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 m2/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 ΔH and ΔS values showed that the sorption process was spontaneous (ΔG < 0), endothermic (ΔH > 0), and had increased entropy (ΔS > 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.

► In this work a new low-cost composite, P(AAm-EP), was synthesized and characterized. ► The composite provide an enhanced adsorption uptake for Tb3+ ions. ► The Langmuir, Freundlich and D–R models can be applied to the composite. ► Thermodynamic parameters indicated adsorption process was spontaneous, endothermic. ► The P(AAm-EP) composite is reused up to 5 times with no loss of removal efficiency.