Effect of dry density on Sr-90 diffusion in a compacted Ca-bentonite for a backfill of radioactive waste repository

How Mobile Are Sorbed Cations in Clays and Clay Rocks?

“…[1][2][3] An intriguing observation has been made for many cationic contaminants at trace concentrations: Often, sorbing cations seem to diffuse at rates larger than predicted from their sorption coefficients and from the diffusive flux of nonsorbing water tracers. 1,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] This increased solute flux was often attributed, without proof, to surface diffusion, that is, movement of sorbed cations along the clay surfaces. 5,10,14,19,20 There is, however, no agreement about the existence and the importance of this phenomenon.…”

“…For the same reasons, clay rocks are envisaged in many countries as potential host rocks for the disposal of radioactive waste. Their transport properties are investigated at different scales. − An intriguing observation has been made for many cationic contaminants at trace concentrations: Often, sorbing cations seem to diffuse at rates larger than predicted from their sorption coefficients and from the diffusive flux of nonsorbing water tracers. ,− This increased solute flux was often attributed, without proof, to surface diffusion, that is, movement of sorbed cations along the clay surfaces. ,,,, There is, however, no agreement about the existence and the importance of this phenomenon. It was for instance concluded that surface diffusion is important for Sr and Am, but not for Cs in London Clay and sandstone, unimportant for Cs in dense clays, unimportant for Na, Sr, and Ca in compacted clays for clay bulk densities up to 1.6 Mg m −3 , or important for Cs, but not for Na and Sr in Opalinus Clay …”

Laboratory Experiments on Bentonite Samples: FY15 Progress

“…with regard to cationic, anionic and neutral species, in a given system). ) (Muurinen et al, 1986;Sato et al, 1992;Kozaki et al, 1996Kozaki et al, , 1998aChoi and Oscarson, 1996;Kozaki et al, 1999a;b, 2001, 2008Lee et al, 1996;Nakajima et al, 1997;Nakashima, 2000Nakashima, , 2002Nakashima, , 2003Nakashima, , 2006Molera, 2002;Molera and Eriksen, 2002;Molera et al, 2003;Sato and Suzuki, 2003;Van Loon et al, 2003a;b, 2004a;b, 2005a;b, 2007;Wang, 2003;Jansson and Eriksen, 2004;García-Gutiérrez et al, 2004;Sato and Miyamoto, 2004;Suzuki et al, 2004;García-Gutiérrez et al, 2009;Wang and Liu, 2004;Wang and Tao, 2004;Melkior et al, 2005Melkior et al, , 2007Melkior et al, , 2009Nakashima and Mitsumori, 2005;Wang et al, 2005;Appelo and Wersin, 2007;Glaus et al, 2011Glaus et al, , 2013Motellier et al, 2007;Glaus et al, 2007Glaus et al, , 2008Glaus et al, , 2010…”