Arsenic is known to be one of the most toxic elements that millions of people worldwide are exposed to risk by polluted drinking water. To decrease the arsenic concentrations, various sorbent have been explored. The first objective of the present study was extraction of amorphous silica from rice husk and its application for synthesize of Fe3O4@SiO2 core/shell magnetic nanoparticles. The second objective of the present study was optimization of process parameters for arsenic removal from aqueous solution by produced sorbent. A central composite design (CCD) combined with response surface methodology (RSM) was employed for maximizing arsenic removal from aqueous solution by using Fe3O4@SiO2 magnetic nanoparticles. Three independent variables namely pH (2-10), initial As (V) concentration (5-100 mg.L-1) and sorbent dosage (0.1-5g.L-1) on adsorption were studied to find the best operating conditions. The synthesized sorbent was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption–desorption isotherms, Fourier-transform infrared (FT-IR) spectrometry and scanning electron microscopy (SEM). The results of XRF analysis reviled that the purity of the obtained silica was 95.55%. XRD patterns revealed that the extracted silica is amorphous and also obtained pattern for Fe3O4@SiO2 indicate that the samples are composed of hematite. The BET results show that, the specific surface area for silica nanoparticles and Fe3O4@SiO2 magnetic nanoparticles were 409.69 and 159.38 m2/g, respectively. The result of SEM analysis shows that the average of the particle sizes is 200±20 nm. The optimum operating conditions were determined as pH, 3.5; arsenic concentration, 15 mg.L-1 and sorbent dosage 1.42 g.L-1. At optimum adsorption conditions, the efficiency (R%) and equivalent metal uptake (qe) of arsenic were 100% and 25.4 mg.g-1.
