PERMEABILITY AND LEACHATE CHARACTERISTICS OF STABILIZED CLASS F FLY ASH

Abstract

A 2-year laboratory investigation of the permeability and leachate characteristics of stabilized fly ash has been completed at West Virginia University. Two class F fly ashes rom coal-fired power plants in West Virginia were amended with either lime, cement, or bentonite. Stabilized specimens were permeated in either rigid- or flexible-wall permeameters. Permeant liquids included distilled water, highly concentrated organic solutions, and acidic solutions. Effluents from the permeability tests were collected periodically during the tests and analyzed for toxic elements. Results from the study indicate, for the ashes tested, permeabilities near 1.0E-06 cm/sec can readily be obtained when 15% (by weight) of lime or cement is added to the fly ash. Much lower permeabilities (1.0E-08 cm/sec) can be obtained by substituting bentonite in place of the lime or cement. Addition of lime or cement appears to stabilize the fly ash with respect to toxic elements being leached from the ash. Bentonite may not be as successful at fixing the elements onto the fly ash. In conclusion, difficulty in using fly ash as a liner material probably does not lie in the ability to obtain low permeability nor in fixing the toxic elements from leaching but rather in combining those two properties into one material. Permeability can be decreased to acceptable values through the addition of bentonite, but some ability to fix elements from leaching may be lost. In addition, ashes from different plants and from different operating periods, as found in this study, can have markedly different properties. To use a particular ash in a liner application, ash must be tested for its behavior to ensure that the correct properties are used in design of the particular liner.