| Phosphogypsum is an industrial by-product containing a variety of harmful chemical substances produced during the production of wet-process phosphoric acid.The main pollutants are phosphorus,fluorine,and sulfate,which will bring many environmental problems.Among them,groundwater pollution is an urgent need to be resolved The problem.Phosphogypsum leachate deposited for a long time will enter the groundwater through the aeration zone,and because of its special self-purification ability,the aeration zone plays an extremely important role in reducing the pollution effect.Therefore,it is particularly important to study the migration law of pollutants in the groundwater.In this paper,the fluoride in phosphogypsum leachate is selected as the research object,and the research method of combining laboratory test,numerical simulation and field application is used to study the migration of fluoride in the aeration zone and groundwater.The main research results are as follows:(1)Through the static leaching of phosphogypsum,the influence of factors such as different solid-liquid ratio,p H and temperature of extractant on the dissolution and release of fluoride in phosphogypsum was revealed,and the law of precipitation and release of fluoride in phosphogypsum was revealed.As the solid-liquid ratio decreases,the leaching concentration of fluoride gradually decreases;the lower the p H value of the leaching agent,the more favorable the leaching of fluoride in phosphogypsum;as the temperature increases,the fluoride concentration in the phosphogypsum leaching solution increases.(2)Through the dynamic leaching experiment,it was found that the initial fluoride concentration was very high,but the fluoride concentration also decreased rapidly.In the subsequent leaching process,soluble fluoride decreases,the rate of decrease in fluoride concentration slows down,and the increase in cumulative amount also tends to be slow.(3)The saturated hydraulic conductivity of the selected soil sample is determined by the water head method,and the saturated hydraulic conductivity of soil sample 1 is 1.27 × 10-3cm / s,and the saturated hydraulic conductivity Ks of soil sample 2 is 1.84 × 10.-2cm / s;in the one-dimensional dispersion experiment,the hydrodynamic dispersion coefficient and dispersion were measured by sodium chloride penetration,and it was found that the hydrodynamic dispersion coefficient of soil sample 1 was 0.456cm2 / min,and the dispersion was 2.039cm;Sample 2 has a hydrodynamic dispersion coefficient of 2.592 cm2 / min and a dispersion of 0.9997 cm.(4)Through the static adsorption experiments of different soil samples on sodium fluoride,the adsorption kinetics and isothermal adsorption laws of fluoride in different soil sample media were studied.The results showed that the adsorption of fluorine on the two soil samples basically reached equilibrium in 2 hours;The three isothermal adsorption models of Henry model,Temkin model and Freundlich model can well describe the isothermal adsorption law of fluorine in soil samples.Among them,the Henry model fits the correlation best,indicating that the adsorption of fluoride on soil samples is linear Adsorption is dominant,and the Langmuir model cannot describe the law of isothermal adsorption of fluorine on soil samples.(5)Fluoride leaching experiment results show that the time for the fluoride ion to penetrate completely is longer than the time for the chloride ion to penetrate.According to the experimental monitoring data of indoor soil columns,the soil moisture parameters and solute transport parameters are simulated and back-calculated to obtain the adsorption parameters,permeability coefficients and dispersion of the three media after inversion.Among them,the adsorption parameter of soil sample 1 is 1.114,the permeability coefficient is 0.809 cm / min,and the dispersion is 1.962cm;the adsorption parameter of soil sample 2 is 0.4910,the permeability coefficient is 1.18 cm / min,and the dispersion is 1.040cm;(6)The numerical simulation prediction results show that without the anti-seepage condition of the phosphogypsum yard,the migration distance of fluoride in the aquifer is large,the influence range and the area exceeding the standard are wide,the concentration of the center point is high,and the stacking of phosphogypsum It caused serious pollution to the surrounding groundwater;through comparative analysis,it was concluded that when the aeration zone was not considered,the concentration of the central point,the influence range,the area exceeding the standard,and the maximum horizontal migration distance of the pollution plume were all greater than those considering the aeration zone. |
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