Sulfur in peat

This chapter reviews research on the abundance of sulfur in major coal basins in the U.S., the forms of sulfur in coals, the distribution of sulfur in coal lithotypes and macerals, and the nature of sulfur-containing organic compounds in coal. Next, the origin of sulfur in coal is reviewed based on the evidence from the distribution and speciation of sulfur in peat, and from stratigraphic, isotopic, and trace element data. Finally, the origin of sulfur in coal is explained by a geochemical model. 

Wieder R. K. and Lang G. E. (1988) Cycling of inorganic and organic sulfur in peat from Big Run Bog, West Virginia. Biogeochemistry 5, 221-242. 

Occurrences of elemental sulfur in peat, coal, and petroleum are described in Chapter 6.4. The role of sulfate reducers in these environments is suggested by the fact that fossil fuels formed in marine environments, where sulfate is in abundant supply, have significantly more sulfide and native sulfur than those formed under freshwater conditions. In fact, a general geological feature of native sedimentary sulfur deposits is their location in sulfate-carbonate rocks and proximity to oil-gas-bearing strata and hydrologic zones where sulfate waters mix with chloride brines (Ivanov, 1964). 

Casagrande, D.J., Siefert, K., Berschinski, C. and Sutton, N., 1977. Sulfur in peat-forming systems of the Okefenokee Swamp and Florida Everglades origins of coal. Geochim. Cosmochim. Acta, 41 161—167. 

Breger, LA. 1977. In Future Supply of Nature-Made Petroleum and Gas. Pergamon, New York, p. 913. Casagrande, D.J. 1987. Sulfur in peat and coal. In Coal and Coal-Bearing Strata Recent Advances, A.C. Scott (Ed.). Geological Society Special Publication No. 32, pp. 87-105. Presentation to Geological Society of... 

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. 

The geochemistry of sulfur in coal is largely controlled by sedimentary environments during peat accumulation, as well as by the geologic conditions during diagenesis following peat formation. In low-sulfur coal, peat... 

Source of Sulfur. Most of the sulfur in high-sulfur coal arises from the occasional seawater inundations over the coastal swamp during peat accumulation or from the seawater that flooded the peat swamp and terminated peat accumulation. Seawater sulfate diffused freely into the underlying peat and was reduced by microorganisms to H2S, S°, and polysulfides. 

In addition, relatively little petrographic work, such as that done by Cohen, Spackman and Dolsen (3) on Florida peats, has been attempted on Mississippi River Delta Plain sediments. This paper describes results of a reconnaissance study undertaken to examine, both chemically and petrographically, the occurrence of sulfur in Mississippi Delta Plain sediments. 

Organic sulfur is the dominant form in peats described in these studies. Pyrite, however, is abundant in brackish and marine peats, occurring in void spaces in or between plant debris (3). In a study of pyrite formation in freshwater peats, Altschuler et al. (5) determined parallel decline in ester sulfate with increases in pyrite as depth increased and concluded that pyrite formed at the expense of organic sulfur. In general, framboidal morphology is present at all salinities. Altschuler et al. (5) and Lowe and Bustin (10) found monosulfides to be minor in peats. 

Figure 1. Framework for main environments examined in studies of sulfur in recent sediments. Freshwater peats, marine peats, marine sediments, and lacustrine sediments occupy comers A, B, C, and D, respectively. Sediments in this study range from A to D and a large proportion are in region I.

Casagrande et al. (1977) found pyrite in peat formed in a marine environment to constitute over 15% of the sulfur present while the pyrite level in freshwater peat was an order of magnitude lower. Carbon-bonded sulfur accounted for 50% of the total sulfur in marine peat, but 70% in freshwater peat. Ester-sulfate constituted 25% of the sulfur in both cases. These authors concluded that the total sulfur found in coal can be incorporated in the peatforming stage. 

Casagrande, D. J., Gronli, K., and Sutton, N. (1980). The distribution of sulfur and organic matter in various fractions of peat Origins of sulfur in coal. Geochim. Cosmochim. Acta 44, 24-32. 

Organic sulfur can represent >50% of the total sulfur found in some coals and can arise from the interaction of peat-type precursors with hydrogen sulfide (Casagrande et al., 1979). On the other hand, there are several lines of evidence (Chou, 1990) which lead to the conclusion that sulfur in plant material is the principal source of sulfur in low-sulfur coal whereas in medium- and high-sulfur coals, seawater is also a predominant source of sulfur (Figure 3.26) (Chou, 1990). 

C.C., and Cohen, A.D. Thermal transformations of nitrogen and sulfur forms in peat related to coalification. 2006 20 635-652. 

Peat Peat is partially decomposed plant matter that has accumulated underwater or in a water-saturated environment. It is the precursor of coal but is not classified as coal. Sold under the term peat moss or moss peat, peat is used in the United States mainly for horticultural and agricultural apphcations, but interest is growing in its use as a fuel in certain local areas (e.g.. North Carolina). Peat is used extensively as a fuel primarily in Ireland and the former Soviet Union. Although analyses of peat vary widely, a typical high-grade peat has 90 percent water, 3 percent fixed carbon, 5 percent volatile matter, 1.5 percent ash, and O.IO percent sulfur. The moisture-free heating value is approximately 20.9 MJ/kg (9000 Btu/lb). 

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