The Synergistic Effects in Organophosphate Extraction Systems

Combinations of dialkylphosphoric acids (HA) and neutral organophosphorus reagents (B) have for some time been known to produce enhanced (synergistic) extraction of and other actinide ions. This effect may be attributed to the formation of a mixed complex—either a substitution product MO₂A₃HB or an addition product MO₂A₄H₂B resulting from the reaction of B with the extraction complex MO₂A₄H₂ normally formed with HA alone. Available extraction data, when analyzed in terms of the competing hydrogen-bonding interactions between HA and B, appear more consistent with an addition product MO₂A₄H₂B. The stability of this mixed complex as a function of the neutral organophosphate used and as a function of the diluent used is consistent with hydrogen bonding or solvation of MO₂A₄H₂ by B. The much stronger and more general synergism found in systems wherein HA is replaced by the β-diketone, Thenoyltrifluoroacetone (HY) may be attributed to the relatively weaker competing interaction between HY and B and to the less coordinatively saturated extraction complexes formed by HY alone.