Mechanisms Controlling the Leaching Kinetics of Fixated Flue Gas Desulfurization (FGD) Material under Neutral and Acidic Conditions

A number of agricultural and engineering uses for fixated flue gas desulfurization (FGD) material exist; however, the potential for leaching of hazardous elements has limited widespread application and the processes controlling the leaching of this material are poorly understood. In this study, a fl...

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Bibliographic Details
Published in:Journal of environmental quality 2007-05, Vol.36 (3), p.874-886
Main Authors: Cheng, C.M, Walker, H.W, Bigham, J.M
Format: Article
Language:English
Subjects:
Air pollution control
Aluminum - chemistry
Arsenic - chemistry
Calcium - chemistry
Chemical composition
Chemical reactions
Chemicals
Clean Air Act-US
Coal
Coal-fired power plants
Desulfurization
Equilibrium
Flue gas
Flue gas desulfurization
Fly ash
Hydrochloric acid
Hydrodynamics
Hydrogen-Ion Concentration
Iron - chemistry
Kinetics
land application
landfills
Leaching
Moisture content
pollutants
Pollution control equipment
Selenium - chemistry
Silicon - chemistry
soil pH
soil pollution
Spectrophotometry, Atomic
Sulfur - chemistry
Temperature
Trace elements
Water Pollutants, Chemical - chemistry
Water Pollution, Chemical - prevention & control
X-ray diffraction
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Summary:A number of agricultural and engineering uses for fixated flue gas desulfurization (FGD) material exist; however, the potential for leaching of hazardous elements has limited widespread application and the processes controlling the leaching of this material are poorly understood. In this study, a flow-through rotating-disk system was applied to elucidate the relative importance of bulk diffusion, pore diffusion, and surface chemical reaction in controlling the leaching of fixated FGD material under pH conditions ranging from 2.2 to 6.8. Changing the hydrodynamics in the rotating disk system did not affect the leaching kinetics at both pH 2.2 and 6.8, indicating that bulk diffusion was not the kinetic-limiting step. Application of the shrinking core model (SCM) to the data suggested a surface reaction-controlled mechanism, rather than a pore diffusion mechanism. The leaching of fixated FGD material increased with decreasing pH, suggesting it can be described by a combination of an intrinsic hydration reaction and a proton-promoted dissolution reaction. X-ray diffraction (XRD) and elemental composition analyses before and after leaching suggests that for most elements a number of solid phases controlled the leaching process.
ISSN:0047-2425
1537-2537
DOI:10.2134/jeq2006.0327