Microcalorimetric study of the effect of calcium hydroxide and temperature on the alkaline activation of coal fly ash

The objective of this research is to know, through the flow of heat released, the effect of the addition of calcium hydroxide and the temperature on the alkaline activation of coal fly ash with a solution of sodium hydroxide. The heat flow of the samples was measured from an isothermal conduction microcalorimeter at 25, 35 and 45 °C, with percentages of calcium hydroxide between 5 and 15 mass% and concentrations of sodium hydroxide between 6 and 10 M. The data obtained were analyzed by the ANOVA technique using a response surface. Calcium hydroxide mainly supplies nucleation sites and increases the rate of reaction during the latent period. Sodium hydroxide increases the degree of reaction, the amount and rate of the reactions up to concentrations of 10 M. The time of the wetting and dissolving processes was 6 min, independent of the temperature and composition of the mixture. The maximum amount of energy released was 200 kJ kg−1, seeking to be minimal in the initial processes and maximum in the end. The calculated apparent activation energy was 361.20 ± 16.47 kJ mol−1 which reflects the importance of the temperature in the alkaline activation processes. The temperature does not significantly affect the amount of energy released, but does affect the rate and number of reactions.The authors thank the Administrative Department of Science, Technology and Innovation of Colombia (Colciencias) for the support of this study through the National Call 567 for Doctoral Studies in Colombia. Likewise, they thank the Ministry of Economy, Industry and Competitiveness of Spain for the project grant BIA2013-47876-C2-1-P, within which a part of the tests of this study was carried out.Peer reviewe