The evolution of textural properties of Na/Ca-bentonite following hydrothermal treatment at 80 and 300ºC in the presence of Fe and/or Fe oxides A. NEAMAN 1 , D. GUILLAUME 2 , M. PELLETIER 1 AND F. VILLIE ´ RAS 1, * 1 Laboratoire Environnement et Mine ´ralurgie (LEM), Ecole Nationale Supe ´rieure de Ge ´ologie, UMR 7569 CNRS- INPL, BP 40, 54501, Vandoeuvre-le `s-Nancy, France, and 2 Ge ´ologie et Gestion des Ressources Mine ´rales et Energe ´tiques (G2R), Universite ´ Henri Poincare ´, UMR 7566 CNRS-UHP-INPL-CREGU, BP 239, 54506, Vandoeuvre- le `s-Nancy, France (Received 15 February 2002; revised 20 November 2002) ABST RACT: The evolution of textural properties of Na/Ca-bentonite from Wyoming (MX-80) was studied by adsorption of nitrogen, water vapour, and ethylene glycol monoethyl ether. Clay suspensions were heated at 80 and 300ºC for up to 9 months in the absence of or in the presence of Fe and/or Feoxides. The treatment without Fe did not change the textural properties of the samples significantly. The treatment at 80ºC in the presence of Fe resulted in a considerable increase in the external surface areas of the samples. The total and external surface areas and swelling capacities of the samples decreased following the treatment at 300ºC in the presence of Fe and Fe oxides. In the case of larger additions of Fe, the treatment at 300ºC resulted in a considerable decrease in the total and external surface areas and swelling capacity of the sample and in the formation of anetwork of large-size pores, in which all the pores were connected. KEYWORDS: textural properties, bentonite, MX-80, nitrogen adsorption, water vapour adsorption, EGME adsorption. Bentonites are frequently recommended as backfill materials associated with the construction of high- level nuclear waste repositories (Madsen, 1998). Bentonites are suitable as a backfill because of their ability to swell, their low hydraulic conductivity when compacted to high density and their high sorption capacity. Some of concepts for disposal of high-level radioactive wastes foresee emplacing steel canisters containing the waste in a tunnel which will be backfilled with compacted bentonite (Madsen, 1998). To this end, the interactions between the bentonite and the container corrosion products are of particular interest. Few data are available on the hydrothermal stability of smectites in the presence of Fe and/or Fe oxides. Madsen (1998) reviewed clay miner- alogical investigations related to nuclear waste disposal. In particular, he mentioned a study by Mu ¨ller-Vonmoos et al. (1991) on hydrothermal reactivity of bentonite samples in the presence of Fe and magnetite powders at 80ºC for up to 29 weeks. No changes in the mineralogy, interlayer charge and cation exchange capacity (CEC) of the samples were detected. The experiments in the presence of the Fe powder resulted in a minor increase in the the Fe content in the exchangeable positions. No change in the composition of exchangeable cations was observed, however, in experiments using magnetite powder. * E-mail: frederic.villieras@ensg.inpl-nancy.fr DOI: 10.1180/0009855033820090 Clay Minerals (2003) 38, 213–223 # 2003 The Mineralogical Society