Research On Leakage And Contamination Of Phosphogypsum Tailings Pond In LongJing Bay Of Central GuiZhou Province Based On The Discrete Fracture Network Model

The karst rock is widely distributed in central Gui Zhou,and the karst is well developed.The area is rich in a variety of mineral resources.Many mines and chemical bases have been built to exploit and utilize all kinds of minerals,resulting in a large amount of tailings and abandoned slag.In order to store and treat the tailings residue,many tailings dumps have been built in gully area of the karst.With the increase of the dumps'service time,the original anti-seepage treatment facilities gradually aged,and some dumps were abandoned or sealed after reaching the service life,the original anti-seepage treatment effect of the dumps gradually decreased,resulting in the tailings leached by atmospheric precipitation and releases pollution ions,which enter into the groundwater pollution system through the dissolution cracks,sinkholes and karst pipes developed in the karst area and cause the leakage and pollution of the tailings which seriously affecting the groundwater environment around the reservoir area.In addition,karst aquifer medium is quite complex,especially in the karst fissure medium,the current study of the tailings leakage in karst fissure medium mostly adopts the traditional equivalent porous medium model,through the fissure medium approximation to the migration of pollutants for porous media are studied,and not a more accurate characterization of karst fissure medium and reflect the characteristics of the migration of pollutants,and discrete fracture network model based on large Numbers of the measured data of joints to karst fissure medium as meticulous complicated fracture network,considering the karst fissure medium inhomogeneity and anisotropy,can better reflect the migration process of pollutants,Therefore,it is beneficial to master the main path and horizon of tailings pond leakage in karst fissure media.Therefore,by using the theories and methods of discrete fracture network model of the characteristics of the tailings leakage in karst area and pollutant migration characteristics,can more accurately reflect the actual characteristics of karst aquifer medium and the migration process of pollutants,to the problem of tailings leakage control and plays an important role in the prevention and control,as well as the protection and management in the tailings of groundwater environment to provide the reference and basis.Based on the regional geological and hydrogeological data,through field investigation,water chemical analysis,high density electrical prospecting,hydraulic pressure tests,geological documentation of drill core and borehole television to study the main pollutant,aquifer permeability,degree of karst development and tailings leakage characteristics of the research area.According to data of the measured cracks,using Frac Man to generate discrete fracture network of the research area on the basis of Mont Carlo method,then dividing the fracture network into different parts by finite element method,combined with the simulation method and the hydrogeological conditions in the area of groundwater seepage field in the study area is established and solute particle migration model,obtained the following understanding:?1?The main cations in the groundwater in the study area are Ca²⁺and Mg²⁺,while the main anions are HCO₃^-and SO₄^2-.The types of hydrochemistry are mainly HCO₃·SO₄-Ca·Mg,SO₄·HCO₃·Ca and SO₄-Ca.SO₄^2-,total phosphorus and F^-in the area exceed the standard seriously,and the source is leachate leakage of tailings.?2?The main area of leakage of phosphogypsum tailings pond in longjing bay is located in the north of the reservoir area?3?The main exposed carbonate strata in the study area are the dolostone strata of sinian dengying formation?Zbdn?,belonging to the exposed and semi-exposed karsts with a high degree of surface karst development.The development of karst in the region has obvious vertical zonal:within the range of 0-80 m,the lugeon is very close to or even over 100lu,and the degree of karst development is relatively high.Within the range of 80-140m,the lugeon is between 1?100lu,and the karst is moderately developed.When the depth is below 140m,the lugeon is below 1lu,and the karst is not well developed.?4?The permeability intensity of dengying formation(Zbdn¹⁺²),the main water-bearing rock group in the region,has obvious vertical zonation.According to the distribution depth,it can be divided into strong permeability zone,strong permeability zone,medium permeability zone,weak permeability zone and micro permeability zone.?5?In the sinian dengying formation(Zbdn¹⁺²),a large number of dissolution fractures are developed.The dominant direction of fracture development is northeast,and the average width of the fractures is 0.502cm,mainly small fractures.?6?The contaminated solute particles in the area are mainly distributed in the range of 30m to 82m underground,where the developed dissolution cracks have good connectivity and are the main strata for particle migration.In the horizontal direction,the migration distance of phosphate particles is far greater than that of sulfate particles.?7?The main area of tailings pond leakage in the area is located at the gully in the north of the tailings pond,and the leachate leakage in the phosphogypsum tailings mainly consists of two ways:the first way is from the tailings dump—gully in the north of the gully and f6 fault fracture zone cutting location—S1 spring point and772 mine hole;the second way is from the tailings dump—north of the dumping field gully and f6 fault fracture zone cutting location—Luo Jia Lin mine hole.