## 3 Results and Discussion
### Slags Characterization
#### 3.1.2 Mineralogical Characterization and Microstructure
Increase of cooling rate prevents the thermodynamic chromite spinel formation from the MW solid solution with temperature drop, preserving Chromium in the MW phase. In high basicity EAF slags, primary crystallization of Chromium occurs in magnesium-[21; 36]. This is illustrated in the microanalyses of the mageniouwustite solid solution phases in the higher basicity air-cooled slag samples 4 and 5, (Table 5). Increase of FeO amount in these solid solutions has also been reported to decrease its reachability from the slag, which is an advantageous property for its further envisaged use [21; 36]. Overall, iron in the examined slags was mainly in the divalent state bound in the MW phase as described above. In slag 5, where limited reduction of iron oxides was targeted through the applied experimental conditions, brownmillerite, Ca\({}_{4}\)Al\({}_{2}\)Fe\({}_{2}\)O\({}_{10}\) (C\({}_{4}\)AF) and calcium ferrite (CaO.2 Fe\({}_{2}\)O\({}_{3}\)) were additionally identified, also indicating presence of trivalent iron in the slag. Brownmillerite is commonly met in the clinker of Portland cement, while calcium ferrite phase in contrast to MW has been reported as phase of hydraulic nature, too [18]. Micro-areas rich in C\({}_{4}\)AF crystals were detected by SEM/EDS examinations in slag 5 sample (Table 5, Figure 3b). Tricalcium silicate 3 CaO.SiO\({}_{2}\) (C\({}_{3}\)S), being the most important phase in cement for early strength development among the calcium silicates, was mainly detected in the slag products, 4-2a, b and 5, where the basicity was higher, while some traces were also found in slag 3-1b. Typical micrograph and microanalyses of identified C\({}_{3}\)S hexagonal crystal in the slags microstructure is shown in Figure 3c and Table 5, respectively. Presence of merwinite, 3 CaO-MgO-2 SiO\({}_{2}\) (C\({}_{3}\)MS\({}_{2}\)), common constituent of EAF steelmaking slags was also identified in the XRD and SEM/EDS analysis of the slags. Characteristic micro-area of solidified merwinite crystals is shown in Figure 3d and representative C\({}_{3}\)MS\({}_{2}\) microanalyses are provided in Table 5. According to [15] low grain size merwinite in EAFs contributes to slags cementitious properties exhibiting a hydration behavior similar to that of di- and tri-calcium silicates. Calcium aluminate phases, such as 3 CaO-Al\({}_{2}\)O\({}_{3}\) (C\({}_{3}\)A) and 12 CaO-7 Al\({}_{2}\)O\({}_{3}\) (C\({}_{12}\)A\({}_{7}\)), which also contribute to strength development upon hydration, participated in the mineralogical composition of the slags, being more abundant in slags 4-2(Table 5, Figure 4), which had the highest content of Al\({}_{2}\)O\({}_{3}\). In addition, gehlenite C\({}_{2}\)AS (2 CaOAl\({}_{2}\)O\({}_{3}\)SiO\({}_{2}\)) was also often detected (Figure 1, Table 5). The retention of some of the water-cooled slags in water during their cooling resulted in the fast hydration of part of the calcium aluminate phases. The presence of sulfur in these slags led to the formation of monosulfate, C\({}_{4}\)ASH\({}_{12}\) (4 CaO-Al\({}_{2}\)O\({}_{3}\)SO\({}_{3}\):12H\({}_{2}\)O), found as thin hexagonal plates, (Figure 4c) or etrtingiteC\({}_{6}\)AS\({}_{3}\)H\({}_{32}\) (6 CaO-Al\({}_{2}\)O\({}_{3}\):3 SO\({}_{3}\):32H\({}_{2}\)O) detected in the form of needles (Figure 5). These hydrated phases were only detected locally in SEM backscattered images. It has also been reported that in most cases it is not possible to detect etrtingite by XRD [37].