Iron sulfides precipitation

Iron is the most abundant, useful, and important of all metals. For example, in the 70-kg human, there is approximately 4.2 g of iron. It can exist in the 0, I, II, III, and IV oxidation states, although the II and III ions are most common. Numerous complexes of the ferrous and ferric states are available. The Fe(II) and Fe(III) aquo complexes have vastly different pAa values of 9.5 and 2.2, respectively. Iron is found predominantly as Fe (92%) with smaller abundances of Fe (6%), Fe (2.2%), and Fe (0.3%). Fe is highly useful for spectroscopic studies because it has a nuclear spin of. There has been speculation that life originated at the surface of iron-sulfide precipitants such as pyrite or greigite that could have caused autocatalytic reactions leading to the first metabolic pathways (2, 3). 

This small increase in attachment to the cells after 1 day was likely because the iron level in culture decreased with time as a result of the metabolic production of sulhde, which complexed with the iron to produce the iron sulfide precipitate, effectively lowering the dissolved iron concentration toward that of the low iron condition. It would seem that when organisms are placed in low-iron environments, they will use their chemotactic response/biologic inductions mechanisms to ensure that the iron requirements of the cells high iron requiring proteins (i.e., cytochromes, ferre-doxin, hydrogenases) are satished. 

A Cameron-Plint friction machine generated tribofilms with two-layer structure a zinc polyphosphate thermal film overlying a mixed short-chain phosphate glass, containing iron sulfide precipitates. A tribochemical reaction between the zinc polyphosphate and the iron oxides species is proposed on the basis of the hard and soft acid and base HSAB principle (Martin, 1999 Martin et al., 2001). 

Surface chemistry and morphology of poorly crystalline iron sulfides precipitated in media containing sulfate-reducing bacteria. Chem. Geol. 144, 87-97. 

The term hydrotroilite has been historically applied to the hydrated form of ferrous sulfide and it has been identified for some time as a common constituent of reducing sediments (Galliher, 1933). It is now believed that the initial iron sulfide precipitate is poorly crystallized mackinawite, FeSo 94 (Ward, 1970). 

Another possible mechanism involves the reaction of HS" with ferrous iron that has dissolved from the minerals to form an iron sulfide precipitate, which can then act as an electron donor. 

In this case, the ion-association model predicted that the connate water would require a minimum dilution with boiler feedwater of 15 percent to prevent halite precipitation (Fig. 8.23). The model also predicted that over-injection of dilution water would promote barite (barium sulfate) formation (Fig. 8.24). Although the well produced F1,S at a concentration of 50 mg/L, the program did not predict the formation of iron sulfide because of the combination of low pH and high temperature. Boiler feedwater was injected into the bottom of the well using the downhole injection valve normally used for corrosion inhibitor injection. Injection of dilution water at a rate of 25 to 30 percent has allowed the well to produce successfully since startup. Barite and iron sulfide precipitation have not been observed, and plugging with salt has not occurred. 

Fortin D, Southam G, Beveridge TJ (1994) Nickel sulfide, iron-nickel sulfide and iron sulfide precipitation by a newly isolated Desulfotomaculum species and its relation to nickel resistance. FEMS Microbiol Ecol 14 121-132... 

In an approximate reversal of this same reaetion, sulfhydryl ion (HS ) would be responsible for further iron sulfide precipitation at the exterior of the growing moimd. A more detailed equation in which water is the oxidizing agent and electron acceptor demonstrates how green-rast (Fe6(0H)i2C03.2H20) and further hydrogen are produced (55) ... 

Iron Precipitation. Rich sulfide ore or Hquated antimony sulfide (cmde antimony) is reduced to metal by iron precipitation. This process, consisting essentially of heating molten antimony sulfide ia cmcibles with slightly more than the theoretical amount of fine iron scrap, depends on the abihty of iron to displace antimony from molten antimony sulfide. Sodium sulfate and carbon are added to produce sodium sulfide, or salt is added to form a light fusible matte with iron sulfide and to faciHtate separation of the metal. Because the metal so formed contains considerable iron and some sulfur, a second fusion with some Hquated antimony sulfide and salt foHows for purification. 

Sodium arsenite can be used to detect the presence of iron sulfide on the metal surface. Iron sulfide is the corrosion product of the reaction between hydrogen sulfide in drilling fluid and iron in the drillpipe. An acid solution of sodium arsenite reacts with the sulfide to form a bright yellow precipitate. 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Methods for chemical precipitation of sulfides the negative effects of sulfide can be avoided by adding metal salts. The most common salts are iron(II) and iron(III) as sulfate or chloride (Hvitved-Jacobsen et al., 1988 Jameel, 1989). In anaerobic wastewater, Fe(III) will be reduced to Fe(II) and the following precipitation of the highly insoluble iron sulfide, FeS, will proceed as an almost immediate process ... 

The simulations depicted in Figure 8.8 also show that arather low hydrogen sulfide concentration is predicted in the gravity sewer. Only minor problems related to hydrogen sulfide production may therefore arise. Until now, the WATS model did not include sulfide release to the sewer atmosphere, sulfide oxidation or sulfide precipitation that may further reduce the concentrations shown. The predicted sulfide concentrations are, therefore, maximum levels. In case a natural capacity of iron salts in the wastewater to precipitate sulfide is inadequate, the sulfide concentrations are considered at a level that can be relatively easily controlled. 

Some of the discharged sulfide particles settle onto the chimney s exterior, where they are buried by the outward growth of anhydrite. Sulfide precipitation within the chimneys, causes copper, zinc, and iron sulfides to deposit and partially replace the anhydrite. Chimneys can build to several meters in height and their orifices range in diameter from 1 to 30 cm. Both the smoke and the chimneys are composed of polymetallic sulfide minerals, chiefly pyrrhotite (FeS), pyrite (FeS2), chalcopyrite (CuFeS2), and sphalerite or wurtzite (ZnS). 

In some locations, high-temperature fluids undergo considerable subsurfece mixing with relatively fresh seawater. This leads to precipitation of the less soluble iron and copper sulfides within the conduits. The fluids discharging into the ocean generally have temperatures less than 400°C and are milky white because of zinc sulfide precipitates. These white smokers also build chimneys, some of which are as much as 13 m high. Because of their lower temperatures, white smokers are typically encrusted with worm... 

Environmental Research and Development, Inc., offers the neutral process, which reduces hex-avalent chromium using sulfide catalyzed by ferrous iron, while precipitating heavy metals at pH ranges from 7.4 to 8.4. The vendor has combined this technology with cross-flow microfiltration to remove heavy metals from contaminated groundwater and wastewater without the need for large clarifiers. The technology has been used at U.S. Department of Defense (DOD) sites and is commercially available. 

The -pH relations for the important iron-water system at 25 °C are summarized in Fig. 15.3 with some simplifications. First, it is assumed that no elements other than Fe, O, and H are involved in a natural water system, the presence of C02 would oblige us to include FeCC>3 (siderite), and sulfur compounds could lead to precipitation of iron sulfides in certain Eh-pH regimes. As it is, the only Fe-O-H solids we have considered are Fe metal, Fe(OH)2, and Fe(OH)3, whereas in practice magnetite (Fe30,i), hematite (a-Fe2C>3), goethite [a-FeO(OH)], and other Fe-O-H phases could be present. Indeed, our choice of solubility products for Fe(OH)2 and... 

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