International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci. International Science Congress Association 63 Simultaneous Removal of NO and SO from Simulated Flue gas using Fe (II) EDTA coupled with Catalytic RegenerationDeshwal Bal Raj1*and Kundu Neha2 Department of Chemistry, A. I. J. H. M. College, Rohtak - 124001 (Haryana), INDIA Department of Chemistry, D. C. R. Univ. of Sci. and Technol., Sonipat: 131001 (Haryana), INDIA Available online at: www.isca.in, www.isca.me Received 6th May 2015, revised 14th June 2015, accepted 19th July 2015 Abstract Experiments were performed in a packed column to investigate the absorption of NO and SO into Fe (II) EDTA complex. The effect of various operating variables such as amount of activated carbon, pH, liquid flow rate, temperature, Ocontent, and sulfitebisulfiteon the absorption of NO and SO by Fe (II) EDTA solution was examined. Fe (II) EDTA was regenerated by catalytic reduction of Fe (III) EDTA by sulfiteionsin the presence of activated carbon. SO2 is almost 100% absorbed in the scrubbing solution during all the experiments. The rate of NO absorption increased with the amount of activated carbon. Absorption of NO increased with pH and reached to the maximum value at a pH of ~7.5 and decreased thereafter. The rate of NO absorption increased with the liquid flow rate and decreased with increasing O2 content. However, NO absorption decreased with theincreasing temperature in the absence of activated carbon and increased in the presence of activated carbon. Further, the rate of NO Absorption improved with the sulfitebisulfite concentration. Keywords: Fe (II) EDTA, nitric oxide, sulfur dioxide, absorption, activated carbon.Introduction Nitrogen oxides (NO) and sulphur oxides (SO) are the major air pollutants found in the flue gases emitted from chemical industries and power plants. NO and SO are responsible for acid-rain, global warming, smog and destruction of forest ecosystems. The removal of acidic gases has become need of the hour in order to comply with stringent environmental emission standards. Technologies for removal of sulphur oxides has achieved an advanced stage of development, however, it is not so in case of controlling NO emission. Nitrogen oxides emitted from industries consist of ~90% nitric oxide (NO) which is quite inert in nature. Absorption of NO can be carried out either by using strong oxidative absorbent or by complex forming reagents. Wet scrubbers have been the workhorses of the chemical industry for decades and successfully used for removal of several acidic gases. Since NO is quite inert in nature, therefore, oxidants are added into scrubbing system to oxidize NO into NO and the later can be subsequently removed by alkaline absorbents. Investigations have been carried out in past using numerous oxidative absorbents such as hydrogen peroxide, per acid, organic tertiary hydro peroxides, sodium chlorite4-8, KMnO9,10and chlorine dioxide11,12 in order to determine their efficiency in the removal of NO1-12. Several other liquid absorbents, namely Urea13, FeSO/HSO14, Fe (II) EDTA15, Na16, NaSO17, and Fenton reagent18have also been explored in the past to remove NO from the exhaust gases13-18Numerous studies have been made to improve NO absorption, including the addition of various Fe (II) chelates to bind NO19-24. Though Fe (II) EDTA has emerged as potential absorbent to achieve a reasonably high NO removal efficiency yet it is easily oxidized to Fe (III) EDTA that is not capable of binding NO, and thus NO removal efficiency decreases immediately25-27. Literature reveals several studies to regenerate Fe (II) EDTA to maintain high NO removal efficiency28-30. Some reducing agents such as hydrazine, Na, NaSO are used to realize the regeneration of Fe (II) EDTA. However due to low rate constants and high consumption, none of these methods have been put into commercial applications. Inadequate studies have been reported to investigate the absorption