Using natural systems evidence to test models of transformation of montmorillonite

Savage, David; Wilson, J. C.; Benbow, Steven; Sasamoto, Hiroshi; Oda, Chie; Walker, Colin; Kawama, Daisuke; Tachi, Yukio

doi:10.1016/j.clay.2020.105741

Cited by 3 publications

(2 citation statements)

References 32 publications

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“…However, the model results were not verified experimentally. Approximating illitization through a dissolution/precipitation reaction was also undertaken by Savage et al (2020), simulating the burial of marine sediments over geological timeframes and increasing temperatures. The smectite fraction within the sediment was included as a K-montmorillonite, with both illite and smectite modelled as discrete minerals rather than mixed layers.…”

Section: Illitizationmentioning

confidence: 99%

Chemical and mineralogical reactions of bentonites in geotechnical barriers at elevated temperatures: review of experimental evidence and modelling progress

Kaufhold,

Dohrmann,

Wallis

et al. 2023

Clay miner.

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Bentonites are proposed to be used as buffers in high-level radioactive waste repositories. The elevated temperatures in repositories may, however, affect bentonites’ desired properties. For instance, heating under dry conditions can cause cation fixation, potentially affecting swelling properties. The kinetics of mineral dissolution and precipitation reactions will equally be influenced by temperature. Redistributions of Ca-sulphates and -carbonates have been observed, as well as illitization of smectite. Illitization, however, has only been observed in laboratory experiments at large solution/solid ratios, whereas it has not yet been unambiguously identified in large-scale experiments. In many large-scale tests, cation exchange is the first observable geochemical reaction. In addition, an enrichment of Mg close to the heater is found in many such tests. The thermal gradient and (incongruent) smectite dissolution are suspected to play a role with respect to the Mg enrichment, but the underlying mechanism has not been unravelled so far. To predict the long-term performance of a bentonite buffer, numerical modelling is required in order to be able to simulate the reactions of all accompanying mineral phases. Smectites, which dominate the bentonite composition, are therefore particularly difficult to characterise, as their dissolution is often observed to be non-stoichiometric. Various model approaches exist to simulate smectite reactions, mostly based on kinetic rate reactions, ideally considering the effect of pH (congruent or incongruent dissolution), temperature and the degree of saturation of the solution. Reassessing and improving the thermodynamic/kinetic data of smectites are prerequisites for improving long-term buffer performance assessment.

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Section: Illitizationmentioning

confidence: 99%

Chemical and mineralogical reactions of bentonites in geotechnical barriers at elevated temperatures: review of experimental evidence and modelling progress

Kaufhold,

Dohrmann,

Wallis

et al. 2023

Clay miner.

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“…CABARET was chosen for the modelling in preference to codes such as PHREEQC, as it allows coupling of porosity evolution (as minerals dissolve and/or precipitate) with diffusive and advective transport. CABARET uses the underlying QPAC Code, which has been used in previous reactive transport modelling studies [27,28]. CABARET uses an adaptive time-stepper to maximise the solver efficiency, which reduces the size of the time-step in response to external events (e.g., time-dependent inputs) or 'emergent events' (e.g., precipitation of secondary minerals or total dissolution of pre-existing minerals) and increases the time-step when the system is evolving less rapidly.…”

Section: Reactive-transport Modelling 271 Cabaret Model Conceptmentioning

confidence: 99%

Evolution of the Reaction and Alteration of Mudstone with Ordinary Portland Cement Leachates: Sequential Flow Experiments and Reactive-Transport Modelling

Bateman

Murayama

Hanamachi³

et al. 2021

Minerals

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The construction of a repository for geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository and the extensive use of cement will result in the development of a highly alkaline porewater, pH > 12.5; this fluid will migrate into and react with the host rock. The chemistry of the fluid will evolve over time, initially high [Na] and [K], evolving to a Ca-rich fluid, and finally returning to the groundwater composition. This evolving chemistry will affect the long-term performance of the repository, altering the physical and chemical properties, including radionuclide behaviour. Understanding these changes forms the basis for predicting the long-term evolution of the repository. This study focused on the determination of the nature and extent of the chemical reaction, as well as the formation and persistence of secondary mineral phases within a mudstone, comparing data from sequential flow experiments with the results of reactive transport modelling. The reaction of the mudstone with the cement leachates resulted in small changes in pH with the precipitation of calcium aluminium silicate hydrate (C-(A-)S-H) phases of varying compositions. As the system evolves, secondary C-(A-)S-H phases re-dissolve and are replaced by secondary carbonates. This general sequence was successfully simulated using reactive transport modelling.

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The impact of cement on argillaceous rocks in radioactive waste disposal systems: A review focusing on key processes and remaining issues

Wilson¹,

Bateman

Tachi

2021

Applied Geochemistry

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Using natural systems evidence to test models of transformation of montmorillonite

Cited by 3 publications

References 32 publications

Chemical and mineralogical reactions of bentonites in geotechnical barriers at elevated temperatures: review of experimental evidence and modelling progress

Chemical and mineralogical reactions of bentonites in geotechnical barriers at elevated temperatures: review of experimental evidence and modelling progress

Evolution of the Reaction and Alteration of Mudstone with Ordinary Portland Cement Leachates: Sequential Flow Experiments and Reactive-Transport Modelling

The impact of cement on argillaceous rocks in radioactive waste disposal systems: A review focusing on key processes and remaining issues

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