The effects of operational parameters and common anions on the reactivity of zero-valent iron in bromate reduction

Bromate reduction by Fe(0) was investigated under various conditions in batch tests. The bromate was primarily reduced to bromide ions with possible adsorption onto iron. Bromate reduction by Fe(0) can be described by pseudo-first-order kinetics. The differences in surface areas, numbers of reactive sites, impurities, pretreatment methods and numbers of repeated uses of iron affected the rates of bromate reduction through reducing or accumulating a passive oxide film on the iron surface. The reduction of bromate was significantly affected by only the dissolved oxygen content at supersaturated concentrations or by decreasing the pH from 6 to 5. Increasing the temperature increased the bromate reduction rate, which followed the Arrhenius relationship with activation energy of 52.6 kJ mol−1 and the reduction rate increased with increased mixing rates. These observations indicate that bromate reduction by iron is a surface-mediated process and diffusion to the surface is essential. Under the test conditions, modest inhibitory effects on bromate reduction by Fe(0) from nitrite, chlorate and bicarbonate were observed and the inhibitory effect from phosphate was relatively larger. Enhanced reactivity of Fe(0) to bromate was observed in the presence of nitrate or sulfate. These findings suggest that bromate reduction by Fe(0) can be an effective method for bromate control.