# Synthesis of Zeolitic Material with High Cation Exchange Capacity from Paper Sludge Ash Using EDTA
## 3 Results and Discussion
The crystallite sizes (D) of hydroxysodalite, hydroxycarcinite, tobermorite, and zeolite-A in the product were calculated using the Scherrer equation:  
\[\text{D (nm)}=\frac{K\cdot\lambda}{\beta\cos\theta}, \tag{3}\]  
where \(K\) is the Scherrer constant, \(\lambda\) is the wavelength of the \(X\)-ray radiation, \(\beta\) is the full width at half maximum (FWHM) of the XRD diffraction peaks, and \(\theta\) is the diffraction angle according to the Bragg formula [56; 57; 58]. It is noted that the separation of the peaks for zeolite-P made it difficult to calculate the crystal size. For the products synthesized without  
Figure 4: XRD patterns of the products synthesized at 80, 120, and 160 \({}^{\circ}\)C: (**a**) without 1 M EDTA and (**b**) with 1 M EDTA (NaOH concentration: 3 M NaOH, Reaction time: 24 h). Figure 5: Concentrations of Si, Al, and Ca in the solutions after synthesis at 80, 120, and 160 \({}^{\circ}\)C (NaOH concentration: 3 M NaOH, Reaction time: 24 h). 1 M EDTA at 80, 120 and 160 \({}^{\circ}\)C, the crystal sizes of hydroxysodalite in the products were 58.0, 57.6 and 50.4 nm, respectively, and those of tobormorite and hydroxycanlinite in the product synthesized at 160 \({}^{\circ}\)C were 9.8 and 49.8 nm, respectively. For the products synthesized with 1 M EDTA at 80, 120, and 160 \({}^{\circ}\)C, the crystal sizes of hydroxysodalite in the products were 67.3 nm, regardless of the temperature, and those of zeolite-A and hydroxycanlinite in the product synthesized at 80 and 160 \({}^{\circ}\)C were 80.1 and 28.5 nm, respectively. It should be noted that temperature and EDTA concentration have little effect on the produced hydroxysodalite, independently synthesizing zeolite-A crystals in the product at 80 \({}^{\circ}\)C with EDTA addition. Figure 5 show the concentrations of Si, Al, and Ca in the solution after synthesis at 80, 120, and 160 \({}^{\circ}\)C. At all the temperatures, the Si concentrations in the solutions with and without EDTA after synthesis were almost the same. Furthermore, the Al concentrations in the solutions without EDTA were higher than those in the solutions with EDTA, while the Ca concentrations in the solutions with EDTA were higher than those in the solutions without EDTA. These results can be attributed to the promotion of the Si-Al reaction owing to the capture of Ca by EDTA. It is noted that Ca-masking with EDTA occurs similarly at 80-160 \({}^{\circ}\)C.  
Table 1 show the chemical compositions of the products synthesized from raw ash with or without 1 M EDTA after a 24 h reaction at 80, 120, and 160 \({}^{\circ}\)C. Regardless of the temperature, the decrease in the Ca content in the product with 1 M EDTA was greater than that without 1 M EDTA, whereas the increase in the contents of Si and Al in the product with EDTA was greater than that without EDTA. These results were corroborated by the concentrations of Si, Al, and Ca determined after the 24 h reaction (Figure 5), indicating that the Si-Al reaction was promoted with the addition of 1 M EDTA because the remaining Ca in the solution was masked by EDTA. Figure 6 show the CECs of PSA and the synthesized products with and without 1 M EDTA at various temperatures. The CECs of all the products were higher than that of raw ash (0.3 mmol/g). Regardless of the temperature, the CECs of the products with 1 M EDTA were higher than those of products without 1 M EDTA. With increasing reaction temperature, the CEC of the product with EDTA decreased from 2.3 mmol/g at 80 \({}^{\circ}\)C to 1.4 mmol/g at 160 \({}^{\circ}\)C, owing to the formation of zeolitic crystal phases with lower CEC, i.e., hydroxysodalite and hydroxycanrinite, instead of zeolite-A and zeolite-P.  
Figure 6: CECs of PSA and the products synthesized from PSA with and without 1 M EDTA at various temperatures (NaOH concentration: 3 M NaOH, Reaction time: 24 h). Figure 7 show SEM photographs of the products synthesized in solutions with or without 1 M EDTA at 80, 120, and 160 \({}^{\circ}\)C. All the products were morphologically different from each other.