Fixed-bed Column Study for Cu (II) Removal from Aqueous Solutions using Rice Husk based Activated Carbon

Transcription

1 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: Fixed-bed Column Study for Cu (II) Removal from Aqueous Solutions using Rice Husk based Activated Carbon Nasehir Khan E M Yahaya a, Ismail Abustan a, Muhamad Faizal Pakir Mohamed Latiff a, Olugbenga Solomon Bello b, Mohd Azmier Ahmad b,* a School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia b School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia Abstract-- In this work, the adsorption potential of rice husk based activated carbon (RHAC) to remove Cu (II) from aqueous solution was investigated using fixed-bed adsorption column. The effects of inlet Cu (II) (5-15 mg/l), feed flow rate (10-30 ml/min) and RHAC bed height (30-80 mm) on the breakthrough characteristics of the adsorption system were determined. The highest bed capacity of mg/g was obtained using 10 mg/l inlet Cu (II), 80 mm bed height and 10 ml/min flow rate. The adsorption data were fitted to three well-established fixed-bed adsorption models namely, Adam- Bohart, Thomas and Yoon-Nelson models. The results fitted well to the Thomas and Yoon-Nelson models with correlation coefficient, Index Term - Activated carbon; Adsorption; Breakthrough; Cu (II); Fixed-bed column; Rice husk. I. INTRODUCTION Today, heavy metal pollution has become one of the most important environmental problems. Copper, one of the heavy metals is widely used in industries such as metal cleaning and plating, paper board, printed circuit board, wood pulp, fertilizer, paints and pigments [1,2]. The Cu (II) effluent from these industries spreads into the environment through soil and water streams and accumulates along the food chain, resulting in a high risk to human health. High of Cu (II) intake causes stomach upset and ulcer, mental retardation, liver and brain damage [3]. Different methods of treating effluent containing Cu (II) have been developed over years which include coagulation, ion-exchange, membrane separation, reverse osmosis, solvent extraction, chemical precipitation and electroflotation [4]. However, most of these techniques have some disadvantages such as complicated treatment process and high cost. Adsorption is a much preferable technique due to ease of operation and costeffectiveness [5]. The most promising adsorbent for This work was supported by the Research University (RU) grant provided by Universiti Sains Malaysia. Mohd Azmier Ahmad and Ismail Abustan are the members of Waste Management Cluster of Universiti Sains Malaysia. Nasehir Khan E M Yahaya, Muhamad Faizal Pakir Mohamed Latiff and Olugbenga Solomon Bello are postgraduate students working on activated carbon. The correspondence author can be contacted via chazmier@eng.usm.my (M.A. Ahmad). adsorption is activated carbon, which has high in term of surface area and adsorption capacity. From the literature, activated carbons were prepared from agricultural wastes such as date stone [5], vetiver roots [6], coffee husks [7], corn grain [8], mangosteen peel [9], durian shell [10], oil palm empty fruit bunch [11] and coconut husk [12]. Rice husk is the major by-product of the rice milling industry, accounting for almost 20% of the rice production [13]. As rice plant is the main cereal crop in Malaysia with an annual output of more than 180 million tons, the production of rice husk is over 36 million tons. Despite its large quantity, some portion of rice husk has mainly been used as an energy resource and the rest is left beside the rice processing mills. In this work, rice husk is used as precursor for preparation of activated carbon for Cu (II) removal from aqueous solution by fixed-bed column. The important design parameters such as inlet of Cu (II) solution, flow rate of fluid and column bed height were investigated. The breakthrough curves for the adsorption of Cu (II) were analyzed using Adam-Bohart, Thomas and Yoon-Nelson models. II. MATERIALS AND METHODS A. Materials Rice husk was obtained from the local rice processing mill in Kepala Batas, Penang, Malaysia. Stock solution of Cu (II) were prepared by dissolving appropriate amounts of Cu (NO 3 ) 2.3H 2 O (Merck, 99% purity) in deionized distilled water. Deionized water was used to prepare all solutions. B. RHAC Preparation and Experimental Setup Rice husk was washed with water and subsequently dried at 105 o C for 24 h to remove the moisture contents. The dried rice husk was ground and sieved to the size of 1-2 mm and mixed with ZnCl 2 pellets with weight ratio of 1:1 before loading in a stainless steel vertical tubular reactor placed in a tube furnace. Carbonization step was carried out at 700 o C for 30 min under nitrogen (99.99%) flow at flow rate of 150 ml/min. Then the activation step was done by changing the gas flow to CO 2 for 2 h at the same temperature. The sample was then cooled to room temperature under nitrogen flow. The sample was washed with hot deionized water and hydrochloric acid (0.1M) to dissolve all the ZnCl 2 pellets. It was further

