Smelting leftovers, also known as slags, are the byproducts of the smelting process. Slags are a combination of fluxes and impurities that are removed from the metal during the smelting process. SLAG is a non-metallic material that is created during the smelting process and is composed of a mixture of silicates and oxides. Slags can be used in a variety of ways, such as for road construction, fertilizer, and even as a source of energy.