CO2 sequestration by mineralisation of coal fly ash in aqueous systems

Carbon dioxide (CO2) mineralisation by industrial wastes can mitigate carbon emissions safely and permanently with low cost. Disadvantages of coal fly ash-based CO2 mineralisation are low CO2 removal efficiency, slow reaction kinetics and low capacity, which restrict application of this technology. My research (i) explores mechanisms in coal fly ash-based CO2 mineralisation; and (ii) develops innovative approaches to enhance carbonation reactions and make them more technically and economically feasible. Five Chinese or Australian coal fly ashes were selected for carbonation experiments to understand fly ash properties affecting CO2 sequestration capacity and kinetics of carbonation reactions. A Chinese ash with 16 % CaO displayed the fastest kinetics while an Australian ash with 32 % CaO and 29 % MgO exhibited the largest CO2 capacity. Carbonation experiments investigated effects of temperature (20−220 °C), solid to liquid ratio (50−200 g/L), and additives (Na2CO3, NaHCO3 and NaCl) on CO2 capacity and reaction kinetics, and mechanisms involved in carbonation reactions. Parameter optimization and introduction of additives can improve carbonation efficiency and enhance carbonation reactions between fly ash and CO2, and the carbonation efficiency could become stable within 1.5 h, but it was still slow for further application. Integrated CO2 absorption−mineralisation, that integrates amine scrubbing, CO2 mineralisation and amine regeneration in a single process, was developed. Regeneration of amines by calcium oxide and fly ash was investigated. Results show that after carbonation reactions with calcium oxide and fly ash at 40 °C in 15 min, amine solutions can be regenerated to a similar CO2 loading compared to traditional thermal regeneration method, and that the CO2 absorbed by amine solutions can be precipitated as calcium carbonate with fast kinetics.