Type of fly ash

In general, lack of equilibrium during the pyro-processing stage and heterogeneity of composition make it impractical to calculate the phase content of fly ash from its chemical analysis. Two other factors, common to all types of fly ash, further complicate evaluation of the potential to use fly ash. One is the presence of unburnt carbon, which should preferably not exceed a few wt% the other is the presence of alkali-sulphates (see Groppo et al., 2004). When used in cementitious formulations, free... 

The total annual output of fly ash in Poland is about 20 million tons (in 2008 over 26 miUion tons) of fly ash fiom the black coal combustion and about 9 million tons of fly ash from the brown coal combustion respectively. The production of fly ash cements started in XX c. in late sixties. The annual fly ash consumption attains 1400 thousands tones. The three types of fly ash generated in the pulverized fuel combustion (frequently determined as conventional ones) can be distinguished (Table 7.3) those from the black coaf from the brown coal in Turoszbw coal-field as well as from the Konin and Belchatow coal-field. 

The possibility of leaching of trace metals from the ash into ground or surface waters is also a possibility. The difference in physical properties between slag and fly ash would suggest a different leaching behavior. In fact, leaching behavior may vary within different types of fly ash especially where there is a size dependence of the physical and chanical properties (Fisher and Natusch, 1979). 

The beneficial effect of pozzolanic materials on sulfate resistance results from calcimn hydroxide consumption and the formation of additional amounts of C-S-H, which results in a reduction of porosity and permeability. Soroushian and Alhozaimi (1992) reported a strong correlation between permeabihty and extent of expansion, irrespective of the type of fly ash or its content. A reduction of the C3 A content in the cement also contributes to improved performance (Irassar and Batic, 1989 Giergiczny, 1997). To obtain a proper... 

The aims of this research are to provide information about these new types of fly-ash, to define the best practices for handling and landfill disposal and to promote valorisation. 

In order to investigate the effectiveness of different types of alkalis, for activation of the fly ash, researchers have, mosdy, adopted NaOH or KOH aqueous solutions by varying the temperature between 80 and 200 °C and activation period between 3 and 48 h. 13 different types of fly ash zeolites have been synthesized by employing this method [3, 5, 6, 19-28]. 

In context to the characterization of the S3uithesized zeolites, it has been reported that the quantity of zeoUtic minerals present in the end product has been found to vary widely ( 20-65 % by weight of fly ash), mainly depending on the various parameters (viz., type of fly ash, alkali concentration, temperature, time and liquid to solid ratio) involved in the synthesis process. A t3q>ical flow chart is depicted in Fig. 3.1 to highlight the different procedural steps required for this method. 

Furthermore, the time of activation has been reduced significantly by employing microwave assisted heating in hydrothermal method. Although, the alkali dissolution of fly ash can be accelerated by fast heating and attack of active water at molecular level, however, it has been found that the end product is of low yield, which has not been explored further. In addition, no efforts have been made for understanding the effects of the physical variation of the fly ash particles on the quality of final products. With this in view, an optimization of the time of micro-wave heating of aqueous matrix of different L/S ratio, alkali concentration as well as the type of fly ash collected from various sources (viz., bottom ash, hopper ash, ash from electrostatic precipitator), needs to be carried out. 

Scott et al. [18] have established that the synthesized fly ash zeolites can be a suitable material for the removal of lead ions from aqueous solution within 24 h of application. They have reported that type of zeolites (viz., zeolites X, Na-Pl, Sodalite and Phillipsite) synthesized in the hydrothermal method can depend on the treatment time, concentration of NaOH solution and the type of fly ash employed in the process. It has been concluded that the type of zeolites and their morphology can influence the rate of lead ion removal. 

---