Adsorption of arsenate from aqueous solution on binary mixed oxide of iron and silicon

Abstract

This paper is related to the adsorption study of arsenate from aqueous solution onto the binary mixed oxide (MO) of iron and silicon in the ratio of 3:1, respectively. The adsorption affinity of arsenate toward various metal oxides/hydroxides was observed to be in the order: mixed oxide>iron hydroxide>iron oxide (nano particles)>iron oxide>silica. Arsenate concentration, pH, ionic strength of solution and thermal treatment of adsorbent were the main parameters investigated in this study for the removal of arsenate by mixed oxide. The decrease in arsenate adsorption with thermal treatment of the mixed oxide was assigned to decrease in surface area of the substrate with increase in its calcination temperature. Arsenate adsorption was found to increase with increase in ionic strength of background solution indicating the formation of inner-sphere complexes. The maximum desorption of arsenate back to the solution from the loaded surface was observed to be 73% at pH 12. Both the maximum adsorption capacity (Xm) and binding energy constant (Kb) values for mixed oxide (MO) calcined at different temperatures were in the order: MOuncalcined>MO300°C>MO550°C>MO750°C. The dramatic decrease in the maximum adsorption capacity of mixed oxide calcined at 750°C was linked to the phase transformation from amorphous to crystalline state. Energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR) and wet chemical analysis also confirmed the adsorption of arsenate by the mixed oxide of iron and silicon.