Research On The Effects Of Humic Acid And Its Iron And Manganese Salts On The Migration Of Uranium(?) In Soil

Pentavalent uranium(?)is a highly harmful radioactive pollutant.Uranium(?)flows into the soil environment with the acid leachate produced by uranium waste rock piles under rain erosion and water immersion scouring,which poses a serious threat to human health and ecological harmony.As essential components of soil,humic acid(HA)and iron and manganese affect the migration and bioavailability of uranium(?)in the environment.Therefore,this paper combined static batch experiment techniques,material characterization methods,theoretical migration experiment simulations and occurrence morphological analysis to investigate the effects of humic acid and its iron and manganese salts on uranium(?)migration.Firstly,in this paper,ferric chloride hexahydrate and manganese chloride tetrahydrate were used to interact with HA to synthesize iron and manganese salts of HA(herein referred to as HA-Fe and HA-Mn).In addition,the effects of contact time,pH of solution,initial uranium concentration and temperature on the uranium(?)adsorption by HA-Fe and HA-Mn were systematically studied.It was confirmed by experiments that the adsorption amounts of HA-Fe and HA-Mn reached 21.64 mg/g and 46.49 mg/g at pH=5 and pH=3,respectively.The analytical kinetics and isotherms showed that HA-Mn was a typical multiphase chemisorption,but HA-Mn was a physical and chemical coexisting monolayer adsorption of the quasi-secondary kinetic model and the Langmuir adsorption isotherm model.Then,the morphology,functional group,crystalline state,specific surface area and pore size distribution of U(?)adsorbed by HA-Fe and HA-Mn were studied by characterization of SEM,FT-IR,XRD,specific surface area and pore size.The results showed that the complexation of uranium(?)with hydroxyl,amino and carboxyl groups of HA-Fe increased the specific surface area and the crystallinity of HA-Fe.However,the crystallinity of HA-Mn itself was quite high,and the complexation of U(?)with the hydroxyl group,amide group,aldehyde group,ketone group and chlorine group of HA-Mn reduced its specific surface area,which was adsorption performance of HA-Mn is stronger than that of HA-Fe.Finally,the results of soil column adsorption experiments showed that with the help of humic acid and its iron and manganese salts,the immobilized uranium content of soil increased from 1598.08 mg to 1902.68 mg,an increase of 19.06%,indicating that humic acid and its iron and manganese salts could inhibit the migration of uranium(?)in soil.Notably,the column desorption experiment found that the uranium(?)immobilized in soil re-migrated under the effect of rain leaching,and more uranium(?)was desorbed by the influent of pH 5 than that of pH 7.The morphological analysis of uranium by BCR method showed that humic acid and its iron and manganese salts increased the specific gravity of Fe/Mn oxide-bound uranium and organic matter/sulfide-bound uranium in soil,two forms of uranium uneasy to migrate in the soil,which facilitated the uranium fixation of soil.The findings could provide a theoretical basis for the soil environmental risk assessment and the final environmental impact assessment of the decommissioning of uranium waste rock heap.