Characterization and comparative study of coal combustion residues from a primary and additional flue gas secondary desulfurization process

An extensive characterization and comparative study was done on two flue gas desulfurization (FGD) residues derived from the same coal. LR residues (originated from Loire/Rhone in the south of Lyon, France) are obtained after a "primary desulfurization" process (SO2 is trapped by reaction with CaO at a temperature of about 1100 degrees C), and LM residues (originating from La Maxe, near Metz in the east of France) are obtained after an additional "secondary desulfurization" process (SO2 is removed further by reaction with Ca(OH)(2) at a temperature of about 120 degrees C). Various and complementary investigation methods were used to determine their chemical, physical, and mineralogical properties: x-ray fluorescence and diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetry analysis, granulometric distribution, pycnometric density, BET specific surface area and pH, conductivity measurements, and chemical analysis of their insoluble fraction. The FGD residues contain basically two main components: a silico-aluminous fly ash part and calcic FGD phases. In the LR residues the two components can be considered as independent, whereas they are linked in the LM residues because chemical reactions have occurred, leading to the formation of silico-calcic gel CSH, hydrated aluminate AFm, and AFt phases. (C) 1998 Elsevier Science Ltd.