## 3 Results  
### Mineral and Chemical Composition  
The results of the semi-quantitative analyses indicate the mineral phases are present in the slag samples. The complete list of the mineral phases found in the samples, along with their chemical compositions and crystal structures, are shown in Table 1. In addition, the distribution of the mineral phases is shown in Figure 1. \begin{table}
\begin{tabular}{c c c} \hline
**Compound Name** & **Chemical Formula** & **Crystal System** \\ \hline dicalcium silicate \(\gamma\) & \multicolumn{2}{c}{Ca2 O4 Si1} & Orthorhombic \\ bedigite (O1) & Ca26.93 Ba0.59 Mg3.62 MnO.86 Si16.00 O64.00 & Orthorhombic \\ bedigite (S1) & Ba0.3 Ca13.5 Mg1.8 MnO4 O32 Si9 & Orthorhombic \\ fluorite & \multicolumn{2}{c}{Ca1 F2} & Cubic \\ magnesiochromic (O1) & Mg6.96 Fe1.04 Cr16.00 O32.00 & Cubic \\ magnesiochromic (O2) & \multicolumn{2}{c}{Cr2 Mg1 O4} & Tetragonal \\ magnesiochromic (S1) & Al7.78 Fe3.59 Mg4.70 MnO.05 Si0.01 Zn0.05 Cr7.78 Ni0.01 Ti0.02 O32.00 & Cubic \\ akermantic (O1) & Ca4.00 Mg1.42 Al1.02 Si3.48 O14.00 & Tetragonal \\ akermantic (S1) & Ca4.00 Mg0.92 Al1.98 Si3.04 O14.00 & Tetragonal \\ cuspidine & \multicolumn{2}{c}{Ca16.00 O38.00 O28.00 F8.00} & Monoclinic \\ merwinite & \multicolumn{2}{c}{Ca3 Mg1 O8 Si2} & Monoclinic \\ dolomite & \multicolumn{2}{c}{Ca3.00 Mg3.00 C6.00 O18.00} & Hexagonal \\ periclase & \multicolumn{2}{c}{Mg1 O1} & Cubic \\ portlandite & \multicolumn{2}{c}{H2 Ca1 O2} & Hexagonal \\ magnesioferrite & \multicolumn{2}{c}{Mg8.00 Fe16.00 O32.00} & Cubic \\ mayenite & \multicolumn{2}{c}{All4 Ca12 O33} & Cubic \\ \hline \end{tabular}
\end{table} 
Table 1: Compound name, chemical formula and crystal system of each mineral found in the slag samples. As can be seen in Figure 1 the slag sample S1 contains the highest number of minerals, since it contains 6 phases with a percentage higher than 5%. Sample O1 follows, where 3 phases constitute approximately 96% of the sample content. Sample O2 is almost a binary system consisting of akermanite and merwinite, as they constitute approximately 93% of the total content. Slag sample S2 is instead a binary system consisting of mayenite and dicalcium silicate \(\gamma\). The complex multi-mineral landfill slags (O1 and S1) seemed to have a more varied structures than the ones taken from AOD (S2) and the EAF (O2) samples. This is not surprising, as the landfill slags are usually made up of a mix consisting of several by-products and they also have been subjected to additional processes while being exposed to the outdoor environment. dicalcium silicate \(\gamma\), akermanite and predigite are the most common phases, which are present in at least 3 samples. This is in accordance with the results of several studies that reported high amounts of dicalcium silicate \(\gamma\) and predigite in several kinds of slags [22; 23; 24]. Another important factor to mention is that besides magnesiochromite and pericase, all the minerals are Ca-bearing. Therefore, Ca resides in several different mineral structures, which likely present different solubilities and reactivities depending on the acid environments and crystal structures, as shown in previous studies that analyzed the dissolution of minerals often present in metallurgical slags [17; 18]. The bulk chemical composition of all the slag samples have been assessed using ICP-SFMS. The analysis measured the concentrations of 32 metallic elements present in the slag samples. The concentrations of the tested elements are shown in Table 2. The most abundant ones in each slag (among the one tested) are also grouped in Figure 2. Overall, Ca is the most abundant element (among the one tested) in all slag samples, where the content ranges from 27% to 32%. Si is the second most abundant element in slag samples O1, O2 and S1. The content ranges from 10% to 14%, while in slag sample S2 it is only 3%. Mg is the third most abundant element for all samples, where the content ranges between 3% and 7%.