pH-Controlled Selective Separation of Neodymium (III) and Samarium (III) from Transition Metals with Carboxyl-Functionalized Ionic Liquids

Abstract

The recovery of rare-earth metals from waste materials is very important due to the risks associated with having a low supply of them in the future. In this work, hydrophobic 1alkylcarboxylic acid-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [(CH 2 ) n COOHmin][Tf 2 N] (n = 3, 5, 7), were synthesized and used to separate neodymium (III) from Fe(III) and samarium (III) from Co(II) in aqueous solutions. The factors affecting the solvent extraction process such as phase volume ratio, contact time, pH value of the aqueous phase, alkyl chain length of the ionic liquids, and temperature of the system were examined systematically. It was found that the maxmium extraction efficiency of the investigated metal ions was as high as 99%, and Sm(III) and Nd(III) could be selectively separated from Co(II) and Fe(III), with separation factors of 10 4 −10 5 , by simply modulation of the aqueous phase pH. After extraction, about 97% of the metal ions could be stripped from ionic liquid phase in a single stripping step by using dilute aqueous HCl or oxalic acid, and the ionic liquids would be recovered and reused in the next extraction process. These results indicate that the ionic liquids developed here are useful for the selective recovery of rare-earth metals from NdFeB and SmCo permanent magnets.

Complex Extraction of Metals in an Aqueous Two-Phase System Based on Poly(Ethylene Oxide) 1500 and Sodium Nitrate

“…By now, a sufficient number of papers have been published on the extraction of non-ferrous, rare-earth, and precious metals in heterogeneous systems without organic solvents based on polymers, surface active agents, and ionic liquids [17,18,19,20]. The results of studies have been summarized in reviews [12,21].…”

Extraction kinetics of mixed rare earth elements with bifunctional ionic liquid using a constant interfacial area cell

“…8 The inner synergistic effects of BILs for solvent extraction of metal ions using [tricaprylmethyl ammonium][di-2-ethylhexyl phosphinate] as extractant have been reported. [9][10][11] The results show that the extraction efficiency of REEs has been enhanced and the selectivity has been changed in the BIL system. Other advantages, such as avoiding saponication wastewater from the application of acidic extractants, low acidity for extraction and good interfacial phenomena, have emerged.…”

Recovery of Rare Earth Elements (REEs) Using Ionic Solvents

“…TSILs bearing a carboxylic group have been proposed, such as hydrophobic [1-alkyl-3-(1-carboxylpropyl)im] [PF6], which requires saponification to be considered for the extraction of yttrium [186]. Chen et al described a pH-controlled selective separation of Nd(III) from Fe(III) by using carboxyl-functionalized imidazolium ionic liquids [C1(CH2)nCOOHim] [NTf2] (n= 3, 5, 7) as the solvent and complexing agent [187]. Taking advantage of carboxylic acids for the extraction of REEs, a carboxyl-functionalized phosphonium IL [P444C1COOH]Cl showed good extraction properties for scandium in an aqueous biphasic system (ABS) [188].…”