Production of metals. Alloys

Of the 118 elements, more than 90 are metals. Active metals occur in nature as salts (NaCl, CaCO₃), moderately active ones as oxides, sulfides and sulfates (Fe₂O₃, ZnS, PbS), and the least active — Cu, Ag, Au, Pt, Hg — partly or wholly in the free state. Metallurgy separates metals from their ores, and every process rests on oxidation and reduction. In pyrometallurgy an oxide is reduced at high temperature by C, CO, Al, Si or H₂: Fe₃O₄ + 4CO → 3Fe + 4CO₂, Cr₂O₃ + 2Al → Al₂O₃ + 2Cr. In hydrometallurgy a metal compound is brought into solution and displaced by a more active metal: CuSO₄ + Fe → FeSO₄ + Cu↓ (gold, silver, zinc and uranium are also obtained by hydrometallurgical methods). In electrometallurgy a melt or solution is electrolysed: alkali metals, alkaline-earth metals and aluminium are made like this (Na⁺ + e⁻ → Na). Iron and its alloys are ferrous metals and the rest non-ferrous; metals with density below 5 g/cm³ are light (Li, Na, Mg, Al) and the denser ones heavy (Cu, Pb, Hg); gold, silver and platinum are noble metals. Uzbekistan has ores of gold (Muruntau and other deposits in the Kyzylkum), silver, copper, tungsten and other metals, and the Almalyk Mining and Metallurgical Complex produces copper and other non-ferrous metals.