The composition of the slag is adjusted by adding an appropriate amount of flux (lime, quartzite, fluorite, etc.). In the smelting process, by controlling the composition and properties of the slag, the products of gangue and oxidized impurities can be smoothly separated from the molten metal or sulfur, the harmful impurities in the metal are removed, and the non-metallic inclusions in the liquid metal are not directly affected. Furnace gas is polluted and enriched with useful metal oxides; it is also a resistance heating element in electric furnace smelting. Slag plays a decisive role in ensuring the smooth progress of the smelting operation, the quality of the smelted product, and the metal recovery rate. For example, in steelmaking operations, there is a saying that "good slag can be made good steel". Magnesia brick

According to different metallurgical processes, slag can be divided into smelting slag, refined slag, and synthetic slag; according to the nature of slag, there are alkaline slag, acid slag and neutral slag. Many slags have important uses. For example, blast furnace slag can be used as raw material for cement; high-phosphorus slag can be used as fertilizer; vanadium and titanium-containing slag can be used as raw materials for refining vanadium and titanium, respectively. Some slag can be used to make slag cement, slag brick, slag glass, etc.

The melt produced by coal in the combustion chamber of the boiler is composed of coal ash. Can be used as raw materials such as bricks and tiles.