The primary biochar(PB)and iron-clay biochar composite(PFB)were prepared by pyrolysis and impregnation co-pyrolysis,respectively,and the reduction of hexavent chromium[Cr(Ⅵ)]was mediated by weak electron donor sodium lactate using PB and PFB as electron shuttles.Through measuring the electrochemical activity,conductivity and the reaction kinetic of biochar mediated reduction of Cr(Ⅵ)to compare the electron shuttle efficiency of PB and PFB,and the mechanism of PFB as electron shuttle mediated reduction of Cr(Ⅵ)by sodium lactate was explored through corresponding characterization analysis.The results show that PFB has higher specific capacitance and charge transfer rate,and can act as electron shuttle to promote sodium lactate to reduce chromium hexavalent.