Pb (II) Biosorption by Ramalina conduplicans Biomass: Adsorption Behavior and Binding Mechanisms

This study presents a rigorous technical evaluation of the sequestration of Lead (Pb (II)), a representative potentially toxic element (PTE), using the biomass of the lichen Ramalina conduplicans Vain. Surface characterization conducted via SEM–EDX, transmission electron microscopy (TEM), X‐ray diffraction (XRD), and Fourier transform infrared (FT‐IR) confirmed that the lichen biomass possesses a heterogeneous, porous, and amorphous structure. The surface is rich in carboxyl, hydroxyl, and amino functional groups, which undergo distinct morphological transformations following Pb (II) adsorption. Batch experiments achieved a maximum removal efficiency of 99.15% at pH 5 and a dosage of 83.33 g L −1 . Kinetic modeling via nonlinear regression identified the pseudo‐second‐order model ( R 2 = 0.965) as the superior fit, while nonlinear Boyd and Weber–Morris models confirmed film diffusion as the primary rate‐limiting step. Equilibrium data were evaluated using five nonlinear equilibrium models, with the Hill model providing the most accurate description ( R 2 = 0.936). The Hill coefficient ( n H = 1.983) reveals positive cooperativity, indicating that the initial Pb (II) binding enhances the affinity of subsequent binding sites. While the Langmuir model ( R 2 = 0.894) estimated a maximum adsorption capacity ( q max ) of 3.889 mg g −1 , the superior fits of Hill, Redlich–Peterson, and Temkin models confirm a complex chemisorption mechanism occurring on a heterogeneous surface. Thermodynamic analysis further categorized the process as both spontaneous and endothermic. In conclusion, R. conduplicans biomass functions as a sustainable and cost‐effective biosorbent for Pb (II) removal. While further optimization is required for industrial scaling, its cooperative binding mechanism and high removal efficiency highlight its potential as a green component in integrated PTE remediation strategies.