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MINISTRY OF EDUCATION & TRAINING MINISTRY OF DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY NGUYEN HOAI NAM STUDY ON THE ADSORPTION OF SOME DISSOLVED ORGANIC COMPOUNDS BY ADSORBENT BASED ON FERRIC[.]
MINISTRY OF EDUCATION & TRAINING MINISTRY OF DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY NGUYEN HOAI NAM STUDY ON THE ADSORPTION OF SOME DISSOLVED ORGANIC COMPOUNDS BY ADSORBENT BASED ON FERRIC HYDROXIDE WITH SiO2 AND IRON AS ADDITIVES Major: Theoretic and physical chemistry code: 62 44 01 19 SUMMARY OF PHD THESIS ON CHEMISTRY HANOI – 2014 Research was accomplished at: Academy of Military Science and Technology – Ministry of Defense Scientific Supervisor: Ass Prof Dr Tran Van Chung Prof Dr Do Ngoc Khue Reviewer 1: Prof Dr Nguyen Huu Phu Reviewer 2: Prof Dr Nguyen Duc Hung Reviewer 3: Ass Prof Dr Le Minh Cam Thesis will be defended in front of PhD thesis examination committee in ………, 2014 at Academy of Military Science and Technology following decision number … /… signed on ………, 2014 by Director of Academy of Military Science and Technology Thesis can be found at: - Library of Academy of Military Science and Technology - National library INTRODUCTION Signification Today, pollution of water resources occurs everywhere at different levels The pollutants can be organic or inorganic, which are toxic, persistent, and hard to decompose in the natural environment In order to remove these pollutants, adsorption is priority method selected In recent years, many studies have been carried out to find out the low cost materials from byproducts/products of agricultural, industrial byproducts or mineral materials etc., which can be used as adsorbent Many studies used ferric hydroxide as an adsorbent due to its sorption affinity for organic and inorganic ions However, this material has low physical strength and easy to disintegrate if submerged under water for long time In order to come over this weakness, some studies used the SiO2 as additive to increase the physical strength, nevertheless adsorption capacity decreases as the ratio of Si/Fe increasing Recently, some studies performed combination of metallic iron and ferric oxide to remove the pollutants The obtained results are very encourage to set a new trend for water and wastewater treatment technologies The aim of this study is to find out the kinetic and thermodynamic of adsorption and the applicable technic to remove 2,4-D and TNT, so topic of thesis has been chosen as follow “research on the adsorption of some dissolved organic by adsorbent based on ferric hydroxide with SiO2 and metallic iron as additive” Objective - To study the process for preparing of adsorbent based on Fe(OH)3 with SiO2 and metallic iron as additive and to characterize the prepared adsopbents including 1TP (Fe(OH)3), 2TP (Fe(OH)3+SiO2) and 3TP (Fe(OH)3+SiO2+Fe0) material - To study the kinetic and thermodynamic of adsorption of 2,4-D and TNT by prepared adsopbents - To propose the treatment technology for polluted water by 2,4-D and TNT using adsorbent based on ferric hydroxide with SiO2 and metallic iron as additives The findings The procedure for preparing of adsorbent based on the ferric hydroxide with SiO2 and metallic iron powder as additive was established Kinetic and thermodynamic of adsorption of 2,4-D and TNT by prepared adsorbents were clarified The model and solution for treatment of contaminated water by 2,4-D and TNT using prepared adsorbent were proposed B – CONTENTS OF THESIS Chapter Literature review Literature on the adsorption phenomena, type of adsorbents, special thermodynamic parameters, factors influence on the adsorption process The methods for preparing of adsorbent based on iron (III) hydroxide, surface properties and adsorption mechanisms of solid