Insight into the kinetic behavior of microwave-assisted synthesis of NaX zeolite from lithium slag

Abstract

Lithium slag is an industrial waste residue of the extraction of lithium carbonate industry, which has the issue of high output and low utilization rate. In order to improve the utilization rate and value of lithium slag, it was directly used as a raw material to synthesize NaX zeolite using a hydrothermal and microwave-assisted method in this paper. The process of synthesizing NaX zeolite from lithium slag was analyzed and characterized by X-ray diffractometry, Fourier transform infrared spectroscopy and solid state nuclear magnetic resonance. The reaction mechanism of NaX zeolite from lithium slag was also proposed. The structure of NaX zeolite synthesized from lithium slag was characterized. The results indicate that during the synthesis, aluminum species in the lithium slag transform from Al^VI to Al^IV, and the silicon species undergo a transition from Q⁴ (0Al) and Q⁴ (1Al) structures to Q⁴ (1Al) and Q⁴ (2Al) structures. The synthesis time of NaX zeolite with the microwave-assisted method is only about 1/3 that of hydrothermal synthesis. Microwave irradiation accelerates the dissolution of lithium slag, the generation of aluminosilicate gels, and the crystallization of the NaX zeolite, but does not change the process of synthesis of NaX from lithium slag. The NaX zeolite synthesized from lithium slag has smaller grains (0.5–0.8 μm) and good stability, and the adsorption capacity of water reaches 32 wt% when the relative humidity is 90%. This study provides technical support for the large-scale production of NaX zeolite from lithium slag.