Influence of cations and low molecular weight organic acids on Cs(I) adsorption on montmorillonite and vermiculite

Abstract

To predict the mobility of radiocesium (RCs) in the environment, it is essential to understand the adsorption and desorption processes. In this study, we focused on the effects of certain environmental factors, including typical cations (K+, Na+, and NH4+) and low molecular weight organic acids (LMWOAs) such as acetic acid, malic acid, and citric acid on the behavior of RCs on montmorillonite and vermiculite. The results showed that montmorillonite possesses the strongest adsorption capacity for Cs+ than that of vermiculite. Since K+ and NH4+ exhibit similar physicochemical properties to Cs+, there is a significant inhibition of Cs+ adsorption on montmorillonite and vermiculite during the competitive interaction with K+ and NH4+. Compared to NH4Cl, the desorption ratios of Cs+ on montmorillonite and vermiculite are higher in the presence of KCl as the background solution. Low molecular weight organic acids can cover the surfaces of montmorillonite and vermiculite to different extents, which effectively blocks the adsorption sites for Cs+, and leads to an obvious decrease in the adsorption and desorption of Cs+. Due to the high expandable performance, Cs+ is primarily reversibly adsorbed by montmorillonite. Nevertheless, the adsorption of Cs+ on vermiculite exhibits typical irreversible characteristics due to the interlayer collapse. After the adsorption of LMWOAs on montmorillonite and vermiculite, the irreversible adsorption of Cs+ is increased obviously, mainly due to the blocking effect of organic matters on the adsorption sites with high affinity to Cs+.