SYNERGISTIC EXTRACTION OF LANTHANIDES(III) BY TRIOCTYLMETHYLAMMONIUM NITRATE AND TRIBUTYL-PHOSPHATE

The synergistic action of tributyl phosphate in the extraction of La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Dy(III), Ho(III), Er(III) and Y(III) with trioctylmethylammonium nitrate was studied. The synergistic effect is diluent dependent. It is pronounced with a mixed dodecane/xylene diluent, and is weak with mixed heptane/xylene and hexane/xylene diluents as well as with pure xylene diluent. Two or three synergistic complexes are formed simultaneously in the organic phase. Their composition is (A+)(Ln(NO3)4.2B-), (A+)(Ln(NO3)4.3B-), and (A+)2(Ln(NO3)5.B2-) (Ln is a lanthanide(III), A+ is a trioctylmethylarnmonium cation and B is a tributyl phosphate molecule). The stability of the synergistic complexes generally decreases with increasing atomic number of the lanthanides(III). The synergism enhaces the efficiency of the lanthanide(III) extraction with trioctylmethylammonium nitrate, but deteriorates its selectivity. The separation factors for the Pr(III)-Nd(III) and Eu(III)-Gd(III) pairs are gradually suppressed at increasing concentration of tributyl phosphate.