Geochemical Cycling Of Hydrocarbon Compounds In Soil Of Typical Coal Mine District

Hydrocarbon compounds like n-alkanes and polycycle aromatic hydrocarbons (PAHs) are prone to be enriched and deposited in soil system. Due to their properties of semi-volatility, PAHs are subject to be transferred between different media which result in a fractionation of individual PAHs pattern which is called"global distillation". In this dissertation, coal mining areas are selected as the main study area. Combined with the various detection methods and analytical technologies, the concentrations and distribution pattern of hydrocarbon compounds in coal, coal gangue and soil were analyzed. What’s more, the multi-sources and the mobility of n-alkanes and PAHs in soil surrounding the coal mining area were explored. Besides, under the laboratory conditions, the impacts of organic pollutants and natural organic matters on the geochemical cycling of iron in soils were studied.The results show as follow:(1) Geochemical parameters of n-alkanes in coal samples from10minable Permian coal seams, Zhuji Mine, Huainan coalfield, China were studied. Total concentrations of n-alkanes in all coal seams ranged from34to481μg/g. C9-C25short-chain n-alkanes are present in the Shanxi Formation while long-chain (n>25) n-alkanes are found in Upper Shihezi Formation and Lower Shihezi Formation. The predominance of C11and C17in coal samples implies that the coal seams were probably deposited in a transitional freshwater to mildly brackish environment. The ratio of pristine/phytane (Pr/Ph) is shown to be a robust indicatorin delimiting marine transgression and regression surrounding studied coal-forming basin. We suggest that the Pr/Ph boundary range of mildly brackish to brackish marine environment is3.20-3.84. Carbon isotope fractionation in coal may be related to the deposited environment rather than the maceral, showing that enriched heavy13C isotope under the oxidative environment, while enriched light13C isotope under the reductive environment.(2) The distribution and transportation behavior of PAHs were analyzed and the environmental impact of the PAHs in the soil of the coal mine was assessed. The concentrations of28kinds of PAHs in the collected soil samples ranged from0.35μg/g to6.21μg/g with the average concentration of1.69μg/g,16kinds of PAHs of which is USEPA priority PAHs. The contents of US EPA priority PAHs ranged from0.23μg/g to3.53μg/g with the average contents of1.00μg/g.The level of PAHs affected by the coal washery and are prone to migrate to nearby area from the dumped gob pile.(3) The total concentration of16PAHs (defined as Σ16PAH, dry weight) in surface soil of Tiefa coal mine ranged from5.1up to5642.3ng/g, with an arithmetic mean of1118.3ng/g. The vertical distribution of PAHs indicated that they can penetrate the deeper layers of the soil, especially the low-rings. Four sources contributed to the PAHs in the study area:coal combustion (49.7%), unburned coal (19.8%), coal gangue (26.7%), and vehicular (3.9%). The dumped gob piles not only polluted the surrounding surface soil but also influenced the lower depths of the soil.(4) Association of natural organic matter coating on mineral and being present in mineral sorption system were investigated. Batch kinetic experiments combined with extended X-ray absorption fine structure spectroscopy (EXAFS) to elucidate the influences of humic acid (HA) and phenanthrene on the formation of Fe (II) precipitates at the γ-Al2O3-water interface. Less impact on the phenanthrene than humic acid in the system was found. Initial Fe (II) uptake decreased with more amount of HA coated onto the γ-Al2O3surface, and the reaction went equilibrium later than the background sample (pure γ-Al2O3). Fe (II) uptake were totally shut down by add HA inside the system after two days reaction. The formation structure of Fe(II)-Al(III)-layered double hydroxides which is similar with the natural mineral nikischerite were found and analyzed by EXAFS with the HA present. In addition, LDH phases increased intensity over time in pre-coated samples, whereas, none HA pre-coat samples shows a slight decrease of LDH phases over time.