Abstract:Purpose: Phosphate modification is considered as a potential strategy to improve the performance of straw biochar (RBC) for removing Cd(II) from acid mine wastewater. In this work, K3PO4 was employed to modify rice straw biochar (KRBC) to improve its adsorption performance of Cd(II) from wastewater. Method: Batch adsorption experiments were used to investigate the effects of initial solution pH, co-existing ions, humic acid concentration, adsorption time and initial concentration of Cd(II) on removing Cd(II) and the potential mechanism of Cd(II) removal by modified biochar was researched. Result: The adsorption experiments showed that KRBC had good removal performance of Cd(II) at a solution pH of 5.0~7.0. Additionally, the co-existing ions of K+, Na+, Ca2+, Mg2+, NO3- and SiO32- had no effect on removing Cd(II) for RBC and KRBC, whereas PO43-, CO32- and humic acid promoted the removal of Cd(II). The proposed second-order kinetic model and Langmuir model could better describe the adsorption process of Cd(II). The maximum adsorption capacity of RBC and KRBC for Cd(II) was 57.93 mg·g-1 and 159.46 mg·g-1, respectively. Potential removal mechanisms included complexation, electrostatic interaction, cation-π interaction, and co-precipitation. After three regenerative experiments, the removal efficiencies of Cd(II) at 50 mg·L-1 by RBC and KRBC were 20.18% and 86.75%, respectively. Conclusion: The above results indicate that K3PO4 modified biochar has more potential for the removal of Cd(II) from acid mine wastewater.