Nature of the sites involved in the process of cesium desorption from vermiculite

Abstract

Three particle size fractions of sodium-saturated vermiculite (10-20, 1-2 and 0.1-0.2 μm), differing only in their ratios of external-to-total sorption sites, were used to probe the nature of the sites involved in desorption of cesium ions. The sorption was investigated for initial aqueous concentrations of cesium ranging from 5.6×10(-4) to 1.3×10(-2) mol/L, and the cesium desorption was probed by exchange with ammonium ions. The results showed that (1) the amounts of desorbed cesium were strongly dependent on the particle size for a given initial aqueous cesium concentration and (2) the amounts of desorbed cations (Na(+) and Cs(+)) strongly decreased with increasing initial cesium aqueous concentration, irrespective of the particle size investigated. Quantitative analysis of these results suggested that cesium ions sorbed on external (edge+basal) sorption sites can be desorbed by ammonium ions. As a contrast, most of cesium ions sorbed on interlayer sites remain fixed due to the collapse of the structure under aqueous conditions. This study provides important information, such as the nature of the sites involved in the exchange process, when the thermodynamic formalism is considered to describe the ion-exchange process involving cesium and high-charge swelling clay minerals in polluted soil environments.

Molecular dynamics simulations of cesium adsorption on illite nanoparticles

“…Recent efforts have deployed a combination of wet chemistry experiments [102,4,26], high-resolution imaging [47,63,95,34], synchrotron Xray spectroscopy [29,42], and atomistic-level simulations [68,93,44,107] to gain detailed insight into Cs adsorption mechanisms, selectivity, and kinetics. The emerging view from these studies is that Cs adsorption involves at least three types of surface sites: basal sites located on the external basal surfaces of illite particles, slow sites located in anhydrous illite interlayers, and high affinity sites of unclear nature.…”

Adsorption of strontium and caesium onto an Na-illite and Na-illite/Na-smectite mixtures: Implementation and application of a multi-site ion-exchange model

“…As clay minerals bear structural negative surface charges, the adsorption of cation, as Sr 2+ and Cs + , is facilitated. The adsorption of these radionuclides onto clay minerals, such as bentonite (Galamboš et al, 2013;Montavon et al, 2006), illite (Fuller et al, 2015;Mahoney and Langmuir, 1991), kaolinite (Chen et al, 2015;Erten et al, 1988;Reinoso-Maset and Ly, 2014) or vermiculite (Dzene et al, 2015;Long et al, 2014), has been extensively studied in the literature. Illite is especially referenced as the major adsorbent for Cs + onto strong affinity low concentration sites, referred as frayed edge sites (Brouwer et al, 1983;Cremers et al, 1988;Sawhney, 1972).…”

The Impact of pH and Ion Exchange on 133Cs Adsorption on Vermiculite

“…Once adsorbed inside the collapsed 2:1 clay interlayer, the small dimension prevents other ions from easily entering and desorbing the Cs through traditional ion exchange. At this point, the Cs becomes nonexchangeable (Comans and Hockley, 1992) and cannot easily be removed from the mineral or the soil containing it (Dzene et al, 2015), since the strongly adsorbed Cs + ions keep the interlayer collapsed around them and the collapsed interlayer keeps the Cs + ions inaccessible.…”