Neptunium 1- EDTA

The only compounds with this type of ligand appear to be the hydrated neptunium(V) complexes with ethylenediaminetetraacetic acid (H4edta), (Np02)2H2(edta)-5H20 and [Co(NH3)6]Np02(edta) -3H20. 

The presence of either HEDTA or EDTA resulted in significantly lower neptunium and plutonium sorption. Complexation of the neptunium and plutonium by HEDTA and EDTA may have caused the reduced sorption. However, this evidence for complex formation was not consistent with the observations made in the solubility studies (HEDTA increased and EDTA decreased neptunium solubility neither affected plutonium solubility). Thus, HEDTA and EDTA may have decreased neptunium and plutonium sorption through some undetermined effect on the sediment minerals. 

Sorption Prediction Equations. Equations predicting radioelement distribution coefficients, K s, as arithmetic functions of component concentrations were obtained for sorption of strontium, neptunium, plutonium, and americium on two Hanford sediments. These equations, presented in Table VH and derived from statistical fits of Box-Behnken experimental designs, were generated for strontium in terms of sodium ion, HEDTA, and EDTA concentrations. Prediction equations for neptunium and plutonium sorption were derived from NaOH, NaA102, HEDTA, and EDTA concentrations. Americium sorption prediction equations were based on NaOH, HEDTA, and EDTA concentrations. 

As shown in Table VII, the equations modeled the data better for neptunium and plutonium than for strontium and americium. The lack of fit for strontium and americium reflected the strong effect that the increased HEDTA and EDTA concentrations had on decreasing the K. The ranges of Kd s observed for strontium and americium were broader, and more difficult to model, than the ranges observed for neptunium and plutonium. 

In contrast, the solubilities of the neptunyl species were increased by HEDTA and unexpectedly decreased by EDTA. Plutonyl(V) solubility was not affected by HEDTA or EDTA. The component most significant to neptunium solubility was NaNOz. Sodium nitrite apparently decreased neptunium solubility by reducing the more soluble neptunyl(VI) to the less soluble (V) state. The existence of two oxidation states complicated interpretation of the neptunium data. Sodium carbonate, phosphate, aluminate, and sulfate all increased neptunium solubility, probably through complexation. Separation of the data... 

Predicted rates of the radioelement transport through sediment were found to depend strongly on HLW compositions. Compositions of HLW that are high in HEDTA/EDTA concentrations resulted in 30 to 40 times faster migration rates for americium and strontium. Neptunium and plutonium migration rates increased by factors of 6 to 40 by changing HLW from dilute/noncomplexed to concentrated/complexed compositions. 

Tabelle 26. Komplexe des Neptuniums mit stickstoffhaltigen Liganden (Unter-suchungsmetkoden bei Np(IV) = Extraktion mit CHCl (8-Hydroxychinolin und Derival) oder mit Cyclohexan (HTTA) bzw. Spektralphotometrie (H EDTA) bei Np(V) = Spektralphotometrie stets ft = 0,1 und 25 °C)... 

In the oxidations of edta and oxalic acid by neptunium(vi) in perchloric acid,carbon dioxide is produced. One mole of edta reacts with six moles of Np, the rate being first-order in both reagents with an inverse hydrogen-ion dependence. On mixing the reactants, a distinct colour change is observed which is ascribed to complex formation, the... 

A ternary vanadium(v)-edta-hydrogen peroxide complex of the type [V(edta)(Ha02)] has been characterized in solutions of pH 1.0—3.4 with little evidence for the occurrence of an intramolecular redox reaction. The reaction with neptunium(v) has been shown to result in an equilibrium between Np and HgOg slowly reduces Np " to Np in strongly... 

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