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 degrees 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 degrees 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 Ce3+ adsorption from aqueous solutions. High purity sodalite showed a higher adsorption capacity of 53 mg/g at pH 6.0 and 25 degrees C as a result of the superior textual properties compared with zeolite A. The adsorption data were suitably fitted by the Langmuir isotherm and pseudo-second-order models. Findings from this study suggest that the kaolinite is a potential source for REE recovery, and the leaching residue is suitable for the synthesis of zeolites, which can be used as promising adsorbents for Ce3+ recovery.

Automated summary

This study focused on the recovery of rare earth elements (REEs) from kaolinite through selective leaching and the synthesis of zeolites from the leaching residue. The results showed that the pH static leaching method achieved over 90% leaching of REEs from metakaolinite, while only extracting less than 2% of the major constituents. Zeolites with different compositions were successfully synthesized, and high purity sodalite exhibited superior adsorption capacity for Ce3+ compared to zeolite A. These findings suggest that kaolinite could be a potential source for REE recovery, and the resulting leaching residue could be used for the synthesis of zeolites as promising adsorbents for Ce3+ recovery.