material based on Fe(OH)3 The researches on the removal of highly toxic organic pollutants were reviewed Overview of the literature showed that: - The research on the removal of 2,4-D and TNT by adsorption using adsorbent based on Fe(OH)3 has significant and practical - The issues that did not interest or unclear should be addressed in this thesis are: + Process for preparing of adsorbent based on ferric hydroxide with SiO2 and metallic iron as additive + Thermodynamic and kinetic properties of the adsorption process of 2,4-D and TNT on adsorbents based on Fe(OH)3 Chapter Experiment and Methodology 2.1 Experiment Adsorbents based on ferric hydroxide including single component (1TP), bi-components (2TP) and three components (3TP) were synthesized Effects of some parameters on adsorption such as pH, temperature, adsorbent weight, initial concentration of organic, contact time and mixing rate were investigated 2.2 Methodology - The physicochemical characteristics of adsorbent were identified using appropriate technics such as surface area by BET, crystalline phase by X-ray diffraction, morphology by SEM, chemical composition by EDX and chemistry analysis - Voltammetry used to evaluate 2,4-D and TNT concentration in the solution during adsorption - HPLC used to quantify of 2,4-D and TNT concentration in the solution before and after adsorption - Adsorption isotherms was studied following Langmuir and Freundlich models - Kinetic was determined using pseudo-first-order and pseudo-second-order - Thermodynamic parameters such as G, H and S were calculated Chapter Results and Discussion 3.1 Preparation of adsorbents based on Fe(OH)3, SiO2 and metallic iron using for adsorption study 3.1.1 Research for optimal conditional selection for adsorbent preparation To be used as an adsorbent, Fe(OH)3 must be produced in the form of particles with size ranging from 2mm or more However, Fe(OH)3 granules can easily disintegrate if submerged under water for a longtime, so SiO2 was chosen as binder to enhance physical strength of Fe(OH)3 granules Theoretically, amorphous Fe(OH)3 is formed by neutralization reaction of ferric salts with an alkaline solution, and sol Si(OH)4 can be produced by reaction of Na2SiO3 with HCl solution Whenever Si(OH)4 in contact with Fe(OH)3, the polymerization of silicic acid will be occurred and silicato-iron (III) complex formed on Efficiency (%) the surface of Fe(OH)3 precipitate 100 95 90 Fe3+ 85 Si4+ 80 0.0 2.0 4.0 6.0 8.0 10.0 pH Figure 3.2: Influence of pH solution on efficiency of co-precipitation reaction of Fe3+ and Si4+ The co-precipitation reaction of Fe3+ and Si4+ can be performed in the range of pH from – In order to achieve high efficiency of coprecipitation reaction, it is necessary to determine the optimal pH of solution after neutralization The results present in Figure 3.2 showed that to precipitate more than 95% of Fe3+, pH solution is around – 3, however to precipitate same amount of Si4+, pH must higher than So pH solution > was chosen for co-precipitation reaction to ensure that almost Si4+ and Fe3+ are precipitated completely X-ray diffraction (Figure 3.3) show that although temperature and aging time are differ from samples however morphological is not different Most of the samples are amorphous and there are not any peaks present for the Fe(OH)3 crystals Therefore, 24 hours aging time at room temperature are satisfaction 400 300 400 Lin (Cps) 100 200 300 400 Lin (Cps) Lin (Cps) 200 300 400 100 200 300 400 10 20 30 40 50 60 70 80 2-Theta - Scale Lin (Cps) M7 - File: M7.raw - Type: 2Th/Th locked - Start: 5.000 ° - End: 79.993 ° - Step: 0.011 ° - Step time: 18.9 s - Temp.: 25 °C (Room) - Time Started: 16 s - 2-Theta: 5.000 ° - Theta: 2.500 ° - Chi: 0.00 ° - Phi: Operations: Import 100 200 300 10 20 30 40 50 60 70 80 2-Theta - Scale 100 