Removal of trace arsenic to below drinking water standards using a Mn–Fe binary oxide

Abstract

A series of Mn–Fe binary oxides with different Mn/Fe mole ratios were prepared by a co-precipitation method for the development of a high performance arsenic adsorbent from arsenic-contaminated drinking water. The Mn–Fe binary oxides and their arsenic adsorption reactions were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, N₂ adsorption and inductively coupled plasma mass spectrometry. The As(III) and As(V) adsorption results reveal that the arsenic adsorption ability is strongly dependent on the Mn/Fe mole ratio and surface area of the adsorbent. The MF4/6-10(H₂O₂) sample which was prepared by alkaline solution containing H₂O₂ shows the excellent arsenic removal of 99.9%, reducing As(III) concentration from 2 mg g⁻¹ to 2 μg L⁻¹, which can clear the new arsenic limit of 10 μg L⁻¹ in drinking water by the WHO. Manganese species in the adsorbent accelerates oxidation of As(III) to As(V), which enhances the As(III) adsorption ability of the adsorbent. Meanwhile, iron species in the adsorbent have a role to form surface OH groups, which is an important factor for the effective adsorption of As(V) by a surface chelating reaction.