Department of Materials Science (IMA), NTNU Norwegian University of Science and Technology, Alfred Getz vei 2B 7034, Trondheim, Norway.
Industrial Ecology Programme, Department of Energy and Process Engineering, NTNU Norwegian University of Science and Technology, Kolbjørn Hejes vei 1B 7034, Trondheim, Norway.
Waste Manag. 2024 Jun 15;182:11-20. doi: 10.1016/j.wasman.2024.04.023. Epub 2024 Apr 15.
Recycling aluminium in a rotary furnace with salt-fluxes allows recovering valuable alloys from hard-to-recycle waste/side-streams such as packaging, dross and incinerator bottom ash. However, this recycling route generates large amounts of salt-slag/salt-cake hazardous wastes which can pose critical environmental risks if landfilled. To tackle this issue, the metallurgical industry has developed processes to valorise the salt-slag residues into recyclable salts and aluminium concentrates, while producing by-products such as ammonium sulphate and non-metallic compounds (NMCs), with applications in the construction or chemical industries. This study aims to assess through LCA the environmental impacts of recycling aluminium in rotary furnaces for both salt-slag management routes: valorisation or landfill. It was found that this recycling process brings forth considerable net environmental profits, which increase for all the considered impact categories if the salt-slag is valorised. The main benefits arise from the production of secondary cast aluminium alloys, which is not unexpected due to the high energy intensity of aluminium primary production. However, the LCA results also identify other hotspots which play a significant role, and which should be considered for the optimisation of the process based on its environmental performance, such as the production of by-products, the consumption of energy/fuels and the avoidance of landfilling waste. Additionally, the assessment shows that the indicators for mineral resource scarcity, human carcinogenic toxicity and terrestrial ecotoxicity are particularly benefited by the salt-slag valorisation. Finally, a sensitivity analysis illustrates the criticality of the metal yield assumptions when calculating the global warming potential of aluminium recycling routes.
在旋转炉中使用盐渣作为助熔剂回收铝，可从难以回收的废物/副产物（如包装材料、浮渣和焚烧炉底灰）中回收有价值的合金。然而，这种回收途径会产生大量的盐渣/盐饼危险废物，如果填埋会对环境造成严重风险。为了解决这个问题，冶金行业已经开发出了从盐渣残留物中回收可再利用盐和铝精矿的工艺，同时生产出硫酸铵和非金属化合物（NMCs）等副产品，可应用于建筑或化工行业。本研究旨在通过生命周期评估（LCA）评估旋转炉中铝的回收对盐渣管理两种途径（再利用或填埋）的环境影响。研究发现，这种回收工艺带来了可观的净环境效益，如果盐渣得到再利用，所有考虑的影响类别都会增加。主要的好处来自于生产二次铸造铝合金，这并不出人意料，因为铝的初级生产需要大量的能源。然而，LCA 结果还确定了其他发挥重要作用的热点，应根据其环境性能，如副产品的生产、能源/燃料的消耗和废物避免填埋等，对工艺进行优化。此外，评估表明，盐渣再利用对矿产资源稀缺性、人类致癌毒性和陆地生态毒性指标特别有利。最后，敏感性分析说明了在计算铝回收途径的全球变暖潜力时，金属产量假设的重要性。
