Adsorption of Cu(II) and Pb(II) in Aqueous Solution by Biochar Composites

In this study, straw biochar (TB) was prepared by pyrolysis at 500 °C, and biochar composite material (TBS) was prepared by a 1:4 mass ratio with sludge (TS). Scanning electron microscopy and Fourier transform infrared spectroscopy were utilized to characterize the material before and after adsorption. The results demonstrated that TBS possesses significant pore structure characteristics and abundant active functional groups such as hydroxyl, carboxyl, and carbonyl groups, providing a structural basis for its efficient adsorption of heavy metal ions in aqueous solutions. The adsorption performance of the remediation materials for Cu(II) and Pb(II) in aqueous solution was systematically investigated. Experimental data showed that TBS achieved maximum adsorption capacities of 60.86 and 46.98 mg/g for Cu(II) and Pb(II) at equilibrium, respectively, exhibiting superior adsorption efficiency. Through fitting analysis using adsorption kinetic models and isothermal adsorption models, it was found that the pseudo-second-order kinetic model and Freundlich isothermal model could more accurately describe the adsorption process of the two heavy metal ions, indicating that chemical adsorption was the dominant mechanism and characterized by multilayer adsorption. Thermodynamic parameter calculations revealed negative ΔG values and positive ΔH and ΔS values, suggesting that the adsorption process was a spontaneous, entropy-increasing, and endothermic reaction. These research results fully validate the excellent removal capabilities of TBS for Cu(II) and Pb(II). This study has shown that TBS can be considered a promising and cost-effective adsorbent, demonstrating its potential to adsorb heavy metal ions in water.