## 3 Results and Discussion
### Changes in the Composition and Structure of Bentonite during Experiments
At the same time, the analysis of the change in the absorption bands of the samples exposed for 1 and 3 months to the water used for leaching the concrete at an elevated temperature shows that the short-range order bonds that are characteristic of dioctahedral smectites did not undergo changes in the course of the experiments. Thus, it can be concluded that the observed changes in the composition of the octahedral networks were weakly manifested and could hardly have a strong effect on the changes in the physico-chemical and physicochemical properties of the bentonite from the 10 th Khutor deposit under the conditions of the DRW. The Mossbauer spectroscopic study of the treated bentonite samples (1 month and 3 months) confirm that the structures of these samples are similar--the parameters of the spectra had very close values (Table 7, Figure 8). The natural (initial) untreated sample had a higher Fe\({}^{2+}\)/Fe\({}^{3+}\) ratio. Thus, under the influence of synthetic waters, Fe\({}^{2+}\) was oxidized in octahedral positions, and then the structure remained stable. To analyze changes in the structure of smectite, a thermal analysis of the bentonite samples was carried out. Two endothermic effects characteristic of smectites were observed (Figure 9). The first, located in the range from 80 to 194 \({}^{\circ}\)C, is associated with dehydration due to the removal of adsorbed and interlayer water [72]. The peak of dehydration at around 140 \({}^{\circ}\)C corresponds to the presence of alkaline earth cations in the interlayer space of smectite [73]. The second endothermic effect is associated with the loss of smectite structural water; it changed from 647 \({}^{\circ}\)C for the original bentonite to 643 \({}^{\circ}\)C for the bentonite that had been exposed to the concrete leaching for 3 months. These changes may be associated with minor changes in the positions of hydroxyls in the octahedral networks of smectites. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Doublets of**} & \multicolumn{1}{c}{**G, mm/s**} & \multicolumn{1}{c}{**\(\delta\), mm/s**} & \multicolumn{1}{c}{**\(\Delta\)fit, mm/s**} & \multicolumn{1}{c}{**Sfit, \%**} & \multicolumn{1}{c}{**Fe\({}^{2+}\)/Fe\({}^{3+}\)**} \\ \hline \multicolumn{5}{c}{initial} \\ \hline (1) Fe\({}^{3+}\) & 0.34 & 0.35 & 0.51 & 11 & \\ \hline (2) Fe\({}^{3+}\) & 1.04 & 0.33 & 0.67 & 72 & 0.19 \\ \hline (3) Fe\({}^{2+}\) & 0.43 & 1.16 & 2.78 & 16 & \\ \hline \multicolumn{5}{c}{1 month} \\ \hline (1) Fe\({}^{3+}\) & 0.27 & 0.37 & 0.55 & 10 & \\ \hline (2) Fe\({}^{3+}\) & 0.86 & 0.34 & 0.70 & 80 & \\ \hline (3) Fe\({}^{3+}\) & 0.40 & 1.19 & 2.60 & 10 & 0.11 \\ \hline \multicolumn{5}{c}{3 month} \\ \hline (1) Fe\({}^{3+}\) & 0.32 & 0.34 & 0.47 & 13 & \\ \hline (2) Fe\({}^{3+}\) & 0.79 & 0.36 & 0.73 & 78 & \\ \hline (3) Fe\({}^{3+}\) & 0.37 & 1.14 & 2.62 & 9 & 0.10 \\ \hline \hline \end{tabular} \(S^{\text{fit}}\) is the integral intensity of fitting doublets; G is the line half-width; \(\Delta\)fit is the quadrupole splitting; \(\delta\) is the chemical shift relative to \(\alpha\)-Fe; \(\chi^{2}\) = 1.12-1.21.  
\end{table} 
Table 7: Parameters of Mössbauer spectra obtained for the bentonite samples. Endothermic effects in the regions of 446 and 478 \({}^{\circ}\)C traced in the original bentonite decreased in the bentonite after 1 and 3 months of the experimental exposure conditions. These effects are associated with the impurity minerals of bentonite, such as kaolinite and carbonates (siderite), which were destroyed during the experiment. This was also confirmed by the X-ray diffraction data (Table 6). The total weight loss of the original bentonite decreased and amounted to 15.6% in the original, 14.2% after 1 month, and 13.6% after 3 months, which correlates with the loss of impurity minerals during the experiment. In general, according to the TG, DTG, and DTA data, there were no visible noticeable changes in the structure of the smectite.