Decomposition Kinetics of CaCO3 Dry Coated with Nano-Additives

Abstract

Decomposition kinetics of surface coated calcium carbonate (CaCO3) is investigated using different weight % (0.25%, 1.0% and 2.0%) of nano-additives (SiO2, TiO2, MgO and Fe2O3). The activation energy was calculated from model-free iso-conversional technique using differential as well as integral methods. The result shows that CaCO3 with 1.0% of nano-additives has lower activation energy then corresponding pure CaCO3. The catalytic activity of nano-additives is possibly due to the fact that nano-additives which has higher thermal conductivity act as heat receptor and increases the surface temperature of the CaCO3. However, coating with higher % of nano-additives increases the resistance of CO2 diffusion and increases the activation energy. The results show that there is a significant reduction in overall heat requirement for ecomposition of CaCO3. This may be due to phase change of nano-additives which is exothermic in nature and releases heat within the temperature range where CaCO3 decomposes. Thus, the decomposition of coated CaCO3 with 1% additives requires lower amount of heat which has significant implications in limestone based energy intensive industries. The reaction model for CaCO3 decomposition could not be predicted by conventional Master plot analysis. However, M´alek’s method found to be more suitable to determine the appropriate reaction model. Experimental data was fitted well with the theoretical model proposed by ? Sest´ak Breggren (SB). The parameters (m and n) in SB model and invariance of activation energy through out the conversion range strongly signify that decomposition mechanism is single step in nature.