Synthesis and characterization of chemically modified Leucaena leucocephala pods for enhanced Pb (II) adsorption from aqueous solutions and landfill leachate

This study investigated the preparation and application of a chemically modified biosorbent derived from Leucaena leucocephala pods (MLLP) for Pb (II) removal from aqueous solutions and landfill leachate. Raw Leucaena leucocephala pods (RLLP) were sequentially treated with hot water, ethanol, and hydrochloric acid, resulting in significant physicochemical modifications. The treatment significantly improved the physicochemical properties of MLLP, increasing the BET surface area from 0.6692 to 1.9687 m²/g, enriching carbon content from 47.21% to 49.22%, enhancing hemicellulose and cellulose fractions, and reducing lignin content from 31.20% to 14.00%. Batch adsorption experiments identified pH 5 and an adsorbent dosage of 10 g/L as the optimum conditions. Regression analysis demonstrated a statistically significant model (p < 0.05), explaining 84.78% of the variation in adsorption capacity and identifying adsorbent dosage as the most influential factor affecting Pb (II) adsorption. The adsorption capacity increased from 0.48 to 6.62 mg/g as the initial Pb (II) concentration increased from 5 to 70 mg/L. The pseudo-second-order model adequately described the adsorption kinetics, while the Freundlich and Sips models showed slightly better agreement with the equilibrium data. Application of MLLP to landfill leachate successfully reduced Pb (II) concentrations to levels compliant with Malaysian discharge standards, demonstrating its potential as a sustainable and low-cost biosorbent for wastewater treatment.