Extraction mechanism and γ-radiation effect on the removal of Eu3+ by a novel BTPhen/[Cnmim][NTf2] system in the presence of nitric acid

Abstract

The extraction mechanism of 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-1,10-phenanthroline (BTPhen) in combination with 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides ionic liquids ([C_nmim][NTf₂], n = 2, 4, 8) in the presence of nitric acid is studied by using Eu³⁺, which has similar properties to trivalent actinides. The dominant complex compound forming between BTPhen and Eu changes from [Eu(BTPhen)₂(NO₃)]²⁺ to [Eu(BTPhen)(NO₃)₃] gradually with the increase of [HNO₃] or the length of the alkyl chain in the [C_nmim]⁺, indicating that the main extraction mechanism of BTPhen/[C_nmim][NTf₂] varies from a cation exchange mechanism to a neutral species mechanism. The irradiation of BTPhen in solid state has no effect on the extraction of Eu³⁺. The abnormally enhanced removal of Eu³⁺ was observed in irradiated BTPhen/[C₂mim][NTf₂] system with 0.1 M nitric acid, and it was attributed to the formation of precipitates between Eu³⁺ and trace radiolytic products of [C₂mim][NTf₂], which could be recovered by water washing before extraction. The extraction of Eu³⁺ was slightly changed for the irradiated BTPhen/[C₂mim][NTf₂] system with 1 M nitric acid, demonstrating good radiation stability of this novel extraction system.