Effects of Er(NO3)3, Nd(NO3)3 and Y(NO3)3 on kinetics of dehydroxylation of kaolinite

Abstract

Comprehensive thermal analysis technologies of thermogravimetry (TG) and differential thermal analysis (DTA) were applied in this paper to explore effects of Er(NO3)3, Nd(NO3)3 and Y(NO3)3 on kinetics of dehydroxylation of kaolinite, and pertinent kinetic parameters in dehydroxylation of kaolinite were calculated through the Coats–Redfern integral method and Achar differential method, leading to the control mechanism and pertinent kinetic parameters, i.e. apparent activation energy (EA) and pre-exponential (frequency) factor(A), etc. in dehydroxylation of kaolinite, and the influences of respective incorporation of three kinds of rare earth nitrates on kinetic parameters in dehydroxylation processes of kaolinite were analyzed. The activation energy was validated by Ozawa method. The obtained results showed that the course of dehydroxylation of kaolinite was controlled by the rate of the third-order chemical reaction (F3) under applied condition. The median values of EA and lnA corresponded to 307.94KJ·mol−1 and 47.8980, respectively. The control mechanism in dehydroxylation of kaolinite was transformed to the rate of the second-order chemical reaction (F2) after incorporation of the three kinds of rare earth nitrates, respectively. The values of EA and lnA for the dehydroxylation of kaolinite mixed with Er(NO3)3, Nd(NO3)3, and Y(NO3)3, respectively were: 192.24KJ·mol−1 and 29.2753, 198.50KJ·mol−1 and 29.8658, and 195.03KJ·mol−1 and 29.4592, which means incorporations of three kinds of rare earth nitrates significantly decreased both EA and A for the dehydroxylation of kaolinite. The activation energy obtained by Ozawa method corresponded to the average value obtained by the Coats–Redfern integral method and Achar differential method. Participation of the –OH connects to –Al in the coordination of rare earth ion leads to decrease of activation energy.