Experimental study of multicomponent diffusion in low permeable sediments

Diffusion coefficients for Na+ and distribution coefficients for Cs+, Ba2+, Ni2+, CO2+, Sr2+ were measured on low permeable samples (3 cm diameter, average length 7 cm) from the deep disposal site Siberian Chemical Combine (SSC) using the end-diffusion technique. The direction of diffusion was perpendicular to bedding. Special equipment for experiment were designed and constructed. Two types of concentration observation were used. For non-sorbing Na+ in time used EC sensors and length distribution of sorbed elements. The synthetic solution used in the experiments was a model of low-activity contaminant of the SSC, and consist NaNO3 (25 g/l) and nitrate compounds: Cs+, Ba2+, Ni2+, Co2+, Sr2+ (100 mg/l each). The measured values of the effective diffusion coefficients De) for Na+ from 7.60×10-7 to 1.51×10-5 m2/day and volumetric dimensionless distribution coefficients (Kdρ) are: Cs+ from 0.21 to 22.1, Ba2+ from 1.1 to 1.45, Ni2+ from 0.3 to 16.4, Co2+ from 1.98 to 24.7, Sr2+ from 1.9 to 14.3. The values of the diffusion coefficient show a large degree of variability. The diffusion coefficients of non-sorbing Na+ measured in this study are in good agreement with pore-scale diffusion simulation on microtomography data.