Isotherm and Thermodynamic Studies of The Biosorption of Cu(II) By Periwinkle (Tympanotonus Fuscatus Var Radula) Shell

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1 Journal of Applied Sciences Research, 7(12): , 2011 ISSN X This is a refereed journal and all articles are professionally screened and reviewed 2517 ORIGINAL ARTICLES Isotherm and Thermodynamic Studies of The Biosorption of Cu(II) By Periwinkle (Tympanotonus Fuscatus Var Radula) Shell 1 N.A. Adesola Babarinde, 2 J. Oyebamiji Babalola and 1 Akinwunmi Kolawole 1 Department of Chemical Sciences, Olabisi Onabanjo University, Ago-Iwoye, Nigeria. 1 Department of Chemical Sciences, Redeemer s University, Redemption City, Nigeria. 2 Department of Chemistry, University of Ibadan, Ibadan, Nigeria. ABSTRACT The biosorption of Cu 2+ from aqueous solutions by periwinkle (Tympanotonus fuscatus var radula ) shell as the biosorbent has been studied under different conditions such as initial ph, contact time, temperature and initial Cu 2+ concentration. The residual Cu 2+ in solution was determined by atomic absorption spectrophotometer. The results obtained indicate that the biosorption is both ph and time dependent. The experimental results fitted well to the Freundlich and Langmuir model isotherms. The Freundlich equation obtained is log = log Ce while the Langmuir equation obtained is 1/ = /Ce The correlation factors are and 0.999, respectively. The standard deviation values are and , respectively. At the temperature of 310 K the free energy obtained is k Jmol -1. The negative value of the free energy change indicates spontaneous nature of the process. The effectiveness of periwinkle shell in the uptake of Cu 2+ shows that it can serve as an excellent biomass for accumulating and recovering Cu 2+ from industrial wastewater. Key words: Periwinkle, biosorption, Freundlich isotherm, Langmuir isotherm, copper Introduction The presence of toxic metals such as copper, lead, cadmium and zinc in the environment is of great concern due to their health implications. Heavy metal ions are present in the wastewaters of some chemical industry such as pulp and paper, petrochemicals and refineries (Pamukoglu and Kargi, 2007). The increasing contamination of aquatic resources with heavy metals has initiated the search for cheaper and newer strategies for their removal (Pradham et al., 2007). Biosorption has been found to be an alternative to conventional methods such as precipitation, ion-exchange, solvent extraction, liquid membrane and electrochemical process of treating solutions having metal ions. The biosorbents are cheap materials often with high affinity and capacity for binding the metal ions (Conrad and Hansen, 2007). Biosorption involves several mechanisms such as ion-exchange, chelation and sorption by physical forces. Some materials have been recently used in the biosorption of heavy metals. Such include pecan shell (Bansode et al., 2003).and crab shell (Kim, 2004; Vijayaraghavan, et al., 2006),. palm shell (Issabayeva et al., 2006), maize leaf (Babarinde et al., 2006, blast furnace sludge (Martin et al., 2005), waste beer yeast (Han et al., 2006) microalgae (Bayraoglu et al., 2006), rice husk (Martins et al., 2007), and water hyacinth (Hassan et al., 2007). Other materials used are wood sawdust (Sciban et al., 2007), bacteria (Pradham et al., 2007), charcoal (Mor et al., 2007), coir (Conrad and Hansen, 2007), and sugarcane bagasse (Karnitz et al., 2007) The periwinkle (Tympanotonus fuscatus var radula) is a mollusc of high economic value in the Niger Delta region of Nigeria because it serves as the major source of protein. Periwinkle shells are used with cement in the suburbs of the region to construct roads and houses. The shells are available as waste in large quantities all over the region. The present study was carried out to determine the biosorption capacity of Periwinkle shell for Cu 2+. Materials And Methods Preparation of Biomass: Periwinkle (Tympanotonus fuscatus var radula) shells used as the biosorbent were collected form Ayagologo station along Elechi Creek in Port Harcourt, Nigeria. They were soaked in 0.1M HCl for 4 hours to remove CaCO 3 (Vijayaraghavan, et al., 2006) and rinsed with distilled water several times. They were air dried Corresponding Author: N.A. Adesola Babarinde, Department of Chemical Sciences, Redeemer s University, Redemption City, Nigeria.

