Adsorption characteristics of phosphate in water by magnetically modified biochar

LYU Xuebin; HUANG Ruiqing; LI Wei; YANG Gaixiu; XIONG Jian

doi:10.13226/j.issn.1006-6772.SWZ25082101

Abstract：To address phosphorus pollution in water bodies,biochar(BC-700)is derived from highland barley straw as a carbon-based material.Magnetic biochar material(MBC-700)is developed by immobilizing iron-based compounds onto BC-700 surfaces through co-precipitation.Adsorption performance of MBC-700 is systematically investigated under varying conditions,including pH,dosage,initial phosphate concentration,and contact time.Characterization techniques(SEM-EDS,XRD,XPS,FTIR,and VSM)combined with kinetic and isothermal adsorption models are employed to elucidate the adsorption mechanism.Results demonstrate that MBC-700 exhibits a porous structure with iron species(FeOOH and Fe3O4)effectively immobilized on its surface,where Fe3O4 contributes to its strong magnetic properties.Post-adsorption analysis reveals phosphate retention primarily as FePO4 precipitates and Fe—O—P complexes.The adsorption process follows spontaneous monolayer chemisorption kinetics,influenced by intraparticle diffusion,surface heterogeneous diffusion,and boundary layer diffusion,achieving a theoretical maximum adsorption capacity of 5.97 mg/g.MBC-700 maintains effective phosphate removal across a broad pH range(3-7),with enhanced performance in acidic conditions and inhibition in alkaline environments.Notably,coexisting anions(CO32-and HCO3-)promote adsorption,while magnetic recovery achieves>98%efficiency.Mechanistic studies identify pore filling,electrostatic attraction,ligand exchange,precipitation,and complexation as dominant adsorption pathways.This work provides scientific insights and technical support for addressing phosphorus pollution and advancing biochar recovery technologies.