Adsorption of cerium (III) by zeolites synthesized from kaolinite after rare earth elements (REEs) recovery

REE recovery tests were performed on a kaolinite and the corresponding metakaolinite using pH static leaching method. Test results show that over 90% of REEs were leached from the metakaolinite sample at pH 0.00 and 25 °C, while less than 2% of the major constituents were simultaneously extracted. Therefore, selective leaching of REEs from the metakaolinite was achieved through pH static leaching. The leaching residue was then subjected to alkaline activation for zeolites synthesis. The effects of hydrothermal temperature and incubation period under various alkaline conditions on the synthesis of zeolites were systematically investigated. The phase compositions, textual properties, and morphology of the synthesized products were characterized. Pure zeolite A with 100% relative crystallinity was successfully synthesized at 80 °C for 6 h when using 3 M NaOH as the alkaline activator. While as the synthesis conditions became increasingly harsh, the metastable zeolite A gradually transformed into more stable sodalite, and three types of zeolites, including zeolite A, sodalite, and their mixtures, were obtained. After that, various types of zeolites were applied for Ce