of NO into Fe (II) EDTA solution coupled with activated carbon to regenerate Fe (II) EDTA to maintain high NO absorption. Activated carbon has been applied in industry successfully as a catalyst due to its large surface area, porous structure, characteristic flexibility and low cost. It is an efficient catalyst which may speed up the regeneration of Fe (II) EDTA in presence of sulfite/bisulfite. The present manuscript attempts to study the absorption of NO as well as SO2 into Fe (II) EDTA complex and to examine the effect of various operation variables such as amount of activated carbon, liquid flow rate, pH, temperature, O content, and sulfite/bisulfiteconcentration on the absorption of NO and SO. This technique is believed to absorb NO and SO efficiently and also to sustain high NO and SO removal for a longer period of time with a low operation cost. International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci.International Science Congress Association 64 Theoretical Backgrounds: SO is moderately soluble in aqueous solution and undergoes hydrolysis to form bisulfite (HSO), sulfite (SO2-) and disulfite (S2-) ions31. The equilibrium concentrations of all these species depend upon partial pressure of SO and pH of the solution. Henry’s constant for NO in water is quite small i.e. 1.218ื10-3M/atm. at 4532. It suggests that NO has poor solubility in water. Fe (II) EDTA tends to bind nitric oxide by coordinate linkage in the liquid phase and thus enhances the solubility of nitric oxide in the aqueous solution as follows: Fe (II) – EDTA2- NO(aq) Fe(II) – EDTA (No)2-(1) However, oxygen coexisting in the flue gas may oxidize Fe (II) EDTA to Fe (III) EDTA as shown below: 4Fe (II) – EDTA2- 2 + 4H 4Fe(III) – EDTA- + 2HO (2) Fe (III) EDTA lacks the ability to bind NO. As a result, NO removal efficiency will decrease quickly. It is, therefore, Fe (III) EDTA must be reduced to Fe (II) EDTA in order to maintain the NO absorption. Sulfite/bisulfate ions are formed by hydrolysis of SO in the scrubbing solution and facilitate the regeneration of Fe(II)-EDTA as follows21,24: 2Fe (III) – EDTA- + 2HSO 2Fe (II) – EDTA2- + S2- + 2H+ (3) 2Fe (III) – EDTA- + 2SO 2Fe (II) – EDTA2- + S2- (4) To accelerate the reduction of Fe (III)-EDTA, activated carbon can be used as a catalyst. It disintegrates Fe (III)-EDTA into Fe3+ ions and EDTA ions as follows: Fe (III) – EDTA- Fe3+ + EDTA4- (5) Standard reduction potential data suggest that sulphite ions ( ) 2243SO/SO E0.936V --=-can easily reduce Fe3+ ions ( ) 32Fe/Fe E0.771V ++32. The reduction of Fe3+ ions by the sulfite ions takes place as follows: 3222324 2FeSOHOSO2Fe2H +--++ ++++ (6) Fe2+ ions thus produced undergo coordination linkage with EDTA ions and regenerate Fe (II)-EDTA as follows: 242 FeEDTAFe(II)EDTA +-- +ฎ- (7) It is therefore, the NO removal efficiency can be sustained for a long time. In view of the above, if Fe(II)-EDTA can be regenerated quickly by sulfite/bisulfite under the catalysis of activated carbon, then this technology will be highly efficient and cost effective for the combined removal of NO and SO from the flue gases. Material and Methods Materials: (99%, Anjeon Gas Co., Korea), SO span gas (99%, Anjeon Gas Co., Korea), and NO span gas (99.9%, Mathieson, Chemical Co., USA) were the standard gases used in the present study. FeSOท7HO (�99.0%), NaEDTA (�99.5%) and NaSO3 (�97.0%) were obtained from Samchun Pure Chem. Co. Ltd., Korea. Activated carbon was obtained from Shanghai Activated Carbon Co., Ltd. Aqueous solution of Fe (II) EDTA is extremely air-sensitive and should be handled under a protective nitrogen atmosphere. The Fe (II)-EDTA solution was prepared by diluting a predetermined amount of NaEDTA solution in degassed water. The pH of the solution was maintained at 9.0 by careful addition of 0.1M HSO solution. When appropriate amount of FeSO-7HO was added to the NaEDTA solution, it gives a slightly green, clear solution with a pH ~5. The pH of the solution