Surfactant-Enhanced Guava Seed Biosorbent for Lead and Cadmium Removal: Kinetics, Thermodynamics, and Reusability Insights

Heavy metal pollution in water resources, particularly cadmium and lead, poses a significant environmental and public health challenge, requiring the development of sustainable, efficient, and cost-effective water treatment methods. Therefore, this study investigates the biosorption capabilities of natural (SN) and surfactant-modified (SM) guava seed biosorbents to remove Cd and Pb from aqueous solutions. Guava seeds, an agricultural waste material, were treated with hexadecyltrimethylammonium bromide (HDTMA-Br) to enhance their adsorption efficiency. The biosorbents were characterized by FTIR, SEM-EDS, and zeta potential analysis to explain the surface modifications and their influence on the adsorption mechanisms. Batch experiments were performed to evaluate the effects of pH, contact time, temperature, biosorbent dosage, and concentration on Cd and Pb removal efficiencies. Adsorption isotherm and kinetic data were analyzed using mathematical models to obtain the basic parameters of the systems under study. The results showed that SM exhibited superior adsorption capacities of 328 mg/g for Cd and 594 mg/g for Pb at 25 °C, significantly outperforming SN. The study analyzed the thermodynamic parameters of adsorption systems, revealing endothermic and exothermic properties for SN and SM. Functional groups like hydroxyl and carbonyl were crucial for metal ion binding. HDTMA-Br introduced active sites and enhanced surface charge interactions. Regeneration tests showed reusability, maintaining over 85% efficiency after four cycles. Guava seeds could be cost-effective and sustainable biosorbents for heavy metal removal.