Preparation and characterization of amorphous aluminosilicate polymers from ash formed in combustion of peat and wood mixtures

Fly and bottom ash samples were collected from a full scale circulating fluidized bed (CFB) boiler combusting a mixture of peat and wood, and their suitability for the preparation of a special type of amorphous aluminosilicate polymers, so called geopolymers, was studied. Both ash types and the corresponding geopolymers were characterized by a field emission scanning electron microscope utilizing an energy dispersive spectrometer (FESEM-EDS), and by powder X-ray diffraction (XRD). Metakaolin and geopolymers prepared from it were included in this study for comparison. Both fly and bottom ash turned out to be suitable materials for the preparation of geopolymers. The diffraction patterns of the materials prepared by using a 5 M solution of NaOH indicated the presence of significant amounts of amorphous material. When using the 10 M NaOH solution, however, several crystalline zeolite phases were identified among the amorphous geopolymeric material. The effect of calcium, magnesium, and iron on the polymer formation was also explored in this work.