Efficient adsorption of Pb2+ from aqueous solutions using papain immobilized on alginate beads

• Immobilized papain in alginate beads removes 91.82% of Pb²⁺ at pH 3. • Adsorption follows Langmuir isotherm and pseudo-second-order kinetics. • Equilibrium is reached within 8 minutes, enhancing process efficiency. • Low-cost, eco-friendly biosorbent suitable for industrial wastewater treatment. • Pb²⁺ adsorption is influenced by pH, contact time, and adsorbent dosage. The increasing contamination of water bodies by heavy metals such as lead Pb²⁺ has driven the search for sustainable technologies for their removal. This study proposes the use of papain immobilized on alginate beads (PIPA) as an effective biosorbent for the adsorption of Pb²⁺ from aqueous solutions. It is hypothesized that the immobilization of papain enhances the stability of the biopolymer and promotes metal ion adsorption. Experiments were conducted in a batch reactor following a multilevel factorial design, evaluating the effect of initial Pb²⁺ concentration, pH, and adsorbent dosage on removal efficiency. The material was characterized by FTIR and SEM before and after the adsorption process. A maximum removal efficiency of 91.82% was achieved using 6 g of PIPA at pH 3 and an initial Pb²⁺ concentration of 10 mg/L. The adsorption process followed the Langmuir isotherm model (R2=0.93), with a maximum adsorption capacity of 0.0765 mg/g and a determination coefficient R² = 0.97, indicating monolayer formation. The kinetics were best described by the pseudo-second-order model, with R² = 0.9966, and equilibrium was reached within 8 minutes. These results suggest that the immobilization of papain in alginate enhances the material’s performance as a biosorbent, providing a promising alternative for the treatment of lead-contaminated water.