Mineral matter in coal

Walker, P. L. Spackman, W. Given, P. H. Davis, A. Jenkins, R. G. Painter, P. C. "Characterization of Mineral Matter in Coals and Coal Liquefaction Residues", Annual Rept. AF-832 from Pennsylvania State University to Electric Power Research Institute, 1978. 

Fly ash particulate matter produced from mineral matter in coal that is converted during combustion to finely divided inorganic material which emerges from the combustor in the gases. 

The above conclusions based on SEM-AIA measurements of association in terms of particle surfaces are somewhat more tentative than the conclusions drawn from bulk association distributions. There are more analytical difficulties when characterizing the particle surfaces than when characterizing the bulk sample. In addition, the factors determining the overall surface nature of a particle are more complex than just the relative amount of the phases present on the particle surface. However, the SEM-AIA results can still provide a useful and heretofore unavailable insight into the nature of mineral matter in coal. 

Coal contains detrital minerals that were deposited along with the plant material, and authigenic minerals that were formed during coalification. The abundance of mineral matter in coal varies considerably with its source, and is reported to range between 9.05 and 32.26 wt% (Valkovic 1983). Minerals found in coal include (Table 2) aluminosilicates, mainly clay minerals carbonates, such as, calcite, ankerite, siderite, and dolomite sulphides, mainly pyrite (FeS2) chlorides and silicates, principally quartz. Trace elements in coal are commonly associated with one or more of these minerals (see Table 2). 

Simultaneously with the efforts to determine the origin of mineral matter in coal, systematic efforts were underway to estimate the quantitative distribution of trace and minor elements in American coals. The early analyses were performed on high-temperature ashes, and as a consequence, the investigators had to be content with determining the nonvolatile metallic oxides. However, with the advent of the low temperature asher and improvisations and advances in wet chemical, radiochemical, and instrumental analytical techniques, we not only can analyze nondecomposed mineral matter but also can study the composition of whole coal. 

Interest in mineral matter in coal arises primarily because some of the materials may have detrimental effects during coal use. Because methods of using coal are becoming more sophisticated and increasingly large amounts of coal are being used at single locations, these detrimental effects should be considered further. 

More recently, there has been much concern about the possible effects of the mineral matter in coal on processes used to convert coal to other fuels such as gasification, liquefaction, and production of clean solid fuels. Not only is removing and disposing of the mineral matter a problem, but also the possible chemical effects such as catalyst poisoning, which might be expected in the methanation of gas from coal, should be considered. 

Not all of the interest in mineral matter in coals is stimulated by its detrimental effects during coal use. In several instances coal is a source of desired elements and materials. Uranium has been produced from lignite germanium and sulfur could be produced from coal and coal ash has been used for construction materials such as brick, lightweight aggregate, and road paving material. 

Silica (Quartz). Quartz is ubiquitous in all coals. Rao and Gluskoter (I) reported that, on the average, 15% of the mineral matter in coals from the Illinois Basin was quartz. O Gorman and Walker (2) found 1-20% quartz in 16 whole coal samples from various parts of the United States. 

Mineral Matter in Coal and High-Temperature Coal Ash... 

Within the past decade the technique of electronic (radiofrequency) low-temperature ashing has been used to investigate mineral matter in coal. In a low-temperature asher, oxygen is passed through a radiofrequency field, and a discharge takes place. Activated oxygen thus formed passes over the coal sample, and the organic matter is oxidized at relatively low temperatures—usually less than 150°C (14). 

Literature of Trace Elements and Mineral Matter in Coal... 

Mineral matter in coal, as the term is generally used, includes the mineral phases (species) present in the coal seam as well as those elements generally thought to be inorganic, even if they are present in coals in organic combination. The major minerals found in coals are silicates... 

The two major problems encountered in investigating mineral matter in coal are that the mineral matter and coal are so intimately mixed that physical separation of the two is not feasible in a quantitative study and that the geochemical system is extremely complicated and difficult to characterize. The first problem is overcome in part by refining the tech-... 

Watt, J. D., The Physical, and Chemical Behaviour of the Mineral Matter in Coal Under Conditions Met in Combustion Plant. Part I, The Occurrence, Origin, Identity, Distribution, and Estimation of the Mineral Species in British Coals, British Coal Utilization Research Association, Literature Survey, 121 p., Leatherhead, Surrey, England, 1968. 

Mackowsky, M. Th., Mineral Matter in Coal in Coal and Coal-bearing Strata (D. G. Murchison and T. S. Westoll, Eds.), p. 309-321, Oliver and Boyd, Edinburgh and London, 1968. 

Thiessen, Gilbert, Composition and Origin of the Mineral Matter in Coal in Chemistry of Coal Utilization (H. H. Lowry, Ed.), v. 1, p. 485-495, John Wiley and Sons, Inc., New York, 1945. 

There is no simple and reliable method of determining the water of hydration of mineral matter. The average value of 8% of the ash is used as the value for water of hydration of mineral matter in coals in the United States. This value is acceptable, although it is an average of values that range from 2 to 3% and up to 15 to 20%. Water of hydration values are used to correct ash to the form of hydrated minerals in mineral matter calculations. 

Several formulas have been proposed for calculating the amount of mineral matter originally in the coal using data from ashing techniques as the basis of the calculations. Of these formulas, two have survived and have been used regularly to assess the proportion of mineral matter in coal the Parr formula and the... 

Determination of a good value for the percent of mineral matter content (% MM) is a very important component of coal analysis. If this quantity cannot be determined directly by the acid demineralization or low-temperature ashing procedure discussed previously, or by other suitable methods, it is possible to calculate a reasonable value for the mineral matter in coal, provided that the necessary data are available. 

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