Arsenic(III,V) Adsorption on Iron-Oxide-Coated Manganese Sand and Quartz Sand: Comparison of Different Carriers and Adsorption Capacities

Abstract

Abstract

This research aimed at improving the effectiveness of arsenic (As) (III,V) adsorption to iron-oxide-coated sand by first using a manganese sand carrier instead of a quartz sand carrier. Although both adsorbents had similar adsorption rates of As(III,V), the maximum adsorption capacities (q_m) of As(III) (2.216 mg/g) and As(V) (5.452 mg/g) by iron-oxide-coated manganese sand (IOCMS) were nearly 3 and 10 times higher than those by iron-oxide-coated quartz sand (IOCQS), respectively. Based on the analysis of scanning electron microscope and total Brunauer-Emmett-Teller surface area, IOCMS exhibited a rougher surface and a larger surface area (9.18 m²/g) than IOCQS (1.03 m²/g). Coated Fe content in IOCMS and IOCQS were 48.7 and 10.2 mg/g, respectively. Larger Brunauer-Emmett-Teller value and Fe content may be responsible for the greater adsorption capacity of IOCMS. Results of X-ray diffraction and X-ray photoelectron spectroscopy analysis confirmed the existence of Fe₂O₃, MnO, MnO₂ and FeOOH on the surface of IOCMS. In addition, IOCQS surfaces only contained SiO₂ and FeOOH. X-ray photoelectron spectroscopy results indicated that the MnO₂ in IOCMS did not oxidize As(III) in the adsorption process. Moreover, the optimum pH for As(III) removal by IOCMS was about pH 7. In contrast, the As(V) removal efficiency by IOCMS decreased with pH, increasing from pH 4 to 10. Further, the influences of anions on the removal of both As(III) and As(V) by IOCMS followed the same sequence of phosphate>silicate>carbonate. In conclusion, IOCMS showed a considerable potential to treat As-polluted water in engineering application.