Study on water inrush pattern of Ordovician limestone in North China Coalfield based on hydrochemical characteristics and evolution processes: A case study in Binhu and Wangchao Coal Mine of Shandong Province, China

Abstract

Groundwater plays a critical role in the mining areas, providing water for human activities and the growth of animals and plants, but also the main object of mine water disaster prevention. A study on hydrochemical characteristics and evolution in the process of mine water inrush has important practical significance for accurately identifying mine water inrush sources. In this study, the water samples of Ordovician limestone water, the 14th limestone water, and inrush water in Binhu and Wangchao Coal Mines of Tengxian Coalfield were collected. The water samples were compared and analyzed to reveal the variation characteristics of major ion concentration and hydrochemical evolution mechanism during floor cracking-Ordovician limestone water inrush. The results indicated that the type of Ordovician limestone water is Cl-Ca type, the 14th limestone water is Mixed type, and all inrush water is Cl-Na type. Na+(K+) is negative with Ca2+ and Mg2+, while Ca2+ is positive with Mg2+. Hydrochemical analysis showed that the degrees of cation exchange in groundwater are inrush water > the 14th limestone water > Ordovician limestone water, and the average cation exchange contents △C(K++Na+) c are 30.85 meq/L, 9.90 meq/L, and 8.10 meq/L, respectively. Cation exchange significantly changed the Ca2+(Mg2+) and Na+(K+) levels in an aqueous solution during water inrush from Ordovician limestone. The concentration of Ca2+(Mg2+) decreased, while the concentration of Na+(K+) increased significantly and finally formed inrush water with high Na+(K+) and low Ca2+(Mg2+) levels. The saturation index (SI) indicated that the minerals CaCO3, CaMg(CO3)2, and CaSO4.H2O are in oversaturation, the cation exchange results in the decreasing Ca2+(Mg2+), and the SI value is limestone water > the 14th limestone water > inrush water. The cluster analysis (CA) results also showed that considering the effect of cation exchange on the ions concentration of groundwater, the Ordovician limestone, the 14th limestone water, and inrush water samples have the same source in the study area. Overall, The cation exchange significantly affects groundwater ion concentration in the process of Ordovician limestone water inrush. These findings provide a new insight into the hydrochemical evolution mechanism of groundwater and reveal the evolution pattern of Ordovician limestone water inrush in the North China Coalfield.