Iraqi Journal of Chemical and Petroleum Engineering Vol.14 No.3 (September 2013) 23- 31 ISSN: 1997-4884 Removal of Phenol Compounds from Aqueous Solution Using Coated Sand Filter Media Asrar Al-Obaidy Chemical Engineering Department-College of Engineering-University of Baghdad-Iraq Abstract Coated sand (CS) filter media was investigated to remove phenol and 4-nitrophenol from aqueous solutions in batch experiments. Local sand was subjected to surface modification as impregnated with iron. The influence of process variables represented by solution pH value, contact time, initial concentration and adsorbent dosage on removal efficiency of phenol and 4-nitrophenol onto CS was studied. Batch studies were performed to evaluate the adsorption process, and it was found that the Langmuir isotherm effectively fits the experimental data for the adsorbates better than the Freundlich model with the CS highest adsorption capacity of 0.45 mg/g for 4- nitrophenol and 0.25 mg/g for phenol. The CS was found to adsorb 85% of 4- nitrophenol and 65% for phenol at an initial concentration of 25 mg/ℓ. Key Words: coated sand, phenol, 4-nitrophenol, adsorption, batch study. Introduction Wastewaters containing phenolic compounds are serious environmental problem , and cannot simply be released into the environment without treatment . Several methods are currently used for the removal of phenol and its derivatives from wastewater , e.g. microbial degradation [1] ,chemical oxidation [2] , incineration [3] , solvent extraction [4] and irradiation [5] . However, by far the most frequently used technology is adsorption by solid phase . Several different adsorbent solids such as activated carbon [6, 7, 8, 9 ], silica [10] , glass powder [11] , polymeric resins [12,13] , fly ash [ 14, 15, 16, 17, 18, 19, 20 ], peat [21, 19], kaolinite [22] and zeolites [23, 24] have all been proposed to remove phenolic pollutants from wastewaters . Recent studies have shown that metal oxides (such as iron oxides, aluminum oxides or manganese oxides) have relatively high surface area and surface charge, and can be applied to the removal of heavy metals and organic matters from water and wastewater [25, 26, 27, 28]. However , most of metal oxides are available only as fine powders or are generated in separation. Beside, due to their low conductivity, the aqueous solutions as hydroxide floc or gel. Therefore, they are limited to reactor configurations incorporating with large sedimentation basins or filtration units because of the difficulty in solid/liquid metal oxides alone are not suitable as filter media [29]. Iraqi Journal of Chemical and Petroleum Engineering University of Baghdad College of Engineering Removal of Phenol Compounds from Aqueous Solution Using Coated Sand Filter Media 24 IJCPE Vol.14 No.3 (September 2013) -Available online at: www.iasj.net Recently, some researchers have developed techniques for coating metal oxides onto sand surface in order to overcome the above problems of using metal oxides powders in water treatment process . In this study kind of iron-oxide-coated sand was prepared by coating process and the phenol and 4-nitro phenol adsorption from aqueous solution was investigated by batch experiments in order to get available CS filter media for effective removal of phenol and its derivatives. Experimental Procedure Adsorbent Material To prepare CS filter media, natural quartz sand (QS), with a particle size ranging from 0.5 to 0.8 mm, was used as the supporting material for iron oxide. Firstly , the sand was pre- washed several times with tap water until run-off was clear . After the sand was dried at 110ºC, it was soaked in 0.1M HCI solution for 24h. Then the sand was rinsed to remove impurities, dried at 110ºC and finally stored in capped bottles. Stock solution of 2.5 M Fe (III) was prepared by dissolving FeClɜ·6H₂O in deionized water. CS was prepared with the following coating processes: The solution containing a mixture of 400 mL of 2.5 M Fe (III) and 1 mL of 10 M NaOH was pourd over 800 mL dried sand placed in a heat- resistant dish . after