Roasting

roasting: see cooking.

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roasting

In metallurgy, usually the first step in smelting ore to extract metal. The ore is heated in the presence of an abundant flow of air to drive off moisture and, if the metal-bearing mineral is a sulfide, convert it to an oxide. Sulfur fumes from ore roasting have been a major source of environmental pollution in the past.

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Roasting 

the process of preparing ores or ore concentrates for subsequent enrichment, nodulizing, or smelting. Roasting changes the physical properties or chemical composition of ore, converts the useful components into extractable form, and removes impurities. The temperature to which the ore is heated depends on the specific ore and on the purpose of roasting.

Iron ore can be subjected to a magnetizing roast, which is usually reductive and converts iron oxides into the magnetic form for subsequent enrichment; this process is carried out in reverberatory kilns, shaft furnaces, or fluidized bed furnaces. Oxidative roasting is used to remove sulfur, carbon dioxide from carbonates, and moisture from hydrates. The extent of industrial roasting of ferrous ores is limited.

Roasting in nonferrous metallurgy sometimes uses reactive additives and can be distillative, oxidative, oxidative-reductive, calcining, sulfatizing, or chloridizing. These types of roasting serve many purposes, including the distillative removal of useful components in the form of gaseous products, the conversion of such components into oxides, the removal of carbon dioxide from carbonates, the oxidation of sulfides to sulfates, and the formation of readily soluble or volatile chlorides. Nonferrous ores are roasted in different kinds of furnaces, including hearth smelting furnaces, tube furnaces, and fluidized bed furnaces.

E. N. IARKHO