Spatial Heterogeneity of Rare Earth Elements: Implications for the Topsoil of Regional Ion-Adsorption Type Rare Earth Deposit Areas in Southern China

The migration and spatial distribution characteristics of topsoil rare earth elements (REEs) are significant for the risk assessment of the external environment. However, the spatial distribution of REEs in the topsoil of ion-adsorption type rare earth element (REE) mining areas is poorly studied. We aimed to determine the differences and control factors of the spatial distribution of REEs in the topsoil of typical rare earth mines in South Jiangxi, South China. Sixty-five topsoil samples and eighteen profile samples were collected and analyzed for their rare earth content to elucidate spatial autocorrelation and heterogeneity using statistical analysis software (IBM SPSS Statistics 26.0.0.0, GS+9.0, and Arcgis10.2.0.3348). Moran index analysis showed that the positive correlation between sampling points was significant within the range of 0-500 m. The best fitting models of the semi-variance variogram were the exponential model, Gaussian model, and spherical model. The sequence of the spatial structure (C0 + C) was Ho > Tb > La > Pr > Nd > Sm > Gd > Tm > Lu > Dy > Er > Yb > Ce > Eu. The spatial fractal distribution pattern was Ho > Tb > Lu > Er > Dy > Yb > Tm > Gd > Ce > La > Eu > Sm > Pr > Nd. This indicated that the light rare earth elements (LREEs) and heavy rare earth elements (HREEs) in the topsoil were significantly different from the other sediments. This study provides new evidence for the environmental quality assessment of the in situ leaching of ionic rare earth ores into the topsoil layer.