Research On The Application Of Polymer Inclusion Membrane In The Separation And Transport Of Rare Earths

At present,solvent extraction is the most common separation method used in the industrial-scale separation of rare earth elements(REEs)in China because this process is mature,simple,and efficient.However,a large number of organic diluents consuming and high pollution problems with the solvent extraction technology limit its application in today's green production requirements.As a new green separation method,polymer inclusion membrane(PIM)is attracting attention in recent years.It is expected to be a supplement or alternative to traditional solvent extraction.The biggest advantage of this technology is the PIM system integrates the extraction and stripping process into one device and makes them carry out at the same time.Moreover,in the PIM process,the organic solvent like kerosene is not required and a much smaller amount of the extractant is needed.In this thesis,basic research on the application of PIM in REEs green separation was carried out.The PIMs composed of di(2-ethylhexyl)phosphinic acid(P227)as the carrier,poly(vinylidene fluoride)(PVDF)or cellulose triacetate(CTA)as the base polymer for the transport and selective separation of Lutetium(Lu(?))were studied.The PIM composed of primary amine N1923 as the carrier,CTA as the base polymer for the transport of scandium(Sc(?))was also studied.The research details were as follow:1.A novel PIM used for Lu(?)transport and separation consisting of 60 wt%PVDF and 40 wt%P227 was prepared by the selection of optimal proportions.SEM,AFM,TGA and ATR-FTIR were used to characterize this P227@PVDF PIM.In addition,the membrane was more effective for the transport of Lu(?)from the small pore side to the large pore side.It was also found that the difference in the PIM transport efficiency arises from the effects of carrier content,temperature,stirring speed and stripping acidity.Furthermore,a dual-membrane transport apparatus was designed to further enhance the Lu(?)transport efficiency.The good stability and reusability of P227@PVDF PIM was finally verified by the successive cycles transport experiments.2.Based on the high-efficiency transport of Lu(?)by P227@PVDF PIM,the selective separation of Lu(?)from La(?)and Sm(?)using this PIM was studied in this part.The PIM was used to selective transport Lu(?)from hydrochloric acid feed solution containing similar concentration of La(?)and Sm(?)by adjusting the feed solution pH to 1.5.The selective transport efficiency when the pH of the feed solution was 4 was also compared.The changes in surface morphology,thickness and water contact angle of PIM with different polymer concentrations were investigated.Furthermore,a process for regenerating PIM was first proposed and implemented.By comparison of the regenerated PIM with the normal PIM,there was almost no difference in the SEM image,ATR-FTIR spectrum and Lu(?)transport efficiency.3.A PIM containing P227 as the carrier,2-nitrophenyloctyl ether(NPOE)as the plasticizer,and cellulose triacetate(CTA)as the base polymer was prepared.The selective separation and transport performance of this P227/NPOE@CTA PIM was investigated.The chemical,physical and morphological characterizations of PIMs were investigated by SEM,TG,FTIR and water contact angle measurements in detail.The extraction and stripping performance of this P227/NOPE@CTA PIM was compared with the CTA-based PIMs containing other popular acidic organophosphorus extracts(P204 and P507).In addition,the influence of the plasticizers on the transport performance was studied.The transport and separation efficiency of Lu(?)from other REEs ions using the P227/NOPE@CTA PIM under different pH value of feed solution were also compared and discussed.Finally,to investigate the stability and reusability of this PIM,a cyclic transport experiment was carried out.4.On account of its low acidity requirement for Sc(?)stripping,N1923 was selected as the extractant carrier to prepared a CTA-based PIM.The transport performance of Sc(?)by this PIM was preliminarily studied.To characterize the PIM,SEM and ATR-FTIR were used.A comparison was made of the addition of NPOE in PIM,and it was found that NPOE in the PIM could prevent hydrogen ions from diffusing into the feed solution.Combining the results of the stripping acid type and stripping acidity experiments,it was determined that the most suitable stripping solution for Sc(?)transport under this experimental conditions was 1 mol L-1 hydrochloric acid.