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Novel Regenerative Hybrid Composite Adsorbent with Improved Removal Capacity for Lead Ions in Water

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journal contribution
posted on 01.04.2021, 10:27 by Melvin S. Samuel, Mingwei Shang, Stanislav Klimchuk, Junjie Niu
Lead is one of the most toxic heavy metals in water systems which poses critical effects on human health. To meet the 10 ppb limit in drinking water recommended by the World Health Organization, a highly efficient adsorbent with extremely low-concentration removal capability is needed. Herein, we develop a hybrid composite adsorbent βCD-AC-CaBent that is composed of β-cyclodextrin, activated carbon, and calcium-enhanced bentonite clay via a chemical method. The enlarged surface area of 41.56 m2/g and increased negative charge of −45.04 mV greatly improved the attraction of Pb2+ to the porous surface, while the large amount of active Ca2+ sites further increased the ion-exchange capacity. By varying the initial Pb2+ concentration, pH value, and contact time, the adsorbent’s lead removal capacity was studied in batch tests, whose results were fitted with pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models and Langmuir/Freundlich isotherms. In parallel, breakthrough curves with Pb2+ concentrations from 12 to 100 mg L–1, flow rates from 10 to 100 mL min–1, and bed heights from 1.2 to 3.2 cm were obtained in a continuous fixed-bed column, which were fitted with Thomas, Yoon–Nelson, and Bohart–Adam models, respectively. The hybrid adsorbent displayed excellent removal efficiency after regeneration, which indicates its promising potential in sustainable applications. The results showed that the capacities of 174.5 mg g–1 at a dosage of 1.0 g L–1 and 434.78 mg g–1 at a dosage of 0.25 g L–1 were, respectively, achieved within about 60 min, which are higher than those of pure bentonite and most of the commercial adsorbents. In column tests, an adsorption capacity of up to 39.78 mg g–1 was obtained. More importantly, the removal uptake capacity of 10.5 mg g–1 at 0.5 ppm Pb2+ concentration and 4.3 mg g–1 at 50 ppb Pb2+ concentration was achieved upon treatment of 75 L of water. As high as 100% Pb2+ ions were removed at the beginning and still 70% Pb2+ ions were removed upon saturation in industrial wastewater. The current results suggest a new hybrid adsorbent that can deliver a high lead removal capacity in water under differential conditions especially with extremely low-ion concentrations.