A study of the mineralogical alteration of bentonite in saline water

Suzuki, Satoru; Sazarashi, Masami; Akimoto, Toshiyuki; Haginuma, Masashi; Suzuki, Kazunori

doi:10.1016/j.clay.2007.11.003

Cited by 22 publications

(8 citation statements)

References 16 publications

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“…For example, Adamcova et al (2008), Suzuki et al (2008), and Dohrmann (2009, 2011) focused their studies on changes in geotechnical parameters; e.g. the swelling pressure or cation exchange capacity (CEC).…”

Section: Introductionmentioning

confidence: 99%

Effects of Chemical Structure on the Stability of Smectites in Short-Term Alteration Experiments

Nguyen-Thanh

Herbert

Kasbohm

et al. 2014

Clays and clay miner.

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Because of their isolating capacity, smectite-rich clays have been proposed as buffer and backfill materials in high-level radioactive waste repositories. These repositories have to guarantee longterm safety for~1 million years. Thermodynamics and kinetics of possible alteration processes of bentonite determine its long-term performance as a barrier material. Smectites in 25 different clays and bentonites were investigated in order to identify possible differences in their rates of alteration. These samples were saturated for 30 days in 1 M NaCl solution and deionized water, and then overhead rotated at speeds of 20 rpm and 60 rpm. Depending on the octahedral and interlayer composition, each of the smectites studied had specific rate of alteration, a so-called specific dissolution potential of smectite. The bentonites were classed as 'slow-reacting bentonite', 'moderate-reacting bentonite', or 'fast-reacting bentonite' corresponding to a relatively low (DP À specific dissolution potential -<À5%), moderate (À5% < DP < À20%), or high specific dissolution potential (DP > À20%), respectively. The larger the amount of octahedral Fe and Mg compared to octahedral Al, the greater the specific dissolution potential. The present study found that the interlayer composition has a discernible impact on the rate of alteration. In experiments with rotation speeds of 60 rpm and a 1 M NaCl solution, Na + was found to be the stabilizing cation in the interlayers of all the smectites. The Na-stabilizing mechanism was identified in only some of the smectites (type A) in experiments with 20 rpm (1 M NaCl solution). A second stabilization mechanism (by interlayer cations; Ca and Mg) was identified for other smectites (type B). Each bentonite has a specific rate of alteration. 'Slow-reacting bentonite' and clay with smectite-illite interstratifications are recommended as potential clay barriers in HLW repositories. The experimental and analytical procedures described here could be applied to potential barrier materials to identify 'slow-reacting bentonite'.

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Section: Introductionmentioning

confidence: 99%

Effects of Chemical Structure on the Stability of Smectites in Short-Term Alteration Experiments

Nguyen-Thanh

Herbert

Kasbohm

et al. 2014

Clays and clay miner.

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“…This is much more than expected in repository conditions; e.g. Suzuki et al (2008) have estimated that the L/S in real repository environment is 0.2 ml/ g. However, the target of our experiments was not to simulate actual repository conditions, but to gain knowledge of bentonite alteration and buffering capacity in alkaline conditions.…”

Section: E X P E R I M E N T a L S E T -U Pmentioning

confidence: 94%

Influence of alkaline (pH 8.3–12.0) and saline solutions on chemical, mineralogical and physical properties of two different bentonites

Tiina¹,

Kumpulainen²,

Vuorinen³

et al. 2013

Clay miner.

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The interaction of two different bulk bentonites (Na- and Ca-types) with three types of simulated cement waters (pH 9.7, 11.3 and 12.0) and one saline groundwater simulate (pH 8.3) as a reference, was studied in batch reactors at 25°C. The solution pH was monitored in order to keep the pH as steady as possible by replacing the leaching solution with fresh one when needed. After 554 days, one set of parallel samples was removed from the experiment in order to investigate the possible changes in the bentonite materials.The buffering capacity of bentonite was clearly observed, especially at the beginning of the high-pH experiments, as the pH of the leaching solutions decreased quite dramatically due to interaction with bentonite. The solution chemistry results showed a decrease of Ca content in all leachate samples, but especially in pH 12.0 experiments. Small amounts of silica were released throughout the experiment. Both bentonites in pH 12.0 experiments also released detectable amounts of Al, while in the lower pH experiments the levels were below detection limit. These observations were also supported by chemical analyses of the bentonite materials. Only minor changes were detected in the mineralogy, and they were mainly concentrated on experiments at pH 11.3 and pH 12.0. The measured swelling pressure showed an increase in pH 12.0 experiments. The results obtained in this research may facilitate modelling of bentonite interaction with high-pH solutions.

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“…Nonetheless, the engineered barriers and rocks which surround waste packages may change their properties due to heating. For example, at temperatures above 100 °C, bentonite clay may show mineralogical alterations [26,81,82] that may lead to a less performing barrier. Also, at temperatures above the boiling point of water, phase changes occur which would invoke several coupled multiphase processes that are difficult to characterize and simulate.…”

Section: Z (M)mentioning

confidence: 99%

Coupled Heat-Mass Transport Modelling of Radionuclide Migration from a Nuclear Waste Disposal Borehole

Lari

Mallants

2022

Geofluids

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Disposal of radioactive waste originating from reprocessing of spent research reactor fuel typically includes stainless steel canisters with waste immobilised in a glass matrix. In a deep borehole disposal concept, waste packages could be stacked in a disposal zone at a depth of one to potentially several kilometres. This waste will generate heat for several hundreds of years. The influence of combining a natural geothermal gradient with heat from decaying nuclear waste on radionuclide transport from deep disposal boreholes is studied by implementing a coupled heat-solute mass transport modelling framework, subjected to depth-dependent temperature, pressure, and viscosity profiles. Several scenarios of waste-driven heat loads were investigated to test to what degree, if any, the additional heat affects radionuclide migration by generating convection-driven transport. Results show that the heat output and the calculated radioactivity at a hypothetical near-surface observation point are directly correlated; however, the overall impact of convection-driven transport is small due to the short duration (a few hundred years) of the heat load. Results further showed that the calculated radiation dose at the observation point was very sensitive to the magnitude of the effective diffusion parameter of the host rock. Coupled heat-solute mass transport models are necessary tools to identify influential processes regarding deep borehole disposal of heat-generating long-lived radioactive waste.

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A study of the mineralogical alteration of bentonite in saline water

Cited by 22 publications

References 16 publications

Effects of Chemical Structure on the Stability of Smectites in Short-Term Alteration Experiments

Effects of Chemical Structure on the Stability of Smectites in Short-Term Alteration Experiments

Influence of alkaline (pH 8.3–12.0) and saline solutions on chemical, mineralogical and physical properties of two different bentonites

Coupled Heat-Mass Transport Modelling of Radionuclide Migration from a Nuclear Waste Disposal Borehole

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