Nitrobenzene degradation induced by oxygen activation in a zero valent IRON/AIR/EDTA/water system

The degradation and mineralization efficiency of NB in the systems looked at in this study were determined by measuring the NB concentration and COD values before and after reaction. The influence of pH, Fe(0)-mass and EDTA on the degradation and mineralization efficiencies were also investigated.

JOURNAL OF SCIENCE OF HNUE Chemical and Biological Sci., 2014, Vol 59, No 9, pp 59-65 This paper is available online at http://stdb.hnue.edu.vn NITROBENZENE DEGRADATION INDUCED BY OXYGEN ACTIVATION IN A ZERO-VALENT IRON/AIR/EDTA/WATER SYSTEM Tran Duc Luong1 , Nguyen Hoai Nam2 and Tran Van Chung3 Faculty of Biochemistry, Nam Dinh University of Nursing Institute of Material Science, Vietnamese Academy of Science and Technology Institute of Chemistry and Material, Academy of Military Science and Technology Abstract Nitrobenzene (NB) is a recalcitrant organic compound that can be degraded and mineralized by oxygen activation induced in a zero-valent iron/air/EDTA/water system The degradation and mineralization efficiency of NB in the systems looked at in this study were determined by measuring the NB concentration and COD values before and after reaction The influence of pH, Fe(0) -mass and EDTA on the degradation and mineralization efficiencies were also investigated Keywords: Nitrobenzene, activation of oxygen, zero-valent iron Introduction Nitrobenzene (NB) and its derivative compounds are widely used in practices that can harm ecological systems and human health [11] NB is a toxic recalcitrant organic compound and a dangerous environmental pollutant that is present in industrial wastewater [1, 3-5, 9, 12] NB from wastewater can be treated using various methods [9] Of these methods, an advanced oxidation process that removes NB with high efficiency is presented in this paper This method, which destroys NB that is present in wastewater using oxygen activated with ZVI and EDTA, is described in detail An aqueous system consisting of oxygen, ZVI and EDTA can producing free radical OH• which can oxidize NB and other recalcitrant organic compounds [1, 3, 5-8, 10] The process of oxygen activation using ZVI with EDTA to produce free radical OH• is suggested in [5] It is hypothesized that the mechanism of the process is the production of reactive oxygen intermediates Intermediates such as hydrogen peroxide are postulated to be continuously produced by the reduction of aqueous oxygen which may take place either on the iron surface or in solution [5] In another way, FeII L complexes (L denoted EDTA) might be Received September 14, 2014 Accepted November 28, 2014 Contact Tran Van Chung, e-mail address: tranchunghhvl@gmail.com 59 Tran Duc Luong, Nguyen Hoai Nam and Tran Van Chung reacting with O2 to form the superoxide radical which leads to the production of H2 O2 and eventually to a Fenton reaction as follows [4]: Fe(0) → Fe2+ + 2eE0red = −0, 44V 2+ Fe II + L = Fe LKf = 10 14.32 FeII L + O2 → FeIII L + O•− II Fe L + O•− + 2H+ → Fe L + H2 O2 III FeII L + H2 O2 → FeIII L + OH• + OH− , kF = 103 M1−1 s−1 (1.1) (1.2) (1.3) (1.4) (1.5) The NB molecules (R) can be oxidized with OH• to produce CO2 , H2 O and mineral salt: R + OH∗ → CO2 + H2 O + meneral salt (NO− 3) (1.6) During the reaction, the oxidation efficiency of NB by reaction with O2 -activationwas determined by measuring the change of NB-concentration and COD (Chemical Oxygen Demand) values The main factors influencing the oxidation efficiency of NB, such as dose of Fe0 , EDTA and pH, were investgated Content 2.1 Materials and methods * Materials All of the chemicals used in this work were of reagent grade EDTA (> 99.0%), NB (yellowish liquid, d = 1.199 g/cm3 ), concentrated sulfuric acid (> 98.0%), sodium hydroxide (> 96.0%) and iron powder (cubic-Fe > 98%, particle size 0.50 µm) were purchased from Shanghai Chemical Reagent Co., Ltd, China All solutions were prepared with distilled water * Experiment Batch experiments were carried out in a 500 mL glass vessel using a 200 mL solution The solutions were continuously stirred with a mechanical stirrer Stock solutions of NB (80 mg/L) were prepared in glass jars using 66.7 mL NB (liquid) diluted to 1000 mL by adding distillated water The pH of all solutions was adjusted with 0.1 M NaOH or H2 SO4 A pre-determined mass of Fe(0) and EDTA was added to the NB - solution to investigate oxygen activation During the reaction, a flow of atmospheric oxygen was passed through the solution to ensure that the saturated oxygen concentration in the sample was mg/L Samples of a certain volume of solution collected from each reaction vessel at regular time intervals were filtered to determine the concentration of NB and COD value remained 60 Nitrobenzene degradation induced by oxygen activation * Analytical methods - The pH solution was monitored using a Toledo pH meter - The concentration of NB was determined by anodic stripping Voltammetry with a mercury hanging drop electrode (HMDE) using Metrohom 797 VA computrace The solution consisting of NB in acid acetic-sodium acetate buffer 0.1 M as electrolyte was removed oxygen for 60 s by N2 gas, then pre-concentrated onto HMDE for 60 s at a potential of -0.90 V, then an anodic stripping Voltammetric current was determined in the potential as being from -0.90 to -0.10 V The current peak height appeared at -0.442 V, this being proportional to the NB concentration used for analysis of this compound The degradation efficiency (ENB ) of NB for the reaction time was determined based on the following expression: ENB = CoNB − CtNB × 100% C0NB (2.1) here C0NB is the initial concentration of NB in the sample and CtNB is the NB concentration for the t-reaction time COD analysis was determined by the usual method using K2 Cr2 O7 and concentrated sulfuric acid [2] The mineralization efficiency (ECOD ) of NB was evaluated by the expression: ECOD = C0COD − CtCOD × 100% C0COD (2.2) here C0COD , mg/L denoted initial COD and CtCOD , mg/L is for t-reaction time 2.2 Results and discussion 2.2.1 The degradation and mineralization of NB by oxygen activation in a zero-valent air/EDTA water system The initial experiments were carried out using various concentrations of components to demonstrate the capacity of NB degradation and its mineralization The experimental results are listed in Table Table Result of degradation and mineralization of NB under the condition: CFe = 0.15 g/L; CEDTA = 6.72 mg/L, O2 = mg/L, pH = 3.0, reaction time: 150 minutes t No CCOD mg/L CNB mg/L COD0 CODt ECOD (%) ENB % 50.0 0.56 96 29 69.8 98.9 30.0 0.24 55 15 72,7 99.2 20.0 0.10 38 81,6 99.5 61 Tran Duc Luong, Nguyen Hoai Nam and Tran Van Chung The data from Table indicate that in the system consisting of Fe(0) , EDTA and O2 , there is a process of degradation and mineralization of NB The NB degradation process takes place much more quickly than does the mineralization This shows that in the system, during a 150 minute time period, NB was converted into intermediate compounds and most of them mineralized to produce CO2 , H2 O and mineral salts 2.2.2 Factors influencing the degradation and mineralization of NB * Influence of pH The influence of pH (from 2.5 to 9.5) on NB degradation and mineralization for a 150 minute reaction time is presented in Table Table Influence of pH in the reaction condition: = 30 mg/L; COD0 = 55 mg/L; CF e = 0.15 g/L; EDTA = 6.72 mg/L O2 = mg/L pH 