Chemical Characteristics Of Groundwater And Groundwater Rock Interaction Under Mining Conditions In Dingbian Plain

Under the coupled effects of global warming and industrialization,the impact of human activities on groundwater environment is increasing.These influences,together with the decrease of groundwater level,deterioration of groundwater quality,and land desertification have greatly restricted the sustainable development of economic society and ecological environment in semi-arid areas.The large areas of high salinity water bodies are distributed around high-quality fresh water,making water quality here complex.The exploitation of fresh water resources may lead to the invasion of inferior water bodies,causing the deterioration or scrapping of water quality in water sources.Therefore,taking Dingbian Plain which located in northern Shaanxi as an example,this paper studies the chemical characteristics and evolution of groundwater.Combining with the actual mining conditions,laboratory tests on the reaction between different proportions of mixed water of salt water and fresh water and different water-bearing media were carried out,so as to find out the water-rock interaction under the mining conditions and provide technical advice for the rational development and utilization of fresh water resources in Dingbian Plain.Results of this paper are as follows:(1)The p H of groundwater in the study area increases with the groundwater flow,and the TDS decreases gradually in the desert area.Spatial concentration of the major anion decreases from large to small along with groundwater flow.The distribution trend of HCO₃^-was opposite to that of TDS here.(2)The controlling element of groundwater is composed of the evaporation concentration and weathering dissolution of minerals in different medium.The major hydrogeological and geochemical processes of groundwater are dissolution precipitation,cation alternate adsorption,and evaporation concentration.The strong evaporation concentration is the key reason for groundwater salinization and dilution.(3)Release of cations from large to small is Mg²⁺>Na⁺>Ca²⁺>K⁺and the anion release is Cl^->SO₄^2->HCO₃^->F^-.In the mixing reaction,concentration of Cl^-and SO₄^2-decreaed firstly and then became stable.After the equilibrium states,the ions of the soil adsorbed were precipitated in different degrees.(4)Whether the medium is fine sand or sandstone in the mixed experiment,the higher the salt water ratio,the less the release of anion in soil.The content of components in saltwater and the composition of geotechnical minerals not only determine the degree of dissolution and precipitation of minerals,but determine the degree of reaction of ion exchange adsorption.The degree of dissolution and precipitation was determined by composition of geotechnical minerals.(5)When the ratio of salt water takes higher,equilibrium time become longer;while when the fresh water is relatively low,the adsorption desorption effect of soil is not obvious,and the time reaches equilibrium becomes shorter.When the ratio of deep water takes higher,the more intense the fluctuation of reaction reaches equilibrium.(6)Release of anion and anion ions in different soil types is quite different,with fine sand>silty clay;the smaller the salt water ratio,the higher the mineral saturation index,the more the mineral reaction trend tends to precipitate.In equilibrium state,the sulfate dissolution(calculated according to SO₄²⁺)is from large to small,silty clay>silty fine sand,while carbonate precipitation(calculated by Ca²⁺is larger to smaller,silty sand>silty clay).