This study investigated the products of kaolinite thermal activation and the process of the alkaline reaction, using XRD,FTIR, Al-27 MAS NMR, SEM, TEM and XPS methods; moreover, the effect of Er(NO3)(3) addition on this process was analyzed. The results demonstrated that the addition of Er(NO3)(3)( )enhanced the destruction of the microstructure in the thermal activation process of kaolinite, increased the disorder degree, and promoted the transformation of the thermal activation product from Al-VI to Al-V. With the progress of the alkali reaction and increase in the alkali concentration, the zeolite A phase was gradually transformed into a sodalite phase by dealumination. In this process, extra-framework aluminium derived from dealumination was enriched on the surface of the alkali reaction products. The addition of Er(NO3)(3) accelerated the formation of zeolite and the transformation of the zeolite phase into the sodalite phase. (C) 2019 Elsevier B.V. All rights reserved.