Minerals inherent

Once thermal reactions begin, the coal undergoes structural changes through spontaneous bimolecular reactions between coal constituents or solvent species (75) or through catalytic reactions accelerated by added catalysts or the inherent mineral components (76). Hence, the reactivity changes with the progress of these reactions. 

There are two types of minerals in coal (1) extraneous mineral matter and (2) inherent mineral matter. Extraneous mineral matter consists of materials such as calcium, magnesium, and ferrous carbonates pyrite marcasite clay shale sand and gypsum. Inherent mineral matter represents the inorganic elements combined with organic components of coal that originated from the plant materials from which the coal was formed. 

Some inorganic elements were drawn into plant tissues through their roots from the swamp water and peaty soil this material is known as "inherent" mineral matter (30) in the final coal. Ultimately the swamp was drowned by rivers or sea water from which sand and mud were deposited onto the dying forest. Peats covered with seawater were injected with sulfate, but those covered by thick and impermeable river muds (fresh water) remained more or less free of sulfate. 

The silicate species occur in coal chiefly as separate strata and large particle inclusions, and this mode of occurrence is termed the "adventitious" mineral matter. Figure la shows a typical sample of the adventitious silicate mineral particles, density separated from pulverized coal. The density separation technique does not remove the small silicate particles, chiefly alumino-silicate species, the "inherent" mineral matter, in the coal substance (Figure lb). 

The ash content of bituminous coals delivered to utility power station is usually between 10 and 25 per cent (4,8). About 25 per cent of the ash is present in the form of inherent mineral matter of dispersed small particles and also as mineral elements reacted with the coal substance. 

The term, mineral matter , usually applies to all inorganic, noncarbonaceous material in the coal and includes those inorganic elements which may occur in organic combination. Physically, the inorganic matter can be divided into two groups—inherent mineral matter and extraneous mineral matter. Inherent mineral matter originates as part of the growing plant life from which coal was formed. Under the circumstances, it has a uniform distribution within the coal. Inherent mineral matter seldom exceeds 2 to 3 percent of the coal [12]. 

Extraneous mineral matter generally consists of large bits and pieces of inorganic material typical of the surrounding geology. In some cases the extraneous matter is so finely divided and uniformly dispersed within the coal it behaves as inherent mineral matter. Coal preparation can separate some of the extraneous ash from the coal substance, but it seldoms removes any of the inherent mineral matter. 

Extraneous materials can behave as discrete mineral particles comprised of a single species or a multiplicity of species. As already indicated, a portion of this material may be so finely divided it can behave as inherent mineral matter. During combustion the larger particles respond individually to the rising temperature of the environment. In the absence of carbon or other exothermic reactants, the particle should always be at a temperature somewhat less than the local gas temperature. However, the particles may be subjected to either reducing or oxidizing conditions. As each particle rises in temperature, it loses water of hydration, evolves gas, becomes oxidized or reduced, and eventually sinters or melts, depending on its particular composition or temperature level. 

The specific role of pyrite (FeS2) as a catalyst has been under investigation since pyrite was identified as the most active inherent mineral for coal liquefaction. Under liquefaction conditions, FeS2 is transformed into a nonstoichiometric iron sulfide, Fei-x (0 X 0.125). Thomas et al. (15) studied the kinetics of this decomposition under coal liquefaction conditions, and concluded that the catalytic activity of FeS2 is associated with radical initiation resulting from the... 

The term inherent mineral matter, or ash is a commonly used phrase in the coal literature (1). phrase refers to that fraction of... 

Himus, G. W. and Basak, G. C., Analysis of Coals and Carbonaceous Materials Containing High Percentages of Inherent Mineral Matter, Fuel, 1949, 28, 57. 

Inherent mineral components that are in intimate contact with the coal substance or even chemically bonded with it and finely distributed throughout the dense phase. The sodium and chlorine ions tend to be associated with the coal substance and usually evenly distributed throughout the coal mass, but not... 

Since the inherent mineral matter is intimately associated vrith the coal particles it usually attains a higher temperature during combustion than the surrounding flue gases. Under such conditions, fusion and chemical reaction are likely to occur. Conditions near the flame will probably cause the particles to experience a reducing environment for relatively long periods, that will also influence the character of the chemical reactions, particularly those involving the variable oxidation states of iron. 

The terms extraneous mineral matter and inherent mineral matter were usually used to describe an ashforming material, separable and nonseparable from coal... 

Mineral matter in coal (Chapter 7) is often classified as inherent mineral matter or as extraneous mineral matter. The inherent mineral matter is the inorganic material that originated as part of the plant material that formed the organic debris in the source bed. On the other hand, extraneous mineral matter is that inorganic material which was brought into the coal-forming deposit by various means from external sources. 

Mineral matter is always present in raw coal and forms ash when the coal is burned. The ash-forming mineral matter is nsnaUy classified as either inherent or extraneous. Ash-forming material organically combined with the coal is considered as inherent mineral matter. Generally the inherent mineral matter contained in coal is about 2 percent or less of the total ash. Extraneous mineral matter is ash-forming material that is foreign to the plant material from which the coal was formed. It consists usnaUy of slate, shale, sandstone, or limestone. 

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