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  • 1. ISSN (Print): 2328-3777, ISSN (Online): 2328-3785, ISSN (CD-ROM): 2328-3793 American International Journal of Research in Formal, Applied & Natural Sciences AIJRFANS 14-224; © 2014, AIJRFANS All Rights Reserved Page 45 AIJRFANS is a refereed, indexed, peer-reviewed, multidisciplinary and open access journal published by International Association of Scientific Innovation and Research (IASIR), USA (An Association Unifying the Sciences, Engineering, and Applied Research) Available online at http://www.iasir.net Red Mud as Low Cost Adsorbent for Zn(II) ion – Kinetic, Thermodynamic and Equilibrium Study Sujata Kumar,1 Dhanesh Singh,2 Saroj Kumar 3 Lecturer, Kirodimal Institute of Technology Raigarh (C.G), INDIA Associate Professor, K.Govt. Arts & Sc. College Raigarh (C.G), INDIA Assistant Professor, K.Govt. Arts & Sc. College Raigarh (C.G), INDIA Abstract: In the present study, red mud has been used as low cost adsorbent to remove Zn(II) ions from aqueous solutions. The effect of different parameters such as initial Zn(II) ion concentration, temperature, pH and particle size have been studied. For kinetic study, Lagergren first order equation and pseudo second order equation have been used. For equilibrium study, Langmuir equation as well as Freudlich equation have been discussed . Thermodynamic parameters such as Gibbs free energy change,entropy change and enthalpy change have been calculated and discussed. Key words : Red mud, Zn(II) ion, Langmuir isotherm, Freundlich equation, Lagergren first-order equation, pseudo- second- order equation. I. Introduction Zinc is used in industries like galvanization, diecasting, plastic, paints, cosmetics etc. From these industries, the effluents going to the nearby river pollute water and soil and cause severe health problems. A number of methods such as ion-exchange,reverse osmosis,membrane filtration etc. have been reported to remove the metals from polluted water. However, either these methods are costly or having insufficiency of technique. Among various methods, adsorption method has been of much interest to scientists in recent past, since it is both effective and easy to handle. A large number of substances have been studied as adsorbent [1]-[4]. In the present study, red mud , a waste by-product of aluminium industry has been used as adsorbent. II. Material and Methods Red mud was obtained from BALCO, Korba (C.G., India). It is alkaline in nature and so was washed till neutral,dried at 105o C and sieved. SEM, FTIR and XRF analysis were obtained from IIT-Bombay to characterise it. A.R. quality Zn(NO3)2 was used to prepare the stock solution. Batch mode experiments were carried out for the study by shaking 1.0 g of red mud with 25 mL aqueous solution of Zn(II) of given concentration in different glass bottles. After pre-determined time interval, the solution was centrifused and filtered and the solution was analyzed for concentration of Zn(II) ion by Systronic Spectrophotometer 118 model. Various parameters were contact time (20,40,60,80,100,120 and 140 min.), pH (2.0, 4.0, 6.5 and 8.0), temperature (303K, 313K and 323K) and particle size (45µ,75µ and 150µ). Initial Zn(II) concentration used were 25,50,75,100,125,150,175, 200, 225 and 250 mgL-1 for the equilibrium study and for rate study it was 100,150, 200 and 250 mgL-1 . III. Results and Discussion Characterisation of red mud Red mud obtained from different sources contain the same basic chemical elements but in different proportions. Chemical composition of the present red mud obtained from XRF studies are : SiO2 (43.17%), Al2O3(13.25%), Fe203(41.20%), CaO(1.09%), MgO(0.73%) and TiO2(1.26%). The FTIR spectra of red mud before and after adsorption is shown in figure-1(a) and 1(b). It shows a broad band around 3500 cm-1 , which is attributed to surface -OH group of silanol groups ( -Si-OH) and adsorbed water molecules on the surface. A peak around 1400 cm-1 – 1600 cm-1 is attributed to presence of carbonate. A strong peak at 995.22 cm-1 is due to stretching vibration of Si(Al)-O group[5]. New peaks obtained are due to zinc and confirm the adsorption.
