Skip to main content Accessibility help

Avoiding unrealistic behaviour in coupled reactive-transport simulations of cation exchange and mineral kinetics in clays

  • Steven Benbow (a1), James Wilson (a1), Richard Metcalfe (a1) and Jarmo Lehikoinen (a2)


Bentonite clay is often included as a buffer, backfill and/or sealing material in designs for deep geological repositories for radioactive wastes. It is expected that bentonite materials may undergo some mineralogical alteration as they interact with in situ groundwaters over long timescales on the order of thousands to millions of years. Long-term modelling of these materials is therefore important in order to demonstrate confidence that the engineered designs will continue to perform as required over their intended lifetimes (required assessment timescales can be up to 1 million years). The key geochemical processes that must be considered in such modelling are mineral dissolution and precipitation and cation exchange. These processes are expected to occur simultaneously and so modelling of their coupled effects and their rates (kinetics) is necessary. Illustrative reactive-transport models of the geochemical alteration of montmorillonite (the primary mineral in bentonite exhibiting cation exchange) are presented which demonstrate that one possible approach to fully coupling cation exchange and clay mineral dissolution kinetics, referred to here as the ‘all-component coupling’ approach, may lead to unrealistic behaviour due to feedback that may occur in the formulation. This feedback can be avoided if a ‘common-component’ conceptual model for the dissolution of exchanger end members is adopted, where only the saturation of the exchanger ‘structural unit’ is considered when evaluating the potential for dissolution of the mineral. Such considerations have been proposed historically in stability analyses for montmorillonite, but have not been explored widely in the modelling literature.


