The extraction behavior of several lanthanides (La3+, Eu3+, Lu3+) from nitric acid (HNO3) solution was studied using a novel extraction system based on 2,6-bis(5,6-dihexyl-1,2,4-triazin-3-yl) pyridine (isohexyl-BTP) as extractant in 1-alkyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide ([Cnmim][NTf2]) ionic liquid. Isohexyl-BTP in ionic liquids exhibited remarkably better extraction performance for lanthanides than that in octanol-dodecane (3:7 v/v) system. Lower HNO3concentration and short alkyl chain length of [Cnmim]+were more favourable for removal of lanthanides. Besides, it was confirmed that isohexyl-BTP in ILs formed a 1:3 complex [Ln(BTP)3(NO3)n](3-n)+(n=0, 1) by slope analysis. In addition, [C2mim][NTf2] preferred to extract lanthanides via a cation exchange mechanism at lower acidity, which was proved via UV-Vis measurement. It was speculated that extraction mechanism shifted from cation exchange to neutral species extraction with increase in HNO3concentration and alkyl chain length of [Cnmim]+due to the H+completion, NO3-inhibition and hydrophobicity of IL.
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