AN EXTRACTION STUDY OF LANTHANIDE NITRATO COMPLEXES THE ADOGEN-464NO₃- NH₄NO₃SYSTEM.

Extraction of lanthanides and yttrium was studied in the interval of ammonium nitrate concentrations from 1 to 10M, and of Adogen-464 nitrate concentrations from 0·00039 to 0·39M. From the aqueous phase separation factor and from the published stability constant for Eu, stability constants for 1:1 complexes of La, Nd, Gd, Ho, Tm, Lu and Y have been determined, at 1M ammonium nitrate concentration. It was found that stability constant decreases from 2·7 for La to 2·3 for Lu. It has been shown that in the interval of Adogen-464 nitrate concentrations employed, lanthanides from La to Nd appear in the organic phase as 1:5 complexes, whereas lanthanides heavier than Nd appear also as 1:4 complexes. Relative values (with regard to lanthanum) of Gibbs energy, enthalpy (from the temperature effect) and entropy for formation of 1:5 complexes,and the position of yttrium within lanthanides have been determined. It is concluded from the experimental data that the extracted 1:4 and 1:5 complexes are of the inner sphere type, with nitrate ions acting as bidentate ligands, and that the contribution from covalency to bonding is the same in the aquo ion and in the 1:5 nitrato complex.

Hali tarjima qilinmagan