The RecAL project aims to close the loop in Europe’s aluminium supply by developing a range of Circular Amplification Technologies (CATs). Among these CATs are new sorting methods utilizing A.I., as well as designs for brand-new alloys, both of which will significantly improve aluminium scrap upcycling capabilities. Additionally, innovations in the way we use and process another key ingredient—salt slag—could lead to a range of efficiency gains and reclaimed material from the aluminium recycling process.
Stena Alumnium’s scrap melting facility
One waste product from aluminium scrap melting, salt slag, is being targeted by the RecAL project for recovery and recycling to reduce environmental impact and reclaim valuable materials. An intensive week of trials took place in June 2024 at Swerim’s pilot facilities in Luleå, in northern Sweden, marking a significant step forward in converting hazardous waste into valuable material or products. During these trials, the focus was on recovering and recycling salt from aluminium scrap melting, in collaboration with Swedish partner Stena Aluminium and British partner Altek Europe. The process aimed not only to recycle the salt for use in processing aluminium scrap but also to produce treated slag that could be utilized in the steel industry. The trials are part of RecAL’s effort to develop new technologies, involving 19 partners across Europe, including UK-based Altek Europe, who are collaborating with Swerim and Stena on improving salt slag upcycling.
Salt is a key material used during the aluminium melting process. This process takes place within a gigantic rotating cylindrical furnace, with scrap material charged into the furnace several times as the aluminium continues to melt. Salt is applied on top in the later stages of this process as the slurry becomes more fluid, creating a physical barrier that minimizes oxidizing losses as the melting metal coalesces, preventing unwanted reactions with the atmosphere. The liquid metal is then tapped out, and the final stage is to empty the furnace of the remaining waste and salt slag—hitherto unusable waste brimming with impurities.
To date, the reuse or upcycling of salt slag has been challenging due to the presence of impurities, including compounds such as aluminium nitrates, which can lead to the creation of unpleasant gas formations.
Most processes involve hydrochemical techniques using water to recover the salt. from the salt slag. These processes are complicated and the end product apart from the recovered salt is mainly aluminum oxide which has a low value.
Salt Slag produced during trials
During the recent RecAL trials in Sweden, the team at Swerim experimented with melting the slag at 1,600 degrees Celsius, a temperature at which the salt evaporates and can be collected as salt dust. The remaining non-salt components, such as aluminium oxide, magnesium oxide, and iron oxide, are preserved in the slag and can later be used in the steel-making process. These components, together with other additions, lower the melting point at which phases of the steel-making process occur, thereby reducing the amount of energy needed to make steel.
The method tested was shown to both evaporate salt dust for further treatment within RecAL and produce a product for steel making, currently reaching an impressive Technology Readiness Level (TRL) 6, according to the project’s scientists. Future steps to further increase that TRL will involve Altek designing an additional upscaled facility on-site, including the purification and upgrading of the salt slag. This will further address impurities and improve its physical form (e.g., re-crystallizing the salt dust) so that it’s suitable for industrial use. This extensive technical collaboration between Swerim, Stena Aluminium, and Altek is crucial to RecAL’s goals, leveraging specific expertise and machinery to advance one of the vital processes needed to close the loop for aluminium.
Looking ahead, the partners aim to take the process to TRL 7, 8, and 9, focusing on refining materials, enhancing efficiency, and exploring energy sources for the process. In parallel, efforts are underway to improve the sorting and refinement of scrap in collaboration with partners like Ferimet in Spain, AELS in the Netherlands, and Alumil in Greece. This holistic approach ensures constant feedback and continual improvement, driving the RecAL project towards its goal of sustainable and efficient aluminium production at every stage of the chain.
Salt Dust produced during trials
Tristan Bath (RTDS Group)
Tristan Bath is EU Project & Communication Manager at RTDS Group in Vienna.
