DOM characteristics and sources of mine water in themiddle Yellow River Basin based on parallel factor method

The middle section of the Yellow River Basin is a top area of coal resource endowment in China，and it is al⁃ so an important coal production area. A large amount of mine water is produced in the process of high intensity coal mining. Due to the leakage of oil in underground mining equipment，some organic pollutants generally appear in mine water，and the types and characteristics of pollutants are not clear，which greatly limits the safe reuse of mine water. In order to find out the characteristics and sources of organic pollutants in mine water，this study took 15 coal mines in the middle part of the Yellow River basin bordering Mongolia and Shaanxi as research objects. On the basis of detecting and analyzing the conventional physicochemical indexes of mine water in the central underground water sump，the detection of dissolved organic matter(DOM)in mine water was conducted by using TOC-VCPH analy⁃ zer， UV spectrophotometer， 3D fluorescence spectrometer and other equipment. Using the parallel factor method，the component characteristics of DOM in mine water were determined，and then combined with principal com⁃ ponent analysis and correlation analysis methods，the sources and influencing factors of DOM in mine water were ana⁃ lyzed. The results showed that the suspended solids were the conventional pollutants in mine water in the study area. High turbidity mine water accounted for 100% of the total dissolved solids(TDS)，fluoride and nitrate were the characteristic pollutants in mine water in the study area，among which the hydrogeochemical vertical zonation led to higher TDS concentration in the deeply buried aquifer. Fluoride was most significant in the mines with coal seams buried at a depth of about 300 m in Yushen mining area，and the exceedance rate of nitrate in some mines is 20.0%-55.8%. Four types of fluorescent components appear in the mine water of 15 coal mines based on the calcula⁃ tion of parallel factor analysis. The protein⁃like substances represented by tyrosine are the main components of DOM in mine water，with an overall contribution rate of 63.0%-89.0% to DOM，which mainly comes from underground phe⁃ nols，dichlorobenzene，benzene and other aromatic hydrocarbons generated from emulsified oil leaks. Three⁃dimensional fluorescence analysis reveals that the mine water of these 15 coal mines has the same fluorescence index characteris⁃ tics:autogenic index(BIX)less than 2.0(0.8-1.4)，humification index(HIX)less than 4.0(0.6-2.5)，and fluorescence intensity(FI)greater than 1.0(1.5-2.2)，indicating that DOM in the study area generally originates from protein⁃like substances. The principal component analysis and correlation analysis further verify that the downhole oil contaminants are the main source of DOM in mine water in this study area. The standard three⁃dimensional fluores⁃ cence fingerprints and fluorescence characteristics of DOM in mine water obtained from this study based on parallel factor analysis provide a scientific basis for the safe and sustainable utilization of mine water in the middle section of the Yellow River basin.