Abstract:The straws of rice, maize and rape were selected as raw materials for preparing biochars. The biochars were modified with H2O2 and HNO3/H2SO4, respectively, and the unmodified biochar and HCl treated biochar were used as control. The above biochars were added to an acidic paddy soil from Langxi, Anhui Province at the rate of 3%. The mixed soil samples were submerged for one month at 25℃, and then dried naturally. After a wet/dry cycle, Cd(II) adsorption/desorption experiments were carried out. Results indicate that the modifications of H2O2 and HNO3/H2SO4 increase the number of proton binding sites on biochars and HNO3/H2SO4modification leads to greater increase in the number of proton binding sites due to the greater increase of carboxyl functional groups than H2O2 modification. The addition of modified biochars improve the adsorption capacity of the acidic paddy soil for Cd(II), especially the addition of HNO3/H2SO4modified biochar. Therefore, adding HNO3/H2SO4 modified biochar could be used as a new method for adsorption and immobilization of Cd in acidic paddy soils.