"Treatment of Heavy Metal Ions and Dyes-containing Aqueous"
Treatment of Heavy Metal Ions and Dyes-containing Aqueous Solutions by a Fenton-like Process Yung-Shuen Shen1 Jin-Yei Peng2 Jia-Wei Wu1 Ji-Ming Ma3 1 Department of Environmental Engineering, Da-Yeh University, 112 Shan-Jeau Rd., Chang-Hwa, 515, Taiwan, Republic of China 2 Department of Risk Management, Kainan University. 3 Abstract This study aims to explore the reaction behaviors of the removal 同時 of heavy metal ions and dye compounds in aqueous solutions with a combining process of cementation and Fenton process. Iron powder is used to be as the exchangeable metal to replace the lead ion in wastewaters by a cementation reaction, and then the generated Fe2+ can be as a catalyst to react with the added oxidant, H2O2, and to produce OH. radicals which can degrade the coexisting organic dyes molecular . In addition, the extra Fe2+ ions were added in combing reaction system for further comparison. 2007/10/1 The study mainly includes three kinds of batch experiments: the cementation process， Fenton process, and the combination process of cementation and Fenton process. The purpose is to investigate the removal rate of the aqueous solution with individual Red141 individual Pb2+ and both of the two mentioned mixed compounds. ， ， The results show that the combination of these two processes can efficiently treat the waste water with dyes and heavy metal simultaneously. When DO < 0.5mg/L, pH = 3.5， the concentration of dyes ranging from 20 to 200mg/L，Pb2+ = 99.27mg/L, H2O2 = 100mg/L，and Fe = 500mg，the experimental time is 150 minutes. The experimental results also show that，compared with cementation only process， using the process combining with cementation process and Fenton process to treat the mixed solution，the removal rate of Pb2+ increases 50%. And the removal rate of dye increases 5% when compared with the Fenton only process. The Fenton process and the combining process already show good results in the removal of Red141. However，the combining process and Fenton process show even better removal rate. The removal rate is higher with existing Pb2+ when treating dyes in the cementation process. Key words : cementation；Fenton process；H2O2； Fe2+； OH. 1. Introduction The cementation process uses exchangeable metals in solid state, to replace the removed or recycled metal ions. As a result, it makes all the metals be educed in solid states. The advantages include low energy consumption, high speed reaction, and easy control. The pH value, ion effect, soluble oxygen, temperature, and the stirring speed are the determinative factors in the reaction [1~4]. The driving force is the redox potential. n+ mP + nP → mP + nP n+ (1) 1 2 1 2 n+ P1 : the to-be reduced metal ion in liquid phase P2 ：the exchangeable metal solid in solid phase m，n : chemical measurement coefficient Take lead-iron system for example, the semi-reaction can be expressed as follows : Anode： Fe → Fe2+＋2e- Eao＝ 0.440V (2) Cathode： Pb2+＋2e- →Pb Eco＝- 0.126V (3) → Pb + Fe2+ ２＋ Total reaction : Fe + Pb ΔE = 0.314V (4) Fenton process is an in-phase high oxidized process. H2O2 was regarded as oxidant, Fe2+ as catalyst, and the reaction was carried out under acid condition (pH=2~4) to generate the high oxidative OH. The redox potential is 2.80V, and the relative oxidized ability is second to fluorine, with its non-selective feature. It is effective to dissolve dyes and decolorization when the hard-dissolving organic material of oxidized water could analysis macromolecule into small molecule, destroying the ion binding of color groups. When Fe2+ oxidizes to Fe3+, it starts to coagulate and mix. Effective factors are pH value, Fe2+ concentration, H2O2 concentration, temperature. The main reaction mechanism of Fenton process is expressed as follows [5~11, 14] : Fe2 + +H2O2 →Fe3++OH‧+ OH- (5) H2O2+OH‧→H2O+HO2‧ (6) H2O2+HO2‧→O2+ H2O +OH‧ (7) 2+ 3+ - Fe +OH‧→Fe +OH (8) OH．