Study On The Influence Of Phosphogypsum Site Leakage To Karst Groundwater Environment

Phosphogypsum is the byproduct from the process of phosphoric acid production,the environmental risks during the stockpiling have been widespread concern from domestic and foreign scholars.As one of the largest waste yard in Guizhou Province,the Wengfu phosphogypsum site is a serious threat to the local karst water environment.This paper choose Wengfu phosphogypsum site and its surrounding water as object of study.The leachate,groundwater,surface water were collected during the wet season(May 2016),the normal season(August 2016)and the dry season(December 2016).Variable parameter(Such as T,pH,EC,Eh,DO,etc.),water chemical components(cations etc.),and total phosphorus,fluorine and metal contents were tested.The water quality of the groundwater in the karst area is preliminarily revealed by the traditional water chemistry combined with the multivariate statistical analysis method.At the same time,the groundwater quality is evaluated and the hydrogeochemical modeling is established.The stage conclusions are as follows:(1)Phosphogypsum leachate is strong acidity and high salinity,the parameters of the leachate mainly depends on the wet system of phosphoric acid and wet storage process.The main characteristics of the pollutants are P,F-,SO42-,the contents are as follows: 5182 mg/L,2039 mg/L,422 mg/L;and the metal pollutants are mainly Fe,Mn,the content is 41.6 mg/L and 7.52 mg/L.During the three seasons,the polluted groundwater in the study area is acidic,others are neutral to weakly alkaline,and surface water is weakly alkaline.The EC value of groundwater is higher than that of surface water in the same period,DO value is lower than the surface water in the same period.The water of the study area is oxidized.(2)The main ions in the study area are Mg2+,Ca2+,HCO3-,SO42-which accounting for about 90%.The main water chemistry type is Ca2+-HCO3-type,and the chemical type of groundwater under the influence of pollution has the tendency to evolve to Mg2+-Ca2+-SO42-in the study area.The spatial distribution of contaminants in the study area shows that the phosphogypsum leachate leaks into groundwater is non-uniform diffusion and shows obvious characteristic of direction,which may be closely related to karst fissures or underground karst channels.(3)The phosphogypsum site mainly affects the groundwater in the direction of G1(Facaidong)by karst fissure or pipeline leakage,and does not show the characteristics of radiant pollution to the surrounding groundwater.Groundwater from G10(Longjing)direction mainly by the leakage of Wengfu plant area,which pollution level is far less than G1(Facaidong).The water quality of groundwater in the study area is mainly excellent and good,the groundwater quality of G10(Longjing)is poor,and G1(Facaidong)is seriously polluted.(4)The mixing ratio of groundwater and leachate in different periods were: 1: 0.038,1: 0.215,1: 0.575.It can estimate that the flow rate of the Facaidong in different season is 76.5,18.6 and 7.7 m3/hr respectively.During the leakage process in wet season,the dolomite and gypsum are dissolved and accompanied by the action of dolomitization.These reactions will accelerate the karst development of underground carbonate rocks.PO43-and Fe from leachate will easy to form precipitation of hydroxyapatite,Fe(OH)3,vivianite during the migration under the pH and ion concentration changes.In the process of leakage in normal and dry season,the dissolution of calcite and dolomite accelerates the water-rock reaction.Fe(OH)3 and vivianite will precipitate from groundwater.(5)From the wet season to the dry season,the reaction of the water rock involved in the calcite,dolomite and the dissolved amount of the pollutants(SO42-,PO43-,F-)gradually increased,while the precipitation amount of Fe(OH)3 and the vivianite gradually reduced.The change of ion concentration under the influence of leakage mainly comes from the dilution of groundwater,at the meantime the Ca2+ and Mg2+ contents may rise from the water-rock reaction accelerated by leachate infiltration.The apparent increase of SO42-content may be due to the phosphogypsum hydration,and a small decrease in PO43-,F-may be due mainly to the presence of physical adsorption in karst pipelines.