2 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: washed with distilled water until the ph of the washed solution reached Finally the sample was dried in an oven at 110 o C for 24 h. The fixed-bed column was made of Pyrex glass tube of 1.2 cm inner diameter and 19.5 cm height. The column performance of Cu (II) adsorption onto RHAC was studied at different Cu (II) (5-15 mg/l), bed height (60-80 mm) and flow rate (10-30 ml/min). The bed depths taken were 30 mm (2.15 g), 60 mm (3.21 g) and 80 mm (4.50 g). The Cu (II) solution was pumped to the column in a down-flow direction by a peristaltic pump. Sample was collected at regular intervals. All the adsorption experiments, the of Cu (II) ions was measured using a Hanna copper meter (model HI93702). C. Column model The loading behavior of Cu (II) to be removed from solution in a fixed bed was usually expressed in term of C t /C 0 where (C t = effluent Cu (II) ion and C 0 = influent Cu (II) ion in mg/l). C t /C 0 is then plotted against time in other to obtain breakthrough curve. The maximum column capacity, q total (mg), for a given feed and flow rate is equal to the area under the plot of the adsorbed Cu (II), C ad (C ad = C 0 -C) versus effluent time (t, min) and is calculated from Eq. (1): where t total, Q and A are the total flow time (min), volumetric flow rate (ml/min) and the area under the breakthrough curve, respectively. The equilibrium uptake (q eq(exp) ) is calculated as follows : (1) D. Kinetic models In this work, three models were used namely Adam- Bohart, Thomas and Yoon-Nelson models for kinetic studies. The Adam-Bohart model is used for the description of the initial part of the breakthrough curve. The expression is expressed as [14]: where k AB is the kinetic constant (l/mg min), F is the linear flow rate (ml/min), Z is the bed depth of column (cm), N 0 is the saturation and t is time (min). Parameters describing the characteristic operations of the column (K AB and N 0 ) were calculated using linear regression analysis according to Eq. (5). From a linear plot of ln (C t /C o ) against time (t), values of K AB and N 0 were determined from the intercept and slope of the plot (figure not shown). The expression of Thomas model for an adsorption column is given as follows: where q o the equilibrium Cu (II) uptake per g of the RHAC adsorbent (mg/g). The values of K TH and q o were determined from a plot of C t /C o against t using linear regression analysis (figure not shown). Yoon and Nelson [15] developed a model based on the assumption that the rate of decrease in the probability of adsorption of adsorbate molecule is proportional to the probability of the adsorbate adsorption and the adsorbate breakthrough on the adsorbent. The linearized Yoon-Nelson model for a single component system is expressed as: (5) (6) (2) where m is the total dry weight of RHAC in column (g). The total amount of Cu (II) sent to the column (W total ) is calculated from equation below: Total removal percent of Cu (II) is the ratio of the maximum capacity of the column (q total ) to the total amount of Cu (II) sent to column (W total ). For the successful design of a column adsorption process, it is important to predict the breakthrough curve for effluent parameters. Various kinetic models have been developed to predict the dynamic behavior of the column. (3) (4) where K YN (1/min) is the rate velocity constant, τ (min) is the time required for 50% adsorbate breakthrough. From a linear plot of ln[c t /(C o -C t )] against sampling time (t), values of K YN and τ were determined from the intercept and slope of the plot (figure not shown). III. RESULT AND DISCUSSION A. Effect of inlet initial Cu (II) The effect of inlet initial Cu (II) for bed height of 60 mm and solution flowrate of 10 ml/min is shown by the breakthrough curve in Fig. 1. At the interval of 50 min, the value of C t /C o reached 0.76, 0.85 and 0.95 for inlet initial s of 5, 10 and 15 mg/l, respectively. The larger the inlet, the steeper is the slope of breakthrough curve. This is due to the increases of driving force and decreases in the adsorption zone length [16]. Similar trends were obtained in literature for removal of lead (II) from synthetic and real effluents using immobilized Pinus sylvestris sawdust [17] and removal of nickel (II) from aqueous solution using crab shell particles [18]. (7)

