| Rare earth metal is an indispensable strategic resource in modern times and known as"industrial vitamin".It has a wide range of applications in the fields of aviation,automobiles,household appliances and the defense industry.With the continuous exploitation of rare earth resources in China,the rare earth grade in the ore is extremely low.However,conventional enrichment extraction methods such as precipitation and solvent extraction can cause disadvantages which produce high impurity content and impure product.Therefore,it is necessary to explore a new low-concentration rare earth enrichment extraction method.The microemulsion membrane method has the characteristics of fast mass transfer rate and large enrichment ratio,which is a research hotspot of rare earth extraction.In recent,the research on ionic liquid microemulsions constructed by ionic liquids in combination with or in place of microemulsion components has made great progress in domestic and abroad.It can solve the limitations of the traditional microemulsion system for the enrichment and separation of rare earths,possessing the special properties of ionic liquids and microemulsions at the same time,which has good application prospects in the fields of medicine and material preparation,but there are few studies in the field of extraction.In this paper,ionic liquid microemulsions of different systems were constructed,and the prepared ionic liquid microemulsion was applied to the research field of rare earth enrichment and separation.The extraction behavior of light rare earths(La3+,Ce3+,Pr3+,Nd3+,etc.)was investigated.It not only broadens the application range of ionic liquids,but also plays an important role in the development of new research fields of microemulsion extraction and the improvement of low concentration rare earth extraction chemistry.Results were shown as below:(1)OP-4+OP-7/benzyl alcohol/kerosene/P204/[Omim][BF4]/HCl microemulsion system was prepared.The microemulsion structure was characterized by surface tension and FTIR,and the system was applied to the light rare earth extraction and separation.The results showed that the critical micelle concentration of[Omim][BF4]in HCl was 0.226%;with the increase of the water phase content,the vibration peak position of O-H bond moved to high frequency region,and the bound water content increased.The ionic liquid microemulsion system was used as the organic phase to study the extraction and separation of La3+,Ce3+,Pr3+and Nd3+under the same experimental conditions.When the concentration of[Omim][BF4]was 3.71%,the concentration of feed solution was 0.004mol/L,volume ratio of feed solution to microemulsion was 3:1,pH=3,t=8min,and the maximum extraction rates of La3+,Ce3+,Pr3+and Nd3+were respectively 97.5%,92.5%,92.11%and 84.81%.In addition,when the concentration of[Omim][BF4]was 3.7%,the volume ratio of feed solution to microemulsion was 5:1,and pH=3,the separation coefficient of La3+ and Ce3+could reach a maximum of 5.5;the concentration of[Omim][BF4]was 3.7%,the volume ratio of feed solution to microemulsion was 4:1,and pH=4,the separation coefficient of Pr3+ and Nd3+could be a maximum of 4.5.(2)OP-10/benzyl alcohol/cyclohexane/P204/[Omim][BF4]/HCl microemulsion system was prepared.The structure and extraction mechanism of the microemulsion were characterized by conductivity and FTIR.And the system was applied to the rare earth extraction.The research showed that the system became a W/O structure when the concentration of the aqueous phase was low;the mechanism of[Omim][BF4]for extracting RE3+ might be that RE3+and the hydrogen ion of imidazole ring C-H undergo electrophilic substitution reaction formed C→RE complex.In the extraction experimental study,the optimal extraction conditions for Sm3+:when[Omim][BF4]concentration was 5.84%,the concentration of the feed solution was 0.004mol/L,volume ratio of feed solution to microemulsion was 2:1,pH=4,t=15min.Under the condition,the extraction rate was 87.39%.In addition,the results of the study of[Omim][BF4]replacing single component showed that[Omim][BF4]could be used as surfactant,organic solvent and extractant in this system.La3+was extracted by an ionic liquid microemulsion system consisting of[Omim][BF4]/benzyl alcohol/HCl.In the extraction experiment,the optimal extraction conditions for La3+:when the concentration of the feed solution was 0.004mol/L,volume ratio of feed solution to microemulsion was 2:1,pH=5,t=15min.Under this condition,the extraction rate could reach more than 85%.(3)Adopting separately[Omim][BF4],[Omim]Cl and[Omim][PF6]replaced the organic solvent of CTAB/n-butanol/n-octane/HCl system to finish preparation of ionic liquid microemulsion.The results showed that only[Omim]Cl could replace the organic solvent with CTAB/n-butanol/HCl to form ionic liquid microemulsion system,and could use this system to extract La3+,when the concentration of the feed solution was 0.004mol/L,volume ratio of feed solution to microemulsion was 2:1,pH=3,t=15min.Under this condition,the extraction rate was up to 34%. |
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