Adsorption and resistance properties of Pb2+ by modified calcium bentonite @ biochar composite barrier

To enhance the performance of bentonite-based barrier systems under heavy metal contamination, this study introduced corn straw biochar as an adsorptive amendment into polymer-modified calcium bentonite, successfully developing a polymer-modified calcium bentonite-biochar composite barrier material (PB8@C8). Through systematic evaluation of compressive strength, permeability coefficient, swell index, and adsorption performance, the optimal biochar content was determined to be 8 %. At this ratio, the material exhibited significant improvements in permeability coefficient, swell index, and adsorption capacity. Although the compressive strength slightly decreased, it still met the engineering requirement of 103.4 kPa. Microstructural characterization techniques such as XRD, SEM, FTIR, and BET confirmed the successful incorporation of biochar into the modified calcium bentonite, introducing abundant hydroxyl and carboxyl functional groups as well as a larger specific surface area, thereby enhancing the adsorption performance. Analysis of the Pb 2+ adsorption behavior indicated that the adsorption process of PB8@C8 better conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model, suggesting monolayer chemical adsorption as the dominant mechanism. Under the conditions of pH = 6, an adsorbent dosage of 0.25 g, and an initial Pb 2+ concentration of 500 mg/L, the adsorption capacity of PB8@C8 for Pb 2+ reached 195.98 mg/g.