Characteristics and sources of typical pollution components in mine water in the border area of Inner Mongolia and Shaanxi

The border area between Mongolia and Shaanxi is the core area for China’s energy security. However, a large number of mine water produced in the process of coal mining contains a variety of pollution components. Only by finding out the sources and characteristics of pollution components can we deal with and utilize mine water resources more scientifically and reasonably, which is also in line with the requirements of high-quality de-velopment of the Yellow River region. Based on the investigation of the geological, hydrogeological and coal mining disturbance conditions in the border area between Mongolia and Shaanxi, the hydrogeochemical charac-teristics of coal seam roof aquifer and the characteristics of typical pollution components in mine water were studied, and the sources of these typical pollution components were analyzed. The results showed that the border area between Mongolia and Shaanxi was located in the Yishan slope. According to the coal seam buried depth conditions, it could be divided into shallow buried area, medium deep buried area and deep buried area. The mine water in the shallow buried area came from all aquifer water of the coal seam roof, and the mine water in the medium deep buried area came from aquifer water of the Yan’an formation and the Zhiluo Formation (divided into complete bedrock section and weathered bedrock section) of the coal seam roof. The concentration of TDS in the Quaternary and Jurassic groundwater in the shallow buried area and the medium deep buried area was lower than 1 000 mg/L. The mine water in the deep buried area came from the aquifer water of the Jurassic Yan’an Formation and Zhiluo Formation in the roof of the coal seam. The Jurassic aquifer was relatively closed and stagnant. The long-term water rock interaction led to the concentration of TDS in groundwater upper than 1 000 mg/L, and the main exceeding standard components were Na⁺, Ca²⁺ and \rmSO_4^2- . The pollution components in mine water included two categories: one was from the roof aquifer water, and the long-term water rock interaction led to the entry of ion components into mine water. The other came from the underground production activities of coal mines. The release of coal cuttings, dust and oil led to the dissolution of suspended solids, nitrogen, organic matter and other pollution into mine water. The concentration of TDS in mine water in the shallow and medium deep buried areas was lower than 1 000 mg/L, which is mainly weakly alkaline HCO₃-Ca water, and the main cation and anion (including Na⁺, Ca²⁺, Cl⁻, \rmSO_4^2- ) basically did not exceed the standard. The TDS concentration in the mine water in the deep buried area (including the Xiaojihan coal mine) was 1 824.00−3 684.00 mg/L, which was slightly higher than that in the roof water. The increase of Na⁺ and \rmSO_4^2- ion concentration accounted for the largest proportion, which was mainly due to the further water rock interaction in the goaf. The concentration of COD in mine water of most coal mines exceeded the standard, but the TOC concentration and UV₂₅₄ value were low, it showed that the organic matter in the mine water was mainly suspended. The 3DEEM spectrum detection results showed that the dissolved organic matter was mainly natural amino acids and humus, the fluorescence intensity of all kinds of organic matter was low, and there were few organic pollutants in mine water.