WWRC 94-29
Immobilization of Contaminants in Alkaline Solid
Wastes Derived from Fossil Energy Conversion Process
Abstract
The combustion of fossil fuels (eg coal, oil shale) to generate energy results in the
production of alkaline solid wastes (fly ash, clean coal technology (CCT) ash,
spent shale etc). Reactions involving calcium (Ca) and carbon dioxide (C02)
usually control the pH and mobility of inorganic contaminants such as Cd, Pb and
Se in alkaline solid wastes. Samples of fly ash, spent shale and CCT ash were
reacted with CO2 at different pressures, moisture levels and for various reaction
times. Treated and untreated samples were subjected to X-ray diffraction (XRD)
and AB-DTPA (ammonium bicarbonate diethylenetriamine pentaacetic acid)
extraction studies. Some CO2 treatment conditions effectively precipitated calcite,
and therefore lowered the pH and extractable concentrations of inorganic
contaminants (eg Cd, Pb, Zn, Mn, As and Se) in alkaline solid wastes. Thus, the
risk of these elements contaminating soils and groundwater resources could be
reduced when CO2 treated alkaline solid wastes are disposed in landfills.
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