# Utilization of Industrial Ferronickel Slags as Recycled Concrete Aggregates
## 3 Results
### Raw Materials Characterization
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Chemical Formula** & **Percentages (\%)** \\ \hline Spinel group & (Mg, Fe, Mn, Ni)(Cr, Al, Fe, V)O\({}_{4}\) & 35 \\ Wustite & FeO & 45 \\ Merwinite & C\({}_{3}\)MS\({}_{2}\) & 7 \\ Beta dicalcium silicate & C\({}_{2}\)S & 11 \\ Gehlenite & C\({}_{2}\)AS & <3 \\ \hline \hline \end{tabular}  
* In the semi-quantitative analysis, the amorphous phases are not included. It was calculated <30%.  
\end{table} 
Table 2: *** Mineral composition % of the studied FeNi slag. Figure 5: (a) XRD pattern of FeNi slag; (b) XRD pattern of Electric Arc Furnace slag (1: Gehlenite, 2: C\({}_{3}\)MS\({}_{2}\), 3: C\({}_{2}\)S, 4: Spinel, 5: W\(\prime\)stite, 6: Quartz, 7: Periclase). \end{table}
Table 3: *** Mineral composition % of the studied Electric Arc Furnace slag. SLAG slag presents LOI (loss on ignition) 1.21, while the FeNi slag does not present any value of LOI. As for the trace elements, FeNi slag is more enriched in Ni, while ELECTRIC ARC FURNACE SLAG slag is more enriched in Cr, Sr, Ba and V (Table 4). The slags have basicity value which range from 2.42 (ELECTRIC ARC FURNACE SLAG) to 3.31 (FeNi) which as calculated according to the following equation:  
\[\text{Basicity}=(\%\text{CaO}+\%\text{MgO})/\%\text{SiO}_{2}\]  
where %CaO, %MgO and %SiO\({}_{2}\) are the contents of those mentioned oxides (wt%) in the studied slags. Analyses with Scanning Electron Microscope (SEM) and Energy Dispersive X-ray mapping were conducted to determine the distributions of several major elements (Si, Al, Ca, Mg, Fe, Cr, K and Na) in the studied slags. SEM observations are in accordance with the petrographic features and XRD analyses as indicated in Figure 5 where spherical crystals of w\(\ddot{\text{o}}\)site and curved subhedral spinels are shown. These minerals are surrounded by microcrystalline calc-silicate phases (C\({}_{2}\)S). FeNi slag presents uniformly distributed porosity of brick type (Figure 6). Regarding ELECTRIC ARC FURNACE SLAG slag, in Figure 7 it is proved that it consists of spherical crystals of w\(\ddot{\text{o}}\)site, elongated spinels, calc-silicate phase (C\({}_{2}\)S) and microcrystalline gehlenite (Figure 7a). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Oxides** & **FeNi** & **ELECTRIC ARC FURNACE SLAG** \\ \hline SiO\({}_{2}\) & 3.77 & 11.81 \\ TiO\({}_{2}\) & 0.02 & 0.57 \\ Al\({}_{2}\)O\({}_{3}\) & 0.43 & 7.29 \\ Fe\({}_{2}\)O\({}_{3}\)\({}^{\ddagger}\) & 37.25 & 10.41 \\ MnO & \textless{}DL & 1.74 \\ MgO & 2.30 & 1.74 \\ CaO & 10.21 & 26.85 \\ Na\({}_{2}\)O & 0.04 & 0.10 \\ K\({}_{2}\)O & 0.04 & 0.03 \\ P\({}_{2}\)O\({}_{5}\) & 0.33 & 0.39 \\ LOI & 0 & 1.21 \\ \hline ppm & & \\ Cr & 2561 & 4537 \\ Co & 379 & 31 \\ Ni & 1327 & 20 \\ Cu & 27 & 156 \\ Zn & 12 & 115 \\ Rb & \textless{}DL & \textless{}DL \\ Sr & 39 & 486 \\ Y & 15 & 34 \\ Zr & \textless{}DL & 86 \\ Nb & \textless{}DL & \textless{}DL \\ Pb & \textless{}DL & \textless{}DL \\ Ba & 171 & 1203 \\ V & 31 & 207 \\ W & 37 & 28 \\ La & 1 & 12 \\ Ce & 58 & 94 \\ Th & \textless{}DL & \textless{}DL \\ Sc & \textless{}DL & \textless{}DL \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the chemical composition of the tested samples (<DL: <below detection limit). The results of SEM-X-ray mapping are presented in Figures 6 and 7. The SEM-X-ray mapping analysis result in FeNi slag indicates that Fe is uniformly distributed on the entire surface of the slag (Figure 6f). In addition to Mg, components in the slag that are in lower amounts are Si, Cr, Ca, K and Na (Figure 6b-e,g-i). Regarding ELECTRIC ARC FURNACE SLAG slag, the mapping results are in accordance with the chemical compositions and the  
Figure 6: Back-scattered electron image of spherical crystals of w/stite (W), spinels (Sp) and microcrystalline calc-silicate phase (C\({}_{2}\)S), as well as pores (P, distinguished as black) in FeNi slag (**a**) and mapping of major elements (Al, Si, Ca, Mg, Fe, Cr, K and Na, respectively) (**b–i**).