SOLVENT-EXTRACTION OF YTTRIUM FROM CHLORIDE MEDIA BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID IN KEROSENE - SPECIATION STUDIES AND GEL FORMATION

The distribution of yttrium(III) between acidic aqueous chloride solut ions and organic solutions of di(2-ethylhexyl)phosphoric acid, D2EHPA, in kerosene has been examined as a function of various chemical param eters at constant aqueous ionic strength 2.0 M and different ranges of metal concentration. For low and middle metal concentration, 1.5 x 10 (-4)-2.587 x 10(-2) M (13-2300 mg l(-1)), the distribution of yttrium has been examined as a function of the extractant concentration and at fixed [H+] of 1.0 M. The distribution data has been analyzed by both graphical and numerical methods. The results for the low metal concent ration may be explained by the formation of two organic metal species, YA(3) . 2HA and YA(3) . HA (HA refers to D2EHPA). Equilibrium constan ts have been determined and they are compared with corresponding const ants in nitrate media and with results reported in the literature. Pos sible mixed extracted complexes containing chloride were rejected by t he numerical calculations. Such prediction was confirmed by separate a nalysis of the chloride content in the organic phase. When the metal c oncentration is increased, the system shows a major complexity which i s attributed to the formation of aggregates in the organic phase. For the highest metal concentration, a gel is observed to form under some of the experimental conditions. These results are discussed in terms o f polymeric metal complexes.