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One of the strategic issues for contemporary manhood is production of a sufficient amount of energy for further technological development. Despite numerous attempts to use new, practically inexhaustible energy sources, such as solar energy (Li, 2002), wind energy (Belanger & Gagnon, 2002) and high and low tides (Omer, 2002), for example, instead of conventional sources, i.e., coal, petrol or gas, the latter ones, nevertheless, remain unavoidable factors in balancing the energy demands of most countries, including Serbia, at the beginning of the 21st century. On the basis of investigations of coal genesis, its composition, as well as general characteristics of coal deposits, coal can be defined as a combustible sedimentary rock, originating mainly (some coals are algal) from residues of terrestrial and aquatic plants, and of minerals (< 50 %) (Wood et al., 1983). Chemical and physical characteristics of coal are predetermined by the nature of precursor plants, the amount of inorganic material, and by the nature, intensity and duration of biochemical and geochemical processes that are responsible for coal formation. Almost all natural elements have been found in coal (Finkelman, 1993), in variety of forms (Eskenazy & Valceva, 2003; Yudovich & Kertis, 2005), which are responsible for the coal’s technological, economical but also ecological impact. Elements can be variously associated (Font et al., 2005). Further, association types may vary within the same deposit (Kuehn & Kurzbach, 1992; Vyazova & Kryukova, 1997). During coal combustion in power plants, practically only the organic part of coal burns, producing carbon dioxide and water, i.e. its vapor. The inorganic components of coal mainly do not burn, but remain in the ash, which is a by-product of combustion. Since coal, by definition, contains more than 50 % of organic substances, which are not found in the ash, or are found in the very low concentrations, it is clear that the main part of the inorganic components of coal, including trace elements, is concentrated in the ash. During combustion different processes occur, which influence the non-uniform distribution of the elements and phases in different fractions of the combustion products (Xu et al., 2004; Goodarzi, 2006; Ward & French, 2006). One of the basic mechanisms which are present is “evaporation-condensation” (Schultz et al., 1973). Namely, during coal combustion at high temperatures certain elements evaporate. At the lower temperatures, which are typical for the higher parts of the reactor in which the combustion occurs, part of the substances which

Distribution of Trace and Major Elements in Lignite and Products of Its Combustion-Leaching Experiments and Cluster Analysis