Clay Mineral Transformations after Bentonite/Clayrocks and Heater/Water Interactions from Lab and Large-Scale Tests

Dear Colleagues,

We are pleased to announce the launch of a new a Special Issue of the journal Minerals that shall present a set of themed articles on “Clay Mineral Transformations after Bentonite/Clayrocks and Heater/Water interactions from Lab and Large-Scale Tests”. The main focus will be on geochemical and mineralogical processes observed from heating/hydration experiments performed at different scales, which may alter the structure and properties of bentonites and/or clayrocks used as barriers in the context of deep geological disposal of nuclear fuels and radioactive waste.

Bentonites and clayrocks are an essential component of the multi-barrier system securing the long-term safety of the final disposal of nuclear waste. The efficiency of such engineered and natural clay barriers relies on their physical and chemical confinement properties. Therefore, the long-term preservation of these properties over large periods is an important issue. From a geochemical point of view, the clayey mineral’s function to isolate the canisters from water and retard the migration of radionuclides also means maintaining a suitable chemical and mineralogical environment for canister integrity, radionuclide retention, and mechanical stability over time, buffering possible alteration/deterioration processes of the nanoporous clay materials.

One scientific approach used to tackle the prediction of long-term clay barrier behavior is through the analysis of results from experiments conducted in laboratory, large-scale mock-up tests, and in situ experiments conducted in underground research laboratories (URL) at real scale and under realistic conditions. These tests provide the opportunity to understand and quantify the processes and to evaluate the behavior of the clay minerals.

Different experiments have been performed over time using bentonites and natural clayrocks. Around 40 years ago, a few commercial high-quality bentonites were acquired for their study as buffer and backfill materials in the construction of engineering barrier systems (EBS) for the isolation of high-level radioactive waste. Today, highly compacted bentonite blocks, high-density bentonite pellets or a mixture thereof are being used both in laboratory and large-scale in situ experiments (FEBEX, LOT, ABM, FE experiment, etc.).

In the case of clayrocks, these experiments are conducted in URLs. Twenty-six URLs were set up in 10 countries between 1965 and 2006. In Europe, three of them were constructed in clayrocks environments: HADES (Belgium, 1980- , Boom Clay plastic clayrock), Mont Terri (Switzerland, 1995- , Opalinus Clay consolidated clayrock), and Meuse/Haute-Marne or Bure URL (France, 2000- , Callovo-Oxfordian consolidated clayrock), where many geochemical/mineralogical studies are currently being performed.

An overview of the results found up to date may contribute to establish the know-how about the understanding of the thermo-/hydro-chemical processes affecting to the clay minerals, and their response to different perturbations (e.g., desaturation, corrosion, gases produced and consumed, interactions with other materials, and inorganic/organic species), which may produce physico-chemical changes affecting their mechanical (swelling, permeability, etc.) and sorption properties. This may contribute to validate applied technologies, to the design of future experiments for unresolved questions, and to validate modeling tools required for interpretation and prediction of the evolution of such processes.

Thus, our Special Issue will cover a broad range of relevant topics of interest. Insights related to the following aspects will be included in this Special Issue:

1. Mineral alteration: dissolution and redistribution of primary mineral phases and precipitation/neoformation of secondary minerals;
2. Physico-chemical properties modification (cation exchange capacity, cation exchange population, surface complexation, crystallochemical structure, layer charge and swelling ability);
3. Microstructure changes affecting sorption processes (porosity, water adsorption, ion exchange, radionuclide sorption, etc.);
4. Clayrock- or Bentonite-groundwater interactions;
5. Changes in pore water chemistry;
6. Corrosion and metal/interface processes;
7. Smectite and other clay mineral structural stability;
8. Redox Chemistry and redox state evolution, affecting the structural stability and speciation of dissolved ions and radionuclides;
9. Influence of gases produced and consumed under oxidized and reducing conditions and/or a desaturation phase on geochemistry/mineralogy;
10. Organics and their influence on geochemistry/mineralogy;
11. Microbial-mediated mineral alteration and geochemical evolution;
12. Geochemical modeling, reactive transport and computational quantum mechanical modeling.

Dr. Ana María Fernández
Dr. Stephan Kaufhold
Prof. Dr. Markus Olin
Dr. Lian-Ge Zheng
Dr. Paul Wersin
Dr. James Wilson
Guest Editors

Manuscript Submission Information

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