## 3 Results
### Elemental and Structural Analysis  
As seen in Figure 1, the SOW sample consists of a majority of aluminium and alumina with a substantial number of impurities, mainly fluoride, as well as sodium that comes from the material processing reactants, in addition to Ca and Fe, regular additives to aluminium alloys, though nitrogen was not explicitly identified in the measured sample. The average elemental analysis is visible in Table S1. XRD analysis shows that the present samples were crystalline structures composed of corundum, calcium fluoride, and other components, such as sodium fluoride and aluminate. The nitride content changes a material's thermal properties substantially and makes it difficult to physically process. Even in our processing experience, the preparation of samples was complicated, as the separation and grinding of samples took a lot of tools and time, thus proving yet again that recycling this material in a conventional way is time and energy-consuming. Figure S2 shows additional SEM-EDS measurement points and the elemental distribution of the said sample. In addition, we see a variation in morphology, which affirms the XRD results, as multiple types of crystalline structures are visible. The estimated content of Al in SOW is a little below 50%. Sample RM consists of Al, O, K, Mg, Ca, Na, F, V, Fe, and Ti. The impurities are not evenly distributed, and we can see a variation of morphology, as shown in Figure 2a,b. Although the impurities are a small part of the total concentration, some parts show a higher amount of fluorine. The Al content varies from 30% to 45%, and oxygen varies from 43 to 59%; other trace elements also change substantially. The composition is shown in Table S2. It is known that the composition of samples will have a substantial effect on hydrogen production. Thus, it is expected to have lower reactivity and hydrogen production rates for the RM sample. On the other hand, crystalline structure shows a lower number of  
Figure 1: XRD and SEM-EDS analysis of sample SOW. (**a**) XRD diffractogram of the sample, where various crystalline phases are present; (**b**) EDS measurement, where atomic content corresponds to crystalline phases; (**c**) SEM micrograph of SOW sample, where flat flakes are visible, indicating relatively large surface area. components, such as Al nitride, oxide, and vanadium oxide. In comparison to the SOW sample, the number of crystalline components is lower, and it is mostly composed of oxides, as seen in Figure 2a. Using EDS and SEM, as seen in Figure 3a,b, we see that the HDC sample is somewhat homogeneous, without visible crystalline structures, which is corroborated by the XRD results, as the crystalline forms provide Bragg peaks of metallic Al. Moreover, Si, CaF\({}_{2}\), and MgO are visible in the diffractogram pattern; see Figure 3c. Metallic Al, calcium fluoride, and magnesium oxide were detected. Notably, no nitrides or alumina were detected in the HDC sample. Thus, it consists of the following elements: Al, Mg, F, Si, Ca, and O, with a relatively even distribution across the sample area. Despite a seemingly even distribution and morphology, the elemental content was determined to be between 53 and 58% Al, with significant Si content, as seen in Table S3. In addition, in the O/N gas analysis, we see similar results, where the composition of samples is widely dispersed, and the results can be seen in Table S4. Elemental analysis shows that depending on the processing stage of aluminium, dress has variations of compositions and structures, complicating the recycling and reusing of these materials. The simplified estimated energy consumption of 1t of dress is 454 kWht\({}^{-1}\) in oil and 72 kWht\({}^{-1}\) in electricity, with a yield of 0.45 t of metallic Al [18]. It is noteworthy that often the exact composition of used dress is not revealed or even not known. Nonetheless, it is not very easy to compare any results on composition as it will depend on the stage of sample collection. Figure 3: SEM, EDS, and XRD analysis of the HDC sample.