The distribution of sulphur forms in high-S coals of the Maritza West Basin, Bulgaria


Authors: Kostova I, Marinov S, Stefanova M, Markova K, Stamenova V

Published in: Bulletin of Geosciences, volume 80, issue 1; pages: 23 - 32; Received 30 July 2004; Accepted in revised form 14 January 2005;

Keywords: coal, sulphur in coal, Maritza West Basin, Bulgaria,

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The present article concerns the Upper Miocene coal of the Kipra seams from the Maritza West Basin. A number of petrological investigations were carried out, including lithotype, quantitative maceral and mineral analyses, proximate and ultimate analyses, X-ray, and optical and scanning electron microscopy (SEM). We also examined the mineral matter from above, below, and within the coal layers. The proportions of sulphur in total (St), pyritic (Sp), organic (So) and sulfate(Ss) forms were also determined. The investigated coals have high sulphur contents, commonly above 7wt%, and can range from about 4wt% to more than 11wt%. The average sulphur proportions are 7.5wt% (4.1-13.5wt%) total sulphur, 1.6wt% (0.6-3.2wt%) pyritic sulphur, 4.2wt% (1.8-6.0wt%) organic sulphur, and 1.7wt% (0.3-2.9wt%) sulphate sulphur. Pyrite and gypsum are the major sulphur-bearing minerals. The syngenetic pyrite occurs mainly as isolated or clustered framboidal bodies and well-shaped euhedral crystals along stratification bands among humodetrinite and humotelinite. Epigenetic massive and infilled cell lumens of pyrite have also been observed. Well shaped prismatic crystals of gypsum were found as lenses, fine crusts, or fillings in cross bedding marks and cracks in the coal. Total sulphur slightly decreases from the base to the top of the coal bed. The highest content of total, sulphate, and pyritic sulphur near clay coal layers has been established. The highest content of organic sulphur has been found within the middle part of the coal bed.