200 10 20 30 40 50 60 70 80 2-Theta - Scale M5 - File: M5.raw - Type: 2Th/Th locked - Start: 5.000 ° - End: 79.993 ° - Step: 0.011 ° - Step time: 18.9 s - Temp.: 25 °C (Room) - Time Started: 22 s - 2-Theta: 5.000 ° - Theta: 2.500 ° - Chi: 0.00 ° - Phi: Operations: Import 100 10 20 30 40 50 60 70 80 2-Theta - Scale M4 - File: M4.raw - Type: 2Th/Th locked - Start: 5.000 ° - End: 79.993 ° - Step: 0.011 ° - Step time: 18.9 s - Temp.: 25 °C (Room) - Time Started: 22 s - 2-Theta: 5.000 ° - Theta: 2.500 ° - Chi: 0.00 ° - Phi: Operations: Import 10 20 30 40 50 60 70 80 2-Theta - Scale M3 - File: M3.raw - Type: 2Th/Th locked - Start: 5.000 ° - End: 79.993 ° - Step: 0.011 ° - Step time: 18.9 s - Temp.: 25 °C (Room) - Time Started: 22 s - 2-Theta: 5.000 ° - Theta: 2.500 ° - Chi: 0.00 ° - Phi: Operations: Import Figure 3.3: X-ray diffraction of samples with different temperature and aging time According to references, the formation of different structures of Fe(OH)3 is affected by presence of ions in solution Therefore, it is necessary to assess the impacts of the presence of additives to the formation of morphology and adsorption capacity of product The results showed that Si ratio does not effect on the morphology and efficiency of TNT adsorption which only effects on the 2,4-D adsorption (Figure 3.6 and 3.7) Based on this experiment, the ratio of SiO2 is 10% by weight was selected 100 100 2,4-D 75 50 25 Efficiency (%) Efficiency (%) Lin (Cps) M6 - File: M6.raw - Type: 2Th/Th locked - Start: 5.000 ° - End: 79.993 ° - Step: 0.011 ° - Step time: 18.9 s - Temp.: 25 °C (Room) - Time Started: 21 s - 2-Theta: 5.000 ° - Theta: 2.500 ° - Chi: 0.00 ° - Phi: Operations: Import TNT 75 50 25 0 1TP 2TP5 2TP10 2TP15 2TP20 1TP 2TP5 2TP10 2TP15 2TP20 Figure 3.6 and 3.7: Removal efficiency of 2,4-D and TNT by adsorbents with different additive ratios Due to its characteristic, Fe(OH)3 is easily converted into different morphology under appropriate condition of temperature and humidity This effect on its adsorption ability Therefore, drying temperature must be controlled to obtain the desired product with acceptable physical strength and adsorption ability The results showed that drying temperature in the range of 100 - 1500C for hours is appropriate (Figure 3.8) 0.3 C/C0 0.2 0.1 0.0 room 50 100 150 Temperature 200 250 (0C) Figure 3.8: 2,4-D remaining after adsorption by 2TP10 dried at different temperature In order to have additional adsorption capacity metallic iron was added into adsorbents Results (Fig 3.10 and 3.11) showed that removal efficiency of 2,4-D and TNT increased if amount of metallic iron higher To balance the ratio of components, physical strength and longevity of adsorbent, mass of metallic iron was chosen at 10% by weight Efficiency (%) 75 2,4-D 50 25 Efficiency (%) 100 100 75 TNT 50 25 0 3TP2.5 3TP5.0 3TP7.5 3TP10 3TP2.5 3TP5 3TP7.5 3TP10 Figure 3.10 and 3.11: Adsorption efficiency of 2,4-D and TNT by 3TP 3.1.2 Identification of physicochemical characteristic of adsorbent X-ray diffraction showed that samples are amorphous and there are not any peak presence for the Fe(OH)3 crystal Compared with references, the obtained X-ray diffraction is consistent with the morphology of ferrihydrite 1TP 2TP10 3TP10 Figure 3.13: SEM images of Fe(OH)3 with different additives SEM images showed that sample 1TP and 2TP10 have large segments bound together whereas 3TP10 has small spherical particles attached and capillaries are created in between Therefore, sample 3TP10 has large surface area than that of other samples this creates more favorable for adsorption Table 3.1: The EDX analytical results Sample 1TP 2TP10 O Na Element (% weight) Al Si Cl 20.96 24.35 0.22 0.31 0.32 0.03 4.76 2.48 4.84 Fe S 76.22 65.46 0.05 3TP10 24.15 0.08 3.73 0.52 70.79 The element composition of samples in