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

Clay Minerals ◽  
2018 ◽  
Vol 53 (4) ◽  
pp. 745-763 ◽  
Author(s):  
S. Kaufhold ◽  
R. Dohrmann ◽  
K. Ufer ◽  
F. Kober
Keyword(s):  
Cation Exchange ◽  
Large Scale ◽  
Test Site ◽  
Exchange Capacity ◽  
Metal Corrosion ◽  
Special Role ◽  
Exchangeable Cation ◽  
Bentonite Buffer ◽  
The Face ◽  
High Level

ABSTRACTThe 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.

Mineralogical investigations of the first package of the alternative buffer material test – II. Exchangeable cation population rearrangement

Clay Minerals ◽  
2013 ◽  
Vol 48 (2) ◽  
pp. 215-233 ◽  
Author(s):  
R. Dohrmann ◽  
S. Olsson ◽  
S. Kaufhold ◽  
P. Sellin
Keyword(s):  
Cation Exchange ◽  
Large Scale ◽  
Vertical Direction ◽  
Exchange Capacity ◽  
Maximum Temperature ◽  
Exchangeable Cation ◽  
Water Tank ◽  
Material Test ◽  
Buffer Material ◽  
Iron Tube

AbstractBentonites are candidate materials for the encapsulation of radioactive waste. In the ‘Alternative Buffer Material test’ (ABM), compacted ring-shaped blocks of eleven different buffer materials (mainly bentonites) were packed vertically on top of each other with an iron tube as heater in the centre. These buffer materials started with various exchangeable cation populations (ECpopulation). The first ‘ABM package’ was terminated 28 months after installation and the bentonites had been exposed to the maximum temperature (130°C) for about one year. The aim of the present study is first: to describe modification of the cation exchange population, and second to understand the influence of the groundwater on cation exchange at different scales. No significant horizontal variation of any exchangeable cation (EC) was detected between 1 and 7 cm distance from contact with the iron tube. Large total differences of the ECpopulations, however, were observed for the individual blocks after the field experiment (n = 21 blocks) with respect to the composition of the reference materials. The average cation exchange capacity (CEC) values of the analysed bentonites (n = 9 blocks) decreased by 5.5 meq/100 (1.1 – 8.8 meq/100 g) after the experiment. Exchangeable Na+ and Mg2+ decreased on average, whereas Ca2+ increased. This trend was pronounced in the top region of the parcel (upper seven blocks). Although most changes occurred on the large scale of the whole test parcel, small but important changes were also recorded in the vertical direction on the centimetre scale. The observed differences cannot be explained assuming simply that a bentonite reacts only with neighbouring blocks, which would mean that the system was more or less closed. The differences are much larger and the only conclusion from this observation is that the whole package seems to be influenced by the groundwater which was added from a water tank at the experiment site, enabling at least partial equilibration between the different blocks.

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

Clay Minerals ◽  
2017 ◽  
Vol 52 (1) ◽  
pp. 127-141 ◽  
Author(s):  
H. Sasamoto ◽  
T. Isogai ◽  
H. Kikuchi ◽  
H. Satoh ◽  
D. Svensson
Keyword(s):  
Exchange Capacity ◽  
Exchangeable Cations ◽  
Exchangeable Cation ◽  
Exchange Reactions ◽  
Swelling Properties ◽  
X Ray ◽  
Set Up ◽  
The Stability ◽  
High Level ◽  
Physical And Chemical

AbstractIn 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.

Geochemical Processes at the Carbon steel/bentonite Interface in Repository Conditions

2006 ◽  
Vol 985 ◽  
Author(s):  
Elena Torres ◽  
María Jesús Turrero ◽  
Pedro Luis Martin
Keyword(s):  
Carbon Steel ◽  
Exchange Capacity ◽  
Spent Fuel ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Geological Repository ◽  
Geological Formation ◽  
Gaseous Corrosion ◽  
High Level

AbstractThe Deep Geological Repository (DGR) is currently the most accepted management option for the isolation of high level radioactive wastes. The DGR is based on a multibarrier system, which will limit releases of mobile radionuclides to the biosphere. In the design of the repository the spent fuel is encapsulated in canisters of carbon-steel. The space between the canister and the host geological formation will be filled with bentonite buffer clay. Under the prevailing conditions in a DGR, both localized and generalized corrosion phenomena are possible.Corrosion of the canister will result in formation of solid and gaseous corrosion products, which can influence the behaviour of both the canister and the bentonite. Many studies have been carried out in order to improve the knowledge on the reactivity of these barriers. Most of them have focused on the mineralogical alteration of the bentonite as a function of temperature, time, iron/clay and liquid/rock ratio in batch conditions. The aim of this study is to provide experimental evidences, at repository conditions, on chemical and mineralogical changes during the canister-compacted bentonite interaction: determination of secondary minerals and their alteration reactions, the advance of the corrosion front in the compacted bentonite, and changes in porosity, permeability and cation exchange capacity.

