## 3 Results and Discussion  
### Instrumental Analysis  
The specific surface area and pore diameters of vermiculite were analyzed before and after the activation of NaOH and citric acid. Densitometric analysis makes it possible to establish the density of the material. The results for density (apparent, actual, bulk and relative) and porosity (total and open) are listed in Table 3. Figures 1 and 2 present sorption isotherms and the distribution of pore volume for raw and activated material. Vermiculite is a mesoporous material. Activated vermiculite compared to the raw material is characterized by a smaller specific surface area and a bigger share of mesopores (Figure 2). Basic or acid treatment caused leaching of octahedral layers and dissolution  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model** & \multicolumn{2}{c}{**Nonlinear Form**} & **Linear Form** & **Plot** \\ \hline Bohart-Adams & \(\frac{\zeta}{\zeta_{\rm o}}\,=\,\exp\left(k_{BA}\cdot C_{0}\cdot t-k_{BA}N_{0} \cdot\frac{H}{u}\right)\) & \(\ln\frac{\zeta}{\zeta_{\rm o}}\,=\,k_{BA}\cdot C_{0}\cdot t-k_{BA}\cdot q_{max} \cdot\frac{H}{u}\) & \(\frac{\zeta}{\zeta_{\rm o}}\,\,\mathrm{vs}\,\,\mathrm{t}\) \\ [PERSON] & \(\frac{\zeta}{\zeta_{\rm o}}\,=\,\frac{1}{1+\left(\frac{H}{\zeta_{\rm o}}\right) \cdot\tanh\cdot C_{0}\cdot\tanh\cdot C_{0}\cdot\tanh\cdot C_{0}}\) & \(\ln\left(\frac{\zeta_{\rm o}}{\zeta_{\rm o}}-1\right)\,=\,\left(\frac{k_{BA}}{ \zeta_{\rm o}}\right)\cdot q_{max}\cdot m-C_{0}\cdot k_{Th}\cdot t\) & \(\frac{\zeta}{\zeta_{\rm o}}\,\,\mathrm{vs}\,\,\mathrm{t}\) \\ Yoon-Nelson & \(\frac{\zeta}{\zeta_{\rm o}}\,=\,\frac{\zeta_{\rm o}\,\,\mathrm{vs}\,\, \mathrm{t}}{1+\rho^{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{      }}}}}}}}}}}}}}}\) & \(\ln\frac{\zeta}{\zeta_{\rm o}-\zeta}\,=\,k_{YN}\cdot t-k_{YN}\cdot\tau\) & \(\frac{  
of the amorphous phase leaving a material. Chemical activation decreased the layer charge of the material, facilitating ion exchange [29]. The smaller specific surface area is compensated by a high total porosity, which translates into its sorption capacity. Raw vermiculite, vermiculite modified with sodium hydroxide solution or citric acid solution, and vermiculite following the adsorption of metal ions, were subjected to XRD analysis (Figure 3). The analyzed samples were characterized by high purity. [PERSON] et al. analyzed the structure of vermiculite and distinguished characteristic reflexes for it, including 5.6 \({}^{\circ}2\theta\), 9.5 \({}^{\circ}2\theta\), and 28.6 \({}^{\circ}2\theta\). The results of analysis suggest damage to the crystalline structure of vermiculite as a result of the base and acid action. The results of chemical analysis confirm that components of the octahedral layer were dissolved under base action to a large extent. A decrease in the crystalline form of vermiculite was also confirmed by studies carried out on nitric and citric acid-modified vermiculite [29]. The changes in vermiculite structure were also confirmed by FTIR analysis (Figure 4). A broad peak between 900 and 1100 cm\({}^{-1}\) confirms the presence of Si-O and Si-O-Si groups. Characteristic vermiculite bands are summarized in Table 4. The main change in structure of vermiculite is the presence of a nitro group (-O\({}_{2}\) stretching), which is confirmed by the presence of the peak at 1350 cm\({}^{-1}\) (Figure 4D). The presence of nitro groups results from nitrate ions entering the AgNO\({}_{3}\) salt solution. Figure 1: Sorption isotherms: (**A**) Raw vermiculite, (**B**) basic-activated vermiculite, (**C**) acid-activated vermiculite, (solid line-adsorption, dashed line–desorption).