This review summarizes the preparation methods of support ionic liquids （SILs） and their applications in rare metals separation The rare metals separation includes the recovery of high value metal ions and the removal of heavy metal ions from wastewater. SILs can be used as a kind of highly efficient multifunctional separation materials. The preparation methods of SILs include chemical immobilization technique in which ILs moieties are supported on solid supports via covalent bonds and physical immobilization techniques in which ILs are immobilized on solid supports via physical method such as simple im- pregnation, sol-gel method. According to the difference of solid supports, this review summarizes the application of polymer supported ionic liquids （P-SILs）, silica based material supported ionic liquids （SM-SILs） and membrane supported ionic liq- uids （M-SILs） in rare metals separation, P-SILs and SM-SILs prepared by chemical method with N-methylimidazolium group can be used as highly efficient anion exchangers with high thermal stability and good chemical stability for adsorption of Cr（Ⅵ）, Re（Ⅶ）, Ce（Ⅳ）. P-SILs prepared via simple impregnation afforded IL functionalized solvent impregnated resins （SIRs） which showed high separation efficiency and selectivity in the separation of rare earths（Ⅲ） （REs（Ⅲ））. SM-SILs prepared via sol-gel method with IL doped in the support as porogens or extractant show high removal efficiencies and excellent stability for the separation of RE（Ⅲ）, Cr（Ⅲ） and Cr（Ⅵ）. M-SILs with IL as plasticizer or carrier show improved stability, high perme- ability coefficient and good selectivity for Cr（VI） transport. Different supports and different supporting methods were suffi- ciently compared. Based on the different practical application, different forms of SILs can be prepared for separation of rare metals with high separation efficiency and selectivity.
Uniform nanorods of rare earth phosphate(REPO_4, RE = La–Gd) nanocrystals were prepared in a properly designed ionic liquid extraction system by a stripping precipitation method. Rare earth ions were extracted into the organic phase at first; after that, the loaded organic phase was stripped by aqueous solution of PO_4^(3-) under stirring at room temperature within 5 min.The extractant used here is a bifunctional ionic liquid extractant called [A336][cyanex272]. The products are hexagonal phase in crystal structure, and their morphology is nanorods. The diameter of the products is from 30 to 50 nm, and the length increases from 200 nm to 2 μm gradually. Besides, the ionic liquid-absorbed CePO_4:Tb^(3+) nanorods show improved luminescent emitting intensity and lifetime. Based on the results, a possible growth mechanism of the REPO_4(RE = La–Gd) nanorods is proposed, where the extractants here also play roles of structure-directing agents and surfactants during the formation process of nanocrystals.
This paper reports on the selective transport of Lu(Ⅲ)from La(III)and Sm(III)through a polymer inclusion membrane(PIM)composed of 40 wt%di(2-ethylhexyl)phosphinic acid(P227)and 60 wt%poly(vinylidene fluoride)(PVDF).Basically,the changes in surface morphology,thickness and water contact angle of this PVDF-based PIM containing P227(P227@PVDF PIM)with different polymer concentrations were investigated.By solvent extraction experiments,it is found that Lu(Ⅲ)can be selectively extracted from La(Ⅲ)and Sm(Ⅲ)at pH 1.5 in hydrochloric acid solution.According to this result,P227@PVDF PIM was used to selectively transport Lu(Ⅲ)from hydrochloric acid feed solution containing similar concentration of La(Ⅲ)and Sm(Ⅲ).The recovery factor of Lu(III)is 91% after 36 h,and about 5%of Sm(Ⅲ)was also transported through the PIM.The concentration of La(III)in the feed solution and the stripping solution does not change.Furthermore,to overcome the ubiquitous decline of transport efficiency caused by the loss of carrier or the damage of membrane structure after long-term use of PIMs,a process for regenerating PIMs was first proposed and implemented.By comparison of the regenerated PIM with the normal PIM,there is almost no difference in the SEM image,ATR-FTIR spectrum and Lu(III)transport efficiency.It is expected that P227@PVDF PIMs have the potential to be applied to the grouped separation of rare earth elements(REEs),and this study also can be as an inspiration for the further study on the PIMs regeneration process.
