LAUSR

Abstract Fly ash and bottom ash from thermal power stations are industrial wastes which are susceptible to weathering in the environment. First manifestations of transformations occur immediately after deposition of ashes in a disposal site and they continue in technogenic soils (Technosols) developing from the ashes on surfaces of such sites. Technosols developed from bituminous coal and lignite ashes in Poland were studied in order (a) to identify the most important mineral transformations during the first several decades of soil development, and (b) to discuss the evolution of these soils. Mineral transformations can serve as good indicators of pedogenesis in the studied Technosols. Quantitative X-ray diffraction analyses, Fourier transform infrared spectroscopy, optical microscopy, and scanning electron microscope-energy dispersive spectroscopy studies showed that the mineral transformations proceeded more dynamically in Technosols developed from lignite ashes, whereas they were less expressed in soils formed from bituminous coal ashes. Technosols developed from bituminous coal ashes contained mineral phases inherited from ashes (aluminosilicate glass, mullite, quartz, magnetite, hematite, and traces of maghemite and barite) as predominating constituents. Small contents of pedogenic calcite, iron oxyhydroxides, and most likely short-range order Si- and Al-containing phases originated within ~ 60 years of pedogenesis. Technosols developed from lignite ashes contained aluminosilicate glass, quartz, hematite inherited from fly ash, as well as a variety of secondary minerals (vaterite, calcite, bassanite, gypsum, ettringite, hydrotalcite, and brucite) which were formed as an effect of rapid mineral transformations after ash deposition. After about 40 years, pedogenesis (accelerated by reclamation and a few years of intense cultivation) led to the formation of a new mineral assemblage with the predomination of calcite, gypsum, and hydrotalcite. A concept of evolution of the studied Technosols comprising four stages of evolution was proposed: I – formation of ash during combustion of fuel (coal or lignite) in a thermal power station, II – transport and deposition of ash in a disposal site accompanied by the first weathering alterations, III – early pedogenesis, and IV – further (predicted) evolution.