Reactivity of Nitrate with Zero-Valent Iron

Abstract

Elevated nitrate concentrations in groundwater and surface water supplies can negatively impact the quality of the environment and human health. Recent studies have examined the use of zero-valent iron technology to treat nitrate-contaminated groundwater. Mechanistic aspects of nitrate reduction by zero-valent iron are unresolved. This project investigated the kinetics and mechanism of nitrate reduction by zero-valent iron under anoxic conditions and under oxic conditions. Stirred-batch reactions were studied over environmentally relevant ranges of reactant concentration, pH, and temperature. A complex rate expression was derived with a 1.8 order dependence on nitrate, a 1.4 order dependence on zero-valent iron, and a fractional order (0.8) dependence on proton concentrations under anoxic conditions. An apparent activation energy of 35 kJ mol−1 was observed indicating that nitrate reduction was diffusion controlled under our conditions. Furthermore, the calculated entropy of activation value of −162 J mol−1K−1 indicates that this reaction occurred by an associative mechanism. Under oxic conditions, there was a lag period in nitrate reduction where oxygen was preferentially utilized, leading to a slower rate of nitrate reduction when compared with anoxic conditions. These rate data can be used in predicting nitrate disappearance in nitrate-contaminated groundwater and wastewater treated with zero-valent iron.

Synergizing Fe2O3 Nanoparticles on Single Atom Fe‐N‐C for Nitrate Reduction to Ammonia at Industrial Current Densities

“…Furthermore, the formation and preservation of the Fe 0 species correspond to a significantly enhanced NO 3 RR performance, which is in agreement with previous works demonstrating the effectiveness of lower oxidation state Fe species towards the NO 3 RR. [ 43,44 ] The maintained Fe speciation and boosted activity are supported by a 24 h NO 3 RR electrolysis at −1.0 V, following a pre‐reduction activation step. To circumvent ultrahigh NH 3 concentrations in the electrolyte and subsequent loss of NH 3 in the gas phase, the electrolysis was performed in eight 3‐h segments.…”

Nitrate removal from groundwater by microscale zero‐valent iron and activated carbon: A nonpumping reactive wells experiment

“…The highest pH increase was observed for B9 (reaching 9 after 40 h), where GAC and MZVI were added with 2.0 g and 0.5 g, respectively. The reason for the increasing pH of the solution can be explained by the high consumption of protons for NO 3 − reduction as the ratio of 10:1 mole: [ 51 ] $$$$\begin{equation*}{\rm{NO}}_3^ - + 4{\rm{F}}{{\rm{e}}^0} + 10{{\rm{H}}^ + } \to 4{\rm{F}}{{\rm{e}}^{2 + }} + {\rm{NH}}_4^ + + 3{{\rm{H}}_2}{\rm{O}}\end{equation*}$$$$…”

“…The reason for the increasing pH of the solution can be explained by the high consumption of protons for NO 3 − reduction as the ratio of 10:1 mole: [51] NO…”

Synergizing Fe2O3 nanoparticles on single atom Fe-N-C for nitrate reduction to ammonia at industrial current densities

“…Furthermore, the formation and preservation of the Fe 0 species corresponds to a significantly enhanced NO3RR performance, which is in agreement with previous works demonstrating the effectiveness lower oxidation state Fe species towards the NO3RR. 41,42 The maintained Fe speciation and boosted activity are supported by a 24 hour NO3RR electrolysis at -1.0 V, following a pre-reduction activation step. To circumvent ultrahigh NH3 concentrations in the electrolyte and subsequent loss of NH3 in the gas phase, the electrolysis was performed in eight 3-hour segments.…”