Simultaneous reductive and sorptive removal of Cr(vi) by activated carbon supported β-FeOOH

Abstract

An activated carbon (AC)-supported nanocomposite was prepared by precipitating β-FeOOH onto KOH activated soybean meal-derived biochar (SYBK). The as-prepared β-FeOOH/SYBK composites were characterized by N₂-Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), X-ray diffractions (XRD) and X-ray photoelectron spectroscopy (XPS). XRD results confirmed that β-FeOOH was impregnated by AC. The chromate (Cr(VI)) removal capacity was investigated in a batch experiment with different conditions. The ratios of β-FeOOH and AC were compared for Cr(VI) removal and a loading quantity of 20 wt% β-FeOOH was considered as the most efficient amount. This was possibly ascribed to it having the highest surface area (670.65 m² g⁻¹) of the β-FeOOH/SYBK nanocomposites. It was found that 20β-FeOOH/SYBK could remove as much as 96% Cr(VI) at pH 1–2 with 2 mmol L⁻¹ EDTA and 2.0 g L⁻¹ nanocomposites. The maximal Cr(VI) removal by 20β-FeOOH/SYBK was 37.04 g kg⁻¹, as estimated by a Langmuir isotherm model. The removal mechanisms were examined by studying the speciation of Cr on sorbents as well as in aqueous solution. The XPS analysis of spent sorbents and chemical speciation of Cr in aqueous solutions revealed that partial Cr(VI) was reduced to Cr(III) on sorbents and in aqueous solution. This suggests that Cr(VI) can be removed by simultaneous sorption and reduction by the as-prepared nanocomposites.