Phyllosilicate clays

Phyllosilicates (clay minerals) - layered silicates such as Al4Si4O10(OH)8 (kaolinite) and (Ca,Na)o.7(Al,Mg,Fe)4(Si,Al)802o(OH)4.nH20 (montmorillonite, also called smectite). 

There has been considerable interest in the development and application of phyllosilicate clays (HSCAs) to selectively chemisorb aflatoxins in aqueous suspensions, including milk, reduce the uptake of aflatoxin by blood and its distribution to body organs such as the liver, reduce the transmission of aflatoxin Mi to milk in lactating animals and to decrease the toxic effect of aflatoxin to many animal species (Phillips et al., 1995). It is believed that the HSCAs when added to feeds act by the selective chemisorption of the aflatoxin in the gastrointestinal tract of the animal resulting in a marked reduction in the bioavailability of the aflatoxins. 

Detailed experimental procedures have been previously reported (Ko, 1998 Ko et al., 1998a,b) therefore, they are only briefly described here. Phenanthrene (Aldrich, 99.5+%), naphthalene (Aldrich, 99+%), SDS (Sigma, 99.5+%), and Tween 80 (Aldrich, no purity reported) were used as received selected physicochemical properties for these compounds are shown in Table 1. Kaolinite, a nonswelling 1 1 layer phyllosilicate clay and common constituent of many subsurface environments, was used as received from Sigma. Solution pH and ionic strength were adjusted as necessary with 0.5 M HC1 and/or 0.5 M NaOH and NaCl, respectively. Aqueous phenanthrene and naphthalene concentrations were quantified by fluorescence (PTI, Inc.) at the excitation/emission wavelengths of 250/364 and 278/322 nm, respectively. A total organic carbon (TOC) analyzer (Shimadzu Model 5050) was used to determine aqueous SDS concentrations and Tween 80 concentrations were determined by UV absorbance at 234 nm. 

Bleam, W.F (1990). The nature of cation-substitution sites in phyllosilicates. Clays Clay Miner., 38 527-536. 

Sarr AB, Mayura K, Kubena LF, et al. 1995. Effects of phyllosilicate clay on the metabolic profde of aflatoxin B1 in Fischer-344 rats. Toxicol Lett 75 145-151. 

Phyllosilicate clays are built from tetrahedral sheets made of SiO silicate units and of octahedral sheets resulting from the condensation of octahedra — such as the aluminate AlO octahedron — centered on a divalent or on a trivalent cation. Layers can be constituted of one tetrahedral sheet associated with one octahedral sheet (1 1). Or they can be made of one octahedral sheet sandwiched in-between two tetrahedral sheets (2 1). There are other combinations, associating up to four sheets. 

The tetrahedral and octahedral sheets can be stacked on top of each other to form a phyllosilicate layer. Indeed, the first classification of phyllosilicate clay... 

From the discussion above, it can be seen how the atomic structure of phyllosilicate clays plays a key role in determining the final state of clay particles in aqueous media. The presence of structural charges, neutralizing cations, and the capacity of forming hydrogen bonds between different layers produces a system that can be completely delaminated, completely flocculated, or in an intermediate state having floes mixed with isolated layers. Whether the more stable situation corresponds to isolated layers, floes, or a mixture depends on the type of clay, its concentration, pH, concentration and type of supporting electrolyte, and so on. 

White, G.N. and Zelazni, L., Analysis and implications of the edge structures of dioctahedral phyllosilicates, Clays Clay Miner., 36, 141, 1988. 

Hectorite is a naturally occurring phyllosilicate clay of the smectite (montmorillonite) group and is a principal component of bentonite clay. Hectorite is a mineral with an approximate empirical formula owing to the variability in cation substitution see Table I. 

Phyllosilicate/clay smears These are developed by the deformation of material with high concentrations of phyllosilicates. The type and continuity of the clay smear (Fig. 2b) depends on the architecture or proximity of the shale units, the lithifi-cation state of the phyllosilicate rich units at the time of deformation and the amount of shearing or fault offset. 

PZCs/IEPs of aluminosilicates, phyllosilicates, clays and clay minerals are presented in Tables 3.1229 through 3.1356. Aluminosilicates, phyllosilicates, clays, and clay minerals have variable composition, and complicated classi licalion and terminology. The same or similar specimens are named differently in different publications. In the present survey, aluminosilicates, phyllosilicates, clays, and clay minerals are sorted alphabetically according to their names used in the original publications. These names may refer to specihc minerals, to groups of minerals, to clays, or to rocks. Specimens, mostly of natural origin, have been usually comminuted and/or purified. Several modihed natural specimens and synthetic materials are also included. 

Heller-Kallai L, Rozenson 1 (1980) Dehydroxylation of dioctahedral phyllosilicates. Clays Clay Minerals 28 355-368... 

Manceau A, Calas G (1987) Absence of evidence for Ni/Si substitution in phyllosilicates. Clay Minerals... 

The X-ray diffraction (XRD) pattern of the as-synthesized aminoclay shows a low-angle reflection with a doa spacing of 1.4 nm corresponding to the bilayer arrangement of propylamino groups (Fig. la). The broad in-plane reflections at higher angles (4)20.110 = 0-41 nm, d 3o.2oo = 0.238 nm) and the characteristic (060) reflection at 0.156 nm confirm the formation of 2 1 trioctahedral Mg-phyllosilicate clay with talc-like structure. The XRD pattern... 

Reacted samples remeasured 3 months later showed that all of the reduced Fe had subsequently reoxidized to Fe(III). Previous studies have demonstrated that little clay dissolution occurs during redox cycles of phyllosilicate clays (18, 36, 44). This permits the clay to be defined as a catalyst in the truest sense. The clay facilitates the oxidation of TPB but the clay itself is not destroyed. The redox of Fe in smectites is essentially reversible (15, 38), hence the reactivity of this system is in contrast to the widely studied Fe-oxide and Mn-oxide facilitated reactions in which the oxide typically reductively dissolves and transforms during the reaction (19,20). 

Since PCNs are used as structural materials, layered silicates (e.g., dioctahedral 2 1 phyllosilicate clays) have attracted academic and industrial attention. The... 

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