Decomposition of carbonate minerals

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. 

In the absence of other substances, dolomite [CaMg(C03),] begins to decompose rapidly in air at about 750°C, giving initially periclase and a carbonate of higher Ca/Mg ratio. The decomposition temperature is much affected by the presence of other substances. 

The mechanism and kinetics of calcite decomposition have been much studied. The reaction proceeds by the movement inwards from the surface of an interface, behind which the material is converted into lime, thus producing a highly porous pseudomorph. The interface moves at a constant rate, implying that the rate at any instant is proportional to the area of the interface. In principle, the rate is controlled by the slowest of the following five steps  

Very different conditions exist in a precalciner, where the raw meal is dispersed in hot gas. The reaction still proceeds by the movement of an interface inwards, but the rate is controlled by the chemical reaction, and the temperature within the particle is virtually that of the surrounding gas (V2,B26). The rate is much higher than in a rotary kiln, and, as seen in Section 3.2.3 decomposition is normally 90-95% complete within a few seconds. 

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Three methods for determining mineral carbon dioxide in coal were investigated using bituminous coal. The titrimetric method is claimed to be superior to either of the then-used British standard gravimetric or manometric methods (BS 1016). The procedure involves the decomposition of carbonate minerals with hydrochloric acid and absorption of the evolved carbon dioxide in a mixture of benzylamine, ethanol, and dioxan. This mixture forms a stable salt of benzylcar-bamic acid, which is then titrated with sodium methoxide. The method was said to be suitable for all concentrations of carbon dioxide. It is especially accurate for low concentrations, and it is much more rapid than other methods tested. 

Decomposition of kerogen Decomposition of carbonate minerals Reaction of carbon with C02 Reaction of carbon with 02 Thermal degradation of oil Release of fixed water... 

Ra = R3 -h (10Rc)/0.9. The RC (residual carbon) term represents heavy bitumens or recycled kerogens not directly volatilized by pyrolysis, but that could be oxidized to CO2 or CO in the separate oxidation step (Lafargue et al. 1997). Flowever, the Kuparuk formation often contains cements, siderite among others, which decompose to CO2 or CO at temperatures reached in the oxidation step of Rock-Eval 6 analysis. Unacceptable variability in RC was observed in pyrolysis of Kuparuk samples, possibly because of decomposition of carbonate minerals. Therefore, a Y coefficient was adopted to correlate Rock-Eval 6 pyrolysis results to petroleum density, where F=(R1+R2)/ (R1 +R2 + R3). 

Another source of CO2 can be thermal decomposition of carbonate minerals, or their destruction by acid waters during the oxidation of sulphide ores. 

Carbonate Decomposition. The carbonate content of Green River oil shale is high (see Table 4). In addition, the northern portion of the Piceance Creek basin contains significant quantities of the carbonate minerals nahcoUte and dawsonite. The decomposition of these minerals is endothermic and occurs at ca 600—750°C for dolomite, 600—900°C for calcite, 350—400°C for dawsonite, and 100—120°C for nahcohte. Kinetics of these reactions have been studied (19). Carbon dioxide, a product of decomposition, dilutes the off-gases produced from retorting processes at the above decomposition temperatures. 

Uydrate of potassa is a most valuable agent to the chemist, and especially in the estimation of the carbon of organic bodies. It is also used to displace metallic oxides from their combinations, ae a solvent for oxides or zino and alumina, also for the decomposition of silicioua minerals by fusion, for drying certain gases, and a variety of ether purposes. In surgery, it is used in the solid stata, cost into sticks, as a most powerful caustie. In medicine, its solution is also frequently employed, especially os an antacid. 

Many studies of the impact of chemical diagenesis on the carbonate chemistry of anoxic sediments have focused primarily on the fact that sulfate reduction results in the production of alkalinity, which can cause precipitation of carbonate minerals (see previous discussion). However, during the early stages of sulfate reduction (—2-35%), this reaction may not cause precipitation, but dissolution of carbonate minerals, because the impact of a lower pH is greater than that of increased alkalinity (Figure 4). Carbonate ion activity decreases rapidly as it is titrated by CO2 from organic matter decomposition leading to a decrease in pore-water saturation state. This process is evident in data for the Fe-poor, shallow-water carbonate sediments of Morse et al. (1985) from the Bahamas and has been confirmed in studies by Walter and Burton (1990), Walter et al. (1993), and Ku et al. (1999) for Florida Bay, Tribble (1990) in Checker Reef, Oahu, and Wollast and Mackenzie (unpublished data) for Bermuda sediments. 

The ash that is produced in the gasifier always has a lower density than the minerals from which they originate, due to loss of water, decomposition of carbonates, and the presence of some carbon. The bulk density of the ash in particular may be low due to the formation of hollow ash particles. This means that special attention has to be given to the transformation and transport of such ashes.3... 

