Study On The Boron-removing Performance Of Waste Water In Nuclear Power Plant With Reverse Osmosis

Membrane separation technology is a new and efficient separation technology.Because of its characteristics of no phase change,low energy consumption,high decontamination coefficient,good quality of effluent,simple equipment and convenient operation,membrane separation technology is widely applied to all kinds of wastewater treatment.In this paper,firstly,how to use reverse osmosis membrane technology to improve the removal rate of boron in radioactive waste water from nuclear power plant has been studied.A commercial reverse osmosis membrane unit was set up in the experiment.The RO(TW30-1812-50)membrane was selected to remove boron in the radioactive boron containing wastewater.The effects of the independent membrane elements,pH,sorbitol and mannitol complex on the retention were investigated in detail.The retention rate of boron in solution increases with the increase of pH value.When pH value is 11,the retention rate of boron in solution is the highest,which is 76.1%.When sorbitol and control substance ratio was 1:1,the rejection rate was the highest,which was 44.6%.When mannitol and control substance ratio was 1:1,the highest rejection rate was 30.81%.It can be seen that the two complexes have the highest retention rate of boron when the mass ratio is 1:1,and when the amount of material is same,sorbitol is more efficient than mannitol,but it only reaches 44.6%.It can be seen that the commercial reverse osmosis membrane has a low rejection rate,and there are more radioactive elements in the nuclear waste water.The change of conditions may cause secondary pollution.Therefore,developing a new high-performance reverse osmosis membrane has become the focus of this stage.In order to solve the above problems,a new polyethersulfone RO composite membrane was prepared and the performance test was carried out.The pure water flux and the interception rate of the membrane were analyzed.The polyethersulfone membrane was prepared by impregnation precipitation phase transformation method,and the sulfonated polyethersulfone infiltration liquid and basement membrane were prepared.The new polyethersulfone RO composite membrane was prepared by the pulling method in sulfonation polyethersulfone.At the same time,the concentration of polymer,the time of infiltration,the concentration of wetting liquid and the method of drawing are changed,and the optimum preparation conditions are studied.Further 2 MPa pressure was applied to prepress 30 min for the composite membrane,and the NMP of cast membrane solution was chosen to test the performance of the composite membrane.The results showed that when the polymer concentration was 20%,the infiltration time was 50 s and the polymer concentration of the infiltration solution was 7%,the retention rate of boron was higher,which was 56.82%.The other was the characterization of the microstructure by scanning electron microscopy,the hydrophobicity characterization and contact angle measurement of commercial RO membrane and PES RO composite membrane and the charge,carries on the contrast analysis to the interception rate.It is found that the new polyethersulfone RO composite membrane has more compact and neat pore structure than the commercial RO membrane,and the pore size is smaller.The channel inside the membrane is narrower,indicating that the new polyethersulfone RO composite membrane has smaller water flux and higher rejection rate.The water contact angle test shows that the new polyethersulfone RO composite membrane has smaller contact angle than the commercial RO membrane,indicating that the new polyethersulfone RO composite membrane has better hydrophilicity than the commercial RO membrane.This may be due to precipitation in the application of immersion phase inversion membrane preparation process,the mass transfer between solvent and non-solvent is carried out at the same time as the change of the physicochemical properties of the polymer solution and the microscopic phase separation of the polymer solution.With the increase of polymer concentration in casting solution,the content of solvent will be reduced,resulting in the increase of the viscosity of casting solution.Therefore,during the phase transformation of impregnation and precipitation,the pore size of membrane surface will decrease,and the channel inside the membrane will also narrow,resulting in the decrease of water flux and the increase of rejection rate.By introducing sulfonic group,the hydrophilicity of the new polyethersulfone RO composite membrane can be improved,and the water molecules are easier to pass through the pore size of the membrane,and at the same time,it is more difficult for the pollutants to pass through the pore size of the membrane.In addition,due to the introduction of sulfonic group,the charge on the surface of reverse osmosis membrane changed,from the original electric neutrality to electronegativity,and repulsive force with negative electric borate ion,so as to improve the separation efficiency of reverse osmosis membrane.To sum up,the new polyethersulfone RO composite membrane shows a stronger separation performance than commercial RO membrane in the process of treating boron containing wastewater.The composite membrane prepared has potential application value in the treatment of nuclear power waste water.