Characteristics of the Hopper Fly Ash and Residues

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 

6 Major Findings of the Three-Step Activation Technique 

Further, as a result of Step-2 (i.e., R1 and represented by third data point in Fig. 6.3 on time axis), variations in these oxides amidst randomness elucidate significant interaction between the residues and the filtrates, as discussed above. Interestingly, from Fig. 6.3a-h it can be noticed that recycling causes both loss and gain in the major oxides present in the fly ash (refer Fig. 6.3a-h). Such gains are 

From Fig. 6.4a-d and Tables 5.12 and 5.13 it can be noticed that there is increase in specific gravity, G, due to step-1 (the FT), whereas, only minor variations during the R1 and R2 steps of the treatment. This can have direct correlation with the dissolution of Si and A1 species and creation of pores in the particles. 

From Fig. 6.5a-d and Tables 5.15, 5.16, 5.17 and 5.18 it can be noticed that, SSA increases with the increase in step of recycling of the AAF. bicidentally, contrary to all other AAFs, there is significant increase in the SSA, in the residue, 1.5-PT-36 (refer Fig. 6.5c). This can be attributed to an intensive etching of the ash particles, leading to its dissolution, which helps the development of micro-sized pores in AAFs. In addition, treatment steps of 36 h exhibits trends, contradictory to other trends. This can be attributed to creation of extra fine particles which may be amorphous in nature and nano-sized zeolite crystals. 

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