## 4 Discussion  
In contrast to GGBFS, non-ferrous metallurgical slags are not widely adopted as supplementary cementitious materials for the production of cement-based materials. This could, for the most part, be due to the presence of toxic elements and corrosive anions, leading to environmental concerns and long-term damages to the host concrete member. The low reactivity of such slags, mostly due to their chemistry (high iron oxide and low calcium oxide and alumina contents) and their mineralogy (crystalline oxides and iron silicates), would also make such slags less obvious candidates for use as SCMs. The above reasons make the application of a high-temperature metallurgical treatment prudent for the recovery of valuable metals and the reduction/removal of other heavy metals from slag. Incorporation of calcareous and aluminum additives to slag in the course of thermal treatment to modify the chemistry and the application of rapid cooling can promote the reactivity of the slag to a large extent. Nevertheless, the reactivity of the treated slag can vary across a wide range. [PERSON] et al. (2018) concluded that slags generated from lead, copper and zinc production have been widely studied in the literature as SCMs with strength performance levels ranging from those of an inert filler to exceeding those of typical coal fly ash. In the case of slags studied in this research, it was clearly shown that they have poor/mild pozzolanic performance evidenced by (1) the similar bound water and heat release patterns of the slag-blended pastes and the pastes blended with quartz powder, (2) a lack of significant reactions up to 7 days according to SEM image analysis results, and (3) the low strength activity indexes. In comparison with the reactivity results reported in the literature for similar non-ferrous slags, the slags studied in this research (real and synthetic) showed rather low reactivity. [PERSON] et al. (2018) reported a comparable R3 bound water content for a similar ferro-silicate slag (3.5 g/100 g of SCM) but a considerably higher strength activity index at all ages (74%, 84% and 88% at 7, 28 and 91 days, respectively, for a slag with similar fineness, 92% amorphous content and 3.9% CaO, 11% Al\({}_{2}\)O\({}_{3}\) and 32.3% SiO\({}_{2}\)). [PERSON] et al. (2018) reported an R3 7-day cumulative heat release in the range of 200-240 J/g SCM for NFM slag with Blaine fineness of 4500-6500 cm\({}^{2}\)/g, which is higher than the heat release values observed for TS1-TS3. In comparison to TS1-TS3, the slags used in their study contained high iron oxide and low silica content, more calcium oxide (15-20 wt.%), less alumina content, equal or less amorphous content and slightly higher fineness (especially compared to TS3). Given the higher reactivity reported by [PERSON] et al. despite high iron oxide and low silica contents, and also the fact that the rather wide variations in the iron oxide and silica contents in TS1-TS3 did not cause much change in reactivity, it could probably be argued that these two elements are not the primary factors influencing reactivity. For \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Mortar Label** & **Slag Source** & **As** & **Ba** & **Cr** & **Pb** & **Zn** & **Sb** & **Ni** \\ \hline M\_PC & – & \textless{}0.15 & 13 & 0.2 & \textless{}0.1 & \textless{}0.1 & \textless{}0.2 & \textless{}0.05 \\ M\_TS1 & TS1: Treated S1 & \textless{}0.15 & 15 & 0.52 \({}^{*}\) & \textless{}0.1 & \textless{}0.1 & \textless{}0.2 & \textless{}0.05 \\ M\_TS2 & TS2: Treated S2 & \textless{}0.15 & 12 & 0.29 & \textless{}0.1 & \textless{}0.1 & \textless{}0.2 & \textless{}0.05 \\ M\_TS3 & TS3: Treated S3 & \textless{}0.15 & 20 & 0.16 & \textless{}0.1 & 0.1 & \textless{}0.2 & \textless{}0.05 \\ \hline \multicolumn{1}{c}{VLAREMA limits} & 0.8 & 20 & 0.5 & 1.3 & 2.8 & 1 & 0.75 \\ \hline \end{tabular} \({}^{*}\) Exceeding the standard limitation.  
\end{table} 
Table 11: The batch-leaching test result of the crushed mortar mixtures: metal content is expressed in mg/kg dry-mass basis.