Adsorption characteristics of UO22+ and Th4+ ions from simulated radioactive solutions onto chitosan/clinoptilolite sorbents

Adsorption features of UO22+ and Th4+ ions from simulated radioactive solutions onto a novel chitosan/clinoptilolite (CS/CPL) composite as beads have been investigated compared with chitosan cross-linked with epichlorohydrin. The effects of contact time, the initial metal ion concentration, sorbent mass and temperature on the adsorption capacity of the CS-based sorbents were investigated. The adsorption kinetics was well described by the pseudo-second order equation, and the adsorption isotherms were better fitted by the Sips model. The maximum experimental adsorption capacities were 328.32 mg Th4+/g composite, and 408.62 mg UO22+/g composite. The overall adsorption tendency of CS/CPL composite toward UO22+ and Th4+ radiocations in the presence of Cu2+, Fe2+ and Al3+, under competitive conditions, followed the order: Cu2+ > UO22+ > Fe2+ > Al3+, and Cu2+ > Th4+ > Fe2+ > Al3+, respectively. The negative values of Gibbs free energy of adsorption indicated the spontaneity of the adsorption of radioactive ions on both the CS/CPL composite and the cross-linked CS. The desorption level of UO22+ from the composite CS/CPL, by using 0.1 M Na2CO3, was around 92%, and that of Th4+ ions, performed by 0.1 M HCl, was around 85%, both values being higher than the desorption level of radiocations from the cross-linked CS, which were 89% and 83%, respectively.