blast furnace Cylindrical smelting furnace. It is used in the extraction of metals, mainly iron and copper, from their ores. The ore is mixed with coke and a flux (limestone in the case of iron ore). A blast of hot, compressed air is piped in at the bottom of the furnace to force up temperatures so that the oxide ore is reduced to impure metal. The molten metal sinks to the bottom and is tapped off. Waste ‘slag’ floats to the top of the metal and is piped off. See also oxidation-reduction

blast fur·nace • n. a smelting furnace in the form of a tower into which a blast of hot compressed air can be introduced from below. Such furnaces are used chiefly to make iron from a mixture of iron ore, coke, and limestone.