Plutonium complexes, hydrogen peroxide

The kinetics of the formation of the brown plutonium(rv)-hydrogen peroxide complex have been investigated and the following rate law found d[complex]/dt = [H202][PuIV]2 A 2[H+]-i -I- A 3[H+]-2 ... 

Because of the ease of oxidation of protactinium(IV) and uranium(IV), peroxides and peroxo complexes are limited to their higher oxidation states. The compounds M04"JcH20 precipitated from dilute acid solutions of neptunium(IV) and plutonium(IV) by hydrogen peroxide appear to be actinide(IV) compounds. Soluble intermediates of the type [Pu( U-02)2Pu]4+ are formed at low hydrogen peroxide concentrations. 

Plutonium Purification. The same purification approach is used for plutonium separated from sediments or seawater. In case reduction may have occurred, the plutonium is oxidized to the quadrivalent state with either hydrogen peroxide or sodium nitrite and adsorbed on an anion exchange resin from 8M nitric acid as the nitrate complex. Americium, curium, transcurium elements, and lanthanides pass through this column unadsorbed and are collected for subsequent radiochemical purification. Thorium is also adsorbed on this column and is eluted with 12M hydrochloric acid. Plutonium is then eluted from the column with 12M hydrochloric acid containing ammonium iodide to reduce plutonium to the non-adsorbed tervalent state. For seawater samples, adequate cleanup from natural-series isotopes is obtained with this single column step so the plutonium fraction is electroplated on a stainless steel plate and stored for a-spectrometry measurement. Further purification, especially from thorium, is usually needed for sediment samples. Two additional column cycles of this type using fresh resin are usually required to reduce the thorium content of the separated plutonium fraction to insignificant levels. 

Among plutonium oxidation states from 4-3 to 4-6, the most stable forms are 4-3 and 4-4. Conversion between oxidation states is used for purification from other radionuclides. Plutonium is oxidized to the 4-4 state by hydrogen peroxide, permanganate, and nitrite, and reduced to the 4-3 state by bisulfite and ascorbic acid. A strongly acidic or complexing solution is needed to maintain the selected state and avoid hydrolysis with polymerization (Coleman 1965). 

---