Physical and Chemical Properties of Limestone

The physical and chemical properties of limestones vary widely depending on the route by which they were formed, the sedimentary environment and the changes brought about by diagenesis (see section 2.1). For this reason, many of the properties given below should be regarded as typical. 

The Chemical Abstracts Service (CAS) registry numbers for limestone, CaC03 and MgCOs are 1317-65-3, 471-34-1 and 546-93-0 respectively. The EINECS (European Inventory of Existing Commercial Substances) reference for limestone is 207-439-9. 

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Most classifications have been developed by and for geologists. However, when selecting a limestone deposit for quarrying, the developer is concerned with its physical and chemical properties and their influence on the suitability of the products for the intended end-uses. Similarly, a lime producer would be interested in the characteristics of the limestone fed to the kilns, how it responds to heating, and the physical and chemical properties of the resulting lime products. These aspects are considered in greater detail in later chapters. 

Another important parameter is the deactivation rate constant which appear in the deactivation models. Its value was reported to vary between 10 - lO" s This constant was also reported to depend upon temperature. Of course, its value might also depend upon the physical and chemical properties of the limestone. The activation energy of the deactivation constant is tabulated in Table 2.5. 

The above calculation is quite tedious and gets complicated by the fact that the properties which ultimately control the magnitude of these fourteen unknown quantities further depend on the physical and chemical parameters of the system such as reaction rate constants, initial size distribution of the feed, bed temperature, elutriation constants, heat and mass transfer coefficients, particle growth factors for char and limestone particles, flow rates of solid and gaseous reactants. In a complete analysis of a fluidized bed combustor with sulfur absorption by limestone, the influence of all the above parameters must be evaluated to enable us to optimize the system. In the present report we have limited the scope of our calculations by considering only the initial size of the limestone particles and the reaction rate constant for the sulfation reaction. 

The chemical and physical properties of limestone vary tremendously, owing to the nature and quantity of impurities present and the texture, ie, crystallinity and density. These same factors also exert a marked effect on the properties of the limes derived from the diverse stone types. In addition, calcination and hydration practices can profoundly influence the properties of lime. 

Fillers may be used at concentrations of 10% to 50%, targeted at some desired physical or chemical properties, but also frequently useful as cheape-ners. Wherever their major utility is to stiffen and strengthen, they will be termed "reinforcement," and in most cases have a fibrous structure. Useful fillers include limestone, quartz, silica, talcum, alumina and other minerals. Particle size and distribution are of highest importance. Low-cost fillers for thermosets (eliminating brittleness) include sawdust, paper or jute. The use of ground limestone (or precipitated Ca CO3) is mainly found in PVC and unsaturated polyester in the fields of construction and flooring. Currently,... 

What is the chemistry of the deterioration of marble by sulfuric acid Marble is produced by geological processes at high temperatures and pressures from limestone, a sedimentary rock formed by slow deposition of calcium carbonate from the shells of marine organisms. Limestone and marble are chemically identical (CaC03) but differ in physical properties because limestone is composed of smaller particles of calcium carbonate and is thus more porous and more workable. Although both limestone and marble are used for buildings, marble can be polished to a higher sheen and is often preferred for decorative purposes. 

Cement generally begins with a mixture of limestone and sand placed in a kiln, which heats it to about 1480°C. As the mixture is heated, its chemical and physical properties change. After heating, the solid that remains is ground into a fine powder. This is cement. To make concrete, the cement is mixed with fine particles, such as sand, coarse particles, such as crushed stone, and water. 

The COt Acceptor Gasification Process is discussed in light of the required properties of the CaO acceptor. Equilibrium data for reactions involving the CO% and sulfur acceptance and for sulfur rejection jit the process requirements. The kinetics of the reactions are also sufficiently rapid. Phase equilibrium data in the binary systems CaO-Ca(OH)t and Ca(OH)jr-CaCOs show the presence of low melting eutectics, which establish operability limits for the process. Data were obtained in a continuous unit which duplicates process conditions which show adequate acceptor life. Physical strength of many acceptors is adequate, and life is limited by chemical deactivation. Contrary to earlier findings both limestones and dolomites are equally usable in the process. Melts in the Ca(OH)2-CaC03 system are used to reactivate spent acceptors. 

Quicklime is produced by the thermal dissociation of limestone. Its principal component is ealcium oxide. Its quality depends on many factors including physical properties, reaetivity to water and chemical composition. As the most readily available and cost-effective alkali, quicklime plays an essential part in a wide range of industrial processes. 

The production cost of limestone depends on a number of factors. The nature of the deposit can be important massive deposits with little overburden, horizontal strata and consistent physical/chemical properties favour low extraction costs, particularly if linked with a large-scale operation. Selection of appropriate equipment to keep the combined costs of labour, capital charges and other operating costs to a minimum is important to ensure a strong competitive position (see chapters 4 and 5). 

Unlike the catalytic reaction discussed above, gas-solid reactions involve the solid particle as well as the gas in the reaction. Typical examples of industrial applications include spent FCC catalyst regeneration, calcination, coal combustion, gasification, and silicon chlorination. Owing to the solid particle involvement in the reaction, significant changes in the chemical compositions and physical properties of the particles occur during the reaction. Particles reduce in size and/ or increase in porosity in some reactions like coal combustion, whereas particles increase in size and/or decrease in porosity in other reactions such as limestone sulfation. As a result, the particle properties vary unlike those particle properties in catalytic reactions. However, as with catalytic reactions, gas-solid reactions take place on the particle surface as gas reactant adsorbs to the surface. 

A solution which is both favourable from the process engineering standpoint and relatively simple in terms of mechanical equipment consists in feeding the two components, at controlled rates, from separate feed hoppers, each delivering its material by its own feeder (Fig. 23). Thus, by means of two apron feeders with speed control, the crusher can be fed with a correctly proportioned mixture of raw materials which conforms quite closely to the specified chemical composition. The limestone-clay mixture can usually be handled without difficulty by the hammer crusher even if the clay has very unfavourable physical properties. 

The activation energy values reported in the literature are summarized in Table 2.3. Temperature dependence of solid difhision coefficient is given in Figure 5. The activation energy estimated from this figure is also given in Table 2.3. The differences of diffusion coefficients reported in the literature are majorly due to differences in chemical and physical properties of the limestones, differences in experimental techniques and differences in proposed models from which D, values were evaluated by fitting the experimental data. 

Lime is made by heating limestone, including chalk, to a temperature between 1100°C and 1200°C in a current of air, at which point carbon dioxide is driven off to produce quicklime (CaO). Approximately 56 kg of lime can be obtained from 100 kg of pure limestone. Slaking and hydration of quicklime take place when water is added, giving calcium hydroxide. Carbonate rocks vary from place to place both in chemical composition and physical properties so that the lime produced in different districts varies somewhat in its behaviour. Dolostones also produce lime however, the resultant product slakes more slowly than does that derived from limestones. 

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