Matrix Diffusion and Transport Properties in Crystalline Rocks

Matrix diffusion and transport properties in crystalline rocks govern the movement of fluids and dissolved species within low‐permeability rock matrices that surround high‐permeability fractures. In crystalline formations such as granites and gneisses, connected pore networks are often submicrometre in scale, resulting in slow diffusive exchange compared with advective flow in fractures. Matrix diffusion refers to the process by which solutes migrate from fractures into the rock matrix via molecular diffusion, thereby attenuating and tailing solute pulses. Transport properties are quantified by porosity (the volume fraction of pore space), tortuosity (the complexity of pore pathways), effective diffusion coefficients (which integrate porosity and tortuosity effects) and sorption parameters, such as distribution coefficients that describe reversible binding to mineral surfaces.

These parameters underpin safety assessments for deep geological disposal of radioactive waste, where radionuclide migration must be predicted over geological timescales. Beyond waste management, insights into matrix diffusion inform groundwater resource evaluation, geothermal energy extraction and contaminant remediation in fractured crystalline aquifers. Advances in imaging techniques—such as autoradiography and X-ray tomography—paired with refined laboratory experiments (including electromigration cells) and multi-dimensional advection–dispersion modelling have improved quantification of how mineral heterogeneity, alteration zones and pore connectivity influence solute transport. Integration of empirical data with numerical models now enables more reliable predictions of long-term solute behaviour in complex crystalline environments.

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Matrix Diffusion and Transport Properties in Crystalline Rocks publication trend

The graph below shows the total number of articles in matrix diffusion and transport properties in crystalline rocks across all publications each year (not limited to Nature Index journals).

Technical terms

Matrix diffusion: Exchange of solutes between fractures and adjacent low-permeability rock matrix by molecular diffusion.

Effective diffusion coefficient (De): Bulk diffusion rate in the rock matrix, accounting for porosity and tortuosity.

Porosity: Fraction of rock volume occupied by connected pore space through which fluids can move.

Sorption (distribution coefficient, Kd): Process and parameter describing reversible adherence of solutes to mineral surfaces.

Advection: Transport of solutes by bulk fluid flow through fractures or pore channels.

Breakthrough curve: Plot of solute concentration over time at an observation point, used to characterise transport behaviour.

Tortuosity: Measure of the complexity of pore pathways relative to straight-line distance, affecting diffusion path length.

References

1. Electromigration experiments for studying transport parameters and sorption of cesium and strontium on intact crystalline rock. Journal of Contaminant Hydrology (2018).
2. Comparison of phosphor screen autoradiography and micro-pattern gas detector based autoradiography for the porosity of altered rocks. Scientific Reports (2020).
3. Sorption behavior of Sr(II) in granitic rock: the effect of MX-80 bentonite colloids. Journal of Radioanalytical and Nuclear Chemistry (2023).
4. Solving Diffusion Time in Heterogeneous Microscale Rock Matrix by 3D Computations: Non-Fickian Dispersion Observed in Porous Media. Journal of Geoscience and Environment Protection (2019).
5. Modeling of a radionuclide transport experiment in granitic rock matrix at the Grimsel Test Site (Switzerland). The role of advection.. Applied Geochemistry (2024).
6. Radium sorption on crystalline rock; spatial distribution and sorption modeling study. Applied Geochemistry (2024).