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Cohesive sediments
Published in Arved J. Raudkivi, Loose Boundary Hydraulics, 2020
The montmorillonite s are known as the expanding three-layer clays and are derived from the neutral three-layered pyrophyllite (Al) and talc (Mg) by isomorphous substitution of other atoms. The tetravalent Si atom may be replaced at some locations by trivalent Al. In the octahedral sheet replacement of Al by divalent Mg may take place. Al atoms could also be replaced by Fe, Cr, Zn, Li and other small atoms which fit in the space of Si and Al atoms. A replacement by an atom of lower valance leads to a deficit of positive charge. The excess negative lattice charge leads to cation adsorption on the surface. The latter are too large and do not fit into the lattice. The amount of these cations is expressed in milliequivalent (meq) per 100 g of dry clay and is known as the cation exchange capacity or the base exchange capacity of the clay. In contact with water, the water molecules penetrate between unit layers and this leads to swelling. The structure of montmorillonite is illustrated in Figure 10.4. Montmorillonite is the main clay mineral in bentonite rock, which originates from volcanic ash. Other members of the group are hectorite, saponite, sauconite, vermiculite, volchonskonite, nontronite. Montmorillonites are less common in sediments older than Mesozoic and represent an intermediate stage of weathering. They are common clay fractions in silty soils of temperate regions which have developed under trees and grass.
Physico-Chemical Effects of Salts upon Infiltration and Water Movement in Soils
Published in R.J. Wagenet, P. Baveye, B.A. Stewart, Interacting Processes in Soil Science, 2020
The degree of interaction between soil solution and soil particles depends on types and amounts of soil clays. The dominant clay mineral in the semi-arid and arid regions is montmorillonite (a member of the smectite group). Kaolinite is common in the more humid regions while illite is common in both regions. The colloidal properties of clay minerals depend on their specific surface areas (surface area per gram of clay), which depend on the size and shape of the clays. The specific surface areas of montmorillonite, illite, and kaolinite are 750, 120, and 30 m2 g−1, respectively. This explains why montmorillonite is the most reactive constituent among soil mineral colloids. However, clay reactivity also depends on the cationic composition and on the free electrolyte concentration in the equilibrium solution.
Nanomaterial-based FRs
Published in Asim Kumar Roy Choudhury, Flame Retardants for Textile Materials, 2020
Phyllosilicates include muscovite (KAl2(AlSi3O10)(OH)2), talc (Mg3(Si4O10)(OH)4), and mica. Chemically, montmorillonite is hydrated sodium calcium aluminium magnesium silicate hydroxide (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O. Montmorillonites swell or expand considerably more than other clays due to water penetrating the interlayer molecular spaces and concomitant adsorption. By exchanging sodium cations for organic cations, the surface energy of MMT decreases and the interlayer spacing expands. The resulting material is called organoclay (Singla et al., 2012).
Effects of salt and pH on microstructure and physico-mechanical behaviors of clay sediments：A references review
Published in Marine Georesources & Geotechnology, 2023
Chang-lin Hou, Xiong-ying Ma, Xin Kang
The alteration of swelling characteristics of clay exerts an important influence on engineering endeavors. Swelling has the potential to modify volume, which is observable at a macroscopic level as uplift or settlement of the foundation, often affecting the safety of the superstructure. In addition, in the case of the underground deep landfill, the decrease in swelling will lead to the decrease in closure and the subsequent decrease in closure effects. Therefore, the influence of pore water chemistry on swelling and the internal mechanism have been widely concerned. For kaolin, due to the strong interlayer bond force, the interlayer expansion in response to water is prevented. Therefore, the expansibility of kaolin is smaller (Pedrotti and Tarantino 2018). Montmorillonite, however, as an active clay, possesses a large specific surface area and cation exchange capacity, resulting in a considerable swelling potential. Therefore, the studies of clay expansibility primarily focus on montmorillonite.
Evaluation of terrestrial radionuclide levels and concomitant radiological risks of bentonites used in many industries
Published in International Journal of Environmental Health Research, 2022
Aslı Kurnaz, Şeref Turhan, Onur Metin, Aydan Altıkulaç, Celalettin Duran
Bentonites consist of montmorillonite that is one of the smectite groups of clay minerals, regardless of its formation or origin (Eisenhour and Reisch 2006; Reichl and Schatz 2021). Bentonites have unique physical and chemical properties such as high cation sorption, cation exchange capacity, and large surface area. Bentonites generally occur in two main varieties: calcium (or non – swelling) bentonite the most commonly occurring, and sodium bentonite (or swelling bentonite) industrially the more important (Eisenhour and Reisch 2006; Reichl and Schatz 2021). Bentonites have a very wide utilization area such as drilling muds, pet litters, waterproofing and sealing applications, animal feed additives, oil and grease absorbents, agricultural carriers, filtration, clarification, decolorizing agents, asphalt emulsions, catalysts, and additives in the ceramics, cement, and concrete industry, etc. (Eisenhour and Reisch 2006).
Equilibrium, kinetic and hydraulic study of different Indian bentonites in presence of lead
Published in European Journal of Environmental and Civil Engineering, 2022
Saswati Ray, Anil Kumar Mishra, Ajay S. Kalamdhad
Since the number of edge charges presents on the outer surfaces is lower than the number of layer charges in the inward surfaces; therefore, in the inner surfaces, the cation exchange is higher for the most part in contrast with the adsorption on the outside surfaces. The crystal assembly of montmorillonite in the interior surfaces comprises octahedral and two tetrahedral layers. The trivalent aluminium particles (Al3+) in the tetrahedral layers can displace focal tetravalent silicon (Si4+) layers, and divalent cations (normally Mg2+ and Fe2+) in the octahedral layers can displace the trivalent aluminium particles (Baylan & Meriçboyu, 2016). Thus, the layers turn out to be negatively charged. By the hydrated cations in the inside surfaces, these negatively charged layers are balanced. The cations are reinforced with electrostatic forces of attraction to these interior surfaces; thus, they can be displaced with different cations. Cations can be reinforced into the crystal lattice when the cation size is like the pore sizes in the assembly of montmorillonite, and accordingly, they diminish the negatively charged layer (Baylan & Meriçboyu, 2016). Sheta et al. (2003) investigated the sorption properties of natural zeolite and bentonite in the presence of zinc and iron and concluded that metal uptake was strongly dependent on the mineralogical properties of the soil and type of metals.