Absorption, Regeneration, Resource Reuse And Harmless Utilization Of Absorbent In Fe～ⅡEDTA Absorption Of Nitric Oxide In Flue Gas

The absorption of NO by Fe^â…¡EDTA was developed in1980s. Compared with other methods, wet process of NO by means of Fe^â…¡EDTA is highly efficient. The main issue this method confronts is high cost which prevents it from wide use in industry. In present paper the absorption and this drawback were discussed. The regeneration was realized by reduction methods with it kinetic studies also studied. Finally the resource utilization and cost accounting was investigated for the purpose of establishing a whole schematic diagram.Experiments showed that the regeneration mechanism of Fe^â…¡EDTA by Na₂SO₃ and by electrochemical reduction were not the same. When Na₂SO₃ was added into EDTA to absorb NO, Na₂SO₃ adjusted pH value of absorption solution toward weak alkaline and reduced the oxidized Fe^â…¡EDTA. In result the absorption easily ran. When there was SO₂ residual after FGD, SO₂ hydrolyzed and formed SO₃^2- which compensated the consumed Na₂SO₃. It was confirmed by cyclic voltammetry that the final reduction products formed from SO₃^2- were S₂O₆^2- and SO₄^2- when Na₂SO₃ was applied to reduce Fe^â…¡EDTA. Electrochemical reduction proved that Fe^â…¢EDTA reduction was a fast reversible process with one electron transferred on Pt electrode surface. Standard rate constant k⁰ of Fe^â…¢EDTA reduction at 298 K was found to be 0.0263 cm s^-1. According to the calculated diffusion activation energy of 24.93 kJ mol^-1, apparent activation energy of 25.74 kJ mol^-1 and the electron transfer activation energy of 16.56 kJ mol^-1, the rate determining step for Fe^â…¢EDTA reduction was diffusion step.Recycle of EDTA and resource reuse include two steps. First, NaOH and H₂SO₄ were employed to recycle EDTA. The results showed that the recycle efficiency was 67%. And then ammonia was added into the recycled solution to make fertilizers.As a consequence, (NH₄)₂EDTA, NH₄NO₃ and (NH₄)₂SO₄ were produced. This method provided a new pathway to realizing wastes water resource reuse and harmless utilization of absorbents, meanwhile, promoting the industrialization of wet absorption of NO by Fe^â…¡EDTA.