Geology bentonites

Kayabali, K. 1997. Engineering aspects of a novel landfill liner material bentonite-amended natural zeolite. Eng Geology 46 105-114. 

The isolation and safety functions of HLNW deep geological repositories are based upon the multibarrier concept, where a number of containment and isolation barriers are put in place. A schematic view of the multibarrier HLNW concept is given in Fig. 1. The main barriers of the system are the waste matrix itself a metallic container (either corrosion resistant like Cu or Ti, or based upon stainless steel) a buffer material (normally bentonite) and finally the host rock itself (essentially granite or clay, although salt domes are also being considered). 

Missana, T., Alonso, U. Turrero, M. J. 2002. Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository. Journal of Contaminant Hydrology, 61, 17-31. 

Bentonite, widely distributed geographically and geologically, also varies widely in properties. 

Cave, M. R., Reeder, S., Entwisle, D. C., Blackwell, P. A., Trick, J. K., Wragg, J., and Burden, S. R. (1998). Extraction and Analysis of Pore Waters from Bentonite Clay. WI/98/9C, British Geological Survey. Keyworth, Nottingham. 

Manjanna, J., T. Kozaki, and S. Sato. 2009. Fe(III)-montmorillonite Basic properties and diffusion of tracers relevant to alteration of bentonite in deep geological disposal. Appl. Clay Sci. 43 208-217. 

In this chapter, the relationship of geological origins and interfacial properties of bentonite clay will be reviewed first. Then we will discuss the migration of water-soluble substances in rocks and soil, and the effect of sorption on the migration. A linear model will be derived by which the quantity of ion sorbed on rocks can be estimated when the mineral composition and sorption parameters of the mineral components are known. Surface acid-base properties of soils will be discussed, and the sorption of an anion (cyanide ion) will be shown on different soils and sediments. 

RELATIONSHIP BETWEEN INTERFACIAL PROPERTIES AND GEOLOGICAL ORIGIN OF BENTONITE CLAY... 

Bentonite rocks have many uses in the chemical and oil industries and also in agriculture and environmental protection. The usefulness of bentonite for each of these applications is based on its interfacial properties. These properties are determined by geological origin, chemical and mineral composition (especially montmorillonite content), and particle size distribution, and they include the specific surface area (internal and external), cation-exchange capacity (CEC), acid-base properties of the edge sites, viscosity, swelling, water permeability, adsorption of different substances, and migration rate of soluble substances in bentonite clay. 

As seen previously, bentonite samples from the same bentonite deposit (Sajobabony) show no significant differences in the montmorillonite content, but the circumstances of their geological formation are different. The sedimentary bentonites (B-I.b. and B-II.a.) show similar interfacial properties, while the bentonitic tuff (B-II.b.) behaves differently. This is probably caused by the large amount of the x-ray amorphous phase. 

The swelling of bentonites in water and, as will be discussed in Section 3.2.2, the migration of a nonadsorbing ion show no direct relationship to the montmoril-lonite content or other geological characteristics in this narrow range (35%-48% montmorillonite content, Table 3.1). However, they are influenced by several other factors, for example, the quality of the exchangeable cation (Chapter 2, Section 2.1), particle size distribution, aggregation, density, free pore size, other minerals, etc. 

As a consequence of this, the properties and possible application of bentonites are determined by both the montmorillonite content and geological origin. The origin appears in the particle size and external surface properties. 

Before discussing the practical applications of bentonite, its different properties have to be studied in order to determine how the various bentonite rocks can be used. In the scope of this book, some agricultural and environmental applications are mentioned. In these applications, natural or chemically modified bentonite rocks are in direct contact with the soil or the geological environment. As an example, we can mention the bentonite barriers used for waste disposals. 

