## 3 Results and Discussion
### Chemical Analyses and Leaching Results  
As intended, the FeO/SiO\({}_{2}\) ratio decreased with the quartz addition from above three to almost one in both experiments, being in good agreement with the calculated ratios via FactSageTM (1.12 and 1.06). In the pilot scale experiments, the FeO/SiO\({}_{2}\) ratio increased for the remelted slag samples from above three to above four (Table 1). The CaO/SiO\({}_{2}\) ratio also decreased significantly, resulting in a more acidic melt and a higher MgO input from the crucible and refractory material compared to the remelted samples. The basicity achieved experimentally was also in good agreement with the calculated ratios by FactSageTM (0.62 and 0.74). The remelting and the targeted modification during the remelting had a significant influence on the amount of Cr and V leached from the slag (Table 1 and Figure 5) in both the laboratory and pilot scale experiments. Due to the small sample size (approximately 260 g) derived from the laboratory experiments, only leaching tests with distilled water (natural pH) were conducted (Table 1). The samples derived from the pilot scale experiments (10-20 kg per sample) were investigated over the pH range from 2-14 (Figure 5). The leaching experiments are described in detail in Section 2.4. The leached amounts of Cr and V at natural pH as well as the total content of MgO, Al\({}_{2}\)O\({}_{3}\), V\({}_{2}\)O\({}_{3}\), and Cr\({}_{2}\)O\({}_{3}\) in the solid samples and the FeO/SiO\({}_{2}\), respectively, the CaO/SiO\({}_{2}\) ratios are given in Table 1. The complete chemical characterization of the original samples A, B and C is provided in Table S23. In order to compensate for differences in chemical composition caused by crucible and refractory material interactions during the experiments or by the dilution of the melt, the leached amount is discussed as % of the total content. The original sample A showed elevated leaching for V and Cr compared to sample C (Table 1). Remelting the slags already decreased Cr and V concentrations in the leachate from \(1.1\times 10^{-03}\)% of the total Cr content to \(9.0\times 10^{-06}\)% of the total Cr content, and from 0.34% of the total V content to 0.07% of the total V content after the conducted laboratory experiments. The quartz sand addition lowered the leaching of V even further to 0.01% of the total V content, and therefore led to absolute leaching values of 10 to 100 times below the limit value for the use of recycling building materials (1.0 mg/kg DM) in Austria [14]. Chromium leaching after the modification was comparable to leaching after the remelting experiments. The higher CaO input during the formation of original sample B led to the formation of larnite. According to [PERSON] et al. (2017) [7], V is released during the dissolution of larnite, but may be incorporated in newly formed calcium silicate hydrates. This is supported by the fact that the V leaching from sample B at natural pH (with distilled water) was already lower than for original samples A and C (Table 1). However, the conducted pH dependence leaching tests (Figure 5) revealed that this was only valid for leaching with distilled water. A low release of V throughout the pH range from 8 to 12 was only achieved for the modified samples and original sample C, which were characterized by low wuestite and high spinel abundance as well as high calcium silicate phase formation such as melilite and olivine (with low solubility), but no larnite (with high solubility). The V release from the original sample A, but even more significantly from original sample B, increased below pH 11. This led to the assumption that during aging and carbonation of the slag samples, which leads to a pH decrease of the leachates [37; 38], more V was leached from the original sample compared to the conditioned slag samples. The formation of less soluble calcium silicate phases due to the quartz sand addition is represented by the pH-dependent release of Ca and Si (Figure 5).