Mineral decomposition

X-ray diffraction has been applied to certain AB cements. For example. Crisp et al. (1979), in a study of silicate mineral-poly(acrylic acid) cements, used the technique both to assess the purity of the powdered minerals employed and to monitor mineral decomposition in mixtures with poly(acrylic acid), in order to indicate whether or not cement formation had taken place. They employed Cu radiation passed through a nickel filter for most of the samples, a seven-hour exposure time was found to be adequate for the development of a discernible diffraction pattern. Samples were identified by reference to published powder diffraction data. 

Reactions below about 1300°C, of which the most important are (a) the decomposition of calcite (calcining), (b) the decomposition of clay minerals, and (c) reaction of calcite or lime formed from it with quartz and clay mineral decomposition products to give belite, aluminate and ferrite. Liquid is formed only to a minor extent at this stage, but may have an important effect in promoting the reactions. At the end of this stage, the major phases present are belite, lime, aluminate and ferrite. The last two may not be identical with the corresponding phases in the final product. 

The dissociation pressure of calcite reaches 0.101 kPa (1 atm) at 894°C (S20) and the decarbonation reaction is highly endothermic (Section 3.1.4). The rate of decarbonation becomes significant at 500-600°C if a sufficiently low partial pressure of COj is maintained or if the calcite is intimately mixed with materials, such as quartz or clay mineral decomposition products, that react with the calcium oxide. Even in a precalciner, such mixing occurs, aided by agglomeration caused by the presence of low-temperature sulphate melts. 

Ponomareva, V.V. and Ragim-Zade, A.I., 1969. Comparative study of fulvic and humic acids as agents of silicate mineral decomposition. Sov. Soil Sci., No. 3, 157—166. 

This suggested mechanism is consistent with a number of observations made here and with previous work reported in the literature. For example it was found that recarbonation rates were relatively insensitive to temperature. This would indicate non-activated chemisorption and, as Fischbeck and Snaidt report (10), mineral recarbonation is often independent of temperature when the temperature dependencies of the decarbonation rate conr-stant and the equilibrium constant are similar. This is exactly what is observed in western oil shales (Ref (9), Equations (6) and (7)). Previous work has also pointed to the role of chemisorption phenomena in mineral decomposition reactions. Spencer and Topley (11) have suggested that finely grained oxides can chemisorb HoO as well as H2 and Soni and Thomson (12) observed higher recarbonation rates when CO2 was produced on the surface during oil shale char combustion. 

Figure 3. Mass loss due to mineral decomposition. Conditions helium purge, heating...

Buffering by aluminosilicate mineral decomposition. In moderately to strongly acid soils (pH < 5.5), variable-charge mineral surfaces as well as layer silicate edges accept protons to generate anion exchange sites, for example at A1 sites ... 

Procedures. Since the char reactions can be accompanied by mineral decomposition reactions, some of which are catalytic, every attempt was made to isolate the pertinent reactions. Of course there is always the possibility that significant interactions will be missed by this procedure and thus it is important to state the procedures which were employed. 

The kinetics of oil shale char gasification have been studied for Colorado oil shale from the Parachute Creek member. Reaction rate expressions similar to those previously reported for coal char were obtained for the H20-char, C02-char and water gas shift reactions. Evidence is presented to suggest that CaO, a product of mineral decomposition, catalyzes the H20-char reaction and that indigeneous iron catalyzes the water gas shift reaction. 

We used two plasma ashing devices International Plasma Corporation, Model 1003B-248AN and LFE Corporation, Low Temperatures Asher, No. LTA-600.) Since the plasma combustion temperature does not exceed 50°C we avoid the possibility of mineral decomposition (especially of carbonates) encountered during high temperature combustion. 

Mineralization Decomposition of organic matter yields CO2, NH, NO, PO j-,aiid SO2- A source of nutrient elements for plant growth... 

The chemical reactions below 1300°C are calcination, decomposition of clay minerals as well as the reaction of calcium carbonate (calcite) CaCOg or calcium oxide (lime) CaO with quartz and clay mineral decomposition products. Calcination of calcite, decomposition of clay minerals are endothermic reactions, while reaction of calcife or lime with quartz and clay mineral decomposition products are exothermic. Calcination of pure calcium carbonate is done according to the reaction ... 

TGA and differential thermoanalysis (DTA) can trace the mass loss and the appearance of reaction enthalpies from a sample. As a TGA curve is usually obtained to determine the reactivity of a coal sample, the peaks for the mineral decomposition occur frequently in overlap with volatile matter release. 

By the temperature of appearance, the mineral decomposition reaction can be identified. Heating and cooling a sample in a DTA may even reveal much more information because transformation reactions of the certain compounds also can be detected (e.g., quartz). 

Perkins, A. T., R. D. Dragsorf, E. R. Lippincott, J. Selby, and W. G. Fateley, 1955. Products of clay mineral decomposition as related to phosphate fixation. Soil Scl 80 109. 

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