Distribution Characteristics Of Sulfur-oxygen Isotope And Identification Of Groundwater Pollution In Taiyuan Xishan Mining Area

The Xishan Mining Area of Taiyuan,Shanxi Province,is a typical coal industry agglomeration area with a variety of coal-related industries such as coal mines,coal preparation plants,power plants and coking plants.There are many types of industries and complex sources of pollutants in coal-related industrial agglomeration areas,and the impact on regional surface water and groundwater cannot be ignored.In this thesis,samples of gangue leachate,mine water,atmospheric precipitation,surface rivers,pore water and karst groundwater were collected from Xishan mining area,the hydrochemical characteristics of different types of water samples were analyzed,the sulfur-oxygen isotope distribution characteristics of sulfate from different pollution sources were discussed,and the sources and contribution rates of sulfate pollution in surface water and groundwater were identified through the analysis ofδ³⁴S_SO4 andδ¹⁸O_SO4 isotopic composition,and the following main conclusions were obtained:（1）The water chemical characteristics of different water bodies in the study area were analyzed in depth.The results show that the conventional ions in surface water and groundwater are mainly affected by the coal industry,the pollution components include TDS,SO₄^2-,Fe,Mn,etc.,and the pore water and karst groundwater in the Xishan mining area exceed the standard of 66.7 and 63.6 sulfates,respectively,from the recharge area to the excretion area,the karst groundwater water chemical type gradually changes from HCO3-Ca·Gradual transition of type Mg to SO4-Ca·Mg type;Anions and cations in groundwater were mainly controlled by rock weathering,but the proportion of SO₄^2-input from human activities increased in local areas,among which the sulfate content of karst groundwater in Niujiakou village reached 2000mg/L and TDS reached 3016 mg/L.（2）There are obvious differences in sulfur and oxygen isotopes in different water bodies.The thiooxygen isotope test results showed that the values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in karst groundwater ranged from-6.72～+24.42‰and+0.20～+12.40‰,respectively,and the values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in pore groundwater ranged from-6.78～+0.70‰and+0.30～+4.80‰,respectively,and the sulfur-oxygen isotopic values of gangue leachate,mine water and some karst groundwater were close to those of sulfide mineral dissolved terminals.It was shown that its sulfate mainly came from the oxidation of sulfide minerals（Fe S₂）,especially pyrite,in coal and gangue.The pore groundwater and Niujiakou,Baijiazhuang and silkworm villages were located in the sulfide mineral oxidation terminal element,indicating that the sulfur oxygen isotopes of karst groundwater in Yinjiagou,Huanglou,Wangjiazun and Pingquan villages were located in gypsum dissolution terminal elements,indicating that they were mainly affected by gypsum.（3）The use of sulfur-oxygen isotopes to identify the pollution sources of different water bodies in the study area.The calculation results of Bayesian model based on R language show that sulfate 80.2 in pore groundwater comes from sulfide mineral oxidation in leachate mine water,and Yinjiagou karst groundwater is greatly affected by gypsum dissolution in deep evaporative rock,accounting for 84.5;the sulfur-oxygen isotope values in surface water are slightly higher than those in pore groundwater,of which leachate mine water accounts for 49.7,atmospheric precipitation accounts for26.8,gypsum dissolution accounts for 23.5;The results showed that karst groundwater in the recharge area was greatly affected by atmospheric precipitation recharge,accounting for about 44,the proportion of karst groundwater pyrite oxidation in the runoff area and discharge area increased significantly（the highest 90.1）,and the proportion of gypsum in the Pingquan area was about 70.（4）Calculation of groundwater saturation index and element occurrence form based on water chemistry simulation.The calculation results of Phreeqc software show that the SI values of anhydrite,gypsum and CO₂ along the karst groundwater flow path increase slightly and are less than 0,indicating that these minerals are in an unsaturated state.Aragonite,calcite,and dolomite all had SI values close to 0 in all water samples,indicating that they were all in equilibrium of dissolution and precipitation;The calculation results of the occurrence of elements in groundwater show that the proportion of cations combined with sulfate to form sulfate gradually increases along the direction of groundwater flow,which also confirms the characteristics of the gradual deepening of sulfate pollution in groundwater,which provides a scientific basis for the control of sulfate pollution in mining areas.