来源: Science Direct
The reason for the higher extraction rate of light rare earth elements (LREY) than that of heavy rare earth elements (HREY) during the extraction of rare earth elements (REY) from coal gangue (CG) by the calcination-acid leaching method has rarely been studied in depth. Based on the identification of rare earth minerals in CG, rare earth minerals were synthesized, and calcination-acid leaching experiments were carried out to explore differences in leaching reaction mechanisms between LREY and HREY. X-ray powder diffraction (XRD) analysis shows that rare earth fluorocarbonate and phosphate were synthesized. After calcination at 600 °C, rare earth fluorocarbonates decompose into rare earth fluoroxides, and some rare earth fluoroxides further decompose into rare earth oxides and rare earth fluorides; as the radius of trivalent ions decreases, the content ratio of rare earth oxides gradually increases, thereby increasing the leaching efficiency. The leaching efficiency of monazite-type rare earth phosphates increases gradually from LaPO4 to EuPO4, whereas that of xenotime-type rare earth phosphates decreases markedly from TbPO4 to LuPO4. The overall leaching efficiency shows an "inverted V" phenomenon, and the leaching efficiency of LREY is greater than that of HREY. The REY leaching efficiency of equimolar proportional all-element rare earth fluorocarbonate and its calcined products gradually increases with the decrease of rare earth ion radius, while the law of equimolar proportional all-element rare earth phosphate and its calcined products is opposite. Kaolinite has no significant effect on the thermal decomposition of rare earth fluorocarbonates. This study suggests that rare earth phosphate dissolution controls the leaching differences between LREY and HREY in CG. This study provides a theoretical basis for the calcination-acid leaching extraction of LREY and HREY from CG.