## 3 Results
### Mineralogical, MIP, and Microstructural Characterization  
The mineralogical analysis performed on the sintered samples have highlighted that independently by particle size of the mixture (V125, V75), all samples show some crystalline phases: Quartz (SiO\({}_{2}\)) as main crystalline phase (ICDD #078-2315), albite calcian ordinate (Na, Ca)(AlSi\({}_{3}\)O\({}_{8}\)) (ICDD #076-0927), and wollastonite (CaSiO\({}_{3}\)) (ICDD #002-0689), as neo-formation phases. Figure 4 reports the evolution of the crystalline phases identified as a function of temperature for V75 mixture. As reported above the two mixes showed similar crystalline phases but the finer mixture (V75) showed higher intensity of the crystalline phases. Figure 4: XRD spectrum of the V75 sintered samples at different temperatures (soaking time 60 min) showing the development of Q (quartz), W(wollastonite) and A (albite calcian ordinate) crystalline phases. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline Thermal & \multicolumn{2}{c}{**Apparent Density**} & \multicolumn{2}{c}{**Absolute Density**} & \multicolumn{2}{c}{**Young’s Modulus**} & \multicolumn{2}{c}{**Poisson**} & \multicolumn{2}{c}{**Fleuzzi Strength (MPa)**} \\
**Treatment** & \multicolumn{2}{c}{**(kg/m\({}^{3}\))**} & \multicolumn{2}{c}{**(kg/m\({}^{3}\))**} & \multicolumn{2}{c}{**(kg/m\({}^{3}\))**} & \multicolumn{2}{c}{**E (GPa)**} & \multicolumn{2}{c}{**Ratio**} & \multicolumn{2}{c}{**Fleuzzi Strength (MPa)**} \\ \hline \multicolumn{1}{c}{**V125**} & **V755** & **V75** & **V125** & **V75** & **V125** & **V75** & **V125** & **V75** & **V125** & **V75** \\ \hline
800 \({}^{\circ}\)C, 30 min & 1690 \(\pm\) 0.007 & 1720 \(\pm\)  
Kaolinite (Al2 Si2O5(OH)4), corundum (Al2O3) and calcite (CaCO3) phases present in the starting sludge disappeared during thermal treatments. Coarser quartz grains withstand to high temperatures and are present in the sintered product, but it is interesting to note that the increase of temperature provokes a diminution of quartz phase due to the solubility in the glassy phase formed. This statement is demonstrated by the decrease of intensity of the Quartz peak (3.34 A d-spacing): 2884 counts (800 \({}^{\circ}\)C, 60 min); 2530 counts (900 \({}^{\circ}\)C, 60 min); 1490 counts (1000 \({}^{\circ}\)C, 60 min). The glassy phase is favored by the temperature as evident by the broad band in the range 20-35\({}^{\circ}\) 2\(\Theta\). The newly formed calcium(II) silicates phases probably derived from the solid-state reactions between the calcium oxide (provided by calcite (CaCO3) decomposition) with reacting silica (SiO2) and corundum (Al2O3) derived from the ceramic sludge. Mullite, the typical crystalline phase of porcelain stoneware tile products it is not present in these sintered materials. The formation of plagioclase phase interferes with the kinetic of mullite formation since the phase formation takes place at minor temperature than that necessary for the mullite one [40]. This is confirmed in studied compositions by DTA data where an exothermic peak is observed around 870 \({}^{\circ}\)C.  
From the MIP measures, cumulative intrusion curves show the relationship between pore volume and pore diameter in the range of 180 to 0.006 \(\upmu\)m (Figure 5), these curves permit to observe the effect of the firing temperature on the sintering. Between 800-900 \({}^{\circ}\)C not more differences are found with a trend of porosity decrease (28% to 23%) by the increase in temperature. The specimens fired at 1000 \({}^{\circ}\)C show a significative decrease of the pore volume indicating a high sintering degree in agreement with the results reported in Figure 3. The pore volume data ranged between 0.1373 mL:g\({}^{-1}\) (800 \({}^{\circ}\)C) to 0.043 mL:g\({}^{-1}\) (1000 \({}^{\circ}\)C).