Study on NO Removal Characteristics of the Fe(II)EDTA and Fe(II)PBTCA Composite System

Fe²⁺ complexation wet denitrification technology has become a research hotspot. It is very important to achieve efficient regeneration of the absorbent and increase NO absorption in the Fe²⁺ complexation system. They are the key to the industrial application of the Fe²⁺ complexation absorption process. In this paper, 2-phosphonate-butane-1,2,4-tricarboxylic acid and ethylenediamine tetraacetic acid were used as ligands to prepare a composite system for the first time. The characteristics of NO removal were investigated under different temperatures, pHs, Fe²⁺ concentrations, O₂ contents, NO concentrations, CO₂ contents, and SO₂ concentrations. Compared with the single ligand, the results show that the denitrification performance of the solution with a complex ligand is significantly improved. In this system, pH 9, 40 °C temperature, and 20 mmol/L Fe²⁺ concentration are the economic ideal conditions for NO removal. The system can realize simultaneous removal of NO and SO₂, but SO₂ in flue gas has a dual effect on the NO removal reaction.

Promoting Effect of H+ and Other Factors on NO Removal by Using Acidic NaClO2 Solution

In this study, NaClO2 was selected as a denitration oxidant. In order to clarify the mechanism of NaClO2 as an oxidation agent for NO removal efficiency, the effects of H+ and other factors (NaClO2 concentration, temperature, and the other gas) on the NO removal efficiency were investigated. NaClO2 showed a promotional ability on NO removal, whose efficiency increased with the increase of NaClO2 concentration. One hundred percent removal efficiency of NO could be achieved when the NaClO2 concentration was 0.014 mol/L. Furthermore, raising the reaction temperature benefited the removal of NO. The lower the pH, the better the NO removal efficiency. The promoting effect of H+ on the NO removal was studied by the Nernst equation, ionic polarization, and the generation of ClO2. Under the optimal conditions, the best removal efficiency of NO was 100%. Based on the experimental results, the reaction mechanism was finally speculated.

Simultaneous Biological and Chemical Removal of Sulfate and Fe(II)EDTA-NO in Anaerobic Conditions and Regulation of Sulfate Reduction Products

In the simultaneous flue gas desulfurization and denitrification by biological combined with chelating absorption technology, SO2 and NO are converted into sulfate and Fe(II)EDTA-NO which need to be reduced in biological reactor. Increasing the removal loads of sulfate and Fe(II)EDTA-NO and converting sulfate to elemental sulfur will benefit the application of this process. A moving-bed biofilm reactor was adopted for sulfate and Fe(II)EDTA-NO biological reduction. The removal efficiencies of the sulfate and Fe(II)EDTA-NO were 96% and 92% with the influent loads of 2.88 kg SO42−·m−3·d−1 and 0.48 kg NO·m−3·d−1. The sulfide produced by sulfate reduction could be reduced by increasing the concentrations of Fe(II)EDTA-NO and Fe(III)EDTA. The main reduction products of sulfate and Fe(II)EDTA-NO were elemental sulfur and N2. It was found that the dominant strain of sulfate reducing bacteria in the system was Desulfomicrobium. Pseudomonas, Sulfurovum and Arcobacter were involved in the reduction of Fe(II)EDTA-NO.

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.

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.