Adsorption Performance and Mechanism of Phosphate in Water by Magnesium Oxide-Corncob Biochar

In this study, magnesium oxide-corncob biochar (MgO-CB) was prepared by MgCl2 modified corncob biomass for the adsorptive removal of phosphate from water. The adsorbents were characterized by scanning electron microscopy (SEM), x-ray diffractometer (XRD), and Fourier transform infrared spectroscopy (FT-IR), and the adsorption mechanism of the adsorbents was studied. Batch adsorption experiments studied the adsorption performance of MgO-CB for phosphate, and the effects of solution pH, adsorbent dosage, and coexisting ions on the adsorption effect were also investigated. The results showed that the theoretical maximum adsorption capacity of MgO-CB could reach 158.98 mg/g when the initial phosphate concentration was 120 mg/L. MgO-CB exhibited good adsorption performance in the pH range of 3 to 10, and the coexisting ions CO32− and SO42− significantly impacted the adsorption. The adsorption process of MgO-CB for phosphate proceeded relatively fast in the first 400 min and basically tended to equilibrium around 600 min. The adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir isothermal adsorption model, indicating that the adsorption process was dominated by chemisorption. Thermodynamic analysis showed that the change in temperature from 15°C to 45°C had little effect on the adsorption capacity of MgO-CB for phosphate, and the adsorption process was spontaneous, endothermic, and entropy-increasing. The mechanism of phosphate adsorption by MgO-CB involved electrostatic attraction, chemical precipitation, and ligand exchange to form inner-sphere complexation.