Chemical characterization of feed coals and combustion-by-products from Brazilian power plants

Abstract

In this work, coal, bottom ash, and fly ash from coal-fired power plants located in the South of Brazil (Figueira/PR, Capivari de Baixo/SC, Candiota/RS, São Jerônimo/RS, and Charqueadas/RS) were evaluated and compared, mainly with respect to chemical composition. Major elements (Si, Al, Fe, P, Ca, Mg, Ti, Na, and K) concentrations were determined by X-ray fluorescence spectrometry (XRF), whereas the concentrations of minor and trace elements (Ag, As, Au, B, Ba, Be, Cd, Ce, Co, Cr, Cu, Ga, Ge, Li, Mn, Mo, Nb, Ni, Pb, Pt, Rb, Sb, Se, Sr, Ti, U, V,Y, Zn, and Zr) were determined by inductively coupled plasma mass spectrometry (ICP-MS) and/or inductively coupled plasma atomic emission spectrometry (ICP-OES). Mercury was determined by cold vapour atomic absorption spectrometry (CV-AAS). It was observed that the concentrations of minor and trace elements (mainly As, Cd, Mo, Pb, TI, U, Zn, and Hg) are, in general, highest in the coal and combustion-by-products from Figueira/PR, with statistical analysis showing that the coal and fly ash from Figueira/PR are significantly different from the other areas. Leaching tests using water and mechanical agitation demonstrated that the yield of minor and trace elements extraction from fly ash was higher than in bottom ash. The extraction of As, B, Ge, Li, Mo, Se, and Sr by water was typically in the range of 5 to 50%, whereas the other elements showed lower leaching. The pH of the leachates of both fly and bottom ashes is alkaline (average pH ranging from 8.04 to 10.0), with the exception of the bottom ash from Candiota (the average pH is 5.34).