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Lm3519611971

  1. 1. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 RESEARCH ARTICLE www.ijera.com OPEN ACCESS Adsorption Equilibrium, Kinetics and Thermodynamics of Cd (II) and Pb (II) Removal from Synthetic Wastewater Using Plantain Peel Charcoal J.A.O. Oyekunle1, E.H. Umukoro1, O. Owoyomi1, A.O. Ogunfowokan1 and I.A. Oke2 1. Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria 2. Department of Civil Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria Abstract The adsorption equilibrium, kinetics, and thermodynamic properties of plantain peel charcoal for the removal of Cd2+ and Pb2+ from synthetic wastewater were investigated along with the effects of pH, temperature and contact time on the adsorption capacity of the adsorbent. The charcoal used as the adsorbent was generated from properly washed unripe plantain peels. Investigations of the adsorption process established the optimum working pH (5 for Pb2+ and 7 for Cd2+) at 30 and 40oC, but with more metal ions removed at 40oC. It was revealed that the adsorption of Cd2+ and Pb2+ on plantain peel charcoal was best described by the pseudo-second order kinetic model with correlation coefficient (R2) ≥ 0.9975 at different temperatures. The adsorption followed the Langmuir, Freundlich and Tempkin isotherms but could best be approximated with the Langmuir model. The thermodynamic study showed that the adsorption of Cd2+ and Pb2+ from synthetic wastewaters using plantain peel charcoal was a physisorption process which was spontaneous and endothermic in nature. It could be concluded that plantain peel charcoal has the potential to serve as an efficient alternative adsorbent in clean-up systems designed for the removal of heavy metals from industrial wastewaters. Key words: Heavy metals, adsorption, charcoal, isotherms, wastewater, kinetic models. I. Introduction Rigorous coordination of water resources all over the world is increasingly becoming complex and crucial because with population growth, more pollutants are being added to the world’s inelastic water reservoirs and a higher demand is simultaneously being placed on water uses. One of the main sources of water pollution is wastewater which contains environmental and industrial pollutants [1]. These pollutants are chemicals such as volatile organic compounds, heavy metals and dyes that are toxic to human and aquatic lives [2]. The major sources of heavy metals such as lead, copper, zinc and cadmium are textile and dye, electroplating, solder, battery, pigment and paint, agro allied, plastics and metallurgical industries. Most organic pollutants are susceptible to biological degradation unlike these heavy metals which are not degradable into harmless end-products [3]. During their transport within an aquatic medium, for example, heavy metals may merely undergo numerous changes in their speciation due to dissolution, precipitation, sorption and complexation phenomena [4]. This makes heavy metals bioavailable to living things to varying degrees. Some heavy metals can readily bioaccumulate in the bodies of organisms and become biomagnified along the food chains to reach such levels that cause harm to human organs and systems [5]. Chronic exposure of human beings to Cd can lead www.ijera.com to renal and skeletal malfunctioning and death while high exposure to Pb can cause damage to the kidney, nervous, circulatory and reproductive systems. It can also result to rheumatoid arthritis, anaemia, dizziness, headache and insomnia. Over the years, heavy metals treatment and removal have been carried out by several techniques such as electrodialysis, ion exchange resin, ultrafilteration, cementation, solvent extraction, chemical precipitation, reverse osmosis and phytoremediation [6-11]. However, adsorption has some advantages over these