SOLUBILITY OF NEPTUNIUM(IV) HYDROUS OXIDE IN AQUEOUS-SOLUTIONS

The solubility of neptunium(IV) hydrous oxide in water and NaClO4 solu tions was measured from over- and undersaturation directions at 25.0 0 .2 degrees C over a pH range of 5.30 to 13.7, in the presence of reduc ing agents (Na2S2O4 metallic Fe or metallic Cu). Equilibration periods ranged from 1 to 119 days. All procedures were performed in a control led atmosphere in a chamber containing high purity Ar (<1 ppm O-2). St eady concentrations appeared to be reached within 28 days from the ove r- and undersaturation directions in dilute solutions (water and 0.1 M NaClO4), with the Np(IV) concentrations reaching approximately the sa me value (10(-7)-10(-8) M) from both directions. However, the concentr ations decreased slowly to less than 10(-9) M over subsequent periods of tens of days.