KINETICS OF THE OXIDATION OF URANIUM (IV) BY IRON (III) IN AQUEOUS SOLUTIONS OF PERCHLORIC ACID

Abstract

The kinetics of oxidation of uranium (IV) by iron (III) in aqueous solutions of perchloric acid have been investigated at four temperatures between 3.1 °C. and 24.8 °C. The reaction was followed by measurement of the amount of ferrous ion formed. For the conditions (H + ) = 0.1–1.0 M, ionic strength = 1.02, (Fe III ) = 10 −4 –10 −5 M, and (U IV ) = 10 −4 –10 −5 M, the observed rate law is d(Fe 2+ )/dt = −2d(U IV )/dt[Formula: see text]K 1 and K 2 are the first hydrolysis constants for Fe 3+ and U 4+ , respectively, and K′ and K″ are pseudo rate constants. At 24.8 °C., K′ = 2.98 sec. −1 , and K″ = 10.6 mole liter −1 sec −1 . The corresponding temperature coefficients are ΔH′ = 22.5 kcal./mole and ΔH″ = 24.2 kcal./mole. The kinetics of the process are consistent with a mechanism which involves, as a rate-controlling step, electron transfer between hydrolyzed ions.