## 3 Results and Discussion
In a very recent paper, the stabilization mechanism was proposed and discussed--it was shown that dissolved amorphous silica and alumina (derived from BA) in the presence of calcium ions (and in a highly alkaline environment) promote a pozzolanic reaction with FA, with the formation of cementitious compounds such as C-S-H and calcium aluminate hydrates (C-A-H). Furthermore, carbonation reactions occurred, due to the calcium hydroxide that is present in the used wastes (for example in FGD residues) [28; 29]. In particular, considering the pH of all raw FA and final stabilized eco-materials, it means that all FAs have a starting pH about 12 (see Table 2). Instead, stabilized materials have a pH of about 11 (see Table 3) and 8 (see Table 4), depending on the procedure used for stabilization. Indeed, carbonation produces a reduction of pH [30]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Samples** & **FA-Line 1** & **FA-Line 2** & **FA-Line 3** & **BA-Line 1** & **BA-Line 2** & **BA-Line 3** \\ \hline
**pH** & **11.89** & **11.92** & **11.9** & **12.09** & **12.2** & **12.18** \\ \hline
**Element** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** \\ \hline P * & 40.3 \(\pm\) 16.0 & 25.4 \(\pm\) 8.4 & 21.9 \(\pm\) 5.7 & 5.4 \(\pm\) 2.5 & 9.3 \(\pm\) 2.6 & 12.7 \(\pm\) 5.3 \\ S * & 273 \(\pm\) 48 & 267 \(\pm\) 63 & 217 \(\pm\) 61 & 71 \(\pm\) 3.6 & 131 \(\pm\) 21 & 81 \(\pm\) 21 \\ Cl & 8890 \(\pm\) 193 & 5969 \(\pm\) 954 & 6545 \(\pm\) 958 & 62 \(\pm\) 36 & 318 \(\pm\) 185 & 408 \(\pm\) 81 \\ K & 1087 \(\pm\) 126 & 711 \(\pm\) 280 & 595 \(\pm\) 161 & 111 \(\pm\) 17 & 81 \(\pm\) 21 & 105 \(\pm\) 32 \\ Ca & 6387 \(\pm\) 1044 & 4930 \(\pm\) 913 & 4677 \(\pm\) 706 & 651 \(\pm\) 68 & 979 \(\pm\) 175 & 995 \(\pm\) 258 \\ Cr & \textless{}LOD & \textless{}LOD & \textless{}LOD & \textless{}LOD & \textless{}LOD & \textless{}LOD \\ Mn & \textless{}LOD & \textless{}LOD & \textless{}LOD & \textless{}LOD & \textless{}LOD & \textless{}LOD \\ Fe & 0.4 \(\pm\) 0.2 & 0.2 \(\pm\) 0.1 & 0.2 \(\pm\) 0.2 & 0.2 \(\pm\) 0.1 & 0.07 \(\pm\) 0.03 & 0.09 \(\pm\) 0.04 \\ Cu & 0.23 \(\pm\) 0.05 & 0.09 \(\pm\) 0.03 & 0.33 \(\pm\) 0.05 & 4.5 \(\pm\) 0.5 & 5.6 \(\pm\) 0.7 & 6.1 \(\pm\) 0.7 \\ Zn & 11.7 \(\pm\) 1.4 & 9.0 \(\pm\) 0.4 & 10.1 \(\pm\) 1.4 & 0.3 \(\pm\) 0.2 & 0.7 \(\pm\) 0.2 & 0.61 \(\pm\) 0.03 \\ Br & 211 \(\pm\) 26 & 183 \(\pm\) 19 & 236 \(\pm\) 21 & 1.7 \(\pm\) 0.3 & 1.9 \(\pm\) 0.2 & 1.8 \(\pm\) 1.0 \\ Rb & 7.3 \(\pm\) 1.5 & 7.1 \(\pm\) 0.9 & 7.6 \(\pm\) 0.8 & 0.4 \(\pm\) 0.2 & 0.2 \(\pm\) 0.0 & 0.25 \(\pm\) 0.02 \\ Sr & 16.0 \(\pm\) 4.3 & 13.8 \(\pm\) 0.4 & 27.8 \(\pm\) 3.9 & 3.9 \(\pm\) 0.4 & 5.5 \(\pm\) 0.6 & 4.7 \(\pm\) 0.2 \\ Pb & 92.0 \(\pm\) 15.6 & 94.1 \(\pm\) 6.8 & 127.1 \(\pm\) 5.4 & 0.58 \(\pm\) 0.04 & 1.6 \(\pm\) 0.3 & 1.6 \(\pm\) 0.4 \\ \hline \hline \end{tabular} Values are expressed as the average \(\pm\) standard deviation of three TXRF measurements. Relative sensitivities for elements with * were calculated based on a calibration curve. LOD-lower detection limit.  
\end{table} 
Table 2: Results of the Total-reflection X-ray Fluorescence (TXRF) analysis and pH values of leachate solutions of Sewage-MSWI FA and Sewage-MSWI BA derived from different combustion lines. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Samples** & \multicolumn{4}{c}{**FA + BA Line 1**} & \multicolumn{4}{c}{**FA + BA Line 2**} & \multicolumn{4}{c}{**FA + BA Line 3**} \\ \hline
**Time** & **1 M** & **2 M** & **3 M** & **1 M** & **2 M** & **3 M** & **1 M** & **2 M** & **3 M** \\ \hline
**pH** & **13.5** & **12.1** & **10.5** & **13.5** & **12.0** & **10.8** & **13.8** & **12.1** & **11.2** \\ \hline
**Elements** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** & **(mg/L)** \\ \hline P \({}^{*}\) & \(42.8\pm 5.6\) & \(57.4\pm 6.9\) & \(33.2\pm 10.5\) & \(28.9\pm 15.2\) & \(59.6\pm 9.0\) & \(33.3\pm 13.6\) & \(37.2\pm 26.7\) & \(58.3\pm 18.2\) & \(24.9\pm 6.2\) \\ S \({}^{*}\) & \(423\pm 168\) & \(358\pm 21\) & \(436\pm 81\) & \(318\pm 5