Dynamic Experimental Study On Fluoride In Saturated-Unsaturated Soil And Numerical Simulation

Contaminant transportation and transformation in soil and groundwater is an important research topic in soil and environmental science. For many kinds of contaminants, the fluoride pollution had already been paid more and more attention on environment problems. On account of fluorine ion has special chemical characteristic, its chemical property was complex in course of migration in porous media. At present, the soil column test was used to study the rule of contaminant transportation and transformation in saturated-un- saturated soil. By way of the test study in laboratory, we can analysis in- fluencing factors and migration mechanism on solute transport in porous media. At the same time, it can solve some problem which decreased test investment, shorted test periods, controlled uncertain factor difficulty and son on. Therefore, it shorted test research periods. On the basis of solute transport theory in the porous media, the whole test were carried out in laboratory, including small soil column test and large soil tank test with homogeneous and heterogeneous in saturated-unsaturated soil. The rule of migration and transformation of the fluoride(chlorine) was studied by virtue of test and numerical simulation in this dissertation ,and curve fitting analysis were doned about soil water retention curve and unsaturated hydraulic conductivity in different soil. Some achievements were drawn as follows.The rule of transportation of fluoride(chlorine ) were obtained through different texture and heterogeneous soil by a large number of soil column tests in saturated-unsaturated soil. The effects of input solute on F"and Cl~- ion transport was especially discussed by series of experiments . Results showed that the value of coefficient of hydrodynamic dispersion (D) and retardation factor (R_d)in soil (sand and kaoline mix) was greater than that in sand .In the way of input solute , the appearing time of maximum value of concentration with input mix solute (NaF and NaCl) was slower than that with input solute(NaF),and concentration apexes was also smaller .But in the course of input water ,the concentration of F" ion in input mix solute was bigger than that in input solute(NaF).This showed that sodium chloride accelerated transportation of F~- ion in different soil.The soil water retention curve and the unsaturated hydraulic conductivity were obtained by various soil experiment. Parameter fitting were studied by using V-G model, applying these result to model calculation of soil column in saturated-unsaturated soil, and model parameter was corrected. This providea basis for primary application of transport model and obtained parameter. The dynamic migration test of F' and Cl" was carried out by large earth column and large soil tank in laboratory. We obtained different migration rules of F" and Cl" ion .The parameter with small scale soil column test was used to calculate model parameter with large soil tank, and corrected parameter according to measured data. In the course of numerical simulation, in order to decrease influence for F" and Cl" transportation owing to variable velocity ,the average velocity was not used ,instead of changed velocity with time segment. The calculated values with variable velocity was close to the observed data.In order to study eluviation and decontamination process for F" concentration in horizontal and vertical direction, empirical formula was used to fit rule of F" concentration attenuation .The result showed that exponential function was in accorded with rule. In order to study correlativity curve between F" concentration attenuation and distance , quadratic polynomial was used to fit data in horizontal and vertical direction, the both fitting result accorded. Based on much test theory in laboratory and numerical simulation, combined with present status of pollution of region in Shanxi province, trend of contaminant transportation with time and distance was forecasted by mathematical model and parameter from tests according to hydrogeologic condition and pollution status in studied region, and measures preventing from pollution was pointed out. This provided a basis.in effect for studying ground water environment of Shanxi province.