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Smelting is a method by which metals are taken from their original ore. Smelting is done in specially built furnaces. The blast furnace for making pig iron is as tall as a 10-story building. Iron ore, coke, and limestone are fed through the top of the furnace. Hot blast (preheated air) enters at the bottom. This burns the coke and generates the gases and heat required to reduce iron from its oxide minerals in the ore and to form slag by the reaction of limestone and such unwanted ore components as silicon and phosphorus. Molten slag and iron are removed through openings in the bottom. Furnace gas is removed at the top. Industry also uses blast furnaces to smelt other ores to produce copper, lead, and ferroalloys (alloys containing iron).
The reverberatory furnace is a type of smelter commonly used to refine copper. This smelter uses hot combustion gases to melt both the solid ore and certain flux materials that are added to promote melting and to prevent oxide formation. In flash smelting of copper ores, heat is generated by the reaction of oxygen with the sulfur in the ore minerals. The sulfur oxides that result can be used to make sulfuric acid as a by-product. During flash smelting, the copper sinks to the bottom of the smelter in a liquid form called matte. Matte, which contains iron sulfides and other sulfide compounds, is then refined to isolate copper.