+ organics → by-products + CO2 + H2O (9) In the combining process, we used iron powder to do chemical exchange with the lead ion in aqueous solution, and then Fe2+ and Pb would be generated. Fe2+ can catalyze H2O2, and generate OH‧ radicals, which are able to oxidize dye molecules. As a result, dye molecules were decomposed to form CO2 and H2O. The reaction steps are expressed as follows : Fe + Pb2+ → Fe2+ + Pb (10) Fe2+ + H2O2 → Fe3+ + OH‧+ OH- (11) OH‧+ dye → CO2 + H2O + by-products (12) When treating the heavy metals and organic in the wastewater, the combining process can achieve the goal of better treatment with the advantages of these two processes. 2. Method The experiment uses the batch reactor, to separately carry out the cementation, Fenton process, and the combining process to treat lead ion, dye, and the lead ion with dye in the aqueous solution. And then, we take a sample to analyze water quality in the fixed time. 2.1. Mechanism of the reaction Using iron to do chemical exchange with the lead ion in cementation reaction can generate iron ion and lead. Iron ion then react with H2O2 to generate OH‧radicals, which can be decomposed to form CO2 and H2O. The ideal reaction mechanism follows the following steps : Fe + Pb2+ → Fe2+ + Pb (13) 2+ 3+ - Fe + H2O2 → Fe + OH‧+ OH (14) OH‧+ dye → CO2 + H2O + by-products (15) Other possible reaction steps include  : 2H+ + Fe → H2 + Fe2+ (16) + 2+ O2 + 4H + 2Fe → 2H2O + 2Fe (17) + 2+ 3+ O2 + 4H + 4Fe → 4H２O + 4Fe (18) 3+ 2+ 2Fe + Fe → 3Fe (19) 3+ 2+ 2+ 2Fe + Pb → Pb + 2Fe (20) + 3- 2+ 2- 2H + Fe + NO → Fe + NO + H2O (21) - Fe + OH → Fe(OH)2(s) (22) 2.2. Kinetics model This study uses power law to calculate the reaction rate and reaction orders. − ra = kc n (23) Where n represents reaction orders and k represents pseudo n-order reaction rate constant. The integrated formulas are expressed as follows: c 1− n − c 1− n = (n − 1)kt 0 n≠1 (24) c ln( ) = − kt n=1 (25) c0 Where C0 represents the initial concentration of the reactant. 3. Result and discussion 3.1. Cementation process 3.1.1. Concentration effect of lead ion Under the condition with temperature =27℃, rotational speed=1300rpm, initial pH value =4, Fe =500mg, Pb2+ concentration is 28.35, 70.91 and 99.27mg/L, respectively, the remaining rate of Pb2+ is shown in Figure 1. When the time is 150 minutes, the best removal rate could reach up to 80%. The higher Pb2+ initial concentration results in the worse removal rate. After the reaction, the pH value can reach to above 7. The possible reason can be inferred as that the surface of Fe forms O2 membrane, which would block the deposition of lead. At low pH value, the hydrogen ion in the solution could remove the oxide on the surface of the exchangeable metals, generating the active sites to accelerate the reaction speed. At high pH value, the corrosive speed on iron is the fastest, which is unfavorable to the reaction of lead ion [4, 12, 13]. 1.2 System:Fe-Pb2+ 28.35mg/LPb2+ Fe=500mg/L 1 70.91mg/LPb2+ Initial pH=4 99.27mg/LPb2+ pH adjut:HCl Rotation rate:1300rpm Temperature=27℃ 0.8 Pb2+c/c0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig.1 The lead ion effect of cementation Fe-Pb2+ system 3.1.2. Dyes Red141 effect The initial concentration of Red141 is 20, 50, 100, 200 mg/L, and the remaining rates of Red141 are shown in Fig. 2. The removal rate could be up to over than 100% when the reaction time is 150 minutes with the concentration of 20mg/L. However, the removal rate is only 51% when the concentration is 200mg/L. The reason why the dyes can be decolorized is that Fe powder has been oxidized and lost its electrons, transforming into Fe2+. The molecule of dyes has received electrons, which makes the structure of Red141 become unstable, binding ruptured, fading chromaticity. Fe → Fe2+ + 2e- (26) Dye + 2e- →Intermediate product (27) 3.1.3. Pb2+-Red141 coexistence effect In the Fe-Pb2+-Red141 cementation process, Pb2+ remaining rate is shown in Fig. 3, and the Red141 remaining rate is shown in Fig. 4. Our findings indicate that the removal rates of both Red141 and Pb2+ have significant improvement of removal (the removal rates are over 98%), compared with when one exists alone in the solution. 