| The massive consumption of fossil fuels leads to global warming,for this reason,the exploration of new energy has become the primary goal,and nuclear energy develop rapidly.As the main source of energy in nuclear energy,uranium is bound to produce a large amount of radioactive waste water containing uranium in the process of fuel cycle.Uranium has chemical toxicity and radiation toxicity to human body.Once radioactive uranium is released into the environment,it will cause great harm to the natural environment and even the human body.Therefore,the separation and enrichment of uranium from radioactive wastewater is of great practical significance not only in terms of environmental treatment but also in terms of sustainable development.In recent years,membrane adsorption has been paid more and more attention.Membrane adsorption combines the dual functions of membrane separation and adsorption,which not only overcomes the low separation efficiency of membrane separation,but also solves the problem of difficult recovery of adsorption,and has a broad application prospect in the neighborhood of heavy metal separation and enrichment.The membrane preparation process of electrospinning can prepare nano-sized fibers,and the prepared membrane has good porosity and specific surface area.In this paper,PVA/PAA nanofiber membrane was prepared with polyvinyl alcohol(PVA)and polyacrylic acid(PAA)as raw materials.PVA/PAA nanofiber membrane has high hydrophilicity,can contact with water quickly,it has good stability in water,and PVA/PAA nanofiber membrane has high mechanical strength and can withstand huge water pressure impact.However,the traditional PVA/PAA nanofiber membrane has low selectivity for uranium in water,so it can not be used as a good material for adsorption and separation of uranium.In this paper,three kinds of adsorbents with good adsorption and selectivity for uranium,layered metal sulfides KMS-1,KMS-2 and KTS-3,were synthesized by hydrothermal method.At the same time,three kinds of natural mineral compounds,hydroxyapatite,montmorillonite and zeolite,which are recognized to have ultra-high adsorption to uranium,are selected.Three kinds of layered metal sulfides and three kinds of natural mineral compounds were compounded with polyvinyl alcohol(PVA))and polyacrylic acid(PAA)to form mixed nanofiber films by electrospinning technology.The physical and chemical properties of nanofiber films were characterized by SEM,XRD,contact angle and stretching test.The adsorption mechanism of the membranes was investigated by static adsorption methods such as p H value,ionic strength,initial concentration,time and temperature.The practical application performance of the membrane was investigated by membrane experiments such as the effect of feed concentration and flow rate on membrane filtration of uranium.The stability and reusability of the material were investigated by the selection of eluent and the number of elution times.The static experimental results show that the optimum adsorption p H value of KMS-1@PVA/PAA,KMS-2@PVA/PAA and KTS-3@PVA/PAA nanofiber membrane materials is 5.5,and the coexisting ion strength has a certain effect on the adsorption of U(VI).The material shows an adsorption process with ion exchange as the main role.The four membrane materials of PVA/PAA,KMS-1@PVA/PAA,KMS-2@PVA/PAA and KTS-3@PVA/PAA all conform to the pseudo-second-order kinetic model and are mainly controlled by chemical interaction,and the adsorption of uranium by the four membrane materials is more consistent with the Langmuir adsorption isotherm model,and the theoretical maximum adsorption capacity is 59.38 mg/g,182.49 mg/g,182.49mg/g,213.15 mg/g,and 196.86 mg/g,respectively.The adsorption of uranium by the four materials is a spontaneous endothermic process with an increase in entropy;the HCl solution of 1.0 mol/L has the best elution effect on uranium,all of which are more than 95.8%,and after repeated adsorption-elution for 5 times,the adsorption properties of the materials have only decreased by 10.4%,9.2%,14.2% and 12.0%,respectively.In the membrane separation experiment,the three kinds of nanofiber membranes KMS-1@PVA/PAA,KMS-2@PVA/PAA and KTS-3@PVA/PAA are more consistent with the dose-response model.The theoretical maximum uranium treatment capacity of adsorbents in the initial uranium concentration of 10mg/L is 234.78mg/g,254.18mg/g and 205.05mg/g,respectively.HAP/PVA/PAA,MMT/PVA/PAA and zeolite/PVA/PAA nanofiber membrane materials are greatly effected by p H,and the coexisting ionic strength has no effect on U(VI)adsorption,which shows that the complexation on the inner sphere surface is the main adsorption process.HAP/PVA/PAA,MMT/PVA/PAA and zeolite/PVA/PAA membrane materials all conform to the pseudo-second-order kinetic model,and the materials are mainly controlled by chemical.The adsorption of uranium by HAP/PVA/PAA,MMT/PVA/PAA and zeolite/PVA/PAA membrane materials is more consistent with the Langmuir adsorption isotherm model,and the theoretical maximum adsorption capacities are 159.76mg/g,170.53mg/g and 205.75 mg of HAP/PVA/PAA,MMT/PVA/PAA and zeolite/PVA/PAA,respectively.The adsorption of uranium is a spontaneous endothermic process with an increase of entropy.The desorption experiment of adsorbed uranium was carried out with the HCl solution of 1.0mol/L.After repeated adsorption-elution for 5 times,the adsorption properties of the materials only decreased from 96.7%,96.9% and 98% to 87.5%,77.9% and 90.4%,respectively. |
