Enhanced Cr (VI) reduction and removal by Fe/Mn oxide biochar composites under acidic simulated wastewater

Chromium (Cr (VI)) can cause severe damage to the ecosystem and humans because of its toxicity. In this paper, the adsorbed Fe/Mn ions Bacillus cereus ZNT-03, lotus seeds, and graphene oxide were co-cultured as the raw materials. Fe/Mn oxide biochar composite (FMBC) was prepared to treat Cr (VI) by one-step pyrolysis. FMBC has high-density micropores, and the average pore size is about 0.82 nm. Fe (II), Mn (II), and N-containing functional groups could serve as electron donors for Cr (VI) reduction. The removal of Cr (VI) is monolayer chemisorption and pH-dependent. The maximum adsorption capacity of FMBC is 21.25 mg g^-1. Cr (VI) is reduced and adsorbed on FMBC by physical adsorption, reduction, complexation, electrostatic attraction, and coprecipitation. The contribution ratio of the reduction mechanism to Cr (VI) is 72.25%. The packed column and regeneration experiments indicated that FMBC had excellent adsorption stability even after soaking in acidic simulated wastewater after 180 days (pH 1.5). These results indicate that FMBC can provide rapid reduction and efficient adsorption for Cr (VI), making it possible to apply in water treatment.