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Insights into Carbonation Kinetics of Fly Ash from Victorian Lignite for CO2 Sequestration
journal contribution
posted on 2018-01-08, 00:00 authored by Long Ji, Hai Yu, Bing Yu, Ruijie Zhang, David French, Mihaela Grigore, Xiaolong Wang, Zuliang Chen, Shuaifei ZhaoMineral
carbonation of fly ash can both capture and store CO2 permanently
in a single process without long-term monitoring.
Previous studies indicate that fly ash with high calcium and magnesium
contents exhibit promising CO2 fixation capability. However,
the reaction mechanisms and kinetics involved in the carbonation reaction
of fly ash is still not fully understood. In this study, a typical
Victorian brown coal fly ash from Hazelwood power plant was selected
to sequestrate CO2 in a direct aqueous carbonation process.
Experiments were conducted in a vessel reactor at various temperatures
(40, 50, 60, and 70 °C), stirring rates (900, 1050, 1200, and
1350 rpm), and CO2 pressures (3, 4, 5, 6, and 7 bar) to
investigate the reaction kinetics and identify the rate-limiting steps
of carbonation. The results show that both the carbonation rate and
the maximum carbonation efficiency could be improved by optimizing
parameters and by the introduction of NaHCO3. Also, the
complex effects of the operating parameters on the carbonation rate
and the maximum carbonation efficiency were investigated. The kinetic
data can be well fitted by the surface coverage model with the R2 ≥ 0.98, indicating that the carbonation
of fly ash can be physically expressed by this model. The maximum
carbonation efficiency of fly ash could also be well-predicted by
the model. In addition, the assumed mechanisms of the carbonation
reaction were validated by particle size, surface area, and porosity
changes of the fly-ash particles after carbonation reactions. The
observation of scanning electron microscope equipped with energy-dispersive
X-ray spectroscopy before and after carbonation also confirmed that
the newly formed precipitates were not only deposited on the active
surface but also filled the pores of the fly-ash particles.