The decreased release of heavy metals from fly ashes by adding alunite

The fly ashes from hospital waste incinerator were blended with natural alunite to decrease the release of heavy metals. The change in surface chemistry of fly ashes in the absence and presence of alunite was characterized by XRD, TEM, FTIR and potentiometric titration. According to potentiometric titration, the concentration of surface reactive sites of fly ashes blended into alunite (FA1) was 3 times higher than fly ashes (FA0). The release of Cu2 +, Pb2 +, Cd2 + and Zn2 + from FA0 and FA1 as a function of extracted time and acid concentration was investigated by batch techniques. The kinetics showed that extracted amount of heavy metals from FA0 and FA1 was in the order of Zn2 + > Cu2 + > Cd2 + > Pb2 +. According to the analysis of FTIR spectra, the heavy metals were adsorbed to the amorphous alumina hydrolyzed from alunite under acidic conditions. The batch extractions dictated that the leached amount of heavy metals from FA1 was significantly lower than FA0, suggesting that natural alunite can potentially be served as an efficient retardant for the immobilization of heavy metals from fly ashes.