## 3 Results  
### Characterisation of Source Material and Composite Adsorbents  
The source components of the composite adsorbents (SK, KB and KF) were analysed for semiquantitative chemical composition, phase composition and surface properties (Table 1). The S\({}_{\text{BET}}\) values (Table 1), indicating the primary adsorption affinity of the source materials, differed markedly for all tested materials. This parameter directed the predicted adsorption efficiency in the order KB >> KF > SK [31; 32]. The pH\({}_{\text{ZPC}}\) values of the source materials showed typical cation-selective behaviour of SK and anion-selective behaviour of KB and KF in solutions with a pH of \(\geq\)5 (Section 2.6). The principal phase composition of the source materials (Table 2) illustrated a similar composition of both FA and the phase purity of used SK. The composite adsorbents were characterised identically to the source material, focusing on the changes related to different preparation temperatures (20 \({}^{\circ}\)C, 65 \({}^{\circ}\)C and 110 \({}^{\circ}\)C in \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Material** & & \multicolumn{4}{c}{**Chemical Composition (wt\%)**} & \multicolumn{4}{c}{**S\({}_{\text{BET}}\) (m\({}^{2}\).g-1)**} & \multicolumn{1}{c}{**pH\({}_{\text{ZPC}}\)**} \\  & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **TiO\({}_{2}\)** & **CaO** & **MgO** & **SO\({}_{3}\)** & **K\({}_{2}\)O** & & \\ \hline SK & 53.9 & 35.7 & 0.5 & 0.0 & 1.6 & 1.6 & 0.0 & 3.2 & 17.6 & 2.2 \\ KB & 42.1 & 17.0 & 5.0 & 1.5 & 24.0 & 2.5 & 0.7 & 4.3 & 48.4 & 11.1 \\ KF & 41.8 & 28.9 & 3.9 & 1.1 & 11.9 & 1.2 & 3.4 & 2.6 & 26.1 & 11.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Semiquantitative chemical composition, S\({}_{\text{BET}}\) and pH\({}_{\text{ZPC}}\) of source materials. \begin{table}
\begin{tabular}{c c} \hline \hline
**Material** & **Mineralogical Composition** \\ \hline SK & kaolinite, muscovite, quartz \\ KB & muscovite, quartz, calcite, anhydride, anorthite \\ KF & muscovite, quartz, calcite, anhydride \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Phase composition of source materials. an autoclave, respectively). For the comparison of a possible phase transformation, only the marginal temperatures (20 \({}^{\circ}\)C and 110 \({}^{\circ}\)C) were selected. The mineralogical composition of composite adsorbents prepared at 20 \({}^{\circ}\)C and at 110 \({}^{\circ}\)C in an autoclave (Figures 2 and 3) proved only negligible phase changes. The phases originated by the preparation of SK+KB at 20 \({}^{\circ}\)C (Figure 2a) corresponded to the composition of the source materials, with a dominance of quartz, muscovite and calcite. During the autoclave treatment at 110 \({}^{\circ}\)C (Figure 2b), the kaolinite disappeared, with a noticeable growth in the amorphous portion. In the case of SK+KF prepared at 20 \({}^{\circ}\)C (Figure 3a), the phase composition corresponded to the source materials again, revealing the major phases of muscovite, kaolinite  
Figure 3: XRD patterns of source materials and SK+KF prepared at different conditions. (**a**) 20 \({}^{\circ}\)C; (**b**) 110 \({}^{\circ}\)C in autoclave (SK+KF-A). Figure 2: XRD patterns of source materials and SK+KB prepared at different conditions. (**a**) 20 \({}^{\circ}\)C; (**b**) 110 \({}^{\circ}\)C in autoclave (SK+KB-A). and quartz, with the presence of anhydrite and calcite. Autoclave treatment at 110 \({}^{\circ}\)C (Figure 3b) caused the extinction of kaolinite, with the concurrent growth of a new phase of gypsum. This time the crystallinity of the autoclave composite remained the same as for the 20 \({}^{\circ}\)C adjustment (compare Figure 3a,b). The SEM micro-observation of the composite adsorbents prepared under different temperatures (Figure 4) proved structural changes consisting of a higher homogeneity of the material in connection with the higher preparation temperature.