Clay-based chemistry

Multi-component clay-based chemistries involving reactions between clays and lime and pozzolans are of interest in the area of soil stabilization. Thermogramst for kaolinite and montmorillonite treated with lime are presented in Fig. 18. Addition of lime results in the gradual diminution of the primary kaolinite dehydroxylation peak (500-600°C) to a greater extent than can be accounted for by dilution alone. All samples have a small peak at about 130°C and a broad endothermic peak at about 210°C. The decomposition of carbonated lime is associated with endothermic reactions at 700-800°C. 

As a second example, consider the liquid/solid interface in a nanosized environment representative of the interlayer space of clay minerals. The hydrophilic and swelling properties of these minerals is the result of structurally induced perturbations of acid-base chemistry in nanosized spaces. 

T 0 bring to closure the plethora of possible examples on this subject we cite two more. Each illustrates a specific domain of intrinsic practical importance in which the acid-base properties of microporous solids play a dominant role in determining a broad range of applications. The examples examine the gas/solid and liquid/solid interfaces, respectively. For the gas/solid interface, the interdependence of acid-base properties and microporous structure is revealed by the catalytic properties of zeolites, especially by their shape-selective properties. It is impossible to review all the literature in this area, and only a few recent views are summarized. For the liquid/solid interface, we focus on the role of acid-base chemistry in interlayers of clay minerals. 

To date, potentiometric titration is still a main approach to study the surface acid base chemistry of clay minerals. Only some papers deal with the dissolution of a solid matrix resulting in various hydrolyzed aluminum species, silicic acid and their product hydrous aluminosilicates, though their interaction with a clay surface should be considered in the modeling description. The surface complexation model (SCM) was successfully applied in a recent paper [6] to interpret surface acid-base reactions involving the dissolution of illite clays during prolonged titration. Voluminous literature on ion adsorption and surface complexation... 

The hot-water separation process involves extremely compHcated surface chemistry with interfaces among various combinations of soUds (including both silica sand and alurninosilicate clays), water, bitumen, and air. The control of pH is critical. The preferred range is 8.0—8.5, achievable by use of any of the monovalent bases. Polyvalent cations must be excluded because they tend to flocculate clays and thus raise viscosity of the middlings in the separation cell. 

Silicon shows a rich variety of chemical properties and it lies at the heart of much modern technology/ Indeed, it ranges from such bulk commodities as concrete, clays and ceramics, through more chemically modified systems such as soluble silicates, glasses and glazes to the recent industries based on silicone polymers and solid-state electronics devices. The refined technology of ultrapure silicon itself is perhaps the most elegant example of the close relation between chemistry and solid-state physics and has led to numerous developments such as the transistor, printed circuits and microelectronics (p. 332). 

Much of the early work in characterizing the environmental behavior of chemicals was accomplished in the area of agricultural chemistry. Work surrounding the behavior of plant nutrients in the soil has provided a large base of information about the processes of environmental chemistry. Workers investigating the effectiveness of soil-applied herbicides determined that the herbicidal activity of organic chemicals varied with soil properties. It was determined that clay and OM contents of the soil were related to the ability of a soil to diminish the effectiveness of an organic herbicide applied [17,21]. 

In this study, the flotation performance of a series of newly developed hy-droxamate-based collectors was evaluated on different crude clays from Georgia, USA. These new collectors provide improved selectivity over the standard tall oil chemistry and the commercial hydroxamate reagent. Aero Promoter 6493 (AP 6493). The modified hydroxamates have the advantages of higher activity, easier... 

For the development of a sustainable chemistry based on clean technologies, the best solvent would be no solvent at all. For this reason, considerable efforts have recently been made to design reactions that proceed under solvent-free conditions, using modern techniques such as reactions on solid mineral supports (alumina, silica, clays), solid-state reactions without any solvent, support, or catalyst between neat reactants, solid-liquid phase-transfer catalysed and microwave-activated reactions, as well as gas-phase reactions [37-42]. However, not all organic reactions can be carried out in the absence of a solvent some organic reactions even proceed explosively in the solid state Therefore, solvents will still be useful in mediating and moderating chemical reactions and this book on solvent effects will certainly not become superfluous in the foreseeable future. 

Encapsulation chemistry similar to that described above (exchange of anilinium, followed by oxidation with peroxydisulfate) was foimd to produce polyaniline not only in zeolite Y, but also in montmorillonite clay. 5 Spectral features (UV-VIS, IR and EPR) of the products were indicative of emeraldine salt and base formation, respectively. The change in basal spacing of the montmorillonite upon intercalation provided additional evidence for the inclusion polymerization. 

Based on their hydrothermal experiments, Aja et al. (1991a, 1991b) and Aja and Rosenberg (1992) have concluded that the I/S clays are not two-phase mixtures, but have several defined compositions. They have inferred these compositions from the solution chemistry and the slopes of reaction boundaries. For example, their data in Fig. 9.12, suggest the most stable I/S solids are Ko.48 io( H)2 Ko.69 U o(OF1)2 at 25°C, and Ko.3i/Oio(UH)2 and Ko,g5/0 o(OH)2 at 125°C. The... 

So far we have used phase diagrams to visualize clay mineral stabilities and phase relations involving the clays in natural waters. Given the complex chemistries of mixed-layer clays in particular, geochemical computer codes offer a more rigorous way to evaluate their stabilities. The thermodynamic data bases of most of these codes list stability constants for a variety of clay minerals which, except for kaolinite, are usually of nonideal composition. Most of these stability constants have been obtained from solubility measurements and are of mixed reliability. It is appropriate to... 

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