Optimizing the Biosorption of Cadmium and Lead Ions on Agave Biomass Using Box–Behnken Response Methodology

Abstract

This research explored the potential of Agave leaf biomass (ALB) as a biosorbent for the removal of Pb(II) and Cd(II) ions from an aqueous solution. FT-IR, XRD, and SEM techniques were used to characterize the adsorbent biomass. A series of batch experiments at varying contact times, pH, adsorbent doses, initial metal concentrations, and salt concentrations were conducted. Box–Behnken design (BBD) was used for statistical analysis of the adsorption parameters for metal ion removal, modeled by response surface methodology (RSM). The proposed quadratic model was found to be suitable and highly significant for the experimental data, with predicted values < 0.05 for the adsorption efficiency, showing a strong agreement with the experimental results, confirming a significant regression coefficient at a 95% confidence interval (R² = 0.9717 for Pb(II) and R² = 0.9717 for Cd(II)). Salt concentration and initial metal ion concentration have a significant effect on the percentage removed. The optimum conditions of 0.8 and 0.2 mmol/L concentration and 0.18 and 0.17 g adsorbent dose at pH 3 and pH 6 can achieve a removal of 97.76% and 79.38% for Pb(II) and Cd(II) respectively. The adsorption mechanism confirmed that the Freundlich isotherm model provided the best fit due to its higher linear regression coefficient compared to other models (R² = 0.97 for Pb(II) and R² = 0.98 for Cd(II). The kinetic data of metal ion adsorption were well described by pseudo-second-order kinetics. The reusability of the adsorbent shows that it retains approximately 68.52% and 50.39% of its adsorption for Pb(II) and Cd(II), respectively, after seven successive adsorption–desorption cycles, suggesting that the studied adsorbent has a significant potential for industrial wastewater treatment applications.