The use of X-ray CT to measure diffusion coefficients of heavy ions in water-saturated porous media

X-ray computerized tomography (CT) was applied for the first time to the measurement of diffusion coefficients of heavy ions in water-saturated clay and rock. The mass absorption coefficient of X-rays is high for heavy elements. Thus the migration of heavy ions in the porous samples was measured by the spatio-temporal change in intensity of X-ray CT images. The measurements of diffusion coefficients of I− in bulk water, synthesized saponite (96.6 wt% H2O) and rhyolitic lava (porosity 24%) were demonstrated successfully. The one-dimensional transient migration of I− was imaged by a medical X-ray CT scanner with an in-plane resolution of 0.31 mm. The measured I− diffusivity in bulk water agreed well with that of the literature. Because non-destructive, quick and three-dimensional data acquisition is possible, X-ray CT has advantages over conventional methods for laboratory experiments on heavy-element diffusion in porous media.