Nonferrous Heavy Metal

any of a group of nonferrous metals, the members of which include Cu, Ni, Co, Pb, Sn, Zn, Cd, Bi, Sb, and Hg. Annual world production of Cu, Pb, Zn, and Ni is in the millions of tons. The raw materials for the production of nonferrous heavy metals are sulfide and oxide complex-metal ores, which ordinarily contain many noble metals, rare elements, and other valuable elements, which are recovered as by-products.

The existence of a large number of varied and rather complex methods for the extraction of nonferrous heavy metals, which are intended to ensure the most complete recovery of all of the valuable constituents of the raw material, is brought about by the multitude of ore types and metals. Two types of methods, pyrometallurgical and hydrometallurgical, are used in the production of nonferrous heavy metals. Pyrometallurgical methods are carried out at high temperatures and usually involve the melting of the entire mass of raw material; hydrometallurgical methods are based on the selective dissolution of valuable constituents in aqueous acid solutions or other solvents, with subsequent separation from the solution by electrolysis or cementation techniques (seePYROMETALLURGY and HYDROMETALLURGY). Pyrometallurgical processing is usually preceded by mechanical beneficiation of the ores, which involves the partial separation of valuable minerals and minerals of barren rocks by flotation or gravity dressing. The ferrous metals obtained during one of these processes are subsequently refined.

Nonferrous heavy metals are used both in their elemental state and in the form of various alloys with other nonferrous metals and iron. Many chemical compounds of nonferrous heavy metals are widely used in industry and agriculture. Some compounds—for example, PbS, CdS, ZnS, HgTe, and CdTe—have valuable semiconductor properties and play an important role in the development of electronic technology.

The properties, production, and applications of individual non-ferrous heavy metals are discussed in the articles on the corresponding metals (see, for example, COPPER, NICKEL, and COBALT).