Synthesis and characterization of a new low-cost composite for the adsorption of rare earth ions from aqueous solutions
We synthesized and characterized a novel composite, poly(acrylamide-expanded perlite) [P(AAm-EP)] and investigated its adsorptive features for Tb3+. We achieved the synthesis by using free-radical polymerization and a number of structural characterization methods, including scanning electron microscopy (SEM) and BET-porosity swelling tests. We successfully performed free-radical polymerization of acrylamide (AAm) over expanded perlite (EP). We cross-linked expanded perlite with acrylamide to enhance its chemical resistance. P(AAm-EP) composite has a specific surface area of 31.7 m(2)/g. We evaluated the composite of adsorptive features for Tb3+ in light of the dependency of the ion concentration, pH, temperature, time, and reusability. The composite was able to bind Tb3+ ions with strong chemical affinity. The adsorption results were fitted to the classical Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) sorption models. The composite was used in the removal studies of the Tb3+ ions. The adsorption of Tb3+ ions increased as the pH increased and reached a plateau value at around pH 3.0. Variations in the Delta H and Delta S values showed that the sorption process was spontaneous (Delta G < 0), endothermic (Delta H > 0), and had increased entropy (Delta S > 0). We also found that the adsorption kinetics followed the pseudo-second order model and that the rate-controlling step was chemical adsorption. We were able to reuse the composites 5 sequential times. (C) 2012 Elsevier B.V. All rights reserved.