Acidic esters of phosphonic acid as selective extractants for metallic cations-selected M(III) tracer studies

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The extraction of Pm(III), Cm(III) and Cf(III) from aqueous mineral acid phases of constant ionic strength into solutions of (G′O)(G)PO(OH) in toluene as carrier diluent has been investigated as a function of hydrogen ion concentration in the aqueous phase, extractant concentration in the organic phase and the nature of G, 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 each of the M(III) examples studied, to have an inverse third-power dependency upon the hydrogen ion concentration in the aqueous phase and a direct third-power dependency upon the extractant concentration in the organic phase.For both Pm and Cm the value of Ks (an extraction constant empirically defined in the text) increases as G progresses: 2-ethyl hexyl to phenyl to chloro-methyl, the over all range exceeding 105.Selected (G′O)2PO(OH) studies were included for comparison. In the one instance in which a direct comparison was made, in which G was 2-ethyl hexyl, the Ks in the (GO)(G)PO(OH) system was lower than that in the (GO)2PO(OH) system by a factor of fifty for Pm and 100 for Cm.The effect of a varying μ upon Ks and upon the application of liquid-liquid extraction to the determination of stability constants of metallic complexes in an aqueous phase has been investigated briefly.The system, 2-ethyl hexyl hydrogen phenyl phosphonate (in toluene carrier diluent) vs aqueous HCl + NaCl, μ = 1·0, has been demonstrated to differentiate in favour of Cf with respect to Cm by a factor of approximately 105.The same extractant vs. an aqueous HCl phase differentiates between adjacent lanthanides(III) by a factor of 2·8, the log K vs. Z plot being a line of constant positive slope throughout the range studied. The Ks for a specific lanthanide(III) in this system exceeds that in a comparable bis(2-ethyl hexyl) phosphoric acid vs. HCl system by a factor of approximately 200.