Study On The Treatment Of Simulated Uranium Containing Radioactive Waste Liquid Using Nanofiltration Membrane Separation Technology

A large amount of chemically toxic and radioactive uranium-containing wastewater is produced during the operation of nuclear power and the front and end of the nuclear fuel cycle,which not only pollutes the environment,but also affects human health.Membrane separation technology can selectively separate radionuclides from impurities through different driving forces.In the process of using nanofiltration membrane separation technology to treat wastewater,not only relying on pore size screening,but also electrostatic attraction/repulsion also play an important role.Therefore,interception effect on multivalent ions is better,and it is useful for removing divalent ions in radioactive wastewater.In this paper,the process of treating simulated uranium-containing radioactive wastewater by nanofiltration membrane separation technology is studied.Three kinds of nanofiltration membranes（NF270,NF60,NF30）were selected to filter the simulated radioactive waste water,which contained UO₂²⁺,Cu²⁺,Ni²⁺and Ca²⁺.Firstly,the rejection of nanofiltration membrane on single uranium solution was considered,and the influence factors of pressure were explored.Under the condition of lower pressure（0.5,1,1.5MPa）,the rejection of three nanofiltration membranes on uranyl ion was better,which were all above 85%.Moreover,the highest retention was achieved at 1 MPa,which were 98%（NF270）,96%（NF60）,and 97%（NF30）.The influence factors of p H were explored.When the p H was from 3 to 5,the retention increased gradually.When the p H is greater than 4,uranyl gradually precipitates,and the rejection is greater than 85%.In general,the retention of NF270 on UO₂²⁺is better than that of NF60 and NF30 among the three nanofiltration membranes,and the highest retention was achieved at p H=5.The effect of uranyl ion concentration was further explored.In the range of 0.1-100 ppm,the rejection of NF270 was better than that of NF60 and NF30membranes.With the increase of concentration,the rejection and flux showed a downward trend.Then,the nanofiltration membrane was used to treat the mixed solution,and the effect of Na Cl concentration on the rejection of uranyl ions was studied.By changing the salt concentration(0.5-50 g L^-1),NF270 has a rejection rate of uranyl as high as 92%The rejection of Ca²⁺,Ni²⁺,and Cu²⁺increased first with the increase of salt concentration,and then remained stable.In general,at different salt concentrations,the maximum rejection rate of Ca²⁺,Ni²⁺,and Cu²⁺by nanofiltration membrane NF270 was less than 65%,which was unsatisfactory.The separation layer of commercial nanofiltration membrane NF270 is aromatic polyamide,which contains carboxyl groups.The hydrolysis of the carboxyl groups will cause the membrane to be negatively charged and attracts multivalent cations.In order to improve the rejection on Ca²⁺,Ni²⁺and Cu²⁺,glutaraldehyde was used as a cross-linking agent,and m-Aminoacetanilide was grafted onto the surface of the nanofiltration membrane.Then,positively charged modified nanofiltration membrane was prepared.The nanofiltration membranes before and after modification were characterized and analyzed by scanning electron microscope and Fourier transform infrared spectrometer.The results proved that m-Aminoacetanilide was successfully grafted to the surface of NF270 separation layer.The effects of modifier concentration and time on the membrane rejection were investigated,and the optimum m ass fractions of glutaraldehyde and m-Aminoacetanilide were respectively 0.15%and 2%,and the optimal reaction time was 1.5 h.Under the optimum conditions,the rejection of UO₂²⁺Ca²⁺Ni²⁺and Cu²⁺were 96%,76%,82%and 71%,respectively.