Enhancing Cd(II) Adsorption on Rice Straw Biochar by Modification of Iron and Manganese Oxides

Abstract

Metal oxide-modified biochar exhibited an excellent adsorption performance in the treatment of wastewater. Iron nitrate and potassium permanganate were oxidative modifier, by which Oxygen-containing groups and iron-manganese oxides could be introduced into biochar. In this study, Fe-Mn oxide-modified biochar (BC-FM) was synthesized using rice straw biochar, and its adsorption process, removal effect and mechanism for removing Cd(II) from the wastewater were explored by batch adsorption experiments and characterization. Adsorption kinetics showed that the maximum adsorption capacity for Cd(II) by BC-FM was 120.77 mg/g at 298 K, which was about 1.5 to 10 times the amounts of other modified biochar mentioned in the paper. The Cd adsorption of BC-FM was well fit by pseudo-second-order adsorption model and Langmuir model, and was a spontaneous and endothermic process. The adsorption process was mainly controlled by a chemical adsorption mechanism. Moreover, BC-FM can maintain Cd removal rate of about 50% even reused for three times. The capture of Cd(II) by BC-FM was realized by coprecipitation, surface complexation, electrostatic attraction and cation-π interaction. In addition, the loaded iron-manganese oxides also played important role in the removal of Cd(II) by the redox reaction and ion exchange in BC-FM. The results suggested that BC-FM could be regarded as an efficient adsorbent in the treatment of Cd contamination wastewater.