Geochemical Characteristics Of Trace Elements In Groundwater And Water Source Identification In Panxie Mining Area

The hydrogeological conditions of coal mines in my country are complex and diverse.As the demand for coal resources increases year by year,the mining depth is gradually increasing,leading to an increase in the threat of water inrush from coal mines.This paper takes Huainan Panxie mining area as the research area.According to the distribution of mines in the research area,samples of loose aquifer,the Carboniferous karst aquifer of Taiyuan formation and the Ordovician karst aquifer were taken from top to bottom from the hydrological boreholes and underground water outlets of each production coal mine A total of 65,testing and analysis of macro ions and trace elements in different aquifers,studying the geochemical characteristics of groundwater water-rock interaction mechanism in the mining area,and establishing a water source identification model based on rare earth elements,which is useful for the identification of water inrush water sources in the study area.Through the analysis of macro water chemical indicators,it could be known that the groundwater in the study area was weakly alkaline as a whole,and the water quality types were Cl-Na and Cl·HCO₃-Na.In addition to the dissolution of rock salt,the Na⁺content in groundwater had other sources.In the loose layer water,the dissolution of evaporative salt rock and carbonate rock occurs,and the dissolution of evaporative salt rock was slightly obvious.Desulfurization in limestone water may be one of the sources of HCO₃^-.The source of calcium and magnesium ions in groundwater was mainly related to the dissolution of evaporite rocks,and carbonate rocks have little contribution to it.Groundwater had alternate cation adsorption,and the loose layer water had the strongest effect,and Ordovician karst aquifer has the weakest.The content of each trace element in different aquifers of groundwater in the study area was not uniform,and the content of each trace element in the same aquifer was also quite different.Trace elements were less sensitive to differences in acidity and alkalinity in water.Trace elements are positively correlated with p H except Mn(Ba),indicating that alkaline environment can promote the movement of the above elements in water bodies The environment hindered its migration in groundwater to a certain extent,while the acidic environment can promote its migration in groundwater.The ability of p H value to control trace elements can be judged by the absolute value of the correlation coefficient between the two.It could be seen from comparison that the order of the control ability of p H value on trace elements in the groundwater in the study area was Rb(As,Cu)>Nb>Mo(Cd)>V>Cr>Mn(Ba).The order of the enrichment rate of trace elements affected by p H value is Rb(As,Cu)>Mn(Ba)>Mo(Cd)>V>Cr>Nb.Mn in the groundwater in the study area moved in the water body in the form of chloride,and Zn is easily concentrated in sulfide minerals.The main source of Fe and Cu in the groundwater in the study area was not metal sulfide deposits,but was controlled by various factors.Such as the dissolution of halogen salts,weathering and hydrolysis of minerals,etc.The content of rare earth elements in groundwater was related to the adsorption of metal oxides(such as iron and manganese)or the co-precipitation of carbonate rocks(such as calcite).In water with low alkalinity,p H had a significant effect on controlling the total amount of rare earth elements in the water.The complexation of related anions in water with high alkalinity may interfere with its effect.The complexation reaction of carbonate and the adsorption/complexation reaction of iron colloids or oxides and rare earth elements were the controlling factors of the distribution mode of the enrichment of heavy rare earth elements in groundwater.The negative Ce anomaly in the study area was closely related to the inherited parent rock,and the positive Eu anomaly was mainly related to the preferential chemical weathering and dissolution of Eu-rich minerals(such as feldspar)in the sediments.The complex state of carbonate was the main inorganic complex form of rare earth elements in water,and most of the complex forms of rare earth elements are in the form of Ln(CO₃)₂^-and Ln CO₃⁺.Using 12 rare earth elements in the study area as identification factors,a Fisher water source identification model based on rare earth elements was established.The model's recognition of Carboniferous karst aquifer of Taiyuan formation and the Ordovician karst aquifer reached 94.4%and 90.9%,respectively.There is a certain hydraulic relationship between loose layer water and limestone water in the mining area,and the existence of mixing phenomenon may be the reason why the recognition accuracy of loose layer water is not ideal.From the overall perspective of the three aquifers in the study area,the accuracy of the model reached 84.3%.