Extraction of water-soluble impurities from fly ash

This study focuses on the behavior of major and trace water-soluble impurit ies in fly ash during leaching processes. The objective is to assess potent ial decontamination procedures in order to reduce the content of undesirabl e species in coal combustion by-products and to increase their potential in dustrial applications. Fourteen fly ashes were selected for this study. Maj or impurities considered were lime and portlandite, sulfate, and some poten tially hazardous trace elements such as As, Ba, Be, Cd, Co, Cr, Cu, Ge, Mn, Mo, Ni, Pb, Se, Th, U, V, and Zn. Water was used for the extraction experi ments, with a solvent/fly ash ratio of 50 mL/g. Anhydrite was completely dissolved in all fly ashes studied, except the Cer cs and Escatron fly ashes. Lime and portlandite were completely dissolved o r carbonated from all fly ashes with exception of the Cercs fly ash. Bulk c alcium contents were reduced from 9% to 18% in all fly ashes with the excep tion of the Compostilla and Espiel fly ashes (4-5%). From 17% to 79% of the sulfur was extracted from the bulk content. The results show a relatively higher extraction for S, Se, As, B, Mo, and Ca, and an intermediate extract ion for As, Ge, Cd, Li, Sr, Na, V, Cr, Sn, P, and Ba. The results suggest that the alkalinity is induced during the extraction ma inly by free lime. The high alkalinity accounts for the high Al and Si conc entrations in the leachates and the relatively low mobility of some trace e lements, with the exception of As, B, Mo, and Se.