Biosorption and Isotherm Modeling of Heavy Metals Using Phragmites australis

This study investigates the biosorption of heavy metal ions (Pb, Fe, Cu, Cd, Zn, and Mn) from wastewater using the powdered biomass of Phragmites australis (common reed) under varying conditions, including temperature, pH, retention time, plant powder size, and biosorbent weight. The results showed that plant powder size significantly influenced the biosorption efficiency, with the 0.5 mm diameter powder yielding the highest removal rates for the heavy metal ions. The optimal temperature for biosorption was found to be between 30 and 50 °C, achieving up to 99.94% removal for Pb. The ideal pH for the biosorption of all metals was seven, and the best retention time for ion removal was 30 min, with a mean biosorption rate of 99.82% for Fe. A biosorbent weight of 10 g/L was also identified as the most effective for metal ion removal. Furthermore, two forms of P. australis, dry pieces and powdered biomass, were tested, with the powdered biomass exhibiting a superior biosorption performance. FTIR analysis revealed the involvement of carboxyl and hydroxyl functional groups in the biosorption process, while SEM imaging confirmed the surface interactions between metal ions and the plant material. The adsorption of heavy metals onto P. australis was effectively described by both Langmuir and Freundlich isotherm models, indicating a mix of monolayer coverage and heterogeneous interactions. The Langmuir model showed the highest adsorption capacities for Mn2+ (6.29 mg/g) and Cd2+ (5.10 mg/g), with strong affinities for Pb2+ (KL = 0.0122 L/mg), Fe2+ (KL = 0.0137 L/mg), and Cu2+ (KL = 0.0130 L/mg). Similarly, the Freundlich model indicated favorable adsorption (n > 1) for all ions. Cu2+ and Fe2+ had the highest adsorption intensities (n = 2.06), with the strongest capacities being observed for Fe2+ (Kf = 0.231) and Cu2+ (Kf = 0.222). These findings confirm the high potential of P. australis as a sustainable and eco-friendly biosorbent.