Construction of biomass-based sodium alginate microspheres for the removal of Cr (VI): Characterization, optimization...

Hexavalent chromium (Cr (VI)) presents a severe risk to both planetary ecosystems and public health because of its highly toxic and carcinogenic properties. In this study, biomass-based sodium alginate (SA-C) microspheres incorporating activated carbon were synthesized via a CaCl₂-induced sol-gel crosslinking method. The physicochemical properties of the SA-C were systematically characterized using SEM, BET, FTIR, XRD, and XPS. Using a Box-Behnken design (BBD), response surface methodology (RSM) optimized solution pH, adsorbent dosage, initial Cr (VI) concentration, and contact time for enhanced Cr (VI) removal by analyzing parameter interactions. Analysis of variance confirmed the statistical significance and robustness of the developed model, showing a very high correlation between predicted and experimental values. The optimal conditions predicted by the model for maximum Cr (VI) removal efficiency (97.32 %) were: solution pH of 1.6, adsorbent dosage of 1.2 g/L, initial Cr (VI) concentration of 19.2 mg/L, and contact time of 6 h. Validation experiments conducted under these conditions yielded an average removal efficiency of 97.30 %, closely matching the prediction and confirming the model's reliability. Adsorption kinetics followed pseudo-second-order behavior, and equilibrium data fitted the Langmuir isotherm with a q_max of 82.83 mg/g, confirming monolayer adsorption. Moreover, the SA-C microspheres demonstrated good reusability, retaining over 75.81 % of their initial adsorption capacity after five regeneration cycles. This study highlights the synergistic enhancement of heavy metal adsorption by combining activated carbon with sodium alginate, offering a promising strategy for sustainable and cost-effective wastewater treatment.