Synthesis of zeolite A from coal fly ash using ultrasonic treatment – A replacement for fusion step

Abstract

The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis of coal fly ash production and disposal in South Africa. In recent studies, South African fly ash was proven to be a suitable feedstock for the synthesis of essential industrially used zeolite A. However, the process involves a costly energy intensive step whereby fly ash is fused at high temperatures, which may make the process economically unattractive on a large scale. The aim of this study is to investigate the possibility of replacing high temperature fusion with less energy intensive sonochemical treatment for the synthesis of zeolite A. Sonochemical treatment was first thought possible due to the violent cavitation caused by high intensity sonication. The results of the study showed that fusion can be replaced by 10 min of high intensity sonication. The incorporation of sonication also consequently reduced the crystallization temperature of the process making it possible to synthesize a pure phase zeolite A at lower temperatures and reduced times. This study effectively developed a novel process to replace the energy intensive fusion step with a short, easy and inexpensive treatment. Scale up of this synthesis approach may proffer a promising alternative option to the anticipated energy demand of the synthesis of fly ash-based zeolite with fusion method.

Synthesis of zeolite Na-P from coal fly ash by thermo-sonochemical treatment

“…Increasing hydrothermal treatment time to 3.5 h and decreasing the UST irradiation time from 3 h to 0.5 h in a 0.5 h UST time interval resulted in decreasing the peak intensity (crystallinity) of product by $1-4% each time. This decreasing of crystallinity due to increasing of UST energy (power output) as Ojumu et al reported that increased temperature reduces the performance of the ultrasound with respect to power output [9]. The results showed that the late sonication including hydrothermal treatment (at least 1 h) and UST irradiation (at least 0.5 h) are necessary for successful conversion of CFA to Na-P zeolite.…”

“…On the other hand, late irradiation is effective rather than the overall irradiation during the zeolitization. While Ojumu et al successfully synthesized zeolite from CFA with 10 min sonication (600 W) [9], however, in this work zeolite was produced with 30 min sonication (125 W) at least after 1 h hydrothermal. This is due to the difference in the power of ultrasonic which 600 W is 6 times strong of 125 W and Bukhari et al found that the amount of ultrasound energy and reaction temperature play a significant role in the zeolitization process [8].…”

“…In the past four decades, researchers have focused on using CFA as a source of silicon and aluminum for manufacturing different types of synthetic zeolites such as Na-Y [6], zeolite X and sodalite [7], zeolite A [8,9], and Na-P zeolite [10][11][12][13][14][15][16][17][18][19]. Na-P zeolite is one of the most interesting synthesized zeolite because of its high cation exchange and adsorption capacity.…”

The zeolite modified by chitosan as an adsorbent for environmental applications

“…Thus, the search for effective and inexpensive ways of managing wastes from the coal combustion is necessary. In the last few years, there has been a growing interest in zeolites obtained from FAs (Ojumu et al, 2016;Visa, 2016;Wu et al, 2008). Considerable attention has been paid to synthetic zeolites due to much better sorption properties than those of natural zeolites.…”

Improved removal of Cr(VI) from aqueous solution using zeolite synthesized from coal fly ash via mechano‐chemical treatment

“…In China, coal‐fired power stations generate significant amount of fly ash. Synthesis of zeolite from coal fly ash is a technically promising approach to utilize the waste fly ash . Coal fly ash has been investigated as synthesizing zeolite since 1985 .…”