Study On Migration Law Of Pollutants In Phosphogypsum In Unsaturated Zone-saturated Zone And Pollution Control In Storage Areas Of Shifang City

Shifang City is located in the hinterland of Sichuan Basin,the northwest of Sichuan Plain,which is mainly Shiting River alluvial fan.Shifang phosphogypsum storage areas are located in the alluvial fan of Shiting River.With the abundant phosphate rock resources,the city is one of the traditional phosphate bases in China.However,because when the stockyards began to use at the end of the last century or at the beginning of the century,no overall impermeable measures or improper impermeable measures were taken in the phosphogypsum stockyards,which caused that the pollutants in the phosphogypsum with the effect of rainfall and eluviation entered in the unsaturated-saturated aquifer with the strong acidic percolate,it damaged the surrounding groundwater environment seriously.The paper took multiple means of field reconnaissance,sampling,laboratory test and experimental simulation studied the phosphogypsum and pollutant’s migration and pollution mechanism in the unsaturated-saturated system deeply.In this study,the paper studied the features,rules and mechanisms of phosphogypsum pollutants to the groundwater pollution the phosphogypsum piles,it can provide the scientific basis for controlling the phosphogypsum stockyard leakage and pollution in time.At the same time,it researched the methods of reducing the phosphogypsum inventory quantity effectively,which solved the environment pollution problems caused by leakage from the source.Besides,it discussed the prevention and repairing materials for phosphogypsum stockyard and groundwater,which laid the foundation for governing the main pollutants of phosphogypsum stockyards.This peper obtained the following aspects of research achievements:（1）The research area was one part of Shiting River alluvial fan,the emergence stratums were mainly Q₄^al+pl,Q₄^al,the groundwater type was mainly sand and gravel pore water,the meteoric water was the main supply source of groundwater in the research area,the main flow direction of groundwater was from northwest to southeast,and excreted to Shiting River by flow.At the initial stage of stockyard operation,the regular ions in the groundwater(Ca²⁺、Na⁺、K⁺、Cl^-)and regular indexes（total hardness,total dissolved solids）were lower than that in 2011（the stockyard operates for about 10 years）,which indicated that the phosphogypsum stockyard had the certain influence to the hydrogeochemistry features in the research area;（2）It revealed the pollutant leaching release rules in phosphogypsum by the indoors static leaching experiment under different conditions,then it combined with Friedman inspection and Wilcoxon inspection and analyzed the different pollutants response in the phosphogypsum leaching solution to different conditions;besides,it discussed the dissolution release rules of pollutants in phosphogypsum in the effect of pure water and different acid rain p H values,and it confirmed the influence of different acid rain p H value to the leaching concentration of different pollutants by Wilcoxon inspeciton,which provided the theoretical foundation for researching the pollutant leaching mechanism and major pollutants recognition in phosphogypsum,meanwhile,it compared and analyzed the major pollutant difference in phosphogypsum produced from different enterprises,and provided the basis for the later numerical simulation research and the comprehensive utilization of phosphogypsum;（3）It confirmed the different mediums to the phosphorus and fluorine absorption models by the static isothermal adsorption experiment.It researched the migration rules of phosphorus and fluorine from configured solution and those from phosphogypsum solution in different unsaturated-saturated mediums by pillar experiments,then it took the comparative analysis on the phosphorus and fluorine migration rule difference in the phosphogypsum percolate with co-existing ion and that without co-existing ion.At the same time,it took the numerical simulation on different sources of phosphorus migration in the unsaturated medium sand medium based on balanced and unbalanced models,then it illuminated the phosphorus migration mechanism in the unsaturated sand pillar,and took the contrastive analysis on the difference with co-existing ion influence.At the same time,it took the numerical simulation on the fluorine migration in the unsaturated medium sand medium based on the balanced and unbalanced models,it obtained the relevant parameters and confirmed the migration mechanism respectively,both provided parameters for the later unsaturated numerical simulation researches.Besides,it discussed the migration influence of phosphorus and fluorine in saturated zones under different concentrations and different flow strengths by the saturated sand pillar experiments;（4）It established the unsaturated-saturated solute transport models in the combination of hydrogeological condition,and which provided the scientific foundation for the groundwater pollution governance.（5）It took the phosphogypsum resource utilization research by the static adsorption experiment and dynamic leaching experiment,confirmed the effects in different splitting temperatures and different additive amounts of charcoal to reduce the pollutants in phosphogypsum,then it proved that adding the charcoal can reduce the accumulation of phosphogypsum pollutants in crops obviously and reduce the pollution to the groundwater environment,which offered ways to expand the scientific and safe utilization of phosphogypsum;（6）It took the descriptive statistical analysis and obtained the dynamic variation rules of all the components of monitoring well by the long-term sampling on the stockyard surrounding and monitoring the specific index（p H）and the concentration of components（total phosphorus（TP）,fluoride（F）,Zinc（Zn）,Arsenic（As）,Mecury（Hg））,then it evaluated the groundwater quality in the stockyard and the pollution level by Nemero index evaluation method（PI）and Stockyard water quality index method（LWPI）.The result indicated that the water quality of most monitoring wells around the stockyards was poor or extremely poor except the respective background well,it stated that the groundwater around the stockyard had been polluted seriously,and then it analyzed the polluted reasons in the different monitoring wells around the stockyards upon LWPI results;It took the penetration experiment on phosphorus and fluorine in the phosphogypsum percolate by the pillar experiment with charcoal as PRB repairing materials,it confirmed that charcoal was the ideal material to repair phosphogypsum stockyard and groundwater,then it fit the experimental data from 4kinds of penetration experiment models（Thomas、Yoon-Nelson、Adams-Bohart、Clark）,and it obtained the optimal fitting parameters of different volumes of charcoals by the non-linear regression method,which provided the theoretical basis for charcoal as PRB repairing materials.