Preparation of Modified Biochar and Its Adsorption of Cr(VI) in Aqueous Solution

In recent years, wastewater containing heavy metal chromium has been discharged into water bodies. Metal chromium not only destroys the water environment but also poses a threat to human life and health. In order to solve the problem of chromium pollution more effectively, this study used corn straw as raw material to prepare biochar (MB) and used three methods: acid (HCl), alkali (NaOH) and metal salt (FeCl3) to modify biochar (HMB, NaMB and FeMB) and investigated the strengthening effect of modified biochar on Cr(VI) adsorption. The morphology and surface chemical composition of biochar were studied by XRD, SEM, XPS, FITR and other characterization methods. It was found that the modification of HCl, NaOH and FeCl3 improved the physical and chemical properties of MB (such as crystal structure, specific surface area, pore size and surface composite film), thus promoting the adsorption of Cr(VI). At the same time, an adsorption single-factor experiment, adsorption kinetics experiment, isothermal adsorption experiment and cyclic regeneration experiment were carried out on the four adsorbents. The effects of biochar on Cr(VI) adsorption performance under different pH, Cr(VI) initial concentration, biochar dosage and time were compared, and the adsorption mechanism of four adsorbents on Cr(VI) in aqueous solution was studied. It was found that the FeCl3-modified biochar provided more adsorption sites for chromium ions due to the successful loading of Fe, Fe3+ and iron oxide particles onto the MB surface to form a composite film, and the Fe-O groups introduced by the composite film formed a coordinated adsorption with dichromate ions. At 25 °C and pH = 2, FeMB reached saturation at 1440 min, the maximum adsorption capacity was 23.4 mg/g and its removal rate of Cr(VI) remained above 45% after five cycles. The adsorption of Cr(VI) was significantly enhanced.