Sulfur under reducing conditions

Wan J, TK Tokunaga, E Brodie, Z Wang, Z Zheng, D Herman, TC Hazen, MK Firestone, SR Sutton (2005) Reoxidation of bioreduced uranium under reducing conditions. Environ Sci Technol 39 6162-6169. Weiner JH, DP Macisaac, RE Bishop, PT Bilous (1988) Purification and properties of Escherichia coli dimethyl sulfoxide reductase, an iron-sulfur molybdoenzyme with broad substrate specificity J Bacterial 170 1505-1510. 

Groundwater. Groundwater under reducing conditions in the presence of hydrogen sulfide converted ethyl bromide to sulfur-containing products (Schwarzenbach et al., 1985). 

The ground mixture is heated to about 750 °C under reducing conditions, normally in a batch process. This can be done in directly fired kilns with the blend in lidded crucibles of controlled porosity, or muffle kilns. The heating medium can be solid fuel, oil, or gas. The sodium carbonate reacts with the sulfur and reducing agent at 300 °C to form sodium polysulfide. At higher temperatures the clay lattice reforms into a three-dimensional framework, which at 700 °C is transformed to the sodalite structure, with entrapped sodium and polysulfide ions. 

Because of strong metal-sulfur bonds, regeneration under reducing conditions is impractical use of oxidative conditions is a much more promising approach. 

Sulfur is also produced from sulfide ores (pyrites) by thermal decomposition in the absence of air, by roasting/smelting under reducing conditions, or by reaction of the ore with S02. Hydrometallurgical processes have produced sulfur from metal pyrites as a by-... 

Sulfur undergoes cyclic transformations, which can be viewed at different levels of organization and complexity. Under reducing conditions (pe < — 2) various microorganisms (e.g., Desulfovibrio) mediate the reduction of S04 by organic... 

In oxidized surface waters and sediments, dissolved iron is mobile below about pH 3 to 4 as Fe and Fe(lII) inorganic complexes. Fe(III) is also mobile in many soils, and in surface and ground-waters as ferric-organic (humic-fulvic) complexes up to about pH 5 to 6 and as colloidal ferric oxyhydroxides between about pH 3 to 8. Under reducing conditions iron is soluble and mobile as Fe(II) below about pH 7 to 8, when it occurs, usually as uncomplexed Fe ion. However, where sulfur is present and conditions are sufficiently anaerobic to cause sulfate reduction, Fe(H) precipitates almost quantitatively as sulfides. Discussion and explanation of these observations is given below. Thermodynamic data for iron aqueous species and solids at 25°C considered in this chapter are given in Table A12.1. Stability constants and A//° values computed from these data are considered more reliable than their values in the MINTEQA2 data base for the same species and solids. 

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