CO2 uptake capacity of coal fly ash: Influence of pressure and temperature on direct gas-solid carbonation

Coal ashes are normally considered as a waste obtained by the coal combustion in thermal power plants. Their utilization inside the site where are produced represents an important example of sustainable process integration. The present study was performed to evaluate the application of a gas-solid carbonation treatment on coal fly ash in order to assess the potential of the process in terms of sequestration of CO2 as well as its influence on the leaching behavior of metals and soluble salts. Laboratory tests, performed under different pressure and temperature conditions, showed that in the pressure range 1 ÷ 7.5 bar the CO2 uptake increased with temperature, shortening the time required to capture higher percentage of CO2. Conversely, in the pressure range 10 ÷ 15 bar, the carbonation kinetics slowed down and the effect of temperature was less evident. The best CO2 uptake was found to be 18.2 wt% corresponding to a maximum carbonation efficiency of 74%, estimated on the basis of the initial CaO content. The high degree of ash carbonation achieved in the present research, which was conducted under mild conditions, without add of water and without stirring, showed the potential use of coal fly ash in CO2 sequestration by means of direct gas-solid mineral carbonation.