Preparation of low density ceramic support from coal fly ash

Low density ceramic support was prepared with fly ash as a starting material for the application to the biological aerated filter (BAF) system, and the effect of additives and sintering atmosphere on the apparent and bulk density of the carrier was examined. Borax, Na₂O and glass powders were added to produce liquid phase. The density of the support decreased as the amount of borax increased. The bulk density of 0.79 g/cm³ and the apparent density of 1.10 g/cm³ were obtained when the fly ash with 15% of borax was sintered at 1160°C for 15 minutes. The density also decreased as the plate glass powders of 212 μm size were mixed. When the fly ash with 12% of glass powder was sintered at 1280°C for 10 minutes, the bulk and apparent density were 0.90 g/cm³ and 1.00 g/cm³, respectively. Apparent density of 1.6-1.8 g/cm³ was obtained when the fly ash was sintered at 1200°C in a weak reducing atmosphere. By maintaining the reducing atmosphere at a high heating rate, the liquid phase was formed from the reduced components of fly ash. This resulted in the formation of closed pores that produced low apparent density.