Slag

Slag is a non-metallic byproduct produced during the smelting and refinement of ores and metals. It forms when fluxes used to remove impurities react with silicates and oxides within the melt, and it solidifies into a glassy, crystalline, or vesicular material. The precise composition depends on the production process and ore, but common constituents include calcium, magnesium, silicon, aluminum oxides, and various trace metals.

In steelmaking, slag forms on the surface of the molten metal and serves to remove impurities, regulate temperature, and protect the metal from oxidation during processing. Slag is also produced in the smelting of copper, zinc, lead, nickel, and other metals, as well as in some coal combustion contexts where it forms as molten ash on furnace walls and is later quenched or cooled.

Slag can take several forms. Granulated blast-furnace slag (GBFS) is produced by rapidly quenching molten slag with water and is widely used as a supplementary cementitious material in concrete. Air-cooled slag can be crushed and used as an aggregate in road construction and as an acceptable fill material. Slag wool or rock wool is a fibrous insulation material made from slag; vitrified slag can form glass-ceramics.

Uses and disposal: Slag is valued as a construction material and for potential metal recovery through further processing. When properly managed, slag-based products can improve concrete durability, pavement performance, and soil stabilization. However, slag can contain trace metals, so disposal and reuse are governed by environmental regulations to prevent leaching.