1. High-Iron and Manganese Mine Water: Iron and manganese mine water in coal mines is mainly formed by the infiltration of iron and manganese-bearing groundwater from the strata. The iron and manganese in the mine water exist in the form of divalent iron or divalent manganese. Due to the effects of coal mining, iron and manganese mine water in coal mines has characteristics different from those of iron and manganese-bearing groundwater.
2. Acidic Mine Water: The physical and chemical properties of acidic mine water vary considerably from region to region, but a common characteristic is a low pH value, generally between 2 and 5. Since acidic mine water is produced by the oxidation of sulfides, mainly pyrite (FeS2), the concentration of Fe and SO42- in the water is very high. Total iron content is generally between 300 and 800 mg/L, with some mine water exceeding 1 g/L. Fe²⁺ content is typically 200–300 mg/L; SO₄²⁻ content ranges from several hundred to tens of thousands of mg/L, sometimes reaching as high as 15 g/L, significantly exceeding the upper limit of 250 mg/L for drinking water.
3. High Turbidity Mine Water High turbidity mine water has a high suspended solids content and poor sensory properties; the suspended solids are small in size, have a low specific gravity, and settle slowly; floc formation is difficult during coagulation, resulting in poor sedimentation.
4. Water Quality Characteristics of High-Saltification Mine Water High-saltification mine water is the result of groundwater contacting carbonate and sulfate rock layers in coal-bearing strata. The dissolution of these minerals in the water increases the levels of Ca2+, Mg2+, HCO3-, CO32-, and SO42- in the mine water. In some acidic mine waters, the carbonate rock layers neutralize, leading to increased salinity. In other mining areas with arid climates and annual evaporation far exceeding precipitation, the strata have high salinity, resulting in correspondingly higher groundwater salinity. A few mining areas are located in regions where seawater and mine water mix, thus increasing the salinity of the mine water.