conventional methods because adsorption techniques are low cost, display metal selectivity, high efficiency, maximization of chemical and low biological sludge, regeneration of adsorbent and possible metal recovery [12]. Several adsorbent materials such as plantain peel charcoal [5], untreated powdered egg shell [13], Sago waste [14], almond shell [15], wood saw dust [16], coconut husk and shell [17, 18], sea weeds [19] , bagasse ash [20], and so on, have been utilized for adsorption purposes. The harmful effects of high levels of toxic and heavy metal ions such as As, Cd, Pb, Hg, Cu, Mn and Zn on the environment in general have prompted the need to look for easy - to - afford and suitable technologies for their removal from industrial effluents before being discharged into water bodies. In an earlier investigation involving four adsorbents generated from different agricultural waste 1961 | P a g e
  2. 2. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 products [5], charcoal from plantain peel gave the best adsorption performance. However, the mechanism by which this was done was not investigated. Hence, its technological applications in heavy metal removal from wastewaters were not adequately highlighted. Thus in the present study, the kinetics, equilibrium and thermodynamics of Cd2+ and Pb2+ removal from synthetic wastewater using plantain peel charcoal was investigated in order to determine the mechanism by which this adsorption is carried out. This understanding could further enhance applications of plantain peel charcoal as a suitable alternative adsorbent to expensive ones in wastewater control and management especially in the developing countries. II. Materials and Methods 2.1. Preparation of adsorbent The method adopted in an earlier study [5] was used in this study to generate adsorbents from locally available materials. Unripe plantain peels collected from villages around the Obafemi Awolowo University, Ile-Ife, Nigeria, were cut into pieces, washed thoroughly and rinsed with tap and distilled water respectively to remove debris and other impurities. The plantain peel chips obtained were oven dried at a temperature of 105oC for 72 hours. The dried chips were carbonized by packing them into an earthenware pot, covered and heated at high temperature. The pot content was stirred occasionally so as to obtain a uniform combustion product. The covering was necessary to reduce the amount of air contact such that complete combustion of the plantain peel chips was prevented and well formed charcoal was ensured. When the smoke that was coming out of the pot had stopped, the charcoal formed was allowed to cool and was powdered by grinding in an agate mortar with a pestle to increase the adsorbent surface area of contact. The powdered charcoal was fractionated using a test sieve of 500 microns pore size. The sieved charcoal was activated and leached using 0.2 M sulphuric acid by soaking in the acid for 48 hours after which the charcoal was filtered, rinsed thoroughly with doubly distilled water and dried overnight in a Gallenkamp Oven (Model Ov-160, England) at 130ºC. 2.2. Apparatus sterilization All the glassware used, such as measuring cylinders, volumetric flasks, beakers, conical flasks, watch glass and sample bottles (polyethylene containers) were washed thoroughly with hot liquid detergent solution, and then rinsed with a mixture of acetone and n-hexane. The washed polyethylene sample bottles were further soaked in 10% HNO3 for 48 hours and subsequently rinsed with distilled water. All the chemical reagents used were of analytical grade. www.ijera.com www.ijera.com 2.3. Adsorption procedure All experiments were carried out using a 200 mL solution of 50 mg.L-1 of the metal ions solution mixture in contact with 1.5 g of the charcoal in a 250 mL beaker. Each experimental solution was appropriately adjusted to the desired pH value using buffer solutions. Mixing was done by means of a mechanical stirrer at an average rate of three cycles per second for 20 minutes in a thermostated water bath. The charcoal was filtered from the solution using Whatman No. 42 filter paper. This process was repeated for similar solutions at 40, 60, 80, 100, 120, 140, 160 and 180 minutes respectively. 