# Arsenic Removal from Water by Adsorption onto Iron Oxide/Nano-Porous Carbon Magnetic Composite
## 2 Experimental
### Batch Adsorption Experiments  
Batch studies were conducted to study As (III) adsorption onto the prepared composite. Adsorption experiment included the effect of process variables viz. contact time, pH, adsorbent dose, and adsorption isotherm. A definite amount of composite adsorbent was placed in different 100 mL stoppered conical flask containing 25 mL of As (III) solution. The mixtures were agitated on an electric shaker (Digital VDRL Rotator) at 160 rpm at room temperature. After equilibrium, the suspension was filtered, and As concentration in the filtrates before and after adsorption was determined by molybdenum blue method using spectrophotometer at 840 nm. A calibration curve was constructed by plotting absorbance against concentrations of arsenic solution (mg/L). The concentration of arsenic (mg/L) of unknown solutions was measured using the calibration curve. For arsenic determination, atomic adsorption, SDDC (silver diethylditiocarbamate), and molybdenum blue methods are widely used. Among them, the SDDC method and molybdenum blue methods are very fast, simple, reliable, and cost-effective. This method has a limit of the detection range of 1-50 \(\upmu\)S/L in 5 mL solution [40].  
Comparisons of percentage adsorption: Comparisons of adsorption percentage of As adsorptions onto plain AC and composite was studied with composite adsorbent and plain AC 1 g/L respectively, initial concentration 5 mg/L, contact time 60 min at pH 6.5.  
Effect of pH: Effect of pH on the percentage of As adsorption by the composite adsorbent was studied in the pH range of 2 to 11. Other parameters, such as adsorbent dose 1 g/L, initial As concentration 5 mg/L, and contact time 60 min, were kept constant. The pH of the solution was adjusted by adding 0.1 N HCl and 0.1 N NaOH. A pH of the solution was determined by using Digital pH meter, DICA, India.  
Effect of dose: The effect of adsorbent dose on a percentage of As adsorption by composite adsorbent was studied by varying the adsorbent dose from 1 g/L to 2.2 g/L. During the study, other parameters were kept constant, such as the initial As concentration 5 mg/L, contact time 60 min, and pH 6.5.  
Effect of contact time: The effect of contact time on the percentage of As adsorption by composite adsorbent was studied at different contact time from 5 to 140 min. Other parameters were kept constant, such as the adsorbent dose 1 g/L, initial As concentration 5 mg/L, and pH 6.5. All the experiments were carried out at room temperature. The percentage removal of As (III) adsorbed was calculated by using the following equation.  
\[\text{Removal percentage}=\frac{(\text{C}_{\text{o}}-\text{C}_{\text{e}}) \times 100}{\text{C}_{\text{o}}} \tag{1}\]where \(\rm C_{o}\) = Initial concentration of Arsenic (mg/L); \(\rm C_{e}\)= equilibrium concentration of Arsenic (mg/L).  
Adsorption isotherms: Adsorption isotherms study was conducted with As solutions of different initial concentrations from 2 mg/L to 120 mg/L. The other parameters were kept constant, such as adsorbent dose 1g/L and contact time 60 min, during the experiment. The milligram of arsenic adsorbed per gram of adsorbent, \(\rm q_{m}\) (mg/g), was calculated by using the following equation.  
\[\rm q_{m}\left(\frac{mg}{g}\right)=\frac{(C_{o}-C_{e})\times V}{M} \tag{2}\]  
where V = volume of As (III) solution (L) and M = mass of the adsorbent (g).