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

• A pure phase zeolite A was synthesized by replacing fusion step with ultrasound.
• A 10-min of sonochemical treatment of the coal fly ash prior to hydrothermal treatment was necessary.
• Sonochemical treatment reduced the crystallization temperature and synthesis time.
• A pure phase zeolite A was synthesized at lower crystallization temperatures within shorter periods.
• A novel process to replace the energy intensive fusion step with a short, easy and inexpensive treatment.

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.