Waste minimization protocols for the process of synthesizing zeolites from South African coal fly ash
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Date
2013
Journal Title
Journal ISSN
Volume Title
Publisher
MDPI
Abstract
Production of a high value zeolite from fly ash has been shown to be an avenue
for the utilization of South African fly ash which presently constitutes a huge disposal
problem. The synthesis of zeolites Na-P1 and analcime on a micro-scale has been
successful and preliminary investigation shows that scale-up synthesis is promising.
However, the post-synthesis supernatant waste generated contains high levels of NaOH
that may constitute a secondary disposal problem. A waste minimization protocol was
developed to reduce the volume of waste generated with a view to enhancing the feasibility
of the scale synthesis. Series of experiments were conducted in 100 mL jacketed batch
reactors. Fly ash was reacted with 5 Mol NaOH on a 1:1 mass basis during the aging step,
followed by hydrothermal treatment in which ultrapure water was added to the slurry. This
study shows that by re-introducing the supernatant waste into the experiments in such a
way that it supplies the required reagent (NaOH) for the zeolite synthesis, zeolite
Na-P1 and analcime can be synthesized. It also shows that the synthesis process can be
altered to allow up to 100% re-use of the supernatant waste to yield high value zeolitic
products. This study effectively constructed two protocols for the minimization of waste
generated during the synthesis of zeolites from South African coal fly ash. This result
could be used to establish a basis for legal and environmental aspects involved in the
commission of a full-scale plant synthesizing zeolites NaP1 and analcime.
Description
Keywords
Zeolite Na-P1, Fly ash, Waste minimization, X-ray diffraction, Atomic emission spectrometry, Scanning electron microscopy, Zeolite analcime
Citation
Du Plessis, P. W. (2013). Waste minimization protocols for the process of synthesizing zeolites from South African coal fly ash. Materials, 6: 1688-1703