Magnetic iron pyrites

Mann, S. Sparks, N.H.C. Couling, S.B. Lar-combe, M.C. Frankel, R.B. (1989) Crystallo-chemical characterization of magnetic spinels prepared from aqueous solution. J. Chem. Soc. Faraday Trans. I. 85 3033-3044 Mann, S. Sparks, N.H.C. Frankel, R.B. Bazy-linski, D.A. Jannasch, H.W. (1990) Biomineralization of ferrimagnetic greigite (FejS4) and iron pyrite (FeS2) in a magnetotactic bacterium. Nature 343 258—261... 

Iron and Sulphur—Subsulphides of Iron—Ferrous Sulphide—Ferric Sulphide-Double Sulphides—Iron Pyrites—Marcasite—Magnetic Pyrites—Ferrous Sulphite—Ferri-sulphites—Ferrous Sulphate—Double Sulphates—Fern-sulphates—Alums—Anndo-sulphonates, Thiosulphate, Disulphate, and Thionates of Iron. 

Occurrence.—Free, in small quantity only, in platinum ores and meteorites. As FeoOs in red heematite and specular iron as hydrates of FeaOa in brown heematite and oolitic iron as FeaO in magnetic iron as FeCOj in spathic iron, clay ironstone and bog ore and as FeSa in pyrites. It is also a constituent of most soils and. clays, exists in inany mineral waters, and in the red hlood pigment of animals. 

Syn. Iron Pyrites.—This a very abundant mineral, of a yellow colour and metallic lustre, crystallising in cubes or octahedrons. When heated in close vessels, it loses nearly half its sulphur, which may be collected, magnetic pyrites being left. Iron pyrites is often contaminated with arsenic, which accompanies the sulphur, and is found in the sulphuric acid made from it. 

In the Magnex process, crushed coal is treated with vapors of iron carbonyl [Fe(CO)5 ], followed by the removal of pyrite and other high-ash impurities by dry magnetic separation. Iron carboiyl in this process decomposes on the sitrfaces of ash-forming minerals and forms strongly magnetic iron coatings the reaction with pyrite leads to the formation of pyrrhotite-like material. 

The Outokumpu process, which was developed in Rnland, consists of flash roasting pyrites in a nonoxidizing atmosphere in a fluidized bed. About half of the sulfur content is recovered as elemental sulfur, and the remainder is in the residue, pyrrhotite, a magnetic iron sulfide. The pyrrhotite may be roasted in an oxidizing atmosphere to recover the remaining sulfur as sulfur dioxide. 

Many of these sulphides occur naturally, for example iron(ll) sulphide, FeS (magnetic pyrites), and antimony(III) sulphide, Sb S, (stibnite). They can usually be prepared by the direct combination of the elements, effected by heating, but this rarely produces a pure stoichiometric compound and the product often contains a slight excess of the metal, or of sulphur. 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

Magnex A process for removing mineral matter from coal by first rendering it magnetic. The coal is treated with iron carbonyl vapor, which deposits a thin skin of magnetic material on the pyrite and other mineral matter, but not on the coal. Conventional magnetic separation is then used. Developed by Hazen Research in 1976. 

Charles Hatchett analyzed magnetic pyrite and stated that the discovery of iron in pyrite is comparatively recent. According to Henckel, said he, this was first noticed by our countryman Martin Lister, a member of this learned Society [the Royal Society]. .. (182). 

The preceding method is applicable to any of the ordinary classes of iron ore, such as the hematite, brown oxide, magnetic, cetera. Sulphides are never used for the manufacture of the metal hut even these, such as the common pyrites, may also he tested in the same way,... 

The same effect is produced by magnesia whitened, arsenikon transformed, cadmia calcined, sandarach unburned, pyrites whitened, and cerussa digested with sulphur. You can soften iron by mixing with it magnesia or a small portion of sulphur, or a little magnetic stone, for the magnetic stone (lodestone) has an attraction for iron. Nature charms Nature.24... 

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-... 

PYRRHOTITE. The mineral pyrrhotite, sometimes called magnetic pyrites, is a sulfide of iron with varying amounts of sulfur. Analyses indicate formulae Fe S, Pyrrhotite exists in two modifications it is monoclmic below, and hexagonal above (280°F). It is a brittle... 

Figure 3. Schematic of weight change observed continuously as pyrite in coal or lignite is analyzed. The change in the weight-scale factor from XI to X20 is due to the large increase in apparent weight (saturation magnetization) as the Fe2Os present at G is reduced to ferromagnetic iron.

The pyrrhotite or magnetic pyrites is essentially iron sulphide, Fe,Sg or 4FeS.Fe3S4 chalcopyrite or copper pyrites, Cu2S.Fe.jS3, contains some 35 per cent of copper, whilst the pentlandite contains the nickel as sulphide associated with iron sulphide, thus, NiS.2FeS, and contains approximately 22 per cent, of nickel. 

A double sulphide of copper and iron known as Chalmersite, CuFe2S3, occurs in the ore deposits of the Prince of Wales Sound, Alaska,2 and in small quantities in Brazil.3 It is massive, pale yellow in colour, and strongly magnetic, which latter property enables it to be readily separated from the copper pyrites with which it is intimately associated. Density 4 04 to 4 68. The crystals arc rhombic,... 

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