Reduction of nitrate, bromate, and chlorate by zero valent iron (Fe0)

Oxo-anions occur in drinking waters, pose potential health risks, and should be controlled. It may be possible to incorporate zero-valent iron (Fe-0) into water treatment processes to remove oxo-anions. Under near neutral pH (similar to7) and aerobic conditions, the three oxo-anions studied (NO3-, BrO3-, ClO3-) were electrochemically reduced by Fe-0 in batch and continuous-flow packed column experiments. Mass balances provided strong evidence that ammonia is the primary reduction by-product from nitrate, chloride from chlorate, and bromide from bromate. Protons were consumed during the reaction, resulting in an increase in pH (i.e., production of hydroxide). Oxo-anion removal rates decreased as follows: BrO3->ClO3->NO3. Differing rates of oxo-anion removal between batch and continuous flow column tests suggested that higher solid (Fe-0) to liquid ratios increase oxo-anion electrochemical reduction, and scaling up of batch kinetic data to larger scale must consider the solid-liquid ratios. The atomic structure (atomic radii, electron orbital configuration, electron affinity) of nitrogen, chlorine, and bromine elements of the oxo-anions, and the bond dissociation energy between these elements and oxygen, were good indicators for the relative rates of reduction by Fe-0.