Smelting

Smelting is a metallurgical process in which ore concentrate is heated with a reducing agent to extract metal. Unlike roasting, which removes volatile components, smelting reduces metal oxides to metal.

The operation typically requires fluxes to form slag, which helps remove impurities and carries away sulfur and other contaminants. Ore is crushed and concentrated, then charged into a furnace with a reducing agent such as coke, charcoal, or carbon monoxide. The reaction produces metal and gaseous byproducts.

Equipment and approaches vary by metal and scale. In ironmaking, a blast furnace uses coke and limestone to produce pig iron and slag. In copper smelting, sulfide concentrates are roasted to oxides before reduction in a reverberatory or flash furnace, often followed by converting and refining. Other metals such as lead, zinc, tin, and nickel are produced by direct smelting or smelting followed by refining.

The product is typically an ingot or molten metal that requires refining to remove remaining impurities. Slag is separated and may be used for cement or other applications. Emissions from smelting include sulfur dioxide, carbon dioxide, and particulates, prompting controls to limit air pollution.

Smelting has been important since ancient times and underpinned the industrial production of metals. Early copper and bronze smelting appeared in the Neolithic and Bronze Ages, iron smelting developed in the Iron Age, and later technologies expanded capacity and scope.