Formation of Meso- and Micro-pores by TSA

Researchers [36, 38] have characterized NaOH activated fly ash residues (zeolites) and have ascertained their highly zeolitic nature [7]. It has also been opined [37,39] that the purity of these residues is mainly decided by their cation exchange capacity, mineralogy and morphology. However, study of pore characteristics (viz., size and volume) of such residues has not been explored in detail. 

In this context, efforts were made to demonstrate the formation of pores and their effect on specific gravity, specific surface area and cation exchange capacity of three types of residues (produced by using NaOH aqueous solution and its spent solution (the filtrate), respectively). Based on N2 gas absorption, isotherms and infrared transmittance spectra, residues obtained from second and third steps (each of 24 h) of the treatment by filtrates of 1.5 M NaOH were established to be significantly enriched in finer meso- and micro-pores, respectively, as compared to a pure and macro-porous zeolite 4A (zeolite RZP). 

In agreement to the findings reported in the literature [33] it has been observed that there is an increase in specific gravity, G, and specific surface area, SSA, of the residues 1.5-PT-24 as compared to its counterparts (refer Table 6.11). 

Sample Total ptne volume (cm /g) % Volume contribution of various pore sizes (nm)  

6 Major Findings of the Three-Step Activation Technique 

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