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

Abstract

Many studies have shown that the adsorption of ions like K+ and Cs+ on 2:1 clay minerals can prompt the collapse of their interlayers and render the adsorbing ions nonexchangeable. This study sought to better understand this unique adsorption mechanism through the generation of an adsorption envelope for 133Cs adsorption on vermiculite and the exploration of the kinetics of interlayer collapse. The collapse of the vermiculite interlayer was confirmed via X‐ray diffraction (XRD), and the timing of interlayer collapse was determined by placing Cs+ in competition with K+ at different time intervals. The adsorption envelope for Cs+ on vermiculite showed that although H+ competition does affect the adsorption of Cs+ on vermiculite, the effect of this competition is quite limited, even at very low pH values. This hypothesis is supported by the fact that XRD demonstrated a significant decrease in interlayer dimension after Cs+ adsorption. Finally, kinetics experiments showed that the irreversible adsorption of K+ and the collapse of the interlayer may take place on a much longer time scale than previously considered. Core Ideas Cesium adsorbs extremely strongly on vermiculite, even at very low pH. Cesium adsorption collapses vermiculite's interlayer by >63% to ∼1.1 Å. Attempts to quantify vermiculite interlayer collapse by K+ gave conflicting results.

Cycling Stability of Calcium-Impregnated Vermiculite in Open Reactor Used as a Thermochemical Storage Material

“…However, the same is not seen for the counter ion (chloride), as levels show no statistical change and are at a consistent level (RSD < 15% for repeat analysis) over the course of the trial (Figure 7). It is postulated that the calcium ions are not lost from the material, as a decrease in chloride content would also be apparent, but calcium may in fact stabilize within the vermiculite structure over successive cycles, by binding or chelating to the structure, making it less likely to leach out [28][29][30][31][32]. Whereby the chloride ions remain free to dissolute and are less tightly bound.…”

Soil Chemistry and the One Health Initiative: Introduction to the Special Section

“…This study demonstrates how ecosystem health can be part of the risk assessment process in evaluating management regimes for rights-of-way. Ferreira et al (2018) investigated the influence of pH on Cs adsorption to vermiculite and the interlayer collapse on Cs adsorption. Radioactive 137 Cs is a primary isotope released from nuclear power plant incidents and contaminates the soil in the regions affected by a nuclear accident.…”