can be adjusted to the desired value by the addition of 0.1M NaOH or HSO solution. Flue gas treatment unit: It composed of simulated flue gas supply system, packed column, circulation tank, regeneration reactor, pH control system, data acquisition system, and gas analysis system. The schematic diagram of the experimental apparatus is shown in figure-1. Absorption of NO and SO were performed in a packed column (I.D. = 20 mm, height = 1000 mm). The Fe (II)-EDTA regeneration was carried out in a reactor (I. D. = 20 mm, height = 800 mm) packed with activated carbon. The temperature of the packed column and regeneration reactor was controlled by water thermostat (WBC-1506D, JEIO TECH, Korea). Auto-pH control system (KFC-MK-250, Korea) was designed to control the pH of reaction solution wherein 0.1M NaOH/HSO solution was added continuously with the help of peristalsis pump (Cole-Palmer Co., USA). Mass flow controllers (MFC) were used to mix SO, NO, and N in the appropriate ratio in order to obtain a simulated flue gas. The desired level of O2 in the scrubbing solution was maintained by supplying air into the reactor with help of air pump. Fe (II)-EDTA solution together with appropriate amount of NaSOwas added into circulation tank. The simulated flue gas with a feeding rate of 0.3 L/min is passed from the bottom and scrubbing solution is continuously introduced from the top of the packed column. The initial sulfite concentration was adjusted by adding appropriate amount of NaSO into the Fe (II)-EDTA complex. The absorbent coming out from the packed column was fed into the circulation tank. Fe (II)-EDTA is recycled in the regeneration reactor and then it is directly supplied into the packed column. The experimental conditions and various operating variables are listed in table -1. International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci.International Science Congress Association 65 Figure-1 A schematic diagram of experimental system 1 –Packed column, 2 – Regeneration reactor, 3 – pump, 4 – Sample conditioner, 5 – Gas cylinder, 6 – Mass flow controller, 7 – pH control system, 8 – Circulation tank, 9 – NaOH/HSO solution, 10 – Gas analyzing systemTable-1 Experimental conditions and operating variables Absorbent Fe (II) EDTA Complex Inlet NO concentration 500 ppmv Inlet SO 2 concentration 1500 ppmv Sulfite/bisulfate Concentration Zero to 0.06 mol/L Activated Carbon 5 - 80 g Gas feeding rate 0.3 L/min Liquid flow rate 10- 50 mL/min pH 5.5 to 8.5 Temperature 35 – 65 o C Oxygen Zero – 8 % Gas analysis: The moisture of the inlet and outlet flue gas supply was removed in the sample conditioner before the gas analysis.The composition of inlet and outlet gas was analyzed with help of SO analyzer (Model-Ultramat 23, IR type, Siemens, Germany), NO analyzer (Model-42C, Chemiluminescent type, Thermo Environmental Instruments Inc., USA), and DO meter (835A, Thermo Orion, USA).Results and Discussion Effect of the amount of activated carbon on NO removal: The effect of the amount of activated carbon on the absorption of NO was examined by performing several experiments with different amounts of activated carbon. It is pertinent to mention here that SO2 is almost 100% absorbed in the scrubbing solution during all the experiments. Figure-2 illustrates that NO absorption increased with the amount of activated carbon. On completion of 2 hour operation, absorption of NO was merely 56.2% in absence of activated carbon; however, it was observed 89.2%, 91.9%, 96.9% and 97.1% with 5, 10, 20, 40 and 80 g of activated carbon in the regeneration reactor respectively. Activated carbon catalyzed the regeneration of Fe (II) EDTA. Activated carbon is surface catalyst. More is the amount of activated carbon; more will be its surface area and more number of active sites, thus Fe (II) EDTA regeneration becomes faster with the amount of activated carbon. The rate of NO absorption did not increase significantly when the amount of activated carbon