Development And Application Of Nano-Modified Ultrafiltration Membrane For Mine Water Treatment

In the desalination process of mine water with high salinity,ultrafiltration-reverse osmosis is the most mature process method currently used,it has the advantages of no phase change,low operating cost and high separation efficiency.The ultrafiltration membrane needs to effectively retain the pollutants that are not completely removed during the pretreatment process of"coagulation-precipitation-multi-stage filtration" of mine water,as the front end of the reverse osmosis influent,to ensure that the water entering the reverse osmosis system is safe and reliable.However,further development of the process has been limited,due the membrane fouling problem caused by the hydrophobic properties of ultrafiltration membranes.In order to solve this problem,this paper starts from the perspective of membrane modification,and the morphology,structure and chemical properties of polyethersulfone（PES）ultrafiltration membranes were regulated by surface coating modification and blending modification to prepare nano-modified membranes,and analyze the antifouling mechanism of modified membrane in high salinity mine water.（1）The anti-fouling properties of ultrafiltration membranes were improved by surface coating modification.Molybdenum disulfide（MoS₂）and boron nitride（BN）nanoparticles were selected to modify the surface of PES ultrafiltration membrane.Taking typical organic compounds humic acid（HA）and bovine serum albumin（BS A）in mine water as target pollutants,the anti-pollution properties of the modified membrane were evaluated;The results show that,compared with the PES membrane,The HA flux recovery rates of PES/MoS₂ and PES/BN increased from 45%to 60%and 56%,respectively;The BSA flux recovery rate increased from 87.09%to 96.77%and 93.10%,respectively;Combined with the real mine water pollution fitting model,the results show that,the surface coating modification of nanoparticles can enhance the anti-fouling performance of the membrane,the electronegativity of the nanoparticles itself and the morphology of the coated membrane surface have a direct impact on its performance.（2）For the agglomeration behavior of nanoparticles in the process of blending membrane formation,the effects of MoS₂ nanoparticle modification conditions on the membrane formation kinetics and antifouling properties of the casting solution were investigated.MoS₂ was modified with polyacrylic acid（PAA）to prepare PES/MoS₂-PAA blend modified ultrafiltration membrane;The experimental results show that PAA modification can improve the hydrophilicity of MoS₂ and enhance the electrostatic repulsion and steric hindrance effect between nanoparticles,to inhibit its agglomeration in the process of blending membrane formation;The addition of MoS₂PAA to the casting solution can promote the solvent-nonsolvent exchange rate during the phase inversion process,accelerates the gelation rate during the membrane formation.Compared with the PES membrane,under the optimal modification conditions,the pure water flux of the modified membrane increased from 230L/（m²·h）to 359L/（m²·h）,this is because the addition of nanoparticles improves the porosity of the membrane and the interpenetration between the pores.The flux recovery rate of the modified membrane for HA increased from 61%to 90%,because MoS₂-PAA increased the hydrophilicity of the membrane surface;Combined with the agglomeration rate of MoS₂ and the kinetic theory of membrane formation of the casting solution,and the results of anti-pollution experimental data,it shows that the modification of MoS₂ can change the gelation rate of the membrane formation process and then affect the separation of the modified membrane.（3）For bacterial pollutants in mine water,improve the antibacterial properties of nanomodified ultrafiltration membranes.Inspired by marine organisms mussel adhesion proteins,the hydrophilic modification is completed by the self-polymerization of dopamine（DA）on the surface of MoS₂ nanoparticles to generate polydopamine（PDA）,the catechol group in PDA undergoes Michael addition and Schiff base reaction with polyethyleneimine（PEI）under weak alkaline conditions to obtain MoS₂-PDA-PEI nanoparticles,to prepare PES/MoS₂-PDA-PEI blend modified membrane;Compared with the PES membrane,the contact angle of the membrane surface decreased from 82.9° to 62.9°,indicating that the introduction of modified MoS₂ increased the hydrophilicity of the membrane surface;Compared with the PES/MoS₂,the roughness Ra of the modified membrane was reduced from 13.1 nm to 6.99 nm,indicating that the modification of MoS₂ increased its compatibility with the membrane matrix;At the same time,the pure water flux of the modified membrane increased from 230 L/（m²·h）to 364.28 L/（m²·h）,the HA flux recovery rate and the antibacterial rate of Escherichia coli were as high as 98%and 99%.It shows that the introduction of MoS₂-PDA-PEI improves the membrane porosity,reduces the roughness of the membrane surface,and effectively improves the flux and antibacterial and antifouling properties of the membrane.（4）Aiming at the oil pollutants in mine water,the oleophobic performance of the ultrafiltration membrane is further improved.At the same time,the PES membrane matrix and MoS₂ were modified;Firstly,a polyethersulfone/sulfonated polysulfone（SPSF）membrane matrix with a hydrophilic functional group-SO₃H was synthesized,its structure is regulated by changing the molecular weight and concentration of polyethylene glycol（PEG）porogen in the casting solution.At the same time,the use of tannic acid（TA）instead of PD A to reduce the cost,and to coordinate deposition with Cu²⁺to modify MoS₂;On the one hand,the sulfonic acid groups in the membrane matrix can increase the electronegativity of the membrane surface,and produce electrostatic repulsion to negatively charged mine water pollutants,on the other hand,the introduction of TA not only increases the hydrophilicity of the modified membrane and forms a more stable hydration layer on the membrane surface,but also has a coordination reaction with Cu²⁺,which enhances the antibacterial properties of the modified membrane and interacts with the membrane matrix.The experimental results show that the pure water flux of the PES/SPSFMoS₂-TA@Cu²⁺is as high as 459 L/（m²·h）,and the rejection rates of HA and BSA are as high as 95%and 98%,respectively.The flux recovery rates of humic acid and gear oil contamination were as high as 95%and 96.8%,respectively,and the antibacterial rate of Escherichia coli was as high as 95%,indicating that the hydrophilicity and electronegativity of the modified membrane were further enhanced can effectively improved the antifouling and bacteriostatic properties of the membrane.（5）The application effect of the modified membrane in the treatment of mine water was evaluated,and the fouling model was used to simulate and analyze the dynamic fouling process of the membrane;Using the XDLVO theory,according to the ion characteristics of mine water,taking HA as the target organic pollutant,the coupling fouling mechanism of pollutants to the membrane and the antifouling mechanism of the modified membrane were analyzed.The results show that the modification of the membrane makes the hydration layer effect and electrostatic repulsion effect around the membrane pores and the membrane surface,which helps to weaken the membrane fouling,and the introduction of-OH and-SO₃H hydrophilic functional groups can increase the polar force on the membrane surface to pollutants and increase their interfacial interaction energy,thereby improving the anti-fouling performance of the membrane.