gentle agitation , the mixture was heated for 96 h at 110ºC and then at 200ºC until it appeared to be dry. After cooling , the coated sand was washed with tap water until run-off was clear , then the coated sand was dried at 110ºC . After above coating step was finished , the sand was coated again according to the same step , and stored in polystyrene bottles for further use [30] . Adsorbate Material The stock solution was prepared by diluting the required quantities of phenol or 4-nitrophenol with distilled water to obtain adsorbate solution of various initial concentrations. The effect of pH, contact time and (CS) loading was studied using 25 mg/ℓ of phenol or 4-nitrophenol and 5 gm of CS was adjusted with either dilute HCl or NaOH solution to a constant value. All the pH measurements were done with a pH meter (827 pH Lab, Metrohm). Each flask was capped and inverted 3 times to mix the contents thoroughly and then allowed to stabilize for 10 to 15 min . The effect of CS loading at 307 K were conducted by contacting initial phenol and 4-nitrophenol concentrations of 20 mg/l with varying quantities of CS ( 1 to 7 ) g in a series of 25 ml Pyrex conical flasks at a pH of 3.12 ± 0.10 . The effect of initial concentration of phenol and 4-nitrophenol was studied using different initial concentrations of (20, 40, 60, 80, 100 mg/l) with 1 g of CS, stirred at 180 rpm for 3 hours. The concentration changes of the individual compounds in the solutions were determined by means of UV-VIS spectrophotometry (SQ- 4802 Double Beam). The maximum absorbance for each solute from the highest standard solution prepared were found using scanning spectrophotometry at the respective wavelength maxima λ . The λse used were 270 nm and 320 nm for phenol and 4-nitrophenol respectively. The calibration plot of absorbance vs. concentration for all the standards showed a linear working range up to 30 mg/l with correlation coefficient ≥ 0.99. the supernatant solutions obtained after adsorption Asrar Al-Obaidy -Available online at: www.iasj.net IJCPE Vol.14 No.3 (September 2013) 25 were also analysed using the same wavelengths . Adsorption Kinetics Kinetic tests using a mixture of phenol or 4-nitrophenol were performed in a batch fashion . The initial solutes mix was analyzed to determine the initial concentration of the solutes before mixing with the CS. For each adsorption data point , a 25 ml aliquot of the adsorb ate solution having an initial phenol or 4-nitrophenol concentration of 20 mg/l , constant CS loading of 5 g at temperature of 307 K were introduced into a series of 25 ml Pyrex conical flasks for different contact times and at a pH of about 3. The conical flasks were placed and shaken in a Labcon platform shaking incubator ( Model FSIM- SPO16 ) where the last sample was collected after 300 min of contact time and at a constant stirring speed of 200 rpm . The samples were covered throughout the experiment and the supernatant solution filtered through whatman micro-fiber filters of 0.45 µm to determine the concentration of each solute left after different time intervals of agitation (15,30,60,….,300 min) .The flasks were shaken in a Labcon platform shaking incubator ( Model FSIM- SPO16 ) to attain equilibrium after about 22 h of contact time and at a constant stirring speed of 200 rpm. Adsorption Isotherms The ability of the prepared CS to remove the phenol or 4- nitro phenol from aqueous solutions was determined under batch mode conditions. The equilibrium isotherms were determined by mixing 5 gram of CS with different concentrations (20, 40, 60, 80 and 100 mg/l) of each solution of phenol or 4- nitro phenol in conical flasks. Flasks were shaken at 200rpm overnight to assure that equilibrium was reached. The residual concentration was analyzed using Atomic Absorption Spectrophotometer. Data obtained from the adsorption isotherm tests were used to determine the adsorption capacity of CS . The equilibrium adsorption uptake and percentage removal of phenol from the aqueous solution qe (mg/g) was determined using the following relationship : Amount adsorbed ( ) …(1) (mg of adsorb ate / g of adsorbent) and, % removal = ( ) …(2) Where: Co is the initial sorbet concentration (mg/ℓ) Ce is the equilibrium sorbet concentration (mg/ℓ) V is the volume of solution (ℓ) w is the mass of the adsorbent (g) Results and Discussions Characterization of CS Filter Media QS and CS surface photographs are shown in Fig.1. Magnification by SEM of 2000 and 25000x is made to show the morphology of the surfaces. It can be seen that the deposition had changed the smooth surface of sand. New cracks occurred on the surface with new microspores appeared between the new crystals or cubes deposited of iron oxide. It can be concluded that the coating step changed the morphology of natural sand. The amount of iron ox hydroxide deposits onto sand was determined to be about 30 mg-Fe/g-sand Jianbo et al [30] had used the same coating procedure and analyzed this amount to be 31.13mg-Fe/g-sand. Removal of Phenol Compounds from Aqueous Solution Using Coated Sand Filter Media 26 IJCPE Vol.14 No.3 (September 2013) -Available online at: www.iasj.net (a) QS (b) CS (c) QS (d) CS Fig.1, SEM for natural sand QS (a and c) and the prepared CS (b and d). (a) and( b) at 2000 magnification. (c) and (d) at 25000 magnification Adsorption Time Fig. (2) Represents the results for the effect of contact time on the removal of phenol and 4-nitrophenol from aqueous solution at an initial concentration of 20 mg/ℓ. It can be seen that the amount of all the adsorbents adsorbed onto CS increases with time and about 65%, 70% of phenol and 4-nitrophenol had been removed within the first 15 min of agitation, respectively, after which the process approaches equilibrium. The time profile for adsorbents is a single, smooth, and continuous curve leading to saturation, which suggests possible monolayer coverage of the adsorbents on the surface of the CS. Fig. 2, Effect of contact time on percentage removal Adsorption Isotherms The analysis of the adsorption isotherms is important for design Asrar Al-Obaidy -Available online at: www.iasj.net IJCPE Vol.14 No.3 (September 2013) 27 purpose. Therefore, experimental data were analyzed with well-known two- parameter adsorption isotherm models including the Langmuir, Freundlich isotherms. Fig. 3, Adsorption isotherms of phenol and 4- nitrophenol on CS Phenol and 4-nitrophenol adsorption isotherms obtained for CS are shown in Fig.3. Ttese isotherms represent the adsorption behavior of phenolic compounds at various temperatures as a function of equilibrium aqueous concentration, for a contact time of 24 h. The rearranged Langmuir isotherm can be described as: = + ( ) ( ) …(3) Where: β is an adsorption equilibrium constant related to the binding energy The Langmuir adsorption isotherm is based on the concept that solid surfaces have finite adsorption sites. When all the adsorption sites are filled, the surface will no longer be able to adsorb solute from the solution. The maximum amount of solute (Qm) adsorbed in a particular system can be estimated from the isotherm parameters. The plot of ⁄ vs. ⁄ should yield a straight line. The slope is ⁄ and the intercept is ⁄ . The freundlich adsorption isotherm can be written in the form: Log Q = log Kf + ⁄ log Cₑ …(4) The freundlich isotherm predicts that the adsorb ate concentration on the surface of an adsorbent will increase when there is an increase in the initial adsorb ate concentration in the aqueous solution. The experimental data obtained are plotted as log Qₑ versus log Cₑ, to obtain the constants K and ⁄ . The constant Kf is a comparative measure of the adsorption capacity of the adsorbent, while is an empirical constant. The magnitude of gives an indication of the favorability of adsorbent/adsobate system. Values of signify that the solute has a low affinity for the adsorbent at low concentration. Likewise, a value of is an indication of favorable adsorption and a high affinity between the solute and solid phase. The freundlich (Kf and ⁄ ) and Langmuir constant (β and Q ) determined from the adsorption isotherm for phenol and 4-nitrophenol depicted in figs. 3 