Kinetic analysis of thermal dehydration and hydrolysis of MgCl₂·6H₂O by DTA and TG

The thermal decomposition of MgCl₂·6H₂O (non-dried and partly dried) and the kinetics of the process were studied by DTA, TG, DTG, IR, X-ray diffraction and chemical analysis of Mg and Cl. The reactions which occurred in the course of the thermal analysis were identified as dehydration (in steps), thermal hydrolysis of MgCl₂·H₂O and dehydrochloridization of magnesium hydroxy chlorides. Melting of the phases MgCl₂·6H₂O, MgCl₂·4H₂O and MgCl₂ was also identified in the thermal curves. Thermal weight loss continued up to 800 °C in flowing air or nitrogen, but only up to 700 °C in static air. MgO was the end-product of thermal treatment in both cases. The kinetic parameters of the reaction, the activation energy E, pre-exponential factor A and apparent order of reaction b, were computed by several methods. The activation energy and the apparent reaction order of dehydration were found to increase with decreasing hydration number of the Mg. The dehydrochloridization process had the highest activation energy.