| Based on the previous research results,the multi-disciplinary relevant theories of the groundwater dynamics,porous medium fluid dynamics, environmental chemistry and hydrogeology,and the combination of the theories, experiments and numerical simulation,this paper conducted a series of further investigations on pollution mechanism and laws of coal gangue leaching solution to groundwater system:(1)The bench scale.soaking- leaching and dynamic leaching experiment indicates:the main pollution components released by the coal gangue of different rate of decay under water-rock interaction in Xinqiu open-cut mine are total hardness(Ca2++Mg2+),sulfate(SO42-),sodium(Na+)and total dissolved solid(TDS),the results of which are basically in accordance with the investigation of the 380 plus coal gangue hills in Poland conducted by Szcepanska;The coal gangue is eroded under geophysical function,chemical erosion and natural precipitation in the company of the oxidation, decomposition and dissolution reactions of the pyrite and the dissolution of the carbonate and aluminosilicate minerals.The higher the rate of decay is,the more pollution components the coal gangue releases;The main factors influencing the dissolution-release are the solid-liquid ratio,soak time,acidity, agitation,grain size and water dynamic flow.Moreover,heterogeneous reaction kinetics mechanism of the dissolution-release of the main pollution components was revealed,which abides by the Fick' s law;And builds the index fading equation of the dissolution-release regularity of the main pollution components and precipitation:Cv=C0Vn,which can quantitatively predicts the pollution intensity of the main pollution components to groundwater system under atmospheric precipitation.(2)The laboratory column dynamic simulating experiment reveals the multicomponent transport mechanism and pollution laws of the main pollution components of total hardness(Ca2++Mg2+),sulfate(SO42-)and sodium(Na+)in soil-groundwater system.That is,the transport velocity of the total hardness (Ca2++Mg2+)is the biggest followed by sulfate(SO42-),and sodium(Na+)the lowest.Namely,advection,mechanical dispersion and adsorption are the principal reasons of the transport of the total hardness(Ca2++Mg2+), sulfate(SO42-)and sodium(Na+)and play an vital role in the transport. Adsorption of total hardness(Ca2++Mg2+),sulfate(SO42-)and sodium(Na+) occurs in the soil medium,while the adsorption intensity is different.The adsorption of sodium(Na+)is the strongest followed by sulfate(SO42-),and total hardness(Ca2++Mg2+)the weakest.In general,their adsorption conforms to the linear equilibrium sorption isotherm.The soil conductivity,fluid dynamic dispersivity,adsorption distribution coefficient and retardation factor of total hardness(Ca2++Mg2+),sulfate(SO42-)and sodium(Na+)are also measured.The adsorption distribution coefficient and retardation factor for the three are 1.59×10-2 cm3/g,6.5×10-2cm3/g,4.22×10-1 cm3/gand1.08,1.34,3.21,these offer measured parameters for model verification and numerical simulation.(3)Systematically analyze the essential factors influencing the pollution component transport and build three-dimensional dynamic coupled numerical model to describe the transport of the main pollution components in soil-groundwater system under the consideration of advection,hydrodynamic dispersion,adsorption-desorption and source and sink.The model underwent numerical discretization using finite-difference and the numerical solution was given.(4)Numerical simulation.was conducted to the concentration temporal and spatial distribution of total hardness(Ca2++Mg2+),sulfate(SO42-)and sodium (Na+)in the groundwater system,the results of which indicate:The pollution area enlarges continuously with the passage of time and the longitudinal direction is more remarkable.The pollution scale is bigger in the groundwater downstream,smaller in the upstream,and distributes symmetrically on both sides;The pollutant concentration decreases gradually on either axis and the pollution degree of the leaching solution to the groundwater system is related to the distance of the pollution sources,the farther away from sources of pollution, the concentration of solute lower;In the vertical direction,with the current migration of contaminants at the same time gradually to the bottom of leaks, pollution area continued to expand,and successive decline.In the lower part of the pollution sources within 0-20m depth of the highest.The pollutant concentration in one location increases gradually with the passage of time and finally reaches equilibrium;The transport velocity of total hardness(Ca2++Mg2+) is bigger than that of sulfate and much bigger than that of sodium;In the same simulation time period,the transport scale of total hardness(Ca2++Mg2+)is the largest and then sulfate(SO42-)and sodium(Na+)sequentially.The total hardness(Ca2++Mg2+)comes to equilibrium first followed by sulfate(SO42-) and sodium(Na+)the slowest,so the pollution scale of hardness(Ca2++Mg2+) and sulfate(SO42-)is larger than that of sodium(Na+)and eventually causes more severe pollution to the groundwater.(5)The investigation and monitoring to the water quality of groundwater in the surrounding areas of the coal gangue hills in formal Xinqiu open-cut mine demonstrate that the investigation areas have been polluted heavily by main pollution components of total hardness(Ca2++Mg2+),sulfate(SO42-),sodium(Na +)and total dissolved solid(TDS).The pollution sources is the coal gangue hill. The coal gangue hill is a long-term pollution source and is the main reason of groundwater inorganic salts pollution in the surrounding areas,which is also in accordance with the study conducted in Poland.(6)The simulation results were compared with the many-year monitoring datas of the groundwater in the study region,which demonstrates that the mathematical model built is reliable.The model and numerical simulation method are also applicable to the pollution of inorganic salts to the groundwater in other regions. In the end,the countermeasures were given to the groundwater pollution issues by coal gangue.This study is of great scientific significance to reveal the environmental dynamics of the groundwater pollution by coal gangue.It is also of great theoretical and practical significance to predict,forecast and manage the groundwater pollution and lays theoretical foundations for preventing, controlling and treating the groundwater pollution issues caused by coal gangue in coal mine sites scientifically and efficiently.
|
PDF Full Text Request