## 3 Results and Discussion
### Controlling Cooling  
Brownmillerite was not detected in the slag samples of basicity 2.1, but was detected in every sample of basicity 2.8, by both XRD and SEM-EDS analysis, as seen in Table 6.  
The SEM images in Figure 5 show the slags from the cooling experiments. The hold temperature and altering temperature experiments have the largest spinels. The magnesiowustite in most samples contains darker dots, representing spinels that are beginning to form. The fast cooling rate experiment shows the smallest particle size since the mineral phases had the shortest time to grow. In addition to the phases seen in Figure 5, a phase with chemical composition fitting pleochroite, Ca\({}_{6}\)Al\({}_{8}\)MgSiO\({}_{21}\) was found in the slag at basicity 2.8. The pleochroite did not contain chromium. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **Basicity** & **Larnite** & **Magneiso-** & **Brownmillerite** & **Spinel** \\ \hline  & & **Ca\({}_{2}\)SiO\({}_{4}\)** & **W\(\ddot{\text{a}}\)stite MeO** & **Ca\({}_{2}\)(Al,Fe)\({}_{2}\)O\({}_{5}\)** & **AB\({}_{2}\)O\({}_{4}\)** \\ \hline
**Reference** & 2.1 & XRD & XRD & & XRD \\  & 2.8 & XRD & XRD & XRD & XRD \\ \hline
**Hold. Temp.** & 2.1 & XRD, SEM & XRD, SEM & & XRD, SEM \\  & 2.8 & XRD, SEM & XRD, SEM & XRD, SEM & XRD, SEM \\ \hline
**Alter. Temp.** & 2.1 & XRD, SEM & XRD, SEM & & XRD, SEM \\  & 2.8 & XRD, SEM & XRD, SEM & XRD, SEM & XRD, SEM \\ \hline
**Set Cool.** & 2.8 & XRD, SEM & XRD, SEM & XRD, SEM & XRD, SEM \\ \hline
**Fast Cool.** & 2.8 & XRD, SEM & XRD, SEM & XRD, SEM & SEM \\ \hline \end{tabular}
\end{table} 
Table 6: The major minerals discovered in XRD and SEM-EDS analysis of the samples of different cooling rates. No SEM analyses were performed on the references. Figure 4: Chromium leaching of low-alloy EAF slag remelted with and without the addition of SiO\({}_{2}\) to achieve different basicities. The XRD diffractograms for the different cooling methods can be seen in Figure 6. All slag samples were completely crystalline. The only difference between the samples of basicity 2.1 and basicity 2.8 is the presence of brownmillerite in the latter. Otherwise there were no differences between the different cooling methods at the same basicity, except that there was no strong peak corresponding to spinel in the fast cooling rate sample. Figure 5: SEM image of the slag at basicity 2.1 and 2.8 cooled by different methods. The letters representing the minerals found in the analysis—s: spinel; b: brownmillerite; m: magnesiowustite; l: larrite. The cooling rates affected chromium leaching in both basicities, as seen in Figure 7. The highest leaching of the two different basicities was achieved by different cooling methods. At basicity 2.1, alternating the temperature between 800 and 1000 \({}^{\circ}\)C gave the highest chromium leaching of 0.65 mg/kg; however, at basicity 2.8, holding the temperature at 700 \({}^{\circ}\)C gave the highest leaching of 15.2 mg/kg. As the temperature of the slag in the tipping site at Ovako Hofors is unknown, the methods hold temperature and alternating temperature represent the worst-case scenarios in terms of slag handling with respect to brownmillerite formation. It was therefore anticipated that these methods should cause an increase in chromium leaching. Even with increased chromium leaching at basicity 2.1, brownmillerite was neither seen in SEM-EDS nor XRD, which is still to be explained. Either the amount of brownmillerite was below the detection limit or another mineral was responsible for the chromium leaching. The thermodynamic calculations of the slag at basicity 2.8 showed that 700 \({}^{\circ}\)C was close to the temperature of maximum brownmillerite formation. The 24-h holding period at this temperature giving sufficient time for brownmillerite formation may explain the exceptionally high chromium leaching of 15.2 mg/kg. The lowest chromium leaching, at 1.9 mg/kg, in the slag at basicity 2.8, was  
Figure 6: XRD diffractograms of the slag at basicity 2.1 and 2.8 cooled by different methods.