Minerals oxidation

Od-fumace blacks used by the mbber iadustry contain over 97% elemental carbon. Thermal and acetylene black consist of over 99% carbon. The ultimate analysis of mbber-grade blacks is shown ia Table 2. The elements other than carbon ia furnace black are hydrogen, oxygen, and sulfur, and there are mineral oxides and salts and traces of adsorbed hydrocarbons. The oxygen content is located on the surface of the aggregates as C O complexes. The... 

Many dyes that have no chemical affinity to fibrous substrates can be attached to such substrates by intermediary (go-between) substances known as mordants. These are either inorganic or organic substances that react chemically with the fibers as well as with the dyes and thus link the dyes to the fibers. Mordants are traditionally classified into two main classes, acid and metallic mordants. The acid mordants are organic substances that contain tannins (see Textbox 64) as for example, gall nuts and sumac. The metallic mordants are inorganic substances, mostly mineral oxides and salts that include metal atoms in their composition. Table 94 lists mordants of both these types, which have been used since antiquity. 

The utility of such reagents in the oxidation processes is compromised due to their inherent toxicity, cumbersome preparation, potential danger in handling of metal complexes, difficulties encountered in product isolation and waste disposal problems. Immobilization of metallic reagents on solid supports has circumvented some of these drawbacks and provided an attractive alternative in organic synthesis because of the selectivity and associated ease of manipulation. Further, the localization of metals on the mineral oxide surfaces reduces the possibility of their leaching into the environment. 

Rate constants for the dissolution and precipitation of quartz, for example, have been measured in deionized water (Rimstidt and Barnes, 1980). Dove and Crerar (1990), however, found that reaction rates increased by as much as one and a half orders of magnitude when the reaction proceeded in dilute electrolyte solutions. As well, reaction rates determined in the laboratory from hydrothermal experiments on clean systems differ substantially from those that occur in nature, where clay minerals, oxides, and other materials may coat mineral surfaces and hinder reaction. 

In all physical and chemical processes, and in particular those of relevance to geochemistry, that involve the oxide/aqueous solution interface, it is important to understand the general, non-specific characteristics of that interface before focussing on those specific processes or mechanisms of interest. Due to the structure of mineral surfaces, the mineral oxide/aqueous solution interface will invariably acquire a net charge or electrostatic potential relative to the bulk solution. The electrical state of the interface will depend in part on the chemical reactions that can take place on the mineral surface, and in part on the electrolytic composition of the aqueous environment. 

From the point of view of electrochemistry of flotation, a depressant is, however, defined as a reagent by the addition of which the oxidation of the mineral surface occurs at lower potential than collector oxidation or formation of metal collector salt which may be also decomposed imder the conditions given in the discussions which follow. Under these conditions, the mixed potential model becomes one of mineral oxidation and oxygen reduction, the oxidation of the thio collector or the formation of the metal collector is suppressed, and the mineral will remain... 

Clay minerals, oxides, and humic substances are the major natural subsurface adsorbents of contaminants. Under natural conditions, when humic substances are present, humate-mineral complexes are formed with surface properties different from those of their constituents. Natural clays may serve also as a basic material for engineering novel organo-clay products with an increased adsorption capacity, which can be used for various reclamation purposes. 

N02 has also been observed to be taken up on mineral oxides of types commonly found in particles in the atmosphere. For example, Miller and Grassian (1998) exposed powders of A1203 and TiOz to N02 in both the presence and the absence of water on the surface. At low N02 concentrations (e.g., 5 mTorr), only N02 which was chelated to the metal ion was observed using FTIR for both dry and hydrated oxides. While nitrate was observed at higher N02 concentrations, these are much larger than would be encountered in the atmosphere. Whether the chelated N02 on the surface can react at a significant rate with various atmospheric gases is not clear. 

Miller, T. M., and V. H. Grassian, "Heterogeneous Chemistry of N02 on Mineral Oxide Particles Spectroscopic Evidence for Oxide-Coordinated and Water-Solvated Surface Nitrate, Geophys. Res. Lett, 25, 3835-3838 (1998). 

Figure 11.3 Typical adsorption isotherm for water on a mineral oxide surface.

Note that for the water surface, HAsurf and HDsnrf have been set to 1.0 that is, the H-donor and H-acceptor properties of the water are implicitly included in the b- and c-terms. Therefore, the HAsurf and HDsurf values of bipolar surfaces such as mineral oxide or salt surfaces exhibit values not too different from 1 (Table 11.1). 

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