Mineralogy and environmental geochemistry of lagooned ashes resulted from combustion of Maritza East lignite, Bulgaria

The phase-mineral composition of the feed coal (FC) from Maritza East lignite used in the Maritza East 1 thermo-electric power station (TEPS) and lagooned ashes (LAs) generated from the burning of this lignite was studied. The concentration and behaviour of 19 trace elements in the FC and LAs, as well as in the soils and plants collected from the restored sites of former LA disposals are also described. The minerals and inorganic phases identified in the lignite include quartz, kaolinite, pyrite, illite, plagioclase, gypsum, calcite, sulphur, marcasite, pyrrhotite, magnetite, K-feldspar, barite, szomolnokite, other Fe sulphates, sylvite, Ni carbonate or oxide/hydroxide, and glass. The phase composition of LAs is represented by original lignite minerals (pyrrhotite, magnetite, quartz, kaolinite) and newly formed minerals and phases generated during the combustion process (pyrrhotite, magnetite, hematite, quartz, metakaolinite, mullite, indialite, glass, char) or storage of LAs (sulphur, hematite, Fe hydroxides, gypsum, barite, Fe sulphates, calcite, sylvite). It was found that Cr, Cu, and Ti in the lignite ashes, and Co, Cr, Cu, Mn and Ni in LAs are relatively enriched in comparison with their respective Clarke values (worldwide average contents) for lignite and subbituminous coal ashes. The concentrations of Ag, Ba, Be, Co, Cu, Ga, Mo, Ni, Rb, Sn, and Ti in the soils have contents higher than their Clarke values for soils. The abundance of these elements plus Mn, V, and Zn in soils is probably related to some occurrence of discrete minerals and phases containing such elements. The contents of Be, Cr, Ga, Li, Ni, Pb, Ti, and V in the plants growing on these restored LA sites have concentrations higher than their Clarke values for land plants (dry basis). The water-soluble modes of occurrence of Ag, Ba, Be, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Sn, Ti, and Zn in soils and/or LAs, as well as the plant affinity to these elements should have a leading role for their concentration in plants. The present results reveal that various trace elements with environmental concern could be potential pollutants of surface and subsoil waters, soils and plants in the areas of restored LA sites.