The effect of time, additives and method of measurement on sulfate during the selective oxidation of coal with perchloric acid

Abstract

A reaction scheme, developed at the Ames Laboratory, for the determination of the sulfur forms in coal takes advantage of the selective oxidizing power of perchloric acid. Sulfate, pyritic and organic sulfur are removed sequentially from a single sample of coal by solutions of perchloric acid boiling at 120, 155 and 205 °C, respectively, and converted to sulfate for subsequent turbidimetric measurement. Work in this paper focused on improving the selectivity by trying to remove pyrite at lower temperatures and improving the low sulfur recoveries observed for some coals. The results indicated that pyritic sulfur can be removed at lower temperatures and that possibly two different forms of organic sulfur can be delineated. After several potential explanations for the low sulfur recoveries had been explored, a standard additions technique, when applied to the turbidimetric measurement of sulfate, alleviated the problem of low sulfur recoveries.