Rare earth element geochemistry of groundwaters from coal bearing aquifer in Renlou coal mine, northern Anhui Province, China

Rare earth element (REE) concentrations of two different types of groundwaters (high SO42− water-SW and high alkaline water-CW) from coal bearing aquifer (−400∼−280 m) in Renlou coal mine, northern Anhui Province, China were measured. The results indicated that they had different REE characteristics: the total concentrations of REEs (∑REE) of SW were lower than those of CW in general although they all had heavy REEs enriched relative to light REEs. The dissolved REE inorganic species of SW included Ln3+, LnCO3+, LnSO4+, Ln(CO3)2− and Ln(SO4)2−, whereas the CW are Ln(CO3)2− and LnCO3+ dominant, and the proportions of Ln(CO3)2− increased while other species decreased with pH increasing. Combined with correlation analysis, the enrichment and fractionation of SW (low alkaline water) were considered to be affected by alkaline concentrations via affecting the types and proportions of REE inorganic species. However, the effect of alkaline concentrations to the enrichment and fractionation of REEs of CW (high alkaline water) was less important than total dissolved solids and pH, which reflected the contribution from different rocks they flowed over, different degrees of water-rock interactions and/or REE solid-liquid partition coefficients.