Disproportionation of plutonium (4) ions in aqueous nitric-acid solutions

Temperature effect on tetravalent plutonium disproportionation in aqueous aitric-acid solutions is investigated. Plutonium (4) thermal oxidation to plutonium (6) is found in 0.3 mol/l HNO3 at 40 deg C and higher and in 4 mol/l HNO3 at 90 deg C. The reaction thermal effect is 117 J/mol, while disproportionation activation energy and thermal oxidation energy are 105 and 95 J/mol, respectively. The initial rate of plutonium thermal oxidation is proportional to its concentration to the power 1.9 while the medium rate, to the first power. It is shown that plutonium thermal oxidation consists of two consequently parallel stages: that of Pusup((4)) disproportionation with Pusup((3)) formation and that of Pusup((3)) oxidation up to Pusup((4)) by products of thermal decomposition of nitric acid; the process rate being determined by the first stage