Nitrate reduction to ammonia in Fe/Fe2+ system: A case study on the mechanism of green rust generation

The synthesis of ammonia through nitrate reduction has received increasing attention due to its ability to simultaneously achieve wastewater treatment and energy production. This study investigated the mechanism of high concentration nitrate reduction processes using Fe/Fe 2+ process. Batch tests were carried out in high level nitrate reduction in Fe/Fe 2+ system with different particle size iron powder to investigate the evolution of nitrate, nitrite, ammonium, nitrogen balance, and pH in the liquid phase. The characterization results showed that the solid products were γ-FeOOH when ZVI and nitrate react with lower activity. With the increasing of reduction reactivity, green rusts (GRs) generated and divided the reduction process into two phases. ZVI transformed into GRs and finally produced Fe 3 O 4 . The generation pathways of GRs in this study were mainly consist of the partial oxidation of Fe 2+ and the hydrolysis of Fe 2+ combing with the oxidation of Fe(OH) 2 . The reactivity between ZVI and nitrate plays a pivotal role in the formation of GRs. This study has provided a more comprehensive exploration of the formation mechanism of green rust during nitrate reduction.