Major- and Minor-Element Analysis
Coals may contain a variety of elements. Major elements are those that make up more than 1 percent of a coal; minor elements make up 1 to 0.1 percent, and trace elements make up less than 0.1 percent. The major-, minor-, and trace-element composition must be known for many markets and coal uses. There are several methods for determining the major- and minor-elemental composition of coals, but probably the most standard is X-ray fluorescence (XRF) (ASTM method D4326-11; American Society for Testing and Materials, 2013, p. 562–565).
In this procedure, a coal sample is combusted and the remaining ash (noncombusted material) is analyzed in an X-ray fluorescence spectrometer. X-rays bombard the sample, causing mineral oxides in the sample to emit a secondary or fluorescent X-ray in response. Different elements have different secondary X-ray patterns. The spectrometer detects those different wavelength patterns and measures the relative abundance of different elements (in mineral oxides) in the sample.
Understanding the relative abundance of different elements in coal ash is important in boiler operation, because it helps predict slagging and fouling characteristics (ASTM method D4326-11; American Society for Testing and Materials, 2013, p. 562-565). Also, if coal-ash byproducts will be used in commercial products, there may be quality grade requirements based on chemical processes involved in using the product, or environmental standards for those products, which may have limits on the concentrations of certain elements.
Go to more information about major and minor elements in coal
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