  • 2. Sujata Kumar et al., American International Journal of Research in Formal, Applied & Natural Sciences, 6(1), March-May 2014, pp. 45-50 AIJRFANS 14-224; © 2014, AIJRFANS All Rights Reserved Page 46 Figure- 1. (a) FTIR before adsorption Figure- 1. (b) FTIR after adsorption Effect of initial Zn(II) ion concentration and Contact time The relationship between amount adsorbed (mgg-1 ) and time(min.) at different initial concentration has been shown in figure 3. It is evident from the graph that the amount adsorbed increases with time till equilibrium is reached. The time of equilibrium is independent of initial concentration. Initially the rate of adsorption is fast which might be due to the presence of more number of active sites on the surface of red mud. As the process of adsorption goes on, the number of active sites decreases and so the rate of adsorption also decreases[6] –[7]. . . Figure-3. Effect of initial Zn(II) ion concentration and contact time Figure-4. Effect of pH on adsorption of Zn(II) ion Effect of pH pH of the medium has pronounced effect on the adsorption. From figure-4 it is evident that the amount of Zn(II) adsorbed on red mud increased from 1.64 mgg-1 ( 65.6 %) to 2.38 mgg-1 (95.2 %) by increasing pH of solution from 2.0 to 8.0. Speciation studies [8] have shown that at low pH cadmium remains in the form of Zn++ and at higher pH in the form of Zn(OH)2. It is probable that in acidic medium positively charged surface of adsorbent does not favour the C:Program FilesOPUS_652013-2014EXTERNAL-2014FTIR-152SAMPLE-4.0 SAMPLE-4 SAIF IIT Bombay 03/02/2014 3911.46 3781.32 3707.65 3621.71 3440.87 3284.21 3100.80 2923.05 2262.64 2225.28 1643.28 1455.71 1407.60 994.97 804.95 708.67 562.65 455.60 500100015002000250030003500 Wavenumber cm-1 7580859095100 Transmittance[%] Page 1/1 0 1 2 3 4 5 0 100 200 Amountsorbed,mgg-1→ Time , min → 100mgL-1 150mgL-1 200mgL-1 250mgL-1 -0.5 0 0.5 1 1.5 2 2.5 3 0 100 200 Amountsorbed,mgg-1→ Time , min. → pH 2 pH 4 pH 6.5 pH 8 C:Program FilesOPUS_652013-2014EXTERNAL-2014FTIR-152SAMPLE-1.0 SAMPLE-1 SAIF IIT Bombay 03/02/2014 3620.75 3523.04 3283.06 3103.62 1642.07 1456.77 1406.70 995.22 803.24 686.73 564.32 457.51 500100015002000250030003500 Wavenumber cm-1 30405060708090100 Transmittance[%] Page 1/1
  • 3. Sujata Kumar et al., American International Journal of Research in Formal, Applied & Natural Sciences, 6(1), March-May 2014, pp. 45-50 AIJRFANS 14-224; © 2014, AIJRFANS All Rights Reserved Page 47 association of cationic adsorbate species. In alkaline medium negatively charged surface offers the suitable sites for the adsorption of Zn++ and Zn(OH)2 . Effect of temperature The relationship between qe(mgg-1 ) and time(min.) at different temperatures has been presented in figure 5. It is evident that adsorption of Zn(II) ion on red mud increases from 2.03mgg-1 (81.2 %) to 2.29 mgg-1 (91.6 %) by increasing temperature from 303K to 323K indicating the process to be endothermic The rate constant of adsorption are 3.89x 10-2 , and 4.58x 10-2 per min at 303K and 323K respectively which indicate that the rate of adsorption also increases with temperature. . Figure-5. Effect of temperature on adsorption of Zn(II) ion Figure-6. Effect of particle size on adsorption of Zn(II) ion Effect of particle size Figure-6 shows the effect of particle size of red mud on adsorption of Zn(II) ion. The amount of Zn(II) ion adsorbed on red mud increases from 1.81 mgg-1 (72.4%) to 2.03 mgg-1 (81.20 %) by decreasing particle size of red mud from 150 µ to 45 µ. This increase in amount of Zn(II) adsorbed on red mud is due