Abstract
For the past several decades, researchers have studied the zeolitization of coal fly ash (class-F) by following different methods (viz., open and closed hydrothermal, and fusion followed by hydrothermal). In fact, these methods involve sequential processes like (i) dissolution of silica and alumina from the fly ash, (ii) nucleation of zeolite, and (iii) crystallization (growth of zeolite) in the reactant solution. Also, performance of these processes has been reported to vary with the type of alkali used as reactant and often, NaOH has been preferred for high cation exchange capacity, resulting in sodium zeolites. However, large scale applications of Na-based zeolites in soil and water are questionable due to the presence of high sodium, thereby increasing the sodicity and salinity of the soil/water. In addition, performance of the zeolites, as adsorbent, synthesized by different methods is expected to depend on various characteristics (viz., mineralogy, structural bonding, specific surface area, pore volume, and morphology), of the zeolites. In order to address the above issues, the present study is focused to investigate the various characteristics of the synthesized zeolites by (i) the above mentioned three methods, (ii) using Ca(OH)2 as reactant, and (iii) considering Na and Ca present in the fly ash. Thus, the aim of the study was to ascertain (i) a suitable method out of the three and (ii) characteristics of the blend of Na- and Ca-zeolites from the fly ash, which can be used as a controlled release fertilizer, as sorbent for water and soil decontamination.