2.3.1. Effect of pH The effect of pH was investigated by conducting the experiments at different pH values (3, 5, 7, and 9) at 30 and 40oC to obtain the pH of maximum adsorption. Also, the effects of contact time and temperature were studied at the pH of maximum adsorption at different temperatures (10, 20, 30, 40 and 50oC) for time intervals of 20 minutes within the range of 0 to 180 minutes within which equilibrium had been attained. 2.3.2. Quantitative Estimation of Heavy Metals in the Solutions The initial and residual metal ion concentrations in the supernatant solution were determined using Flame Atomic Absorption Spectrophotometer, FAAS (Buck Model 205 FAAS, East Norwalk, USA). The amount of metal ions adsorbed for each parameter was determined by difference between the initial metal ion concentration and the concentration of metal ions in the supernatant solutions. Each determination was done in triplicate and the mean value for each experiment was calculated and presented. All studies were conducted in triplicates and the mean values determined. A blank experiment was conducted by analyzing doubly distilled water to establish blank level. 2.3.3. Determination of Adsorption Capacities The adsorption capacities, qe and qt, which were the amounts of metal ions adsorbed by the adsorbent (mg.g-1) when equilibrium was attained at time, t, were respectively calculated by the equations: qe  Co  Ce  V M C  Ct V qt  o M (1) (2) where Co = initial concentration of metal ion in solution (mg.L-1); Ce = the final concentration of metal ion in solution at equilibrium (mg.L-1); Ct = the final concentration of metal ion in solution at time t (mg.L-1); M = the mass of adsorbent (g); and V = the volume of solution (L). 1962 | P a g e
  3. 3. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 www.ijera.com The results were also expressed as the percentage removal favoured the adsorption process, it showed that (% Rp) of the metal ions from solution by the plantain peel mobility of the metal ions increased with an increase charcoal using the equation: in temperature thus making the metal ions to interact more with the surface of the adsorbent [27]. C C %R p  o e Co  100 (3) where Co and Ce are the initial and equilibrium concentrations of the adsorbed solute (mg L-1) respectively. III. 3. Results and Discussion 3.1. Effect of pH The effects of pH on the adsorption of Pb2+ 2+ and Cd are illustrated in Fig. 1. The adsorption capacity increased as the pH of the solution increased [21] but decreased after pH 5 for Pb2+ and after pH 7 for Cd2+. The maximum adsorption of Pb2+ occurred at pH 5 with a percentage removal of 90.06 % and that of Cd2+ occurred at pH 7 with a percentage removal of 92.39 %. The value obtained for Pb2+ is comparable to the findings when sago waste [14], tea waste [22] and Moringa oleifera bark [23] were used as adsorbents. The value obtained and the trend for the effect of pH on the adsorption of Cd2+ is comparable to, but higher, in some cases, than that observed for the adsorption of Cd2+ using other adsorbents [24-27]. At lower pH, there might be high competition between the cations and hydrogen ions in solution for the active sites on the adsorbent [25, 28] and this might lead to a decrease in the adsorption of Cd2+. However, as the pH increases, there is a decrease in hydrogen ions and there would be more available sites. As a result, there is an increase in the adsorption of Pb2+ and Cd2+ from the solution. This probably led to an increase in the adsorption capacity as the pH increases. At pH > 8.0, there would be precipitation of cadmium and lead hydroxides [14, 25] and when the hydroxyl ions are in excess in the synthetic wastewater, there would be hydroxyl complexes of cadmium [25]. Hence, for this process to be an adsorption process pH values of 5 and 7 were considered the optimum pH for Pb2+ and Cd2+ and these were used for further studies. 