table 3.1 showed that the presence of Fe and O in almost samples furthermore 2TP and 3TP have additional element – Si On the other hand, sample 2TP10 has some other elements with small percentage and this contamination may occurred during synthesis The results of chemical analysis are conformity with calculated ratio of Fe in 1TP, 2TP10 and 3TP10 that are 65.1%, 61.3% and 76.4% respectively, and ratio of Si (% SiO2) is 0%, 8.1% and 9.3% 50 TG 25 DTA 75 2TP10 50 25 400 600 Heat flow (mW) -200 800 200 400 600 800 100 Weight (%) 200 DTA -200 0 TG 200 75 3TP10 50 25 TG DTA -200 Temperature (0C) Heat flow (mW) 1TP Weight (%) 75 200 Heat flow (mW) 100 200 Heat flow (mW) Weight (%) 100 200 400 600 800 Temperature (0C) Figure 3.15: TG and DTA Figure 3.16: TG and DTA curves curves of samples 1TP and of samples 2TP10 and 3TP10 Fe(OH)3 ferrihydrite The DTA curves show that all samples have endothermic peak from room temperature to 2000C, this is required heat to release adsorbed water At temperature > 3000C, there is only an exothermic peak on the 1TP curve, this is temperature where ferrihydrite is converted to hematite Sample 2TP10 and 3TP10 have not exothermic peak on the curve This demonstrate that there is not morphological transformation of these samples The TG curves show that all samples are lost its weight very much from room temperature to 2000C, this is weight of absorbed water, When temperature higher than 3000C, there is only 1TP sample loss its mass, the weight of samples 2TP10 and 3TP10 change not much due to no morphological transformation occurrence 11 100 69 mg/l 1TP 1TP 112 mg/l 150 75 Efficiency (%) 2,4-D Concentraion (mg/L) 200 157 mg/l 100 185 mg/l 50 50 0 150 300 450 600 100 200 300 400 500 100 69 mg/l 2TP10 Efficiency (%) 2,4-D concentration (mg/L) 200 112 mg/l 150 157 mg/l 185 mg/l 100 50 2TP10 75 50 pH 3,0 pH 4,5 pH 7,0 pH 9,0 25 0 150 300 450 600 200 100 200 300 400 500 100 3TP10 3TP10 69 mg/l 112 mg/l 150 75 157 mg/l 100 Efficiency (%) 2,4-D concentration (mg/L) pH 3,0 pH 4,5 pH 7,0 pH 9,0 25 185 mg/l 50 50 pH 3,0 pH 4,5 pH 7,0 pH 9,0 25 0 150 300 450 Time (minute) 600 100 200 300 Time (minute) 400 500 Figure 3.21: Variation of 2,4-D Figure 3.23: Effect of pH on concentration (adsorbent = g/l adsorption efficiency and pH = 4.5) Results showed that the more adsorbent used the higher efficiency of adsorption, because the number of active sites on the adsorbent surface is higher Experimental results showed that effect of agitation speed on the adsorption is not significant for all adsorbents due to adsorption also depends on the mass transfer and diffusion 12 3.2.2 Adsorption isotherm The adsorption equilibrium data were fitted to the Langmuir and Freundlich isotherm to establish the most appropriate model for the adsorption isotherm Based on the linear equation of Langmuir isotherm, the KL and qmax at different temperature were identified The bigger KL demonstrates that the higher attraction between sorbent and sorbate, hence adsorption capacity will be increased Table 3.4: Langmuir constants of 2,4-D adsorption Adsorbent Temperature Constant ( C) 1TP 2TP10 3TP10 KL (l/mg) 0.03 0.03 0.19 25 qmax (mg/g) 44.25 37.17 30.40 R 0.941 0.944 0.982 KL (l/mg) 0.04 0.04 0.23 30 qmax (mg/g) 48.54 39.06 36.10 R 0.973 0.992 0.984 35 40 KL (l/mg) qmax (mg/g) 0.04 51.55 0.06 46.30 0.42 40.49 R2 KL (l/mg) 0.978 0.04 0.992 0.06 0.988 0.41 qmax (mg/g) R2 64.94 0.994 53.48 0.994 45.25 0.983 The results in table 3.4 showed that 1TP and 2TP10 adsorbent have small value of KL and smaller than that of 3TP10 at all temperature Additionally, correlation coefficients of liner equation are low therefore, Langmuir isotherm is inappropriate to describe the adsorption of 2,4-D by synthesized adsorbents 13 Based on the linear equation of Freundlich isotherm, the KF and n at