A study of the kinetics of the reduction of neptunium(VI) by acetohydroxamic acid in perchloric acid

Abstract

The kinetics of reduction of NpO22+ to NpO2+ by acetohydroxamic acid in 1 mol·L−1perchloric acid media at 10 and 22°C were studied. The reaction rate was monitored using stopped-flow and standard infrared spectroscopy. Under conditions such that acetohydroxamic acid was in excess relative to Np, the reduction rate of NpO22+ is described by the following: where k = 2.57x103 mol−1·L·sec−1 at 10°C. However, when neptunium is in a significant molar excess relative to acetohydroxamic acid, the reduction mechanism is dictated by two distinct reactions. An initial and incomplete reduction occurs as the result of the oxidation of AHA, while a slower and partial reduction of NpO22+ is likely caused by the oxidation products of AHA. The reaction rate of this first-order mechanism was calculated as 3.7x10−4 sec−1 at 10°C and 0.001 sec−1 at 22°C.