LABORATORY SIMULATION OF
COAL ASH LEACHATE
Eric G. Hanson, Manager
Aileen M. Schumacher, Senior Associate Engineer
Industrial Waste Engineering Section
Environmental Science and Engineering, Inc.
Gainesville, Florida 32602
An ash testing study was conducted to predict the characteristics of leachate from two
types of ash, a Western coal ash and an Eastern coal ash. The study was designed to predict
the leachate characteristics that could occur from disposal of the ash in a landfill at a new
coal-fired power plant. Testing consisted of ash shake or extraction tests to simulate the
chemical characteristics of leachate.
The Western ash, obtained from an operating unit in Kansas, was representative of ash
from typical low-sulfur, high-ash, bituminous coal found in Wyoming. The Eastern ash,
obtained from an operating unit in North Carolina, was representative of ash from low-
sulfur, low-ash, bituminous coal from the Powder River, Kentucky, area.
THEORETICAL BACKGROUND AND APPROACH
The concept of an ash shake test is to contact the ash with an eluant (leaching liquid)
for a period of time, separate the eluant from the ash, and analyze the eluant for the presence of specific pollutants. The test involves selection and consideration of the effects of
initial sampling procedure, size of sample, type of eluant, pH, temperature, anaerobic or
aerobic conditions, total solids-to-liquid ratio, particle size, test duration, and method of
agitation. With proper selection of test conditions, an ash shake test should indicate the
pollutant-leaching characteristics of a specific ash.
Ideally, the leaching test would determine the highest "worst-case" pollutant concentration in the leachate, the factors controlling this concentration, the total amount of
pollutant releasable from a given amount of ash, and the release profile of a pollutant with
time. In practice, however, this information can only be obtained by separate tests.
1. To determine the highest concentration of a pollutant in the leachate, one eluant sample
should repeatedly contact fresh ash until theoretical saturation of the eluant is achieved.
An eluant thus repeatedly contacted with fresh ash simulates a "worst-case" leachate
concentration, because an actual leachate will not repeatedly contact fresh ash as it moves
down the landfill.
2. A test can also be designed to attempt to model more realistic conditions through a series
of sequential tests to simulate movement of the leachate through the landfill.
3. To estimate the total amount of a pollutant released from a given amount of ash during a
specific time period, an ash sample can be contacted repeatedly with fresh eluant.
4. A knowledge of the release pattern of a pollutant with time implies the use of kinetic data.
Shake tests are static tests and yield a variety of equilibria dependent on the conditions
of the particular test. However, repetitive eluant test results may be interpreted as kinetic
data.
DESCRIPTION OF TESTS PERFORMED
The eluant selected in this study was distilled water buffered and adjusted to a specific
pH. These parameters were based on actual field data describing local rainfall [ 1 ] so that
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