Elements in Bulgarian coal deposits

pp. 3-24

Geochemical behaviour of K, Na, Li, Rb and Cs has been studied in coals, coaly shales and mineral interlayers from some Bulgarian coal deposits and manifestations. The elements show the following major trends in their distribution: 1. The higher the coal rank, the higher the elements' contents. This tendency is well pronounced for Cs and Jess so for K, Na, Li and Rb. Recalculated to ash, however, the Na content is higher in lignites than in brown and black coals; 2. Sorption ash carries and concentrates Na, and terrigenous ash is a carrier of K, Na, Li, Rb and Cs; 3. Na is typomorphic element in 8 of the deposits studied, Li in 6, and Cs in 2 of them; 4. With the exception of Na, the separate coal lithotypes do not concentrate alkaline elements; 5. The elements are bound with both the inorganic and the organic coal matter. K, Rb, Li and Cs occur mostly as Meinorg· Low ash coal in most of the deposits is dominated by Naorg and in some cases by Liorg as well; 6. The higher Na content in low-ash coals is explained with its greater supply in a dissolved state. Seawater was the source of Na in the Sozopol deposit and, to a lesser extent, in the Burgas and Dobrudza deposits as well. In the other deposits a Na source may have been the terrigenous material supplied into the peat bog from which Na is more readily extracted than the other alkaline elements. The contents of alkaline elements in coals and in coaly shales are positively correlated. Syngenetic and epigenetic hydrothermal fluids as well as underground water are an other sources of alkaline elements.