Geochemistry of beryllium in the Mariza-east lignite deposit (Bulgaria)

Abstract

Beryllium geochemistry in coal has been studied on the basis of its distribution in 1556 individual full channels of coal, coaly shales, partings, and lithotype samples from 11 profiles of the Mariza-east lignite deposit (Bulgaria). This is the largest lignite deposit in Bulgaria, producing coal for three Thermal Power Stations (TPS) and a briquette plant. The Be content was determined in the coal ash (500 °C) by atomic emission spectrography at a detection limit of about 1 ppm Be. The mean Be content for the different profiles ranged from 0.7 to 6.9 ppm Be, similar to that of global average for subbituminous coals. Higher concentrations of Be were found in the first seam with thickness from 1 to 4 m, whereas the second seam reached 24 m. Most of the xylain and vitrain samples showed lower Be content than the whole coal samples from which they were selected. The fusain samples were usually enriched in Be compared to the whole coal samples and the other lithotypes which is a specific feature of the deposit. Distribution of Be along vertical profiles follows that of ash. Beryllium in the lignite occurs predominantly in the inorganic matter as isomorphic admixtures and/or adsorbed on the clay minerals. A small portion is bound to the organic matter. These conclusions were based on circumstantial evidence: such as correlation with ash, aluminium, and germanium content; distribution in lithotypes; sink-float; and leaching experiments. The low Be content and its inorganic affinity are supposed to be the result of several factors: negligible influx of Be in solution in the swamp, large dimensions of the basin, great thickness of the main second seam, and long distance from the source province.