This paper studies possibilities of alkali-activated fly ash (AAFA) for the preparation of systems with preserved certain porosity level. Such systems would be used for example as filtration barriers, which are commonly prepared by both energetically and economically expensive sintering process at high temperatures. Porosity preservation was facilitated by the use of only coarse fraction from fly ash particles together with the use of low water to fly ash ratio and pressure compaction. Two different doses of sodium hydroxide were used to alkali activate fly ash. Prepared specimens were moist cured at 95 °C for 24 hours. Porosity and binder phase among the fly ash grains were investigated using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and capillary flow porosimetry (CFP). The results showed that it is possible to prepare AAFA-based porous systems and modify their properties by changing the activator dose.
A composition of coal combustion fly ash depends on a coal composition and conditions of a combustion process. The main components are SiO2 and Al2O3. An amount of Al2O3 in coal combustion fly ash is relatively high, about 30–40%, and for this reason, the fly ash could be potentially used as a raw material source for alumina production. There are several ways to get alumina. The fly ash could be acid leached or sintered with a suitable additive. One of the possible sintering processes is lime-soda sinter process. The article deals with products of lime-soda sinter process of the fly ash produced from brown coal in Czech thermal power plant. The phase composition of sintered material was determined by X-ray diffraction analysis (XRD). The presence of sodium aluminate and dicalcium silicate was confirmed.
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