Synergistic effects in the extraction of selected metallic cations by mono (2-ethyl hexyl) phosphoric acid

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The effect of synergistic agents upon the extraction of M(III) lanthanides, Y(III), Am(III), Cm(III), Th(IV), and U(VI) by H 2MEHP, mono 2-ethyl hexyl phosphoric acid, in a carrier diluent from aqueous HCl has been investigated as a function of carrier diluent, synergistic agent, concentration of H 2MEHP and Z of M(III) lanthanides. It was found that a plot of log K vs log ( r−0·5) or log ( r−2), depending upon the synergist, is more meaningful than a plot of log K vs F or log F of the synergist, where r is the ratio, ( F of synergist/ F of H 2MEHP). For some elements as r increases from zero, K rises to a maximum (region of positive synergism); in others no positive synergism is noted. In each instance in which a maximum is found, the maximum becomes progressively more pronounced as the synergist is varied from n-decanol to TBP, tri-n-butyl phosphate, to TOPO, tri-n-octyl phosphine oxide. In the negative synergism range, the limiting slope of the log K vs log ( r−0·5) plot for all of the M(III) examples studied (TBP synergist, cyclohexane and toluene diluents) is −3. Similarly, the limiting slope of the log K vs log ( r−2) plot (n-decanol synergist, cyclohexane diluent) is −3 for M(III), −4 for Th(IV) and −2 for U(VI). The extractant dependency for Eu(III) and Am(III) by H 2MEHP in the absence of synergist is shown to be first power in toluene diluent and third power in n-decanol diluent. Z-studies in the diluents toluene, cyclohexane and n-decanol are included. Tentative explanations of the negative synergistic effects are proposed in terms of assumed chemical interaction between synergist and H 2MEHP; and possible applications of these effects are suggested.