Slags

Slag is a non-metallic byproduct produced during the smelting and refining of metals. It forms when molten ore and metal are treated with fluxes that bind impurities such as silica and alumina, producing a molten mixture that separates from the metal and solidifies into a glassy or crystalline mass. The precise composition depends on the ore and the flux, but common constituents include calcium silicates, calcium aluminates, and various oxides of magnesium, iron, and calcium.

Various metallurgical processes generate slag, including blast furnace ironmaking, steelmaking, and non-ferrous smelting. In ironmaking, slag forms from gangue minerals and fluxes; in steelmaking, it helps remove sulfur and phosphorus and protects the metal from oxidation.

Uses: Slag is routinely processed for reuse. Granulated blast-furnace slag (GBFS) is rapidly cooled to a glassy powder and used as a supplementary cementitious material in concrete. Ground granulated slag can replace a portion of Portland cement. Coarse slag or air-cooled slag can be used as aggregate in road construction and concrete. Some slag is refined to recover valuable metals before disposal and other slag remains in regulated storage. Environmental considerations include potential leaching of trace metals and the need for proper handling, processing, and land-use planning to minimize environmental impact.