# Application of Iron-Modified Activated Carbon for Phosphate Removal in Aqueous Systems
## 3 Results and Discussion
### Sorption Isotherm of Iron-Functionalized Activated Carbon
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multicolumn{2}{l}{**FeCl3(M)**} & & & & & & \\ \hline \multirow{3}{*}{0.00} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 1.16 & 1.80 & 7.70 & 14.20 & 34.00 & 128.00 \\  & \(X/m\) & 0.02 & 0.04 & 0.08 & 0.17 & 0.29 & 0.37 \\ \hline \multirow{3}{*}{0.05} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 1.87 & 7.52 & 15.66 & 40.58 & 116.90 & 157.10 \\  & \(X/m\) & 0.07 & 0.14 & 0.27 & 0.48 & 0.66 & 0.74 \\ \hline \multirow{3}{*}{0.1} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 1.61 & 4.95 & 10.23 & 29.19 & 96.90 & 138.40 \\  & \(X/m\) & 0.07 & 0.16 & 0.32 & 0.57 & 0.82 & 0.89 \\ \hline \multirow{3}{*}{0.2} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 2.13 & 1.20 & 34.83 & 17.60 & 68.20 & 114.00 \\  & \(X/m\) & 0.06 & 0.19 & 0.36 & 0.66 & 1.05 & 1.09 \\ \hline \multirow{3}{*}{0.3} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 0.65 & 2.48 & 3.15 & 12.59 & 58.60 & 99.30 \\  & \(X/m\) & 0.08 & 0.19 & 0.38 & 0.71 & 1.14 & 1.23 \\ \hline \multirow{3}{*}{0.4} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 0.64 & 2.21 & 2.93 & 10.65 & 57.00 & 95.70 \\  & \(X/m\) & 0.07 & 0.18 & 0.38 & 0.71 & 1.14 & 1.23 \\ \hline \multirow{3}{*}{0.5} & \(C_{0}\) & 10 & 25 & 50 & 100 & 200 & 250 \\  & \(C\) & 0.61 & 2.13 & 2.67 & 9.81 & 50.00 & 88.40 \\ \cline{1-1}  & \(X/m\) & 0.08 & 0.18 & 0.38 & 0.72 & 1.20 & 1.29 \\ \hline \end{tabular}
\end{table} 
Table 1: Phosphate Adsorption Capacities of SMAC at Various Modification Concentrations. Figure 2: The adsorption curve of AC and SMAC by modified concentration. Absorbent (AC and 0.05 M, 0.1 M-0.5 M FeCl3 SMAC) were shaken at 90 rpm with 40 mL solutions of KH2 PO4 for 24 h. A series of phosphate solutions with concentrations of 10–250 mg/L were prepared. The effect of changes in the n and K values can be visually confirmed in Figure 3. It shows the distribution of iron on the surface of activated carbon, as analyzed through SEM-EDS for AC and SMAC samples modified with 0.2 M and 0.5 M concentrations. The iron detected using the EDS scan mode is represented by orange dots, which are overlapped on the captured SEM image. Figure 3a represents the image of AC, while Figures 3b and 3c correspond to the 0.2 M and 0.5 M SMAC images, respectively. The absence of iron in Figure 3a confirms that no iron was originally present to influence adsorption, supporting the conclusion that the increase in adsorption capacity is solely due to the cationic iron introduced during the modification process. In both Figure 3b,c, iron is found to be evenly distributed throughout the surface. As seen in elemental mapping images, the overall amount of iron is slightly higher in Figure 3c. This explains the K value of 0.5 M SMAC compared to 0.2 M SMAC in Table 2, as it results from the greater overall Fe attachment to the AC surface. While the 0.5 M SMAC contains more iron overall, large iron aggregates were observed in Figure 3b, which may explain why the n value of 0.2 M SMAC is the highest among all the samples. Similar trends of decreased modification efficiency in metal-modified activated carbon have been reported in studies involving copper-modified carbon [39]. It has been shown that the modification efficiency of activated carbon using metals can be improved through methods such as pH adjustment and physical surface treatments [40]. Considering these findings, the optimal modification concentration in this study was confirmed to be 0.2 M, and SMAC was manufactured at this concentration for subsequent experiments.