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 (cm(2)/s)] and its logarithmic expression, the leaching index (LX), were evaluated for each S/S process. Values of 1.51 x 10(-11) (cm(2)/s) less than or equal to D-e less than or equal to 2.14 x 10(-9) (cm(2)/s) for 100% humidity-cured S/S wastes and 1.98 x 10(-11)(cm(2)/s) less than or equal to D-e less than or equal to 4.36 x 10(-11) (cm(2)/s) for water bath-cured S/S wastes were obtained for D-e, leading to LX values of 8.67 less than or equal to LX less than or equal to 10.82 and 10.36 less than or equal to LX less than or equal to 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.