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 CODt mg/L 3 20 35 47 ECOD % 89.1 92.5 92.5 90.9 85.,5 63.6 36.3 14.5 CNB mg/L 0.15 0.081 0.081 0.18 0.33 0.36 0.46 0.82 ENB % 99.5 99.7 99.7 99.4 98.9 98.8 98.4 97.3 C0N B The experimental data in Table indicate that in the range of pH from 3.5 to 4.5, the degradation and mineralization efficiencies of NB were highest, then they decreased slowly This phenomenon can be explained as the formation of free radical OH• in situ from reaction (5) - Fentonreaction In an acid medium, H+ ions will enhance the formation of free radicals and this will increase NB degradation and mineralization efficiency However, at pH < 3.5, the corrosion rate of iron in the sample will be higher than at pH > 3.5, and this leads to a production of more Fe2+ These Fe2+ ions will consume free radical OH∗ and reduce the degradation and mineralization of NB This is consistent with the work [2] * Influence of Fe(0) mass Nr 62 Fe(0) , g/L 0.25 0.50 0.70 1.0 1.5 2.0 2.5 Table Influence of Fe(0) -mass CODt mgO2 /L ECOD (%) CNBtmg/L 31 44.4 3.81 15 71.3 1.86 83.6 0.45 92.5 0.081 90.8 0.26 11 80.1 0.72 26 52.7 0.94 ENB % 87.3 93.8 98.5 99.7 99.1 97,6 96.7 Nitrobenzene degradation induced by oxygen activation The influence of Fe (0) mass on the degradation and mineralization of NB was determined under the experimental condition: C0NB = 30 mg/L; COD0 = 55 mg/L; EDTA = 6.72 mg/L; O2 = mg/L, pH = 3.5; Fe (0) mass changing from 0.25 to 2.5 g/L, with a reaction time of 150 minutes The obtained result is presented in Table The experimental data from Table shows that the degradation and mineralization efficiencies of NB increase when Fe(0) mass increases from 0.25 to 1.0 g/L, then they decreases when Fe(0) mass is increased This can be explained by the reaction of free radicals with Fe(0) or Fe2+ available in the system as follows: OH∗ + Fe2+ → Fe3+ + OH− (2.3) 2OH∗ + Fe(0) → Fe2+ + 2OH− (2.4) These lead to reduced efficiency of NB degradation and mineralization * Influence of EDTA The influence of EDTA on the degradation and mineralization of NB was determined under the experimental condition: C0NB = 30 mg/L; COD0 = 55 mg/L; Fe(0) = 1.0 g/L; O2 = mg/L, pH = 3.5; EDTA changing from 0.83 to 11.7 mg/L, with a reaction time of 150 minutes The obtained results are presented in Table Nr (0) Fe g/L 1.0 1.0 1.0 1.0 1.0 1.0 2.5 Table Influence of EDTA EDTA mg/L CODt mgO2 /L ECOD % 0.83 37 68.4 1.66 16 71.5 3.36 85.2 6.72 92.5 8.38 92.8 10.04 90.1 11.70 86.2 CNBt mg/L 0.57 0.36 0.15 0.081 0.082 0.093 0.98 ENB % 98.1 98.8 99.5 99.7 99.7 99.6 96.7 The obtained data in Table show that the degradation and mineralization efficiencies of NB increase when the EDTA concentration increases from 0.83 to 11.70 mg/L When the concentrations of EDTA were higher than 8.38 mg/L, the efficiencies of NB degradation decreased, perhaps due to the reaction of free radicals with EDTA in the sample 2.2.3 Degradation kinetics of NB by oxygen activation in a zero-valent iron/air/EDTA water system By experimentation, the optimal conditions for oxygen activation in a zero-valent iron/air/EDTA water system were established The optimal conditions were pH = 3.5 63 Tran Duc Luong, Nguyen Hoai Nam and Tran Van Chung 4.5, EDTA concentration = 6.72 - 8.38 mg/L; Fe(0) -mass = 1.0 g/L, and a reaction time of 150 minutes Under these conditions, the change of COD and NB concentrations versus the reaction time of from to 210 minutes are presented in Table Table The change of COD and NB concentration vs time Time, mins 30 60 90 120 150 180 COD, mgO2 /L 55 32 18 10 NB, mg/L 30.0 9.1 2.79 0.85 0.265 0.081 0.025 210 0.012 By simple calculation, the integral reaction rate expressions corresponding to the reduction of NB and