different temperature were identified Table 3.5: Freundlich constants of 2,4-D adsorption Adsorbent Temperature Constant ( C) 1TP 2TP10 3TP10 KF 3.30 3.03 10.34 25 n 1.83 1.98 3.90 30 35 40 R2 KF n R2 KF n R2 KF n R2 0.992 3.39 1.72 0.996 3.87 1.71 0.994 4.06 1.58 0.991 0.990 3.72 1.98 0.995 5.13 1.96 0.997 5.70 1.87 0.998 0.993 12.02 3.47 0.987 15.13 3.00 0.978 16.21 2.78 0.996 The obtained results in Table 3.5 show KF of 1TP and 2TP10 adsorbent are very low and lower than that of 3TP10 Based on the K F and n as well as correlation coefficients R2, it can be concluded that adsorption of 2,4-D onto adsorbents is favorable Therefore, the Freundlich isotherm is more suitable to describe the adsorption of 2,4D by synthesized adsorbents The thermodynamic constants were determined and listed in the table 3.6 The negative value of G (< 0) at studied temperature indicated that the adsorption process is spontaneous The reduction of G follows the order 3TP10 < 2TP10 < 1TP implied that adsorption by 3TP10 is more favorable compare with other adsorbents 14 Table 3.6: Thermodynamic constants of 2,4-D adsorption Temp G S H Adsorbent (K) (kJ/mol) (J/mol.K) (kJ/mol) 298 - 0.896 303 - 1.363 1TP 93.43 26.95 308 - 1.830 313 - 2.297 298 - 0.229 303 - 1.206 2TP10 195.48 58.02 308 - 2.184 313 - 3.162 298 - 4.359 303 - 5.543 3TP10 236.73 66.19 308 - 6.727 313 - 7.91 Value of S is positive (>0) and increases following order 3TP10 > 2TP10 > 1TP showed that randomness increase at solid-solution interface during adsorption process This can be explained by replacement of OH- group on the surface of iron oxide hence randomness is increased The positive H confirms the endothermic character of adsorption process and adsorption capacity increase with increase of temperature 3.2.3 Kinetic adsorption of 2,4-D Based on the Lagergren equation, results showed that k1 is varied with variation of initial concentration this is unacceptable For this reason, pseudo first order model is inappropriate to describe adsorption of 2,4-D by synthesized adsorbents 15 3TP10 2TP10 1TP 3TP10 2TP10 1TP Table 3.7: Pseudo first order constants Initial concentration (mg/l) Adsorbent 25 50 75 100 150 -2 k1x10 (1/ph) 1.15 1.84 1.38 1.6 1.1 qe (mg/g) 6.51 8.27 12.71 27.03 33.1 R 0.978 0.900 0.981 0.998 0.983 -2 k1x10 (1/ph) 1.15 1.84 1.6 1.38 1.15 qe (mg/g) 4.1 16.63 20.89 22.81 31.18 R 0.999 0.931 0.972 0.997 0.982 -2 k1x10 (1/ph) 1.84 2.07 1.38 1.6 1.15 qe (mg/g) 4.7 12.33 12.85 25.76 26.06 R 0.983 0.987 0.988 0.994 0.995 Table 3.8: Pseudo second order constants Initial concentration (mg/l) Adsorbent 25 50 75 100 150 k2 x10-3 2.24 1.66 1.04 0.37 0.17 qe (mg/g) 5.66 9.97 15.60 26.04 37.45 R 0.998 0.993 0.993 0.978 0.998 -3 k2 x10 2.04 0.87 0.42 0.25 0.13 qe (mg/g) 5.24 10.44 17.67 25.51 38.31 R 0.998 0.999 0.993 0.963 0.971 -3 k2 x10 4.48 1.90 0.96 0.51 0.28 qe (mg/g) 5.29 10.71 17.24 25.45 33.56 R2 0.998 0.997 0.995 0.996 0.998 * Unit of k2 is g/mg.min The results of pseudo second order constants showed that k2 is decrease with increase of initial concentration of 2,4-D Calculated qe is almost same to that of experiment 16 Correlation efficient of pseudo second order model of all adsorbents are high (R2 > 0.99) Therefore, it can be concluded that pseudo second order model is more appropriate to describe adsorption of 2,4-D 3.3 Study on the adsorption of TNT 3.3.1 Factors influent on the adsorption of TNT The results showed that adsorption efficiency of 1TP and 2TP adsorbent is quiet low compare with that of 3TP Influent of ratio of metallic iron powder on adsorption efficiency of 3TP can be explained by reduction of -NO2 group to -NH2 hence adsorption ability increase On other hand, 3TP adsorbent has higher surface area and pore volume so adsorption efficiency also increase Efficiency (%) 100 75 50 25 Figure 3.33: