Slag

Slag is a by-product of the metallurgical smelting process. Slag has a double role: it permits removal of impurities, known as gangue, from the melt by forming oxides. It also allows exchange reactions with the liquid metal, permitting control of the process in order for the desirable elements to stay in the melt while the others are removed. (The ore beneficiation process at a mine is designed to remove as much waste and penalty elements as possible prior to transport and smelting.)

The goals of slag recycling efforts are both environmental and economic. Reprocessed slag can replace other more costly ingredients used to make building materials. Recycling slag minimizes waste and disposal costs, reduces energy use, extends furnace life, and lowers the amount of additives needed to make slag.