Leaching of FGD Byproducts Using a CSTX
Leaching studies of coal utilization byproducts (CUB) are often performed to determine the compatibility of the material in a particular end-use or disposal environment. Typically, these studies are conducted using either a batch or a fixed-bed column technique. Fixed-bed columns offer the advantage of a continuous flow of effluent that provides elution profiles with changing elution volume and pH. Unfortunately, clogs can form in fixed-bed leaching columns, either because of cementitious properties of the material itself, such as is seen for fluidized bed combustion (FBC) fly ash, or because of precipitate formation, such as can occur when a high-calcium ash is subjected to sulfate-containing leachates. Also, very fine-grained materials, such as gypsum, do not provide sufficient permeability for study in a fixed-bed column. A continuous, stirred-tank extractor (CSTX) is being used as an alternative technique that can provide the elution profile of column leaching but without the low permeability problems. The CSTX has been successfully employed in the leaching of flue gas desulfurization products that would not be sufficiently permeable under traditional column leaching conditions. The results indicate that the leaching behavior depends on a number of factors, including (but not limited to) solubility and neutralization capacity of the mineral phases present, sorption properties of these phases, behavior of the solubilized material in the tank, and the type of species in solution. In addition, leaching to near-exhaustion of a wallboard produced from FGD gypsum has allowed the isolation of a highly adsorptive phase. This phase appears to be present in at least some FGD gypsums and accounts for the immobilization of trace metals such as arsenic, cobalt, lead, and mercury.
- Research Organization:
- National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR
- Sponsoring Organization:
- USDOE - Office of Fossil Energy (FE)
- DOE Contract Number:
- None cited
- OSTI ID:
- 938809
- Report Number(s):
- DOE/NETL-IR-2005-218; NETL-TPR-1241
- Resource Relation:
- Conference: 22nd Annual International Pittsburgh Coal Conference, Pittsburgh, PA, Sept. 12-15, 2005
- Country of Publication:
- United States
- Language:
- English
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