Recycling of metals: accounting of greenhouse gases and global warming contributions

Greenhouse gas (GHG) emissions related to recycling of metals in post-consumer waste are assessed from a waste management perspective; here the material recovery facility (MRF), for the sorting of the recovered metal. The GHG accounting includes indirect upstream emissions, direct activities at the MRF as well as indirect downstream activities in terms of reprocessing of the metal scrap and savings in terms of avoided production of virgin metal. The global warming factor (GWF) shows that upstream activities and the MRF causes negligible GHG emissions (12.8 to 52.6 kg CO2-equivalents tonne(-1) recovered metal) compared to the reprocessing of the metal itself (360-1260 kg CO2-equivalents tonne(-1) of recovered aluminium and 400 1020 kg CO2-equivalents tonne(-1) of recovered steel). The reprocessing is however counterbalanced by large savings of avoided virgin production of steel and aluminium. The net downstream savings were found to be 5040-19 340 kg CO2-equivalents tonne(-1) of treated aluminium and 560-2360 kg CO2-equivalents tonne(-1) of treated steel. Due to the huge differences in reported data it is hard to compare general data on the recovery of metal scrap as they are very dependent on the technology and data choices. Furthermore, the energy used in both the recovery process as well as the avoided primary production is crucial. The range of avoided impact shows that recovery of metals will always be beneficial over primary production, due to the high energy savings, and that the GHG emissions associated with the sorting of metals are negligible.