Immobilized Anogeissus leiocarpus Biomass as a Sustainable Biosorbent for Pb (II) Removal from Aqueous Solution: Adsorption Isotherm and Kinetic Studies

Abstract

Lead contamination of water remains an environmental and public health concern, motivating the search for affordable, sustainable biosorbents. This study evaluated Pb(II) removal from aqueous solutions using powdered Anogeissus leiocarpus stem bark, leaves, and roots immobilized individually and in combination in calcium alginate beads. Batch experiments examined contact time (30–180 min), initial Pb(II) concentration (10–100 mg/L), biosorbent dose (0.25–1.00% w/v), and biosorbent type, alongside no-adsorbent and alginate-only controls. All biosorbents reached equilibrium within 150–180 min. The combined formulation achieved the highest removal efficiency (99.97%) at a dose of 1.00% w/v and an initial Pb(II) concentration of 100 mg/L. Removal efficiencies for stem bark, leaf, and root beads were 99.82%, 99.39%, and 99.11%, respectively, compared with 35.0% for alginate-only beads. Equilibrium data fitted the Freundlich isotherm better than the Langmuir model (Freundlich R² = 0.801–0.9999), consistent with adsorption onto heterogeneous surfaces. Kinetic data closely fitted the pseudo-second-order model across all biosorbents (R² = 1.000), with calculated equilibrium adsorption capacities closely matching experimental values. Nonzero intercepts in intraparticle diffusion plots suggested an additional contribution from boundary-layer transport. These findings demonstrate high Pb(II) removal by alginate-immobilized A. leiocarpus biomass under the tested conditions, particularly when plant parts were combined. The study supports the potential of these formulations for lead remediation and their further development for wastewater treatment.