SULFUR SOURCES AND SULFUR BONDING OF SOME CENTRAL-EUROPEAN ATTRITAL BROWN COALS

The Tertiary attrital brown coals of Central Europe contain usually between 0.2 and about 5% sulfur. It is well known that the sulfur content consists of sulfide (mostly pyrite), sulfates (gypsum and other sulfates), organic sulfur, and a low percentage of elemental sulfur. Usually, the pyrite sulfur content is said to be the highest, but recently more and more authors have published data showing a high percentage of organic sulfur for several coals. Investigating samples of coals from about 50 deposits from several central European countries, we also obtained such data. By means of a glow discharge-excited, low-temperature ashing technique, we got low-temperature ashes (LTA) containing a wide variety of minerals of different origin, Pyrite, which was shown to be stable during the LTA treatment used, was found only in a few specimens with remarkable amounts. Therefore, it is necessary to search for the bonding and the source of the sulfur in the coals and the LTAs. The LTAs investigated contain a number of detrital minerals (syndeposiionally transported into the coal-forming environment in solid state) which are mostly silicates and do not contain any sulfur. The authigenic minerals (postdepositionally crystallized in the coal) are rare but show a wide variety in their chemical composition. Most of them contain sulfur bound to the common metals of the coal, e.g., calcium, magnesium, iron, and others. In addition, there is a high mineral content in the LTAs, which was formed during the ashing run and these are called artifacts. These artificial minerals frequently have the same chemical composition as the authigenic material but are different in their structural properties. Therefore, the artifacts are qualitatively distinguishable from the authigenic minerals. Both the anions and the cations of the artificial minerals stem from the organic substance of the coal which is slowly destroyed during the LTA process (Fig. 1). Due to the instability of the structural properties of the sulfate artifacts, the detectable differences between them and the authigenic minerals are lost soon. © 1990.