Adsorption Characterization and Mechanism of a Red Mud–Lactobacillus plantarum Composite Biochar for Cd2+ and Pb2+ Removal

Simple SummaryPb2+and Cd2+contamination in water threatens ecosystems and human health. To develop efficient, eco-friendly adsorbents and valorize industrial by-products (red mud, distiller’s grains), this study synthesized a novel ternary composite biochar (RM) by immobilizing red mud andLactobacillus plantarumon distiller’s grain-derived biochar. Characterized via SEM-EDS, XRD, and FTIR, RM exhibited a superior porous structure. Batch adsorption experiments indicated that the adsorption on RM followed pseudo-second-order kinetics, with Cd2+adsorption fitting the Langmuir model and Pb2+fitting the Freundlich model. Key mechanisms included surface complexation, ion exchange, and coprecipitation. RM integrates the synergistic advantages of minerals, microorganisms, and biochar, offering a promising, sustainable solution for heavy metal-contaminated water remediation.Pb2+and Cd2+represent common heavy metal contaminants in aquatic environments, posing significant risks to ecosystem stability and human health. To develop efficient adsorbents for removing Cd2+and Pb2+while achieving resource utilization of industrial by-products (red mud and distiller’s grains), this study synthesized a novel composite biochar—red mud–Lactobacillus plantarumcomposite biochar (RM)—by immobilizing red mud andLactobacillus plantarumonto biochar derived from distiller’s grains. The structural and chemical properties of RM were characterized using SEM-EDS, XRD, and FTIR. Batch adsorption experiments were conducted to evaluate the effects of various experimental factors on Cd2+and Pb2+adsorption. The adsorption process was further elucidated through kinetic and isothermal models, revealing that it follows the pseudo-second-order kinetic model. Equilibrium data were best described by the Langmuir model for Cd2+and the Freundlich model for Pb2+. The maximum adsorption capacities reached 12.13 mg/g for Cd2+and 130.10 mg/g for Pb2+. The primary mechanisms involved in Cd2+and Pb2+adsorption by RM include surface complexation, cation–π interactions, ion exchange, and coprecipitation. These findings demonstrate that RM represents a promising and effective adsorbent for the remediation of heavy metal-contaminated water.