adsorption efficiency of different adsorbents The results illustrated in Fig 3.34 show that TNT concentration is reduced with time However, reduction of different adsorbents is difference TNT concentration is not reduce with time if using 1TP or 2TP, whereas 3TP reduction is significant In general, higher initial concentration of TNT results in higher TNT remaining The contact time is longer so higher removal efficiency and more TNT is adsorbed The results in Fig 3.34 show that time for adsorption equilibrium of 3TP10 is around 200 – 300 minutes 17 pH 3,0 pH 7,0 40 mg/l 80 mg/l pH 4,5 pH 9,0 6.0 150 1TP 120 Efficiency (%) TNT Concentration (mg/l) 20 mg/l 60 mg/l 100 mg/l 90 60 1TP 4.0 2.0 30 0.0 0 200 400 20 mg/l 60 mg/l 100 mg/l 600 40 mg/l 80 mg/l 150 300 pH 3,0 pH 7,0 450 pH 4,5 pH 9,0 8.0 2TP10 120 Efficiency (%) TNT concentration (mg/l) 150 90 60 30 0 200 400 4.0 2.0 0.0 600 150 150 300 450 100 3TP10 120 Efficiency (%) TNT concentration (mg/l) 2TP10 6.0 20 mg/l 40 mg/l 60 mg/l 80 mg/l 100 mg/l 90 60 30 75 3TP10 pH 3,0 50 pH 4,5 pH 7,0 25 pH 9,0 0 100 200 300 400 Time (minute) 500 600 100 200 300 400 Time (minute) 500 Figure 3.34: TNT concentration Figure 3.36: Effect of pH on the variation with time adsorption of TNT The results in Fig 3.36 showed that effect of pH on adsorption of TNT by 1TP and 2TP is not significant whereas 3TP is quite clear Adsorption effective is reduced with increase of pH The effect of pH on the adsorption efficiency can be explained by role of metallic ion In acid condition, the activation of metallic iron is higher so nitro group is easily reduced to amine, so affinity of sorbate and sorbent is higher On other hand, surface of adsorbent is also positive charged so adsorption 18 affinity with dissolved TNT molecules is higher Experimental data showed that effect of temperature on the adsorption by 1TP and 2TP is not significant compared with that of 3TP10 However, temperature has positive effect on the adsorption of 3TP10 because higher temperature, the mass transfer and diffusion are better On other hand, reduction reaction is more favorable so effective is higher Mass of adsorbent has positive effect on the adsorption Amount of adsorbed TNT increase with increase of used adsorbent due to more free activated location available Influent of agitation speed on the adsorption is not significant Because, adsorption process is not only depend on the agitation but also on the mass transfer, diffusion and number of activated location on the surface of adsorbent 3.3.2 TNT adsorption isotherm The adsorption equilibrium data were fitted to the Langmuir and Freundlich model to establish the most appropriate model for the adsorption isotherm The experimental data showed that the KL is very small and difference of adsorption capacity between experiment and calculation is not much The maximum experimental capacity at 250C of 1TP, 2TP10 and 3TP10 are 1,04; 1,46 and 41,66 mg/g, respectively, whereas calculated results based on the Langmuir isotherm model are 1,68; 2,11 and 45,25 mg/g On other hand, the correlation coefficient of linear equations is not high enough Thus, Langmuir model is inappropriate to describe the adsorption of TNT The results based on Freundlich model showed that KF of 1TP and 2TP10 are low compare with that of 3TP10 In addition, this constant is increase with increase of temperature 19 Table 3.10: Langmuir constants of TNT adsorption Material Temp Constant (0C) 1TP 2TP10 3TP10 KL (l/mg) 0.02 0.02 0.54 25 qmax (mg/g) 1.68 2.11 45.25 R 0.991 0.990 0.943 KL (l/mg) 0.02 0.02 0.61 30 qmax (mg/g) 2.15 3.42 46.08 R 0.992 0.976 0.970 KL (l/mg) 0.04 0.02 0.65 35 qmax (mg/g) 2.38 4.37 50.00 R2 0.980 0.991 0.963 KL (l/mg) 0.05 0.03 0.80 40 qmax (mg/g) 3.03 5.06 49.26 R 0.996 0.970 0.982 Table 3.12: Freundlich constants of TNT adsorption