Spectroscopic and electrochemical studies of seleted lanthanides and actinides : in concentrated aqueous carbonate and carbonate-hydroxide solutions and in molten dimethyl sulfone

Electrochemical and spectroscopic studies of neptunium, Plutonium, americium, californium, and terbium in concentrated aqueous carbonate and carbonate-hydroxide solutions have been carried out. Changes in the absorption spectra of Np(VII), Np(V), Pu(VI), Pu(V), Am(VI), and Am(V) in concentrated Na₂CO₃ solution and in the formal potentials of the Np(VI)/Np(V) and Pu(VI)/Pu(V) couples as a function of pH were observed. Heptavalent neptunium in concentrated Na₂CO₃ solution could only be produced at pH values close to or greater than 14. Plutonium(VII) in 2 M Na₂CO₃ solution could only be produced at hydroxide ion concentrations in excess of about 2.5 The Raman spectra of Np(VII) and Pu(VII) in Na2C03-Na0H solution exhibit a single actinide ion vibration at 734 ± 2 cm^-1 and 703 ± 6 cm^-1, respectively. The complexation of Np(VII) and Pu(VII) in Na₂CO₃-NaOH solution seems to be mainly by hydroxide ions. Neptunium(IV) and plutonium(IV) are insoluble in Na₂CO₃ solution above ca. pH 11-12. Neptunium(III) in carbonate solution is rapidly oxidized by water to Np(IV). Plutonium(III) is insoluble in Na₂CO₃ solution. In K₂CO₃ solution Pu(III) is stable to oxidation by water but is very sensitive to air oxidation.

The redox properties of Cf(III) in Na₂CO₃ and K₂CO₃ solutions at pH values from 8 to 14 were investigated. Californium(III) in bicarbonate-carbonate-hydroxide solution could not be oxidized to Cf(IV) chemically or electrochemically.

The oxidation of terbium(lll) in K₂CO₃-KOH solution was studied. The concentrations of terbium, carbonate, and hydroxide ions vi for generation and stabilization of Tb(IV) are critical. Redox titrations of Tb(IV) with Fe(CN)_{6^-4 ion and analysis of Tb(IV) precipitates indicate that the Tb(IV) complex in solution is clustered in nature.}

Spectroscopic and electrochemical studies of cerium, samarium, europium, ytterbium, uranium, neptunium, plutonium, and americium in molten dimethyl sulfone (DMSO₂) at 400 K were performed. Differences in the DMSO₂ solution absorption spectra of trivalent Sm, Eu, and Yb and divalent Eu compared with those in aqueous solution were observed. Complexation effects on the spectra of Ce(III), Ce(IV), U(VI), Np(VI), Pu(VI), and Am(VI) are more noticeable in poorly coordinating DMSO2 than they are in water.