Page 178 - Materials Chemistry, Second Edition

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Recycling Solid Wastes 149

FIGURE 6.8 Automobile shredding operation. (Reproduced with kind permission of Sims Group Limited,
Figure 6.8b [bottom] only.)

houses a large electromagnet (Figure 6.9); a baling press, used to densify objects such as automobiles;
a hydraulic guillotine shear to slice steel I-beams and pipe; and a shredder (Figure 6.10). Several of
these unit operations are discussed in more detail in the next chapter.
Industrial consumers purchase ferrous scrap directly or through a materials broker. These
mills and foundries remelt the scrap and manufacture new products. Basic oxygen furnaces and
electric arc furnaces utilize most of the iron and steel scrap. In the basic oxygen furnace, molten
pig iron is combined with 20 to 30% steel scrap (Rhyner et al., 1995). The electric arc furnace
operates almost exclusively on steel scrap. Melting is accomplished by supplying energy to the
furnace interior. This energy can be electrical or chemical. Electrical energy is supplied via
graphite electrodes and is usually the largest contributor in melting operations. The scrap falls