3.2. Effects of contact time and temperature It was observed that the removal of Pb2+ and 2+ Cd increased as the contact time increased, and equilibrium was reached after 100 min. The adsorption was noticed to be fast initially and then became slower. This can be attributed to the strong attractive forces between the metal ions and the adsorbent [27]. As illustrated in Fig. 2, the relationship between the percentage removal of Pb2+ and Cd2+ with time is both linear and logarithmic (curve). This can be said to be as a result of solute - solute competition, the solute surface interaction, hydration capacity, pH and availability of sites [28]. It was observed that increased temperature resulted in increased adsorption of the metals from the synthetic wastewater. Since increase in temperature www.ijera.com 3.3. Adsorption kinetics The kinetic study of the process of adsorption determines the rate at which the contaminants are removed from synthetic wastewaters. Numerous kinetic models have been proposed which are capable of describing the mechanism by which the adsorption process takes place. In order to investigate the adsorption kinetics of the metals, the experimental data obtained were tested with the pseudo-first order, pseudo-second order, intraparticle and Elovich models to know the controlling mechanism. The equation used is the pseudo-first order kinetic equation [29] stated as follows: dq  k1 qe  qt  dt where qt and (4) q e (mg.g-1) are the amounts of metal ion adsorbed at time t (min) and at equilibrium respectively, and k1(min-1) is the rate constant of the pseudo-first order kinetics. After integration by the application of boundary conditions, t = 0 to t = t, and q = 0 to q = q e , the above equation becomes: ln qe  qt   ln qe  k1t A linear plot of ln qe  qt  (5) against t should give a slope of k1 and an intercept corresponding to ln qe . Linear plot of ln(qe - qt) against t were obtained, and the calculated qe , k2, and R2 were determined and presented in Table 1. The pseudo-second order equation used [30] can be written as: dq 2  k 2 qe  qt  dt (6) where k2 (g mg-1min-1) is the rate constant of pseudosecond order equation. On integrating the equation by applying boundary conditions, t = 0 to t = t and q = 0 to q = qt and on linearizing, it becomes: t 1 t   2 qt k 2 qe qe qe (7) and k2 can be calculated from the slope and intercept of a linear plot of t/qt against t. Straight-line plots of t/qt against t at different temperatures for the adsorption of Pb2+ and Cd2+ are shown in Fig. 3. The adsorption data were processed using the intraparticle diffusion which is given as: 1 2 qt  k p t  I (8) where kp and I are the intraparticle diffusion rate constant (mg.g-1min-1/2) and intercept (mg.g-1) 1963 | P a g e
  4. 4. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 respectively. The value of I explains the thickness of the boundary layer, and the larger the value of I, the thicker the boundary layer. A plot of the amount adsorbed against the square root of time would be linear if intraparticle diffusion takes place in the adsorption process and it is the rate controlling step if the line passes through the origin [31]. The Elovich model is an equation that is based on adsorption capacity of adsorbents [13, 32] and it is generally written as: dqt   exp qt  dt (9) where α is the initial adsorption rate (mg.g-1min-1) and β is the desorption