# Efficient Removal of Lead Ions from Water by a Low-Cost Alginate-Melamine Hybrid Sorbent
## 3 Results and Discussion
### Maximum Adsorption Capacity for Pb\({}^{2+}\)  
The maximum adsorption capacity is the most important characteristic of a adsorbent, which determines the economics and practicability of the adsorbent. In order to measure the maximum adsorption capacity of the designed sorbent, 100 mg of Alg-Mel sorbent was weighed and added into 40 mL of Pb\({}^{2+}\)-containing solution with concentrations ranging from 0.24 to 10.14 mM for 6 h. As shown in Figure 7, the adsorption capacity of Alg-Mel increases with the initial concentration from 0.24 to 4.34 mM, and then remains stable as the concentration increases further. Therefore, the maximum adsorption capacity for Pb\({}^{2+}\) was calculated to be 1.39 mmol/g (287.7 mg/g), which is much higher than that of most reported lead ion-sorbents (Table 2) [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30].  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Alg-Mel** & **Initial Solution (mM)** & **Adsorption (\%)** & **Capacity (mmol/g)** & \(K_{d}\) & \(k\) \\ \hline  & 0.48 (Pb\({}^{2+}\)) & - & 95.4 & - & 0.18 & - & 8.2 & - & - \\  & 0.89 (Cd\({}^{2+}\)) & - & 50.2 & - & 0.18 & - & 0.4 & - & - \\  & 1.57 (Cu\({}^{2+}\)) & - & 59.3 & - & 0.36 & - & 0.6 & - & - \\ Pure water & 1.92 (Cr\({}^{3+}\)) & - & 67.0 & - & 0.49 & - & 0.8 & - & - \\ samples & 1.70 (Co\({}^{2+}\)) & - & 29.1 & - & 0.19 & - & 0.2 & - & - \\  & 0.48 (Pb\({}^{2+}\)) & 1.57 (Cu\({}^{2+}\)) & 84.9 & 12.6 & 0.16 & 0.08 & 2.2 & 0.06 & 39.2 \\  & 0.48 (Pb\({}^{2+}\)) & 0.89 (Cd\({}^{2+}\)) & 82.4 & 37.7 & 0.16 & 0.13 & 1.8 & 0.24 & 7.7 \\  & 0.48 (Pb\({}^{2+}\)) & 1.92 (Cr\({}^{3+}\)) & 77.4 & 29.6 & 0.15 & 0.22 & 1.3 & 0.16 & 8.1 \\  & 0.48 (Pb\({}^{2+}\)) & 1.70 (Co\({}^{2+}\)) & 94.5 & 14.7 & 0.17 & 0.10 & 6.6 & 0.07 & 99.5 \\ \hline Tap water sample \({}^{1}\) & 0.48 (Pb\({}^{2+}\)) & - & 94.1 & - & 0.17 & - & 6.0 & - & - \\ \hline River water sample & 0.48 (Pb\({}^{2+}\)) & - & 90.7 & - & 0.17 & - & 3.7 & - & - \\ \hline Battery plant wastewater & 0.08 (Pb\({}^{2+}\)) & 0.05 (Cd\({}^{2+}\)) & 95.1 & 46.6 & 0.03 & 0.01 & 7.4 & 0.33 & 22.4 \\ \hline \hline \end{tabular} \({}^{1}\) Tap and River water samples spiked with standard Pb\({}^{2+}\).  
\end{table}
Table 1: Adsorption abilities of Alg-Mel for various metal ions.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**adsorbent** & **Target Heavy Metals** & \begin{tabular}{c} **Maximum Adsorption** \\ **Capacity (mg/g)** \\ \end{tabular} & **Reference** \\ \hline Alginate-melamine hybrid & \(\text{Pb}^{2+}\) & 287.7 & Our work \\ Polydopamine microspheres & \(\text{Pb}^{2+}\) & 165.8 & [15] \\ \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles & \(\text{Cu}^{2+}\), \(\text{Pb}^{2+}\) & 34.0 (Cu\({}^{2+}\)), 69.0 (Pb\({}^{2+}\)) & [16] \\ Fe\({}_{5}\)O\({}_{4}\) nanoparticles & \(\text{Cr}^{6+}\), \(\text{Pb}^{2+}\) & 41.5 (Cr\({}^{6+}\)), 96.8 (Pb\({}^{2+}\)) & [17] \\ Magnetic chitosan/graphene oxide & \(\text{Pb}^{2+}\) & 79.0 & [18] \\ imprinted Pb\({}^{2+}\) & \(\text{Pb}^{2+}\) & 18.3 (Cd\({}^{2+}\)), 57.7 (Pb\({}^{2+}\)) & [19] \\ Amino functionalized mesoporous silica & \(\text{Cd}^{2+}\), \(\text{Pb}^{2+}\) & 222.2 & [20] \\ Alginate-SBA-15 composite & \(\text{Pb}^{2+}\) & 51.5 (Pb\({}^{2+}\)) & [21] \\ Longan shell & \(\text{Pb}^{2+}\) & 18.9 & [22] \\ Silica modified calcium alginate-xanthan & \(\text{Pb}^{2+}\) & 120.8 (Cd\({}^{2+}\)), 115.0 & \\ gum hybrid bead composite & \(\text{Cd}^{2+}\), \(\text{Cu}^{2+}\), \(\text{Pb}^{2+}\) & \
\begin{tabular}{c} 120.8 (Cd\({}^{2+}\)), 115.0 \\ (Cu\({}^{2+}\)), 235.6 (Pb\({}^{2+}\)) \\ Pb\({}^{2+}\) ion imprinted polymers \\ Activated carbon-calcium \\ alginate composite \\ Magnetic alginate beads \\ \end{tabular} &
\begin{tabular}{c} 23] \\ \(\text{Pb}^{2+}