## 3 Results and Discussion
### Heavy Metals  
#### 3.2.1 Effect of Temperature at Low Initial Concentrations  
The influence of temperature on the removal of heavy metals at initial concentrations of 30 mg Cu/L and 7.5 mg Zn/L in addition to empirically fitted relationships linking these two parameters,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material/Parameter** & **Activated Carbon** & **Diatomite** & **Zeolite** & **Limestone Sand** & **Halloysite** \\ \hline pH (1:5) & 8.68 & 6.48 & 7.20 & 8.27 & 6.58 \\ EC (1:2.5) (\(\mu\)S/m) & 0.620 & 0.103 & 0.187 & 0.095 & 0.270 \\ CEC (meq/100 g) & 5.97 & 13.88 & 118.02 & 1.12 & 10.76 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Physico-chemical properties of the reactive materials.  
Figure 2: SEM images along with EDS analysis.  
are presented in Figure 3, whilst the Pearson's correlation coefficients are presented in Table 3. The relationships have been presented as polynomials only in the case of statistical significance of all function terms, otherwise a linear relationship is assumed. The intensity of removal of copper and zinc ions changed with temperature and was dependent on the reactive material and metal; however, correlation analysis showed a positive relationship between these variables. Only in the case of Zn removal using limestone sand were the values of Pearson's correlation coefficient (\(R\) = 0.224) and statistical significance (\(p\) = 0.3288) such that the relationship was statistically not significant.  
Removal of Cu was least influenced by the changes of temperature for activated carbon (\(\Delta Q_{e}\) = 0.075 mg/g) and most influenced for limestone sand (\(\Delta Q_{e}\) = 0.933 mg/g). The reactive materials  
Figure 3: Impact of temperature on the efficiency of Cu and Zn removal with equations describing the relationship at initial concentrations of 30 mg Cu/L and 7.5 mg Zn/L (error bars mark the standard deviation, dashed line is the theoretical curve.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Halloysite** & **L limestone Sand** & **Zeolite** & **Activated Carbon** & **Diatomite** \\ \hline Copper & 0.763 & 0.889 & 0.794 & 0.794 & 0.794 \\ Zinc & 0.0000 & 0.0000 & 0.0000 & 0.0000 & 0.0000 \\ Zinc & 0.0000 & 0.224 & 0.883 & 0.817 & 0.756 \\ \hline Ammonium ions & 0.045 & 0.049 & 0.040 & 0.046 & 0.6907 \\ Phosphates & 0.878 & 0.470 & 0.048 & 0.854 & 0.897 \\  & 0.00001 & 0.00001 & 0.00001 & 0.00001 & 0.00001 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Values of Pearson’s coefficients (\(R\)) for the relationship between the equilibrium sorption capacity (\(Q_{e}\)) of the reactive materials and temperature (\(n\) = 21; initial concentrations: 10 mg NH\({}_{4}\)-N/L; 10 mg PO\({}_{4}\)-P/L; 30 mg Cu/L; 7.5 mg Zn/L).  
used in the investigations can be arranged with regard to the change of the equilibrium sorption capacity (\(\Delta Q_{e}\) for Cu ions) as follows: activated carbon < diatomic (\(\Delta Q_{e}\) = 0.230 mg/g) < zeolite (\(\Delta Q_{e}\) = 0.341 mg/g) < halloysite (\(\Delta Q_{e}\) = 0.631 mg/g) < limestone sand. An analogous series obtained for zinc ions is as follows: zeolite < halloysite < activated carbon < diatomic, and for this contaminant, the changes of the equilibrium sorption capacity did not exceed 0.051 mg/g. The series does not include limestone sand, because a continuous increase of \(Q_{e}\) with temperature increase was not noted.  
The probable reason for the shape of the curves describing the obtained results (Figure 3) was the restricted mass of Cu and Zn (below the maximum sorption capacity), which was insufficient to fill the available negatively charges sites. At initial Zn concentrations equal to 7.5 mg/L (lower than for Cu), temperature change in the range of 3 \({}^{\circ}\)C to 40 \({}^{\circ}\)C had no practical significance, whereas at initial Cu concentrations equal to 30 mg/L, decrease of temperature to 3 \({}^{\circ}\)C resulted in restricting the degree of ion removal particularly on limestone sand and halloysite.