Separation of lanthanum(III) and barium(II) as their thenoyltrifluoroacetone complexes with dibenzo-18-crown-6 by means of synergistic extraction.

A new method for the separation of lanthanum(III)and barium(II)as their thenoyltrifluoroacetone(TTA)complexes with dibenzo-18-crown-6(DB18C6)in o-dichlorobenzene has been established by means of synergistic extraction and back-extraction combined with inductively coupled plasma atomic emission spectrometry(ICP-AES).When the mixtures of La(III)and Ba(II)were extracted for 5min at pH 4.5, only lanthanum(III)was extracted quantitatively, whereas barium(II)remained in the aqueous phase.After the phases were separated, barium(II)was extracted quantitatively for 5min at pH 7.9 again.Then, the two phases were each shaken with 0.1M HCl in order to back-extract lanthanum(III)and barium(II)from the organic phases;both metal ions were determined by ICP-AES.In the process, lanthanum(III)and barium(II)TTA chelates in o-dichlorobenzene formed stable adducts with DB18C6(La(TTA)3·nDB18C6 and Ba(TTA)2·nDB18C6, n=0-2).The stability constants(βn)of the adducts determined by means of curve-fitting method were log β1=3.7 and log β2=5.9 for lanthanum(III), and log β1=3.8 and log β2=7.9 for barium(II).The extraction constant(log K)of lanthanum(III)adduct was −3.7.