## 3 Results and Discussion  
### Controlling Basicity  
The analyses of the modified slag samples can be seen in Table 4. The basicity, CaO/SiO\({}_{2}\) ratio, of the samples corresponded to the desired basicity. The MgO content in the samples increased from 9.1 wt% due to the slag reacting with the MgO crucible. The changes in the composition were too small to be significant and could therefore be due to variations in the slag, but the results indicate that more MgO was dissolving into the slag as the basicity decreased.  
Table 5 shows the minerals detected by XRD and SEM-EDS. Magnesiowustite and spinel were found for all basicities. Larnite was not found at basicity 1.5, but merwinite was. Brownmillerite was only detected by SEM-EDS and XRD at basicity 2.4 and higher. The results from these experiments confirm the results from the thermodynamic calculations: by changing the basicity, the formation of brownmillerite can be avoided without forming merwinite.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **CaO** & **MgO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **FeO** & **MnO** & **Cr\({}_{2}\)O\({}_{3}\)** \\ \hline
**Basicity 2.3** & 31.5 & 10.5 & 13.5 & 6.4 & 26.2 & 5.1 & 2.8 \\
**Basicity 2.0** & 30.6 & 11.0 & 15.3 & 6.4 & 25.2 & 5.1 & 2.7 \\
**Basicity 1.5** & 28.3 & 11.7 & 18.8 & 5.8 & 24.1 & 4.6 & 2.4 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Composition in wt% of the modified slag samples.  
Figure 2: Figure conceptualizing the different cooling rates used in the laboratory cooling controlled experiments.  
The diffractograms for the slags of different basicities can be seen in Figure 3. For basicity 2.3, the brownmillerite peaks could almost not be distinguished from the background noise. At basicity 1.5, the larnite was exchanged for merwinite.  
Figure 4 shows the chromium leaching of the reference and the autoclaved slag samples. The aged reference slag leached 2.2 mg/kg originally. Remelting the reference slag decreased the leaching of chromium to less than 0.04 mg/kg, which is not shown in Figure 4. Autoclave treatment returned the chromium leaching to 1.8 mg/kg, the same magnitude as the aged slag. Henceforth, only leaching from autoclaved samples were presented and discussed, since autoclave treatment causes slag to leach as aged slag. The decrease in basicity from 2.7 to 2.3 resulted in significantly less chromium leaching, and the leaching decreased continuously as the basicity was lowered to 2.0. As a result of brownmillerite being absent at basicity 2.0 and below, decreasing the basicity further than 2.0 did not result in significantly less chromium leaching. The chromium leaching decreased with decreasing brownmillerite content, indicating that chromium leaching and brownmillerite content were related. The chromium that usually is included in brownmillerite relocates to another chromium-containing mineral when brownmillerite is not present. If the only minerals chromium can enter at this point do not dissolve in water, there can be no chromium leaching. Thereby, it is possible to prevent most of the chromium leaching by having a basicity at which neither brownmillerite nor merwinite are formed.  
Figure 3: XRD diffractograms of the basicity modified slag. The letters represent the minerals found in the analysis—s: spinel; b: brownmillerite; m: magnesiowüstite; l: larnite; e: merwinite.