Electrochemical Oxidation of Americium in Pyrophosphate Solutions

We studied the electrochemical oxidation of Am(III) in H/sub 4/P/sub 2/O/sub 7/, Na/sub 4/P/sub 2/O/sub 7/, and (NH/sub 4/)/sub 4/P/sub 2/O/sub 7/ solutions over a wide pH range, i.e., 0.5 to 10. Trivalent americium at +1.9 V anodic oxidized completely to Am(IV) in 0.1-1 M pyrophosphate solutions at pH less than or equal to 1. The Am(III) in alkaline solution fully oxidized to Am(VI) which could then be reduced to Am(V). At higher oxidation states americium is stable enough in pyrophosphate solutions to be useful in analytical methods. We measured formal oxidation potentials of Am(IV)/Am(III) and Am(VI)/Am(V) couples in pyrophosphate solutions and found them to reach record low values of +1.24 V in 1 M (NH/sub 4/)/sub 4/P/sub 2/O/sub 7/ at pH 6 (the IV/III couple) and +1.06 V in 0.1 M Na/sub 4/P/sub 2/O/sub 7/ at pH 10 (the VI/V couple).