## 3 Results and Discussion  
### Chemical Composition Analysis  
The key to the bloat of lightweight aggregates lies in two conditions [44; 45]. One is that the material must produce a high-temperature glassy phase with a viscosity high enough to trap the gases released as the mineral decomposes. Another is that a substance must be present to release the gas at the temperature at which the glassy phase is formed. [PERSON] proposed a three-phase diagram of the chemical composition of raw materials, as is shown in Figure 6[46]. The \"bloating area\" suggested in the diagram can help identify whether the composition of the sludge material meets the requirements for bloating. Therefore, the content of silicon dioxide (SiO\({}_{2}\)), aluminum oxide (Al\({}_{2}\)O\({}_{3}\)), ferric oxide (Fe\({}_{2}\)O\({}_{3}\)), fluxing oxides (fluxing), and the ratio of (SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\))/fluxing of each sludge component will be discussed, respectively, in the following section in order to understand the feasibility of sintering these various sludges into lightweight aggregates. Table 2 shows the percentages of the various sludge chemical components that were obtained via XRF analysis. 1.1 Discussion on the Content of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\)  
As far as lightweight aggregates are concerned, the main elements that affect its formation of glassy melt are SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\). With respect to the composition, when the content of SiO\({}_{2}\) accounts for more than 50% and the total content of Al\({}_{2}\)O\({}_{3}\) and Fe\({}_{2}\)O\({}_{3}\) accounts for around 10-30%, it is possible to produce glass at a high temperature, thus successfully producing lightweight aggregates [14; 17; 18; 47]. Among the sludge components, SiO\({}_{2}\) will affect the viscosity of the vitreous material when the lightweight aggregate is sintered. When the SiO\({}_{2}\) content is high, the viscosity of the glass will increase, but the strength of the aggregate will be reduced. As far as Al\({}_{2}\)O\({}_{3}\) is concerned, it will affect the sintering temperature, and the sintering temperature will be higher when its content is higher. When the content of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) is too low, it will affect the smoothness and strength of the shell of the sintered aggregate; however, when the content is too high, the melting point will increase, the viscosity will be higher, and the bloat will be poor [48]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sludge Type**} & \multicolumn{8}{c}{**Chemical Constituent (\%)**} \\ \cline{2-10}  & \(\mathbf{SiO_{2}}\) & \(\mathbf{Al_{2}O_{3}}\) & \(\mathbf{Fe_{2}O_{3}}\) & \(\mathbf{Na_{2}O}\) & \(\mathbf{CaO}\) & \(\mathbf{K_{2}O}\) &
\begin{tabular}{c} **Loss on** \\ **Ignition** \\ \end{tabular} & **Other** & **Total** \\ \hline Sample A & 14.35 & 44.83 & 0.59 & 6.76 & 0.45 & 7.29 & 19.70 & 6.03 & 100 \\ Sample B & 6.86 & 17.55 & 1.38 & 0.40 & 0.47 & 0.11 & 66.08 & 7.15 & 100 \\ Sample C & 4.43 & 24.07 & 0.71 & 0.21 & 1.25 & 0.04 & 59.77 & 9.52 & 100 \\ WPS & 58.84 & 19.30 & 6.63 & 1.15 & 1.75 & 3.55 & 4.94 & 3.84 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical compositions of the different sludge sources. Figure 6: Bloating area in three-phase diagram. It can be seen from Table 2 that the total content of the SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) in the water purification sludge was 84.77%, and it was estimated that this could be sintered into lightweight aggregates with a smooth shell. However, regarding the textile sludge, the content of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) in Sample A was 59.77%, Sample B was 25.79%, and Sample C was 29.21%, all of which showed levels far below 75%. From this point of view, the textile sludge would not be able to produce glassy melt, and thus could not be sintered into lightweight aggregates.