Hopper ash

The hydration of CAC does not result in the formation of Ca(OH)2. This contributes to enhanced resistance in the presence of phenols, glycerols, sugars, etc. The formation of aluminum hydroxide gel during hydration provides resistance to dilute acids and sulfates. CAC has many industrial applications. It is used in flues, sewers, effluent-tanks, coal hoppers, ash sluices flues, and in industrial plants, e.g., oil refineries, breweries, dairies, and tanneries. 

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. 

Keywords Fly ash Hopper ash Lagoon ash Alkali activation Hydrothermal Fusion Grinding Residues Supernatant Characteristics ZeoUtization... 

As well, RFA was collected from lagoon of the thermal power plant. To differentiate the original hopper ash (OHA) and lagoon ash (OLA) from their residues obtained after alkali activation (viz., activated hopper ash, AHA, and activated lagoon ash, ALA) the samples have been designated as listed in Table 5.2. 

Table 5.1 Sample designation for different types of hydrothermal activation of hopper ash by TSA... 

Though, in general, G values for the ALA and AHA samples are seen to increase with an increase in the molarity of the NaOH (M < 2.0), randomness in the value of G for the AHA with time, T is noticeable. Incidentally, the residues AHA7 (i.e., the hopper ash treated with 1.0 M NaOH solution for 36 h) and ALA6 (i.e., the lagoon ash treated with 1.0 M NaOH solution for 24 h), exhibit very high G values (2.73 and 2.53, respectively). The increase in G value can be attributed to the... 

In contrast, Table 5.37 also exhibits an increase in Si02 in some of the residues (i.e., ALA2 to ALA6) of the hopper ash, as compared to the lagoon ash. Also, AI2O3 has been noticed to be on the higher side, as compared to the OLA, in these samples except for ALAI. 

Based on the findings presented in this chapter, it can be opined that the hydrothermal treatment of the fly ash collected from the hopper yields much better zeolites as compared to its counterpart (the fly ash collected from the lagoon). The three-step activation of the hopper ash with NaOH results in several changes (viz.,... 

It can be observed from Tables 5.20, 5.21, 5.22, 5.23 and 5.36 that the sum total of major oxides (AI2O3 + SiOa + Fe203) present in the raw fly ash, RFA (i.e., the original hopper ash) is about 95 % and hence it can be characterized as Class-F fly ash (ASTM C618-08) [3]. It can be noted from Fig. 6.3 and Tables 5.20, 5.21, 5.22 and 5.23 that activation of this fly ash with NaOH results in loss of SiOa (in majority) and AI2O3 (in traces) in the residues (the alkali activated fly ash, AAF), which is represented as the second data point, from the origin, on the duration axis, for all the durations. Incidentally, reduction in the value of oxides increases with an... 

Fig. 6.23 A FEG-SEM micrograph of the hopper ash (REA), where PP and SP designate pillar shaped and spherical shaped particles...

FT-IR spectra of the RFA (the hopper ash), superior residues of the TSA (i.e., both hydrothermal and fusion method) and the commercial grade, reference zeolite 4A powder (RZP), are presented in Fig. 6.41. From this figure it is apparent that the residues of TSA are having more or less similarities with the RZP zeolite at many FT-IR bands in terms of their wave numbers (viz., 3466.3, 1650.3, 1008 and 541.3 cm ). On the contrary, the bands at 2974, 1473.14 and 859.8 cm become decisive wave numbers of importance between the RZP and the residues of the TSA. 

Based on the hndings presented in this chapter, it can be concluded that the three-step activation of the hopper ash with NaOH results in minor variation in pH and reduction in electrical conductivity of the supernatant. Such activation is also responsible for reduction in Si and A1 contents of the supernatant, obtained after recycled treatments. Hence, the ftnal grade of the fly ash zeohtes gets improved (with high CEC and specific surface area, enhanced specific gravity, nano-sized fine particles of zeohtes and micro-sized new pores). The three-step activation of the fly ash by adopting the fusion technique has also been found to be effective for zeolitization of the fly ash. However, the presence of impurities in the ash residues obtained from the fusion process makes them inferior as compared to those obtained from the hydrothermal treatment. 

Chapter 6 Major Findings of the Three-Step Activation Technique This chapter deals with the inferences derived from the novel method three step activation of the hopper ash, which has been ascertained to be the superior ash over the lagoon ash, as described in Chapter-5, by following hydrothermal activation method. Furthermore, this chapter also showcases the outcome of the three-step activation of the fly ash by fusion method to synthesize high grade zeolite-X. 

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