## 1 Introduction  
In today's world, one crucial problem is the recycling of various types of waste in tandem with energy production. In general, aluminium (Al) recycling is a well-established industry with somewhat known parameters, such as packaging and beverage can recycling. The classification of aluminium scraps has been established and is currently dictated by the standards EN12258 and ISO/IEC 80079-34 [1, 2, 3]. Moreover, aluminium-rich solid waste materials are not suitable for disposal in non-hazardous waste landfills, as defined by the EU criteria. In fact, the EU regulations classify aluminium-rich by-products as a type of hazardous waste capable of creating flammable gases and forming explosive mixtures with the ambient air (hazard class codes: HP10; HP11; HP12; HP13; European Waste Code, EWC: 100323*). Aluminium recycling is not only an energy-intensive endeavour, but there is also a limitation to the recycling extent. There are Al wastes that have high recyclability, such as cans (containing ca. 94 wt.% Al, 1 wt.% oxides, and 5 wt.% other inclusions), and there are also large amounts of unrecyclable or hard-to-recycle waste, e.g., dross. Nowadays, recycled aluminium amounts to ca. 35% of the total primary Al production and requires 10-15 times less energy consumption [4; 5; 6]. In industrial production, the first step in aluminium recycling is the separation of the metallic components from non-metallic ones [4; 7; 8] by applying various screening techniques or even their combination, such as magnetic separation, eddy current separation, density separation and others [7; 8; 9; 10; 11; 12; 13]. It is well known that the aluminium-water reaction can produce hydrogen, leading to the hazardous nature of Al waste in landfills; it can be used for electricity production, where a by-product is aluminium hydroxide. As the amount of aluminium products increases, the dress will also increase; thus, there is a need to understand its applicability in renewable fuels. One of the crucial components of the use of the Al-H\({}_{2}\)O reaction and the utilisation of waste Al is the mitigation of CO\({}_{2}\) emissions, as proven by [PERSON] et al. in a life cycle analysis, where this reaction decreased the energy requirement to only 2% of that of the conventional method, leading to 4% of CO\({}_{2}\) emissions [14]. The literature has concluded that impurities largely influence the production yield as well as the amount of by-products created in the Al-water reaction. The Al-water reaction is distinguished by the absence or presence of a catalyst. It is known that aluminium reacts with ambient oxygen to create a protective surface layer. A piece of aluminium, placed into water, already has a surface layer of aluminium oxide or alumina, Al\({}_{2}\)O\({}_{3}\), which reacts with water even at moderate temperatures to produce a boehmite AlOOH layer. This is the so-called induction step:  
\[\text{Al}_{2}\text{O}_{3}+\text{H}_{2}\text{O}\to 2\text{AlOOH}, \tag{1}\]  
At the induction step, the boehmite film grows; in the meantime, the diffusion of OH' ions through the AlOOH layer occurs. As a result, hydrogen bubbles appear at the Al-Al\({}_{2}\)O\({}_{3}\) interface:  
\[6\text{AlOOH}+2\text{Al}\to 4\text{Al}_{2}\text{O}_{3}+3\text{H}_{2} \text{ (g)}, \tag{2}\]  
The aim of catalyst usage is to eliminate the protective layer of aluminium oxide that hinders the reaction with water. In large-scale hydrogen production, the most common are alkaline catalysts, namely, sodium or potassium hydroxide.