Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions.

The pH evolution and corresponding changes in the UV-Vis-NIR absorption spectra of oxygenated neptunium (NpO and NpO) and uranyl ions (UO) in nitric acid are investigated during titration with an aqueous NH solution. The speciation and precipitation regimes between acidic (pH 1.5) and alkaline (pH 10) conditions at room temperature are discussed to assess the suitability of Np(V) or Np(VI) in sol-gel conversion processes for fuel target fabrication.