Determination of total fluorine in coal by use of oxygen flask combustion method with catalyst

A rapid and convenient analytical method has been developed for the determination of total F in coal by use of oxygen flask combustion (OFC) method with catalyst. Coal was combusted with excessive oxygen in a quartz flask and the resulting gas was absorbed in water, and the fluoride ion in the solution was determined with a fluoride-ion selective electrode (F-ISE). Seven certified reference materials of coal were tested. The effects of the repetition of OFC procedure, the use of catalyst, and the particle size of coal were investigated. The F concentrations in these coals determined by the proposed method gave good recoveries for their certified or reference values. The use of proper catalyst was necessary especially when coals of high F concentrations (above ca. 150 μg g−1) were analyzed. For the catalyst, the combined use of WO3 and Sn was the most efficient, and the mechanism was studied. Twenty brands of Japanese standard coals (SS coals) were analyzed by the present method, and the data were compared to those obtained from the pyrohydrolysis method.