Removal of As(III) from aqueous solution by the oyster shell powder–treated rice husk ash composite (OS-TRHA) pellet

Abstract

OS-TRHA pellets prepared from oyster shell (OS) powder and treated rice husk ash (TRHA) were used as the adsorbent for arsenite (As(III)) removal from contaminated water. The effect of the OS:TRHA ratio on As(III) removal performance was investigated via batch tests. The most appropriate ratio of OS and TRHA for OS-TRHA pellet preparation was 0.7:0.3 since it provided the acceptable As(III) adsorption capacity of about 26.2 mg g−1 without cracking. The OS-TRHA pellets before and after As(III) adsorption tests were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The mechanism of As(III) adsorption by OS-TRHA pellets was proposed. The experimental data correlated with the pseudo-second-order adsorption rate, and the adsorption behavior was better described by the Langmuir adsorption isotherm. The results of XRD, SEM, As(III) adsorption tests and calculation based on the Ca balance indicated that 25 wt% of OS-TRHA pellets was CaO that could react with As(III) and formed Ca-As-O (CaHAsO3) on the surface of the OS-TRHA pellets, while the other 75 wt% of OS-TRHA pellets was composed of CaSiO3 and C-S-H compounds which bound the precursor powders into stable pellets without cracking.