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پنج شنبه ۹ فروردین ۱۴۰۳
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Sodium Bentonite is an absorbent aluminium phyllosilicate clay consisting mostly of montmorillonite. It was named by Wilbur C. Knight in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming.

The different types of bentonite are each named after the respective dominant element, such as potassium (K), sodium (Na), calcium bentonite (Ca), and aluminium (Al). Experts debate a number of nomenclatorial problems with the classification of bentonite clay. Bentonite usually forms from weathering of volcanic ash, most often in the presence of water. However, the term bentonite, as well as a similar clay called tonstein, has been used to describe clay beds of uncertain origin. For industrial purposes, two main classes of bentonite exist: sodium and calcium bentonite. In stratigraphy and tephrochronology, completely devitrified (weathered volcanic glass) ash-fall beds are commonly referred to as K-bentonites when the dominant clay species is illite. In addition to montmorillonite and illite another common clay species that is sometimes dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically associated with coal.

Bentonite clay have been planned to be used in various applications in order to backfill and seal the repository for high level spent nuclear fuel and in bentonite drilling mud. The buffer around the waste canister composes of pre-compacted bentonite blocks while bentonite may also be used in backfilling and sealing of disposal tunnels and other underground facilities. Bentonite clays have certain desirable material properties such as swelling ability and high sorption capasity. These properties depend on the mineralogy and geochemistry of the material. There are various potential commercial bentonite products available in the markets but they are not necessary similar in respect to mineralogy and chemical composition.

The differences between the mineralogy and geochemistry of different bentonites are usually due to differences in the geological history of the source occurrences. Bentonites are usually formed by alteration of volcanic ash or tuff, mainly rhyolitic or dacitic, either in situ or transported and redeposited. Characteristic for bentonites is that they are mainly composed of smectites, a group of expandable clay minerals with a wide range of chemical compositions. The desired material properties of bentonites, like swelling ability, plasticity, cation exchange capacity etc are dependent on the amount of smectite minerals in the bulk material, smectite species and on the exchangeable cations in the interlayer position. Also interlayering of smectites with another clay mineral, illite is common in bentonites. Bentonite powder has different mesh by bentonite suppliers.

For bentonite specifications, It is important to characterise the mineralogy of potential bentonites in detail to be able to evaluate their suitability for buffer and backfilling purposes, and to be able to evaluate their effects on the long-term safety of the repository. In order to obtain comparable characterization results suitable investigation methods need to be evaluated and determined. The first part of this report summarizes the methods that can be used and discusses their suitability in bentonite research. Recommendations are also given on the characterization methods. Detailed information is included on methods of sample preparation and analysis in cases different methods possibly give diverting results. In the second part, a mineralogical and geochemical research of fourteen bentonites and smectitic clays is reported. The method recommendations presented in part 1 by bentonite suppliers are applied and need for further investigations are identified.

سفارش سئو  ,  ket bilietai nemokamai 2020  Ket Bilietai   ,  Ket Testai , ket bilietai nemokamai , خرید بک لینکبک لینک

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