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 solutions and organic solutions of di(2-ethylhexyl)phosphoric acid, D2EHPA, in kerosene has been examined as a function of various chemical parameters 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 concentration may be explained by the formation of two organic metal species, YA3·2HA and YA3·HA (HA refers to D2EHPA). Equilibrium constants have been determined and they are compared with corresponding constants in nitrate media and with results reported in the literature. Possible mixed extracted complexes containing chloride were rejected by the numerical calculations. Such prediction was confirmed by separate analysis of the chloride content in the organic phase. When the metal concentration is increased, the system shows a major complexity which is attributed of 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 of polymeric metal complexes.