Photochemical reactions in analytical chemistry. XV. Photochemical oxidation of cerium(III) to cerium(IV)

The photochemical oxidation of cerium(III) to cerium(IV) in carbonate solutions has been stdied. The oxidation proceeds fastly in K/sub 2/CO/sub 3/ solution, a bit slower in Na/sub 2/CO/sub 3/, very s lowly in KHCO/sub 3/ and NaHCO/sub 3/, and does not proceed at all in (NH/sub 4/)/sub 2/C O/sub 3/. The photochemical oxidation rate increases with increasing K/sub 2/CO/sub 3/ concentration in the solution to be irradiated. The irradiation duration, necessary for the complete cerium(III) oxidation is proportional to its initial concentration. The mechanism of the autooxidation and photochemical oxidation of cerium (III) to cerium(N) has been stdied: in both cases dissolved oxygen is the oxidizing agent which molecule intrudes into a carbonate complex of cerium; then the latter turns into a peroxide complex of cerium(N). The uv-irradiation accelerates the process, in particular that of decomposition of hydrogen peroxide formed. The photochemical oxidation of cerium(III) to cerium(N) in K/sub 2/CO/ sub 3/ solution can be used for separation of cerium microamounts from other rare earths by coprecipitation with lanthanum hydroxide. (auth)