The distribution of rare earth elements and sources in Maoshitou reservoir affected by acid mine drainage, Southwest China

Abstract

Acid mine drainage (AMD) is a major source of water pollution in coal mining areas. The Maoshitou Reservoir in the Xingren Coalfield, Southwest China, is severely acidified because of ongoing AMD discharges in recent decades. In this study, the concentrations of rare earth elements (REEs) were determined in parent rocks, and also in water and sediments from the reservoir and the river that flows into the reservoir. Comparison with the North American Shale Composite (NASC)-normalized REEs indicated that the AMD-type acidic river water was more enriched in middle rare earth elements (MREEs) than light rare earth elements (LREEs) and heavy rare earth elements (HREEs), perhaps because of preferential dissolution of MREEs from parent rock under acidic conditions. The distribution of REEs in the sediment from the mine pit corresponded with the distribution in the AMD, while the curve of the NASC-normalized REEs distribution in river sediments was nearly flat along the flow direction, this may be related to the addition of rock weathering residues in the catchment. The REEs distributions were similar in reservoir water and the inflowing river water, and the REEs in the reservoir sediments were slightly enriched by LREEs. The REEs in the reservoir sediments did not vary either spatially or with depth. The REEs were significantly and positively correlated with Al, Zr, Hf, Nb, Ta, Rb, Sr, Th, Sc, Ti, K, and Na, and were negatively correlated with Fe, As, and S, which indicates that REEs in the reservoir sediments were mainly from terrigenous detrital particulate material rather than chemical deposits. The provenance index showed that the reservoir sediments were mainly from coal-bearing strata.