Evaluation and Prediction of CadmiuM Removal from Aqueous Solution by Phosphate-Modified Activated Bamboo Biochar

The pollution of heavy metals, especially cadmium in wastewater, is a big concern for the environment and humans. In this study, biochar was prepared by the pyrolysis of bamboo particles after the impregnation of phosphate (Na2HPO4). The biochars before and after modification were characterized by environmental scanning electron microscope (ESEM), Brunet-Emmet-Teller (BET), and X-ray diffraction (XRD) analyses. The results indicate that the biochar surface properties are improved and the phosphate compounds chemically bound to the functional groups on the biochar surface. The adsorption of Cd(II) by the modified biochar obeys pseudo-first-order kinetic model and the Langmuir adsorption isotherm model. The results of batch-adsorption experiments demonstrate that the phosphate modification increases the absorption capacity of pristine biochar by almost 10 times to 202.66 mg/g and increases the removal efficiency of Cd(II) by 85.78%. The wastewater treatment process in a continuous-flow stirred tank reactor (CSTR) was modeled by using the PHREEQC-3 program, taking into account the influence of various operational parameters. Simulation results show that the modified biochar has better performance during the wastewater treatment; moreover, the shorter residence time and the larger fluid pH value are favorable.