Chemical processing and extraction of cerium phosphate from Mongolian monazite-bearing apatite ore

Abstract

Mongolia possesses substantial rare earth element resources however, industrial-scale extraction and processing remain underdeveloped. This study presents an optimized hydrometallurgical route for the selective recovery of cerium as cerium phosphate (CePO₄) from monazite-bearing apatite ore of the Mushgai Khudag deposits in Southern Mongolia. Alkaline cracking was conducted at a solid: liquid ratio of 1:4 using 8.75 N NaOH at 140 °C for 3 h, enabling effective decomposition of the monazite matrix and liberation of REE species. The optimized process achieved a maximum cerium recovery of 89.97% under controlled conditions. The resulting alkaline leachate was subjected to sequential acid purification (HCl and HNO₃) followed by controlled pH adjustment (pH 3-4.5), facilitating preferential cerium separation from co-existing rare earth elements. Final precipitation at pH 11 and subsequent reaction with monoammonium phosphate (NH₄H₂PO₄) yielded an amorphous cerium phosphate precursor, which was calcined at 1000 °C to obtain crystalline CePO₄ with 93.71% purity. The crystalline phases, morphology, and chemical composition of the products were characterized by X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray fluorescence spectroscopy. The proposed process demonstrates an effective approach for the selective precipitation of cerium and provides a feasible hydrometallurgical strategy for the utilization of Mongolian monazite resources.