Identification of mixing water source and response mechanism of radium and radon under mining in limestone of coal seam floor

Abstract

With the gradual increase of the coal mining depth, the mixing of multiple water sources intensifies and the activity of radium and radon in groundwater increases. Identifying the source of mine water inrush by using radium and radon isotopes is a new choice. In this paper, the mathematical statistics method, radioactive isotope decay theory, the mass conservation principle, and the numerical simulation method are used to analyze the influence of total dissolved solids (TDS), pH, and the hydrochemical ion content in groundwater on the isotope activity of radium, radon, uranium, thorium, and lead. The activity of thorium and lead is lower than the detection limit of the instrument, and the influence of coal mining activities on it is small. The simulation of the radium–radon mass balance in groundwater shows that the greater the adsorption coefficient (k) of solid particles in groundwater is, the more obvious the adsorption effect and the greater the influence on the radium–radon activity balance are. The radium–radon dating method is used to calculate the groundwater age. Results show that the groundwater age in the closed pit coal mining area is generally older than that in the mining coal mining area. Combined with the 222Rn, 226Ra, and 234U radioactive isotopes and temperature, a mixing water source identification model of limestone in the coal seam floor is constructed. The model shows that the radium activity and temperature of the groundwater are inversely proportional to the mixing ratio of the Permian sandstone water. From the closed pit coal mining area to the mining coal mining area, the radium radon activity of the groundwater increases gradually, the groundwater age decreases significantly, the water cycle is accelerated, the mixing ratio of the Permian sandstone water decreases gradually, the mixing ratio of the Ordovician limestone water increases gradually, and the risk of coal mine water inrush increases. The research results prove the feasibility of the new method for accurately discriminating the mixing water sources in coal mine areas, which is of great significance to the improvement of the theory of coal mine water disaster prevention and control.