exceeded 20g. It may be due to the fact that Fe2+ ions may also be adsorbed over the surface of activated carbon; thereby reducing the rate of absorption of NO. 020406080100Amount of Activated Carbon (g) 20406080100Absorption of NO (%) Figure-2 Effect of amount of activated carbon on NO removal(Fe (II) EDTA = 0.01M, NO = 500 ppm, SO2 = 1500 ppm, O2 = 4%, pH = 7.5, 45C, Run = 2hr) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci.International Science Congress Association 66 It can be concluded from the above experimental results that activated carbon has excellent catalytic activity to regenerate Fe (II) EDTA. It not only improved absorption of NO by Fe (II) EDTA scrubbing solution but also helped to maintain a persistently high SO and NO removal efficiency. Effect of pH on NO removal: pH is a crucial factor in the absorption of NO in the scrubbing solution. Numerous experiments were carried out to examine the effect of pH on NO absorption. Figure-3 demonstrates that effect of pH on absorption of NO in absence of activated carbon. Absorption of NO decreased after one hour of experimental operation because Fe (II) EDTA is not being regenerated in absence of activated carbon. A weakly alkaline solution absorbed the NO efficiently and the optimum pH for high NO removal efficiency was found to be ~7.5. After an experimental run of 2 hour, maximum absorption of NO was observed at a pH of 7.5. The decrease in rate of NO absorption at lower pH is due to the fact that the reaction as mentioned in equation-3 shifted to backward direction. Moreover, reduction of Fe3+ to Fe2+ by sulfite ion is also not favored at low pH as can be visualized from equation-6. In addition, O gas will readily oxidize Fe (II) EDTA into Fe (III) EDTA, thereby leading to poor NO absorption. On the other hand, decrease in rate of NO absorption at a pH higher than 7.5 is attributed to the formation of Fe(OH) precipitates. Under alkaline conditions, Fe2+ ions readily combine with OH ionsand produce Fe(OH) which further undergoes oxidation to Fe(OH) instantaneously. Therefore, Fe (II) EDTA concentration will also reduce in the strongly alkaline solution and so the ability to absorb NO.02040608010012014020406080100 A b s o r p t i o n o f N O ( % ) Time (min) pH = 5.5 pH = 6.0 pH = 6.5 pH = 7.5 pH = 8.5Figure-3 Effect of pH on NO removal in absence of activated carbon (Fe (II) EDTA = 0.01M, NO = 500 ppm, SO2 1500 ppm, O2 = 4%, 45C, Run = 2hr) The experiments have also been carried out to investigate the influence of pH on NO removal in presence of 20g activated carbon. Figure-4 demonstrates that the rate of NO absorption increased as the pH increased from 5.0 to 7.5. After 4 hour continuous run, the NO removal efficiency of 71.1, 79.8, 86.8, 89.1, 91.2 and 85.8% was observed at a steady state at the pH of 5.5, 6.0, 6.5, 7.0, 7.5, and 8.5 respectively. The optimum pH for NO absorption was again found to be ~7.5. 56789 p H 20406080100Absorption of NO (%) Figure-4 Effect of pH on NO removal in presence of activated carbon (Fe (II) EDTA = 0.01M, AC = 20g, NO = 500 ppm, SO2 = 1500 ppm, O2 = 4%, 45C, Run = 4hr) Effect of liquid flow rate on NO removal: The experimental results to investigate the effect of liquid flow rate on the absorption of NO are depicted in figure-5. The rate of NO absorption increased with the increasing liquid flow rate. NO absorption was observed almost 99% in the beginning of the operation; however, it decreased to 62.2 % when the liquid flow rate is 10 mL/min. NO absorption is sustained at 87.8% when the liquid flow rate is 20 mL/min. NO absorption increased slightly at a liquid flow rate above 20 mL/min. It is due to fact that NO absorption is liquid film controlling at slow liquid flow rates. The liquid mass transfer coefficient increases and the mass transfer resistance in the liquid become small with the increasing liquid flow rate. Therefore, rate of NO absorption increased with the liquid flow rate. However, at a liquid