The effect of temperature and ionic strength on the diffusion of HTO parallel to the

direction of compaction through 5 highly compacted clay minerals (bulk dry

density, ρb,d = 1.90Mg/m3), namely montmorillonite (Na- and Ca-form), illite (Na

and Ca-form), and kaolinite, was studied. The diffusion experiments were carried

out at between 0 and 60C and at ionic strengths of 0.01M and 1M NaCl for the Naform

clays and kaolinite, and of 0.005M and 0.5M CaCl2 for the Ca-form. The

ionic strength had an insignificant influence on the values of the effective diffusion

coefficient (variation by less than 10%) for the clays under study at this degree of

compaction. The effective diffusion coefficients followed the order Namontmorillonite

< Ca-montmorillonite < Ca-illite < Na-illite ≤ kaolinite. It was

thought that the differences between Na- and Ca-montmorillonite originate from

the larger size particles, and thus the lower tortuosity of the latter; whereas the

differences between Na- and Ca-illite were related to the different degree of

solvation of the Na and Ca cations. The activation energies were successfully

calculated using the Arrhenius law. Swelling clays (Na- and Ca-montmorillonite)

had slightly larger activation energy values (20kJ/mol) compared to bulk water

(17kJ/mol); Ca-illite (16kJ/mol), Na-illite (13kJ/mol) and kaolinite (14.4kJ/mol)

lower values than that of bulk water. The low activation energies of the last three

clays may be related to weaker H-bonds between water and the clay surfaces

compared to those in bulk water.

Self-Diffusion of Water and Its Dependence on Temperature and Ionic Strength in

Highly Compacted Montmorillonite, Illite and Kaolinite. F.G.Sánchez, L.R.Van

Loon, T.Gimmi, A.Jakob, M.A.Glaus, L.W.Diamond: Applied Geochemistry,

2008, 23[12], 3840-51