1.2 System:cemetation-Pb2+、 Red141 20ppm Red141 Fe=500mg/L 1 PB2+= 99.27ma/L 50ppmRed141 Initial pH=4 100ppmRed141 pH adjut:HCl 200ppmRed141 Rotation rate:1300rpm 0.8 Temperature=27℃ Red141C/C0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 2. The Red141 remaining rate in Fe-Red141 cementation system We used ultraviolet ray spectrophotometer separately to scan the simples alone and the mixed samples of lead ion and Red141, in order to find most absorbent wavelengths. At pH =4, the absorbance of simple Pb2+ is nearly to 0 in range of visible light. The absorbance of Red141 and the mixed samples showed overlapped, and the most absorbent wavelength is 541nm. This result shows that there is no disturbance of the absorbent wavelength between Pb2+ and Red14l, as shown in Fig. 5. The results show that the concentration of Fe2+ has decreased, as shown in Fig. 6. The possible reason could be that Fe2+ would form a solid state compound, which is favorable for the reaction of Fe+Pb2+ →Fe2++Pb, which means the reaction goes rightward. Also, it is helpful for Pb2+ and Red141 to perform reaction when the co-existence of Fe, Fe2+ and Red141 appears. 1.2 0ppmRed141 System:cementation-Pb2+、Red141 Fe=500mg/L 20ppm Pb2+=99.27mg/L 1 50ppm Initial pH=4 100ppm pH adjut:HCl Rotation rate:1300rpm 200ppm Temperature=27℃ 0.8 Pb2+ C/C0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 3. The Pb2+ remaining rate in Fe-Pb2+-Red141 cementation system 1.2 20ppmRed141 System:cementation- 50ppmRed141 Pb2+.Red141 1 Fe=500mg/L 100ppmRed141 Pb=99.27ppm Initial pH=4 200ppmRed141 0.8 pH adjut:HCl Rotation rate:1300rpm Temperature=27℃ Red141c/c0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 4. The Red141 remaining rate in Fe-Pb2+-Red141 cementation system 2.5 Red141 2 Red141+Pb2+ 1.5 Pb2+ abs 1 0.5 0 190 240 290 340 390 440 490 540 590 640 690 740 790 840 890 940 990 1040 1090 nm Fig. 5. The absorbance wavelength comparison of the sample Red141, Pb2+ and the mixed sample 1 0ppmRed141 0.9 20ppmRed141 50ppmRed141 0.8 100ppmRed141 200ppmRed141 System:cementation- 0.7 Pb2+.Red141 Fe=500mg/L Pb=99.27ppm 0.6 Initial pH=4 pH adjut:HCl Fe2+mM 0.5 Rotation rate:1300rpm Temperature=27℃ 0.4 0.3 0.2 0.1 0 0 20 40 60 time(min) 80 100 120 140 160 Fig. 6. The mole of Fe2+ in Fe-Pb2+-Red141 cementation system 3.2. Fenton procedure In Fenton process, and Fenton containing Pb2+ (Pb2+=99.37mg/L) process, the initial concentration of dyes Red141 were set to 20, 50, 100, 200 mg/L, respectively. The remaining rates of Red141 are shown in Fig.7 and Fig. 8. Both figures show that the removal rate of dyes can reach about 90~98% within 10 minutes. And the concentration of Pb2+ does not vary too much，as shown in Fig. 9. This also indicates that Pb2+ does not affect the removal of Red141. 1.2 20ppm Red141 System:Fenton-Red141 50ppm Red141 Fe2+=18.38mg/L 1 H2O2=100ppm 100ppm Red141 pH=3 200ppm Red141 pHadjut:HCl 0.8 Rotation rate:1300rpm Temperature=27℃ Red141 c/c0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 tme(min) Fig. 7. The remaining rate of Red141 in Fenton process 1.2 System:Fenton-Red141.Pb2+ 20ppm Red141 Fe2+=18.38mg/L 1 50ppm Red141 Pb2+=99.27mg/L 100ppm Red141 H2O2=100ppm pH=3 200ppm Red141 pHadjut:HCl 0.8 Rotation rate:1300rpm Temperature=27℃ Red141 c/c0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 tme(min) Fig. 8. The remaining rate of Red141 in Fenton process when existing Pb２＋ 0.6 0.5 0.4 Pb2+mM System:Fenton-Red141.Pb2+ 0.3 Fe2+=18.38mg/L Pb2+=99.27mg/L H2O2=100ppm 0.2 pH=3 pHadjut:HCl 20ppm Red141 Rotation rate:1300rpm 50ppm Red141 Temperature=27℃ 0.1 100ppm Red141 200ppm Red141 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 9. The mole of Pb２＋-Red141 system in Fenton process 3.3. The combining process In the combining process of cementation and Fenton processes, the conditions are listed as follows : Fe =500mg, Pb2+ =99.27mg/L, H2O2= 100 ppm, and rotational speed =1300rpm, pH =3.5, the initial concentration of Pb2+ is 99.27mg/L. We show that the remaining rate of Pb2+ and dyes in Fig. 10 and Fig. 11, respectively. The results show that the removal rate of Pb2+ in the mixed solution is 50% higher than that in the single compound solution. Furthermore, the dye removal speed in this combining process is also very fast, and its removal rate has increased 5% from the Fenton process. In this combining system, the removal mechanism of dyes not only relies on the OH‧radicals generated from Fenton process, but also the contribution of reducing function of electron of Fe powder (as the following formula show). Fe2+ + H2O2 → Fe3+ + OH‧+ OH- (28) Dye + OH‧→ intermediate product (29) Fe → Fe2+ + 2e- (30) Dye + 2e- → intermediate product (31) 1.2 System:Fenton&cementation-Red141、Pb2+ Fe=500mg 20ppmRed141 Pb2+=99.27mg/L 1 50ppmRed141 H2O2=100ppm pH=3.5 100ppmRed141 Rotation rate:1300rpm 0.8 Temperature=27℃ 200ppmRed141 Pb2+C/C0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 10. The remaining rate of Pb2+ in the combining process 1.2 System:Fenton&cementation-Red141、Pb2+ 20ppmRed141 Fe=500mg 1 Pb2+=99.27mg/L 50ppmRed141 H2O2=100ppm 100ppmRed141 pH=3.5 0.8 200ppmRed141 Rotation rate:1300rpm Temperature=27℃ Red141c/c0 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 11. The remaining rate of Red141 in the combining process 3.4. Combining process with Fe2+ added We also added Fe2+ in the combining process, and the reaction conditions are described as follows : Fe =500mg, Fe2+ =18.38mg/L, H2O2=100ppm, Pb2+ =99.27mg/L, rotational speed =1300rpm, pH =3.5, dyes Red 141=20, 50, 100, 200 mg/L. The remaining rates of Pb2+ and Red141 are shown in Fig. 12 and Fig. 13. However, the result shows that the lead ion remaining rate shows slightly slower than other groups (20~100ppm), except the group of Red141=200ppm. The dyes can be reacted completely within 10min (See Fig. 13), possible due to the addition of Fe2+ in the reaction . Fig. 14 shows that comparison of pseudo first order reaction constant k in the cementation and in the combining process with Fe2+ added. The result shows that the reaction speed of cementation is 3~20 times higher than in the combining process. The possible reason can be that the oxidative ability generated from Fenton reaction would block the Pb2+ reduction reaction. Compare the three processes, cementation process, cementation containing Red141, and combining process, we have found that the pseudo first order reaction constant k of Pb2+ in different initial concentrations of dyes follows the order : cementation > combining process with Fe2+ added >combining process(＊前後中文不符，請原作者 再看一次結果). Under the lower initial concentration, the pseudo first order reaction constant of Pb2+ is higher, and this indicates that dye has little effects on Pb2+ reduction. 1.2 20ppmRed141 System:Fenton&cementation- 50ppmRed141 Red141、Pb2+(add Fe2+) 1 100ppmRed141 Fe=500mg 200ppmRed141 Fe2+=18.38mg/L Pb2+=99.27mg/L 0.8 H2O2=100ppm pH=3.5 Rotation rate:1300rpm Pb2+c/c0 0.6 Temperature=27℃ 0.4 0.2 0 0 20 40 60 time(min) 80 100 120 140 160 Fig 12. The remaining rate of Pb2+ in combining process with Fe2+ added 1.2 System:Fenton&cementation- 20ppmRed141 Red141、Pb2+(add Fe2+) 1 50ppmRed141 Fe=500mg Fe2+=18.38mg/L 100ppmRed141 Pb2+=99.27mg/L 0.8 200ppmRed141 H2O2=100ppm pH=3.5 Red141c/c0 Rotation rate:1300rpm 0.6 Temperature=27℃ 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time(min) Fig. 13. The remaining rate of Red141 in combining process with Fe2+ added 0.045 0.04 Cementation-Pb2+ Cementation&Fenton 0.035 0.03 0.025 Pb2+ k 0.02 0.015 0.01 0.005 0 0 20 40 60 80 100 120 140 160 ppm Pb2+ Fig. 14. pseudo first order reaction constant k value of Pb2+ in cementation process and the combining process with Fe2+ added 0.07 0.06 Cemetation-Pb2+.Dye 0.05 Cemetation&Fetnon-Pb2+.Dye(add Fe2+) Cemetation&Fenton-Pb2+.Dye 0.04 Pb2+ k 0.03 0.02 0.01 0 0 50 100 150 200 250 ppm Red141 Fig. 15. pseudo first order reaction constant k value of Pb2+ in cementation process, cementation process containing Red141, and combining process 4. Conclusions 1.The Fenton process and the combining process, which have shown better treatment results in the removal efficiency of Red141, provided useful information for application. 2. Combining of these two types of processes can efficiently treat dyes and heavy metals in waste water simultaneously. The results show that the combining process can increase the removal rate of Pb2+ to 50%. And the removal rate of dyes in the combining process increases 5% than in the Fenton process. 3. For the dye treatment in the cementation, the removal rate is higher when Pb2+ existing in the process. 4. The pseudo first order reaction constant k values of Pb2+ in different processes follow the orders: cementation> combining process with Fe2+ added > combining process. 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