Efficacy of green alginate beads for multi-metal removal from aqueous solution

Metals from industrial and agricultural sectors often end up contaminating surface and subsurface water. The trend to use alginate beads for removal of metals has been observed in recent years. Current work focuses on development of green materials for the remediation of metals. Here, the comparison of efficacy of 3 types of Na-alginate beads namely Zero Valent Iron (ZVI), Activated Carbon (AC) and ZVI-AC are tested for the removal of the following targeted metals i.e. cadmium, chromium, and lead. The study was performed at initial concentration of 2.5–10 mg ​L^-1 for a contact period of 0–180 min and at constant adsorbent dose of 10 mg ​mL^-1. The elements were analyzed with ICP-OES. FE-SEM-EDS and FTIR were used to study the surface morphology and functional groups of the synthesized beads. The removal efficiency of beads for metals followed a trend of Pb (≈96%) ​> ​Cr (≈59%) ​> ​Cd (≈39%), suggesting a selectivity order of metal uptake. The study shows ZVI-AC-Na alginate bead as the most effective green material. The experiment equilibrium data follows pseudo first order kinetic model, suggesting the multilayer adsorption uptake mechanism. The functional groups mostly responsible for the adsorption of these metals were identified as hydroxyl (-OH) and carboxyl (-COO) groups. The study concluded with the Pb being most easily adsorbed metal and ZVI-AC Na alginate beads being the better adsorbent than the ZVI – Na alginate and AC- Na alginate beads.