Extraction Behavior of Sr (II) from High-Level Liquid Waste using Ionic Liquid Extraction System with DtBuCH18C6

The extraction behavior of Sr(II) from high-level liquid waste (HLLW) has been investigated using 4',4'(5')-di-(tert-butyl cyclohexano)-18-crown-6 (DtBuCH18C6) as an extractant in combination with three types of ionic liquids, [C_nmim][NTf₂] (n = 2,4,6) as solvents, where [C_nmim]⁺ is 1-alkyl-3-methylimidazolium and [NTf₂]^- is bis(trifluoromethylsulfonyl)amide. DtBuCH18C6 in the [C_nmim][NTf₂] system can be used as a good choice for matching, and a higher D_Sr can be achieved. Within the acidity range studied, the D_Sr follows the order of [C₂mim][NTf₂] > [C₄mim][NTf₂] > [C₆mim][NTf₂]. In their extraction systems, D_Sr decreases with increasing concentration of HNO₃ in the aqueous phase. Thermodynamic parameters for the extraction of Sr(II) tested elements were calculated using the Van't Hoff equation, showing that the reaction is spontaneous and exothermic. Existence of inorganic salts such as KNO₃ usually reduces E_Sr for all systems, and the decreasing degree is much larger than that of NaNO₃. The extraction systems exhibited high extraction efficiency and high selectivity for Sr(II) from simulated HLLW containing 25 typical elements and 2M HNO₃. From the results, the DtBuCH18C6 in [C_nmim][NTf₂] system may provide an alternative for extraction of Sr(II) under HLLW conditions.