Orthogonal array design for the optimization of stripping Sr(Ⅱ) from ionic liquids using supercritical CO2

The strontium ions extracted from the aqueous phase into 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(CmimNTf2) with dicyclohexyl-18-crown-6(DCH18C6) was stripped effectively by supercritical CO(sc-CO).Hexafluoroacetylacetone(HFAA)-acetonitrile was found to be an excellent modifier of sc-COto enhance the stripping efficiency.In the orthogonal array design(OAD),OA(5~5)matrix was employed to optimize the stripping of Sr(Ⅱ) from the DCH 18C6-CmimNTfsystem.Effects of five experimental factors:temperature,pressure,concentration of HFAA,static and dynamic extraction times as well as each factor at five-levels on the stripping of Sr(Ⅱ) were optimized.The effects of these parameters were treated by the analysis of variance(ANOVA).The results showed that Sr(II) could be nearly 100%extracted from the IL phase at 308 K,30 MPa,40 min of dynamic extraction and 60 mmol·LHFAA in acetonitrile,respectively.Finally,the stripping mechanism was studied by ESI-MS.