| Polymer inclusion membranes(PIMs)have much application potential for the separation and purification of metal ions.However,its selectivity is largely dependent on the extractant.In addition,highly selective extractants are very limited,and the synthesis of new extractants is difficult,which limits the practical application of polymer inclusion membrane in the field of selective separation of metal ions.In this study,a new technique was proposed to improve the selectivity of PIM separation process by adding complexing retardant to metal ion mixture solution.At the same time,the mechanical properties of conventional PIM films are poor and easy to be broken,which limits their industrial applications.In this thesis,a new type of polymer containing composite membrane(PIM composite membrane)based on Polytetrafluoroethylene(PTFE)membrane is preparationed to improve the mechanical properties of the membrane and the antiloss ability of the membrane.PIM composite membrane makes up for the poor mechanical properties of conventional PIM membrane and provides a new idea for the strengthening of PIM membrane materials.The specific research content includes the following three parts:(1)In order to reveal the retardant enhancement mechanism,a new mass transfer mathematical model was established.Contrast experiments showed that the complexing retardant could significantly improve the overall separation coefficient βoverall.The βoverall,exp of a blank experiment using a conventional PIM system for Zn2+ and Cu2+was 61.8,while βoverall,exp increased to 853.4 after the retardant was added.This confirms that the complexing retardant has a significant enhancement effect on the selectivity of PIM for the separation of Zn2+and Cu2+.That is,complexing retardant(e.g.,citric acid)selectively inhibit the migration of impurity ions(such as Cu2+)in the raw material solution,thus improving the separation effect of PIM.In addition,in order to carry out subsequent simulation and optimization studies of different experimental conditions in the enhanced PIM system,the key model parameters under these different experimental conditions were experimentally predicted.The main model parameters experimentally determined include the partition coefficient and film thickness.(2)In order to optimize the PIM system strengthened by retardant,the effects of complexing retardant concentration,initial pH of feed solution,film thickness,extractant dosage,plasticizer dosage and other factors on the separation performance of the system were studied through experiments and modeling.Model calculation results agreed well with the experimental data.The maximal βoverall,exp 17525.7 was obtained at the optimal PIM separation conditions of[CA]f,0=0.02M,pHf,0=4.5,[H2SO4]s,0=0.5 M,and the optimal composition of the PIM casting solution,i.e.,PVC:P507:DBP:THF=0.125 g:0.125 mL:0.032 mL:10 mL.Further studies indicated that the retardant mechanism was reflected in the difference increase of partition coefficients PZn2+,f and PCu2+,f at the interface between the feed solution and the membrane.Through an analysis of the relationships of conditions,parameters,and separation effects,the optimization strategies of the separation effects for the retardant-enhanced PIM system are discussed in depth.(3)In order to improve the mechanical strength of the membrane,a new PIM composite membrane was prepared and its mechanical properties and separation performance were investigated.The mechanical properties and separation properties of PIM composite membrane materials were investigated by means of SEM,FT-IR,tensile and rupture strength representation,metal ion membrane separation efficiency and membrane reuse tests.The effects of extractant dosage,plasticizer dosage and film thickness were discussed.In addition,conventional PIM was prepared under the same conditions,and the two membranes were compared.The results showed that PIM composite film had better tensile properties and tensile strength than conventional PIM film.And its rupture strength value is higher,can withstand a pressure of more than 0.2 MPa.On the contrary,most of the rupture strength of conventional PIM films measured is less than 0.2 MPa.In the separation effect test,the conventional PIM membrane has a faster diffusion rate of metal ions.However,in the reuse experiment,the stability and reusability of the PIM composite membrane were significantly better than that of the conventional PIM membrane.The above results show that the new PIM composite membrane has a greater performance improvement in mechanical strength and separation stability compared with the conventional PIM membrane.In addition,complexing retardant can significantly improve the selectivity of PIM composite films to Zn2+ and Cu2+.In this paper,the method of improving the selective separation ability of PIM membrane with complex blocker and the preparation of new PIM composite membrane with good mechanical properties are proposed,which is expected to provide a new technical idea for highly selective separation of metal ions. |
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