Magnetite, 1.27

Just as vivianite is regarded as the simplest example of a mineral with isolated clusters of Fe2+-Fe3+ octahedra showing IVCT transitions, so too is magnetite considered to be the classic example of a structure-type with infinite chains of Fe2+ -Fe3+ octahedra exhibiting electron delocalization. Magnetite, Fe304 or Fe2+Fe3+204, has the spinel structure illustrated in fig. 4.18 with an inverse cation distribution ( 6.4). Thus, half the Fe3+ ions occupy isolated tetrahedral sites, 

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Magnetic - from a place called Magnesia where magnetic iron oxide (Magnetite) occurred naturally. 

Barbieri A, Weiss W, Van Hove M A and Somorjai G A 1994 Magnetite Fe204(111) surface structure by LEED crystallography and energetics Surf. Sc/302 259-79... 

After aluminium, iron is the most abundant metal and the fourth most abundant of all the elements it occurs chiefly as oxides (for example haematite (FCjO,), magnetite (lodestonej (FC3O4) and as iron pyrites FeSj- Free iron is found in meteorites, and it is probable that primitive man used this source of iron for tools and weapons. The extraction of iron began several thousand years ago, and it is still the most important metal in everyday life because of its abundance and cheapness, and its ability to be cast, drawn and forged for a variety of uses. 

The mixed oxide Fc304 (tri-iron tetroxide) is a black solid, which occurs naturally as magnetite it is formed when iron(III) oxide is strongly heated, and its structure is effectively made up of oxide (O ) and iron(II) and iron(III) ions. 

Pig. 6. A 0.3-mm-diameter cosmic spherule coUected from the ocean floor. The particle is composed of oUvine, glass, and magnetite and has a primary element composition similar to chondritic meteorites for nonvolatile elements. The shape is the result of melting and rapid recrystaUi2ation during... 

Minerals. Iron-bearing minerals are numerous and are present in most soils and rocks. However only a few minerals are important sources of iron and thus called ores. Table 2 shows the principle iron-bearing minerals. Hematite is the most plentiful iron mineral mined, followed by magnetite, goethite, siderite, ilmenite, and pyrite. Siderite is unimportant in the United States, but is an important source of iron in Europe. Tlmenite is normally mined for titania with iron as a by-product. Pyrite is roasted to recover sulfur in the form of sulfur dioxide, leaving iron oxide as a by-product. 

Parameter Hematite Magnetite Goethite Siderite Ilmenite Pyrite... 

The Utah deposit is located in southwestern Utah near Cedar City. The iron ore deposits are of contact metamorphic origin. The cmde ore contains 35 to 65% iron, primarily in the form of magnetite and goethite. Mining is done by the open pit method. The cmde ore is cmshed, screened at —75 mm (—200 mesh size) and shipped as lump ore containing 54% iron. The ore is rescreened at the steel mill to produce lump ore (10—64 mm) for the blast furnace and sinter feed (0—10 mm) for the sinter plant. 

Low intensity magnetic separators are used to upgrade iron ores containing magnetite. Dry separators are used for coarse (up to 100 mm in size) ore and wet separators are used for fine (—9.5 mm) ores. 

The reduction of iron ore is accompHshed by a series of reactions that are the same as those occurring in the blast furnace stack. These include reduction by CO, H2, and, in some cases soHd carbon, through successive oxidation states to metallic iron, ie, hematite [1309-37-17, Fe202, is reduced to magnetite [1309-38-2], Fe O, which is in turn reduced to wustite [17125-56-3], FeO, and then to metallic iron, Fe. The typical reactions foUow. 

Iron compounds (qv) in limestone are seldom injurious to a lime product unless a very pure lime is required. Normally, the iron compounds are in the form of limonite [1317-63-1] (ferric hydroxide) and pyrite [1309-36-0] EeS2. Occasionally, hematite, magnetite, marcasite, and other forms of iron are found in limestone. 

Sintering consists of heating a mixture of fine materials to an elevated temperature without complete fusion. Surface diffusion and some incipient fusion cause the soHd particles in contact with one another to adhere and form larger aggregates. In the processing of hematite, Fe202, or magnetite,... 

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