Rapid Adsorption Of Radionuclides In Water By Modified LDHs Composites And Its Mechanism

Nuclear industry wastewater contained a large number of radionuclides.If it is not treated properly before entering water,radionuclides would pose a serious threat to the ecological environment.In addition,radionuclides dissolved in the aqueous medium,they might be absorbed by microorganisms,algae,plankton,plants or crops.Then,they accumulated and transferred through the food chain,resulting in unforeseen and serious effects on human health.Uranium(U),as a typical nuclear fuel,was widely used in various nuclear industries.U(VI)destroys biological tissues,and even leads to death.On the other hand,Cs was a by-product of U fission process and also widely existed in various nuclear industry wastewater.After the accident at the Fukushima nuclear power plant,Cs(Ⅰ)was detected in many countries such as Europe and Asia.It could cause serious diseases such as cancer,leukemia once Cs(Ⅰ)enter the human body.Therefore,removing U(VI)and Cs(Ⅰ)becomes an urgent problem in the world.Layerd double hydroxides(LDHs)had large specific surface area,low cost and good adsorption performance.It could fix U(VI)and Cs(Ⅰ)because the surface of the metal cation and complexation reaction.However,LDHs was easy to be aggregated and thus its adsorption capacity was greatly reduced.This limits its application.This paper intends to modified LDHs to remove the radionuclides in water(U(Ⅵ)and Cs(Ⅰ)).The conclusion is as follows:(1)Novel Ni Si O@NiAlFe hollow spheres were prepared by hydrothermal method.NiAlFe LDHs’ grafting towards Ni Si O hollow spheres could avoid LDHs’ aggregation,and thus enhanced the adsorption capacity.Results indicated that Ni Si O@NiAlFe LDHs hollow spheres had sufficient adsorption capability towards Cs(Ⅰ),and the adsorption process could reach the equilibrium in only 20 minutes.The adsorption kinetics satisfied the pseudo-secondorder adsorption model,Temkin model and Langmuir isotherm model.The adsorption process was efficient at the alkaline condition(p H=10).The maximum adsorption capacity of Cs(Ⅰ)towards Ni Si O@NiAlFe hollow spheres was estimated to be 61.5 mg/g.Moreover,the adsorption thermodynamics indicated that the adsorption was exothermal,feasible and spontaneous.(2)MgAlFe LDHs were prepared by hydrothermal method,and were then gelated by freeze-drying technique to synthesize the calcium alginate aerogels doped with MgAlFe LDHs(CAA@MgAlFe).The adsorption kinetics indicated that The adsorption kinetics satisfied the pseudo-second-order adsorption model.The adsorption of U(VI)and Cs(I)could reach the equilibrium rapidly in only about 5 mins.The adsorption isotherms showed that U(VI)and Cs(I)matched well with the Langmuir and Freundlich models,respectively,witch indicated that the competition between the two adsorption performance was weak.The maximum adsorption capacities of U(VI)and Cs(I)were calculated by Langmuir model to be 532.5 and 57.6 mg/g,respectively.CAA@MgAlFe could be easily separated and compressed,and its application on sea water was proved to be feasible.(3)The porous spongy structure of CAA/GO@MgAlFe was synthesized by combining GO with calcium alginate aerogel and disperzing MgAlFe LDHs in CAA/GO aerogel framework.The adsorption was efficient at the p H=4.The adsorption kinetics satisfied the pseudo-second-order adsorption model.The adsorption of U(VI)and Cs(I)could reach the equilibrium rapidly in only about 7 mins.The adsorption isotherms showed that U(VI)and Cs(I)matched well with the Langmuir and Freundlich models,respectively.The maximum adsorption capacities of U(VI)and Cs(I)were calculated by Langmuir model to be 564.6 and96.5 mg/g,respectively.The mesh structure of GO enhanced the strength and stability of calcium alginate aerogel skeleton.XPS spectrum showed that the adsorption mechanism on U(VI)included complexation and reduction,while that of Cs(I)was electrostatic attraction.DFT simulation showed that Cs had three adsorption sites on the MgAlFe LDHs without constructing O—H vacancy,which were Mg(-0.994 e V),Al(-1.093 e V)and Fe(-1.091 e V).The MgAlFe LDHs with an O—H vacancy constructed by Cs was a hollow adsorptive site.The U atom could not be adsorbed on the MgAlFe LDHs without constructing an O—H vacancy,but the MgAlFe LDHs with an O—H vacancy could adsorb on the O—H group,and the adsorption energy was-6.11 e V,which was much higher than that of Cs.This paper focused on LDHs and its composites,mainly around the promotion materials for U(Ⅵ)and Cs(Ⅰ)adsorption.In this article,system one revolves around how to overcome the defect of LDHs was easy to gather research,preparation of Ni Si O@NiAlFe of Cs(Ⅰ)has good adsorption performance;System two focused on how to improve the solid-liquid separation ability of materials,CAA@MgAlFe materials for preparation of aerogels,easy solidliquid separation,and could at the same time,the adsorption U(Ⅵ)and Cs(Ⅰ);System three focused on DFT calculation and dynamic adsorption experiments.The adsorption mechanism was further revealed and the theoretical basis was provided for engineering application.