Leaching characteristics of stabilized/solidified fly ash generated from ash-melting plant.
This study was designed to elucidate the leaching characteristics of stabilized/solidified (S/S) fly ash generated by ash-melting. For this study, pH-dependent leaching tests, sequential extraction procedures, and column leaching tests were carried out. The pH-dependent leaching test results for Pb, Cu, and Zn showed that the heavy metal concentrations in the high-pH range were lower than the predicted values for hydroxide and carbonate. During sequential extraction, Cu and Pb were principally distributed in the S/S ashes' organic matter fraction in the chelating agent, suggesting that metals bind to the chelating agent. The percentage of the water-soluble fraction for Pb and Cu was low (<0.2 %). The fly ashes treated with a chelating agent and cement had low leachability potential for metals in the high-pH range. Column tests for S/S fly ashes showed that two leaching stages were distinguishable: one for short time, corresponding to faster metal leaching, and another for the leaching rate. Kinetic speciation was then applied to data obtained from column leaching tests. The first-order reaction/diffusion model showed a better fit for Ca, Pb, and Cu, suggesting that the initial dissolution of soluble compounds, such as metal chloride, was controlled by the first-order reaction (surface wash off). Subsequently, insoluble compounds such as hydroxide or carbonate might penetrate into the porous matrix by diffusion.
Suzuki
Kazuyuki
K
Graduate School of Environmental Science, Okayama University, 1-1 Tsushima-Naka, 3-chome, Okayama 700-8530, Japan. kazuyuki@cc.okayama-u.ac.jp
Ono
Yoshiro
Y
D002244:Carbon / Q000737:chemistry*; D060729:Coal Ash; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000032:analysis*; D008956:Models, Chemical; D052638:Particulate Matter / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D060729:Coal Ash; D019216:Metals, Heavy; D052638:Particulate Matter; D014874:Water Pollutants, Chemical; D002244:Carbon