Reactive transport modelling of groundwater-bentonite interaction: Effects on exchangeable cations in an alternative buffer material in-situ test

Wallis, Ilka; Idiart, Andrés; Dohrmann, R.; Post, Vincent

doi:10.1016/j.apgeochem.2016.07.005

Cited by 12 publications

(5 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Taking into account these corrections, the exchangeable Ca 2+ values remained around the value for the reference bentonite. In the long-term test of buffer material project (LOT), no such gradients of ECs were detected (Karnland et al , 2009), but various gradients were observed in the first package of the ABM project (ABM-I; Dohrmann et al , 2013; Wallis et al , 2015) and in the second package (ABM-II; Dohrmann & Kaufhold, 2017).…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Interactions of bentonite with metal and concrete from the FEBEX experiment: mineralogical and geochemical investigations of selected sampling sites

et al. 2018

Self Cite

View full text Add to dashboard Cite

The FEBEX experiment, a full-scale, high-level radioactive waste repository test, ran for ~18 years and hence is the longest-running disposal test to date. The test consisted of a heater emplaced in an envelope of compacted bentonite at the Grimsel test site, Switzerland. The water content of the bentonite was somewhat lower near the heater and increased towards the granite. This phenomenon probably led to gradients in the exchangeable cation population at various locations within the bentonite buffer. The cement (shotcrete) bentonite interface of one block was characterized by a thin (0.1–1.0 mm) reaction zone in which bentonite constituents, carbonates and sulfates occurred. Cation exchange and a slight decrease of the cation exchange capacity were observed near the heater. Oxic corrosion was observed predominantly at the bentonite/steel liner interfaces, pointing towards a role of air entrapped between the liner and heater during emplacement. At the liner surface, intimate intergrowth of bentonite constituents, metal and corrosion products was observed. At the face of the heater, the bentonite blocks were in direct contact with the heater surface without any signs of metal corrosion. Instead, a significant increase in the Mg content was recorded, which is in agreement with previous large-scale disposal tests. The FEBEX experiment proved that the Mg increase and corrosion were independent processes. The increase in Mg may be explained by the formation of trioctahedral domains or the precipitation of neoformed silicates. For the first time, however, brucite was identified as an additional phase that formed at the metal/bentonite interface, pointing towards a special role for Mg mobility in the bentonite barrier.

show abstract

Section: Resultsmentioning

confidence: 99%

“…Most dissolution/precipitation reactions (involving e.g. carbonates, sulfates, selected silicates) and cation exchange may be explained based on geochemical modelling (Arcos et al , 2000; Wallis et al , 2015). The mechanisms behind corrosion and Mg enrichment, in contrast, are still under discussion (Kaufhold et al , 2015, 2016).…”

mentioning

confidence: 99%

Interactions of bentonite with metal and concrete from the FEBEX experiment: mineralogical and geochemical investigations of selected sampling sites

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…Single-exchanger site models (Wallis et al, 2016;Chaparro et al, 2021) as well as multi-site numerical representations of clay minerals have been employed (Liu et al 2004;Tournassat et al, 2007;Fuller et al 2014). Multi-site ion-exchange models thereby simulate different types of ion-exchange sites on clays, including basal planes on crystal surfaces and interlayer sites on crystal edges.…”

Section: Cation Exchangementioning

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.

View full text Add to dashboard Cite

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.

show abstract

“…This kind of exchangeable-cations behaviour was similar to the results reported by Dohrmann et al (2013) for the JNB02 sample. Thus, the observed exchange of Na + and Ca 2+ in bentonite could be interpreted as being driven by large Ca concentrations in the contacting groundwater (Dohrmann et al, 2013;Wallis et al, 2016). A slight gain in Mg 2+ compared to the reference material may be caused by ion exchange with the contacting groundwater and/or dissolution of dolomite which exists in the Kunigel V1 bentonite as an accessory mineral (∼3 wt.%; Ito et al, 1993).…”

Section: Chemical Propertiesmentioning

confidence: 99%

Mineralogical, physical and chemical investigation of compacted Kunigel V1 bentonite in contact with a steel heater in the ABM test package 1 experiment, Äspö laboratory, Sweden

Sasamoto

Isogai²,

Kikuchi³

et al. 2017

Clay miner.

View full text Add to dashboard Cite

In many countries, compacted bentonite is a candidate engineering barrier material for safe disposal of high-level radioactive waste. The Swedish Nuclear Fuel and Waste Management Company (SKB) set up an in situ experiment (the ABM project) to compare the stability of different bentonites under the conditions of exposure to an iron source and to elevated temperature (up to 130°C) at the Äspö Hard Rock Laboratory, Sweden. Results for the Japanese bentonite (Kunigel V1) are summarized in the present study.Mineralogical investigation using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) suggested no transformation of smectite or neoformed clay phases. However, a distinct change in exchangeable cations of smectite was indicated (i.e. from Na type to Fe type and/or Ca type) in the bentonite in the vicinity of the steel heater.Measurements of hydraulic conductivity and swelling properties suggest that no significant changes occurred in the bentonite even in the vicinity of the steel heater. This is attributed to the limited portion of the bentonite affected by the iron–bentonite interactions and the incomplete ion-exchange reactions. The methylene blue cation exchange capacity and the determination of the exchangeable cations showed that the lateral distribution for these parameters was constant. However, the total exchangeable cation population has changed significantly compared to the initial sample.

show abstract

Reactive transport modelling of groundwater-bentonite interaction: Effects on exchangeable cations in an alternative buffer material in-situ test

Cited by 12 publications

References 24 publications

Interactions of bentonite with metal and concrete from the FEBEX experiment: mineralogical and geochemical investigations of selected sampling sites

Interactions of bentonite with metal and concrete from the FEBEX experiment: mineralogical and geochemical investigations of selected sampling sites

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

Mineralogical, physical and chemical investigation of compacted Kunigel V1 bentonite in contact with a steel heater in the ABM test package 1 experiment, Äspö laboratory, Sweden

Contact Info

Product

Resources

About