flow rate above 20 mL/min, the mass transfer in the liquid become very small and the mass transfer resistance in the gas phase may become the main mass transfer resistance thus, NO absorption rate increased marginally. Effect of temperature on NO removal: The experiments were carried out for a period of 2 hour with a liquid flow rate of 25 mL/min, and pH of 7.5 at 35, 45, 55, 65C to investigate the effect of temperature on NO absorption into Fe (II) EDTA solution in absence of activated carbon. The rate of NO absorption decreased with temperature as can be seen in figure-6. After experimental run of 2 hour, absorption of NO was International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci.International Science Congress Association 67 found 58.4, 52.6, 47.2 and 44.6% at 35, 45, 55, 65C. The rate of NO absorption decreased with temperature. It is due to the fact that solubility of NO decreases with the rise in temperature. 0204060 L i q u i d F l o w R a t e ( m L / m i n ) 20406080100Absorption of NO (%) Figure-5 Effect of liquid flow rate on NO removal (Fe (II) EDTA = 0.01M, AC = 20g, NO = 500 ppm, SO2 = 1500 ppm, O2 = 4%, pH = 7.5, 45C, Run = 4hr) 3040506070 T e m p e r a t u r e ( o C ) 20406080100Absorption of NO (%) In absence of activated carbon In presence of activated carbon Figure-6 Effect of temperature on NO removal in presence as well as absence of activated carbon (Fe (II) EDTA = 0.01M, NO = 500 ppm, SO2 1500 ppm, O2 = 4%, pH = 7.5, Run = 2hr) Experiments were also performed at 35, 45, 55, 65C for a period of 2 hour with a liquid flow rate of 25 mL/min, and pH of 7.5 to investigate the effect of temperature on NO absorption into Fe (II) EDTA solution in presence of 20g activated carbon. It is evident from figure- 6 that absorption of NO increases with the rise in temperature. It is due to the fact that higher temperature favors the regeneration of Fe (II)-EDTA and thus enhances the absorption of NO. Effect of oxygen on NO removal: Since flue gases always contain oxygen, therefore, it is necessary to determine the effect of oxygen content in the flue gas on the absorption of NO. Figure-7 demonstrated that oxygen present in the flue gas hampers the absorption of NO into Fe (II) EDTA solution. After experimental run of 4 hour, the absorption of NO dropped slightly from 99 to 96.8% in absence of oxygen gas. However, NO removal reduced to 94.6, 86.8 and 70.2% in presence of 2, 4, 8 % oxygen content in the simulated flue gas. It is due the fact that oxygen present in the flue gas oxidizes Fe (II) EDTA into Fe (III) EDTA. The later lacks the ability to bind NO. In addition, oxygen may oxidize sulfite/bisulfite to sulphate ion and thus concentration of reductant in the scrubbing solution also decreases that is why regeneration of Fe (II) EDTA does not take place efficiently. 0246810 (%) 20406080100Absorption of NO (%) Figure-7 Effect of oxygen on NO removal (Fe (II) EDTA = 0.01M, AC = 20g, NO = 500 ppm, SO2 = 1500 ppm, pH = 7.5, 45C, Run = 4hr) Effect of sulfite/ bisulfite concentration on NO removal: Sulfite/bisulfite ions are the major reducing agents present in the scrubbing solutions which are formed by dissolution of sulfur dioxide into the aqueous solution. Sulfite/bisulfite ions not only reduce Fe (III) EDTA into Fe (II) EDTA but also reduce Fe3+ions into Fe2+ ions as suggested in equation-4 and equation-6. Therefore, it is highly desirable to investigate the effect of concentration of sulfite/bisulfite on the absorption of NO. A series of experiments were performed for a period of 2 hour at 45C, pH of 7.5 with different initial sulfite/bisulfite International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci.International Science Congress Association 68 concentrations in the scrubbing solution. The experimental results in figure-8 indicate that the presence of sulfite/bisulfite in the scrubbing solution improved the absorption of NO. After an experimental run of 2 hour, NO absorption