Loss of soil organic matter following cultivation of long-term pasture: effects on major exchangeable cations and cation exchange capacity

Soil Research ◽  
2015 ◽  
Vol 53 (4) ◽  
pp. 377 ◽  
Author(s):  
D. Curtin ◽  
P. M. Fraser ◽  
M. H. Beare
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Crop Production ◽  
Exchange Capacity ◽  
Exchangeable Cations ◽  
Exchangeable Cation ◽  
C Stocks

Cultivation of grassland is known to lead to the depletion of soil organic matter (SOM), but the effect on the size and composition of the exchangeable cation suite has not been documented. We measured cation exchange capacity (CEC) and exchangeable cations (calcium, Ca; magnesium, Mg; potassium, K; sodium, Na), as well as soil carbon (C) and nitrogen (N) (0–7.5, 7.5–15, and 15–25 cm), 8 years after conversion of long-term ryegrass–white clover pasture (grazed by sheep) to annual crop production. The trial was near Lincoln, Canterbury, New Zealand. The trial included three tillage treatments: crops established using intensive cultivation (mouldboard ploughing), minimum tillage (shallow cultivation, ~10 cm), or no-tillage. The 8-year rotation was barley, wheat, pea, barley, pea, barley, barley, barley. A sheep-grazed pasture was maintained as an experimental control. The experiment also included a permanent fallow treatment (maintained plant-free using herbicides; not cultivated). After 8 years under arable cropping, soil C stocks (0–25 cm) were 10 t ha–1 less, on average, than under pasture. The vertical distribution of soil organic matter (SOM) was affected by tillage type, but the total amount of organic matter in the top 25 cm did not differ (P > 0.05) among the tillage treatments. Under permanent fallow (C loss of 13 t ha–1 relative to pasture), total exchangeable cation (Ca + Mg + K +Na) equivalents declined by 47 kmolc ha–1, a 20% decrease compared with pasture. Loss of exchange capacity resulted in the selective release of cations with lower affinity for SOM (K, Na, Mg). Smaller losses of exchangeable cations were recorded under the arable cropping rotation (average 31 kmolc ha–1), with no differences among tillage treatments. Effective CEC (at field pH) decreased under permanent fallow and cultivated treatments because of: (1) depletion of SOM (direct effect); and (2) soil acidification, which eliminated some of the remaining exchange sites (indirect effect). Acidification in the permanent fallow can be attributed to the N mineralisation process, whereas in the cropped systems, excess cation removal in harvested straw and grain accounted for about half of the measured acidification. There was evidence that the organic matter lost under arable cropping and fallow had lower CEC than SOM as a whole.

scholarly journals Discussion of parameters used to distinguish suitable from less suitable HLRW bentonites

2021 ◽  
Vol 1 ◽  
pp. 125-126
Author(s):  
Stephan Kaufhold
Keyword(s):  
Thermal Conductivity ◽  
Hydraulic Conductivity ◽  
Large Scale ◽  
Swelling Pressure ◽  
Mineralogical Composition ◽  
Metal Corrosion ◽  
Dry Density ◽  
Exchangeable Cation ◽  
Surrounding Water ◽  
Fe Content

Abstract. Bentonites will be used in the construction of some high-level radioactive waste (HLRW) repositories mostly in combination with crystalline host rocks. They will be used both as a geotechnical barrier (compacted bentonite blocks) around the canisters and for backfilling. The bentonite should be stable in contact with cement pore water, minimize metal corrosion, be stable against erosion and various salt solutions, retard radionuclides, prevent canister displacement, possess high thermal conductivity, be stable against radioactive radiation, keep its swelling capacity even when dried, and, most importantly, should have a low hydraulic conductivity. Bentonites are natural materials (clays) which are dominated by swelling clay minerals called smectites. All bentonites, therefore, possess high water uptake capacity, swelling, and cation exchange properties. Different bentonites from different deposits worldwide differ with respect to their chemical and mineralogical composition, composition and charge distribution of the smectites, particle size and morphology, microstructure (arrangement of particles relative to each other), and interlayer population. All these parameters affect the performances of bentonites in different applications. The bentonite industry, therefore, compares different bentonites based on empirical investigations to produce superior products. Specifications which could be used to select a suitable HLRW bentonite were discussed by Kaufhold and Dohrmann (2016). Additional information has been published later (Kaufhold et al., 2020a, b). First of all, some of the above listed desired bentonite properties depend more on the degree to which it is compacted compared to the natural variability. High compaction decreases the hydraulic conductivity and increases thermal conductivity. In order to prevent canister displacement only a small swelling pressure is needed which is easily achieved by compaction with all bentonites. Generally, the type of exchangeable cation is the most important parameter determining bentonite properties such as swelling and rheology. Large scale deposition tests, however, proved that the cation population will readily equilibrate with the surrounding water. The initial type of exchangeable cation is, therefore, less relevant. More important is the Fe content which negatively affects the thermal and chemical stability. Structural Fe of the smectites can be reduced or oxidized by bacteria and radiation. The Fe content of the bentonite should therefore be low. Highly charged smectites proved to be less corrosive in combination with iron canisters because they provide more reducing conditions compared to low charged ones. Bentonites containing highly charged smectites should be preferred if Fe canisters are used. In the case of Cu canisters no effect of the charge could be found. Also, soluble or at least partly soluble components such as sulphates, sulphides, carbonates, and organic matter should be absent since their possible dissolution would decrease the dry density and hence the swelling pressure. The presence of reactive silica in some bentonites proved to buffer the dissolution reactions at the cement bentonite interface and hence could have a beneficial effect.

