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.)
Slag is generated in large quantities and has the potential to become a significant source of landfill waste and pollution. But slag itself has value, and technologies have emerged to recycle and reuse reprocessed, granulated slag in different building materials, such as cement, brick, concrete aggregates, wall materials, and glass-ceramic tiles.