The extraction of Ce（Ⅳ） in H2SO4/H3PO4 system was investigated systematically using bifunctional ionic liquid extractants（Bif-ILES） [A336][P507],[A336][P204] and [A336][C272] in n-heptane.The effects of H2SO4 concentration,extractant concentration and salting-out agent concentration were observed in detail.The extraction mechanism of Ce（Ⅳ） in H2SO4/H3PO4 system was obtained.The comparison with other extractants such as Cyanex923,TBP was also studied.Thermodynamic functions of the extraction reaction were calculated,showing that the extraction was an exothermic process.The separation of Ce（Ⅳ） from RE（Ⅲ） and Th（Ⅳ） was also investigated.The result indicated that Ce（Ⅳ） could be selectively extracted in this system.CePO4 nanoparticles were obtained in the process of stripping using H2O2 in H2SO4/H3PO4 system.X-ray diffraction（XRD）,scanning electron microscopy（SEM） and spectroscopy were adopted for the characterization of the sample.
Ionic liquid (IL) trihexyl (tetradecyl) phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL 104) was impregnated on XAD-7 resin. The solvent impreganated resin (SIR) was prepared and applied in Cr(VI) removal. The morphology and the thermal stability of the resins were explored. The effects of equilibrium time and initial pH value on Cr(VI) adsorption were investigated. Adsorption isotherm, separation and desorption of the SIR, and selectivity of SIR were also explored. The results show that Cyphos IL 104 exists in the inner XAD-7 resin, and the optimum pH value range of the SIR for Cr(VI) extraction is 0 to 2. When NaOH used as desorption solution, the Cr(VI) can be effectively desorbed from the SIR.
The kinetics of nitric acid leaching of cerium was investigated for the oxidation roasted Baotou mixed rare earth concentrate. The effects of leaching temperature, HNO_3 concentration, liquidesolid ratio(L/S)and stirring rate on rare earth extraction were studied. The XRD and SEM mapping analysis of the samples before and after acid leaching shows that the roasted bastnaesite is completely leached. Besides,the decomposition process of oxidizing roasting was also obtained by TGe MS and XRD. Different kinetics models were applied in this leaching process. The results of dynamic fitting show that the leaching process can be described by a new variant of the shrinking-core model. And the leaching rate is controlled by both the interfacial transfer and diffusion through the product layer. The apparent activation energy is calculated as 76.78 kJ/mol and the reaction orders with respect to HNO_3 concentrations and liquidesolid ratio are determined to be 7.609 and 2.516, respectively. Besides, an empirical rate equation is obtained to describe the process.
The current recovery technique of Sc was complicated and the chemical consumption was high,This was due to the low content of Sc in resources and the difficulty of stripping.In this research,the isooctanol was added into the 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester(P507)extraction system to reduce the extraction and improve the stripping of Sc.The maximum stripping ratio of Sc from loaded organic phase by sulfuric acid can increase from 10%(without isooctanol)to 99%(with 15 vol%isooctanol).In the extraction test of the simulated red mud leaching liquor,the separation factors between Sc and Zr,Sc and Ti are 36 and 350,separately.At the same time,other metals are almost not extracted.The high selectivity and stripping of Sc suggest that the P507 with isooctanol extraction system can be applied in the practical Sc recovery process.
Chuanying LiuLi ChenJi ChenDan ZouYuefeng DengDeqian Li
A new kind of hydrophobic ionic liquids [1-alkyl-3-（1-carboxylpropyl）im][PF6] has been synthesized, and their extraction.properties for Y（III） in the nitric acid medium was also investigated. The effects of extractant concentration, equilibrium pH of aqueous phase, salt concentration, temperature etc. were discussed. The results show that this kind of Task-Specific Ionic Liquid （TSIL） needs to be saponified before being used for the Y（III） extraction, and the extraction is-acid dependent,-and the extraction efficiency increases with the aqueous phase acldity decreasing. Furthermore, the loaded organic phase is easy to be stripped; more than 95% Y（III） could be stripped from the loaded organic phase when the stripping acidity is higher than 0.07 mol-L-1. The slope analysis technique is used to investigate the extraction mechanism, and a possible cation-exchange extraction mechanism is proposed in the oresent extraction system.
