An alkali modified biochar for enhancing Mn2+ adsorption: Performance and chemical mechanism

Manganese (Mn) could enter into water bodies from natural or anthropogenic sources and directly threaten human life. In this study, a novel NaOH modified biochar (MBC) derived from pomelo peel was prepared for Mn2+ adsorption. The results showed that the adsorption capacity of MBC was up to 163.194 mg g(-1) when initial Mn2+ concentration was 3000 mg L-1. The adsorption kinetic was best fitted in pseudo-second-order model (R-2 = 0.963-1.000), indicating that the chemical adsorption dominated the adsorption process. The adsorption isotherm was best fitted in Freundlich model (R-2 = 0.961), revealing that the adsorption occurred on the heterogeneous surface of MBC. Further analysis showed that the modification process significantly improved pore structure of MBC, which was beneficial for MBC to improve the absorption ability for Mn2+. Moreover, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) evidenced that the modification process introduced -COO- and CO32- on MBC, which could be combined with Mn2+ to form -COOMn+ and MnCO3 through cation exchange and surface precipitation. This might be the main reason why the adsorption performance of MBC was improved. The novel modified pomelo peel adsorbent in this study has great potential in the treatment of Mn-containing wastewater.