Persulfate Ion in the Chemistry of f-Elements

Abstract

The properties and stability of the S2O82– ion and mechanisms of its reaction with ions of f-elements in aqueous solutions in a wide range of pH values are considered. S2O82– are converted to SO4 ion radicals. The decomposition is accelerated by Н+, ОН–, Ag+, Co2+ ions, and others. The decomposition in solutions with [H+] > 0.5 or [OH–] > 0.5 M yields monoperoxysulfuric acid, with its hydrolysis generating Н2О2. The SO4– radicals oxidize ions of f-elements and convert ОН– and СО32– ions to oxidizing radicals ОН and СО3– and transform H2PO4– and NO3– ions into reducing compounds. In aerated alkaline solutions, the ОН radicals are transformed to ion-radicals О3–,which oxidize Np(VI), Pu(VI), and Am(VI) to the heptavalent state. In weakly acidic solutions of heteropolycompounds, SO4– radicals transform Tb(III), Am(III), Cm(III), Cf(III) to the tetravalent state. The mixture of Ag+ and S2O82– is used to oxidize Np(VI) to Np(VII) in an alkaline medium, Pu4+ to PuO22+ in acid solutions, Am(III) to Am(IV) in Н3РО4 solutions and in the presence of heteropolycompounds in 5 M HNO3 or 3 M H2SO4 solutions, Am3+ to AmO22+ in acid solutions. The decomposition of S2O82– into radicals occurs under exposure to light or radiation. The reactions of oxidation of f-element ions by SO4– radicals occur by the zeroth-order rate law. To one more group of reactions belongs the interaction of S2O82– with NpO2+, Pu3+, Am3+ ions. The reactions occur with a first-order rate with respect to the f-ion. In the case of U4+, Np4+ in acid media and, Pu(IV) in a solution of K2СО3, complexes of these ions with S2O82– are formed. The complexes decompose by the first-order rate law. Studies are planned of studying reactions involving S2O82– and ions of f-elements, including those in fluoride solutions containing actinides and fission products, and reactions of SO4– radicals at low temperatures to give actinides in higher oxidation state.