The characteristics of rare earth elements in the main water filling sources of Sunan mining area

This study employs rare earth elements to investigate the features and procedures of water-rock interactions within aquifers of loose strata, sandstone, and limestone in the Sunan mining region of North Anhui, China. Through a comparison of the differential characteristics of rare earth elements across primary water sources, we are able to uncover the influence of water-rock interactions on the transfer and conversion of rare earth elements within various water-sediment systems. Indeed, the normalization of water compositions against host rock concentrations revealed a distinct pattern of rare-earth elements for each group of waters. Not only did the absolute concentrations of the elements in each sampling site change, but also the normalized patterns. In contrast to sediment samples, all water samples exhibit a clear enrichment of MREEs, but they also reveal a trend of HREEs enrichment. This is attributed to the differential adsorption effect of oxides on rare earth elements, which is influenced by pH, and the complexation reactions between rare earth elements and carbonate ions. The significant Ho and Ce anomalies in the water-sediment system are associated with robust water rock interactions, whereas the high Ba content significantly impacts the Eu anomaly. The enrichment of Eu is attributed to the interaction between the water environment and the dissolution of minerals rich in Eu. Furthermore, we utilize decision trees and recursive feature elimination techniques for selecting indices, and create a model that incorporates triangular fuzzy numbers (TFN), CRITIC, D-S evidence theory (DSET), factor space (FS), and set pair cloud model (SPCM) to differentiate, describe, and evaluate three distinct groups of waters with varying hydrofacies. The conclusion drawn is that sandstone and limestone aquifers are the main sources of water inrush, with a mixing ratio exceeding 50%. Moreover, this marks the inaugural attempt to utilize patterns of rare-earth elements for establishing a comparison between various water groups, thereby enabling us to distinguish and differentiate depletion patterns resulting from dilution processes from those resulting from precipitation processes, with the aim of determining the contribution rates of mine water. The findings offer valuable insights for predicting water disasters in the Sunan mining area.