Partial Oxidation Of Sulfide Research Articles

Reduced sulfur in euxinic sediments of the Cariaco Basin: sulfur isotope constraints on organic sulfur formation

Reduced sulfur accumulation in Holocene and latest Pleistocene euxinic marine sediments from the Cariaco Basin, Venezuela, was investigated to constrain the timing and possible pathways of organic matter (OM) sulfurization. Data were collected for a diverse suite of sulfur species, including concentrations and sulfur isotope compositions of pore-water sulfide, pore-water sulfate, pyrite sulfur, total organic sulfur (TOS), kerogen sulfur (KS), and polar bitumen sulfur (PBS). Results suggest that there was a period during which almost no diagenetic pyrite formed in the sediments of the Cariaco, coincident with a shift from high to lower sedimentation rates and a concomitant change in the delivery of organic matter to the sediments. The sulfur isotope composition of organic matter was predicted based on assumed pathways using weighted isotopic mass balance calculations and compared to measured isotope values for organic sulfur. These results indicate that organic sulfur is derived primarily from pore-water sulfide, with minor contributions from primary bio-sulfur (e.g., in proteins derived from algae and bacteria). The predicted sulfur isotope values of organic sulfur compounds (OSC) suggest that pore-water sulfide is the ultimate source of reduced sulfur for incorporation into organic matter. It is possible, however, that reactive sulfur intermediates such as elemental sulfur or polysulfides react directly with organic matter. These intermediate sulfur species are likely formed through partial oxidation of sulfide by anaerobic sulfide-oxidizing microbes living in the sediments.

Synthesis of poly(thio-1,4-phenylene) by oxidative coupling reaction of diphenyl disulfide with potassium persulfate in strongly acidic solutions

The synthesis of poly(thio- 1,4-phenylene) (PPS) at room temperature by the reaction of diphenyl disulfide with potassium persulfate (K2S2O8) in non-basic solvents, in the presence of trifluoromethanesulfonic acid, is reported. The reaction in chlorinated solvents, such as dichloromethane and tetrachloroethane, resulted in partial oxidation of sulfide to sulfoxide and sulfone. On the other hand, the polymerization proceeded well in nitrobenzene and the PPS formed was free of branches, crosslinks and thianthrene units. The molecular weight of the polymers formed in different solvents were in the range 2000–8000. The reaction proceeded under identical conditions with bis(2,6-dimethylphenyl) disulfide as well, but the polymer yield was lower.

Bioleaching of metals from soils or sediments

Bioleaching can be one of few techniques applicable for the removal of toxic metals from polluted soils or sediments. Its principle is a microbial production of sulphuric acid and leaching of metals with it. The use of bioleaching can benefit from the use of low-cost substrates and from a possible coupling to other processes of microbial sulphur cycle, like sulphate reduction to treat spent bioleaching liquor, or partial sulphide oxidation to recycle sulphur. For the evaluation of bioleaching, the existence of different leaching strategies is considered, i.e. intensive or extensive extraction. The intensive extraction uses high concentrations of acid at short extraction times, whereas low acid additions and long treatment times are used in extensive processes. On a reference study with wetland sediment receiving mine drainage we demonstrated that the bioleaching is a typical extensive process. The bioleaching experiments involved the use of the different sulphur substrates, i.e. orthorhombic sulphur flower and microbially produced, recycled sulphur from partial sulphide oxidation process. The latter type of sulphur substrate performed considerably better.

Occurrence of particle‐bound polysulfides and significance of their reaction with organic matters in marine sediments

Inorganic polysulfides (Sn2−, where n > 1) contribute to the incorporation of sulfur into organic matter in reducing sediments, especially when conditions exist for partial oxidation of sulfide. Inorganic polysulfides have been assumed previously to exist only in the aqueous phase. Our results suggest that a significant fraction of inorganic polysulfides is bound to the particulate‐phase of sediments and can react with carbon‐carbon unsaturated bonds in organic matter, thereby attaching it to the particulate phase through polysulfide linkages. This mechanism may affect the bioavailability of the reactive organic matter in sediments and hence may play an important role in the preservation of organic matter in anoxic marine sediments.

Anoxie transformations of radiolabeled hydrogen sulfide in marine and freshwater sediments

Radiolabeled hydrogen sulfide (H 35S −) was used to trace the anoxic sulfur transformations in marine and freshwater sediment slurries. Time course studies consistently showed a rapid 35S 2O 3 − formation and a progressive accumulation of 35SO 4 − and thus indicated an anoxic sulfide oxidation to sulfate. Thiosulfate was partly turned over by oxidation or disproportionation and was found to be an intermediate in the 35SO 4 − formation. The results demonstrate that oxidative and reductive sulfur cycling may occur simultaneously in marine and freshwater sediments. When added as exogenous oxidant, nitrate (NO 3 −) stimulated the anoxic sulfide oxidation to sulfate. Ferric iron, added in the form of lepidocrocite (γ-FeOOH), caused the precipitation of iron sulfides and only partial sulfide oxidation to pyrite and elemental sulfur.

The sources of alkalinity in Lake Miklavatn, north Iceland

Lake Miklavatn, north Iceland, is highly stratified with an 8–9‐m layer of freshwater overlying saline and anoxic deeper water. Sulfide and ammonia concentrations are high in the stagnant and saline layer, and titration alkalinity exceeds conservative alkalinity in the deepest part of the lake by a factor of 3–4. Reduction of sulfate was estimated by direct measurement of the sulfate concentration. With one exception the decrease in sulfate was found to exceed the measured sulfide concentration. This is explained by partial oxidation of sulfide due to mixing with oxygenated water from the upper layer. The excess alkalinity is 92–93% accounted for by sulfate reduction and formation of ammonia, whereas excess metal carbonates do not seem to be a source.

On the volumetric determination of hydrogen sulfide and soluble sulfides

Two procedures for the determination of sulfides are compared. In one, the sulfide, contained in a weakly alkaline cadmium acetate solution, is added to a neutral solution containing potassium iodide and potassium iodate, which is then acidified. It is shown that, when this order is followed, errors are introduced, which are probably due to the partial oxidation of sulfide to sulfate instead of to elemental sulfur. In the other method the sulfide in the cadmium acetate solution is added first to an acid solution, followed by the addition of the potassium iodide-iodate solution. The theoretical yield was obtained.