2 2518 at room temperature and crushed to smaller particle size then screened through a mesh of size 0.25mm. This produced a uniform material, which was stored in a dry place till the time of usage. Preparation of Metal Solution: The chemicals used for this study were analytical grades of NaOH, HNO 3, HCl and CuSO 4.5H 2 O. Stock solution of 1000 mgl -1 of Cu 2+ was prepared from CuSO 4.5H 2 O. The initial ph of each solution was adjusted to the desired ph by drop wise addition of 0.1M HNO 3 and/or 0.1M NaOH solution. Fresh dilution of the stock solution was done for each biosorption study. Biosorption Studies: All the studies were conducted at 27 0 C in order to determine the effects of initial solution ph, contact time, and initial metal ion concentration on the biosorption of Cu 2+, except for the effect of temperature. Each of the batch biosorption studies was carried out by contacting 2.5g of the biomass with 25ml of the metal ions under different conditions for a period of time in a glass tube held in a thermostated water bath (Haake wia model). The residual metal ions were analysed using atomic absorption spectrophotometer. The Cu 2+ uptake was calculated by simple concentration difference. The mean value was also calculated. Effect of Initial Solution PH on Biosorption: The effect of ph on the biosorption of metal ions was carried out within the range that would not be influenced by the metal precipitated (Pavasant et al., 2006). It has been reported that the suitable ph ranges for the sorption of different metal ions were slightly different. As a result, the suitable ph ranges for Cu(II), Cd(II), Zn(II) and Pb(II) ions should be 1-6, 1-8, 1-7 and 1-7.5, respectively. The procedure used is similar to those earlier reported (Vasudevan et al., 2003 and Xu et al., 2006; Babarinde et al., 2006). The ph of each of the solutions was adjusted to the desired value with 0.1M NaOH and /or 0.1M HNO 3. The studies were conducted at ph values of 1, 2, 3, 4, 5 and 6. The glass tubes containing the mixture were left in a water bath for 24 hours. The studies were conducted at 27ºC to study the effect of initial solution ph on the biosorption of the metal ions by contacting 2.5g of the periwinkle shell with 2.5ml of 100 mgl -1 Cu 2+ solution in a glass tube and left in a thermostated water bath for 24 hours. Each study carried out in duplicates for each ph. The biosorbent was removed from the solution by centrifuging and decanting. The residual ion concentration in the solution was determined and the mean value calculated for each ph. The optimum ph value obtained was used for other studies in this work Effect of Contact Time on Biosorption: The biosorption for Cu 2+ by periwinkle shell was studied at various time intervals (0-300mins) at constant concentration of 100mgL -1 and temperature of 27 o C. 2.5g of the biomass was introduced into 25ml of Cu 2+ in a glass tube at ph 5. The samples were then withdrawn at different time intervals. Each was immediately centrifuged and decanted, then the solution was analysed. Each study was conducted in duplicates and the mean value was calculated. The optimum time was used for other studies in this work. Effect of Initial Cu 2+ Concentration on Biosorption: Batch sorption tests were conduced at different concentrations of mgL -1 at constant ph 5 for an optimum contact time of 3h and temperature of 27 O C. 2.5g of the sorbent was introduced into 25ml of the Cu 2+ solution in a glass tube. The solution was left in the water bath for 3h, then centrifuged and decanted. The study was conducted in duplicates and the residual Cu 2+ in each solution was determined. Effect of Temperature on Biosorption: The effect of temperature on the biosorption of Cu 2+ by periwinkle shell was carried out by contacting 2.5g of it with 25 ml of 100 mgl -1 Cu 2+ at ph 5.0. The glass tubes were introduced into the thermostated water bath at different temperatures of 294, 297,300, 307 and 310 K for 3h. The solutions were then centrifuged, decanted and analysed.

