## 3 Results and Discussion
### Kinetics
As the reaction proceeded, the reaction rate was limited to a certain extent due to the high resistance of the boundary layer, which led to the slowing down of the reaction rate and eventually to the equilibrium [34]. The fitted \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample** & **Carrier** & \begin{tabular}{c} **Initial Con-** \\ **centration** \\ \end{tabular} & **Temperature** & **pH** & \
\begin{tabular}{c} **Dosing** \\ **Amount** \\ \end{tabular} & **Adsorption** & **Reference** \\ \hline Gr-nZVI &
\begin{tabular}{c} granitic \\ residual \\ kaolinite–nZVI \\ \end{tabular} & 50 mg/L & 298 K & 6.0 & 10 g/L & 7.0 mg/g & [34] \\ ZVI & kaolinite & 50 mg/L & 298 K & 5.0 & 5 g/L & 9.24 mg/g & [21] \\ Bentonite composite nZVI & Bentonite & 400 mg/L & 298 K & 5.0 & 5 g/L & 4.58 mg/g & [21] \\ ATP & - & 200 mg/L & 298 K & - & 1 g/L & 16.5 mg/g & [30] \\ nZVI & - & 200 mg/L & 298 K & 5.0 & 1 g/L & 72.33 mg/g & This article \\ nZVI@ATP & ATP & 200 mg/L & 298 K & 5.0 & 1 g/L & 123.3 mg/g & This article \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of the adsorption performance of different materials on Ni\({}^{2+}\). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \(\mathbf{C_{0}}\) & \multicolumn{3}{c}{**Quasi-Level Kinetics**} & \multicolumn{3}{c}{**Quasi-Secondary Kinetics**} \\  & \(\mathbf{q_{m1}}\) & \(\mathbf{k_{1}}\) & \(\mathbf{R_{1}}^{2}\) & \(\mathbf{q_{m2}}\) & \(\mathbf{k_{2}}\) & \(\mathbf{R_{2}}^{2}\) \\ \hline
200 mg/L & 137.2153 & 3.2244 & 0.7830 & 144.9593 & 0.0397 & 0.9729 \\ \hline \hline \end{tabular}  
* Note: \(\mathbf{C_{0}}\) is the initial concentration of the solution (mg/L); \(\mathbf{q_{m}}\) is the adsorption capacity of the material (mg/g); \(k_{1}\) is the quasi-primary adsorption kinetic constant (g/(mg-h)); \(k_{2}\) is the quasi-secondary adsorption kinetic constant (g/(mg-h)).  
\end{table} 
Table 2: Kinetic fitting parameters for Ni\({}^{2+}\) adsorption by nZVI@ATP. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(\mathbf{C_{0}}\) & \(\mathbf{k_{d1}}\) & \(\mathbf{E_{1}}\) & \(\mathbf{R_{1}}^{2}\) & \(\mathbf{k_{d2}}\) & \(\mathbf{E_{2}}\) & \(\mathbf{R_{2}}^{2}\) & \(\mathbf{k_{d3}}\) & \(\mathbf{E_{3}}\) & \(\mathbf{R_{3}}^{2}\) \\ \hline
200 mg/L & 44.0412 & 80.6657 & 0.9918 & 5.2889 & 117.4167 & 0.9680 & 0.4776 & 138.8429 & 0.6988 \\ \hline \hline \end{tabular}  
* Note: \(\mathbf{C_{0}}\) is the initial concentration of the solution (mg/L); \(k_{d}\) is the rate constant of the intraparticle diffusion equation (mg/(g-h\({}^{1/2}\))); and \(E_{i}\) is the intercept (mmol/g).  
\end{table} 
Table 3: Fitting parameters for Weber–Morris of Ni\({}^{2+}\) adsorbed by nZVI@ATP. plots showed that none of the fitted straight lines passed through the origin, indicating that the adsorption rate of Ni\({}^{2+}\) by nZVI@ATP was limited by other factors such as surface diffusion and surface adsorption in addition to the main intra-particle diffusion. Figure 5 represents the variation of Ni\({}^{2+}\) removal by nZVI@ATP with the time at different initial concentrations (100 mg/L, 200 mg/L, and 300 mg/L). Figure 8 represents the kinetic analysis of Ni\({}^{2+}\) adsorption by nZVI@ATP at an initial concentration of 200 mg/L. By comparing Figures 5 and 8, it was found that both the adsorption amount and the removal rate increased with time, and the trend of both was almost the same, in which the results of the kinetic simulation experiments were similar to the removal rate results to the extent of 97.18%.