Complexation and extraction investigation of rubidium ion by calixcrown-C2mimNTf2 system

When the ionic liquid (IL) C(2)mimNTf(2) was used as solvent, Rb+ in neutral aqueous solution was successfully extracted by bis(2-propyloxy)calix[4]crown-6 (BPC6) with high efficiency. The crystallographic data and electrospray ionization mass spectra indicated that BPC6 could form the 1:1 complex with Rb+. Due to a cation exchange mechanism, the addition of NTf2- into aqueous phase was able to improve the extraction efficiency of Rb+, while the extraction was restrained with the addition of C(2)mim(+). With respect to the mixed solution of RbCl and KCl, the molar ratio of K+ to Rb+ decreased remarkably after extraction by using BPC6/C(2)mimNTf(2). The Rb+ in ILs could be stripped into aqueous solution with NH4Cl as back-extractant. Thus, it is believed that Rb+ can be effectively concentrated from the mixed solution of Rb+ and K+ through an extraction-stripping procedure.