## 5 Removal of Arsenic
### Rice Husk as Adsorbent for Removal of Arsenic
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Type of** & **Type of** & **Type of** & **Experimental** & **Maximum** & **Adsorption** & **References** \\
**adsorbent** & **Water** & **Arsenic** & **Conditions** & **Removal (\%)** & **Capacity** & **References** \\ \hline \multirow{6}{*}{**Rice husk** **biochar**} & \multirow{6}{*}{Aqueous solution} & \multirow{6}{*}{As(V)} & Temperature = 298 K & \multirow{6}{*}{25} & \multirow{6}{*}{0.00259 mg/g} & \multirow{6}{*}{[128]} \\  & & & Reaction time = 24 h & & & \\ \cline{1-1} \cline{5-5}  & & & Reaction time = 90 \(\mathrm{\SIUnitSymbolMicro g}\)/L & & & \\ \cline{1-1} \cline{5-5}  & & & Surface area = 155 m\({}^{2}\)/g & & & \\ \cline{1-1} \cline{5-5}  & & & Adsorbent = 8 g & & & \\ \hline \end{tabular}
\end{table} 
Table 10: Adsorption capacities of arsenic by rice husk. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Type of** & **Type of** & **Type of** & **Experimental** & **Maximum** & **Adsorption** & **References** \\
**adsorbent** & **Water** & **Arsenic** & **Conditions** & **Removal (\%)** & **Capacity** & **References** \\ \hline  & & & & Temperature = 298 K & & & \\
**Rice husk** & Aqueous & & pH = 9.5 & & & & \\
**biochar** & Aqueous & As(V) & Initial concentration = 0–200 mg/L & - & 0.35 mg/g & [129] \\  & & & Surface area = 23.2 m\({}^{2}\)/g & & & \\  & & & Adsorbent = 2 g & & & \\ \hline  & & & Temperature = 298 K & & & \\
**Rice husk** & Aqueous & & pH = 8 & & & \\
**biochar** & Aqueous & As(III) & Initial concentration = 3–300 mg/L & - & 19.3 mg/g & [27] \\  & & & Surface area = 25.1 m\({}^{2}\)/g & & & \\  & & & Adsorbent = 5 g/L & & & \\ \hline  & & & Temperature = 298 K & & & \\
**Rice husk** & Aqueous & & Intial concentration = 3–300 mg/L & - & & \\
**biochar** & solution & & Surface area = 25.1 m\({}^{2}\)/g & & & \\  & & & Adsorbent = 5 g/L & & & \\ \hline  & & & pH = 6 & & & \\
**Macromolecule** & & Aqueous & Time = 65 min & & & \\
**crbonized** & & solution & & Initial concentration = 100 \(\mu\)g/L & 85 & - & [120] \\  & & & Adsorbent = 0.2 mg & & & \\ \hline  & & & & pH = 7.8 & & & \\
**Rice husk** & & Contaminated & Temperature = 298 K & & & \\
**(column bed & groundwater & As(III)—60–90\% & Initial concentration = 270 \(\mu\)g/L & & \\  & & & Particle size = 780 \(\mu\)m & 96 & - & [115] \\  & & & Adsorbent = 12 g & & & \\  & & & Flow rate = 0.8 mL/min & & & \\ \hline  & & & pH = 7.6 & & & \\
**Rice husk** & & Contaminated & Temperature = 298 K & & & \\
**(column bed & Groundwater & As(III)—60–90\% & Initial concentration = 596 \(\mu\)g/L & & \\  & & & Particle size = 780 \(\mu\)m & 96 & - & [115] \\  & & & Adsorbent = 12 g & & & \\  & & & Flow rate = 0.8 mL/min & & & \\ \hline  & & & pH = 8 & & & \\  & & & Temperature = 298 K & & & \\
**Rice husk** & & & Initial concentration = 15 mg/L & & & \\
**(column bed & solution & As(V) & Particle size = 710 \(\mu\)m & 90.7 & - & [121] \\  & & & Adsorbent = 42.5 g & & & \\
**method** & & & Flow rate = 7 mL/min & & & \\  & & & Column diameter = 5 cm & & & \\  & & & Bed height = 28 cm & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Adsorption capacities of arsenic by synthesized rice husk.