Experimental Study On The Migration And Transformation Law Of Phosphorus In Phosphogypsum Leachate In Karst Multiple Aqueous Medium

With the accumulation of phosphate ore resources mining time,the total reserves of phosphogypsum in Karst Mountain Area of Guizhou reached 120 million tons.Phosphogypsum stacked in the open air produces leachate during storage,Leachate has the characteristics of high phosphorus,high fluorine and strong acid.Once leakage occurs in the phosphogypsum stockpile,various pollutants in the leachate will enter the underground aquifer through soil pores,rock fractures,pipelines,etc.,causing groundwater environmental pollution.The study of the migration and transformation of phosphorus in karst aqueous medium can provide a theoretical basis for the prevention and control of leakage pollution in phosphogypsum stockpile in karst area and the emergency treatment of accidental leakage in phosphorus chemical enterprises.In this study,a phosphogypsum yard in Guizhou Province was used as the research area.Design and construct indoor physical models through field investigation and sampling,Analysis of phosphogypsum phosphorus leaching characteristics,The migration and transformation of phosphorus in karst multiple aqueous media in phosphogypsum leachate under different conditions was discussed.The main conclusions are as follows: The larger the particle size and solid-liquid ratio,the more conducive to the leaching of phosphorus.(1)The leaching characteristics of phosphogypsum phosphorus were analyzed by static immersion and dynamic leaching experiments.In static immersion experiments,the change law of phosphorus leaching amount decreased first and then increased with time,and then stabilized when it increased to a certain extent.Under acidic conditions,the stronger the acidity,the more conducive to phosphorus leaching,pH=8-9 can increase the leaching of phosphorus,but strong alkali conditions will inhibit the leaching of phosphorus.During immersion,phosphorus is mainly present in soluble form.Under dynamic leaching conditions,the leaching amount of phosphorus decreases with the increase of leaching time,and the initial drop rate of leaching is fast and the concentration is large,and the release concentration is small and the rate is slow in the middle and late stages.The occurrence forms of phosphorus in leachate in dynamic experiments were mainly soluble phosphorus and inorganic phosphorus,and organic phosphorus and granular phosphorus were rare.(2)According to the results of indoor physical simulation experiments,the migration law of phosphorus in karst aqueous medium was obtained.After phosphorus in phosphogypsum leachate enters the red clay,the phosphorus concentration decreases with the increase of soil depth.The concentration of phosphorus in soil at the same depth decreases with increasing migration time and eventually stabilizes.The adsorption of phosphorus by red clay is the main reason for the attenuation of phosphorus concentration,and the greater the thickness,the more significant the effect on leachate retention.When phosphorus migrates in cracks of the same size,the phosphorus concentration decreases with the increase of migration time,and the attenuation of phosphorus is large in the early stage of migration,and the attenuation gradually decreases with time and finally tends to saturation.The migration law of phosphorus in the leachate is different with different gap width,and the attenuation of phosphorus per hour of fracture width is relatively large.Because migration in large fractures is prone to dominant flow,it is not conducive to the attenuation of phosphorus.When phosphorus migrates in pipes of the same size,the phosphorus concentration decreases with increasing migration time.The initial phosphorus decay rate is fast,the later decay rate is slow,and finally the adsorption capacity is saturated and no longer attenuated.Larger pipe sizes are more conducive to the attenuation of leachate phosphorus.Because the contact area between the migration perudate and the limestone in the large pipeline is larger,phosphorus is more likely to react with limestone,and the longer the migration distance of phosphorus in the pipeline,the greater the attenuation of phosphorus.(3)According to the results of indoor physical simulation experiments,the main forms of phosphorus in karst aqueous medium are soluble phosphorus and inorganic phosphorus.The conversion of phosphorus in the pores of red clay in phosphogypsum leaching filtrate is mainly due to adsorption process and precipitation process,and the red clay particles are fine,the clay content is high,and the characteristics of colloidal substances are exhibited,which will adsorb and precipitate phosphorus.The conversion of phosphorus in the pores of red clay in phosphogypsum leachate is mainly due to adsorption process and precipitation process.Red clay has fine particles and high clay content,showing the characteristics of colloidal substances,which will adsorb and precipitate phosphorus.The conversion of phosphorus in fissures and pipelines in phosphogypsum leachate is mainly a chemical reaction with limestone and the formation of precipitate from soluble phosphorus.The soluble phosphorus in the cracks and pipes reacts chemically with the calcium and magnesium ions in the limestone to form a granular state that is difficult to dissolve in water.The attenuation of granular phosphorus is gradually deposited due to weak hydrodynamic conditions.(4)A mathematical model of phosphorus migration in karst aqueous medium was constructed.According to the migration characteristics of phosphogypsum leachate phosphorus in red clay,fissure and pipeline,an exponential function model was constructed,and the fitting degree was high.