Pyrite FeS

Self-Test L.3B Many abandoned mines have exposed nearby communities to the problem of acid mine drainage. Certain minerals, such as pyrite (FeS,), decompose when exposed to air, forming solutions of sulfuric acid. The acidic mine water then drains into lakes and creeks, killing fish and other animals. At a mine in Colorado, a 16.45-mL sample of mine water was completely neutralized with 25.00 mL of 0.255 M KOH(aq). What is the molar concentration of H2S04 in the water ... 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

H2S fugacity (/h2S)- It is thought that /hjS is controlled by pyrite, Fe-oxides such as magnetite, hematite and Fe-silicates such as chlorite. For instance, the following reaction is important for controlling /hjS (Giggenbach, 1997) ... 

If pyrite (FeS) is present, the Mn02 will also react as follows ... 

Not all of the remobilized phosphate is reprecipitated below the redox boundary. Some escapes by diffusing upward through the pore waters. Once this phosphate enters the oxic zone, it is readsorbed by Fe(ni)OOH along with any Fe that has similarly diffused upward. The Fe that diffuses downward into the sulfete-reducing zone precipitates sulfide to form pyrite (FeS). 

Pyrite (FeS ) is more commonly known as fool s gold. It is used as an iron ore and in the production of sulfur chemicals such as sulfuric acid. 

Another phenomenon which proved to be of operational concern was the deposition of iron pyrite, FeS , which I will discuss later. 

Applications of the core shielding factors in X-ray studies of pyrite, Fe(Il) phthalocyanine, and bis(pyridine)(meso-tetraphenylporphinato)iron(II) generally improve agreement with spectroscopic values (Su and Coppens 1996). 

Bituminous coal ash is often higher in pyritic Fe than subbituminous or lignite ashes, which are often higher in Ca and/or other basic elements. As a result of the increased content of pyritic Fe, bituminous coal ashes may form acidic solutions when mixed with water. Conversely, subbituminous and lignite coals often form basic solutions when mixed with water due to their lower content of pyrite and/or their high content of basic cations. Therefore the pH of ash leachate can range from acidic to basic values depending on coal source (see Donahoe, this volume). 

The apparent exceptions to this hypothesis disappear on investigation thus iron, which is a dyad in ferrous compounds (as FeCl,), a tetrad in cubical pyrites (FeS,"), and a hexad in ferric acid (FeO,Ho,), is apparently a triad in ferric chloride (FeCl,) but the vapour-density of ferric chloride shows that its formula must be doubled—that, in ct, the two atoms of the hypothetical molecule of iron (FeJ have not been com-... 

A set of values of tetrahedral covalent radii 7 for use in crystals of these types is given in Table 7-13 and represented graphically in Figure 7-7. These values were obtained from the observed interatomic distances in crystals of these tetrahedral types and of other types in which the atom of interest forms four covalent bonds with neighboring atoms which surround it tetrahedraliy. For example, in pyrite, FeS. each sulfur atom is surrounded tetrahedraliy by three iron atoms and one sulfur atom, with all of which it forms essentially covalent bonds (Fig. 7-8) the substance is a derivative of hydrogen disulfide, H2S2. That the Fe—S bonds are essentially covalent is shown by the magnetic eri-... 

Fig. 7-8.—The arrangement of iron atoms (small circles) and sulfur atoms (large circles) in the cubic crystal pyrite, FeS. Each iron atom is surrounded octahedrally by six sulfur atoms, and each sulfur atom is surrounded tetrahedrally by one sulfur atom and three iron atoms.

Much of this early work was strictly pragmatic without any theory as we would understand it. It was necessary to be able to identify the best and richest ores, to be able to distinguish between superficial resemblances. The ramiliar properties of foots gold, iron pyrites, FeS-, as compared with the dement gold is a well-known example. 

The strategies used in studies of high temperature reactions of metals have been brought to bear on some of the problems associated with the direct liquefaction of coaL Many coals contain sulfur, combined in both organic and inorganic forms, in excess of amounts allowable under current combustion standards. In some coals much of the sulfur is in the form of pyrite, Fe 2> which may, paradoxically, serve as a catalyst or the precursor of a catalyst for the liquefaction process. The information available for the Fe-S-O-H system has been assembled in an attempt to provide a framework for interpreting experimental results, and to facilitate the planning of further experim ents. 

First, it should be noted that pyrite, Fe 2, if finely divided, is usually completely converted to pyrrhotite at temperatures above 350°C in an atmosphere of hydrogen and steam or of synthesis gas within reaction times of less than thirty minutes. The reaction products are a very finely divided pyrrhotite, with a stoichiometry of approximately FeS, and hydrogen sulfide. 

You can produce your own vitriol though it takes some time. Collect together ten to twenty pounds (at least) of iron pyrite (FeS) and grind it to powder. Spread the powder out onto a large flat iron tray then alternately roast it gently and spray with rainwater to moisten, then dry. 

Cobalt-nickel pyrites, (Fe, Co, Ni)Sa, has been found in Westphalia as small cubic crystals, steel-grey in colour, giving a greyish-black streak.3 Density 4 7, hardness 5 to 5 5. Iron nickel pyrites, (Fe,Ni)S2, occurs in Norway 4 and in the Sudbury district, Ontario.5... 

Disulfide group (all containing dianion units in the structure) Pyrite-type (cubic) Pyrite (FeS,), cattierite (CoS,), vaesite (NiS,), etc. 

Suga, S., K. Inoue, M. Taniguchi, S. Shin, M. Seki, K. Sato, and T. Teranishi (1983). Vacuum ultraviolet reflectance spectra and band structures of pyrites (FeS, CoSj and NiSj) and NiO measured with synchrotron radiation. J. Phys. Soc. Japan 52, 1848-56. 

As Fe + ions oxidise HgS, HS and the precipitation of FcgSg free from sulphur is impossible, Monohydrated iron(III) oxide reacts with dry H2S to give primarily FcgSg some of which disproportionates into FeSg and FeS (Pearson and Robinson, 1928). A cobalt(III) sulphide cannot be precipitated from aqueous solution and there is no unequivocal evidence for its formation or that of NigSg in dry reactions. However, disulphides are known, of which the most important is FeS.2. In its commonest form, pyrites, Fe atoms and Sg pairs are arranged in a sodium chloride-type structure with the axes of the sulphur pairs parallel to the four trigonal axes (Fig. 261). 

Observed authigenic reduced sulphide minerals include amorphous FeS, mackinawite (FeS), greigite (Fc SJ, pyrite (FeS ) and to a much lesser extent minerals which incorporate other cations, notably Mn(II). Alabanite (MnS), however, is very rare, and has only been found associated with sedimentary systems where Mn/Fe ratios are exceptionally... 

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