constant (g.mg-1). The equation was simplified [33] by assuming αβt >> t and by applying boundary conditions, t = 0 to t = t and q = 0 to q = q t, to become 1 1 qt  ln    ln t    (10) Thus, if the adsorption by the adsorbent fits the Elovich model, a plot of qt against ln (t) would give a straight line with a slope and an intercept that correspond to (1/β) and 1 /  ln  , respectively. The linearity of the plots for pseudo-second order (Fig. 3) and the values of the coefficient of correlation, which were greater than 0.960, showed that Pb2+ and Cd2+ removal kinetics fitted very well into the pseudo-second order kinetics (Table 1). It can be seen from Table 1 that the values of the experimental qe were in agreement with the calculated qe values obtained from the pseudo-second order linear plots while the R2 values showed that the pseudo-first order, intraparticle diffusion and Elovich models were not significantly involved in the adsorption of the metals.     3.4. Adsorption isotherms In this study, the Langmuir, Freundlich and Tempkin equations were used to estimate the adsorption data. Langmuir adsorption isotherm assumes a monolayer adsorption with a uniform energy on an adsorbent surface [34]. It is given as: QK C qe  0 L e 1  K L Ce where qe (11) is the amount of heavy metal adsorbed on the adsorbent (mg.g-1), -1 Ce is the final concentration of metal (mg.L ) in the solution, Q0 is the maximum possible amount of metallic ion adsorbed per unit weight of adsorbent (mg.g-1) and KL is an equilibrium constant related to the affinity of the binding sites for the metals (L.mg-1). The equation can be rearranged linearly as follows: www.ijera.com www.ijera.com Ce C 1   e qe K LQ0 Q0 (12) The Langmuir isotherm was used to test the experimental data for the removal of both metals using plantain peel charcoal by plotting Ce/qe against Ce (Fig. 4 and Fig. 5), and the values of Q0, kL and R2 were determined and are presented in Table 2. The Freundlich model assumes that there is a heterogeneous surface with a distribution of heat of adsorption that is not uniform over the surface of the adsorbent. The Freundlich adsorption isotherm is mathematically expressed as: qe  k F Ce 1/ n (13) where qe is the amount of metal adsorbed on the adsorbent (mg g-1), Ce is the final concentration of metal (mg.L-1) in the solution, k F is an empirical constant that provides an insight into the adsorption capacity of the adsorbent (L.g-1), and 1/n is an empirical constant that provides an indication of the intensity of adsorption. Equation [13] can be linearized as follows: 1 log qe  log k F  log Ce n (14) Linear plots showing the Freundlich isotherm for the adsorption of Pb2+ and Cd2+ were obtained by plotting log qe versus log Ce. The values of kF, 1/n and R2 were obtained and are given in Table 2. Tempkin isotherm assumes that the fall in the heat of sorption is linear rather than logarithmic. It contains a factor that describes the interactions between the adsorbent and the adsorbates. The Tempkin isotherm is given as follows: qe  RT ln kT Ce b (15) This can be linearized as qe  B1 ln kT  B1 ln Ce where B1  (16) RT b kT is the equilibrium binding constant (L.mg-1) which corresponds to the maximum binding energy. R is the gas constant (8.314J.mol-1K-1), T is the absolute temperature (K) and B1 is related to heat of adsorption (mg.g-1). The plot of qe versus ln Ce gave straight-line plots. The values of kT, B1 and R2 were calculated and are presented in Table 2. The values of R2 (greater than 0.960) showed that the adsorption of Pb2+ and Cd2+ on the surface of plantain peel charcoal can be described with the Langmuir, Freundlich and Tempkin isotherms with the best fit obtained from Langmuir isotherm. This implies that the adsorption process occurs at well 1964 | P a g e
