Smelting residues, also known as slags, are the by-products of smelting, a process used to extract metals from their ores. Slags are composed of the non-metallic components of the ore and the fluxes used in the smelting process. They are usually solid, glassy or granular materials that are removed from the furnace during the smelting process. Slags can be used in a variety of ways, such as for road construction, fertilizer, and cement production.