3 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: Fig. 1. Breakthrough curves for Cu (II) adsorption at different inlet s (bed height = 60 mm, flow rate = 10 ml/min, temp. = 25 o C). The adsorption capacity was increased with increased in inlet initial as shown in Table I. This is due to the high driving force for the adsorption process. For 60 mm bed height and 10 ml/min flowrate, the highest bed capacity of mg/g was obtained using 15 mg/l inlet Cu (II). T ABLE I COLUMN DATA PARAMETERS OBTAINED AT DIFFERENT INLET CU (II) CONCENTRATION, BED HEIGHTS AND FLOWRATES RHAC bed height (ml/mim) q total (mg) q e (mg/g) Fig. 2. Breakthrough curves for Cu (II) adsorption at different flow rates (Cu (II) inlet = 10 mg/l, bed height = 60 mm, temp. = 25 o C). C. Effect of RHAC bed height Fig. 3 shows the breakthrough curve obtained for Cu (II) adsorption on the RHAC for different bed heights of 30, 60 and 80 mm, at a constant flowrate of 10 ml/min and Cu (II) inlet of 10 mg/l. From Fig. 3, the breakthrough time increased with increasing the bed height. As the bed height increased, the Cu (II) had more time to contact with RHAC that resulted in higher removal efficiency of Cu (II) in the column. Higher bed column results in a decreased in the solute in the effluent at the same time. The slope of breakthrough curve was slightly decreased with increasing bed height, which resulted in a broadened mass transfer zone [20]. B. Effect of the solution flow rate The effect of the flow rate on the adsorption of Cu (II) is shown by the breakthrough curve in Fig. 2. The adsorbent bed height and inlet initial Cu (II) were fixed at 60 mm and 10 mg/l, respectively. It was observed that breakthrough generally occurred faster with higher flowrate. The reason is that at higher flowrate, the rate of mass transfer increased, thus the amount of Cu (II) adsorbed onto the unit bed height (mass transfer zone) increased [19]. In addition, the adsorption capacity was lower as shown in Table I due to insufficient residence time of the solute in the column and diffusion of the solute into the pores of the adsorbent, therefore the solute left the column before equilibrium occurred. These results were in agreement with other findings reported in literature [17,19]. Fig. 3. Breakthrough curves for Cu (II) adsorption at different bed heights (Cu (II) inlet = 10 mg/l, flow rate = 10 ml/min, temp. = 25 o C). D. Dynamic adsorption models The Adam-Bohart adsorption model was applied to experimental data for the description of the initial part of the breakthrough curve. After applying Eq. (5) to the experimental data at the 10% breakthrough point, a linear relationship was found for the time for 10% breakthrough (t 0.1 ). For all

4 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: breakthrough curves, respective values of N o, and K AB were calculated and presented in Table II. T ABLE II ADAM-BOHART PARAMETERS AT DIFFERENT CONDITIONS USING LINEAR REGRESSION ANALYSIS. RHAC bed height (ml/min) K AB (L/mg min x 10 3 ) N o From Table II, it is seen that the values of N o increased as the increased but decreased with increased in flow rate. The values of K AB decreased with increased in initial Cu (II) as well as the flow rate. This showed that the overall system kinetics was dominated by external mass transfer in the initial part of adsorption in the column [22]. Although the Adam-Bohart model provides a simple and comprehensive approach to evaluate adsorptioncolumn test, its validity is limited to the range of conditions used [14]. The correlation coefficient, values were between 0.82 and The Thomas model is suitable for adsorption processes where the external and internal diffusions will not be the limiting step [17]. The column data were fitted to the Thomas model to determine the Thomas rate constant (K TH ) and maximum solid-phase (q o ). The determined coefficients and relative constants were obtained using linear regression analysis according to Eq. (6) and the results are listed in Table III. From Table III, as the inlet and flow rate increased the value of q o and K TH decreased. The value of q o increased and K TH decreased with increasing bed height. The values range from 0.97 to T ABLE III THOMAS MODEL PARAMETERS AT DIFFERENT CONDIT IONS USING LINEAR REGRESSION ANALYSIS. (mg/l) RHAC bed height (ml/mim) K TH (ml/ min mg x 10 3 ) q o (mg/g) The values of K YN and τ are listed in Table IV. From Table IV, the rate constant K YN increased and the 50% breakthrough time τ decreased with increasing Cu (II) inlet. With the bed height increased, the τ increased while the