## 3 Results and Discussion
### Mineralogical Results of Laboratory and Pilot Scale Experiments
#### 3.2.2 Pilot Plant Scale  
Figure 4 shows secondary electron (SE) images of the samples BR1-3 and BC1-3 as well as of the original sample B from the pilot scale experiments. The higher CaO input provided in the steel plant during the formation process of slag sample B led to the appearance of different calcium (silicate) phases compared to sample A: instead of olivine phases, larnite (determined via XRD, Figure S2) was formed and brownmillerite occurred instead of melilite. Although the polished sections used for the EMP analyses were prepared without water, larnite was removed on the surface of the original sample B and the remelted samples BR1-3. Figure 3: Back scattered electron (BSE) images and element mappings (Fe, Al, Ca, Cr, Mg Si) of samples derived from the laboratory experiments: (**a**) sample A, (**b**) remelted sample AR2 (moderate cooling) and (**c**) conditioned sample AC2 (moderate cooling). Circles mark the element distribution in the spinel phase as an example. Abbreviations according to [PERSON] and [PERSON] (2010) [28]: wuestite solid solution (Wus), spinel solid solution (Spl), olivine group phase (OI), melilite group phase (MIl), bedigite (Brd), Ca-rich olivine (OI1), Mg-rich olivine (OI2), and pyroxene (Px). Phases identified via x-ray diffraction (XRD) and, if possible, via quantitative electron microprobe (EMP) analyses. Figure 4: Secondary electron (SE) images of original sample B, remelted samples BR1–3, and remelted conditioned samples BC1–3 from pilot scale experiments. Numbers 1–3 represent different cooling rates with (1) fast cooling, (2) moderate cooling, and (3) slow cooling. Abbreviations according to [PERSON] and [PERSON] (2010) [28]: wuestite solid solution (Wus), spinel solid solution (Spl), laronite (Lrn), olivine group (OI), and melilite group (MIl). Phases identified via x-ray diffraction (XRD) and, if possible, via quantitative electron microprobe (EMP) analyses. As with sample A (Figure 3), the remelting of sample B had an effect on the spinel size and abundance, but not on the overall mineral phase composition. However, the quartz sand addition did have several effects: no wuestite was formed and the crystallization of calcium silicate phases such as olivine and pyroxene, which are less soluble phases compared to larnite, was enhanced. The appearance of pyroxene indicates that the SiO\({}_{2}\) content in the slag was slightly higher than that calculated during the experiments. The size of the mineral phases in the remelted samples BR1-3 was not as strongly affected by the cooling rate as in the laboratory experiments, but the influence of the cooling rate was significant for all phases in the conditioned samples BC1-3 (Figure 4). Quantitative EMP analyses (Table S2-S21) were only possible for spinel and wuestite in samples BR1-3 because larnite was removed during the preparation, and for spinel and pyroxene in samples BC1-3 because the acicular olivine crystals were too thin for quantitative analysis. Fe-rich and Cr-rich spinels were present in all samples derived from the pilot scale experiments, but in contrast to the laboratory experiments, the sum of Cr\({}_{2}\)O\({}_{3}\) and FeO was less homogeneously distributed in the remelted samples (samples BR1-3). The Fe and Cr zonation was clearly visible in the recorded element mappings of, for example, sample BC3 (Figure S3). The change in spinel shape in the conditioned samples may indicate changes in the local activities of oxygen and deoxidation metals (e.g., Mn) as well as varying solidification conditions. Similar shapes were described by [PERSON] and [PERSON] (1976) [31] for Fe-Mn-O and Fe-Si-O equilibrium systems with Cr. In all samples, V was detected in hardly any measured spinels, but, if detected, with concentrations ranging from 0.1 mass-% up to 0.6 mass-% (for comparison original sample B: 0.1-0.2 mass-% V). In all measured wuestite phases of samples BR1-3, Cr was detected (0.07 \(\pm\) 0.04 mass-% to 0.4 \(\pm\) 0.07 mass-%) and in few grains V (0.3-0.6 mass-%).