Sorption of arsenate onto magnetic iron–manganese (Fe–Mn) biochar composites

Abstract

Bimetal adsorbents attract much attention because of their good sorption ability to arsenate (As(V)). In this work, biochar-supported bimetal adsorbents were prepared through either direct pyrolysis of Fe and Mn ion treated pinewood biomass (FMM) or co-precipitation of Fe and Mn ions onto pinewood biochar (FMB). The two Fe–Mn biochar composites were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) analyses. Characterization results suggest that maghemite (γ-Fe₂O₃) and manganosite (MnO) are the dominant metal crystals in FMM, while manganese ferrite (MnFe₂O₄) is the dominant bimetal crystal in FMB. Batch sorption experiments showed that the maximal As(V) sorption of FMB and FMM was 3.44 and 0.50 g kg⁻¹ respectively, which are higher than that of the unmodified biochar. As(V) sorption by FMM and FMB decreased with increasing solution pH (between 3–9). Results of this work suggest that co-precipitation is more effective in preparing magnetic Fe–Mn biochar composites for As(V) removal.