Mineralogy and geochemistry of feed coals and combustion residues of the Kangal power plant (Sivas, Turkey)

Abstract

This study focuses on mineralogical and geochemical compositions of feed coal (FC) and combustion residues, namely fly ash(FA) and bottom ash (BA) samples, obtained from the Kangal coal-fired power plant in central Turkey. The X-ray powder diffractiondata indicate that carbonate and clay minerals are dominant phases in the FC samples. In the FA samples, quartz, hematite, anhydrite,lime, and feldspar are generally dominant and abundant phases, whereas calcite, ettringite, and portlandite are generally more abundantin the BA samples. The elements Mo, Cs, and U are significantly enriched in the studied FC, FA, and BA samples. The statistical analysisand SEM-EDX data show that Ca, Ti, and the vast majority of trace elements are inorganically affiliated, and only Tl and U have probable organic affinity in the FC. In addition, the redox conditions in the paleomires presumably resulting in Mo and U enrichment in FC,whereas their enrichment in FA and BA is most likely related to retention by CaO and Ca-sulfate. The Cs enrichment in FA is due toretention by glass. The elements in the FA and BA are distinguished into four groups according to their volatility during combustion. Theelements As, Mo, Cd, Tl, and U (Group I) are the most volatile elements during combustion and condensation in the FA. The elementsLi, Zn, Ga, Rb, Nb, Cs, Ba, La, and Pb (Group IV) did not become more volatile or less volatile during combustion and are located in BA.Nevertheless, Zn and Pb in the BA seem to be related to the presence of unaffected pyrite and sphalerite, and are due to low combustionefficiency of the boiler during the sampling period. Overall, enriched elements and minerals in FA and BA suggest that their disposalshould be undertaken with caution.