Abstract
This work presents a study of cenosphere separation from lignite high-calcium (~24 wt.%) fly ash by centrifugal method; this is the first report for Mae Moh, Thailand, fly ash with this high calcium content using this technique. The effect of centrifugal parameters on cenosphere yield and properties were investigated. Those properties include physical properties, morphology, chemical composition, and mineral phases. The recovery yields are in the range of 0.34–0.64%, approximately one third of the yield obtained from the general gravity settling method. Density, particle size, and morphology of the collected cenospheres appeared to be independent of sequence of the applied speeds and times. Interrelation of chemical composition and mineral phases was established, with the focus on calcium carbonate formation on cenosphere surface and crystallite size study. The study has revealed the preferential formation of calcite–(104) peak is observed–by cenospheres, with stable growth behavior of crystallite sizes obtained from all the centrifugal conditions. The result was compared to that obtained from the sink-float method for a better insight. The influence and limitation of the centrifugal method, the varied parameters, and the relevant reaction pathways on crystal growth process in terms of important dissolving species (i.e., Ca2+ and CO32−) behavior in the ash suspension were discussed.
Highlights
Hollow cenospheres are known as a valuable fraction of fly ash with numerous applications [1,2,3]
The relevant reactions and important dissolving species behavior involving the heterogeneous nucleation of the calcite growth under the specific conditions was described
We presented cenosphere separation of lignite high-calcium (~24 wt.%) fly ash by a centrifugal method using water as a medium
Summary
Hollow cenospheres are known as a valuable fraction of fly ash with numerous applications [1,2,3]. In synthesis and functionalization applications [1], it is important to know the chemical and phase compositions of cenospheres because they have considerable influence on the predictable and controlled properties of the functional materials. Cenospheres composed of different chemical constituents are known to depend on the coal used and the transformation during the combustion process, and different stages of the phase transformation of ash particles determine their molecular structure and overall chemical composition as manifesting in surface texture [23,24]. Low-calcium fly ash is traditionally produced from bituminous coal, and high-calcium fly ash is mostly from lignite coal With their distinctly physicochemical characteristics, the differences lead to different orders of applicability and reactivity in the applications. The high calcium hydroxide content leading to crystals formed on cenosphere surface limits their applicability in the cement industry
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