Bentonite exchangeable cations

Ronnel Hydrolysis and rearrangement Acidified bentonite dominant exchangeable cations H, Ca, Mg, Al, Fe(III) Al-catalyzed suggested reaction... 

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. 

French town (Montmorillon) where it was first discovered. In the USA, bentonite is principally mined in Wyoming - hence the term Wyoming clay . The type of bentonite, the source, and its purity influence its properties (Marchal et al. 1995). Bentonite is a complex hydrated aluminum silicate with exchangeable cationic components (Al, Fe, Mg) Si40io (0H)2 (Na+, Ca++). The most commonly used bentonite form in enology is the sodium bentonite. Sodium bentonite has enhanced protein binding capabilities over calcium bentonite. 

The crystallographic surface area of bentonite clay is about 750 m2/ g (17), although the actual value that is obtained depends on the exchange cation. Quirk (18) has reported the solid-liquid surface area of bentonites with various alkali and alkaline earth exchange cations dispersed in aqueous solution. The sodium-exchanged form of bentonite has a measured surface area of 700 m2/g, which is close to the theoretical... 

Figure 8. Distribution of exchangeable cations concentration in the bentonite barrier at various times...

Hydrolysis mechanisms in clay-water systems also can be dependent on the nature of the exchangeable cation. For example, Pusino et al. (1988) studied the catalytic hydrolysis of quinalphos on homoionic bentonite clays. On the Na- and K-clays, deethylation occurred, resulting in the formation of O-ethyl O-quinoxalin-2-yl thiophosphoric acid, whereas 2-hydroxyquinoxaline is the main reaction product on the Cu-, Fe- and Al-clays. 

Bentonite, A general term for a montmorillonite clay. It is not common in the British Isles, but is found in considerable quantity in the U.S.A. and elsewhere. Bentonites are exceedingly plastic, with a high cation-exchange capacity (about 120 m.e./lOOg), the chief exchangeable cation being Na. Bentonite is often added to bodies to improve their plasticity. 

Suzuki, K., M. Kondo, and R. Horigome. 1977. The fixation of exchangeable cations in bentonite by heating (in Japanese). Paper read at 21st Annual Meeting of the Clay Science Society of Japan, 1977, at Government Industrial Research Institute of Nagoya, no. 12, pp. 18 of Abstracts. 

Other research confirmed the influence of the modification of bentonite in their adsorptive properties. The adsorption isotherms were determined with solutions of phenol in concentrations 50 mg L-i to 1000 mg L L in pH 6.5, at 20°C and 24 h. Structural changes were carried out with tetra-decy 1-trimethyl-ammonium bromide (TDTAB) and hexa-decyl-trimethy 1-ammonium bromide (HDTAB), with changes in 25%, 50% and 100% of capacity exchange cation. The equilibrium time was approximately 7 h and kinetic results indicated the possible presence of heterogeneous regions on the surfaces of clays modified with 25% and 50% of its cation exchange capacity. The clays modified with TDTAB and HDTAB in 100% obtained the best results for the removal efficiencies (Yilmaz Yapar, 2004). 

Smectite clay - Like mica, smectite cl (commonly called bentonite) has either a pyrophyllite or talc structure. Montmorillonite, a common high-aliunimun smectite, can be characterized by die pyrophyllite crystal structure with a small amount of octahedral Al replaced by Mg. The resulting charge imbalance is compensated by exchangeable cations, usually Na or Ca, between the laminae. In addition to diese counterions, oriented water, similar to that in vermiculite, occupies the interlaminar space. When Ca is the exchangeable cation, there are two water l ers, as in vermiculite when Na is the counterion, there is usually just one water layer. Figure 18 shows the montmorillonite structure. 

Sodium bentonite - Sodium bentonite is composed substantially of smectite, usually montmorillonite, with sodium as the major exchangeable cation. As such it is water swellable and will hydrate to form the characteristic colloidal structure. 

Smectite - The smectites are water swellable cl s having a sheet or platelet structure. Smectite is the mineralogical term for this class of clays, which includes montmorillonite, hectorite, and saponite. Montmorillonite clays derive their name from the Montmorillon section of France where this material was first observed and later classified. Most smectites are more commonly known under the geological term bentonite. By convention, a bentonite is understood to be an ore or product with a substantial smectite content. The name bentonite derives from Fort Benton, Wyoming, the site of an important deposit. Lattice substitutions within the smectite clays creates a charge imbalance which is compensated by exchangeable alkali and alkaline earth cations. This contributes to the ability of these clay to swell and impart considerable plasticity in ceramic formulations. When the exchangeable cations are predominately sodium, the individual platelets can separate to produce a colloidal structure in water. 

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