An environment technician monitors air quality at a dust collection point near the Diavik mine
© 2014 Rio Tinto

Sorting and separation of scrap is a mechanical and/or manual process, for which electricity or labour is the main input.

Dust is the main air emission, from equipment such as shredders, which is collected inside the plant via vacuum systems. Thermal pre-treatment of scraps, such as de-coating, removing of oil or other impurities, requires the input of fuel. Organic compounds and dust are the main emissions to air. These air emissions are controlled through process optimisation or after burners. Dust can be collected as filter dust.

Melting and refining of scrap requires the input of fuel and, in many cases the use of salt fluxes. The organic contaminants in the input scraps are the main source of volatile organic compound (VOC) emission. Polychlorinated Dioxins and Furans (PCDD/F) may be formed due to the use of salt fluxes and chlorine mixtures in the process. Furnace design and optimisation provide effective control of these emissions, afterburner treatment of waste gases can also be used to limit such air emissions. Dust is again collected via air filters. Salt slag, when salt fluxes are used, is the main solid waste generated in the melting and refining process. It is treated to recover aluminium metal, metal oxides, and salts, which are used as input material in various industries.

CO2 emissions are the result of fuel combustion. From a life cycle point of view, the amount of fuel required to process scrap into aluminium alloys is approximately 5% of that required for the production of primary ingot.