## 3 Results and Discussion  
### Characteristics of the Materials  
The surface characteristics determined on the basis of nitrogen adsorption/desorption isotherms are presented in Table 1. Activated carbon is a microporous material, as evidenced by the micropore surface and volume values (respectively 366.41 m\({}^{2}\)/g and 0.162 cm\({}^{3}\)/g) and relatively low value of mesopore surface (177.10 m\({}^{2}\)/g) in relation to the total specific surface of the material (782.67 m\({}^{2}\)/g). Diatomite, zeolite and halloysite are mesoporous materials and therefore are characterized by average specific surface areas with mesopores in the shape of narrow fissures with irregular dimensions and shapes. The largest specific surface and volume of mesopores among these minerals were observed in halloysite (respectively 48.33 m\({}^{2}\)/g and 0.193 cm\({}^{3}\)/g), and the smallest in diatomite (respectively 29.32 m\({}^{2}\)/g and 0.05 cm\({}^{3}\)/g). Limestone sand can be classified as a non-porous material. Scanning Electron Microscope (SEM) images and chemical micro-range analyses (EDS) of reactive materials are presented in Figure 2. The observations are in accordance with the results presented in Table 1. It is worth noting that the activated carbon sample has the most expanded porous surface, with spherical pores attaining dimensions from over ten to several hundreds of micrometers. SEM analysis of limestone sand confirmed the carbonate character of this material, whereas micro area chemical analysis of calcium and oxygen pointed to calcite (CaCO\({}_{3}\)). SEM-EDS analyses indicated the presence of minerals from the silica group in the diatomite sample and allowed for the petrographic classification of this material as diatomaceous earth. SEM micro images confirmed the moderately developed surface of zeolite and halloysite, and in the case of the latter material, the presence of characteristic nano tubes, which, however, were not very distinct at this magnification. Additionally, EDS spectra pointed to the presence of: silicon (Si), oxygen (O), aluminum (Al), potassium (K), calcium (Ca) and iron (Fe) in the zeolite sample, and of: iron (Fe), aluminum (Al), silicon (Si), magnesium (Mg), phosphorus (P), calcium (Ca) and titanium (\(\Pi\)) in the halloysite sample. The pH, electrical conductivity (EC) and cation exchange capacity (CEC) of the applied reactive materials are shown in Table 2. Studies of EC have allowed to arrange the analyzed materials as follows in increasing order: limestone sand \(\approx\) diatomite \(<\) zeolite \(<\) halloysite \(<<\) activated carbon. The analyzed materials can be subdivided with regard to pH values into 3 groups: (1) reaction below neutral (pH \(<\) 7)--diatomite and halloysite, (2) reaction between 7 and 8--zeolite, and (3) reaction \(>\) 8--limestone sand and activated carbon. The pH of the materials plays a large role in contamination removal, particularly of heavy metals, but also of ammonium ions [57]. In the case of water pH exceeding 7, beside ammonium ions (NH\({}_{4}\)-N), water contains gaseous ammonia (NH\({}_{3}\)), and at pH = 11.1 free ammonia amounts to 99%. In solutions with larger values of pH heavy metals precipitate as hydroxides. In turn, at pH \(<\) 7 for Pb, pH \(<\) 7.5 for Cu, pH \(<\) 8.7 for Zn and pH \(<\) 9.8 for Ni, the dominant form of metals in solution is their ionic form, which may be removed via adsorption processes. Therefore, it may be assumed that in the case of water containing Zn and Cu with activated carbon and limestone sand, precipitation will play a significant role in the removal of these contaminants due to their high pH values.