Adsorptive features of chitosan entrapped in polyacrylamide hydrogel for Pb2+, UO2(2+), and Th4+

Chitosan (Ch) was entrapped in polyacrylamide (PAA) by direct polymerization of acrylamide in a suspension of Ch. The adsorptive features of PAA-Ch and Ch were then investigated for Pb2+, UO2(2+), and Th4+ in view of dependency on ion concentration, temperature, and kinetics. Additional considerations were also given to their ion selectivity and reusability. Isotherms were L and H type of Giles classification and evaluated with reference to Langmuir, Freundlich, and Dubinin-Radushkevich (DR) models. PAA-Ch had higher adsorption capacity than Ch for all studied ions so that the sequences were Th4+>Pb2+>UO2(2+) concordantly with their affective ionic charges. The affinity of Ch in PAA increased for Pb2+ and UO2(2+) but did not change for Th4+. The values of enthalpy and entropy changed were positive for all studied ions for both Ch and PAA-Ch. The negative free enthalpy change value indicated that the adsorption process is spontaneous in the sequence of Th4+>or=Pb2+>UO2(2+). Free energy values derived from DR model implied that the sorption process is the ion exchange. Well compatibility of adsorption kinetics to the pseudosecond-order model predicate that the rate-controlling step is a chemical sorption. The study for ion selectivity showed that both Ch and PAA-Ch had the highest affinity to Pb2+. The reusability tests for Ch and PAA-Ch for Pb2+ for five uses showed that complete recovery of the ion was possible. The studied features of PAA-Ch suggest that the material should be considered as a new adsorbent. It is envisaged that the use of Ch in PAA will enhance practicality and effectiveness of Ch in separation and removal procedures.