Neptunium , disproportionation

Purex process, 6, 951 Neptunium complexes, 3, 1131-1215 cupferron, 2, 510 Neptunium dioxide ions disproportionation Purex process, 6, 950... 

Neptunium. The fluorite-type Np02 is the stable oxide formed in air when neptunium oxysalts are decomposed, but almost no studies have been carried out in the oxygen-defect region. Ackermann et al. ( ) in studying the vaporization process of NpO observed A-type NP2O3 in quenched samples which had been 70% vaporized. It is likely that the two phases were formed from a nonstoichiometric Np02. x phase by disproportionation as the sample was cooled. 

Neptunium gives a series of reactions analogous to those of uranium, but the individual stabilities are different, thus NpOg is particularly stable (Table 104). A reagent as powerful as cerium(IV) sulphate is required to oxidise Np02 to NpO +. Furthermore, the disproportionation of the NpOg" ion occurs only very slowly in solution ... 

TUE(IV) hydroxides possess weak amphoteric properties, and are known for neptunium and americium. Preparation of fine Pu(V) hydroxide is complicated by the increasing tendency towards PUO2 disproportionation. The preparation of Pu(V) hydroxide by alkalization of Pu(V) solution has been reported [51]. This compound (gray-white in color) with the composition... 

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]. 

The chemistry of uranium in the Purex process is simpler than that of plutonium or neptunium. In the dissolver solution, U is present exclusively. The lower oxidation states (IV) and (V) are both unstable in nitric acid media, U " disproportionating rapidly and U being formed only in... 

Purex process, 951 Neptunium(VI) reduction Purex process, 951 Neptunium dioxide ions disproportionation rex process, 950 Nerve growth factor snake venoms zinc, 613... 

Simple calculations confirm that the sesquioxides of uranium and neptunium are significantly unstable with respect to disproportionation into metal and dioxide, e.g. using enthalpies of formation from Tables 17.5 and 17.14 and estimated entropies,... 

---