Slag

More than 400 million tonnes of iron and steel slags are produced each year. Slags are a mixture of silica, calcium oxide, magnesium oxide, and aluminium and iron oxides.

During smelting, slagging agents and fluxes (mainly limestone or dolomite and silica sand) are added to the blast furnace or steelmaking furnace to remove impurities from the iron ore, steel scrap and other ferrous feeds. As the slags are lighter than the liquid metal, they float and can be easily removed.

Slags are recognised as marketable products. The worldwide average recovery rate for slag varies from over 80% for steelmaking slag to nearly 100% for iron-making slag. There is still much potential to increase the recovery and use of slags in many countries, especially for environmental and economic benefits.