SYNERGISTIC EXTRACTION OF RARE-EARTH ELEMENTS BY TRI-NORMAL-OCTYLMETHYLAMMONIUM NITRATE AND BETA-DIKETONE

The synergistic extraction of rare-earth nitrates was studied, using tri-n-octylmethylammonium nitrate (TOMAN) and beta-diketone (alpha-acetyl-m-dodecylacetophenone: LIX54 and alpha-perfluoro-alkanoyl-m-dodecylacetophenone: LIX51) in xylene as extractants and ammonium nitrate as salting-out agent. The capability of this mixed extractant is essentially identical to that of TOMAN alone in the range of pH = 2-3. With increasing pH a strong synergism appeared, and the degree of adduct complex formation became greater with position in the atomic number series. The extraction of heavier element is, thus, most favored at pH = 6 and least favored at pH = 2. The mixed adducts involved in the extraction were identified as Ln(NO3)2R.5S, Ln(NO3)R2.4S and their aggregates as Ln(NO3)3Ln(NO3)2R.5S and Ln(NO3)3Ln(NO3)R2.4S, where R: anion of beta-diketone and S: monomer of TOMAN. The fraction of adducts containing two molecules of beta-diketone increases with increasing atomic number of the element.