Study on the evolutionary process of sulfate concentration in Ordovician karst water after coal mining in Fengfeng mine

Increases in the concentration of sulfate in water from an Ordovician karst aquifer following mining activity pose a maj or hazard to drinking water safety.Therefore,research into the impact of mining activities on the sulfate concentration is very significant.Hydrochemistry,isotope hydrology and other methods were adopted.Hydraulic connection and sulfur kinetic fractionation processes were investigated in order to evalu-ate sulfate changes in the Ordovician karst aquifer due to mining activity. Fengfeng coal mine is located in the southeast of Taihang Mountain,which is next to Jiu mountain in the west,and North China Plain in the east,with a total area of 340.6 km2 .Based on the characteristics of the water bearing rock,aqueous medium and burial conditions,the main aquifers are,Cambrian oolitic limestone karst fracture aquifer,Ordovician fracture karst aquifer,Taiyuan Carboniferous thin limestone fractured aq-uifer,Permian Shanxi formation sandstone fissure pore aquifer and Quaternary alluvial slope of aeolian sandy soil pore aquifer.The Ordovician fracture karst aquifer is the most important aquifer,with a total area was 2,404 km2 in the mine.The aquifer matrix is composed of brecciated limestone,mottled limestone,lime-stone and marlite,gypsum,etc,and the total aquifer thickness is 470 to 584 m. The results indicate that the sulfate concentration in the groundwater of the Ordovician karst aquifer in-creased after mining activities,with different characteristics and sulfur kinetic fractionation process.The main source of kinetic fractionation was groundwater seepage from pits and pore water flowing through frac-tures,and the ability of minerals in evaporate to dissolve had been enhanced during the de-dolomitization process.The results are useful for evaluating the evolution of sulfate in karst water in areas with similar mining activity,protecting karst water resources,and improving the management of coal resource develop-ment.