Direct reduction

Augustine, Catalytic Hydrogenation, Marcel Dekker, New York (1965) 

cat (d-t-BuQHt, ultrasound (aiyl ketones) Zn, HOAc, (H20), ultrasound Zn, HC1 

BHs py, CF3CO2H (aryl ketones) BH3-f-BuNH2, A1Q3 (aryl ketones) 

Me3Si(OSiHMe) OSiMe3, A1C13 (aryl ketones) EtsSiH, BF3 (ketones, aryl aldehydes) 

Et3SiH, CF3C02H, NH4F (aryl ketones) PhSiMejH CFaCOjH (aryl aldehydes) 

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Benzenediazonium chloride also undergoes direct reduction to phenylhydrazine... 

Ironmaking refers to those processes which reduce iron oxides to iron. By the nature of the processes, the iron produced usually contains carbon and/or other impurities which are removed in downstream processing. There are three principal categories of ironmaking processes, in order of commercial importance blast furnace, direct reduction, and direct smelting. 

Direct Reduction. Direct reduction processes are distinguished from other ironmaking processes in that iron oxide is converted to metallic iron without melting. Because this product, called direct reduced iron (DRI), is soHd, it is most suitable for melting in an electric arc furnace (EAF) as a substitute for scrap (see Furnaces, electric). The briquetted form of DRI, hot briquetted iron (HBI) is used when the product is to be transported. Briquetting increases density and chemical stabiUty. The predominant direct reduction processes (MIDREX and HyL III) are based on natural gas as a fuel and reductant source. They are economically attractive in regions where natural gas is cheap and abundant, especially if iron ore is available nearby (see Iron BY DIRECT reduction). ... 

As can be seen in Figure 8, the proportion of world pig iron produced in the United States has decreased dramatically since 1950. Also notable is the widening gap between pig iron and steel production, indicating the increasing use of recycled iron or scrap (see Recycling, ferrous metals) and alternative iron sources such as DRI and HBI. The increased demand for scrap is reflected in scrap iron prices (Fig. 9), which in turn have spurred growth in direct reduction processes. 

Second, development efforts ia direct reduction and direct smelting processes have also iacreased. Whereas these developmeats require significant commitment of finances and labor to achieve commercialization, the rewards promised by avoiding cokemaking and hy utilizing smaller scale units which have relatively low capital costs make the commitment worthwhile. 

Direct reduction (DR) is the process of converting iron ore (iron oxide) into metallic iron without melting. The metallic iron product, known as direct reduced iron (DRI), is used as a high quaUty feed material in steelmaking. 

The most common method of converting iron ore to metallic iron utilizes a blast furnace wherein the material is melted to form hot metal (pig iron). Approximately 96% of the world s iron is produced this way (see Iron). However, in the blast furnace process energy costs are relatively high, pollution problems of associated equipment are quite severe, and capital investment requirements are often prohibitively expensive. In comparison to the blast furnace method, direct reduction permits a wider choice of fuels, is environmentally clean, and requires a much lower capital investment. 

DRI can be produced in pellet, lump, or briquette form. When produced in pellets or lumps, DRI retains the shape and form of the iron oxide material fed to the DR process. The removal of oxygen from the iron oxide during direct reduction leaves voids, giving the DRI a spongy appearance when viewed through a microscope. Thus, DRI in these forms tends to have lower apparent density, greater porosity, and more specific surface area than iron ore. In the hot briquetted form it is known as hot briquetted iron (HBI). Typical physical properties of DRI forms are shown in Table 1. 

The carbon content of DRI depends primarily on the direct reduction process used and the way the process is operated. Carbon content can be adjusted within limits by operating changes within the DR process. Most steelmakers prefer slightly more carbon than is required to balance the remaining FeO in the DRI. DRI from gas-based processes typically contains 1 to 2.5% carbon, mostly in the form of cementite [12169-32-3] Fe C. DRI containing approximately 6 to 7% carbon in the form of cementite is called iron carbide. DRI from coal-based, rotary-kiln processes contains very low (ca 0.5%) levels of carbon. 

In 1993, 23.9 million metric tons of DRI were produced woddwide. Five principal processes produced 95.6% of this total. Natural gas-based direct reduction accounts for 92.5% of woddwide production and coal-based direct reduction accounts for the other 7.5%. A comparison of the five principal processes is given in Table 4. 

DR Processes Under Development. The 1990s have seen continuous evolution of direct reduction technology. Short-term development work is focusing on direct reduction processes that can use lower cost iron oxide fines as a feed material. Use of fines can represent a 20 30/1 (20%) savings in DRI production cost compared to use of pehets or lump ore. Some examples of these processes include FASTMET, Iron Carbide, CIRCOFER, and an improved version of the EIOR process. 

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

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