The application of the linear model will be shown for cesium-137 and strontium-85 ions. Cs-137 and the different strontium isotopes, especially Sr-90, are important components of nuclear wastes. As seen previously in Table 3.2, the cesium ion has a different sorption property on bentonite samples from the Sajobabony deposit, depending on geological origin and composition. Similarly, different bentonite rocks from the Carpathian Basin (Table 3.4) show different sorption properties, including kinetics and equilibrium (Figure 3.4, Table 3.5 Nagy et al. 2003b Konya et al. 2005). 

Many national programs plan to surround containers of their nuclear waste in a geologic repository, with a backfill of compacted bentonite clay (Fig. 13.33). A chief function of the clay backfill is to adsorb radionuclides and so retard their release from the engineered barrier system. Conca (1992) measured the apparent diffusion coefficient (D ) and apparent distribution coefficient (K [ml/g]) of some radionuclides in bentonite clay as a function of clay moisture content and compaction density. Measurements were made for clay densities from 0.2 to 2.0 g/cm, which correspond to porosities of 93 to 25%, respectively. With decreasing porosity, values declined by roughly 10 to 10 -fold. However, for the same porosity reduction, values were usually lowered by 10-fold and more, indicating less adsorption with compaction (Fig. 13.38). 

The Milk River Formation conformably overlies the Colorado Group and consists of up to 100 m of very fine- to medium-grained sandstone, siltstone and shale. More detailed geological descriptions of the aquifer are presented by Meyboom (1960). The Milk River aquifer, which comprises the lower part of the formation, crops out in the southernmost part of Alberta and northern Montana. Overlying the Milk River Formation is the Pakowki Shale. This unit consists entirely of marine shale with some very thin sandstone and bentonite beds (McCrossan and Glaister, 1964). Other bedrock and glacial drift units overlying the Pakowki have not been further subdivided (Fig. 2). 

Pintado, X., Ledesma, A., and Lloret, A., Back-analysis of thermohydraulic bentonite properties from laboratory tests. Engineering Geology, 64 91-115,2002. 

We have developed and improved the numerical code THAMES to predict and assess the coupled THM behaviour in and around the EBS of the geological disposal of high-level radioactive waste. THAMES is a finite element code for analysis of coupled thermal, hydraulic and mechanical behaviour of a saturated-unsaturated medium. Then, we applied THAMES to calculate this task of the DECOVALEX III. In this task, the evolutions and the distributions of stress, relative humidity and temperature at the specified points in bentonite buffer material are required. 

A buffer of compacted bentonite is planned to be used to prevent the movement of groundwater and the consequential escape of material from a geological repository for spent nuclear fuel. Fluid flow, phase changes, mechanical behaviour of the buffer, rock, and the waste canisters, and the heat produced by the waste constitute a coupled thermohydromechanical system. The aim of the study is to derive a general thermodynamically consistent THM model for an arbitrary mixture. The general theory is applied to the thermohydraulic modelling of a mixture of compacted bentonite, liquid water, vapour, and air. 

Abstract Geological disposal of nuclear fuel wastes relies on the concept of multiple barrier systems. In order to predict the performance of these barriers, mathematical models have been developed, verified and validated against analytical solutions, laboratory tests and field experiments within the international DECOVALEX project. These models in general consider the full coupling of thermal (T), hydrological (H) and mechanical (M) processes that would prevail in the geological media around the repository. This paper shows the process of building confidence in the mathematical models by calibration with a reference T-H-M experiment with realistic rock mass conditions and bentonite properties and measured outputs of thermal, hydraulic and mechanical variables. 

The engineered buffer used in deep geological disposal sites is often pure bentonite or a bentonite - sand mixture. Bentonite is a material with very low permeability and swelling properties. The swelling properties are used as a seal against water intrusion. 

In BMTl a typical deep geological waste repository set-up is studied. Figure 6 shows a detail of the set-up. The waste canister is surrounded by a bentonite buffer material, and the backfill for the tunnel is made of a bentonite-sand mixture. The host rock is granite. Material... 

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