Black ferrous sulfide

Ferrous ions (Fe ) combine with sulfide ions (S ) to form black ferrous sulfide FeS) ... 

Hydrogen sulfide also is formed, and this instantly reacts with iron and steel to form thin deposits of black ferrous sulfide in the superheater tubes ... 

The exterior of iron pipes in marshy (anaerobic) soils are often coated with a black film of material that results from a mode of iron corrosion. The ferrous ions produced at the anode react with sulfide present in the anaerobic soil (bacteria may reduce sulfate to sulfide in the absence of oxygen). The black ferrous sulfide is produced by reactions. 

SRBs reduce sulfate to sulfide, which usually shows up as hydrogen sulfide or, if iron is available, as black ferrous sulfide (Fig. 10.10). In the absence of sulfate, some strains can function as fermenters and use organic compounds such as pyruvate to produce acetate, hydrogen, and carbon dioxide. Many SRB strains also contain hydrogenase enzymes, which allow them to consume hydrogen. Most common strains of SRB grow best at temperatures from 25 to 35°C. A few thermophilic strains capable of functioning efficiently at more than 60°C have been reported. 

The ion S " reacts with ferrous Fe ion to form black iron sulfide FeS corrosion product. The hydrogen ions are reduced by electrons produced by anodic reaction in step 1 and form hydrogen atom H ... 

Black iron sulfide Cl 77540 EINECS 215-268-6 Ferrous monosulfide Ferrous sulfide (FeS) HSDB 5803 Iron monosulfide Iron monosulfide (FeS) Iron protosulfide Iron sulfide (FeS) Iron sulfuret Iron sulphide Magnetkies Pyrrhotine Troillite. A variety of iron pyrites. Used as a source of H2S, in ceramics, as a pigment, in anodes and lubricant coatings. Colorless-grey crystals mp = 1194" d = 4,84 insoluble in H2O, soluble in acids,... 

Color in water is imparted by dissolved material such as tarmins from decaying plants. As a result, colored water is most often brownish in tint. Colloidal organic matter fonnd in wastewater will give receiving waters a gray color if concentrations are high, and swamp waters are often black dne to the presence of ferrous sulfide precipitates. Trae colors are due to dissolved materials but in practice, colors associated with colloidal material are included as a characteristic of water. 

A black coloration that appeared during the experiments at pH values >6.5 indicated the formation of FeS. However, the black disappeared again toward the end of the experiments. Apparently most of the sulfide stored in FeS was also oxidized, and only a small portion of the sulfide may have remained as FeS. This development is not surprising because we worked with excess ferric oxide, in contrast to Pyzik and Sommers study (21) in which FeS could accumulate during the experiments. We concluded that the ferrous iron released after redissolution of FeS adsorbs to the ferric oxide surface and forms a surface complex >FeO-Fe+ (reaction 7), to which poly sulfides may bond. 

Figure 6. An idealized scheme for a sedimentary porous medium with pore walls covered by a biofilm. High sulfate reduction rates are maintained even in depths to which sulfate cannot diffuse because of recycling of sulfate within the biofilm. Numbered points (in black circles) denote the following processes I, Respiration consumes oxygen. 2, Microbial reduction of reactive metal Oxides. Reduction of reactive ferric oxides is in equilibrium with reoxidation of ferrous iron by Os. Thus, no net loss of reactive iron takes place in these layers. 3, Microbial reduction of ferric oxides. 4, Sulfate reduction rate (denoted as SRR). 5, Sulfide oxidation, either microbiologically or chemically. 6, Sulfide builds up within the hiofilm, sulfate consumption increases, reactive iron pool decreases. 7, Formation of iron sulfides.

Solutions of ferrous and ferric compounds yield a black precipitate with ammonium sulfide TS. This precipitate is dissolved by cold 2.7 N hydrochloric acid with the evolution of hydrogen sulfide. 

Testing for Completion. Reduction will not take place in the absence of ferrous iofis, which can be demonstrated by the lack of a black precipitate on spot testing with sodium sulfide solution. The reaction is considered complete when an aliquot no longer increases its take-up of sodium nitrite on further reduction with a stronger reducing agent, such as zinc and hydrochloric acid. 

First, 100 parts of m-dinitrobenzene is added to 1,000 parts of water at 90 C contained in a reducer fitted with a reflux condenser and a propeller-type stirrer. Upon emulsification, 245 parts of sodium sulfide (9HaO), dissolved in a minimum of water, is gradually run in. The dinitro compound is gradually reduced to m-nitroaniline, the end point being determined by the formation of a definite black streak when ferrous sulfate solution is added to filter paper spotted with some of the reducer liquor. 

Fbrric—Are acid, and yellow or brown. (1.) Potash, or ammonium hydroxid voluminous, red-brown ppt. insoluble in excess. (2.) Hydrogen sulfid in acid solution milky ppt. of sulfur ferric reduced to ferrous compound. (8.) Ammonium sulfhydrate black ppt. insoluble in excess soluble in acids. (4.) Potassium ferrocyanid dark blue ppt. insoluble in HCl sohible in KHO. <5.) Potassium sulfocyanate dark-red color prevented by tartaric or citric acid discharged by mercuric chlorid. (6.) Tannin blue-black color. 

Sulfate Reducing Bacteria SRBs have been implicated in the corrosion of cast iron and steel, ferritic stainless steels, 300 series stainless steels and other highly alloyed stainless steels, copper nickel alloys, and high nickel molybdenum alloys. They are almost always present at corrosion sites because they are in soils, surface water streams and waterside deposits in general. The key s5unptom that usually indicates their involvement in the corrosion process of ferrous alloys is localized corrosion filled with black sulfide corrosion products. 

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