Preparation Of Polyamide Nanofiltration Membrane Modified By Carbon Quantum Dots And Its Enrichment Of Rare Earth Elements

With the development of economy,the content and types of toxic and harmful substances in sewage are increasing,which has a serious impact on the ecological environment.In the process of mining ionic rare earth ores,there will be a large number of leaching waste water,which contains low concentration of rare earth ions and heavy metal ions,which will cause serious environmental pollution and waste of resources.Compared with conventional treatment methods,nanofiltration membrane technology has natural advantages in the process of rare earth ion enrichment and recovery due to its own permeability selection characteristics.However,the polymer nanofiltration membrane has the disadvantages of small flux and easy to be polluted.In order to better apply in the field of ion-based rare earth recovery,this study modified the nanofiltration membrane.Carbon quantum dots?CQD_S?were added to enhance the performance of nanofiltration membrane in order to reduce pollution and recycle resources.The main research is as follows:?1?Preparation of ultrafiltration membrane.The ultrafiltration membrane was prepared by phase transformation method.The composition of casting solution was determined to be 17 wt%polysulfone?PSF?,5 wt%polyvinylpyrrolidone?PVP?and4 wt%polyethylene glycol?PEG?.The ultrafiltration membrane was prepared by phase inversion after stirring at 60?for 12 h at 450 r/min.Under the condition of0.1 MPa operation,the pure water flux of ultrafiltration membrane is 262.91 L/?m²·h?,and the flux and rejection of BSA solution are 58.37 L/?m²·h?and 98.39%,respectively.?2?Preparation of nanofiltration membrane modified by carbon quantum dots?CQD_S?.CQD_S was used as an additive in aqueous phase to study the effect of different concentration of CQD_S on the selective permeability of nanofiltration membrane.The results show that the surface of nanofiltration membrane becomes smoother with the addition of CQD_S.When the concentration of CQD_S is 0.003 wt%,the roughness of nanofiltration membrane is the lowest,which is beneficial to alleviate the process of membrane pollution.With the increase of concentration,the roughness of membrane surface becomes larger.Through zeta potential,FTIR,XPS and water contact angle analysis,it can be seen that the surface of CQD_S modified nanofiltration membrane has more hydrophilic groups such as hydroxyl and carboxyl groups,and the hydrophilicity of membrane surface is enhanced,while the electronegativity is decreased.At 0.003 wt%,the retention of Mg₂SO₄ and NaCl by modified nanofiltration membrane was the highest,89.8%and 43.2%,respectively.The comprehensive performance of flux and retention was better.In addition,the influence of the ratio of reagents on the retention of Magnesium Sulfate by nanofiltration membrane was also studied by orthogonal test.The results showed that the effect of the concentration of CQD_S on the performance of nanofiltration membrane was the most significant.The best concentration ratio was0.003 wt%of CQD_S,1.5 wt%of PIP and 0.2 wt%of TMC.?3?Using CQD_S modified nanofiltration membrane to enrich lanthanum ions in the tail water of ion-based rare earth leaching.At 30?and 0.6 MPa,the effect of nanofiltration membrane on the enrichment of lanthanum ions is better.Compared with unmodified nanofiltration membrane,the flux and retention of modified nanofiltration membrane are higher.The retention and flux of lanthanum ions in CQDS modified nanofiltration membrane were 97.30%and 27.95 L/?m²·h?,respectively.