Occurrence State of Rare Earth Elements in the Paleoweathering Crust of Tieling Formation, Northern Hebei Province by X-ray diffraction and Electron Probe Microanalysis

In recent years, the paleoweathering crustal rare earth ores discovered have the advantages of stability and easy mining, but due to the low degree of research on their element occurrence state, the study of the enrichment mechanism of the deposit is restricted, so further study of the element occurrence state will help to improve the metallogenic mode and optimize the subsequent development and utilization process. In this paper, the occurrence state of rare earth elements in the paleoweathering crust of the Tieling Formation was systematically studied by using the testing techniques of stepwise chemical extraction, X-ray diffraction, heavy minerals identification, and electron probe microanalysis. Stepwise chemical extraction shows that rare earth elements in the paleoweathering crust mainly exist in mineral phases, accounting for about 9.38% of the total content. The rare earth elements in aqueous solution, ionic phase, and colloidal deposition phase account for 0.01%, 0.22%, and 0.39% respectively; X-ray diffraction analysis showed that a small amount of rare earth elements in the ionic adsorption state in the paleoweathering crust samples may exist on the surface of clay minerals such as illite. Electron probe microanalysis results showed that the anatase, leucinite and barite in the paleoweathering crust samples contained about 0.1% of light rare earth elements such as Ce, Nd and Sm. In summary, it is preliminarily concluded that the main rare earth elements in the paleoweathering crust exist in mineral phases, some of them exist in anatase, leucinite and barite as similar images, and the rest may exist on the surface of anatase and a large number of clay minerals in nano-scale fine particles. A very small amount of ionic rare earth elements may be adsorbed on the surface of clay minerals such as illite and imon mixed layer. The content of rare earth elements in the water-soluble phase and colloidal sedimentary phase is very low. The study on the occurrence state of rare earth elements in the ancient weathering crust helps to optimize the development and utilization technology, and provides a theoretical for the selection and smelting utilization of rare earth resources.