decreased from initial 99% to 28.6 % in absence of initial sulfite/bisulfite ions however, NO removal is still maintained at 74.8, 84.6 95.4 and 98.2% with the initial sulfite/bisulfite concentration of 0.01, 0.02, 0.04 and 0.06 mol/L respectively. It is due to the fact that sulfite/bisulfite ions facilitate the regeneration of Fe (II) EDTA. It is therefore essential to optimize sulfite/bisulfite concentration in the scrubbing solution in order to achieve high NO absorption efficiency. Further, higher NO removal in alkaline medium is also due to the fact that SO being acidic gas easily combine with alkali and yield sulfite/bisulfite ions which enhance the NO absorption by regenerating Fe (II) EDTA. 00.020.040.060.08Initial conc. of sulfite/bisulfite (mol/)L 20406080100Absorption of NO (%) Figure-8 Effect of sulfite/bisufite concentration on NO removal (Fe (II) EDTA = 0.01M, AC = 20g, NO = 500 ppm, SO2 = 1500 ppm, O = 4%, 45C, pH = 7.5, Run = 2hr) Conclusion The simultaneous absorption of NO and SO into aqueous Fe (II) EDTA scrubbing solution was studied in a packed column. The operating variables included 500 ppm NO, 0.01 mol/L Fe (II) EDTA solution, pH of 5-8.5, and temperature of 35-65C respectively. SO2 is almost 100% absorbed in the scrubbing solution. NO absorption reached to maximum value in slightly alkaline solution of pH ~7.5. Activated carbon emerged as a potential catalyst for regeneration of Fe (II) EDTA. This technology can be efficiently used for combined removal of NO and SO. Absorption of NO increased with the liquid flow rate. Higher temperature is favorable for efficient NO removal in presence of activated carbon as it accelerates the regeneration of Fe (II) EDTA. Higher content of oxygen in the flue gas hampers the absorption of NO by oxidizing Fe2+ into Fe3+ and simultaneously converted sulfite/bisulfite into sulfate ions. Sulfite/bisulfite ions produced by dissolution of SO into the aqueous solution are the major reducing agents which help in regeneration of Fe (II) EDTA. The NO removal efficiency can be enhanced by addition of sulfite/bisulfite in the scrubbing solution. It is pertinent to say that High NO and SO removal efficiencies can be maintained for a long period of time using Fe (II) EDTA complex coupled with catalytic regeneration with help of activated carbon. Acknowledgement Authors are grateful to the Deenbandhu Chhotu Ram University of Science and Technology, Sonipat (Haryana) and All India Jat Heroes’ Memorial College, Rohtak (Haryana)-India for providing the basic research facilities. References 1.Baveja K., Subba Rao D. and Sarkar M.K., Kinetics of absorption of nitric oxide in hydrogen peroxide solutions, J. Chem. Eng. Jpn.,12, 322-325 (1979)2.Littlejohn D. and Chang S., Removal of NO and SOfrom flue gas by per acid solution, J. Ind. Eng. Chem. Res., 29, 420-1424 (1990)3.Perlmutter H., Ao H. and Shaw H., Absorption of NO promoted by strong oxidizing agent: 1. organic tertiary hydro peroxides in n-hexadecane, J. Environ. Sci. Technol., 27128-133 (1993)4.Sada E., Kumazawa H., Kudo I. and Kondo T., Absorption of NO in aqueous mixed solutions of NaCIO2 and NaOH, Chem. Eng. Sci., 33, 315-318 (1978)5.Sada E., Kumazawa H., Kudo I. and Kondo T., Absorption of lean NOx in aqueous solutions of NaClOand NaOH, Ind. Eng. Chem. Proc. Des. Dev18, 275-278 (1979)6.Brogen C., Karlsson H.T. and Bjerle I., Absorption of NO in an aqueous solution of NaClO, J. Chem. Eng. Technol., 21, 61-70 (1998)7.Chu H., Chien T.W. and Twu B.W., The absorption kinetics of NO in NaClO2 /NaOH solutions, J. Hazard. Mater., B84, 241-252 (2001)8.Lee H.K., Deshwal B.R. and Yoo K.S., Simultaneous removal of SO and NO by sodium chlorite solution in wetted-wall column, Korean J. Chem. Eng., 22-2, 208-213 (2005)9.Brogen C., Karlsson H.T. and Bjerle I., Absorption of NO in an alkaline solution of KMnOJ. Chem. Eng. Technol., 20, 396-402 (1997)10.Chu H., Li S.Y. and Chien T.W., The absorption kinetics of NO from flue gas in a