Transport properties of compact clays. II. Diffusion

Area of Science:

• Geochemistry
• Materials Science
• Physical Chemistry

Background:

• Understanding solute transport in porous media is crucial for environmental and geological applications.
• Porous media properties significantly influence diffusion processes.
• Existing models require validation across diverse materials and conditions.

Purpose of the Study:

• To experimentally determine the diffusion coefficient in various porous media.
• To investigate the impact of salt concentration and porosity on diffusion.
• To compare diffusion and electric formation factors.

Main Methods:

• Construction of an experimental system for diffusion coefficient measurement.
• Utilizing mica, sodic montmorillonite, and natural compact clay as porous media.
• Employing various salt concentrations and studying porosity effects.

Main Results:

• Diffusion coefficients were measured across different porous media and salt concentrations.
• Results were approximated by Archie's law, showing independence from clay type and solute.
• Diffusion and electric formation factors showed agreement at high porosities but disagreement at low porosities for clay and montmorillonite.

Conclusions:

• Archie's law provides a useful approximation for diffusion in these porous media.
• Porosity plays a critical role in the relationship between diffusion and electrical transport.
• Discrepancies at low porosities highlight the complexity of ion transport in clays.