## 3 Results and Discussion  
Figures 1-3 show the relationship between the sorption capacity \"q\" of Rockfos\({}^{\text{\textregistered}}\) material and the loss of phosphate concentration in solution. The analysis considered different initial concentrations of phosphate in solution (0.5 mg/L, 1.0 mg/L, and 2.0 mg/L), granulations of sorption material (1.0-1.6 mm, 1.6-2.5 mm, and 2.0-5.0 mm), and selected process running temperatures (5 \({}^{\circ}\)C, 15 \({}^{\circ}\)C, and 25 \({}^{\circ}\)C). Each data series consists of nine points corresponding to different sorbent weights. The results show that the amount of phosphate removed from the solution increases curvilinearly with increasing sorbent weights. The range of these values is strongly influenced by the initial concentration of phosphate in the solution, an observation that has been confirmed by previous studies [18; 29]. At the lowest concentration, 0.5 mg/L, phosphate loss did not exceed 0.4 mg/L, even when using the most considerable sorbent weight (0.800 g). At higher initial phosphate concentrations, namely, 1.0 mg/L and 2 mg/L, maximum phosphate losses reached 0.90 mg/L and 1.24 mg/L, respectively. Preliminary  
Figure 1: Changes in sorption (q) as a function of the equilibrium concentration of phosphate in solution (C\({}_{\rm e}\)) for different granulations of Rockfos® material at 5 \({}^{\circ}\)C.  
Figure 3: Changes in sorption (q) as a function of the equilibrium concentration of phosphate in solution (C\({}_{\rm e}\)) for different granulations of Rockfos® material at 25 \({}^{\circ}\)C.  
Figure 2: Changes in sorption (q) as a function of the equilibrium concentration of phosphate in solution (C\({}_{\rm e}\)) for different granulations of Rockfos® material at 15 \({}^{\circ}\)C.  
studies of the Rockfos(r) material conducted by [PERSON] et al. [29] showed a significant variation in the sorption capacity of the material depending on the initial concentration of phosphorus in the solution. The sorption capacity of the fine fraction of the material at a low phosphate concentration was 0.9 mg/g [48]. When using wastewater with higher phosphate concentrations, the sorption capacities were 9.6 mg/g and 45.6 mg/g [8; 29]. [PERSON] et al. [56] conducted studies on a natural material, dolomite, and reported the phosphate sorption value to be 51.02 mg/g at the initial concentration in a solution of 60 mg/L. In turn, experiments using distilled water (with an initial phosphorus concentration of 0.28 mg/L), groundwater (0.34 mg/L), tap water (0.34 mg/L), and sewage (0.56 mg/L) revealed the sorption capacity of dolomite to be 0.06, 0.072, 0.05, and 0.05 mg/P/g, respectively. The maximum sorption capacities, calculated using the Freundlich and Langmuir models, were 0.12 and 0.093 gP/kg [57], respectively. Column studies using shale conducted by [PERSON] et al. [58] also confirmed the positive relationship between the sorption capacity of the material and the initial concentration of phosphorus in the solution. The maximum sorption capacities for the material were 0.06 and 0.23 mg P/g, with initial concentrations of phosphorus of 5 and 25 mg/L, respectively [58]. It is worth noting, however, that some studies using natural materials came to different conclusions. [PERSON] et al. [59; 60] achieved a maximum sorption capacity of 0.17 g P/kg for shale at an initial concentration of 1000 mg P/L, which can be compared to 0.50 g P/kg at an initial concentration of 100 mg P/L [59; 60]. The effect of the initial adsorbate concentration in a solution on sorption was also reported by [PERSON] et al. [22] for lead sorption on tree fern sorbent; [PERSON] et al. [24] for lead on activated carbon, clinoptiolite, and manganese-dioxide-modified chalcogenite; and [PERSON] et al. [49] for cadmium on orange peel sorbent. [PERSON] et al. [23] showed that lead sorption on phosphoric-acid-activated carbon increases with increasing pH and decreases with an increase in ionic strength (which occurs during ion exchange).