values of K YN decreased. As the flow rate increased, the K YN and τ decreased. Comparing the values of and breakthrough curves, both the Thomas and Yoon-Nelson models can be used to describe the behavior of the adsorption of Cu (II) in a fixed-bed column. The value of for Adam- Bohart model was lower than Thomas and Yoon-Nelson models under the same experimental conditions. T ABLE IV YOON-NELSON MODEL PARAMETERS AT DIFFERENT CONDITIONS USING LINEAR REGRESSION ANALYSIS. RHAC bed height (ml/mim) K YN (1/min) τ (min) IV. CONCLUSIONS From this study, RHAC prepared by ZnCl 2 activation was found suitable for Cu (II) removal from aqueous solution using fixed-bed adsorption column. The fixed-bed adsorption system was found to perform better with lower Cu (II) inlet, lower feed flow rate and higher RHAC bed height. The column experimental data were fitted well to the Thomas and Yoon-Nelson models. REFERENCES [1] Z. Aksu, I.A. Isoglu, Removal of copper (II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp, Process Biochem., 40, 2005, [2] A. Ozer, D. Ozer, A. Ozer, The adsorption of copper (II) ions onto dehydrated wheat bran (DWB): determination of the equilibrium and thermodynamic parameters, Process Biochem., 39, 2004, [3] C.S. Zhu, L.P. Wang, W.B. Chen, Removal of Cu (II) from aqueous solution by agricultural by-product: peanut hull, J. Hazard. Mater., 168, 2009, [4] C. Namasivayam, K. Ranganathan, Removal of Pb (II), Cd (II) and Ni (II) and mixture of metal ions by adsorption onto waste Fe (III) / Cr (III) hydroxide and fixed bed studies, Environ. Technol., 16, 1995, [5] B.H. Hameed, J.M. Salman, A.L. Ahmad, Adsorption isotherm and kinetic modeling of 2,4-D pesticide on activated carbon derived from date stones, J. Hazard. Mater., 163, 2009, [6] S. Altenor, B. Carene, E. Emmanuel, J. Lambert, J. Ehrhardt, S. Gaspard, Adsorption studies of methylene blue and phenol onto vetiver roots activated carbon prepared by chemical activation, J. Hazard. Mater., 165, 2009, [7] L.C.A. Oliveira, E. Pereira, I.R. Guimaraes, A. Vallone, M. Pereira, J.P. Mesquita, K. Sapag, Preparation of activated carbons from coffee husks utilizing FeCl 3 and ZnCl 2 as activating agents, J. Hazard. Mater., 165, 2009, [8] M.S. Balathanigaimani, W.G. Shim, K.H. Park, J.W. Lee, H. Moon, Effects of structural and surface energetic heterogeneity properties of novel corn grain-based activated carbons on dye adsorption, Micropor. Mesopor. Mater., 118, 2009, [9] M.A. Ahmad, R. Alrozi, Optimization of preparation conditions for mangosteen peel-based activated carbons for the removal of Remazol Brilliant Blue R using response surface methodology, Chem. Eng. J., 165, 2010, [10] T.C. Chandra, M.M. Mirna, Y. Sudaryanto, S. Ismadji, Adsorption of basic dye onto activated carbon prepared from durian shell: Studies of adsorption equilibrium and kinetics, Chem. Eng. J., 127, 2007, [11] B.H. Hameed, I.A.W. Tan, A.L. Ahmad, Preparation of oil palm empty fruit bunch-based activated carbon for removal of 2,4,6-trichlorophenol: Optimization using response surface methodology, J. Hazard. Mater., 164, 2009, [12] I.A.W. Tan., A.L. Ahmad, B.H. Hameed, Optimization of preparation conditions for activated carbons from coconut husk using response surface methodology, Chem. Eng. J., 137, 2008, [13] Y.P Guo, D.A. Rockstraw, Activated carbons prepared from rice hull by one-step phosphoric acid activation, Micropor. Mesopor. Mater., 100, 2007,

5 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: [14] G. Bohart, E.Q. Adams, Some aspects of the behaviour of charcoal with respect to chlorine, J. Am. Chem. Soc., 42, 1920, [15] Y.H. Yoon, J.H. Nelson, Application of gas adsorption kinetics. Part 1. A theoretical model for respirator cartridge service time, Am. Ind. Hyg. Assoc. J., 45, 1984, [16] J. Goel, K. Kadirvelu, C. Rajagopal, V.K. Garg, Removal of lead (II) by adsorption using treated granular activated carbon: batch and column studies, J. Hazard. Mater., 125, 2005, [17] V.C. Taty-Costodes, H. Fauduet, C. Porte, Y.S. Ho, Removal of lead (II) ions from synthetic and real effluents using immobilized Pinus svlvestris sawdust: adsorption on a fixed column, J. Hazard. Mater., 123, 2005, [18] K. Vijayaraghavan, J. Jegan, K. Palanivelu, M. Velan, Removal of nickel (II) ions from aqueous solution using crab shell particles in a packed bed up flow column, J. Hazard. Mater., 113, 2004, [19] D.C.K. Ko, J.F. Porter, G. McKay, Optimised correlations for the fixedbed adsorption of metal ions on bone char, Chem. Eng. Sci., 55, 2000, [20] Z. Zulfadhly, M.D. Mashitah, S. Bhatia, Heavy metals removal in fixed-bed column by the macro fungus Pycnoporus sanguineus, Environ. Pollution, 112, 2001,