UPTAKE OF METAL IONS BY A NEW CHELATING ION-EXCHANGE RESIN. PART 6 : CALCULATIONS ON THE EFFECT OF COMPLEXLNG ANIONS ON ACTINIDES

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Abstract
A previous paper reported the effect of increasing concentrations of hydrofluoric, oxalic, sulfuric and phosphoric acids at three fixed HCl or HNO3 concentrations on the retention of Am(III), Th(IV) or Np(IV), and U(VI) by the new chelating ion-exchange resin Diphonix™. In this paper the metal uptake data have been analyzed by calculating the effect that complex formation in solution has on the overall metal uptake by the resin. The calculations performed have allowed us to conclude that in most cases the uptake of Am(III) and U(VI) by Diphonix can be explained by assuming that only the uncomplexed metal cation is sorbed. With tetravalent actinides, on the contrary, the uptake data can only be explained if the simultaneous sorption of the uncomplexed cation and of neutral metal complexes is assumed. Indirect evidence has also been obtained on the existence of anionic fluoride complexes of Np(IV). In all other cases, with minor exceptions, the complex formation data available in the literature seem to describe accurately the behavior of the investigated systems.