Leaching of Coal Combustion Products

Download or read book Leaching of Coal Combustion Products written by Chin-Min Cheng and published by . This book was released on 2005 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: This study combines field monitoring and laboratory experiments to investigate the environmental impacts associated with the re-use of coal combustion by-products (CCPs). The monitoring data obtained from two full-scale CCP applications allowed environmental impacts to be evaluated under real or simulated in-service conditions. A complimentary laboratory leaching study elucidated fundamental physical and chemical mechanisms that determine the leaching kinetics of inorganic contaminants from CCPs. In the first field study, water quality impacts associated with the re-use of flue gas desulfurization (FGD) material as a low permeability liner for a swine manure pond were examined by monitoring the water quality of water samples collected from pond water and sump collection system beneath the liner over a period of 5 years. In the second field study, the release of metals and metalloids from full-scale portland cement concrete pavements containing CCPs was evaluated by laboratory leaching tests and accelerated loading of full-scale pavement sections. To further elucidate the mechanisms controlling the leaching of CCPs, a flow-through-rotating-disk system was applied to investigate the mechanism, e.g., bulk diffusion, pore diffusion, or surface chemical reaction, controlling the leaching process of fixated FGD material. It was found that the leaching process was controlled by surface reaction and can be described by a combination of an intrinsic hydration reaction and a proton-promoted dissolution reaction. Also, the effects of oxalate, citrate, maleate, and Pahokee peat humic acid (PPHA) on the leaching kinetics of fixated FGD material were investigated at pH2.9 and 5. It was found that the leaching process was inhibited in the presence of oxalate at both pHs due to the formation of calcium oxalate on the leaching surface. The effects of maleate and humic acid on the leaching process were more complicated. According to ATR-FTIR analysis, both ligands were adsorbed predominantly as outer-sphere complexes on the leaching surface which either promoted or inhibited the leaching kinetics at pH 5. Both ligands, however, inhibited the leaching process at pH 2.9 by forming both inner- and outer-sphere complexes with the fixated FGD material surface. Unlike other organic ligands tested in this study, citrate significantly promoted the leaching process.