Fluorine in Bulgarian coals

Fluorine in coal is a potentially hazardous element. As its determination needs special methods, there are no fluorine data for many worldwide coals. In this study, the geochemistry of fluorine in seven Bulgarian coal deposits (lignites, subbituminous, bituminous and anthracites) is discussed. Fluorine was determined by pyrohydrolysis in conjunction with a fluorine ion-selective electrode. The mean fluorine content in the deposits varies from 74 to 459 ppm. With the exception of one deposit, fluorine content is higher than its coal Clarke value. Fluorine content is less than 50 ppm in gagates and coalified wood trunk. Fluorine content in fusain is slightly elevated, 1.5 × than its coal Clarke value. The fluorine distribution was not found to be rank-related. Enrichment/depletion of F at the bottom and upper part of the coal seams trends was not observed. Fluorine positively correlates with ash yield. No relation exists between F and elements such as Cl, Br, P, and B. Fluorine in the Bulgarian deposits studied is mostly inorganically associated. In addition to kaolinite, the carriers of F are thought to be montmorillonite, hydrobiotite, and chlorite. However, a small proportion of F is organically associated. Factors favourable for the enrichment of F are supposed to be host rocks presented by gneisses, amphibolates and granites. With the exception of the Pirin deposit, the F content in the coal deposits studied should not be of significant environmental concern.

► Mean F content in the deposits varies from 74 to 459 ppm.
► Fluorine content is not rank-related.
► Fluorine content is mostly inorganically associated.
► Host rocks as amphibolites, gneisses and granites favour the enrichment of fluorine.