Ion exchange properties of vermiculite characterized by sorption equilibria with major cations - CEA - Commissariat à l’énergie atomique et aux énergies alternatives Accéder directement au contenu
Communication Dans Un Congrès Année : 2023

Ion exchange properties of vermiculite characterized by sorption equilibria with major cations

Résumé

Clay minerals are abundant in geological formations and soils. Their chemical retention properties give them an important role in the behaviour of contaminants in soils. Among phyllosilicates, vermiculite is recognised as one of the main sorbents of caesium. To predict the bioavailability of such radionuclide in soils, knowledge of its sorption/desorption capability in soil-water systems is crucial. Nevertheless, cation adsorption/desorption depends on competition with surrounding cations in solution, especially major cations (H+, Na+, Ca2+, Mg2+ and K+). By characterising the retention properties of vermiculite by an ion exchange model, major cation exchange properties need to be determined to accurately describe the caesium behaviour in soil, in interaction with a multi-cation solutions. Major cation exchange data on vermiculite are only partially available to date. In the present study, ion exchange properties of vermiculite are described by using the multi-site ion exchanger model [1] to determine the exchange site capacities and the selectivity coefficients (H+/Mm+) of four major cations (Na+, Ca2+, Mg2+ and K+) found in natural waters. The exchange capacities of three major sorption sites have been previously determined experimentally on Ca-vermiculite, based on saturation curves, considering H+ as reference cation [2]. Here, pH-dependent saturation curves are carried out on a 5-10 µm size fraction of homoionic Ca or Na vermiculite in CaCl2 (4 10-2 mol.L-1) and NaCl (2 10-2 mol.L-1) solutions respectively, over a large pH range (3-11). pH-dependent adsorption isotherms of Ca and Na are performed using 45Ca and 22Na isotopes as tracers. The selectivity coefficients (H+/Mm+) are then determined by adjusting the ion exchange equations on experimental curves. As radioisotopes of K and Mg being not available, the saturation curves of K and Mg are obtained by exchange of Na/K and Na/Mg over a large pH range. The concentrations of Mg and K at equilibrium are analysed by ion chromatography. Adsorption isotherms of K and Mg associated with the Na desorption isotherms make it possible to constrain the model to determine the selectivity coefficients. Previously, it has been shown that high-selective and low-capacity sites control Cs uptake at concentrations below 10-8-10-7 mol.L-1 for both Ca-illite and Ca-vermiculite [2]. The Na+, Mg2+ and K+ selectivity coefficients for this minor site are determined on concentration isotherms at fixed pH. A Na concentration isotherm is acquired by exchange with Ca2+ on Ca-vermiculite in CaCl2 solution with Na concentration ranged between 10-8 and 10-2 mol.L-1. Isotherm concentrations of K and Mg are acquired by exchange with Na on Na-vermiculite in NaCl solution with K or Mg concentrations ranged between 10-6 and 10-2 mol.L-1. K and Mg in solution at equilibrium are analysed by ICP AES. The exchange capacity values of the three main sorption sites obtained for the four cations are compared with each other. The robustness of sorption sites capacities - which are an intrinsic property of the mineral - and selectivity coefficients determined for each cation is finally tested by modeling previous results obtained on the caesium adsorption data in multi-cation solutions on vermiculite [3]. [1]. Reinoso-Maset E., Ly J. (2014). Study of major ions sorption equilibria to characterize the ion exchange properties of kaolinite. Journal of Chemical & Engineering Data 59 (12), 4000-4009. [2]. Latrille C., Bildstein O. (2022). Cs selectivity and adsorption reversibility on Ca-illite and Ca-vermiculite. Chemosphere 288 (2), 132582. [3]. Dubus J., Léonhardt N., Latrille C. (2022). Multi-cation exchanges involved in cesium and potassium sorption mechanisms on vermiculite and micaceous structures. Environmental Science and Pollution Research, https://doi.org/10.1007/s11356-022-22321-4

Domaines

Géochimie
Fichier non déposé

Dates et versions

cea-04326268 , version 1 (06-12-2023)

Identifiants

  • HAL Id : cea-04326268 , version 1

Citer

Christelle Latrille. Ion exchange properties of vermiculite characterized by sorption equilibria with major cations. EUROCLAY 2023, Jul 2023, Bari, Italy. ⟨cea-04326268⟩
8 Consultations
0 Téléchargements

Partager

Gmail Facebook X LinkedIn More