  5. 5. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 defined sites that are homogenous and there was, most likely, a monolayer adsorption onto the surface of the plantain peel charcoal. 3.5. Thermodynamics of adsorption The practical applicability of an adsorption process is indicated by thermodynamic parameters such as changes in Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS). The values of these parameters would determine whether the adsorption process is spontaneous or not, endothermic or exothermic and also determine the degree of disorderliness. The parameters can be determined from the following equations [21,35]: G  H  TS (17) CA (18) CS S H (Van’t Hoff Equation) ln K C   R RT KC  (19) where Kc is the equilibrium constant, CA is the amount of solute adsorbed and CS is the equilibrium concentration of the solute in the solution. The thermodynamic parameters were determined by plotting ln Kc versus 1/T. The values of ΔS and ΔH were calculated from the intercept and slope and are presented in Table 3. At all temperatures under which the adsorption was studied, ΔH was found to be positive and this means that the adsorption process was endothermic. This is supported by the increase in the amount adsorbed as the temperature increased. The positive values of ΔS suggest that there was an increased randomness on the solid - solution interface during the adsorption of the metals on the surface of the plantain peel charcoal. The negative values of ΔG meant that the adsorption process was spontaneous and the decreased values of ΔG as the temperature increased implied that the process was more spontaneous at higher temperatures [21]. Free energy changes for physisorption reaction are usually between -20 to 0 kJ.mol-1 while the values for chemisorption reaction are between -80 to -400 kJ.mol-1 [36]. Thus, the values of ΔG obtained in the present study confirmed the adsorption process to be of the physisorption type. and Tempkin isotherms, but it was the Langmuir isotherm that most fittingly described the data. The thermodynamic studies showed that the adsorption process was endothermic in nature and this was confirmed by the increase in the adsorption capacity with rise in temperature. Also, the adsorption process in each case was a spontaneous physisorption reaction. The results obtained showed that plantain peel charcoal has the potential to effectively reduce the levels of heavy metal ions such as Pb2+ and Cd2+ from synthetic wastewaters and industrial effluents. Hence, it could replace the very expensive adsorbents in water and environmental engineering designs for industrial effluent treatments especially in the third world countries. REFERENCES [1] [2] [ 3] [4] [5] [6] [7] [8] IV. 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  7. 7. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 M.J. Jaycock, and G.D. Parfitt, Chemistry of Interfaces (Ellis Horwood Ltd., Chichester, U.K., 1981). o 30 C o 40 C 3 4 5 6 pH 7 8 -1 6.4 6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 Amount adsorbed (mg.g ) -1 Amount adsorbed (mg.g ) [36] www.ijera.com 9 6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 o 30 C o 40 C 3 4 5 6 7 pH Pb2+ 8 9 Cd2+ Percentage removal (%) percentage removal (%) Figure 1: Effect of pH on the Adsorption of Pb 2+ and Cd2+ on Plantain Peel Charcoal 100 80 60 o 10 C o 20 C o 30 C o 40 C 40 20 0 o 50 C 100 80 o 10 C o 20 C o 30 C o 40 C o 50 C 60 40 20 0 -20 0 20 40 60 80 100120140160180200 -20 0 20 40 60 80 100120140160180200 time (min) time (min) Pb2+ Cd2+ Figure 2: Effect of Time and Temperature on the Adsorption of Pb 2+ and Cd2+ on Plantain Peel Charcoal 20 10 50 100 Time (min) Pb2+ 150 -1 -1 t / qt (min.g.mg ) 30 t / qt (min.g.mg ) o 10 C o 20 C o 30 C o 40 C o 50 C 40 28 26 24 22 20 18 16 14 12 10 8 6 4 2 o 10 C o 20 C o 30 C o 40 C o 50 C 50 100 150 Time (min) Cd2+ Figure 3: Pseudo-second Order Adsorption Kinetics of Pb2+ and Cd2+ Removal by Plantain Peel Charcoal www.ijera.com 1967 | P a g e