COD versus time were found These expressions obey the pseudo first order reaction with the following forms: For NB concentration: YNB = kNB t + b; kNB = −0.03812 ± 7.3 × 10−4 /min; b = 3.31652 ± 0.092 For the COD reduction: YCOD = kCOD t + b; kCOD = −0.01897 ± 3.46 × 10−4 /min; b = 4.04032 ± 0.03745 These results show that the reaction constant of the NB degradation process is always higher than the reaction constant of NB mineralization This is consistent with the experimental data shown in Tables 1, 2, and Conclusion The system consisting of zero-valent air/EDTA/water was successfully applied to show the degradation and mineralization of NB The degradation and mineralization of NB are taken to be due to the appearance of free radical OH• in the samples By experimentation, the optimal conditions for oxygen activated by Fe(0) + EDTA were established: pH =3.5 - 4.5, EDTA concentration = 6.72 - 8.38 mg/L; Fe(0) -mass = 1.0 g/L, and a reaction time of 150 minutes Under these conditions, the degradation and mineralization of NB can reach > 99% for NB and > 92% for COD REFERENCES [1] Akhavan J., 2004 The chemistry of Explosives, 2nd ed., The Royal Society of Chemistry, Cornwall, Chapter 1, p [2] Chen Run-hua, Chai Li-yuan, Wang Yun-yan, Liu Hiu, Shu Yu-de, Zhao Jing, 2012 Determination of organic wastewater containing Cu-EDTA by Fe-C micro-electrolysis Science Direct, Trans Nonferrous Met Soc China, 22, pp 983-990 [3] Chen Y., Liang K., Xun H., & Wang S., Y., 1998 Study of nitrobenzene in wastewater by spectrophotgometry Capital Normal University Transaction (Nature Science) 19, pp 72-76 64 Nitrobenzene degradation induced by oxygen activation [4] Christina E., Noraqdoun I., Francis Cheng, 2005 EDTA degradation induced by oxygen activation in a zerovalent Iron/Air/Water system Environ Sci Technol 39, pp 7158-7163 [5] Darek F., Laine I Francis Cheng, 2007 The destractrion of organic pollutants under mild traction conditions: A review Microchemical Journal 85, pp 183-193 [6] ISO 6060:1989, 1999 Water quality- Determination of the chemical oxygen demand [7] Lotufo G R., Blackburn W M., Gibson, A B., 2010 Toxicity of trinitroluene to sheephead minnows in water exposures, Ecotoxicol Environ Saf 73, 718-726 [8] Matta R., Hanna K., Kone T., Chiron S., 2008 Oxidation of 2,4,6-Trinitrotoluene in the prsence of different iron-bearing mineral at natural pH Chem Eng J 144, pp 453- 458 [9] Ni N., Wang L.,& Kokot S., 2001 Simultaneous determination of nitrobenzene and nitro-substituted phenols by differential pulse voltammetry chemometrics Analytica Chemica Acta 431, pp 101-113 [10] Rosen G., Lotufo G R., 2007 Toxicity of explosive compunds to the marine mussel, Mytilus galloprovincialis, in aqueous exposure, Ecotoxicol Environ Saf 68, pp 228-236 [11] Wang S P & Chen W J., 2002 Separation and determination of nitro benzene by micellar electrokinetics chromatography and high performance liquid chromatography Journal of Chromatography A, 979, pp 439-446 [12] Zhao X K., Yang G P., & Gao X C., 2003 Studies on the sorption behavior of nirtobenzene on marine sedments Chemosphere, 52, pp 917-925 65 ... (Nature Science) 19, pp 72-76 64 Nitrobenzene degradation induced by oxygen activation [4] Christina E., Noraqdoun I., Francis Cheng, 2005 EDTA degradation induced by oxygen activation in a zerovalent... system consisting of zero- valent air/EDTA/water was successfully applied to show the degradation and mineralization of NB The degradation and mineralization of NB are taken to be due to the appearance... initial COD and CtCOD , mg/L is for t-reaction time 2.2 Results and discussion 2.2.1 The degradation and mineralization of NB by oxygen activation in a zero- valent air/EDTA water system The initial