Ligand-immobilized spent alumina catalyst for effective removal of heavy metal ions from model contaminated water

Abstract

Spent alumina catalyst (hereafter Al2O3) is a waste material from the petrochemical industry and primarily contains γ-alumina, beohmite, and organics. To reduce its negative impact on environment, spent alumina catalyst was characterized and utilized in this work to improve the removal efficiency of heavy metal ions from contaminated water in the model by immobilizing organic ligands on it. Dithizone (DTZ) and 2-amine-1-methylbenzimidazole (MAB) in an ethanol-water solution were impregnated in the pores of spent alumina catalyst according to the filling of 25% of the measured total pore volume. The sorption capacities of these new solid-phase sorbents (DTZ-Al2O3 and MAB-Al2O3) were evaluated by the sorption of heavy metal ions (Ni2+, Cd2+, and Zn2+) from model contaminated water. The highest sorption capacities for Ni2+ (0.37 mmol·g−1), Zn2+ (0.54 mmol·g−1) and Cd2+ (1.01 mmol·g−1) were noted for MAB-Al2O3. The MAB-Al2O3 sorbent has a similar sorption for metals in ternary solution with less selectivity but the DTZ-Al2O3 sorbent can adsorb Ni2+ and Zn2+ but not Cd2+. The effects of heavy metal ion concentration, pH, temperature, and contact time on the sorption capacities were studied. The sorption mechanism of heavy metal ions over the MAB-Al2O3 can be considered both the physical sorption of heavy metal ions on the surface of porous Al2O3 and a strong chemical reaction between heavy metal ions and the MAB-Al2O3 sorbent. In addition to the effective removal of heavy metal ions from contaminated water, the prepared solid-phase sorbents have several advantages: waste utilization, recyclability, scalability, low cost and easy preparation.