Selective adsorption of Pb2+ from acid mine drainage through a poly (hydroxamic acid) (PHA) ligand: an HSAB-guided coordination mechanism
Résumé
Introduction Lead (Pb 2+ ) contamination in acid mine drainage (AMD) poses a significant environmental challenge due to its persistence, bioaccumulation potential, and severe toxicity to living organisms. This study evaluated the performance of a Fenton-modified pine cone-derived poly (hydroxamic acid) (PHA) ligand for the selective removal and recovery of Pb 2+ from acidic mine drainage systems. Methods The PHA adsorbent was synthesized through Fenton-assisted oxidation and applied in batch adsorption experiments. The effects of contact time, solution pH, temperature, and adsorbent dosage on Pb 2+ removal were systematically investigated. Adsorption kinetics, equilibrium isotherms, thermodynamic parameters, selectivity, and regeneration performance were evaluated to elucidate the adsorption mechanism and practical applicability of the material. Results Maximum Pb 2+ adsorption was achieved at pH 6, with equilibrium attained after 180 min and an adsorption capacity of 86 mg g -1 under optimal conditions. The adsorption process was best described by the pseudo-second-order kinetic model (R 2 = 1.000), indicating that chemisorption governed the rate-limiting step. Equilibrium data exhibited excellent agreement with the Langmuir isotherm, suggesting predominantly monolayer adsorption. However, the experimentally observed adsorption capacity exceeded the Langmuir-predicted q max , indicating the contribution of strong coordination-driven Pb–O interactions beyond ideal monolayer assumptions. Thermodynamic analysis revealed positive enthalpy values (ΔH° > 0) and negative Gibbs free energy values (ΔG° < 0), confirming that adsorption was endothermic and spontaneous. The adsorbent maintained high Pb 2+ selectivity in complex polymetallic AMD matrices and retained more than 80% of its initial removal efficiency after five adsorption–desorption cycles. Discussion The superior adsorption performance of PHA was attributed to the abundance of hydroxamic acid functional groups capable of forming strong coordination complexes with Pb 2+ ions. The combined selectivity, high adsorption capacity, favorable thermodynamics, and excellent reusability demonstrate that Fenton-modified PHA is a cost-effective and sustainable adsorbent for the selective recovery of Pb 2+ from acid mine drainage and other metal-contaminated wastewaters.
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