Rare earth elements redistribution in mine tailings soil: A comparative study of sunlit and shady slopes after in-situ leaching.

ABSTRACT

The in-situ leaching of rare earth minerals results in ecological differences between sunlit and shady slopes, which may be related to differences in the distribution REEs in the associated soil matrices. Studies of REEs mine tailings in Southern China indicated higher total concentrations of REEs on sunlit slopes compared to shady ones. Specifically, the exchangeable REEs fraction (F1-REEs) was higher on the shady slopes, whereas the Fe/Mn oxides bound REEs fraction (F3-REEs) was higher on the sunlit slopes. In addition, light REE (LREE) concentrations were lower at lower elevations. With the exception of the Ce fraction which remained stable, this indicated a change in all REEs distributions, moving from F1-REEs towards the residual fraction. Hierarchical cluster and principal component analysis revealed a strong correlation between F3-REEs, organic matter bound REEs (F4-REEs), and LREEs, and a positive association of F3-REEs with sunlight exposure. Partial Least Squares Path Modeling analysis suggested that OM promoted the conversion of LREEs to F3 and F4-REEs in soil driven by sunlight exposure. Additionally, as the Feo/Fed ratio decreased, more LREEs were converted to F3. This study suggests that sunlight and elevation both play a critical role in the geochemical dynamics of REEs in in-situ tailings, advocating for environmental evaluations to be undertaken in order to accurately understand the ecological impacts of rare earth mining.