Neptunium reduction/complexation

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

Especially interesting in a discussion of radionuclide speciation is the behaviour of the transuranium elements neptunium, plutonium, americium and curium. These form part of the actinide series of elements which resemble the lanthanides in that electrons are progressively added to the 5f instead of the 4f orbital electron shell. The effective shielding of these 5f electrons is less than for the 4f electrons of the lanthanides and the differences in energy between adjacent shells is also smaller, with the result that the actinide elements tend to display more complex chemical properties than the lanthanides, especially in relation to their oxidation-reduction behaviour (Bagnall, 1972). The effect is especially noticeable in the case of uranium, neptunium and plutonium, the last of which has the unique feature that four oxidation states Pum, Pu, Puv and Pu are... 

Absorption spectra have been obtained for certain actinide ions which are soluble in saturated KF solution U(IV), Np(IV), Np(V), Np(Vl), and Am(III). Oxidation-reduction reactions of neptunium have been studied. Four new complex fluorides have been prepared and identified by x-ray powder patterns a-K NpFe, pi-K NpFs, KNPO2F2, and K3NPO2F3. Three additional complex fluorides, of Np(III), Np(V), and U(VI), have been prepared but not identified. 

The thorium is removed from the column with 12N HCl, since it does not form a chloride complex, to separate it from neptunium and plutonium. The plutonium is removed by reduction to Pu(III) with 12N HCl-O.lM NH4I solution. The neptunium is then removed by dilute acid. The neptunium and plutonium can also be eluted together with dilute acid and the various nuclides determined by alpha spectrometry. 

Pentaralent neptunium is the most stable state in solution. It hydrolyzes only in basic solutions, disproportionates only at high acidity, and forms no polynuclear complexes. As shown by the oxidation-reduction potentials of Table 9.6, hexavalent neptunium is much less stable in solution than is hexavalent plutonium in fact, hexavalent neptunium is a strong oxidizing agent and is easily reduced in the presence of oxidizable substances, such as those present in ion-exchange and solvent extraction separations [K2]. 

Naptbol, l-(2-carboxyphenyla2o)-chromium complex geometrical isomerism, 68 Neptunium breeder reactor fuels Purex process, 955 reprocessing, 954 electrolytic reduction Purex process, 949 environmental chemistry, 961 extraction Purex process, 951 Purex process, 946,950 recovery... 

Attempts to make the octamethylplutonocene derivative by addition of tetramethyl[8]annulene dianion to the tetrachloride resulted in the reduction of Pu(IV) by the tetramethyl[8]annulene dianion to Pu(III).i When the borohydride complexes of neptunium and plutonium are used in place of the halide salts acceptable yields of the bis(tetra-roethyl[8]annulene) complexes were obtained.21... 

The change in stoicheiometry as a function of Cl is considered to arise from differences in the rate of reaction between HOCl and Cl to form Clg or HOCl and vanadium(rv) to form V. Complex formation between and added Cl results in the decrease in the rate. The corresponding reduction of bromate by neptunium(v) in perchlorate solutions, where four moles of reductant are consumed per mole of bromine(v), has been shown to have an induction period in at least one pathway. The rate law is complex, having the form... 

Pu, Zr(+Nb), and Ce and iTithenlum complexes. Neptunium, plutonium, and cerium are made less extractable by reduction to lower oxidation states. Favorable separation of tiranlum from the other elements may be achieved by control.of the nitric acid and saltlng-out agent concentrations. Free halogens are extracted. These elements may be eliminated from solution prior to uranliim extraction. The halogens also combine chemically with a number of solvents eg,. 

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