Influence of Rare Earth Occurrence States on Extraction Rate in Weathered Crust Elution-Deposited Rare Earth Ores

The occurrence of rare earth elements (REEs) in weathered crust elution-deposited rare earth ore is very complicated, and only the exchangeable adsorption state REEs can be utilized by the current extraction process, demonstrating that the REE resources have not been effectively utilized. Two samples from weathered crust elution rare earth ore in southern China were selected. Total REE contents in samples were analyzed by mixed acid digestion–inductively coupled plasma-mass spectrometry (ICP-MS), occurrence states of REEs were analyzed by ammonium sulfate leaching and sequential extraction, and the relationship between ammonium sulfate leaching rates and REE occurrence states was preliminarily discussed. The results were as follows in three aspects: (1) Grinding altered the occurrence state of REEs; the ammonium sulfate leaching rates of REEs in the two samples after grinding decreased by 21.5% and 51.6%, respectively. The ion-exchange REEs in the samples decreased significantly, while the carbonate-bound state increased significantly. The iron-manganese oxide-bound state and humic acid-bound state increased slightly. (2) The occurrence states of cerium (Ce) exhibit special enrichment-depletion characteristics, mainly existing in iron–manganese oxide-bound and residual states. Its enrichment order is significantly different from that of other REEs, which also leads to differences in the ammonium sulfate leaching rate of Ce and the changes in its occurrence state before and after grinding compared with other REEs. (3) The leaching rate of REEs other than Ce is positively correlated with the sum content of the ion-exchange state and iron–manganese oxide-bound state, and negatively correlated with the sum content of the carbonate-bound state and residual state. The ion-exchange state and iron–manganese oxide-bound state REEs are important sources for exchangeable adsorption of REEs. The carbonate bound state and residual state do not contribute to the exchangeable adsorption of REEs, and extraction methods other than ion exchange should be considered. This study provides technical support for establishing evaluation standards for weathered crust elution-deposited rare earth ores and improving the utilization rate of rare earth resources. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202501020002.