Effect of mineral surfaces

A discussion of specific catalytic effects of mineral surfaces must be based on thermodynamic and structural information of the reactive surface species. The first part includes a brief outline of the emerging picture of mineral surfaces as two-dimensional arrays of surface complexes. This part assembles also the kinetic tools that are useful for comparison of the reactivity of aqueous metal ions and their adsorbed surface complexes. The second part presents a reevaluation of the most extensively studied inorganic redox reactions in natural waters the oxygenation of VO2 +, Mn2+, Fe2 + and Cu + in homogeneous and heterogeneous systems. 

ENVIORNMENTAL AND GEOCHEMICAL SIGNIFICANCE OF AlOH POLYMERIZATION Effect of Mineral Surfaces on Al Behavior... 

The effect of the surface area is far from being a simple one. It was shown for titania that when the surface area changes from 110 to 12 m2/g, the average time required for a complete mineralization of organic substrates increased from 40 to 75 and 50 to 75 min for salicylic acid and phenol, respectively [135], These results clearly show that textural properties, particularly the surface area, strongly affect the photoreactivity, although a high-temperature treatment improved their crystallinity [18], Therefore, this phenomenon may be explained only in connection with the catalyst surface dehydroxylation. 

It may be noted that the field data on a per m2 catchment area basis, from different geographical areas are remarkably similar 10-2 — 101 equiv nr2 y1). In order to estimate from these rates, actual rates of dissolution of rocks on a per m2 mineral surface area basis, we have to know, how many m2 of effective (active) mineral surface is available per m2 geographic area. This is not known, but the estimate of 105... 

Abiotic organic reactions that may be influenced by mineral surfaces include hydrolysis, elimination, substitution, redox, and polymerization. The effect of the surface may be either to promote (increase the rate of) or to inhibit (decrease the rate of) reactions that may occur in homogeneous solution. In addition, mineral surfaces may promote reactions that do not occur in homogenous solution by selectively concentrating molecules at the mineral surface... 

The purpose of this chapter is to present a brief overview of the geochemistry of mineral surfaces, including their (1) dissolution mechanisms, (2) development of electrical charge when in contact with aqueous solutions, and (3) uptake of aqueous cations and anions, and to discuss some of the factors that control their chemical reactivity, including (1) defect density, (2) cooperative effects among adsorbates,... 

Effects of Dissolved Metal Species Effects of Mineral Oxide Surfaces... 

The effect of mineral matter is so small that it is completely negligible compared to the combined specific surface of the macropores and transition pores in coals with scattering curves which have a shoulder. 

The practical motivation for understanding the microscopic details of char reaction stem from questions such as How does the variability in reactivity from particle to particle and with extent of reaction affect overall carbon conversion What is the interdependence of mineral matter evolution and char reactivity, which arises from the catalytic effect of mineral matter on carbon gasification and the effects of carbon surface recession, pitting, and fragmentation on ash distribution How are sulfur capture by alkaline earth additives, nitric oxide formation from organically bound nitrogen, vaporization of mineral constituents, and carbon monoxide oxidation influenced by the localized surface and gas chemistry within pores ... 

Giese R. F., Jr. and van Oss C. J. (1993) The surface thermodynamic properties of silicates and their interactions with biological materials. In Health Effects of Mineral Dusts, Rev. Min. 28 (eds. G. D. Guthrie and B. T. Mossman). Mineralogical Society of America, Washington, DC, pp. 327-346. 

Table 2. Mechanical properties of specimen effect of mineral size/surface chemistry.

After eight years of exposure, an extensive examination was started in 1994 to evaluate the effectivity and durability of the water repellent treatments [4]. Macroscopic tests as water uptake measurements were carried out to determine the remaining effect of the protective organosilicon layer. Due to the fact that surface information from hydrophobic treatment of mineral surfaces is supplied by surface sensitive measuring techniques, TOF-SIMS and additional DRJFT-studies on treated and exposed material were performed. 

Although sorption of TCB by the silica surfaces can increase values of KDi over those predicted from /oc and K()C alone, the effect is only weakly apparent until very large quantities of mineral surface and very low/oc values are obtained. Some caution must be exercised in extrapolating these comparisons between the reactions of organic contaminants with organic and mineral surfaces to solutes less hydrophobic than TCB. As noted earlier, specific interactions with mineral surfaces may be more important determinants of sorption for less hydrophobic contaminants. 

Flotation of sparingly soluble minerals such as calcite has not been well understood. Recently, Somasundaran et al. (1985, 1991) and Hu et al. (1995) have done some systematic work on the dissolution equilibria of salt-type minerals in solutions and their effects on the selectivity in flotation. Thus they found that surface conversion of mineral surfaces and precipitation on surfaces of minerals due to interactions among dissolved mineral species and the reagents are the major mechanisms that should be considered in flotation systems of sparingly-soluble minerals. 

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