PNNL

Abstract

The interaction of Cr(III) hydroxides and mixed Fe(III)-Cr(III) and Ni(II)-Cr(III) hydroxides with persulfate ions has been investigated in alkaline media by a spectrophotometric method. The stoichiometric yield of Cr(VI) corresponds to a molar ratio of S2O82-:Cr(III) close to 1.5. The initial rate of the reaction is described by the equation d[Cr(III)]/dt = k[Cr(III)][S2O82-][NaOH]. The activation energy in the range 41.5-95?C is 53 kJ/mole. The V0 value is higher than the rate of thermal decomposition of persulfate; i.e. Cr(III) hydroxide reacts directly with S2O82-. The oxidation of NiCr2O4?nH2O and mixed Fe(III)-Cr(III) hydroxides proceeds faster than oxidation of pure Cr(III) hydroxide. The acceleration is explained by the catalytic effect of Fe(III) and Ni(II). Additions of Co(II) and Cu(II) also accelerate the oxidation. Pu(IV) in alkaline media is oxidized to higher more soluble states by persulfate but may be reduced by the action of appropriate reducing agents.