stirred tank reactor with KMnO/NaOH solutions, J. Environ. Sci. Health, A33, 801-827 (1998) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414Vol. 4(7), 63-69, July (2015) Int. Res. J. Environment Sci.International Science Congress Association 69 11.Jin D.S., Deshwal B.R., Park Y.S. and Lee H.K., Simultaneous removal of SO and NO by wet scrubbing using aqueous chlorine dioxide solution, J. Hazard. Mater., B135, 412-417 (2006)12.Deshwal B.R., Jin D.S., Lee S.H., Moon S.H., Jung J.H. and Lee H.K., Removal of NO from flue has by aqueous chlorine-dioxide scrubbing solution in a lab-scale bubbling reactor, J. Hazard. Mater., 150, 649-655 (2008)13.Warshaw A., Removal of nitrogen oxides from a gas stream, US Patent, 3565575, (1971)14.Kustin K., Taub I.A. and Weinstock E., A kinetic study of the formation of the ferrous-nitric oxide complex, Inog. Chem., , 1079-1082 (1966)15.Teramoto M., Hiramine S., Shimada Y., Sugimoto Y. and Teranishi H., Absorption of dilute nitric monoxide in aqueous solutions of Fe(II)EDTA and mixed solutions of Fe(II)EDTA and NaSO, J. Chem. Eng. Jpn., 11, 450-457 (1978)16.Khan N.E. and Adewuyi Y.G., Absorption and oxidation of nitric oxide (NO) by aqueous solutions of sodium persulfate in a bubble column reactor, Ind. Eng. Chem. Res., 49-18, 8749-8760 (2010)17.Takeuchi H., Ando M. and Kizawa N., Absorption of nitrogen oxides in aqueous sodium sulfite and bisulfate solutions, Ind. Eng. Chem. Proc. Des. Dev., 16, 303-308 (1977)18.Guo R., Pan W., Zhang X., Ren J., Jin Q., Xu H. and Wu J., Removal of NO by using Fenton reagent solution in a lab-scale bubbling reactor, Fuel, 90-11, 3295-3298 (2011)19.Chang S.G., Littlejohn D. and Liu D. K., Use of Ferrous Chelates of SH-Containing Amino Acid and Peptides for the Removal of NO and SO from Flue Gas, Ind. Eng. Chem. Res., 27, 2156-2161 (1988)20.Pham E.K. and Chang S.G. Removal of NO from Flue Gases by Absorption to an Fe(II) Thiochelate Complex and Subsequent Reduction to Ammonia, Nature, 369, 139-141 (1994)21.Sada E. and Kumazawa H., Individual and Simultaneous Absorption of Dilute NO and SO in Aqueous Slurries of MgSO with Fe(II) EDTA, Ind. Eng. Chem. Pro. Des. Dev., 19, 377-382 (1980)22.Yih S.M. and Lii C.W., Simultaneous absorption of nitric oxide and sulphur dioxide in Fe (II) EDTA solutions in a packed absorber-stripper unit, J. Chem. Eng. 42, 145-152 (1989)23.Gambardella F., Winkelman J.G.M. and Heeres H.J., Experimental and modeling studies on the simultaneous absorption of NO and O in aqueous iron chelate solutions, Chem. Eng. Sci.61, 6880-6891 (2006)24.Wang L., Zhao W.R. and Wu Z.B.,Simultaneous absorption of NO and SO by Fe (II) EDTA combined with NaSO solution, J. Chem. Eng., 132, 227-232 (2007)25.Kurimura Y., Ochiai R. and Matsuura N., Oxygen Oxidation of Ferrous Ions Induced by Chelation, Bull. Chem. Soc. Jpn., 41, 2234-2239 (1968)26.Zang V. and Eldik R.V., Kinetics and mechanisms of the autoxidation of iron (II) induced through chelation by ethylenediaminetetraacetate and related ligands, Inorg. Chem., 29, 1705-1711 (1990)27.Wubs H.J. and Beenackers A.A.C.M., Kinetics of the oxidation of ferrous chelates of EDTA and HEDTA in aqueous solution, Ind. Eng. Chem. Res., 32, 2580-2594 (1993)28.Teramoto M. and Hiramimne S.I., Absorption of dilute nitric monoxide in aqueous solutions of Fe (II)-EDTA and mixed solution of Fe (II)-EDTA and NaSO, J. Chem. Eng., 11, 450-457 (1978)29.Wu Z.B., Wang L. and Zhao W.R., Kinetic study on regeneration of Fe (II) EDTA in the wet process of NO removal, J. Chem. Eng., 140, 130-135 (2008)30.Wang L., Zhao W. and Wu Z., Simultaneous absorption of NO and SO by Fe (II) EDTA combined with NaSOsolution, Chem. Eng. J., 132(1–3) 227–232 (2007)31.Huss A. and Eckert C.A., Solubility of sulphur dioxide in aqueous electrolyte solutions at higher ionic strengths - chloride and bromide containing systems, J. Phys. Chem., 81-24, 2268-2270 (1977)32.Dean J.A., Lange’s Handbook of Chemistry, 15th ed., McGraw-Hill, New York, (1999)