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Acidic esters of orthophosphoric acid as selective extractants for metallic cations—tracer studies

1958; Pergamon Press; Volume: 7; Issue: 3 Linguagem: Inglês

10.1016/0022-1902(58)80078-0

1878-1225

D.F. Peppard, G.W. Mason, W.J. Driscoll, R.J. Sironen,

Chemical Synthesis and Characterization

The extraction of Sc(III), Y(III), La(III), Pm(III), Tm(III), and Am(III) into solutions of (GO)PO(OH)2 and (GO)2PO(OH) in toluene as carrier solvent from aqueous mineral acid phases has been investigated as a function of solvent concentration in the organic phase, hydrogen ion concentration in the aqueous phase, the nature of G, and the position of M(III) in the periodic table, using the radioactive-tracer technique. The distribution ratio, K, defined for a given radioactive nuclide as its concentration in the organic phase divided by its concentration in the aqueous phase, has been found, for all of the M(III) examples studied, to have an inverse third-power dependency upon the hydrogen ion concentration in the aqueous phase in both the (GO)PO(OH)2 and (GO)2PO(OH) systems. The solvent dependencies have been found to be direct first-power in the (GO)PO(OH)2 systems and direct third-power in (GO)2PO(OH) systems. Since the (GO)2PO(OH) solvents have been shown to be dimeric, the extracted species is postulated as MIII{H[(GO)2PO2]2}3. The (GO)PO(OH)2 solvents have been shown to be polymeric. A postulated “dimer” mechanism of extraction suggests that the extracted species is MIII{H[(GO)PO3H]2}3. However, an alternative suggested “infinite polymer” mechanism of extraction seems equally likely. Specifically, solvents in which G is 2-ethyl hexyl, symbolized as EH, and para(1,1,3,3-tetramethyl butyl)phenyl, symbolized as Oø, have been investigated. In both the (GO)PO(OH)2 and (GO)2PO(OH) systems the Oø solvent shows a higher K than the EH solvent. In the Oø systems, the KS (an empirical stability constant) for the di-ester is higher than that for the mono-ester for each of the members of the vertical group Sc, Y, La, Ac. In the EH systems, the KS for the di-ester is the larger for Sc by a factor of approximately 30 and the smaller for Ac by a factor of approximately 10−5. In all of the systems that K (and KS) values are compressed toward the bottom of the group in the vertical group, Sc, Y, La, Ac, i.e. the ratio of the K (or KS) of oneelement to that of the element immediately below it decreases downward.