Fly Ash Binders in Stabilization of FGD Wastes

This paper presents a study of the integrated management of solid wastes generated in a high-capacity power plant, i.e., coal combustion fly and bottom ash (BA) and flue gas desulfurization (FGD) sludges. Solidification/Stabilization (S/S) processes were tested by analyzing the influence of the variables: binder type, water needs, and land disposal scenario that affect the final solid leaching characteristics. A factorial design of experiments was used to study the influence of these variables in the final S/S solid. After characterization of the leachates according to European regulations, the chemical stability of the S/S solids was analyzed using a standard dynamic leaching test (DLT). A dynamic leaching model of the contaminants (sulfates) contained in the S/S matrix was formulated from the research on the long-term behavior of the solid matrix, establishing the parameters that have an effect on the mobility of the sulfate. One parameter, the effective diffusion coefficient [D_e (cm²/s)] and its logarithmic expression, the leaching index (LX), were evaluated for each S/S process. Values of 1.51 × 10⁻¹¹ (cm²/s) ≤D_e≤ 2.14 × 10⁻⁹ (cm²/s) for 100 humidity-cured S/S wastes and 1.98 × 10⁻¹¹ (cm²/s) ≤D_e≤ 4.36 × 10⁻¹¹ (cm²/s) for water bath–cured S/S wastes were obtained for D_e, leading to LX values of 8.67 ≤ LX ≤ 10.82 and 10.36 ≤ LX ≤ 10.80, respectively. These values suggest that a high immobility was reached in some of the developed S/S processes. The validity of the leaching parameters obtained after a short-term landfill period (56 days) was confirmed after 1 year.