to increase in surface area of red mud particles with decreasing particle size. Adsorption Isotherm Langmuir adsorption isotherm assumes that monolayer adsorption takes place on a homogeneous surface without interaction between adsorbate and adsorbent particles. The linear form of Langmuir isotherm [9] is given as : Ce/qe = 1/φ.b + Ce/φ where Ce (mgL-1 ) is equilibrium concentration of Zn(II) and φ and b are Langmuir constants related to adsorption capacity and adsorption energy respectively. .. Figure-7. Langmuir isotherm for adsorption of Zn(II) ion Figure- 8. Freundlich isotherm for adsorption of Zn(II) ion Table- 1. Adsorption isotherm constants for adsorption of Zn(II) on red mud The Freundlich equation [10] has also been used for the adsorption of zinc (II) on red mud which is represented as logqe = log Kf + 1/n log Ce where qe is the amount of Zn(II) ion adsorbed (mgg-1 ), Ce is the equilibrium concentration of Zn(II) ion in solution(mgL-1 ) and Kf and n are constants for the adsorption capacity and intensity of adsorption respectively. Plots of Ce/qe vs Ce for Langmuir isotherm and of logqe vs logCe for Freundlich isotherm have been given in figure-7 and 8 respectively. Different parameters obtained have been given in table-1. It is evident from the graphs and table that R2 value obtained for Langmuir model is higher than that of Freundlich and so it may be concluded that data fits better in Langmuir adsorption isotherm. It can also be seen that adsorption capacity φ increases with temperature. 0 1 2 3 0 100 200 Amountsorbed,mgg-1 → Time , min. → 303K 313K 323K 0 1 2 3 0 50 100 150 200 Amountsorbed,mgg-1 → Time , min. → 45 µ 75 µ 150 µ 0 5 10 15 20 0 50 100 Ce/qe(gL-1)→ Ce(mgL-1) → 303 K 313 K 323 K 0.0 0.2 0.4 0.6 0.8 0.0 1.0 2.0 logqe→ logCe → 303 K 313 K 323 K Langmuir Isotherm Results Freundlich Isotherm Results Temp.(K) Correlation coefficient, R2 φ b Correlation coefficient, R2 Kf n 303 0.995 6.29 0.027 0.988 0.354 1.70 313 0.988 6.62 0.040 0.995 0.515 1.79 323 0.996 6.85 0.058 0.977 0.662 1.82
  • 4. Sujata Kumar et al., American International Journal of Research in Formal, Applied & Natural Sciences, 6(1), March-May 2014, pp. 45-50 AIJRFANS 14-224; © 2014, AIJRFANS All Rights Reserved Page 48 Kinetics of Adsorption The Lagergren first order[11] and pseudo-second-order[12] have been used to discuss the adsorption kinetics. The Lagergren first order rate equation is represented as : log (qe – qt) = log qe – k1.t/2.303 Pseudo second order rate equation is represented as : t/qt = 1/k2.qe 2 + t/qt where qe and qt are the amounts of Zn(II) adsorbed (mgg-1 ) at equilibrium and at time t , respectively. k1 is the Lagergren rate constant (min-1 ). k2 (g/mg/min.) is the rate constant of second order adsorption. Plots for both Lagergren first order and pseudo second order equation has been shown in figure -9 and 10 respectively. Different adsorption parameters for both models have been presented in table – 2. Values of qe(cal) and k1 and k2 at different initial concentrations have been calculated from the slope and intercept respectively . These values have been given in table- 2. Figure-9.Lagergren first-order plot for adsorption of Zn(II) ion Figure- 10. Peudo-second-order plot for adsorption of Zn(II) ion . Table- 2. Kinetic parameters for adsorption of Zn(II) ion on red mud Lagergren first order Pseudo- second- order Conc mgL-1 k1 min-1 qexp mgg-1 qcal mgg-1 R2 k2 g/mg/min qcal mgg-1 R2 100 3.22x10-2 2.03 1.32 0.966 3.90x10-2 2.19 0.999 150 2.99x10-2 2.89 1.45 0.892 3.77x10-2 3.06 0.998 200 3.22x10-2 3.71 1.69 0.969 3.75x10-2 