Modelling and prediction of the Cs and Sr adsorption into French soils

Autor: Siroux, B.
Přispěvatelé: amplexor, amplexor, CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)
Jazyk: angličtina
Rok vydání: 2017
Předmět:
Zdroj: 4th International Conference on Radioecology and Environmental Radioactivity
4th International Conference on Radioecology and Environmental Radioactivity, Sep 2017, Berlin, Germany
Popis: International audience; This study is part of the French project DEMETERRES (PIA), which aims at developing innovative methods and technologies in the field of decontamination and remediation of contaminated soils and effluents. Cesium and strontium are two major by-products of the fission of uranium. They are well known to interact strongly and specifically with clay minerals. Thus in this study, the adsorption of these elements in soils was approximated to their adsorption in clay minerals. The first part of this study was to build a coherent thermodynamic databasis in the framework of a model based on the multi-site ion exchange theory (REINOSO-MASET et LY, 2014). It was created from collection and reinterpretation of available experimental data from the literature and from dedicated experiments for those missing or hardly exploitable. To be efficient in French environmental conditions, this databasis was focused on illite and smectite (the two major clay minerals in French agricultural soils) and it was built to be able to predict the behaviours of Cs+ and Sr2+ under Na- and Ca- conditions (the major elements in soils). Described as multi-site ion exchangers, clay minerals are characterized by their different site concentrations and corrected selectivity coefficients (major/proton and trace metal/major). Once completed, the predictability and the efficiency of the model and the databasis were tested on adsorption experiments of Cs and Sr on (i) illite/smectite mixtures and (ii) real soils samples. As the simulations are based on the additivity principle between several reactive phases, the adsorption of Cs and Sr onto illite / smectite mixtures was first tested. These experiments were performed on Na-clay minerals at I = 0.1 M and pH = 7. The predictions of Sr adsorption were satisfactory on the different illite/smectite mixtures. In the case of Cs, predictions are less satisfactory, especially at higher concentrations, but the fair agreements between simulations and experiments seem to confirm the hypothesis of additivity and comfort us on the model and the databasis. They were afterwards confronted with real environmental soil samples. Three samples of soils were collected near French nuclear facilities. Sr and Cs concentration isotherms were performed in 0.033 M CaCl2 solutions. To facilitate simulations, the mineralogical compositions of the samples were approximated to illite/smectite mixtures based on the soils analyses (CEC analysis and DRX). In most cases, simulations are in agreement with the experimental results. Even if these first results were promising, parameters of simulation could be improved. In this study, soils were considering as Ca saturated but taking the other minor exchangeable elements (Na+, K+, Mg2+, Al3+, etc.) could ameliorate these simulations. Moreover, the role of natural organic matter hasn't been taking into consideration although it could intervene in sorption phenomena (especially for Cs) (DUMAT et STAUNTON, 1999, SAMADFAM et al., 2000). The addition of these parameters must be a way to ameliorate the predictive efficiency of this modelling. Dumat C. et Staunton S. 1999 Reduced adsorption of caesium on clay minerals caused by various humic substances. J. Environ. Radioact. 46, 187-200.Reinoso-Maset E. et Ly J. 2014 Study of Major Ions Sorption Equilibria To Characterize the Ion Exchange Properties of Kaolinite. J. Chem. Engin. Data 59, 4000-4009.Samadfam M., Jintoku T., Sato S., et Ohashi H. 2000 Effect of humic acid on the sorption of Sr(II) on kaolinite. J. Nucl. Sci. Technol. 37, 180-185.
Databáze: OpenAIRE
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