Adsorption characteristics of UO 22+ and Th 4+ ions from simulated radioactive solutions onto chitosan/clinoptilolite sorbents

Abstract

Adsorption features of UO 2 2+ and Th 4+ 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 Th 4+/g composite, and 408.62 mg UO 2 2+/g composite. The overall adsorption tendency of CS/CPL composite toward UO 2 2+ and Th 4+ radiocations in the presence of Cu 2+, Fe 2+ and Al 3+, under competitive conditions, followed the order: Cu 2+ > UO 2 2+ > Fe 2+ > Al 3+, and Cu 2+ > Th 4+ > Fe 2+ > Al 3+, 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 UO 2 2+ from the composite CS/CPL, by using 0.1 M Na 2CO 3, was around 92%, and that of Th 4+ 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.