3.89 0.999 250 2.76x10-2 4.25 1.48 0.989 3.37x10-2 4.46 1 It is evident from table- 2 that R2 values are higher in the case of pseudo second order equation than in the case of first order equation. It may be concluded therefore that kinetic data fit better in pseudo second order equation. It can be seen from the table that k2 decreases with increase in concentration. It might be due to the possibility of low competition for active sites at lower concentration of metal ions. At higher concentration of metal ions, the competition for the surface active sites increases which decreases the rate. Other investigators have found the same result [13]. Thermodynamic treatment of the adsorption process The thermodynamic parameters such as free energy, enthalpy and entropy changes have been calculated using the following equations [14]. Kc = Cs/Ce ∆G = - RT ln Kc log Kc = ∆S/2.303 R - ∆H/2.303 RT where Ce is the equilibrium concentration in solution in mgL-1 and Cs is the equilibrium concentration on the adsorbent in mgL-1 and Kc is the equilibrium constant. The Gibbs free energy, ∆G was calculated from the above equation. Slope and intercept of the straight line obtained from the plot between log kc vs 1/T (not shown) gives the value of ΔH and ΔS respectively . These values have been given in Table- 3. The values of activation energy (Ea) and sticking probability (S*) have been calculated from the experimental data using modified Arrhenius type equation related to surface coverage(θ) as follows [15] θ = ( 1- Ce/Ci) S* = (1- θ)e -Ea/RT The sticking probability , S* , is a function of the adsorbate/adsorbent system under consideration, depending on temperature and should satisfy the condition 0<S*<1 .The values of Ea and S* has been calculated from slope and intercept of the plot of ln(1-θ) versus 1/T shown in figure-15 respectively and have been given in Table-3. -2.0 -1.5 -1.0 -0.5 0.0 0 50 100 150 log(qe-qt)→ Time , min. → 100 mgL-1 150 mgL-1 200 mgL-1 250 mgL-1 0 20 40 60 80 0 50 100 150 t/qt→ Time, min. → 100 mgL-1 150 mgL-1 200 mgL-1 250 mgL-1
  • 5. Sujata Kumar et al., American International Journal of Research in Formal, Applied & Natural Sciences, 6(1), March-May 2014, pp. 45-50 AIJRFANS 14-224; © 2014, AIJRFANS All Rights Reserved Page 49 Table-3. Thermodynamic parameters for adsorption of Zn(II) ion on red mud Temp. K ∆G , kJ/mol ∆H , kJ/mol ∆S , J/mol Ea , kJ/mol S*, J K mol-1 303 -3.686 37.68 136.62 32.78 4.20X10-07 313 -5.088 323 -6.417 The negative values of free energy indicates the spontaneity of the process. Positive ∆H value shows the endothermic nature of adsorption. The positive value of ∆S shows the affinity of the adsorbent for the Zn(II) ions. The endothermic nature of the adsorption process is supported by positive value of Ea which is in accordance with the positive values of ∆H. Since S*<<1, it indicates that the probability to stick on surface of red mud is very high [16]. Mechanism Speciation [17] of Zn(II) with varying pH has been shown in figure-11. Figure-11. Speciation of Zn(II) with varying pH It is evident that at lower pH , zinc is in the form of Zn+2 and at higher pH it is in the form of Zn(OH)2 . It is probable that in acidic medium positively charged surface of adsorbent does not favour the association of cationic adsorbate species. In alkaline medium negatively charged surface offers the suitable sites for the adsorption of Zn+2 species [18]. OH- M – OH ----------→ MO- MO- + Zn+2 ----------→ MOZn+ MO- + Zn(OH)+ ----------→ MOZn(OH) where M represents the adsorbent sites on surface. IV. Conclusion It is