Reduction of Nitrate, Bromate, and Chlorate by Zero Valent Iron $\left({\mathrm{Fe}}^0\right)$

Oxo-anions occur in drinking waters, pose potential health risks, and should be controlled. It may be possible to incorporate zero-valent iron $\left({\mathrm{Fe}}^0\right)$ into water treatment processes to remove oxo-anions. Under near neutral pH (∼7) and aerobic conditions, the three oxo-anions studied $({\mathrm{NO}}_3^{-}\text{,}$ ${\mathrm{BrO}}_3^{-}\text{,}$ ${\mathrm{ClO}}_3^{-})$ were electrochemically reduced by ${\mathrm{Fe}}^0$ 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: ${\mathrm{BrO}}_3^{-}>{\mathrm{ClO}}_3^{-}>{\mathrm{NO}}_3^{-}\text{.}$ Differing rates of oxo-anion removal between batch and continuous flow column tests suggested that higher solid $\left({\mathrm{Fe}}^0\right)$ 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 ${\mathrm{Fe}}^0\text{.}$