Material Temp Constant ( C) 1TP 2TP10 3TP10 -2 -2 KF 3.9x10 16.4x10 15.92 25 n 1.77 2.05 2.58 R 0.992 0.984 0.992 KF 5.8x10-2 20.2x10-2 16.63 30 n 1.84 1.89 2.38 R 0.993 0.990 0.997 -2 -2 KF 19.6x10 30.2x10 18.56 35 n 2.92 1.96 2.21 R 0.991 0.987 0.991 -2 -2 KF 31.8x10 46.7x10 19.71 40 n 3.25 2.22 2.11 R2 0.985 0.988 0.995 20 The n of Freundlich isotherm is higher than one this demonstrates that adsorption TNT is more favorable In addition, the correlation coefficient of linear equation of 3TP10 is high Therefore, Freundlich isotherm model is more is appropriate to describe the adsorption of TNT by 3TP10 Table 3.14: Thermodynamic constants of adsorption of TNT Adsorbent 1TP 2TP10 3TP10 Temp (K) G (kJ/mol) 298 303 308 313 298 303 308 313 298 303 308 313 -0.017 -1.595 -3.174 -4.753 -0.014 -0.848 -1.683 -2.518 -7.834 -8.328 -8.822 -9.316 S (J/mol) H (kJ/mol) 315.76 94.08 166.97 49.74 98.79 21.61 The thermodynamic results presented in table 3.14 showed that value of G is negative and follows the order 3TP10 < 1TP < 2TP10 Thus, adsorption process is spontaneous and adsorption by 3TP10 is more favorable than that of 1TP and 2TP10 The positive value of S indicated that randomness is increased This can be explained by replacement of OH- group on the adsorbent surface with sorbate so random is reduced H is positive indicated that endothermic process so adsorption capacity will be increased with increase of temperature 21 3TP10 2TP10 1TP 3.3.3 Kinetic of TNT adsorption In order to identify the kinetic of TNT adsorption, this research used pseudo first order (Lagergren model) and pseudo second order Table 3.16: Constants of pseudo-first-order Initial concentration (mg/l) Adsorbent 20 40 60 80 100 -3 k1x10 (1/ph) 9.2 9.2 9.2 9.2 9.2 qe (mg/g) R2 k1x10-3 (1/ph) qe (mg/g) R2 k1x10-2 (1/ph) qe (mg/g) R2 0.40 0.987 9.2 0.58 0.971 1.1 5.91 0.980 0.80 0.962 7.8 1.06 0.972 1.1 13.47 0.979 0.99 0.964 9.2 1.22 0.988 1.6 34.86 0.991 0.99 0.974 9.2 1.56 0.962 1.1 46.73 0.990 1.06 0.964 9.2 1.69 0.964 2.3 78.34 0.959 Table 3.17: Constants of pseudo-second-order 3TP10 2TP10 1TP Material Initial concentration (mg/l) 40 60 80 5,21 5,65 2,82 2,46 2,50 2,73 k2.10-4(g/mg.ph) qe (mg/g) 20 4,75 1,56 100 2,6 3,18 R2 k2.10-4(g/mg.ph) qe (mg/g) R2 k2.10-3(g/mg.ph) qe (mg/g) 0,779 9,39 1,52 0,983 2,35 9,35 0,977 1,68 5,02 0,702 1,17 19,38 0,984 1,23 5,05 0,983 0,72 28,24 0,733 1,50 5,25 0,748 0,52 36,90 0,686 0,99 5,91 0,813 0,19 51,81 R2 0,999 0,999 0,998 0,996 0,995 22 The results showed that k1 of 1TP and 2TP10 is changed not much with variation of initial concentration of TNT, whereas k2 is not Adsorption using 3TP10, k1 is varied while k2 is decrease with increase of initial concentration Therefore, pseudo first order is more appropriate to describe the adsorption of 1TP and 2TP10 Whereas, pseudo second order is more appropriate to describe the adsorption of 3TP10 3.4 Application of the achieved results to propose the process for 2,4-D (TNT) remove using material based on the ferric hydroxide with SiO2 and metallic iron as additives Based on the parameters such as initial concentration Ci (mg/l), volume of water to be treated V (l) and remaining concentration of contaminants in effluent (mg/l), the equation using to determine adsorption equilibrium will be: 𝑚𝑞𝑒 = 𝑉(𝐶𝑖 − 𝐶𝑡 ) (3.6) In which: m – mass of sorbent to be used (g); qe – adsorption capacity at equilibrium (mg/g) Adsorption of 3TP10 obeys Freundlich isotherm so relationship of m and V can be expressed by equation: 𝑚 𝐶𝑖 − 𝐶𝑡 (3.8) = 𝑉 𝐾 𝐶 1⁄𝑛 𝐹 𝑡 Based on equation 3.8, the mass of adsorbent will be determined This is weight that using to reduce contaminant from Ci (mg/l) to Ct (mg/l) in V (litter) of contaminated water CONCLUSION Adsorbents based on Fe(OH)3 with SiO2 and metallic iron as additives were synthesized which have capable