A comprehensive analytical characterization of Greek lignite bottom ash samples

Abstract

Bottom ash samples were collected from four lignite power plants of Greece. Granulometric analysis was executed and after homogenization four distinct fractions (>1.25, 0.63-1.25, 0.18-0.63, <0.18 mm) were obtained. The samples were analyzed by X-Ray Diffraction (XRD) and Energy Dispersive System (EDS), while thermogravimetry (TG/DTG) and stereomicroscope viewing were applied for the coarse fractions. Furthermore, proximate analysis (moisture, ash, volatiles, fixed carbon) was undertaken and Loss on Ignition (LOI) and calorific values were determined. The particle size distribution revealed that bottom ash satisfies the gradation criteria for concrete and geotechnical applications. The mineral composition included mainly amorphous matter, quartz, plagioclase, calcite and gehlenite and minor amounts of pyroxene, portlandite, hematite, micas etc.. The chemical analysis showed Si, Ca, Al, Mg, Fe, S as major and Ti and K as minor chemical elements, indicating high slagging and fouling potential within the thermal chambers. Based on the chemistry and mineralogy of the bottom ash samples, a potential utilization in concrete manufacturing is discussed, taking into account certain limitations. Based on LOI, proximate analysis, calorific values and TG/DTG profiles of the coarse fractions (>1.25 mm), certain differences in the characteristics of the bottom ash of the younger and the three older power plants were observed. High amounts of unburnt carbon were determined in the coarse fraction (>1.25 mm) of all plants except the younger one, indicating a problematic combustion within the chambers and a potential of reburning these coarse material in a waste to energy application.

Granulometric, Chemical, and Mineralogical Evaluation of Greek Lignite Bottom Ash for Potential Utilization in Concrete Manufacturing

“…The chemical composition (on the basis of point analyses in microscale using SEM-EDS) of four particle-size fractions that were obtained, after homogenization (>1.25, 0.63-1.25, 0.18-0.63, <0.18 mm), from four representative bottom ash samples from the Agios Dimitrios (DIM) power plant, and one bottom ash sample from each of the Meliti (MLT), Kardia (KAR), and Megalopolis (MGL) power plants, is presented analytically in Iordanidis et al (2020, 2021) [16,17]. In Table 2, the range of the major oxides concentration of all the analyzed bottom ash samples is shown, as well as the chemical constituents of Ordinary Portland Cement (OPC) for comparison.…”

“…The range of semi-quantitative mineralogical results of the analyzed bottom ash samples from the four power plants [16,17] are shown in Table 3. It is evident that the amorphous phase is prevailing in all samples, with concentrations ranging between 26 and 46 wt.%.…”

“…However, in Greece, a small proportion (approx. 10%) of fly ash is utilized in the concrete industry, while bottom ash is not used in any form [5]. Large quantities of bottom ash have already been abandoned due to the intensive exploitation of lignite deposits in the last fifty years, which is a threat to the environment and, henceforth, to human health.…”