Kinetics of uranyl ions sorption on heterogeneous smectite structure at pH4 and 6 using a continuous stirred flow-through reactor

Abstract The 2 2 + sorption experiments at pH 4 (1 × 10 − 4 ) and pH 6 (2.0 × 10 − 1 ) in a continuous stirred flow-through reactor. The aim was to evaluate the influence of heterogeneous structure of smectite during the adsorption and desorption processes, where the breakthrough curves (BTCs) were used to model the mass balance. Kinetic models were applied to describe the adsorption – desorption kinetics for a liquid-solid system. Sample PS2 (K-Illite/beidellite/Na,Ca-montmorillonite) adsorbed at pH 4 more 34% and 138% of UO 2 2 + than samples BA1 (beidellite/Ca,Na-montmorillonite) and PS3 (K-illite/Na,Ca-montmorillonite) where the dominant mechanism was the io n -exchange (outer-sphere complexation). The UO 2 2 + amount adsorbed at pH 6 decreased significantly, indicating changes in the sorption mechanism. The desorption experiments at pH 4 suggested a complete reversibility of the UO 2 2 + previously adsorbed, whereas lower reversibility of the UO 2 2 + previously adsorbed and a stronger complexation occurred at pH 6. The kinetics was highly influenced by the structural properties of heterogeneous smectite and the surface complexation mechanism involved. Samples submitted to sorption experiments at pH 4 and 6 were analysed by X-ray photoelectron spectrometry (XPS). Two binding energies were identified at 380.8 ± 0.3 eV and 382.4 ± 0.3 eV, before and after desorption processes at pH 4. The proportion of the higher binding energy component decreased after desorption process, suggesting that the UO 2 2 + weakly adsorbed was previously desorbed. The results obtained at pH 6 show two different binding energies at 380.3 ± 0.3 eV and 381.8 ± 0.3 eV, whose proportions remained unchanged before and after desorption process, indicating the higher retention of UO 2 2 + on smectite.