Evidence of a critical content in Fe(0) on FoCa7 bentonite reactivity at 80 °C

M. Perronnet (1, 2, 3) , M. Jullien (2) , F. Villiéras (1) , J. Raynal (2) , D. Bonnin (4) , G. Bruno (5)

1 LEM - Laboratoire Environnement et Minéralurgie
2 LMTE - Laboratoire de Modélisation des Transferts dans l'Environnement
3 NASA, Lyndon B. Johnson Space Center ES3, Houston, Texas 77058
4 Laboratoire de Physique Quantique, Ecole Supérieure de Physique et Chimie Industrielle
5 IRSN - Institut de Radioprotection et de Sûreté Nucléaire

In order to assess the evolution of the confinement properties of clay engineered barriers (EBS) when in contact with metallic canisters containing radioactive wastes, Fe(0)-bentonite interactions need to be assessed. "45 days-80 °C" tests were performed using powdered FoCa7 bentonite and metallic iron. Since one fundamental parameter may be the available quantity of Fe(0), a wide range of Iron/Clay mass ratios (I/C) from 0 to 1/3 is used. The confinement power of clay material results from the swelling properties and the retention capacity. Thus, the major criterion which is chosen to assess the evolution of the confinement properties in this study is the variation of Cation Exchange Capacity (CEC). In parallel, the physico-chemical evolution of bentonite is studied using XRD and EDS-TEM microanalyses. The evolution of the distribution of iron environments is obtained by 57Fe Mössbauer spectroscopy. This study evidences that both kaolinite and smectite from the bentonite are altered into SiAlFe gels when in contact with Fe(0). These gels maturates into Fe-rich di-trioctahedral phyllosilicates, whose composition is bounded by the one of odinite and greenalite in a Fe-M+-4Si diagram when I/C = 1/3. Most of all, it is evidenced that the reaction depends on the available quantity of Fe(0). When the I/C ratio is between 1/30 and 1/7.5, the exchange capacity of FoCa7 bentonite starts decreasing, the consumption of Fe(0) becomes significant, the alteration of smectites occurs and secondary oxides are formed. The crystallization of Fe-rich phyllosilicates is observable when I/C ratio is higher, from a threshold between 1/7.5 and 1/5. Above I/C = 1/3.75, initial iron oxides are strongly consumed and participate in the incorporation of Fe2+ and Fe3+ in gels or new phyllosilicates octahedra. These experimental results were used as input data for the prediction of the long-term evolution of the EBS using Crunch reaction-transport model. © 2007 Elsevier B.V. All rights reserved.

Mots clés: Bentonite; Crystallization; Energy dispersive spectroscopy; Ion exchange; Iron; Mathematical models; Mossbauer spectroscopy; Transmission electron microscopy; X ray diffraction analysis; Bentonite reactivity; Cation exchange capacity (CEC); Iron-clay mass ratio; Metallic iron; Smectite; Clay minerals; bentonite; crystallization; kaolinite; phyllosilicate; physicochemical property; radioactive waste; smectite; transmission electron microscopy; X-ray diffraction

Domaines: Chimie

M. Perronnet, M. Jullien, F. Villiéras, J. Raynal, D. Bonnin, et al.. Evidence of a critical content in Fe(0) on FoCa7 bentonite reactivity at 80 °C. Applied Clay Science, 2008, 38 (3-4), pp.187-202. ⟨10.1016/j.clay.2007.03.002⟩. ⟨hal-03001452⟩