Quality parameters of lignite of the North Bohemian Basin in the Czech Republic in comparison with the world average lignite

Sulfur is considered to be the most harmful element in atmospheric emissions and fall-out which originate from coal combustion. Total sulfur content (S-t(d)) in lignites of the North Bohemian Basin (NBB) has a geometric mean of 1.61 wt.% at n = 12 979, and is mostly influenced by the presence of iron disulfides. The distribution of sulfur and many trace elements is log normal. A non-uniform distribution of sulfur in lignite was found within the basin, with the lowest SP contents (i.e,, not exceeding 1 wt.% S) confined to the eastern and southeastern margin of the NBB, Contents between 1 and 1.5 wt.% S are most common in lignites of the South-Central NBB. Lower sulfur contents were identified in the area of the Zatec delta and its northern extension. In contrast, high contents of sulfur in lignite (exceeding 1.5 wt.%) are found along the northern margin of the basin at the foot of the Krusne hory Mts and in the westernmost part of the NBB. Three genetically different types of iron disulfides occur in lignite of the NBB-synsedimentary (early diagenetic), diagenetic, and epigenetic. Among those forms, synsedimentary disulfides (mostly pyrite) appear to be most abundant, They form finely dispersed microscopic framboids or veinlets that commonly parallel the coal bedding. The other iron disulfide forms are much less abundant. Dissolved sulfate which was supplied to the NBB during the Miocene is likely to have been derived from sulfides of the Krusne hory Mts crystalline complex. This unit has an isotopic composition of sulfide sulfur varying between - 1 and + 5 parts per thousand. Consequently, the sulfate supplying the NBB should exhibit slightly positive delta S-34 values. Syngenetic pyrites forming microframboids or veinlets in coal show delta S-34 values close to 0 parts per thousand. These values are similar those of sulfur dioxide in gases of power stations burning NBB coal. This implies that no considerable shifts in sulfur isotopic composition occur during thermal oxidation of the dominant pyrite. Arsenic is positively correlated with sulfur (r(2) = +0.89). Its total content (As-t(d)) is 20.53 ppm at n = 9172. (C) 1999 Elsevier Science B.V. All rights reserved.