Degradation of iohexol by potassium ferrate in synthetic water and wastewater effluent: Influencing factors, kinetics, and potential intermediates

Iohexol is one of widely used iodine X-ray contrast media, which are considered as iodine sources potentially yielding iodinated disinfection by-products in environmental waters. Therefore, it is necessary to remove iohexol from the source to ensure the safety of drinking water. This study investigated the effect of potassium ferrate on the degradation of iohexol via evaluating the influences factors, including reaction time, potassium ferrate dose, pH, humic acid, and aqueous coexisting ions. The results presented that a small dose of potassium ferrate could effectively remove iohexol in synthetic water samples in approximately 10 min. As pH increasing from 5 to 8, the removal efficiency of iohexol was improved from 31%–32% to over 90%. However, as applied to spiked lake water, potassium ferrate removed 76.3% (pH = 7) of iohexol and part of the dissolved organic matter. Additionally, humic acid, HCO 3 − ${}_3^{-}$ , and PO 4 3 − ${}_4^{3-}$ were found inhibiting the degradation of iohexol, while SO 4 2 − ${}_4^{2-}$ had no significant effect. The reaction kinetics and degradation pathways iohexol were also studied to understand the removal mechanism of potassium ferrate. The rate law equation demonstrated a second-order reaction under the condition of pH = 9, and the rate constant was 0.515 M −1 s −1 . It was inferred that the possible pathway of potassium ferrate degrading iohexol included dehydrogenation reaction, amide hydrolysis reaction, degradation reaction, deiodination reaction, and hydroxyl addition reaction. Generally, potassium ferrate is promising in practical application of aqueous iohexol removal.