Influence of Fluoride on the Reversible Binding of NO by [FeII(EDTA)(H2O)]2−. Inhibition of Autoxidation of [FeII(EDTA)(H2O)]2−

Electrochemically-mediated reactive separation of nitric oxide into nitrate using iron chelate

Valorization of nitric oxide is a promising solution for addressing the environmental and resource issues related to the nitrogen cycle. However, low concentrations of nitric oxide combined with impurities in exhaust streams limit its potential, and it requires extensive energy to produce high-purity nitric oxide. Here, we propose a synergistic reactive separation system that combines iron-chelate selective absorption with an electrochemical reaction to convert nitric oxide to nitrate. Among the iron-based chelates tested, EDTA was found to be the most effective in capturing gas-phase nitric oxide. Direct electrochemical oxidation of Fe-EDTA-NO solution exhibited Faradaic efficiency and a partial current density toward nitrate of 70% and 30.1 mA cm-2 at 2.2 V vs RHE and pH 7, resulting in a 43-fold enhancement of nitrate partial current density and a 2-fold improvement in Faradaic efficiency compared to simple purging without selective absorbent. Nitrate was then selectively recovered from the Fe-EDTA system using simple polarity reversal following electrooxidation with a separation factor of 13 over background sulfate. This study offers a new approach to gas-phase NO remediation and valorization using an electrified means.

Regeneration of Fe II /Fe III complex from NO chelating absorption by microbial fuel cell

Ferrous chelates (Fe^IIEDTA) can effectively absorb NO, but the regeneration of them usually consumes large amounts of organic matter or energy. In this study, a new approach to regenerate NO absorbed ferrous chelates with simultaneous electricity generation was investigated by a microbial fuel cell (MFC). The performance and mechanisms of Fe^IIEDTA regeneration were evaluated in the cathode of MFC reactor with and without the presence of microorganisms (referring to biocathode and abiotic cathode), respectively. It was found that Fe^IIEDTA-NO and Fe^IIIEDTA could be used as the cathode electron acceptors in MFC. Low pH (pH = 5) was beneficial to electricity generation and Fe^IIIEDTA/Fe^IIEDTA-NO reduction by the abiotic cathode. The biocathode performed better in electricity generation and Fe^IIEDTA regeneration, and achieved a Fe^IIIEDTA reducing rate of 0.34 h^-1 and a Fe^IIEDTA-NO reducing rate of 0.97 L mmol^-1 h^-1, which are much higher that than those for the abiotic cathode (0.23 h^-1 for Fe^IIIEDTA, 0.44 L mmol^-1 h^-1 for Fe^IIEDTA-NO). This was likely because the activation polarization loss and over cathode potential were reduced as a result of the catalytic activity of NO and iron reducing bacteria.

The regeneration of Fe-EDTA denitration solutions by nanoscale zero-valent iron

Fe(ii) ethylenediaminetetraacetate (EDTA) chelate solution is generally considered to be an effective nitric oxide (NO) absorbent. However, since the ferrous active site is occupied by nitric oxide and the ferrous chelate is oxidized to ferric chelate by oxygen in air, its absorption capacity will gradually decrease with the NO absorption process. Here, we propose a method for regenerating the NO-attenuated Fe(ii)EDTA solution by adding nanoscale zero-valent iron (NZVI) under three different pH conditions. Furthermore, compared with the commercially available iron powder, NZVI was also found to be effective not only for the regeneration of expired Fe-EDTA solution but also for the reduction of Fe(iii) EDTA solution. According to the results obtained herein, different acidity levels of solution, from weakly acidic to near neutral, are all suitable for the regeneration–absorption process.

NZVI is very effective for the regeneration of the inactive Fe chelate solution in the NO absorption process.

Nitric oxide removal by combined urea and FeIIEDTA reaction systems

(NH₂)₂CO as well as Fe^IIEDTA is an absorbent for simultaneous desulfurization and denitrification. However, they have their own drawbacks, like the oxidation of Fe^IIEDTA and the low solubility of NO in urea solution. To overcome these defects, A mixed absorbent containing both (NH₂)₂CO and Fe^IIEDTA was employed. The effects of various operating parameters (urea and Fe^IIEDTA concentration, temperature, inlet oxygen concentration, pH value) on NO removal were examined in the packed tower. The results indicated that the NO removal efficiency increased with the decrease of oxygen concentration as well as the increase of Fe^IIEDTA concentration. The NO removal efficiency had little change with a range of 25-45 °C, and sharply decreased at the temperature of above 55 °C. The NO removal efficiency initially increases up to the maximum value and then decreases with the increase of pH value as well as the raise of urea concentration. In addition, the synergistic mechanism of (NH₂)₂CO and Fe^IIEDTA on NO removal was investigated. Results showed that urea could react with Fe^IIEDTA-NO to produce Fe^IIEDTA, N₂, and CO₂, and hinder oxidation of Fe^IIEDTA. Finally, to evaluate the effect of SO₃^2- on NO removal, a mixed absorbent containing Fe^IIEDTA, urea, and Na₂SO₃ was employed to absorb NO. The mixed absorbent could maintain more than 78% for 80 min at 25 °C, pH = 7.0, (NH₂)₂CO concentration of 5 wt%, Fe^IIEDTA concentration of 0.02 M, O₂ concentration of 7% (v/v), and Na₂SO₃ concentration of 0.2 M.

Reactivity of nano-size zinc powder in the aqueous solution of [FeIII(edta)(H2O)]. ENVIRONMENTAL TECHNOLOGY 2017;38:103-107. [PMID: 27227652 DOI: 10.1080/09593330.2016.1186745]

Nitrogen mono-oxide and sulfur dioxide can be removed by simultaneous absorption into aqueous mixed solutions of sulfite and [Fe^II(edta)]H₂O)]^2-, ferrous ion coordinated to an anion of ethylene-diaminetetraacetic acid (EDTA or edta). In the industrial system with coexisting oxygen in the gas phase, [Fe^II(edta)](H₂O)]^2- complex is oxidized to [Fe^III(edta)](H₂O)]^- by molecular oxygen. Because the ferric complex has no capability for reaction with NO, the suppression of this undesired oxidation process is a very important technological problem to be overcome. In our preceding work, we discussed the reduction kinetics of ferric ion by metal powder on the basis of the kinetic data regarding the ferric ion reduction in aqueous solutions of [Fe^III(edta)](H₂O)]^- containing aluminum, tin or zinc powders. Zinc powder of normal size was recognized as an effective reducing agent. In the present work, augmentation of reducing capability of zinc powder was examined more. The rate of reduction of nano-size zinc powder was found to be about 11 times higher than that of normal-size zinc one.