Molecular hydrogen also induces the decomposition and reduction of carbonate minerals, as observed by others (1 ). This can best be seen from our data by comparing the larger yield of total CQrq and lower yield of total C n under H2 in Table IV. This reduction leads to more H20, CH, and CO in an H2 atmosphere. The reactions involved are summarized in Scheme 1. The larger amount of carbonates decomposed in H2 vs. N2 and the comparative yields of H20, C02, CO, and CH (5.2 out of the... 

For comparison purposes, a sample of Eastern U.S. shale was also analyzed by TG-DTG. The absence of the characteristic carbonate decomposition peak in the 700-800°C temperature range is indicative of the lack of carbonate minerals in Eastern U.S. shales. The net organic pyrolysis yield, 47.6 wt%, Table I, is... 

The formation of carbon-mineral adsorbents containing carbon deposits in the form of dendrites, whiskers or carbon black is not advantageous because of the poor mechanical properties of these deposits. The morphology of the coke depends on the mechanism and conditions of its formation on the mineral surface. Two main mechanisms of formation of carbon deposits can be distinguished consecutive reactions and carbide-forming. The latter mode consists in the thermal decomposition of hydrocarbons. 

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 ... 

FIGURE 9.59 Maximum amount of dissolved phosphate released per unit of carbon mineralized during anaerobic decomposition. (Adapted from Roden and Edmonds, 1997.)... 

Introduction Alkaline-earth metal carbonates and especially calcite are the most popular reactants in studying the decomposition kinetics of solids. This is caused, not only by the use of carbonates as mineral raw materials for some industrial processes (in particular, production of lime), but also by the fact that the decomposition of calcite is a convenient model reaction for studying the kinetics and mechanism of solid-state reactions as a whole. An enormous number of papers, summarized in part in several monographs [43, 45, 99] and reviews [100-102], deal with the decomposition of carbonates. A series... 

The clinker formation process is initiated by the dehydration of gypsum to anhydrite at around 100-120°C, followed by a decomposition of clay minerals at around 300-600°C. The decaibonization of the calcium carbonate that is present starts at about 700°C, and is completed before the temperature reaches 900°C. 

Silicification of wood is commonly associated with volcanic ash, which is a rich source of readily available soluble silica (274). Correns (275) suggests that the silica may be precipitated from alkaline natural waters by the carbon dioxide evolved during decomposition of the wood. In this way, silica would be deposited immediately at the surface of the organic material, and as the organic portion dissolved away, it would be replaced by silica. This presupposes that the silica initially formed is amorphous and porous, permitting diffusion of solution through the specimen Since plant tissues contain membranes that can be penetrated by soluble silicic acid but not by colloidal particles of silica, Hellmers (276) believes that silicification occurs immediately after the soluble silica is liberated by decomposition of silicate minerals and before it can polymerize. 

As shown in Figure 5.34, the DTA-TG curves of carbonate mineral show endothermic decomposition with a mass loss 41.25% at 650 °C and an exothermic mass gain at 710 C due to oxidation. TG-DTA curves of carbonate mineral show a similar pattern to those of siderite. However, the temperature of the endothermic peak of siderite is observed at 600 °C and the mass loss is 37.99%. A higher peak temperature and larger mass loss... 

The decomposition of dithionite in aqueous solution is accelerated by thiosulfate, polysulfide, and acids. The addition of mineral acid to a dithionite solution produces first a red color which turns yellow on standing subsequentiy, sulfur precipitates and evolution of sulfur dioxide takes place (346). Sodium dithionite is stabilized by sodium polyphosphate, sodium carbonate, and sodium salts of organic acids (347). 

The most common source is the supersaturation and subsequent scaling of minerals originating in the MU water. Insoluble calcium carbonate in the form of calcite (CaC03) resulting from the thermal decomposition of soluble calcium bicarbonate [Ca(HC03)2] is a classic example. Calcium carbonate quickly forms a white, friable deposit. In addition, the hydrolysis of excess bicarbonate increases... 

B. l-Bromo-2-fluorobenzene. Cautionl This step should be carried outm a hood because the PFS evolved on thermal decomposition of the diazonium salt is poisonous. The apparatus consists of a 1-1., three-necked, round-bottomed flask equipped with a thermometer, a condenser, a magnetic stirrer (optional), and a 250-ml. Erlenmeyer flask that is attached by means of a short rubber Gooch connecting tube. The dry powdered hexafluorophosphate salt is placed in the Erlenmeyer flask, and 300 ml. of heavy mineral oil is placed in the round-bottomed flask. The mineral oil is heated to 165-170° by means of an oil bath or electric heating mantle and maintained at this temperature while the salt is added rapidly in portions over a period of 30 minutes. The flask is cooled rapidly to room temperature, the side flask is removed, and 400 ml. of 10% aqueous sodium carbonate is added slowly through the condenser. The mixture is steam-distilled until no more oil is visible in the distillate. 

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