Corresponding author


Hide All

Associate Editor: Chris Greenwell



Hide All
Appelo, C.A.J. & Postma, D. (2005) Geochemistry, Groundwater and Pollution, 2nd edition. A. A. Balkema Publishers, Amsterdam, The Netherlands.
Bankole, O., El Albani, A., Meunier, A., Pambo, F., Paquette, J.-L. & Bekker, A. (2018) Earth's oldest preserved K-bentonites in the ca. 2.1 Ga Francevillian Basin, Gabon. American Journal of Science, 318, 409434.
Bethke, C.M. (2008) Geochemical and Biogeochemical Reaction Modelling. Cambridge University Press, Cambridge, UK.
Bildstein, O., Trotignon, L., Perronnet, M. & Jullien, M. (2006) Modelling iron–clay interactions in deep geological disposal. Physics and Chemistry of the Earth, 31, 618625.
Fujii, N., Yamakawa, M., Shikazono, N. & Sato, T. (2015) Geochemical and mineralogical characterisation of bentonite interacted with alkaline fluids generating in Zambales Ophiolite, northwestern Luzon, Philippines. Journal of the Geological Society of Japan, 120, 361375 (in Japanese with English abstract).
Gaucher, E.C., Blanc, P., Matray, J.-M. & Michau, N. (2004) Modeling diffusion of an alkaline plume on a clay barrier. Applied Geochemistry 19, 15051515.
Helgeson, H.C., Delany, J.M., Nesbitt, H.W. & Bird, D.K. (1978) Summary and critique of the thermodynamic properties of rock-forming minerals, American Journal of Science, 278A, 204220.
Johnson, J.W., Oelkers, E.H. & Helgeson, H. (1992) SUPCRT92: a software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions for 1–5000 bar and 0–1000°C. Computers & Geosciences, 18, 899947.
Karnland, O. & Birgersson, M. (2006) Montmorillonite Stability with Respect to KBS-3 Conditions. SKB Technical Report TR-06-11. Swedish Nuclear Fuel and Waste Management Company, Stockholm, Sweden.
Kittrick, J.A. (1971) Stability of montmorillonites: I. Belle Fourche and clay spur Montmorillonites. Soil Science Society of America Proceedings, 35, 140145.
Madsen, F.T. (1998) Clay mineralogical investigations related to nuclear waste disposal. Clay Minerals, 33, 109129.
Marty, N., Fritz, B., Clément, A. & Michau, N. (2010) Modelling the long term alteration of the engineered bentonite barrier in an underground radioactive waste repository. Applied Clay Science, 47, 8290.
Quintessa (2013) QPAC: Quintessa's General-Purpose Modelling Code. Quintessa Report QRS-QPAC-11. Quintessa Ltd, Henley-on-Thames, UK. Available at:
Reijonen, H.M. & Alexander, W.R. (2015) Bentonite analogue research related to geological disposal of radioactive waste: current status and future outlook. Swiss Journal of Geosciences, 108, 101110.
Samper, J., Lu, C. & Montenegro, L. (2008) Reactive transport model of interactions of corrosion products and bentonite. Physics and Chemistry of the Earth, 33, S306S316.
Samper, J., Naves, A., Montenegro, L. & Mon, A. (2016) Reactive transport modelling of the long-term interactions of corrosion products and compacted bentonite in a HLW repository in granite: uncertainties and relevance for performance assessment. Applied Goechemistry, 67. 4251.
Savage, D., Noy, D., & Mihara, M. (2002) Modelling the interaction of bentonite with hyperalkaline fluids. Applied Geochemistry, 17, 207223.
Savage, D., Walker, C., Arthur, A., Rochelle, C., Oda, C. & Takase, H. (2007) Alteration of bentonite by hyperalkaline fluids: a review of the role of secondary minerals. Physics and Chemistry of the Earth, 32, 287297.
Savage, D., Benbow, S., Watson, C., Takase, H., Ono, K., Oda, C. & Honda, A. (2010a) Natural systems evidence for the alteration of clay under alkaline conditions: an example from Searles Lake, California. Applied Clay Science, 47, 7281.
Savage, D., Arthur, R., Watson, C. & Wilson, J. (2010b) An Evaluation of Models of Bentonite Porewater Evolution. SSM Technical Report 2010-12. Swedish Radiation Safety Authority, Stockholm, Sweden.
Savage, D., Watson, C., Benbow, S. & Wilson, J. (2010c) Modelling iron–bentonite interactions. Applied Clay Science, 47, 9198.
Steefel, C. (2008) Geochemical kinetics and transport. Pp. 545589 in Kinetics of Water–Rock Interaction (Brantley, S.L., Kubicki, J.D. & White, A.F., editors). Springer, New York, NY, USA.
Vulava, V.M., Kretschmar, R. & Rusch, U. (2000) Cation competition in a natural subsurface material: modeling of sorption equilibria. Environmental Science and Technology, 34, 21492155.
Watson, C., Benbow, S. & Savage, D. (2007) Modelling the Interaction of Low pH Cements and Bentonite. Issues Affecting the Geochemical Evolution of Repositories for Radioactive Waste. SKI Report 2007:30. Swedish Nuclear Power Inspectorate, Stockholm, Sweden.
Wilson, J.C., Benbow, S., Watson, C., Sasamoto, H. & Savage, D. (2015) Fully-coupled reactive transport models of the iron–bentonite interface. Applied Geochemistry, 61, 1028.
Wilson, J., Benbow, S., Metcalfe, R. & Leung, H. (2017) Reactive transport modelling of shale–bentonite interactions in a hypersaline environment. Applied Geochemistry, 76, 6073.
Wilson, J., Savage, D., Bond, A., Watson, S., Pusch, R. & Bennett, D. (2011) Bentonite: A Review of Key Properties, Processes and Issues for Consideration in the UK Context. Quintessa Report QRS-1378ZG Version 1.1 for Radioactive Waste Management Directorate. Nuclear Decommissioning Authority, Harwell, UK.
Yamaguchi, T., Sakamoto, Y., Akai, M., Takazawa, M., Iida, Y., Tanaka, T. & Nakayama, S. (2007) Experimental and modeling study on long-term alteration of compacted bentonite with alkaline groundwater. Physics and Chemistry of the Earth, 32, 298310.


Related content

Powered by UNSILO

Avoiding unrealistic behaviour in coupled reactive-transport simulations of cation exchange and mineral kinetics in clays

  • Steven Benbow (a1), James Wilson (a1), Richard Metcalfe (a1) and Jarmo Lehikoinen (a2)


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed.