Kinetic and thermodynamic investigations of strontium ions retention by natural kaolinite and clinoptilolite minerals

Abstract

Sr2+ / Sorption / Kaolinite / Clinoptilolite Summary. The current study was devoted to the determination of various thermodynamic and kinetic parameters resulting from the fixation of Sr 2+ by natural samples of kaolinite and clinoptilolite minerals. The sorption process followed pseudo second order kinetics, with faster sorption on kaolinite compared to clinoptilolite, where the uptake is affected by intraparticle diffusion. Freundlich and Dubinin-Radushkevich isotherm models described the data more adequately than Langmuir model, and clinoptilolite showed a higher strontium sorption capacity than kaolinite. Thermodynamically, the activation energy of Sr 2+ sorption by kaolinite and clinoptilolite were respectively, −8.5 and −18.4 kJ/mol. The sorption process on both minerals was spontaneous and endothermic at all the studied concentrations, with ∆H• being 11.3 and 9.8 kJ/mol, for sorption on kaolinite and clinoptilolite, respectively. The findings of this study were compared with those of an earlier study on the uptake of Cs + by the same minerals.

A characterization study of some aspects of the adsorption of aqueous Co2+ ions on a natural bentonite clay

“…Hence for the intrinsic sorption reaction to take place, the cation must first undergo partial dehydration in a way that facilitates its migration through the solution to the sites on the sorbent. Based on this and depending on some of our earlier studies, we may conclude, as a first approximation, that cations with relatively low hydration enthalpies (low charge/size ratio, e.g., Cs + ) will demonstrate observed exothermic sorption behavior [12], while cations of higher charge/size ratio (e.g., Sr 2+ , Co 2+ ) will generally show observed endothermic sorption behavior [4,10]. Based on the above statements, the values of H o int could essentially be greater in magnitude than the reported values of H o obs .…”

“…The entropy change of the system accompanying the fixation of Co 2+ by bentonite comes out as positive, indicating that more disorder is generated in the system upon sorption. The increase in the disorder upon sorption was discussed in an earlier study [10]. The positive value of H o marks the endothermic nature of sorption, i.e., that higher temperatures are favored for enhanced removal of Co 2+ ions by bentonite.…”

Geochemical and thermodynamic aspects of sorption of strontium on kaolinite dominated clay samples at Kalpakkam

“…Similar endothermic sorption process for Sr 2? on clay was reported by Akar et al (2005) and Bascetin and Atun (2006). The negative values obtained for DG 0 shows the spontaneous nature of the sorption process.…”

“…On the other hand, Adeleye et al (1994) reported that the behavior of caesium, strontium and europium in batch sorption experiments with kaolinite and other clays is best characterized by the Freundlich-type. Akar et al (2005) also observed that the Freundlich and DubininRadushkevich isotherm models provided better fit than the Langmuir model for strontium ions sorption by natural kaolinite and clinoptilolite minerals. Hence, it is inferred from the literature that the type of adsorption isotherm is dependent on the nature of the clay.…”

Sorption of radioactive cesium and barium ions onto solid humic acid

“…There is a large difference in hydration enthalpies, being −276 kJ/mol for Cs + and −1305 kJ/mol for Ba 2+ ions. In the literature [20], it is reported that metal ions with high hydration energies are well solvated in water and for cations that are solvated well in water, sorption requires that such ions should be stripped to a certain extent of their hydration shell which is a process that requires energy input. If this dehydration energy exceeds the exothermicity associated with the sorption of a metal ion on a solid, then the overall energy balance will lead to an endothermic behavior.…”