State Key Laboratory of Water Resource Protection and Utilization in Coal Mining,China Energy Investment Corporation Limited
School of Water Resources and Environment,China University of Geosciences (Beijing)

There is a large amount of rock in the underground reservoir. During the process of storage in the under⁃ground reservoir,there are water⁃rock interactions such as ion exchange,adsorption and leaching between mine waterand rock in the underground reservoir,which affect the quality of mine water. The rock in the Halagou was collected,its cation exchange capacity (CEC) was measured,and the static adsorption⁃dissolution experiments under differ⁃ent chemical conditions (250 mg/ L for Na+,Mg2+,K+,Ca2+) were carried out. The experimental results show that theCEC of rock is inversely proportional to the particle size. When the particle size is less than 120 mesh,the CEC rea⁃ches 134 mmol+ / kg. The order of exchangeable base ions in rock is Exchangeable Calcium ≫ Exchangeable Magnesi⁃um > Exchangeable Sodium > exchangeable Potassium. After 48 hours of experiment,the ion concentration in eachsystem tended to balance. The cation concentration in the Na+ system solution all increased,but in the other three sys⁃tems,the original ions all decreased,and the K+ decreased the most. The order of the ion concentration exchangedfrom the caving roof rock to the aqueous solution from high to low is:Ca2+ >Na+ >Mg2+ >K+,and the Ca2+ concentrationstill had an upward trend after the end of the test. After the reaction,the CEC of the rock increased to a certain extent,and the maximum CEC value under the Ca2+ system was up to 183.7 mmol+ / kg. Based on XRD and other characteriza⁃tion results,it is further revealed that the leaching of non⁃clay minerals such as microcline,albite and pyrite can in⁃crease the concentration of Ca2+ and Na+ in the solution,while clay minerals such as illite and kaolinite adsorb / ex⁃change cations in the solution through coordination. For cations,if leaching > ion exchange (the initial concentration islow),the concentration increases. On the contrary,it decreased. Therefore,when the content of Ca2+ and Mg2+ in minewater is high,the hardness of mine water can be reduced to a certain extent through water⁃rock interaction. This studyprovides a theoretical basis for the self⁃purification mechanism of mine underground reservoir.