## 3 Results and Discussion
### Characterization of L1 and L2  
The Zn:Al ratio and the amount of Ln absorbed are shown in Table 4. The component analysis result, shown in Table 4, indicates that the molar ratio of Zn/Al is approximately equal to that in the preparing solution, which shows that the dosage of reagents is reasonable. L1 and L2 were dissolved \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Target Ions** & **adsorbent** & **Effect Factor** & \begin{tabular}{c} **Final Concentration** \\ **(\(\upg\)-L\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **Acdsorption** \\ **Capacity** \\ **(\(\upg\)-g\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **Partition** \\ **Coefficient** \\ **(\(\upg\)-g\({}^{-1}\))** \\ \end{tabular} \\ \hline \multirow{6}{*}{Eu} & \multirow{6}{*}{L1} & \multirow{2}{*}{\
\begin{tabular}{c} Contact time \\ (min) \\ \end{tabular} } & 10 & 96.2 & 5.67 & 8.95 \\  & & 30 & 93.5 & 9.83 & 16.0 \\  & & (min) & 60 & 91.3 & 13.1 & 21.9 \\  & & & 120 & 83.4 & 24.9 & 45.5 \\ \cline{2-6}  & & & 10 & 61.2 & 93 & 230 \\  & & & 30 & 38.2 & 127 & 506 \\  & & (min) & 60 & 31.0 & 138 & 676 \\  & & & 120 & 26.4 & 145 & 834 \\ \cline{2-6}  & & & 20 & 7.8 & 24.0 & 468 \\  & & & 50 & 18.2 & 45.0 & 376 \\  & & (\(\upg\)-L\({}^{-1}\)) & 200 & 54.6 & 165 & 275 \\  & & & 300 & 153 & 222 & 220 \\ \hline \multirow{6}{*}{La} & \multirow{6}{*}{L1} & \multirow{2}{*}{
\begin{tabular}{c} Contact time \\ (min) \\ \end{tabular} } & 10 & 98.8 & 1.8 & 2.53 \\  & & 30 & 88.7 & 17 & 26.6 \\  & & (min) & 60 & 86.9 & 19.7 & 31.5 \\  & & 120 & 86.1 & 20.8 & 33.6 \\ \cline{2-6}  & & & 10 & 23.9 & 114 & 341 \\  & & & 30 & 46.3 & 115 & 346 \\  & & (min) & 60 & 46.3 & 119 & 345 \\  & & & 120 & 40.8 & 124 & 405 \\ \cline{2-6}  & & & 20 & 40.7 & 17.4 & 422 \\  & & & 50 & 20.9 & 39.6 & 263 \\  & & (\(\upg\)-L\({}^{-1}\)) & 200 & 101 & 148 & 203 \\  & & 300 & 163 & 205 & 174 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Detailed experimental data of adsorption process under different effect factor. Figure 2: Zeta potential of the L2 dispersed in aqueous solution with different pH. by HNO\({}_{3}\) after adsorption of Ln ions. The amounts of Ln ions in the LDH phase, which were obtained by an ICP-MS are also shown in Table 4. The adsorption ability of REEs ions can be evaluated from these results. The SEM images of (a) L1, (b) L2, (c) L2 after the La(III) adsorption (L2-La), (d) L2 after the Eu(III) adsorption (L2-Eu), and (e) the mapping image of L2-Eu are shown in Figure 3. Panels (b), (c), and (d) indicate that the surface of the adsorbent becomes rough at the end of the adsorption processes. The mapping images indicate that REEs ions are adequately adsorbed onto the adsorbent and that they are distributed uniformly. Figure 4 shows the (003), (006) and (110) peaks, which indicate that the layered structures are observed for all the L1, L2, and L2-Eu. After the intercalation by EDTA and the adsorption process, the (110) peak is still visible, as shown in Figure 4b,c. These figures show that the layer structure was destroyed by the intercalating process neither for EDTA nor for EDTA-Ln(III). However, the layer structure may be destroyed by repeated desorption process, which results in the decrease of the removal efficiency after the cycle adsorption. Based on the angle of peak (003) corresponding to the basal spacing, the basal spacing values of L1, L2 and L2-Eu were estimated to be 0.89 nm, 1.47