A borate fusion method for the determination of fluorine in coal

A new analytical method has been developed for determining fluorine in coal. It incorporates a two stage sinter-fusion procedure using lithium carbonate, lithium tetraborate and zinc oxide. In the sinter stage, coal is ashed at 600 °C and the lithium carbonate and zinc oxide act as collectors to capture volatile species of fluorine. In the second stage, the ash residue is decomposed by fusion with the lithium carbonate and lithium tetraborate at 1050 °C. The fused material is dissolved in nitric acid and the fluoride in solution is determined using an ion selective electrode. The results for a number of coal samples including Certified Reference Materials are reported. These are in good agreement with the certified values and with the results obtained by proton induced gamma ray emission spectrometry. The good agreement confirms that no fluorine is lost during ashing/sintering of the coal and that complete dissolution of the residual ash is obtained by fusion with the lithium carbonate and lithium tetraborate The method is simpler and less labour intensive than pyrohydrolysis and is suitable for use in most commercial coal laboratories.