Freezing-induced bromate reduction through iodide and its implications

Abstract

Freezing, which is the naturally facile process in the cold climate regions, has been extensively investigated as a non-contamination and effective cost method in the environmental treatment. The reactive halogens chemistry has a huge impact on the global environment, especially polar regions. Here, we elucidated the generation of iodine (I2), tri-iodide (I3-), and bromide (Br-) through the bromate (BrO3-) reduction by iodide (I-) in the unfrozen solution of ice while it did not take place in aqueous solution. This appreciably enhanced transformation was attributed majorly to the freeze concentration effect of BrO3-, I-, and protons (H+) in the liquid boundary of ice. The ice grain boundary regions created as well as the consumption of BrO3- in the BrO3-/I-/freezing systemin those regions during freezing were visualized with the confocal Raman microscope. pH decrease (the accumulation of H+) during freezing was measured quantitatively by the UV-Vis absorption spectra of cresol red (as the acid-base indicator). Also, the freeze concentration effect of I- on the BrO3- transformation was verified in the differently experimental conditions of pH and/ or I- concentration. The study on the acceleration of BrO3-/I-/freezing system provides not only an unknown production pathway of bromine and iodine speciation in the polar environment but also the environmentally friendly insight into BrO3- treatment (known as the disinfection byproduct during ozonation in water treatment).