Spatial distribution characteristics of suitability of mine water for irrigation in the Shendong mining area

The Shendong mining area, located in Northwestern China, is characterized by a dry climate and scarce water resources. A large amount of mine water is used for ecological irrigation in this mining area. This study investigated the suitability of mine water for irrigation through on-site sampling and hydrochemical testing of mine water in the mining area. We analyzed the spatial distribution patterns of water quality parameters and hydrochemical types. This study also evaluated and predicted the suitability of long-term irrigation using sodium ion adsorption ratio(SAR), soluble sodium percentage (K_Na), Kelly ratio (KR), permeability index (PI), residual sodium carbonate (RSC), magnesium adsorption ratio (K_Mg) single indicator methods, as well as USSL and Wilcox graphical methods. Taking into account the groundwater level, we discussed soil texture types, climatic conditions of the mining area and the applicability of the evaluative indicators. The results show that the main ions in the mine water of Shendong mining area are sorted by mass concentration. The cations are Na⁺, Ca²⁺, Mg²⁺ and K⁺, and the anions are HCO₃^-, SO₄^2-, Cl^-and NO₃^-. The mine water is weakly alkaline as a whole, and the concentrations of Cl^-and NO₃^- vary significantly with space. There was a significant positive correlation among Na⁺, Cl^-, SO₄^2-, total dissolved solid (TDS), electric conductivity (γ), Ca²⁺ and Mg²⁺, and a negative correlation between F^-and Ca²⁺, Mg²⁺. The hydrochemical type of mine water in the mining area is primarily the NaHCO₃ type. The chemical composition of mine water is mainly affected by ion exchange and evaporation. Na⁺, Cl^-, SO₄^2-, Ca²⁺, Mg²⁺ and F^-in the mine water were abnormally enriched and the TDS and γ values exceeded the standard. The salt accumulation effect is not obvious under the combined influence of groundwater and surface water waterlogging in the mining area, and the soil compaction is not prominent. The PI method and the USSL graphic method are not suitable for evaluating irrigation water quality in this area. The evaluation results based on Wilcox graphical method show that the mine water of Halagou, Shigetai and Daliuta mines are suitable as irrigation water. The mine water from Bulianta, Shangwan, Buerta, Wulanmulun, and Huojitu mines should not be used for long-term direct irrigation. This study has theoretical and practical significance for the rational development and utilization of mine water resources in mining areas.