Businesses in aluminium production convert raw materials or recovered metal into aluminium for use by manufacturers and other industries. Primary production involves refining bauxite into alumina, then using an electrolytic process to produce aluminium metal. Because this process uses substantial amounts of electricity, primary smelting is often carried out at large industrial sites. Some producers also alloy the metal by adding other elements to achieve particular properties. Secondary production involves sorting and processing aluminium scrap, removing coatings or contaminants where necessary, and melting the recovered metal for reuse. Producers typically cast molten aluminium into forms such as ingots, billets, slabs or foundry alloys, which can be supplied for later rolling, extrusion, casting or machining. Production businesses may carry out testing and quality control to check composition and consistency.