# Adsorption of Ammonium, Nitrate, and Phosphate on Hydrochars and Biochars
## 3 Results and Discussion  
### BC and HC Characteristics  
Ultimate and proximate analyses of the BC and HC samples produced under various conditions are presented in Table 1. The results indicate that an increase in residence time led to a corresponding increase in the fixed carbon and ash contents, as well as in the O/C and C/N ratios, for the HCs. Conversely, the volatile matter and H/C ratio decreased with an increase in residence time. The results suggest that the residence times of 30 and 180 min did not significantly affect the production of hydrocarbons, as the values obtained were closely aligned. The observed difference in the C/N ratio can be attributed to the increase in N losses that occurs with longer residence times. The findings obtained are consistent with the outcomes and patterns documented in prior research [27, 28, 29]. The BET method was applied to determine the pore structure. The BET surface area and pore volume of the BCs produced at a low temperature and the HCs are similar, and the values of both parameters increased significantly as the pyrolysis temperature increased, as confirmed in other studies [30, 31]. The surface area of the BC stayed at a stable level after passing 500 \({}^{\circ}\)C, as presented in Table 1.  
The results indicate that an increase in carbonisation temperature led to an increase in the concentrations of fixed carbon and ash, while the volatile matter and atomic ratios (H/C and O/C) decreased for the BCs. The obtained results are consistent with those previously reported in the scientific literature [16,32] for various carbonisation temperatures. According to the findings of previous research, the pyrolysis process primarily results in the transformation of hemicelluloses and cellulose into gaseous products, whereas lignin is predominantly transformed into char at elevated temperatures. The results of this study suggest that increasing the pyrolysis temperature can increase the degree of carbonisation of BC. According to previous research [16], this finding suggests that the BCs produced by this process may have potential benefits for carbon sequestration. Compared to the BCs and HCs, the AC was found to have the highest concentration of fixed carbon and the lowest concentrations of ash and volatile matter [33]. An FTIR spectral analysis plays a crucial role in the identification of distinct functional groups responsible for ion adsorption [18]. As shown in Figure 1, the FTIR spectra of HC30, HC180, BC300, BC500, BC700, and AC were collected and analysed in the presence and absence of NH4\({}^{+}\), NO3\({}^{-}\), and PO4\({}^{3-}\) adsorption. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Ultimate Analysis**} & \multicolumn{4}{c}{**Atomic Ratios**} & \multicolumn{2}{c}{**BET Surface Area**} & \multicolumn{2}{c}{**Pore Volume**} & \multicolumn{2}{c}{**Proximate Analysis**} \\  & \multicolumn{4}{c}{**wt.\%**} & & \multicolumn{2}{c}{**Atomic Ratios**} & \multicolumn{2}{c}{**m\({}^{2}\)/g**} & \multicolumn{2}{c}{**cm\({}^{3}\)/g**} & \multicolumn{2}{c}{**wt.\%**} \\ \cline{2-13}
**Material** & **N** & **C** & **H** & **S** & **O** & **C/N** & **H/C** & **O/C** & & & & **Ash** & **Volatile Matter** & **Fixed Carbon** \\ \hline HC30 & 0.49 & 67.2 & 6.15 & 0.0 & 19.9 & 138 & 0.092 & 0.297 & 1.4 & 0.004 & 4.83 & 48.8 & 46.4 \\ HC180 & 0.36 & 65.2 & 5.77 & 0.0 & 21.2 & 179 & 0.088 & 0.325 & 1.8 & 0.004 & 6.30 & 45.9 & 47.8 \\ BC300 &  
The vibrational spectra of the HCs and BCs were compared, and it was observed that the number of vibrational peaks was significantly greater in the HC spectra than in the BC spectra. The vibrational peaks at 2850 cm\({}^{-1}\), 1698 cm\({}^{-1}\), and 1206 cm\({}^{-1}\) were attributed to C-H stretching, aromatic C=O, and C-O stretching vibrations, respectively, as depicted in Figure 1. The techniques of hydrolysis and pyrolysis exhibited distinct differences in terms of chemical structure.