Trace and minor elements in coal.

Several instrumental techniques have been evaluated for the determination of trace and minor elements in coal.Electrothermal atomisation and atomic-absorption spectroscopy using coal slurries gave accurate results for the determination of arsenic, despite the identification of aluminium spectral interferences. Selenium determined using the method with deuterium arc background correction produced structured backgrounds which were corrected by the Smith-Hieftje system. The method has wide application for trace metal analysis.Scanning electron microscopy and energy-dispersive X-ray analysis produced accurate results for the determination of chlorine and minor elements in pellets of coal powders. The determination of sulphur was inaccurate because this element occurs in different mineralogical forms in coal. Total elemental analyses were also successfully correlated with ash contents of coal.Wavelength dispersive X-ray fluorescence analysis of pellets of powdered coal gave precise and accurate results for determinations of chlorine and phosphorus. The different fluorescent yields of organic and inorganic sulphur in coal caused inaccuracy in determinations of this element. Backscattered radiation was used to estimate ash content and the possibility of multi-element analysis of coal was indicated. Inductively coupled plasma-optical emission spectroscopy was used for multi-element analysis of coal ash. The method gave a five-fold increase in speed of analysis, without loss in accuracy or precision, compared to BS procedures and is recommended for trace element determinations. All these techniques should be regarded as complementary and can be expected to make a significant contribution to coal analysis.The importance of the mode of occurrence of elements in coal has been illustrated by studies of chlorine. Long-held views have been disproved and the likelihood is that chlorine is present in one form, uniformly distributed and linked ionically to coal but evolved as hydrogen chloride at low temperatures. It has no relationship with nitrogen, sodium or other alkali-metals in coal.