Alteration of clay minerals—gamma-irradiation effects on physicochemical properties M. Plo ¨tze * , G. Kahr, R. Hermanns Stengele Swiss Federal Institute of Technology, Division of Geotechnical Engineering, Group Environmental Geotechnics and Clay Mineralogy, 8093 Zu ¨rich, Switzerland Abstract In the present work, the influence of gamma-irradiation (1.1 MGy, 60 Co) on physicochemical parameters (‘‘crystallinity’’, specific surface, cation exchange capacity, main layer charge) of various clay minerals (montmorillonite, illite and samples of the serpentine – kaolin group) were investigated. The influence of gamma-irradiation on the physicochemical properties is generally weak. A reduction of lattice iron during irradiation could be measured, which causes decreasing values of cation exchange capacity (CEC) and main layer charge of the smectites. Aweak loss of ‘‘crystallinity’’ of kaolinite could be observed. The results show that the structure of clay minerals is stable even at high gamma-irradiation doses. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Irradiation; Clay minerals; Physicochemical properties 1. Introduction The long-term disposal of radioactive waste rep- resents an important and at this time, again a current problem. Special problems arise from the extremely high radiation level even for tens of years after disposal, the substantial heat generation over a long period of time and the formation of radioactive and harmful fission products with their own geochemical behaviour. The long-term containment (1000 – 10 000 years) should prevent from radiation additional to the natural background. There are several concepts of radioactive waste containment. Clay barriers with highly compacted bentonite play a key role in these concepts. The safety and long-term performance of underground permanent repositories rely on a combination of several engineered and geological barriers. Different processes of bentonite buffer alter- ation and their influence on physicochemical proper- ties of the buffer material were described in minera- logical and geotechnical investigations related to nuclear waste disposal (e.g. Madsen, 1998; Plo ¨tze et al., 2002). Presently, the influence of high-level ionizing radiation on the crystal structure and on physicochemical properties of clay minerals is insuf- ficiently investigated. 1.1. Radiation level The emplacement of high-level nuclear waste in a deep geological repository will expose the environ- 0169-1317/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0169-1317(03)00103-0 * Corresponding author. ETH Zu ¨rich, CH-8093 Zu ¨rich, Swit- zerland. Fax: +41-1-6331079. E-mail address: michael.ploetze@ethz.ch (M. Plo ¨tze). www.elsevier.com/locate/clay Applied Clay Science 23 (2003) 195 – 202