Effect of Y(III) distribution between aqueous nitrate and organic D2EHPA solutions on the Y(III) precipitation stripping using oxalic acid.

The solvent extraction process of yttrium (III) from nitrate media by di(2- ethylhexyl) phosphoric acid (D2EHPA, represented as HA) has been studied as a first step to accomplish the homogeneous precipitation of yttrium oxalat e from an organic metal loaded D2EHPA solution. The analysis of liquid-liqu id distribution data at low metal concentrations determined YA(3).2HA as th e only metal organic species formed during the extraction, with a formation constant of log beta = 16.410 +/- 0.055. A polymerisation of such organic metal species was observed at high metal loading of the organic phase. A co mparison of these results with previous studies carried out in chloride or perchlorate media reveals a strong influence of the aqueous medium on the m etal species formed in the organic phase, affecting mostly the stoichiometr y of such species. The homogeneous precipitation of yttrium as yttrium oxal ate using oxalic acid has been carried out as direct recovery of the metal from the organic solution. The observed precipitation-stripping kinetics ha s been related to the formation of organic yttrium species. The acidity of the stripping solution and the oxalic acid concentration also affects the k inetics and the precipitation yield. The morphology and particle size distr ibution of the powders obtained support the mentioned influence of the prec ipitation-stripping kinetics.