# Alkali-Activated Materials with Pre-Treated Municipal Solid Waste Incinerator Bottom Ash
## 3 Results and Discussion  
### Characterization of the Precursors  
Table 3 shows the chemical composition of the MIBA and of the FA used. The data show that the sum of the oxides SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\) + Fe\({}_{2}\)O\({}_{3}\) corresponds to 88.7% and 64.3% for FA and MIBA, respectively. When comparing these values with those of ASTM C618-5 [50], it is possible to classify FA as type F, in which the sum of the oxides has a minimum established value of 70%. In the case of MIBA, the classification as per ASTM indicates that the waste can be classified as a type C ash, since the value exceeds the established limit of 50% for the sum of the oxides. According to the literature, 66% of MIBAs comply with this limit [51]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Materials** & **FA (\%)** & **MIBA (\%)** \\ \hline Al\({}_{2}\)O\({}_{3}\) & 25.55 & 8.85 \\ CaO & 2.28 & 18.33 \\ Fe\({}_{2}\)O\({}_{3}\) & 6.92 & 6.69 \\ K\({}_{2}\)O & 2.75 & 1.59 \\ MgO & 1.83 & 4.02 \\ Na\({}_{2}\)O & 1.30 & 6.55 \\ SiO\({}_{2}\) & 56.44 & 48.92 \\ SO\({}_{3}\) & 0.80 & 1.36 \\ Cl\({}^{-}\) & 0.00 & 0.00 \\ Cr\({}_{2}\)O\({}_{3}\) & 0.49 & 0.06 \\ TiO\({}_{2}\) & 1.14 & 0.48 \\ ZnO & 0.02 & 0.35 \\ P\({}_{2}\)O\({}_{5}\) & 0.44 & 2.52 \\ V\({}_{2}\)O\({}_{5}\) & 0.05 & - \\ CuO & 0.00 & 0.16 \\ MnO\({}_{2}\) & - & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical composition of raw materials, FA, and MIBA (% by mass). Figure 1 corresponds to the XRD results of the MIBA samples used in the present study. The crystalline phases observed are quartz (SiO\({}_{2}\)), calcite (CaCO\({}_{3}\)), magnetite (Fe\({}^{2+}\)Fe\({}^{3+}\)2O\({}_{4}\)), fayalite ((Fe\({}^{2+}\))\({}_{2}\)SiO\({}_{4}\)), magnesite (MgCO\({}_{3}\)), microcline (KAlSi\({}_{3}\)O\({}_{8}\)), magnesium phosphate (Mg\({}_{3}\)(PO\({}_{4}\))\({}_{2}\)), sodium calcium iron phosphate, and anhydrite (CaSO\({}_{4}\)). These results are consistent with those of other research works where similar minerals were found for MIBA [52; 53]. The crystalline phases observed for FA, showed on the same figure, are quartz (SiO\({}_{2}\)), lime (CaO), maghemite (Fe\({}^{3+}\)2O\({}_{3}\)), and mulitte. The mineralogical characterization of FA is similar to that reported by other authors [21; 54]. The amount of released hydrogen from MIBA was calibrated using a method involving the reaction of pure aluminum particles. The chemical reaction to produce gaseous hydrogen from metallic aluminum and sodium hydroxide corresponds to Equation (2). Stoichiometric quantities (atomic and molecular weights in grams) are presented in Equation (3). \[2 Al^{0}+2 NaOH+6H_{2}O\ \rightarrow\ 2 NaAl(OH)_{4}+3H_{2}\uparrow \tag{2}\]  
\[54\ \mathrm{g}\ +80\ \mathrm{g}\ +108\ \mathrm{g}\ \rightarrow 236\ \mathrm{g}\ +6\ \mathrm{g}\uparrow \tag{3}\]  
From the stoichiometric quantities, it was determined that 0.11 g of H\({}_{2}\uparrow\) was produced per gram of aluminum consumed (Equation (4)). \[\mathrm{g}\ \mathrm{H}_{2}\ \uparrow=1\ \mathrm{g}\ \mathrm{Al}^{\circ}\times \frac{6\ \mathrm{g}\ \mathrm{H}_{2}\ \uparrow}{54\ \mathrm{g}\ \mathrm{Al}^{\circ}}=0.11\ \mathrm{g} \tag{4}\]  
From the reaction of 0.1 g of metallic aluminum with a 2.5 M NaOH solution (excess reagent), the volume of water displaced by the hydrogen gas produced was measured experimentally in an inverted test tube, which was connected through a glass tube to a three-nozzle balloon (Figure 2). The theoretical value from Equation (2) corresponds to 143.03 mL of H\({}_{2}\) gas. Three trials were carried out to determine the average experimental value and calculate the error as a function of the theoretical value. The temperature at which the reaction was carried out was 43 \({}^{\circ}\)C. This heat was due to the exothermic reaction of NaOH in water. The density of the hydrogen at 43 \({}^{\circ}\)C and 1 atm. of pressure is 0.0766 kg/m\({}^{3}\)[55].