for adsorption of 2,4-D and TNT from aqueous solution: 23 The process for synthesis of adsorbent based on Fe(OH)3 was developed and established in the range of laboratory with basic conditions such as, pH solution after precipitation is – with 24 hours aging time at room temperature Ratio of SiO2 and metallic iron powder should not more than 10% in mass for each additive Drying temperature is lower than 1500C in hours The physicochemical characteristics of adsorbents were evaluated using model analytical methods The results confirmed that: adsorbent is amorphous with capillary structure; the main component is ferric, iron and additives; the surface area of synthesized adsorbents is more than 200 m2/g Based on the experimental data, it can be proved that 3TP adsorbent (a new complex adsorbent) have capable in adsorption of TNT and 2,4-D The findings of this research are: The adsorption of 2,4-D and TNT by complex adsorbents based on Fe(OH)3 was systematical review The study on adsorption of 2,4-D and TNT by types of adsorbent (1TP; 2TP10 and 3TP10) showed that: Adsorption of 2,4-D and TNT by 1TP, 2TP10 and 3TP10 adsorbents is spontaneous (G < 0) Randomness is increase (S > 0) for all adsorption of 2,4-D and TNT by synthesis adsorbents Adsorption of 2,4-D and TNT by studied adsorbents is endothermic (H > 0) Adsorption of 2,4-D by adsorbents obeys pseudo second order and Freundlich isotherm Adsorption of TNT by 3TP10 obeys pseudo second order and Freundlich isotherm Whereas, adsorption of TNT by 1TP and 2TP10 did not clearly indicate which kinetic and 24 isotherm model are applicable Other parameters such as: temperature, pH solution, initial concentration of TNT and 2,4-D are influence on the adsorption The role of SiO2 and its effects on either adsorbent capacity or adsorption efficiency was identified The increase of SiO2 mass lead to reducing in adsorption capacity For this reason, the weight of SiO2 should be kept at 10 % by mass This ratio is enough to increase of physical strength but adsorption capacity is not much affected The role of metallic iron powder in 3TP10 adsorbent and its effects on the adsorption, especially adsorption of TNT were identified The adsorption efficiency of 2,4-D and TNT is increased with increasing of iron powder in 3TP10 PUBLICATIONS Trần Văn Chung, Lê Quốc Trung, Nguyễn Hồi Nam, Phan Bích Thủy, Nguyễn Văn Tuấn, Phan Văn Cường, Vũ Thị Kim Loan (2010), Ứng dụng phương pháp Voltammetry nghiên cứu trình khử nitrobenzene sắt hóa trị khơng, Tạp chí Nghiên cứu Khoa học Công nghệ Quân (Số đặc biệt – HNKHCNMT), tr 120 – 126 Nguyễn Hoài Nam Trần Văn Chung (2010), Chế tạo vật liệu hấp phụ hai thành phần FeOOH/SiO2 theo phương pháp nhiệt thủy phân, Tạp chí Khoa học - Khoa học tự nhiên, Đại học Sư phạm Hà nội, 55 (3), Tr 71 - 81 Nguyễn Hoài Nam, Trần văn Chung, Đỗ Ngọc Khuê (2012), Xác định thông số hoá lý vật liệu hấp phụ sở Fe(OH)3, SiO2, sắt kim loại khả ứng dụng để xử lý 2,4,6Trinitrotoluene nhiễm nước, Tạp chí Hóa học, 50 (4), Tr 477 – 482 Nguyen Hoai Nam, Dao Van Bay, Do Ngoc Khue, Tran Van Chung (2013), Removal of 2,4-Dichlorophenoxyacetic Acid using Fe(OH)3 based complex adsorbent, Asian Journal of Chemistry, 25 (6), pp 3479 – 3483 Nguyen Hoai Nam, Dao Van Bay, Tran Van Chung (2013), The adsorption characteristics of 2,4,6 - Trinitrotoluene (TNT) onto the FeOOH based complex adsorbent in aqueous media, International Journal of Chemistry, (1), pp 14 – 24 Nguyễn Hoài Nam, Trần Văn Chung, Đỗ Ngọc Khuê (2013), Nghiên cứu đặc điểm trình hấp phụ 2,4,6-Trinitrotoluen (TNT) vật liệu tổ hợp dựa Fe(OH)3, Tạp chí Xúc tác Hấp phụ, (3) , tr.117 – 123 Le Quoc Trung, Nguyen Duc Hung, Nguỵen Hoai Nam, Tran Van Chung, I Francis Cheng (2010), Oxidation of 2,4,6Trinitroresorcine using zero-valent iron, Asian Journal of Chemistry, 22 (4), pp 3200 – 3206