- The abundance and spatial distribution of F– in the mine water of the Shendong mining area were determined.
- The hydrogeochemical behaviours and formation mechanisms that further elevate F– levels in mine water during mining activities were evaluated.
- The hydrogeochemical processes of mine water at high F– concentration using stable isotopes (34SSO4, 18OSO4,18OH2O, and D) analyzed.
Mine water poses severe threats to the quality of the water supply and ecological environment of the Shendong mining areas owing to its excessive fluoride (F–) content. However, the geochemical behaviours and enrichment mechanisms responsible for F? enrichment during mining activities are not fully understood. In total, 18 Yanan groundwater and 45 mine water samples were collected to analyse the spatial distribution, hydrogeochemical behaviours, and formation mechanisms related to elevated F– levels by analysing the stable isotopes and water-rock interactions. In this study, F– concentrations in mine water samples varied from 0.16 to 12.75 mg/L, with a mean value of 6.10 mg/L, and 77.78% of the mine water samples had a concentration that exceeded China’s national standards (1.00 mg/L) for drinking water. The F– concentration was markedly high in the mine water samples, with the mean F– concentration being 1.58 times of that in the Yanan groundwater samples. The results of stable isotopes (18OH2O, D, 34SSO4, and 18OSO4) and water-rock interaction analyses suggested that cation exchange and competitive effects were the dominant factors responsible for elevated F– concentration in mine water during mining activities. Thus, the weathering of F-bearing minerals, agriculture, and domestic activities do not play a significant role in the secondary enrichment of F– concentration.