Removal of aqueous Cr(VI) by a magnetic biochar derived from Melia azedarach wood

Magnetic biochar (MMABC) prepared from Melia azedarach wood was used for aqueous Cr(VI) removal. MMABC was a mesoporous material with SBET 5.219 m2/g and superparamagnetic magnetization 17.3 emu/g contributed by the contained Fe3O4. The MMABC showed higher removal efficiency (99.8%) than biochar under conditions of dosage 5 g/L, pH = 3.0, and Cr(VI) concentration 10 mg/L. The saturation magnetization (16.1emg/g) of MMABC still remained after adsorption. According to FTIR and Raman results, the benzene-ring adjacent carbonyl did not showed obvious positive effects on Cr(VI) removal. A potential mechanism and corresponding apparent kinetic model indicated the Cr(VI) removal process by MMABC followed adsorption-reduction-adsorption steps. Cr(VI) was firstly adsorbed on surface and subsequently reduced to Cr(III), which was further adsorbed on MMABC surface. Langmuir isotherm (with maximal adsorption capacity of 25.27 mg/g) and pseudo second-order kinetic model were suitable for adsorption step.