Iron pyrites stable

Rusticyanin is a component in the respiratory chain of the bacterium Thiobacillus ferrooxidans (44-46). This bacterium is capable of growth solely on the energy available from the oxidation of aqua Fe(II) to Fe(III) by O2. It is found in acid mine leachings, and is used commercially in the extraction of copper and uranium (see the review by Ewart and Hughes, this volume). Its ability to take into solution iron pyrites is particularly relevant. It has been suggested that an acid-stable cytochrome mediates electron transfer between rusticyanin and Fe (47, 48). The working pH is —2.0. 

Ray et al. (1979) and Alvin (1974) have reported that both the additive (magnetite) and the reaction product (iron pyrite) are stable, inert high-density materials that do not have adverse effects on mud properties compared to other commercially available zinc-containing scavengers that usually have adverse effects on mud properties. This has been observed on different types of mud, especially the simple formulations like spud and salt mud. 

Beyond these two columns, the removal of all valence electrons is usually not energetically possible. For example, iron has eight valence electrons but forms only two stable cations, Fe and Fe. Compounds of iron containing these ions are abundant in the Earth s crust. Pyrite (FeS2) and iron(II) carbonate (FeC03, or siderite) are examples of Fe salts. Iron(IIt) oxide (Fc2 O3, or hematite) can be viewed as a network of Fe cations and O anions. One of the most abundant iron ores, magnetite, has the chemical formula FC3 O4 and contains a 2 1 ratio of Fe and Fe cations. The formula of magnetite can also be written as FeO FC2 O3 to emphasize the presence of two different cations. 

To run the simulation, we decouple acetate from carbonate, and sulfide from sulfate, and suppress the iron sulfide minerals pyrite and troilite (FeS), which are more stable than mackinawite, but unlikely to form. We set the fluid composition, including an amount of HS small enough to avoid significantly supersaturating mackinawite, and define the rate law for the sulfate reducers. The procedure in REACT is... 

The most common type of troublesome scale is that of amorphous silica and calcium carbonate. Scales of various metallic sulphides is the rule rather than the exception. By far the most abundant sulphide scale consists of iron sulphides. They include pyrite, marcasite, and pyr-rhotite (Kristmannsdottir 1989), but sulphide scale of other metals have also been observed, such as Cu, Pb, and Zn (White et al. 1963 Gallup 1989 Gallup et al. 1995 Hardardottir et al. 2001 Reyes et al. 2002). Sulphide scales are often poorly crystalline and they may be amorphous to X-rays. Moreover, the sulphidebearing scales are known to be enriched in various elements such as Ag, As, Au, Cd, and Mn. Reyes et al. (2002) observed that scales at Rotokawa, New Zealand, also contained elevated concentrations of Hg, Sb, and Se, which were incorporated in pyrite. The quantity of sulphide scale formation is generally very limited and may in fact be beneficial rather than troublesome as the scale forms a stable protective... 

Molybdenite (MoS2) forms stable assemblages with the sulfur-rich portion of the chalcocite-bornite solid solution, with chalcopyrite solid solution, with the iron-deficient portion of the pyrrhotite solid solution, and with pyrite. Similar intergrowths between the respective ore minerals, stable at low temperatures, are known from numerous localities. 

The sulfur-bearing minerals that predominate in coal seams are the iron sulfide ores pyrite and marcasite. Both have the same ratio of sulfur to iron, but their crystallographic properties are quite different. Marcasite has an orthorhombic structure, while pyrite is isometric. Marcasite is less stable and more easily decomposed than pyrite. The latter is the most widespread of all sulfide minerals and, as a result of its greater abundance in the eastern United States, pyrite is recognized as the major source of acid mine drainage. FeS2(s) is used here as a symbolic representation of the crystalline pyritic agglomerates found in coal mines. 

Iron is often described as a ubiquitous element since it forms numerous stable compounds with S and with silicates. Iron represents about 5.0% of the earth s crust, occurring as hematite, magnetite, limonite, siderite, and pyrite. 

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