SYNERGISTIC EFFECTS IN SOLVENT-EXTRACTION SYSTEMS BASED ON ALKYLSALICYLIC ACIDS .1. EXTRACTION OF TRIVALENT RARE-EARTH-METALS IN THE PRESENCE OF ALIPHATIC AMIDES

Aliphatic carboxylic acid amides were found to cause synergistic shift s in the pH(50) values for the extraction of the trivalent rare-earth metals from chloride media by solutions of alkylsalicylic acids in xyl ene. For the different types of amide examined, the synergistic shifts for the extraction of neodymium by 3,5-diisopropylsalicylic acid (DIP SA) generally decrease in the order : R.CO.NR(2)' > R.CO.NHR' > R.CO.N H2, where R and R' are alkyl groups. With the N,N-dialkyl amides (R.CO .NR(2)') and the N-alkyl amides (R.CO.NHR'), the extent of the synergi stic effect decreases with increasing chain-branching in either of the alkyl groups R and R'. For additions to 0.25 M alkylsalicylic acid, t he synergistic effect increases with concentrations of up to 0.1 M ami de, and decreases with higher concentrations. The extent of the synerg istic shift produced by a given amide, as well as the separation in PH 50 values from lanthanum to lutetium, increases with increasing steric bulk of the alkylsalicylic acid used. The separations between adjacen t lanthanides are too small to be of any practical interest, however. Measurement of the solubility of salicylic acids (HA) in xylene contai ning various amounts of N,N-dialkyl amide (L) indicate that essentiall y complete formation of the HA.L adduct takes place. Treatment of meta l-distribution data by slope analysis, and measurement of the solubili ty of the neodymium-DIPSA complex in xylene in the presence of amide s uggest that the mixed-ligand complex has the stoichiometry NdA(3)L(2).