CO2 sequestration by direct mineralisation using fly ash from Chinese Shenfu coal

•Mineral phase changes of fly ash in carbonation were determined by Q-XRD analysis.•Promoted carbonation efficiency was achieved at elevated temperature and pressure.•Na2CO3 is an effective promoter for CO2 carbonation of Shenfu fly ash.•A multiple-cycle carbonation process was developed to regenerate Na2CO3.

Fly ash is a potential source of highly reactive feedstock for CO2 mineral carbonation. It does not require pre-treatment, but it has a low carbonation rate and efficiency. To address these issues, we studied the carbonation performance and mechanism of a fly ash from Shenfu coal of China. The effects of temperature, solid to liquid ratio and gas flow rate on the carbonation efficiency of the fly ash were systematically investigated in a direct mineralisation process. Our results indicated that calcium in lime and portlandite had a higher reactivity towards CO2 than that in other calcium bearing phases either crystalline or amorphous. Solely increasing the temperature did not improve carbonation efficiency. However, experiments in a batch reactor under elevated temperature (140, 180, and 220 °C) and pressure conditions (10 and 20 bar) using recyclable additives showed that a combination of high temperature and pressure significantly improved carbonation efficiency in the presence of 0.5 mol/L Na2CO3. Our multiple-cycle experiments showed that Na2CO3 facilitated the precipitation of calcium carbonate and was well regenerated in the process.

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