, distribution, and speciation of sulfur in coal. Many of these properties are determined by geological environments and processes of coal formation. 

In order to identify the chemical nature of phosphorus and sulfur in complex matrices such as antiwear tribofilms, it is essential to compare the spectra of films with different model compounds in which the local chemical environments of phosphorus and sulfur are known. The high resolution of the technique allows characterization of the chemical nature of phosphorus and sulfur in the tribofilm. Investigators have shown that the chain length of polyphosphate is related to the length of alkyl groups in ZDDP. By comparison of the L-edge XANES spectra of the tribofilms with the spectra of model compounds with known structures, it has been possible to speciate the chemical nature of phosphorus and sulfur in the antiwear tribofilms. 

The variety of common oxidation states encountered for iron(II, III) and sulfur(—II, 0, II, IV, VI) results in complex and varied speciation for these elements in natural environments. Limiting the scope to only those oxidation states and species that commonly support anaerobic respiration, narrows the discussion to primarily the oxides of iron(III) and sulfur(II, IV, VI). Oxides of Fe(III) are primarily found as insoluble oxide or hydroxide particle coatings and aggregates (Thamdrup, 2000), and can comprise several mass percent of freshwater or marine sediments... 

The degree to which a pollutant is taken up, which also determines its potential toxicity, is determined by its bioavailability. Bioavailability refers to the ability of a chemical to move from the environment into a living organism. Bioavailability depends upon the ionization state and speciation of a chemical. Because certain organic compounds and clays can strongly bind various hydrocarbon chemicals and metals, the amount of organic carbon and clay in the soil, sediment, and water determines the bioavailability of these compounds. Bioavailability of metals is also dependent on the amount of sulfur precipitates of other metals in soils and sediments. 

---