Green synthesis of zeolites from a natural aluminosilicate mineral rectorite: Effects of thermal treatment temperature

This article reports the effects of thermal treatment temperature on the physicochemical properties of a rectorite mineral and the chemical reactivity and crystallization behavior of the activated rectorite products for zeolite synthesis purposes. The raw rectorite mineral and its thermal activation products were systematically characterized by XRF, XRD, FTIR and 29Si and 27Al MAS NMR techniques and the resultant zeolites were characterized by XRD technique. The results showed that after being thermally treated in the temperature range of 25–1300 °C, the rectorite experienced the following four stages: dehydration at 150–300 °C, dehydroxylation at 600–700 °C, structure collapse at 1000 °C, and new phase formation at above 1100 °C. Moreover, it was found that after being thermally treated at ca. 1000 °C, the SiO4 tetrahedral units in the rectorite mineral are distorted, while the AlO6 octahedral units are decomposed and thus the maximum contents of active SiO2 and Al2O3 can be simultaneously achieved, and as a result, zeolite P is obtained when using the rectorite calcined at 1000 °C as the starting material for fabricating zeolites. Our results further revealed that like kaolin rectorite after thermal activation at a suitable temperature can be used for zeolite synthesis and thus demonstrates itself a promising feedstock for the green synthesis of zeolites directly from natural aluminosilicates without experiencing intermediate chemicals.