## 2 Materials and Methods
### Materials  
The mining waste was collected at the Neves Corvo mine, operated since 1988 by SOMINCOR (Sociedade Mineira de Neves Corvo S.A.), owned by the Lundin Mining Corporation. It was mostly included as an inert, in terms of alkaline activation reactions, and not as a precursor, and was recovered from one of the ponds located inside the mine compound (Figure 1), i.e., with a high water content. It was immediately transported to the laboratory, where it was separated from most of the constituent water and mixed with different percentages of FA, provided by the company _PEGOP_, responsible for the Portuguese thermo-electric power plant _Central do Pego_. The aggregate was a sandy soil (GS), collected on a bank of the river Tamega, located in the region of Chaves in the north of Portugal.  
The chemical composition of the three materials, obtained by X-ray fluorescence (XRF), is shown in Table 1. The main elements of the MT are sulphur trioxide (41%) and iron (28%), although some heavy metals were also detected in smaller percentages. The FA presented mostly silica (45.2%) and alumina (28.5%). Finally, the aggregate, as expected, was basically silica (86.8%).  
Figure 1: General view of the ponds.  
The particle size distribution (PSD) of the MT and GS, determined using sieves and sedimentation (for particles below 0.063 mm), is presented in Figure 2, which also includes the PSD of the FA, determined by laser granulometry. The fines contents (particles smaller than 63 microns) represented 91%, 98%, and 4% of the MT, FA, and GS compositions, respectively. The density of the MT (32.85 kN/m\({}^{3}\)) was significantly higher than those of the GS (25.81 kN/m\({}^{3}\)) and FA (21.75 kN/m\({}^{3}\)). The MT showed some plasticity, with a plastic limit of 10.4% and a liquid limit of 26.3%.  
In terms of mineralogy, the X-ray diffraction analysis of the FA showed a main presence of quartz and mullite. The amorphous content of the FA is evidenced by a halo between angles 17\({}^{\circ}\) 20 and 33\({}^{\circ}\) 20. However, the precise quantification of the reactive content in coal fly ash type F is not straightforward, as demonstrated by [PERSON] and [PERSON] [41], who divided the FA into three different materials: reactive, partially reactive, and inert. They showed that the contribution of the cenospheres (i.e.,  
\begin{table}
\begin{tabular}{c c c c} \hline
**Element** & **Fly Ash** & **Tailings** & **Soil** \\ \hline  & **(wt\%)** & **(wt\%)** & **(wt\%)** \\ \hline Na\({}_{2}\)O & 1.18 & 0.41 & 0.47 \\ SiO\({}_{2}\) & 45.2 & 18.5 & 86.77 \\ Al\({}_{2}\)O\({}_{3}\) & 28.5 & 7.25 & 7.20 \\ MgO & 1.07 & 1.48 & 0.11 \\ K\({}_{2}\)O & 1.56 & 0.61 & 4.02 \\ CaO & 6.04 & 0.95 & 0.24 \\ TiO\({}_{2}\) & 2.62 & 0.15 & 0.08 \\ Fe\({}_{2}\)O\({}_{3}\) & 10.7 & 27.5 & 0.58 \\ ZnO & 0.04 & 1.15 & - \\ ZrO\({}_{2}\) & 0.09 & - & - \\ BaO & 0.38 & - & 0.04 \\ PbO & 0.12 & 0.40 & - \\ As\({}_{2}\)O\({}_{3}\) & - & 0.35 & - \\ CuO & 0.05 & 0.44 & - \\ SO\({}_{3}\) & 1.36 & 40.6 & 0.03 \\ Co\({}_{3}\)O\({}_{4}\) & - & 0.04 & - \\ Cr\({}_{2}\)O\({}_{3}\) & 0.05 & 0.04 & 0.06 \\ Sb\({}_{2}\)O\({}_{3}\) & - & 0.05 & - \\ MnO & 0.12 & 0.08 & 0.01 \\ P\({}_{2}\)O\({}_{5}\) & 0.91 & - & 0.07 \\ Rb\({}_{2}\)O & 0.01 & - & 0.02 \\ L.O.L & 6.47 & 1.16 & 0.80 \\ \hline \end{tabular}
\end{table}
Table 1: Chemical composition.  
Figure 2: Particle size distribution.  
partially reactive fraction) is restricted to the outer layer, which makes it almost impossible to accurately quantify the overall contribution. The diffractogram of the MT revealed, as expected, the presence of pyrite and quartz as the dominant minerals, with some arsenopyrite, muscovite, and chamosite. The GS mostly constitutes quartz.