Determination of Rare Earth Elements Contents and Study on Occurrence Forms in Weathering Crust Ion Adsorption Rare Earth Ore

The weathering crust ion adsorption type rare earth deposit has the characteristics of complete REEs types, low radioactivity, high heavy rare earth contents, and easy mining, making it an extremely important type of rare earth deposit. At present, most of the research on the determination of REEs in this deposit only measures the total amount and ionic phase components of REEs, and some methods have complicated operating procedures, while there is relatively little research on the analysis of various REEs forms. However, when studying the mineralization laws of weathering crust ion adsorption type rare earth deposits, it is not only necessary to analyze the total amount of REEs, but also to analyze the chemical forms that affect the mineralization background, migration, enrichment process, long-term differences, and availability of REEs in the deposit. Therefore, it is necessary to accurately determine the total amount and contents of various occurrence REEs forms in weathering crust ion adsorption type rare earth deposits. This article uses five acid mixed digestion as a pretreatment method for determining the total amount of REEs in weathered crust ion adsorption type rare earth ore samples, and compares the results of rare earth elements speciation analysis determined by BCR method and Tessier method. ICP-MS is used as the detection method to explore the distribution of the total amount and various REEs forms in the samples. The results showed that the five acid mixed digestion can completely dissolve all REEs in the rare earth ore sample, and the operation is simple. The precision (RSD) of this method is between 0.82% to 5,19%, the detection limit is between 0.002 to 0.027µg/g, and the relative error between the measured values and the recognized values of each element is between-4.70% to 6.65%. The ∑LREEs/∑HREEs is between 1.25 to 16.50, covering the enrichment of light rare earths and heavy rare earths. After comparing results of the BCR method and Tessier method, The relative deviation (RD) of rare earth various forms extracted by the two methods is 0.79% to 8.07%, and the extraction results can basically correspond and match each other. The rate of recovery ∑REEs is between 84.75% to 107.13%. The relative deviation of ∑REEs determination values is between 0.62% to 21.00%, and the relative error (RE) is less than 40%. In contrast, the BCR method has a simpler pre-processing flow, but the partitioned forms are not as intuitive and specific as the Tessier method, which cannot obtain more detailed data on each form, and under the conditions of this experiment, the Tessier method may have good adaptability for rare earth forms analysis. REEs in the fully weathered layer samples of the weathering crust mainly exist on the surface of clay minerals in the form of ion adsorption, resulting in the highest content of ion exchange state. As the depth of the weathering crust profile increases and the pH rises, REEs are more likely to bind with carbonate or bicarbonate ions, leading to an increase in the rare earth contents in the carbonate bound state. Ce element is easily oxidized from Ce³⁺to Ce⁴⁺in this layer, and remains in place in the form of precipitation, forming Ce anomaly; REEs in the parent rock are mainly enriched in the independent mineral lattice, with the highest residual content. The variation patterns of all REEs under different occurrence forms are basically consistent.