Predictive Numerical Modeling of Artificial Tracers Migration in the Large-Scale Heating and Hydration Experiments of the FEBEX Project

1997 ◽  
Vol 506 ◽  
Author(s):  
J. Samper ◽  
J. Delgado ◽  
J. Molinero ◽  
R. Juncosa
Keyword(s):  
Numerical Modeling ◽  
Large Scale ◽  
The Novel ◽  
Additional Insight ◽  
Bentonite Buffer ◽  
Waste Repository ◽  
Engineered Barrier ◽  
High Level ◽  
Insight Into ◽  
Artificial Tracers

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository. In the FEBEX experiment the bentonite barrier will be subject to heating and hydration during at least three years. One of the novel aspects of FEBEX is the use of artificial tracers, which are intended to provide additional insight into the hydrodynamic and geochemical behavior of the bentonite buffer. Here the results of the numerical prediction of tracers migration are presented. Numerical modeling of the experiments has allowed the identification of the most relevant parameters and will be useful for the design of post-morten analyses.

scholarly journals Study on the Adsorption Behavior between an Imidazolium Ionic Liquid and Na-Montmorillonite

Molecules ◽  
2019 ◽  
Vol 24 (7) ◽  
pp. 1396 ◽  
Author(s):  
Jingjing Pei ◽  
Xuesong Xing ◽  
Boru Xia ◽  
Ziming Wang ◽  
Zhihua Luo
Keyword(s):  
Ionic Liquid ◽  
Cation Exchange ◽  
Ph Value ◽  
Exchange Capacity ◽  
Adsorption Behavior ◽  
Exchangeable Cation ◽  
Imidazolium Ionic Liquid ◽  
Cationic Group ◽  
Adsorption Amount ◽  
Thermal Stability Of

Interactions between 1-butyl-3-methylimidazolium tetrafluoroborate (IL), an ionic liquid, and Na-montmorillonite (Na-MMT) were studied under different kinetic conditions to investigate the adsorption behavior of IL by Na-MMT. The adsorption of IL by Na-MMT was rapid, with a fast rate, reaching a capacity of 0.43 mmol/g, lower than Na-MMT’s cation exchange capacity (CEC) of 0.90 mmol/g. Meanwhile, the highest adsorption rate occurred at the IL concentration of 1000 mg/L. The exchangeable cation of Na-MMT could not be completely substituted by the cation group of IL regardless of the IL concentration. Stoichiometric desorption experiments confirmed that the cation exchange was the dominating adsorption mechanism for the IL adsorption by Na-MMT. The pH value of the solution between 2 and 11 had a negligible effect on the adsorption amount of IL by Na-MMT. The cation group of IL interacted into the interlayer of Na-MMT successfully, resulting in the change in the wettability of Na-MMT. A bilayer formation of the cationic group should occur in the interlayer of the modified Na-MMT and the configuration of IL was dependent on the adsorption amount of IL. Furthermore, the thermal stability of the modified Na-MMT was also dependent on the adsorption amount of IL.

Social inequality in the evolution of human societies

2019 ◽  
pp. 98-120
Author(s):  
Georgi Derluguian
Keyword(s):  
Social Inequality ◽  
Large Scale ◽  
Human Beings ◽  
Mass Violence ◽  
Public And Private ◽  
Tangible Assets ◽  
Transition To Agriculture ◽  
New Institutions ◽  
High Level ◽  
Political Economic

The author develops ideas about the origin of social inequality during the evolution of human societies and reflects on the possibilities of its overcoming. What makes human beings different from other primates is a high level of egalitarianism and altruism, which contributed to more successful adaptability of human collectives at early stages of the development of society. The transition to agriculture, coupled with substantially increasing population density, was marked by the emergence and institutionalisation of social inequality based on the inequality of tangible assets and symbolic wealth. Then, new institutions of warfare came into existence, and they were aimed at conquering and enslaving the neighbours engaged in productive labour. While exercising control over nature, people also established and strengthened their power over other people. Chiefdom as a new type of polity came into being. Elementary forms of power (political, economic and ideological) served as a basis for the formation of early states. The societies in those states were characterised by social inequality and cruelties, including slavery, mass violence and numerous victims. Nowadays, the old elementary forms of power that are inherent in personalistic chiefdom are still functioning along with modern institutions of public and private bureaucracy. This constitutes the key contradiction of our time, which is the juxtaposition of individual despotic power and public infrastructural one. However, society is evolving towards an ever more efficient combination of social initiatives with the sustainability and viability of large-scale organisations.

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