Conclusions Carbon footprint Agriculture GHG emissions Crop nitrous

Fig. 11 shows the rate constants at different reaction temperatures for the three tested fly ashes.
Fig. 11. Plot of Arrhenius law for the carbonation of fly ash at different temperatures.Figure optionsDownload full-size imageDownload as PowerPoint slide
The estimated values of Ea for S1, S2 and S3 fly ashes are 46.4 kJ/mol, 41.1 kJ/mol, and 34.5 kJ/mol respectively. These values are much better in terms of KU-60019 requirements compared with the values of 180 kJ/mol and 98 kJ/mol for direct gas solid carbonation between CaO and CO2 in the absence and presence of 15% water in the system, respectively ( Wang et al., 2007). However, Sun et al. (2012) obtained an even lower activation energy value of 12.7 kJ/mol for the carbonation of brown coal ash-derived leachate. However, since the overall carbonation reaction is exothermic in nature, there is no requirement to provide energy into the system. Compared to direct gas solid carbonation, the present system of aqueous carbonation at mild temperatures and pressures with continuous stirring would provide an efficient method of CO2 sequestration.