Sediments sulfide minerals

The cycle of iron solubilization will continue as long as bacteria and/or plants produce organic ligands.The cycle will stop when sulfate reduction rates are high and organic ligand production is low. At this point soluble hydrogen sulfide reacts with Fe(II) to form sulfide minerals. The iron cycle shown in Fig. 10.15 for salt marsh sediments may also occur in other marine sedimentary systems. 

Gharacterization of inorganic sulfur speci-ation in marine and freshwater porewaters is critical to our understanding of metal and sulfur cycling in sediments. Since coprecipitation and/or adsorption on FeS(g) and formation of discrete authigenic sulfide minerals can effectively remove trace metals, many metal cycling studies are... 

Like estuary and marine sediments, arsenic may also migrate into deeper sediments where bacteria reduce sulfate to sulfide (Figure 3.4). In such highly reducing environments, arsenic might be incorporated into relatively stable sulfide minerals (Ford, Wilkin and Hernandez, 2006). 

Detrital iron (oxy)(hydr)oxides, organic matter, and other arsenic-bearing materials in sediments may be transported by water or wind into wetlands and contribute arsenic to peats. Once buried, reductive dissolution releases sorbed arsenic from iron (oxy)(hydr)oxides. Under sulfate-reducing conditions, the arsenic coprecipitates in sulfide minerals or organic matter. During diagenesis, additional arsenic may be released from the organic matter and coprecipitate in sulfide minerals (Eskenazy, 1995), 253. 

Mine tailings Rocks, minerals, sediments, soils, and other wastes that result from the mining of ore deposits or coal. Mine tailings often contain pyrite and other sulfide minerals, which oxidize in the presence of oxygen and water to form acid mine drainage. 

Lein, A. Y. Formation of carbonate and sulfide minerals during diagenesis of reduced sediments, in Environmental biogeochemistry and geomicrobiology 1 (ed. Krumbein, W. E.) p. 339, Ann Arbor Mich. Ann Arbor Publishers Sci. 1978... 

Cooper, D.C. and Morse, J.W. (1998) Extractability of metal sulfide minerals in acidic solutions application to environmental studies of trace metal contamination within anoxic sediments. Environ. Sci. Technol., 32, 1076. 

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... 

First we review controls on the amount and isotopic composition of various forms of sulfur in lacustrine environments. Next, we summarize the diverse behavior of sulfur in sediment from two freshwater environments in sediment from three modern, productive, saline lakes and in oil shales deposited in freshwater and saline lacustrine environments. Lastly, our results are integrated in order to produce models that 1) predict the extent of formation and isotopic composition of sulfide minerals in response to major controls on sulfur geochemisty and 2) show the formational pathway of organosulfur in lacustrine oil shale and its derivative oil. 

The elemental sulfur (Sq) in Equation 3 is generally dissolved as a polysulfide ion. In iron-poor sediment or sediment in which iron resides largely in refractory minerals, only small amounts of sulfide minerals form. Excess H2S in these sediments slowly reacts with organic matter to form organosulfur. 

Sediments deposited in Flodelle Creek spring pool and the Great Lakes have similar and relatively uncomplicated sulfur geochemistry that is controlled by two processes. These processes are the assimilation of sulfur into living biota and its subsequent deposition as organosulfur when the organism dies, and the complete reduction of the pore-water sulfate to H2S that forms sulfide minerals. Low dissolved sulfate concentrations limit the amount of sulfide minerals formed. The 834S value of most of the Smin is essentially the same as the dissolved sulfate. The possible exceptions are minerals formed in sediment from which some 34S-depleted H2S had diffused. 

Walker Lake sediment contains variable amounts of Smin. 0.10 to 2.2 wt%, and 834Smin values ranging from -42%o to +25%o. On the average, 44% of the sulfur in sulfide minerals resides in monosulfides and 56% resides inpyrite. Both minerals coexist in many samples and have similar 834S values. The exact reason for monosulfide preservation in this sediment is not known however,... 

Berner (3J5.) attributes monosulfide preservation in Black Sea sediment to insufficient elemental sulfur (polysulfides) to completely convert FeS to FeS2 (Equation 3). Both sulfide minerals in sediment from Walker Lake are typically depleted in 34S with a 834Smin average of -15%o. At a few depths, however, 834S values are similar or enriched in 34S relative to the sulfate in the modern lake (834S +10%o calculated from pore-water sulfate data). 

Pyrite was the only sulfide mineral observed in sediment from Great Salt Lake. The Smin concentrations are linearly dependent on total-iron concentrations... 

Iron monosulfides comprise about 20% of the iron sulfide minerals in the noneuxinic sediment and about 50% in the euxinic sediment. Their greater preservation in the euxinic sediment, as in sediment from Walker Lake, is probably a result of insufficient elemental sulfur formation in this extremely reducing environment. Seasonally aerobic conditions at the sediment-water interface of the noneuxinic sediment would promote elemental sulfur formation from the oxidation of H2S that accumulates in pore water. 

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