Arsenic removal in aqueous solution by a novel Fe-Mn modified biochar composite: Characterization and mechanism

•Fe-Mn impregnated biochar (FMBC) was prepared through an easily synthetized method.•Fe-Mn impregnated biochar (FMBC) had greater absorption capacity on As(III).•Mn oxides (Mn3O4, Mn2O3) resulted in As(III) oxidized to As(V).•The sorption process of Fe-Mn impregnated biochar (FMBC) was mainly controlled by chemisorption.

The aim of this study was to develop a cost-effective method for As removal from aqueous systems. To this end, pristine biochar (BC) was impregnated with Fe-Mn oxides and a comparative analysis was conducted on the adsorption capacities of BC, Fe-Mn binary oxide (FMO), and Fe/Mn modified biochar (FMBC). The ferromanganese oxides increased the specific surface areas of BC. FMBC presented greater adsorption of As (Qmax = 8.25 mg g−1) than FMO and BC. Energy dispersive spectrometer analysis and electron microscope scanning revealed numerous pores of FMBC with the existence of Fe-Mn oxide using. Distinguished binding energy shifting of the As3d, Fe2p, O1s, and Mn2p3/2 regions after As sorption were found, indicating that Mn(III) oxidation and interaction of oxygen-containing function groups in the FMBC promoted the conversion of As(III) to As(V). Furthermore, chemisorption was found to be the main mechanism for As sorption on FMBC. Thus, the results suggest that FMBC could be used as an inexpensive and highly efficient adsorbent for As removal from water environment.