Removal of Pb2+from Aqueous Media by Solidago canadensis L.-Derived and Crab Shell-Derived Biochar: Adsorption Behavior and Optimization of Adsorption Conditions

Pb2+, as a heavy metal ion, has been recognized for its strong toxicity and imperative removal from industrial wastewater. In pursuit of resource efficiency, this study employed biochars preparate by limited-oxygen pyrolysis at elevated temperatures, using Solidago canadensis L. (SC) and discarded crab shells (CS) as raw materials. The objective was to investigate the adsorption behaviors and capacities of the resultant biochars for Pb2+. Response Surface Methodology (RSM) was utilized to optimize the environmental conditions for the adsorption of Pb2+ by the biochars. Adsorption kinetics indicated that Pb2+ primarily adhered to the biochar via chemical bonding. Isotherm analysis revealed that Pb2+ was fixed by biochar through monolayer adsorption, with the CS-700 demonstrating superior adsorption capacity (93.29 mg/g). The adsorption mechanisms of Pb2+ by SC biochar and CS biochar involved complexation, precipitation, electrostatic attraction, and pore filling. Moreover, the solution pH influenced the adsorption efficiency by altering the speciation of Pb2+, while the concentration of dissolved organic carbon showed a biphasic effect, initially enhancing and then diminishing the adsorption capacity of CS-700 for Pb2+. RSM can accurately predict the removal rate of Pb2+by CS-700 under different environmental conditions. For the given adsorption system, the optimal conditions for the removal of Pb2+ by CS-700 were achieved at a solution pH of 8.65, with an adsorbent dosage of 0.019 g, and a dissolved organic carbon concentration of 11.85 mg/L. This research provides a valuable approach for the recycling of waste materials and the remediation of heavy metals in contaminated water.