Study On Adsorption,migration And Transformation Of Radionuclides U And Th In Soil By Phosphate

In this study,farmland soils surrounding the tailings of uranium mines and farmland soils in the suburbs of Nanchang City were selected as research objects to study the adsorption and migration of radionuclides uranium and plutonium under the action of phosphates.The initial pH was studied through static adsorption experiments.Adsorption of uranium and thorium as radionuclides under the influence of factors such as temperature,adsorption time,soil particle size,and different phosphates;leaching experiments to study the migration of radioactive uranium and thorium in the soil under different phosphate action The effects of transformation and occurrence patterns;and the mechanism of soil adsorption of uranium and plutonium.The research results can provide a certain reference for the restoration of soil radioactive pollution.The main conclusions are as follows:?1?Single-factor adsorption U and Th static tests for the mining area and non-mining area soil show that when the particle size is 200 mesh,the adsorption time is 4h,the adsorption temperature is 25°C,and the initial pH is 4-5,the mining area and the non-mining area The adsorption effect of U on the soil was the best.When the particle size was 200 mesh,the adsorption time was 4h,the adsorption temperature was 25°C,and the initial pH was 7,the adsorption of Th on the soil in the mining area and non-mining area was the best.The static experimental studies of different phosphates on U and Th show that under the action of four phosphates,the adsorption performance of U in soils of mining area and non-mining areas is stronger than that of Th,and the ability of adsorption of U and Th in soils of non-mining areas is stronger than The ability of the soil in the mining area to adsorb U and Th.?2?In the column leaching experiment under the effect of phosphate,the leachate pH of both the experimental group and the control group gradually increased with the increase of the leaching time,and the leachate pH ratio of the added phosphate was not added.Phosphate leachate has a low pH and soil pH is higher than the initial pH of the soil.No matter whether the conductivity of the leachate after the addition of phosphate or the conductivity of the leachate in the control group is decreasing with the increase of the leaching time,the change in the conductivity of the leachate and the pH of the leachate are exactly the same.completely opposite.?3?In the column leaching experiment under the effect of phosphate,the concentration of U in the leachate of the experimental group and the control group was very low.It shows that uranium pollution has little effect on groundwater.The concentration of Th in the leachate is much higher than that of U,which indicates that the earthworm is more likely to cause pollution of groundwater.Phosphate addition facilitates the immobilization of Th into the soil and reduces the impact on groundwater.?4?Phosphate leaching increased the residual content of uranium in the soil.Among them,the monobasic potassium dihydrogen phosphate had the best inerting effect,and the residue content was high.It showed that the addition of phosphate caused the uranium in the soil to be inerted,and to a certain extent restored the uranium contamination in the soil.However,there was no significant effect on earthworms in the soil.This may be due to the fact that earthworms are easily fixed in the soil and are not easy to migrate due to their own characteristics.?5?Frenudlich fitting of U,Th static adsorption data in soils of mining area and non-mining area under the action of ammonium dihydrogen phosphate,potassium dihydrogen phosphate,calcium dihydrogen phosphate,and hydroxyapatite,and it was found to be suitable for Freudlich equations.The U,Th static adsorption processes in the soils of mining areas and non-mining areas under the action of hydroxyapatite,potassium dihydrogen phosphate,calcium dihydrogen phosphate,and hydroxyapatite were described.The adsorption capacities of U and Th in the soils of various phosphate mining areas and in the mining areas were compared.The Kf values of the adsorption U and Th in the non-mining area soils under the effect of phosphate were significantly greater than the Kf values in the soils under the effect of phosphates.It shows that the non-mining soil under phosphate action has stronger ability to adsorb U and Th than the soil in the mining area.?6?SEM-EDX was used to analyze the surface morphology and elemental characteristics of uranium and plutonium before and after adsorption of hydroxyapatite in the mining area and non-mining area.Adsorption SEM images can show the adsorption of hydroxyapatite on the soil surface.A certain amount of uranyl and quinoid structure.EDX analysis showed that U and Th elements appeared in the soil under the action of hydroxyapatite,indicating that it has a good adsorption effect on uranium and plutonium.FTIR analysis showed that the adsorption of uranium and thorium by hydroxyapatite was mainly adsorbed by active groups-OH,-NH₂,-NH,etc.