The decomposition kinetics of FeO42- in the aqueous NaOH solutions of 7.0 mol·L-1, 10.0 mol·L-1 and 14.0 mol·L-1 were determined by spectrophotometry with and without ultrasonic action at 500 W and 25 kHz.The results showed that the decomposition followed first-order kinetics and the rate was faster with ultrasonic action than without ultrasonic action.The decomposition activation energies were 52.4 kJ·mol-1, 70.5 kJ·mol-1 and 91.5 kJ·mol-1 without ultrasonic action, and 49.6 kJ·mol-1, 66.6 kJ·mol-1 and 85.9 kJ·mol-1 with ultrasonic action, in the aqueous NaOH solutions of 7.0 mol·L-1, 10.0 mol·L-1 and 14.0 mol·L-1 respectively.The fact that the activation energies increased with increasing concentrations of NaOH indicated that FeO42- was much stable in a higher concentration NaOH solution.The effect of ultrasound on the decomposition kinetics of FeO42- decreased with operating temperature.
