SYNERGISTIC EFFECTS IN SOLVENT-EXTRACTION SYSTEMS BASED ON ALKYLSALICYLIC ACIDS. III. EXTRACTION OF THE TRIVALENT LANTHANIDES AND YTTRIUM FROM CHLORIDE MEDIA IN THE PRESENCE OF DIALKYL AND DIARYL SULPHOXIDES

Abstract

ABSTRACT DialkyI and diaryl sulphoxides were found to cause synergistic shifts in the pH50 values for the extraction of the trivalent lanthanides and yttrium from sodium chloride media by solutions of alkylsalicylic acids in xylene. The extent of the synergistic shift for a given sulphoxide increases with increasing steric bulk of the alkylsalicylic acid used. With the homologous series of dialkyl sulphoxides R2SO, where R = n-butyl, n-hexyl, and n-octyl, there is little variation in the size of the synergistic shift for a given alkylsalicylic acid. For a series of sulphoxides containing similar numbers of carbon atoms, the extent of the shift increases with the introduction of alicyclic rings, but decreases when aromatic rings are introduced, for example, in the order of R: cyclohexyl > n-hexyl > phenyl, although the effect is not very marked. For a given extractant mixture, the pH50 values decrease from lanthanum to samarium and then increase from samarium to lutetium. The separation between the pH50 values for lanthanum and lutetium increases with increasing steric bulk of both the alkylsalicylic acid (HA) and the sulphoxide (L), but the separations between adjacent lanthanides are in all cases too small to be of any practical use. Slope-analysis treatment of metal-distribution data, and measurements of the solubility of the neodymium-alkylsalicylic acid complex in xylene solutions of the sulphoxides are consistent with the extraction of a mixed-ligand complex of the type NdA3L2.