Redistribution and chemical speciation of rare earth elements in an ion–adsorption rare earth tailing, Southern China

Mining is an activity that will change the distribution and chemical speciation of rare earth elements (REEs), thus posing a serious threat to the natural environment. However, the distribution and chemical speciation of REEs in ion–adsorption rare earth tailings remain poorly understood. In this study, we investigated the contents and forms of REEs and associated geochemical behavior in rare earth tailings in southeast China. Total rare earth elements (TREEs) contents were lower while the ratios of light REEs (LREEs) to heavy REEs (HREEs) were higher in tailings than in an unmined area. In the unmined area, the distribution characteristics of TREEs and LREEs remained consistent, whereas HREEs differed with increasing depth. However, in the tailing area, the distribution characteristics of TREEs, LREEs and HREEs tended to be consistent, reflecting the outcomes of mining activities on vertical distribution characteristics of REEs. The REEs were dominated by residual and exchangeable forms in the unmined area, while residual and exchangeable REEs accounted for 80% and 20% of the TREEs, respectively, in the three tailings. Additionally, the exchangeable and carbonate–bound REEs increased but Fe/Mn oxide–bound and organic–bound REEs declined in the unmined area, whereas their distribution characteristics were irregular in the tailings. These results suggest that mining activity could curtail REEs contents and redistribute their chemical speciation, further altering geochemical behaviors in the tailings and posing serious risks to adjacent environments.