# The Effect of Cu (II) on Swelling and Shrinkage Characteristics of Sodium Bentonite in Landfills
## 3 Results
### Mineralogy Results  
The results from the mineral analysis included XRD and XRF. The d (001) diffraction peak of montmorillonite was obtained by small-angle diffraction. The experimental diffraction pattern was shown in Figure 7. The content of elements in sodium bentonite was determined by XRF.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Coefficient**} & \multicolumn{4}{c}{**c(g/L)**} \\ \cline{2-5}  & **0** & **2.5** & **5** & **10** \\ \hline \(A_{1}\) & 0.610 & 0.411 & 0.449 & 0.410 \\ \(A_{2}\) & 5.698 & 5.580 & 4.659 & 5.045 \\ \(t_{0}\) & 5.350 & 5.267 & 5.236 & 6.199 \\ \(p\) & 5.640 & 4.907 & 6.744 & 4.082 \\ \(R^{2}\) & 0.980 & 0.983 & 0.988 & 0.973 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Summary of correlation coefficient and undetermined coefficient.  
Figure 6: Logarithmic curve of shrinkage.  
Figure 7: X-ray diffraction spectrum.  
Figure 7 shows that the d (001) diffraction peak intensity of quartz was low, which indicates that the removal treatment was effective. The position of d (001) diffraction peak of different groups were 5.2\({}^{\circ}\), 6.24\({}^{\circ}\), 7.12\({}^{\circ}\), and 7.16\({}^{\circ}\). It shows that with the increase of Cu (II) concentration, the position of d (001) peak of montmorillonite shifts to the right. According to [PERSON]'s theory: the high expansion of sodium bentonite was usually observed in the low interlayer space of montmorillonite [24; 34]. The results show that the swelling ability of bentonite was weakened due to the changes of the interlayer space of montmorillonite. The differences in the width of the characteristic peaks can be observed because of the error from sample preparation.  
The content of various elements in bentonite were measured by XRF and can be used for evaluating the erodibility of Cu (II) which happens between clay particles and ions in surrounding electrolytes. The content of each element obtained from the experiment were shown in the form of oxide. The results were shown in Figure 8.  
The variation of elements Ca, Fe, K, Mn, P, Ti, Al, Na, Mg, and Si were analyzed in this experiment. Figure 8 shows that Ca, Fe, K, Mn, P, Ti, and Al did not change significantly in four environments of different concentration, and the corresponding variation of these elements were not less than 0.1%. However, the elements of Na, Mg, and Si changed significantly. Herein the change rate of Na is the most significant with 2.4%. Meanwhile, the content of Mg and Si in a high concentration environment (5 g/L and 10 g/L) were lower than that in a low concentration environment (0 g/L and 2.5 g/L), which indicates that Mg and Si only participated in the reaction in high concentration environment.  
The decrease of Na and Mg shows that some interlayer cations such as Na\({}^{+}\), Mg2\({}^{+}\) were involved in ion exchange reactions [35]. It caused the reduction of the involved element content. Especially for sodium bentonite, the main interlayer cation of montmorillonite was Na\({}^{+}\). So change of Na element was the most obvious. The decrease of Si was caused by  
Figure 8: Element content of bentonite: (**a**) Ca, Fe, K, Mn, P, and Ti (**b**) Al and Na, (**c**) Mg (**d**) Si.  
the partial existence of Cu (II) in solution with the form of [Cu(H\({}_{2}\)O)\({}_{6}\)]\({}^{2+}\). The structure of [Cu(H\({}_{2}\)O)\({}_{6}\)]\({}^{2+}\) was octahedral which shows strong bonding ability in X and Y axes. When pH > 4, the Si-O pressed on the surface of clay particles adhere to [Cu(H\({}_{2}\)O)\({}_{6}\)]\({}^{2+}\)[36, 37]. The following reaction happens:  
\[\equiv\text{Si-O-Si}\equiv+\text{Cu(OH)}^{+}+\text{H}_{2}\text{O}\rightarrow \equiv\text{Si-O-CuOH}+\equiv\text{Si(OH)}+\text{H}^{+}\]