Biosorption of heavy metals from wastewater via agro waste derived biosorbents emphasizing mechanisms kinetics isotherm models and modification strategies

Heavy-metal contamination remains a critical environmental issue due to the persistence and toxicity of metals such as Pb, Cd, Cr, Ni, and Mn. Agricultural waste–derived biosorbents have emerged as cost-effective and sustainable alternatives to conventional treatment methods, with clear performance differences across materials. Rice husk typically achieves 75–90% removal with adsorption capacities of 60–150 mg g⁻¹ and retains around 70–80% efficiency after 4–5 regeneration cycles, while banana peel commonly shows 80–95% removal with higher capacities of 80–180 mg g⁻¹ and maintains 75–85% efficiency across 3–4 cycles. Sugarcane bagasse offers 70–88% removal with capacities of 50–140 mg g⁻¹ and remains effective for up to four cycles, particularly when chemically modified. Chemical modification often enhances biosorption efficiency, with many agro-waste materials showing 1.5–3-fold improvements in adsorption capacity compared with their raw forms. This review integrates these comparative trends by analysing adsorption performance, the influence of chemical and physical modification, kinetic and isotherm behaviour, and regeneration efficiency to provide a clear picture of biosorption potential across agro-waste materials. By highlighting biosorbents that combine efficiency, stability, affordability, and reusability, the review supports the identification of candidates suitable for practical heavy-metal remediation. Further studies are required to evaluate biosorbents using real wastewater, optimise biomass characteristics and operating conditions, and improve regeneration and safe handling of spent materials so that biosorption can progress toward reliable large-scale application. Graphical abstract