Do you want to talk about D the effective diffusion coefficient of the dissolved constituent in the fluid of the rock matrix? If this is indeed it, then:

The effective diffusion coefficient, D, is dependent on the diffusion coefficient of the dissolved constituent in water and the pore structure of the rock matrix:

D = Phi x Dd

where Dd is the free-water diffusion coefficient of the dissolved constituent and Phi is the formation factor that scales the free-water diffusion coefficient to account for diffusion in the tortuous pore structure of the rock matrix.

The formation factor is a dimensionless term that is less than 1 and can range over several orders of magnitude, depending on the type of rock under consideration (Novakowski and Van der Kamp 1996).

Regards

Dear Dr. Achour,

Thank you for the answer. Indeed I was looking for effective diffusion coefficient.

However, now I winder how two determine the Dd, which is the free-water diffusion coefficient of the dissolved constituent.

Also, I am sorry for my limited knowledge in this field.

Best Regards

Amar

Dear Amar,

The free-water diffusion coefficient for the dissolved constituent under consideration is generally known because it is given by the literature according to the type of dissolved constituent.

Regards