Design, Synthesis And Characterization Of Phosphine-functionailzed Ionic Liquids And Application For Extraction Of Rare-earth

In recent years, rare-earth elements (REEs) have been regarded as vitally important mater-ials in many high-tech applications, such as lasers, optic data transmission, superconductor,magnetism, etc. The recovery of REEs is essential for an efficient use of RE resources. Devel-oping a new extraction system for the REEs extraction and separation is important.In this art-icle, design, synthesis and characterization of phosphine-functionailzed ionic liquids (PFILs)and their application for extraction of rare-earth Nd(Ⅲ) have been investigated.(1) Preparation of alkyl imidazoles:1-(β-cyanoethyl) imidazole was obtained by mixingacrylonitrile and imidazole in methanol as a solvent.1-bromoalkane was added to the reactionsolution, to give the N-alkyl-imidazoles bromide by the quaternization, followed by givingN-propyl imidazole, N-butyl-imidazole and N-pentyl-imidazole byelimination reaction inalkaline solution. Three products were characterized by1H NMR, MS and FT-IR spectrum.(2) Preparation of3-bromopropyl phosphine oxides: Dichlorophenylphosphine or chlorodi-phenylphosphine and ethanol were mixed to give two products—diethyl phenylphosphoniteand ethyl diphenylphosphinite by nucleophilic substitution reaction. Then triethyl phosphite(Commercially available), diethyl phenylphosphonite or ethyl diphenylphosphinite respecti-vely were mixed with1,3-dibromopropane to give3-bromo-propyl phosphonate,3-bromo-propyl phenyl ethoxylphosphine oxide and3-bromopropyl diphenylphosphine oxide byArbuzov reaction.The structure of three complexes was characterized by31P NMR,1HNMR,13C NMR, FT-IR and MS spectra.(3) Preparation of PFILs: Under microwave assisted conditions, alkyl imidazole or triethyl-amine respectively were mixed withthree3-bromopropyl phosphine oxide, then anion excha-nge occurs by adding bis(trifluoromethylsulfonyl)amide lithium salt to give nine PFILswithsingleP=O functional group. In ethanol solution, imidazole reacted with3-bromo-propylpho-sphornate and then anion exchange occurs by adding Lithiumbis(trifluoromethanesulphonyl)-imide or potassium hexafluorophosphate salt to aqueoussolution, to give two PFILs with diff-erent anions and cations containing double P=O functional group of imidazole. PFILs werecharacterized by31P NMR,1H NMR and13C NMRand MS and FT-IR spectra.(4) PFILs application for extraction of rare-earth Nd(Ⅲ): Two ionic liquid which have out-standing extraction ability,(3-diethoxylphosphoryl)propyltriethylaminebi(trifluoromethanes-ulfonate)imide([TENP(OEt)2][Tf2N]) and1,3-bi-(3-diethoxylphosphoryl)-1-H-imidazole bi-(trifluoromethanesulfonate)imide([BDPPIm][NTf2]) were chosen for the extraction of Nd(Ⅲ)from eleven PFILs. Using these two PFILs as extractant respectively, wesystematically inve-stigated the effect of different diluents, extraction time, pH of initial solutionaqueous, conce-ntration of extractant,and temperature on the extraction efficiency of NdIIII), and the condit-ions of stripping and the mechanism of extraction. Extraction mechanism has been proposed.Base on the result of extraction of Nd(Ⅲ) by [TENP(OEt)2][Tf2N], some conclusions can bemade by follows:(1) Higher extraction percentage of Nd(Ⅲ) can be obtained in EtOAc.(2)Extraction equilibrium is fast to achieve.(3) The influence of pH values is notable; The pHvalues of initial aqueous solutions higher than1.6are favorable for metal extraction while theratio of stripping is more than97%at pH1.1.(4) The extraction process is exothemic andlower temperatures are preferable for extraction.(5) Preliminary studies show that the extrac-tion process may involve ion-pair mechanism. Base on the result of choosing [BDPPIm][NTf2]as extractant, some conclusions can be made by follows:(1) Higher extraction percentage ofNd(Ⅲ) can be obtained in EtOAc.(2) Extraction equilibrium is fast to achieve.(3) pH valueis a notable influence on extraction; Initial aqueous solutions with pH values higher than3.0are favorable for extraction while the ratio of stripping is haigher than99%at pH1.1.(4)Theextraction process is exothemic and room temperature is suitable for extraction.(5)Theextraction process may involve the ion-pair mechanism.