Mineralogy and chemical composition of technogenic soils (Technosols) developed from fly ash and bottom ash from selected thermal power stations in Poland

Abstract

The aim of the study was to determine the mineral and chemical composition of technogenic soils (Technosols) developed from fly ash and bottom ash from power plants in which bituminous coal and lignite was combusted. The mineral composition of the “fresh” wastes (i.e. fly ash and bottom ash) and soil samples derived from them was examined by X-ray diffraction (XRD) and using a scanning electron microscope (SEM). The chemical composition (content of major elements) was determined using ICP-AES method. Quartz, mullite, and amorphous substances (glass) predominated in the mineral composition of wastes after bituminous coal combustion. Magnetite was also found there. Soils developed from wastes after bituminous coal combustion contained all above mentioned minerals inherited from fly ash and bottom ash. Moreover, small amounts of secondary calcite were identified. In some soil horizons containing large amounts of inherited magnetite, secondary iron oxides and oxyhydroxides (goethite and lepidocrocite) also occurred. Quartz predominated in the mineral composition of the “fresh” wastes after lignite combustion. Relatively small amounts of iron oxides (magnetite and hematite) were also found there. In “fresh” fly ash, apart from minerals mentioned above, anhydrite and calcium oxide (lime) was identified. Soils developed from wastes after lignite combustion contained inherited quartz, magnetite, and hematite. Furthermore, calcite which sometimes was a predominating mineral in certain soil horizons occurred. Moreover, sulphates (gypsum, bassanite, and ettringite), and vaterite (a polymorph of Ca carbonate) were also found in soils. Silicon predominated among major elements in “fresh” ashes after bituminous coal combustion and soil derived from them followed by Al, Fe, K, Ca, Mg, Ti, Na, P, and Mn. On the other hand, the contents of major elements in the samples (ashes and soils) after lignite combustion can be arranged as follows: Si, Ca, Fe, Al, Mg, Ti, K, Mn, Na, and P. However, in some horizons (i.e. in calcareous materials deposited in the topsoil of some profiles) in soil developed on landfills near TPSs combusting lignite, Ca was a predominating element.

Keywords

• fly ash
• bottom ash
• Technosols
• X-ray diffraction
• scanning electron microscopy
• major elements