3 2519 Results and Discussion Effect of Initial PH on The Biosorption: The ph of the solution is perhaps the most important parameter in the biosorption of Cu 2+. The charge of the adsorbate and the adsorbent often depends on the ph of the solution (Han et al., 2006). To understand the adsorption mechanism, the biosorption of Cu 2+ as a function of ph was measured and the result is shown Fig.1. It is observed that there was an increase in the biosorption capacity of the biomass with increase in ph from 1.0 to 5.0. As a result of net negative charge on the cell wall of the biosorbent above the isoelectric point the ionic state of the ligands such as carbonyl, phosphate and amino gropus favours reaction with Cu 2+. On the other hand, on decreasing ph, the net charge on the cell wall is positive thereby inhibiting the approach of positively charge ions (GÐksungur et al., 2005). As the ph increased, the ligands in periwinkle shell would be exposed, increasing the attraction of metal ions with positive charge and allowing the biosorption on the shell surface. The result suggests that optimum biosorption is obtained from ph 5.0 to 6.0 and that initial ph would play a vital role in the removal of Cu 2+ from aqueous solutions using periwinkle shell. Effect of Contact Time on Biosorption: The effect of contact time on the biosorption of Cu 2+ by periwinkle shell was studied and the result shown in Fig 2. From Fig. 2, it is observed that the biosorption capacity of periwinkle shell for Cu 2+ increased as the contact time increased. The biosorption process was rapid for the first 50 min and equilibrium was nearly reached after 150 min. Hence, in the present study, 180 min was chosen as the equilibrium time. 100 % Cu (II) ions biosorbed ph Fig. 1: Effect ph on the biosorption of Cu 2+ using periwinkle shell 100 % Cu (II) ions biosorbed Time (mins) Fig. 2: Time course of the biosorption of Cu 2+ using periwinkle shell

4 2520 Biosorption of metal ions has been reported to be biphasic (Liu et al, 2006). The initial fast phase occurs due to surface adsorption on the biomass. The subsequent slow phase occurs due to diffusion of the metal ions into the inner part of the biomass. It is observed in Fig. 2 that the Cu 2+ biosorption rate was high at the beginning but plateau values were obtained in 100 minutes, similar to what was reported by Liu and coworkers (Liu et al, 2006). Effect of Initial Cu 2+ Concentration on Biosorption: The effect of initial Cu 2+ concentration on the biosorption capacity is shown in Fig. 3 and 4. The results obtained were analysed using both Freundlich (Freundlich, 1907) and Langmuir (Langmuir, 1918) isotherms. The Freundlich isotherm in linearised form is log ' log C e Fig. 3: Freundlich isotherm of the biosorption of Cu 2+ using periwinkle shell / ' ( /L) /Ce (mgl -1 ) Fig. 4: Langmuir isotherm of the biosorption of Cu 2+ using periwinkle shell log Г = (1/n)log C e + log K (1) Where n and K are Freundlich constants. The linearised form of the Langmuir isotherm is b m Ce 1 m (2) Where b m is a coefficient related to the affinity between the sorbent and sorbate, and Г m is the maximum sorbate uptake under the given condition. The data fitted well into both isotherms. The isothermal biosorption parameters for these isotherms are shown in Table 1.These Freundlich and Langmuir isothermal parameters compare well with those of other

