Effect of ionic strength on the transport parameters of tritiated water, iodide and H14CO3- in Boom Clay

The possible disposal of radioactive waste in Boom Clay will generate perturbations, which can affect the transport parameters values. After NaNO3 leaching from bituminized waste, the ionic strength of the Boom Clay porewater will increase, compressing the electrical double layer and resulting in a higher diffusion accessible porosity  of anions. Migration experiments are performed with tritiated water (HTO), iodide and H14CO3- in Boom Clay cores, equilibrated with porewater at four different ionic strengths (Boom Clay porewater, 0.1M, 0.5M and 1.0M). As expected, for HTO the values of R (with R the retardation factor) do not depend on ionic strength, with an average value between 0.38 and 0.40. The average R value of iodide increases with ionic strength: from 0.17 for Boom Clay porewater to 0.28 at 1.0 M. The same trend is observed for H14CO3-. For titriated water and iodide, the retardation factor is supposed to be one. The R values for H14CO3- at 0.5 M and 1.0 M (respectively 0.49 and 0.56), being higher than for tritiated water, can only be explained by a slight retardation (R > 1). The anistropy of the dispersion coefficients is around 2.8.