evident that initial Zn(II) ion concentration, contact time, pH and temperature have marked effect on adsorption. The equilibrium data are best explained by Langmuir adsorption isotherm. Kinetics of adsorption follows second order rate equation. Thermodynamic parameters also favour the adsorption. It is expected that red mud may be used as an efficient adsorbent under suitable conditions. Acknowledgement .We are thankful to SAIF, IIT Bombay, for SEM and FTIR analysis of red mud. References 1. Bhatnagar A. and Minocha A.K., Conventional and non-conventional adsorbents for removal of pollutants from water – A review, Indian J.Chem.Tech.,13,203-217 (2006) 2 Karthika C. and Sekar M., Removal of Hg(II) ions from aqueous solution by acid acrylic resins : A study through adsorption isotherms analysis, I.Res.J.Environment.Sci.,1(1),34-41(2012) 3 Singh Dhanesh and Singh A.,Chitosan for the removal of chromium from waste water.,I.Res.J.Environment.Sci. 1(3), 55-57(2012) 4. Nadaroglu H. and Kalkan E., Removal of cobalt(II) ions from aqueous solutions by using alternative adsorbent andustrial red mud waste material.l, Int.J.Phy.Sciences.,7,1386-1394(2012) 5. John C., Interpretation of Infrared Spectra, A Practical Approach,Encyclopedia of Analytical Chemistry, R.A.Heyers(Ed.), John Wiley & Sons Ltd. Chichester, 10815 – 10837( 2000) 6 Ekrem Kalkan, et.al., .Bacteria – Modified Red Mud for Adsorption of Cadmium Ions from Aqueous Solutions, Pol.J.Environ. Stud.22(2), 417 – 429 (2013) 7. Tsai W.T. and Chen H.R., Removal of malachite green from aqueous solution using low-cost chlorella-based biomass, J Hazard Mater., 175(1-3), 844-849 (2010) 8. Brummer G.W., Importance of Chemical Speciation in Environmental Process (Springer Verlag, Berlin) (1986) 9. Bello O.S., Olusegun O.A. and Nioku V.O., Fly ash-An alternative to powdered activated carbon for the removal of Eosin dye from aqueous solutions, Bull.Chem.Soc. Ethiop., 27(2), 191-204 (2013) 10. Anirudhan T.S. and Radhakrishnan P.G., Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell, J.Chem.Thermodynamics., 40(4),702- 709 (2008)
  • 6. Sujata Kumar et al., American International Journal of Research in Formal, Applied & Natural Sciences, 6(1), March-May 2014, pp. 45-50 AIJRFANS 14-224; © 2014, AIJRFANS All Rights Reserved Page 50 11. Lagergren S., About the theory of so-called adsorption of soluble substsnces,der Sogenanntenadsorption geloster stoffe Kungliga Svenska psalka de Miens Handlingar., 24,1-39(1898) 12. Ho Y.S. and Mckay G., The kinetics of sorption of divalent metal ions onto sphagnum moss peat., Water Res. 34(3),735-742 (2000) 13. Kumar P.S.,Ramakrishnan K., Kirupha S.D and Sivanesan S. Thermodynamic and Kinetic studies of cadmium adsorption from aqueous solution onto rice husk, Braz.J.Chem.Eng.27,347,2010 14. Arivoli S., Hema M., Karuppaiah M. and Saravanan S., Adsorption of chromium ion by acid activated low cost carbon- Kinetic,Mechanistic,Thermodynamic and Equilibrium studies, E-Journal of Chemistry., 5(4),820-831(2008) 15. Senthilkumar P., Ramalingam S., Sathyaselvabala V., Kirupha D.S. and Sivanesan S., Desalination, 266(1-3), 63- 71 (2011) 16. Nevine K.A., Removal of direct blue-106 dye from aqueous solution using new activated carbons developed from pomegranate peel: Adsorption equilibrium and kinetics, J. Haz. Mat.., 165(1-3), 52-62 (2009) 17. Singh Dhanesh.and Rawat N.S., Bituminous coal for the Removal of Cd rich water, Ind. J. Chem. Technol., 1,266- 270,(1994) 18. Singh Dhanesh. and Rawat N.S., Sorption of Pb(II) by bituminous coal, Ind. J. Chem. Technol., 2, 49-50 (1995)