5 2521 biosorbents that have been reported. (Pavasant et al, 2006). The Freundlich equation obtained is log = log Ce while the Langmuir equation obtained is 1/ = /Ce The correlation factors are and 0.999, respectively. The standard deviation values are and , respectively. The values of the parameters show that periwinkle shell is a good biosorbent for the uptake of Cu 2+ from wastewaters. The removal efficiency of the biosorption process was equally determined using the same data as shown in Fig. 5. The removal efficiency of the Cu 2+ was calculated as follows: % Removal = 100 (C i -C e ) / C i (3) Where C i is initial metal ion concentration (mgl -1 ), C e the equilibrium metal ion concentration (mgl -1 ) The result shows that up to 100 % of the metal ions was biosorbed at the initial metal ion concentration of 100 mgl -1. The efficiency decreased as the initial Cu 2+ concentration increased. The gradual decrease in the efficiency of the biomass shows nearness to saturation of the available binding sites on it. 100 % Removal efficiency Initial Cu 2+ concentration (mgl -1 ) Fig. 5: Removal efficiency of the biosorption of Cu 2+ using periwinkle shell Thermodynamics of biosorption of Cu 2+ by periwinkle shell: The biosorption experiement can be regarded as a heterogeneous and reversible process at equilibrium. The apparent equilibrium constant for the process has been shown (Khan et al., 2005; Sawalha et al., 2006) to be K c = C ad / C e (4) The change in Gibbs free energy of the biosorption process is thus given as ΔG o = - RTlnK c (5) Where ΔG o is the standard Gibbs free energy change for the biosorption (Jmol -1 ), R the universal gas constant (8.314 Jmol -1 K -1 ) while T is the temperature (K). The effect of temperature on the biosorption of Cu(II) by periwinkle shell is reported in Fig. 6. From thermodynamics, ΔG o = ΔH -T ΔS (6) or ΔG o = - ΔS (T) + ΔH (7) A plot of T against ΔG o gives a straight line with slope ΔS and an intercept of ΔH. In Fig. 6, the slope is Jmol -1 K -1 while the intercept is kjmol -1. Therefore, the values of the entropy and enthalpy are Jmol -1 K -1 and 66.55kJmol -1, respectively. The decrease in the value of the free energy with increase in temperature indicates that the biosorption process is endothermic and it is thereby

6 2522 favoured with increase in temperature. It is observed in Fig. 6 that the free energy values decrease with increase in temperature. This implies that the spontaneity of the biosorption process increased with increase in temperature. Gibbs free energy Change ( jmol -1 ) Temperature (K) Fig. 6: Change in Gibbs free energy with temperature of the biosorption of Cu 2+ using periwinkle shell Table 1: Freundlich and Langmuir isothermal adsorption parameters for the biosorption of Cu 2+ ions at 27ºC and ph 5 using periwinkle shell. Freundlich parameters Langmuir parameters n K R S.D. b m Г m R S.D The free energy change ( G o ) obtained for the biosorption of Cu(II) at 310K, initial Cu(II) concentration of 100mgL -1, and ph 5 is kJmol -1. The large negative value of G o obtained for the biosorption of Cu(II) shows spontaneity of the biosorption process at that temperature. Conclusions: This work indicated that the periwinkle shell could be used as an effective biosorbent for the treatment of copper bearing wastewater streams. The biosorption capacity was dependent on initial solution ph, contact time and the temperature. The maximum biosorption was obtained within 3h at ph 5 and 310 K for initial Cu 2+ concentration of 100 mgl -1.. The removal efficiency decreases with increase in initial Cu 2+ concentration due to reduction in available binding site on the biosorbent for Cu 2+. Acknowledgement The authors are grateful to Mr J. Adegoke of the Department of Chemical Sciences, Olabisi Onabanjo University, Ago-Iwoye, for technical assistance. References Babarinde, N.A.A., J.O. Babalola and R.A. Sanni, Biosorption of Lead ions from aqueous solution by maize leaf. International Journal of Physical Sciences, 1(1): Bansode, R.R., J.N. Losso, R.M. Marshall and R.J. Portier, Adsorption of metal ions by pecan shellbased granular activated carbons Bioresour. Technol., 89(2): Conrad, K., H.C.B. Hansen, Sorption of zinc and lead on coir Bioresour. Technol., 98: Freundlich, H., Ueber die Adsorption in Loesungen Z. Physic. Chem., 57: Gõksungur, Y., S. Üren and U. Güvenc, Biosorption of cadmium and lead ions by ethanol treated waste baker s yeast Bioresour. Technol., 96(1): Han, R., H. Li, Y. Li, J. Zhang, H. Xiao and J. Shi, Biosorption of Copper and lead ions by waste beer yeast. Journal of Bazardous Materials B137: Khan, A.R., H. Tahir, F. Uddin and U. Hammed., Adsorption of Methylene Blue from aqueous Solution on the Surface of Wool Fiber and Cotton Fiber Journal of Applied Science and Environmental Management., 9(2):

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