and 4 are summarized in Table 1. The correlation coefficient values determined for each of the adsorption isotherm indicates that the Langmuir model effectively fits the experimental data better than the Freundlich model. The adsorption capacity for phenol and 4-nitrophenol at the maximum residual concentration was calculated using the Langmuir constant β at an initial concentration of 20 mg/l for all the adsorbents and the values obtained were 3.779 mg/g, 3.679 mg/g for phenol and 4-nitrophenol, respectively. Removal of Phenol Compounds from Aqueous Solution Using Coated Sand Filter Media 28 IJCPE Vol.14 No.3 (September 2013) -Available online at: www.iasj.net Table 1, Adsorption isotherm models for phenol and 4-nitrophenol on CS Model Parame ter ph PNph Langmuir Qm 3.779 3.679 β 0.784 1.115 R 2 0.837 0.962 Freundlich ⁄ Kf 4.265 0.728 n 37.07 37.53 R 2 0.764 0.998 Fig. 3, The linearized Freundlich adsorption isotherm for phenol and 4-nitrophenol mixtures onto CS Fig. 4, The linearized Langmuir adsorption isotherm for phenol and 4-nitrophenol mixtures onto CS Effect of Initial pH The pH of the aqueous is an important variable that influences the adsorption at the solid-liquid interface. The effect of variation of the initial solution pH (3,4,5,6,7,8,9,10,11,12,13) on the adsorption of phenol and 4- nitro phenol is illustrated in Fig.5. for CS, the adsorption removal percentage decreases with an increase in pH from 3.6 to 10.2 and from 3.5 to 8 for phenol and 4-nitrophenol respectively. Fig.5 also shows that 70% maximum removal percentage of phenol is achieved at pH value of 3.6.While for 4-nitrophenol, a maximum removal percentage of 97% is obtainedat pH of 3.5.Therefore, the values of 3 6 and 3.5 are considered to be the best pH for removal of phenol and 4-nitrophenol, respectively. Fig. 5, Effect of solution pH on percentage removal Effect of Initial Concentration The effect of initial concentration of phenol and 4-nitrophenol was studied using different initial concentrations of (20, 40, 60, 80, and 100) with 1 g of each CS, stirred at 180 rpm for 3 hours. This effect is shown in Fig.6. Increasing initial concentration of phenol and 4-nitrophenol decreases the removal efficiency as can be seen in Fig. 6, especially for phenol. This can Asrar Al-Obaidy -Available online at: www.iasj.net IJCPE Vol.14 No.3 (September 2013) 29 be due to the absence of adsorption sites for the extra molecules at a constant amount of the adsorbent, while for the adsorption of 4- nitrophenol, which have smaller radius, it slightly different is high for all concentrations. Fig. 6, Effect of initial concentration on the removal efficiency Effect of Adsorbent Loading The effect of adsorbent loading is studied using 25 ml of solution of initial concentration of 20 mg/ℓ using (1, 2, 5 and 7g) of CS, stirred at constant speed of 200 rpm for 3 hours. The removal efficiency increased as the amount of CS increased as it appears in Fig.7. The increase in the efficiency can be explained by the increasing surface area or binding sites where the adsorption takes place with the increasing of CS dosage. Fig. 7, Effect of adsorbent loading on the removal efficiency Conclusions 1. A maximum 4-nitrophenol removal percentage of 97% were obtained at 3.5 solution pH and 300 min contact time, and a maximum 4- nitro phenol removal percentage of 87% at 20 mg/ℓ initial concentration solution stirred at 180 rpm for 3 hours. 2. The adsorption process obeys first- order kinetics. The Langmuir isotherm fits and describes the adsorption mechanism better than the Freundlich one for the two phenol derivatives. 3. The prepared coated sand CS was found to have good adsorption properties and can provide an effective technology based on adsorption/ filtration using CS filter media for phenol derivatives removal from water and wastewater. References 1- Munaf E., Zein R., Kurnidi R. and Kurnidi I. (1997), The use of rice husk for removal of phenol from waste water as studied using 4- aminoantipyrine spectrophotometric method. Environ. 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