## 3 Results and Discussion
The data in Figure 6 show an apparent effect of temperature on the amount of phosphate sorption on Rockfos(r) material. The 5 and 10 \({}^{\circ}\)C results were included in one group, \"a\", as they differed slightly from each other. In contrast, the average sorption values for the other temperatures were so different from each other that they were modeled in separate groups, \"b\", \"c\", and \"d\". The ANOVA and Kruskal-Wallis ANOVA tests showed that at an initial phosphate concentration of 0.5 mg/L in the solution, there were no significant differences in the sorption capacity of the material across the various process temperatures. However, at higher initial concentrations (1.0 and 2.0 mg/L), the sorption capacity at 20 \({}^{\circ}\)C and 25 \({}^{\circ}\)C was significantly higher than that observed at lower temperatures. This pattern applied to each granulation of the Rockfos(r) material. In the literature [25; 46], these graphs initially (at low sorbent doses) have a strong upward trend, and from a certain mass of sorbent onward, the graph stacks upward horizontally. A strong upward trend in sorption modeled by the Langmuir isotherm with increasing temperatures was shown by [PERSON] et al. [62], who studied melanin sorption on buckwheat husks but at higher temperatures of 40 \({}^{\circ}\)C, 50 \({}^{\circ}\)C, and 60 \({}^{\circ}\)C.  
Figure 7 shows the effects of phosphate removal from the solution as a sorbent weight function at different sorption process temperatures. The points from 1 to 9 on the horizontal axis refer to the increasing sorbent weight, given in Section 2.2. A close proportional relationship between the effects of phosphate removal from solution and sorbent mass can be observed in all of the data series. However, the amplitude of the values is closely related to the temperature at which the sorption process was carried out. At 5 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, and 15 \({}^{\circ}\)C, the course of the curves is similar, and the determined effects range from 1.5-2.6% to 37.2-41.7% (Figure 7). At 20 \({}^{\circ}\)C and 25 \({}^{\circ}\)C, the effects were noticeably higher and, depending on the sorbent mass, ranged from 1.1-61.0% to 3.1-66.1%, respectively. The increase in efficiency as a function of temperature is not always so clear-cut. As shown in the study carried out by [PERSON] et al. [53], efficiency increased with increasing temperatures for black eriochrome-induced color removal and decreased for blue maximlon removal. Similarly, the sorption of lead on tree ferns [22], cadmium on eucalyptus bark [27], cadmium on orange peel [49], and phosphate on calcium silicate hydrate (C-S-H) increased with increasing temperatures [34; 49], as did the sorption of sodium oleate on a quartz surface [63] and melanin on buckwheat husks [62]. The opposite is true during the sorption of gases, as sorption decreases with increasing temperatures (e.g., carbon dioxide on selected coal samples) [64; 65]. Inconclusive results have been obtained regarding the sorption of heavy oil in quartz nanopores at high temperatures [66]. Figure 6: Sample results of GLM modeling of the effect of temperature on sorption. Additional measurements of pH, total hardness, and calcium concentration were made to evaluate the influence of ion exchange processes on the sum effect of sorption. The choice of these indicators was dictated by previous reports of a strong impact of opoka on solution pH [8; 13; 33; 34; 44; 45] and the chemical composition of the rock [11; 12; 29; 44; 45; 67]. The hardness of the solution increased during the tests; its average value at the most negligible weight of sorbent was 1.56 \(\pm\) 0.79 \({}^{\circ}\)dh, while it was 7.09 \(\pm\) 1.98 \({}^{\circ}\)dh at the most significant weight. The calcium concentration increased from 12.76 \(\pm\) 5.47 mg Ca/L to 46.27 \(\pm\) 11.87 mg Ca/L. This indicates a significant role of ion exchange, during which phosphates react with calcium, leading to the precipitation of calcium phosphate as a residue.