Solid/liquid interface, mineral

Modifications of surface layers due to lattice substitution or adsorption of other ions present in solution may change the course of the reactions taking place at the solid/liquid interface even though the uptake may be undetectable by normal solution analytical techniques. Thus it has been shown by electrophoretic mobility measurements, (f>,7) that suspension of synthetic HAP in a solution saturated with respect to calcite displaces the isoelectric point almost 3 pH units to the value (pH = 10) found for calcite crystallites. In practice, therefore, the presence of "inert" ions may markedly influence the behavior of precipitated minerals with respect to their rates of crystallization, adsorption of foreign ions, and electrokinetic properties. 

Radium may be transported in the atmosphere in association with particulate matter. It exists primarily as a divalent ion in water, and its concentration is usually controlled by adsorption-desorption mechanisms at solid-liquid interfaces and by the solubility of radium-containing minerals. Radium does not degrade in water other than by radioactive decay at rates that are specific to each isotope. Radium may be readily adsorbed by earth materials consequently, it is usually not a mobile constituent in the environment. It may be bioconcentrated and bioaccumulated by plants and animals, and it is transferred in food chains from lower trophic levels to humans. 

Fubini B, Mollo L, Giamello E. Free radical generation at the solid/liquid interface in iron containing minerals. Free Radic Res 1995 23 593-614. 

Many theories have been advanced concerning the mechanisms involved in surfacing the mineral particles so as to create a hydrophobic hydrocarbon film on the mineral surface, and many investigations have been carried out to define these mechanisms. When firoth flotation is used in an aqueous medium that carries the solids to be separated (together with dispersed air bubbles and possibly an organic liquid) a three- or possibly a four-phase system must be considered. In most froth flotation processes, the solid particles are initially completely water-wetted, and the solid-liquid interface must be replaced by... 

There has been considerable interest in recent years in the formation of condensed films of purine and pyrimidine bases at the solid-liquid interface. It is well recognised that non-covalent affinities between base pairs play a prevalent role in determining nucleic acid conformation and functionality. Likewise, there has been interest in the role of substrate and non-covalent intermolecular interactions in the configuration of ordered monolayers of purine and pyrimidine bases. There is also more general interest in the interaction of bases with metal surfaces and metal complexes. In the latter case it is noted that the biological role of nucleic acids and certain nucleotides are dependent on metal ions, particularly Mg, Ca, Zn, Mn, Cu and Ni. " Also certain metal complexes, notably of platinum, have the anti-tumour activity, which is linked to their ability to bind to bases on DNA. On a different note, the possibility that purine-pyrimidine arrays assembled on naturally occurring mineral surfaces might act as possible templates for biomolecular assembly has been discussed by Sowerby et al. 

Applications of redox reactions on mineral surfaces in areas such as water treatment have been reviewed by Segal and Sellers (1984) Voudrias and Reinhard (1986) discussed the organic transformations at the solid-liquid interface. Here the discussion is confined to selected inorganic redox reactions. Table 1 lists some of the more important heterogeneous processes of inorganic... 

On the other hand, various hypotheses concerning the properties of the solid-liquid interface and the composition of the double layer have been proposed in order to explain the observed kinetics. These hypothese are, however, often purely speculative. Here again, direct evaluations of properties of the mineral surface and of the interface are barely existing and severely lacking. 

In mineral-reagent systems, surface precipitation has been proposed as another mechanism for chemisorption. The solubility product for precipitation and the activities of the species at the solid-liquid interface determine the surface precipitation process. Under appropriate electrochemical conditions, the activity of certain species can be higher in the interfacial region than that in the bulk solution and such a redistribution can lead to many reactions. For example, the sharp increase in adsorption of the calcium species on silica around pH 11 has been shown to be due to surface precipitation (Somasundaran and Anan-thapadmanabhan, 1985 Xiao, 1990). Similar correlations have been obtained for cobalt-silica, alumina-dodecylsulfonate, calcite/apatite/dolomite-fatty acid, francolite-oleate and tenorite-salicylaldoxime systems. The chemical state of the surfactant in the solution can also affect adsorption (Somasundaran and Ananthapadmanabhan, 1985). 

Another example of the usefulness of microcalorimetry to study the solid-liquid interface has been reported by Draoui et al. [118]. They analyzed the adsorption of Paraquat on different minerals, which are part of the soil, to study the retention process of this pesticide by soils. In the particular case of silica they concluded that the main driving force for adsorption is electrostatic. They found a linear decrease of the adsorption enthalpy in the range of -25 to -20 kJ/mol. Nevertheless, the Paraquat molecule has two charges the heat evolved during adsorption is of the same order as in the case of other single-charged molecules. This fact is explained assuming that the... 

An understanding of the acid-base properties of solid surfaces is extremely important in almost all fields of science and engineering. For example, the solid/ gas interface intervenes when solid acids (or bases) are used as heterogeneous catalysts in the oil refining and chemical industries. The solid/liquid interface between rocks, minerals, and soils and natural waters is continuously transformed by weathering processes that result in the geohydrochemical circuit of elements. These are only two examples in which the primary reactivity factor is determined by the acid-base chemistry at solid interfaces, usually confined to molecule-sized spaces. 

B. Solid/LIquid Interface Acfd-Base Reactions in Interlayers of Layered Minerals... 

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