  8. 8. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 www.ijera.com o 10 C o 20 C 6 Ce / qe(g.L-1) C e / qe (g.L -1 ) 3.2 5 4 3.0 2.8 2.6 18 20 22 13 -1 Ce (mg.L ) 14 -1 Ce (mg.L ) 15 o 40 C o 30 C 1.5 C e / qe (g.L-1) Ce / qe (g.L-1) 3.0 2.8 2.6 2.4 1.0 0.5 2.2 12 13 4 14 Ce (mg.L-1) 6 -1 Ce (mg.L ) 8 Ce / qe (g.L-1) 50oC 0.6 0.4 0.2 2 3 Ce (mg.L-1) 4 Figure 4: Langmuir Isotherms for Pb2+ Removal by Plantain Peel Charcoal www.ijera.com 1968 | P a g e
  9. 9. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 www.ijera.com o 20 C o 10 C 2.5 Ce / qe (g.L-1) -1 Ce / qe (g.L ) 2.0 2.0 1.5 1.5 1.0 1.0 6 8 10 Ce (mg.L-1) 4 12 6 8 Ce (mg.L-1) 10 12 o o 40 C 1.5 Ce / qe (g.L-1) Ce / qe (g.L-1) 30 C 1.0 4 6 8 Ce (mg.L-1) 2 1 5 10 Ce (mg.L-1) o 50 C Ce / qe (g.L-1) 1.5 1.0 0.5 2 4 6 Ce (mg.L-1) 8 Figure 5: Langmuir Isotherms for Cd2+ Removal by Plantain Peel Charcoal www.ijera.com 1969 | P a g e
  10. 10. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 www.ijera.com Table 1: Kinetic Constants for Pb2+ Adsorption on Plantain Peel Charcoal at Different Temperatures (T (oC); (qe) exp (mg.g-1); (qe) cal (mg.g-1); k1 (min-1); k2 (g.mg-1.min-1); kp (mg.g-1.min-1/2); α (mg.g-1.min-1); and β (g.mg-1)) Pb2+ (qₑ) exp. Pseudo-first Order (qₑ) calc. k₁ R² Pseudo-second Order (qₑ) calc. k₂ R² Intraparticle Diffusion Elovich Model I kp R² α β R² 4.3870 1.6120 0.0110 0.5732 4.4283 0.0453 0.9975 3.3064 0.0841 0.6924 318.0316497 2.7180 0.7789 4.9810 1.0045 0.0188 0.6807 4.9831 0.1005 0.9996 4.5056 0.0347 0.7453 2.7166E+11 6.7485 0.7894 5.1430 0.3580 0.0151 0.0117 5.0335 95.1079 0.9995 4.7860 0.0231 0.2508 1.14433E+16 8.6987 0.4210 6.2290 1.1427 0.0221 0.3677 6.2625 0.0817 0.9995 5.4052 0.0680 0.6083 1117053.774 3.2215 0.7607 6.4740 0.8464 0.0357 0.3003 6.5479 0.0784 0.9999 5.9056 0.0473 0.8258 84664117007 4.9015 0.8976 Cd2+ 6.0050 1.9567 0.0483 0.6432 6.2570 0.0259 0.9987 4.5061 0.1278 0.7622 211.2068 1.8080 0.8356 6.1190 2.6072 0.0276 0.8834 6.3569 0.0216 0.9986 4.5976 0.1217 0.9015 515.1650 1.9668 0.9088 6.1400 1.6810 0.0258 0.9144 6.3040 0.0316 0.9994 5.0347 0.0885 0.9298 35815.2586 2.7023 0.9401 6.1600 3.8145 0.0518 0.6992 6.4616 0.0209 0.9990 4.4268 0.1464 0.8449 78.3989 1.5846 0.9159 6.5380 5.5849 0.0546 0.8055 6.7986 0.0238 0.9990 5.0757 0.1217 0.8729 1190.9028 1.9491 0.8995 www.ijera.com 1970 | P a g e
  11. 11. J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971 www.ijera.com Table 2. Isothermal Constants for Pb2+ and Cd2+ Adsorption on Plantain Peel Charcoal at Different Temperatures (Q0 (mg.g-1); KL (L.mg-1); KF (L.g-1); KT (L.mg-1); and B1 (mg.g-1)) Pb2+ Langmuir Freundlich Tempkin T Kₑ Q₀ R² KF 1/n R² KT B1 R² 10 -0.1248 2.3619 0.9976 29.4965 -0.6694 0.9958 0.0112 -2.6621 0.9984 20 -0.2590 3.4695 0.9996 13.2306 -0.3846 0.9987 0.0053 -1.8503 0.9993 30 -0.2952 3.6369 0.9991 12.1143 -0.3508 0.9966 0.0044 -1.7288 0.9981 40 -1.6537 5.1637 0.9989 7.2482 -0.1235 0.9785 0.0001 -0.7262 0.9830 50 -7.5986 5.9280 0.9998 6.6190 -0.0545 0.9835 0.0000 -0.3429 0.9854 Cd2+ 10 -0.7956 4.5286 0.9987 8.2120 -0.1938 0.9879 0.0007 -1.0680 0.9916 20 -1.0165 4.7831 0.9980 7.7625 -0.1632 0.9790 0.0003 -0.9247 0.9847 30 -1.3310 5.0462 0.9987 7.4574 -0.1385 0.9821 0.0001 -0.8052 0.9865 40 -1.0052 4.6685 0.9970 7.7300 -0.1663 0.9695 0.0003 -0.9326 0.9780 50 -5.7019 5.5853 0.9986 6.5423 -0.0646 0.9467 0.0000 -0.3957 0.9546 Table 3: Thermodynamic Parameters for Pb2+ and Cd2+ Adsorption on Plantain Peel Charcoal (T/K; ΔS/kJ mol1.K-1; ΔH/kJ.mol-1 ; and ΔG/kJ.mol-1) ΔG(kJ.mol-1) ΔS (J.mol-1.K-1) ΔH (kJ.mol-1) 283K 293K 303K 313K 323K 2+ 0.1965 54.8191 -0.7875 -2.7524 -4.7173 -6.6822 -8.6471 Cd2+ 0.1092 26.2154 -4.6764 -5.7680 -6.8596 -7.9512 -9.0428 Metals Pb www.ijera.com 1971 | P a g e

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