Pyrometallurgy

pyrometallurgy [¦pī·rō′med·əl‚ər·jē]

(metallurgy)

Processes that use chemical reactions at elevated temperatures for the extraction of metals from raw materials such as ores and concentrates, or for the treatment of recycled scrap.

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Pyrometallurgy

The branch of extractive metallurgy in which processes employing chemical reactions at elevated temperatures are used to extract metals from raw materials, such as ores and concentrates, and to treat recycled scrap metal.

For metal production, the pyrometallurgical operation commences with either a raw material obtained by mining and subsequent mineral and ore processing steps to produce a concentrate, or a recycled material such as separated materials from scrapped automobiles, machinery, or computers.

Pyrometallurgical preparation processes convert raw materials to forms suitable for future processing. Reduction processes reduce metallic oxides and compounds to metal. Oxidizing processes oxidize the feed material to an intermediate or a semifinished metal product. Refining processes remove the last of the impurities from a crude metal. See Electrometallurgy, Metallurgy, Pyrometallurgy, nonferrous

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Pyrometallurgy 

the science and technology of high-temperature metallurgical processes.

Pyrometallurgy is the principal and oldest branch of metallurgy. From ancient times until the end of the 19th century the production of metals made almost exclusive use of pyrometallurgical processes. At the end of the 19th century the other major branch of metallurgy, hydrometallurgy, became industrially important, although pyrometallurgy continues to maintain a leading position both in scale of production and variety of processes. In the early 20th century, various electrical methods for providing heat, including electrical-arc and inductive methods, were first added to the already existing methods, which used a flame as a heat source. Also at about this time, the electrolysis of molten chemical compounds in the production of aluminum and other nonferrous metals was introduced into industry. Plasma smelting of metals as well as zone and electron-beam smelting became widespread after 1950. Metallurgical processes that use an electric current can be considered an independent area of pyrometallurgy that is called electrometallurgy. In modern metallurgy, pyrometallurgy is of major importance in the production of many of the most useful metals, including iron, steel, lead, copper, and nickel.

The procedures that are used in pyrometallurgy are roasting, smelting, conversion, refining, and distillation. With roasting, the material retains its solid state while undergoing a change in composition and some degree of grain enlargement. Roasting in fluidized-bed furnaces is an efficient process that is widely used in nonferrous metallurgy. Roasting is also performed in muffle furnaces to treat rare metals and in multihearth furnaces, for example, in the production of copper and ferromolybdenum. Iron concentrates are magnetically roasted in tube furnaces. Sinter machines can also be used for various applications of roasting.

Smelting involves the complete conversion of the charge to a melt, which is then separated, usually into two layers: one consists of the metal, and the other of slag or matte. This process is carried out in shaft furnaces and is used, for example, in blast-furnace production as well as in the production of lead, nickel, and copper. Smelting is also carried out in reverberatory furnaces for open-hearth refining and for reverberatory smelting of copper concentrates; in electrical furnaces for the production of steel, ferroalloys, copper, and nickel; and in cyclone chambers for treating raw materials that contain copper and zinc. Thermal reduction is a special type of smelting process that extracts metals from their compounds by using chemically more active metals; these reactions take place with the evolution of considerable heat.

Conversion, which may be considered a type of smelting, involves passing air or oxygen through molten pig iron or matte with an additive of fluxes and a small amount or such raw materials as scrap or rich concentrates. Conversion makes use of the heat that is generated by exothermic reactions and is carried out in converters to produce steel, copper, and nickel.

Molten metals are refined by using additives of salts, alkalies, or metals as well as by introducing special slags. Other refining methods involve oxidation of impurities and evaporation of the melt under a vacuum. Sometimes refining is carried out while the molten metal is crystallizing. Copper, gold, and zinc melts are refined in reverberatory furnaces, while kettles are used for lead and tin.

With distillation, a reducible metal is vaporized and subsequently condensed. Retorts are used to distill zinc; shaft furnaces are used to distill lead, zinc, and tin; and fluidized-bed furnaces are used to distill titanium.

REFERENCES

Esin, O. A., and P. V. Gel’d. Fizicheskaia khimiia piromelallurgicheskikh protsessov, 2nd ed., parts 1–2. Sverdlovsk, 1962–66.
Vol’skii, A. N., and E. M. Sergievskaia. Teoriia metallurgicheskikh prolsessov. Moscow, 1968.
Zelikman, A. N., and G. A. Meerson. Metallurgiia redkikh metallov. Moscow, 1973.
Vaniukov, A. V., and V. Ia. Zaitsev. Teoriia pirometallurgicheskikh protsessov. Moscow, 1973.

N. V. GUDIMA