GEOCHEMICAL CHARACTERIZATION AND MERCURY CONTENT OF FEED COALS AND FLY ASHES FROM RUSSE THERMOELECTRIC POWER PLANT, BULGARIA

Feed coals and fly ashes collected from each row of ESP of Russe TPP were characterized with respect to their Hg content, geochemical and mineralogical compositions. In comparison with all studied coals and FAs from other Bulgarian TPPs the present one can be characterized by very low-mercury content. The distribution FA pattern shows that the concentration of Hg consecutive increase from the 1st toward the 3rd ESP row, i.e. the Hg amount is the lowest in the coarsest FAs and the highest in the finest FA fraction. The low Hg concentration may be due to the nature of feed coals, which are bituminous, with very low sulphur content and it is known that the Hg in such high-rank coals is preferably connected with the sulphide minerals. The minerals in coals are mainly quartz, illite, and calcite. The major phases of FAs include glass, quartz, and illite, while hematite, magnetite, anhydrite and mullite are present in minor amount. Hence, the FAs are enriched in some typical inorganic sorbents such as clay minerals, anhydrite, and magnetite-hematite, and, despite the obvious preferable association of Hg with FA char, some Hg capture could also be attributed to these minerals. The geochemical data show an extremely high enrichment of Au (up to 37 times greater than the Clarke value) in studied FAs. The other elements which have an increased concentration are Cd, Be, Se, Ag and Mn, and partially Zr, Ga, Ba, Cs, Ni and Hf. The Hg has positive correlations with O, C, total S, moisture, sulphide and sulphate S content. The data indicate that char, mostly enriched in C has a leading role for the partial capture and retention behaviour of Hg in studied FAs, but total and sulphide S also have a contribution to some extent.