Reduction of iron 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. 

Direct Reduction of Iron Ore Bibliographical Survey, The Metals Society, London, 1979. 

Manufacture and Processing. The largest volume of coal is carbonized in batch coke ovens to produce a hard coke suitable for blast furnaces for the reduction of iron ore. Oven temperatures, as measured in the flues, are between 1250 and 1350° and residence time varies between 17 and 30 h. The gas made in this process is mainly used as fuel and other appHcations in the steel works (see Fuels, synthetic). 

A discussion of retention time in rotary Idlns is given in Brit. Chem. Eng., 27-29 (Januaiy 1966). Rotary-ldln heat control is discussed in detail by Bauer [Chem. Eng., 193-200 (May 1954)] and Zubrzycki [Chem. Can., 33-37 (Februaiy 1957)]. Reduction of iron ore in rotaiy Idlns is described by Stewart [Min. Congr J., 34—38 (December 1958)]. The use of balls to improve solids flow is discussed in [Chem. Eng., 120-222 (March 1956)]. Brisbane examined problems of shell deformation [ Min. Eng., 210-212 (Februaiy 1956)]. Instrumentation is discussed by Dixon [Ind. Eng. Chem. Process Des. Dev., 1436-1441 (July 1954)], and a mathematical simulation of a rotaiy Idln was developed by Sass [Ind. Eng. Chem. Process Des. Dev., 532-535 (October 1967)]. This last paper employed the empirical convection heat-transfer coefficient given previously, and its use is discussed in later correspondence [ibid., 318-319 (April 1968)]. 

L. von Bogdandy and H.J. Engell. The Reduction of Iron Ores. Springer Verlag, Berlin (1971). 

When coal is heated to a high temperature in the absence of air, it undergoes decomposition volatile products (coal gas and coal tar) distill away and a residue called coke remains. Coke is a valuable industrial material which finds its chief use in the reduction of iron ore (iron oxide) to iron for the manufacture of steel. Coke is essentially carbon that still contains the mineral substances that are present in all coals (and form the ash that results when coal or coke is burned). 

FIGURE 16.39 The reduction of iron ore takes place in a blast furnace containing a mixture of the ore with coke and limestone. Different reactions take place in different zones when the blast of air and oxygen is admitted. The ore, an oxide, is reduced to the metal by reduction with carbon monoxide produced in the furnace. 

Gas-solid where the solid may take part in the reaction or act as a catalyst. The reduction of iron ores in blast furnaces and the combustion of solid fuels are examples where the solid is a reactant. 

The authors would like to express their appreciation to researchers at BHP in Australia for providing information on the recent developments in smelting reduction of iron ore. 

Ibaraki, T., Kanemoto, M., Ogata, S., Katayama, H., and Ishikawa, H., Development of Smelting Reduction of Iron Ore - An Approach to Commercial Ironmaking, Iron Steelmaker, 17(12) 30 (1990)... 

Historically, the production of coke from coal resulted from the pressures exerted by environmental and economic forces. In the late 1500s, demand for wood in England began to surpass supply. At that time, wood was converted into charcoal for use as a reductant of iron ore by the burgeoning metallurgical industries. By 1710, Abraham Darby of Coalbrookdale m Shropshire, England, commercialized the production of pig iron by utilizing the coke from coal... 

The reduction of iron ores is carried out on the large industrial scale in the ironmaking blast furnace, where CO is the reducing gas and the product is liquid... 

Burning of coal Roasting of ores Attack of solids by acids Gas-liquid absorption with reaction Reduction of iron ore to iron and steel... 

Wustite, FeO, is the other iron oxide which contains only divalent Fe. It is usually non-stoichiometric (O-defident). The structure is similar to that of NaCl and is based on ccp anion packing. Wustite is black. It is an important intermediate in the reduction of iron ores. 

Isomorphous substitution of iron oxides is important for several reasons. In the electronics industry, trace amounts (dopants) of elements such as Nb and Ge are incorporated in hematite to improve its semiconductor properties. Dopants are also added to assist the reduction of iron ores. In nature, iron oxides can act as sinks for potentially toxic M", M and M heavy metals. Investigation of the phenomenon of isomorphous substitution has also helped to establish a better understanding of the geochemical and environmental pathways followed by Al and various trace elements. Empirical relationships (e. g. Fe and V) are often found between the Fe oxide content of a weathered soil profile and the levels of various trace elements. Such relationships may indicate similarities in the geochemical behaviour of the elements and, particularly for Al/Fe, reflect the environment in which the oxides have formed (see chap. 16). 

A small amount of Cr could be incorporated in wiistite at 1350 °C (Bogdandy Engell, 1971) and MgO and MnO were completely miscible with FeO the mixed phases are important in the reduction of iron ores. Wiistite can be doped with small amounts of Mn, Mg, Ca and <10 g kg Si or Al to promote reduction (Moukassi et al., 1984). In green rust Fe has been replaced by Ni" (Refait Genin, 1997) and by Mg (Refait et al. 2001). 

Reduction of iron ores in preparation of iron and steel making is described under Iron Metals. Alloys, and Sleets. 

The iron used for this prehistoric ax was made by the reduction of iron ore with charcoal. 

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