Oxidation of X-ray compound ditrizoic acid by ferrate(VI)

Iodinated X-ray contrast media (ICM) such as diatrizoic acid (DTZA) is used in large amounts in hospitals to enhance imaging of organs and blood vessels during radiography. Due to its persistence and non-biodegradability, it is found in treated water, sewage effluent, surface waters, and aquatic environments. This paper presents the kinetics of the oxidation of DTZA by ferrate(VI) (FeVIO42-, Fe(VI)) as a function of pH (7.1-9.6) at 25 degrees C in order to determine the effectiveness of Fe(VI) to remove DTZA from water. The reaction was determined to be first-order with respect to concentrations of Fe(VI) and DTZA. The rate of the reaction was found to be pH dependent and the rate decreased nonlinearly as the pH increase from 7.1 to 9.6. The speciation of Fe(VI) (HFeO4- and FeO42-) was used to explain the rate dependence on pH. The calculated rate constant of Fe(VI) with DTZA at pH 7.0 was compared with nitrogen-containing pollutants and is briefly discussed.