On the behaviour of neptunium (7) in carbonate solutions

It was established by a spectrophotometric method that the conversion of the neptunium(VII) cation to an anion in pure solutions occurs in the range of Ph=5.5-7.5. In the presence of carbonate ions, the rearrangement occurs at pH=10-11.5. These results permit the conclusion that the neptunium(VII) cation forms a complex with carbonate ions. Neptunium(VII) in carbonate solution is unstable and gradually passes into a hexavalent state. The rate of reduction of neptunium(VII) is first order with respect to the metal and with respect to hydrogen ions in the interval pH=9-11. A possible mechanism of the process is discussed