Efficient Adsorption Of UO₂²⁺ On The Mg/Al LDH/calcined LDO And Their Application In Uranium Extraction From Seawater

With the development of social economy,the demand for energy is increasing.In order to solve the energy exhaustion and environmental pollution produced by the burning of fossil fuels,nuclear energy,as an efficient and clean energy,is being employed.However,some radioactive pollution will occur in the development and utilization of nuclear energy,which will produce irreversible toxic effects on humans and the natural environment.Therefore,the removal of radioactive pollution is also one of the research directions of current research scholars.Meanwhile,uranium resource as a non-renewable resource made human pay more attention to search for alternative energy sources.Seawater is the one that the uranium content is about 1000 times of Land.Therefore,how to extract uranium from seawater is another major problem for people.Compared with other methods,adsorption method is the optimal method because of its advantage,such as abundant sources,low cost and easy operation..Layered double hydroxides?LDHs?as a part of natural soil is environmental friendly.Because of its exchangeable anions in layers and the"memory effect"of the metal oxides,LDHs is a good adsorption material for the removal of environmental pollutants.This study is mainly carried out from the following aspects:1.Mg/Al LDH with different Mg/Al molar ratios were prepared by co-precipitation.The adsorption properties of Mg/Al LDH on UO2²⁺were studied by XRD,BET,FT-IR,SEM,XPS and other characterization methods.The results are as follows:?1?The two materials with the molar ratios of 2:1 and 4:1?Mg/Al-2 LDH and Mg/Al-4 LDH?with good crystal were successfully prepared,respectively;?2?The morphology of Mg/Al-2 LDH showed petal clusters with larger specific surface area,while Mg/Al-4 LDH was flaky and stacked;?3?The adsorption of Mg/Al-2 LDH and Mg/Al-4 LDH on UO2²⁺was more in accord with the Langmuir adsorption model and pseudo-second-order model,with the maximum adsorption capacity of 895.02 mg/g and 868.21 mg/g,respectively,and the increase of temperature was in favour of the adsorption;?4?According to XRD,FT-IR and XPS analysis,the mechanism of adsorption of Mg/Al LDH on UO₂²⁺is that a ternary complex was occurred after the UO₂²⁺was reacted with hydroxyl and carbonate on Mg/Al LDH.2.LDO300,LDO500,and LDO700,obtained by calcining Mg/Al-2 LDH at different temperatures of 300??500??and 700?,respectively,were used to study the adsorption capacities on UO2²⁺.The results are as follows:?1?FT-IR,XRD,and SEM analysis before adsorption showed that the higher calcination temperature,the less OH^-and CO3^2-in the material,and the worse the crystal structure,with the generation of magnesium aluminum oxides;?2?The single-factor experiment results showed that LDO500 had the optimum adsorption capacity of 1115.24 mg/g on UO2²⁺,followed by LDO300 and LDO700,with the maximum adsorption capacity were 969.48 mg/g,and 852.67 mg/g,respectively.It was found that the Langmuir isothermal adsorption model and pseudo-second-order adsorption model were more suitable;?3?According to FT-IR and XRD analysis,the adsorption mechanism of LDO300 on UO2²⁺is that LDO300 perform"memory effect"to restore lamellae structure,and UO2²⁺only forms ternary complexes with OH^-and CO3^2-on LDO300,but not enter into the enterlayer.The adsorption mechanism of LDO500 on UO2²⁺is that the"memory effect"played a major role,where UO2²⁺enters into the enterlayer,and generate complexation with OH^-and CO3^2-on LDO500.The similar adsorption mechanism was found for LDO700,but a part of LDO700 loss"memory effect"because of excessive calcination.?4?The adsorption of LDO500 on UO2²⁺could reach the adsorption balance instantly within 10 min,and it still had a good adsorption effect on UO2²⁺under alkaline environment,so it could be used as the emergency adsorption material for uranium pollution and uranium extraction material from seawater.3.The adsorption column penetration experiment of simulated seawater were applied to study the feasibility of uranium extraction from seawater by using LDO500 as raw material.The effects of major marine cation ion such as K⁺,Na⁺,and Ca²⁺,anion such as CI^-CO₃^2-,SO₄^2-,PO₄^3-,and some metal ions on the adsorption of UO₂²⁺by LDO500 were studied.The results showed that:?1?K,Na,and Ca had little effect on adsorption;?2?In the presence of CI^-,it increased the adsorption removal rate of UO2²⁺by Mg/Al LDH,but had no effect on the adsorption of UO₂²⁺by LDO.However,in the presence of CO₃^2-and PO₄^3-,the adsorption of UO₂²⁺was inhibited.The increase of SO₄^2-had no obvious effect on the adsorption of UO₂²⁺,and the removal rates were above 95%.?4?The presence of metal ions such as Ni²⁺?Cd²⁺?Cu²⁺?and Pb²⁺could promote the adsorption of UO₂²⁺by LDO500,and the removal rates from 86.8%increased to more than 95%.?5?Simulated seawater adsorption column penetration experiment had a good adsorption effect on low UO2²⁺concentration in dynamic environment,indicating that LDO500 can be used as a enrichment and extraction material of uranium resources collection from seawater.