Geochemical characteristics of rare earth elements in groundwater of Banji Coal Mine

Abstract

Rare earth elements possess stable and similar geochemical properties, making them widely utilized in the study of groundwater-aquifer interactions and geochemical processes. In this study, taking the Banji Coal Mine in the Huainan Coalfield as the research area, water samples including sandstone water, gray overburden water, and mixed water from mined-out areas were collected. These samples were tested and analyzed for their rare earth element contents, as well as conventional water chemistry ions. The objective was to investigate the hydrochemical characteristics of groundwater in the mining area, the distribution of the rare earth element as well as the related controlling factors. The results showed that the average mass concentrations of Na^++K^+, Cl-, and HCO_3^-in the groundwater of the mining area were determined to be 669.1, 820.3, and 344.0 mg/L, respectively. Based on the water quality types, we classified the groundwater primarily into Cl-Na type, Cl-HCO_3-Na type, and HCO_3-Na type. Generally, the rare earth element contents in the groundwater fell within a lower concentration range. However, three mixed water samples exhibited significant enrichment of heavy rare earth elements, while most of the water samples demonstrated light rare earth enrichment. Notably, Eu displayed the highest content, primarily due to its separation from the rare earth element group during crystallization and precipitation with calcium minerals. Correlation redundancy analysis unveiled a linear relationship between Eu and Fe in the groundwater samples of the area. The adsorption of Fe oxides with rare earth might be a significant controlling factor influencing the rare earth element content. This study is of significance to a comprehensive understanding of the geochemical processes in the groundwater system of the Banji Coal Mine in the Huainan Coalfield. Furthermore, it provides a scientific basis for the evaluation and management of groundwater in the mining areas.

Keywords

• water chemistry
• coal mine groundwater
• rare earth elements
• geochemical characteristics