- Email: [email protected]
Biosorption of copper(II) and lead(II) onto potassium hydroxide treated pine cone powder
Journal of Environmental Management 91 (2010) 1674e1685
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Biosorption of copper(II) and lead(II) onto potassium hydroxide treated pine cone powder A.E. Ofomaja*, E.B Naidoo, S.J. Modise Department of Chemistry, Vaal University of Technology, Vanderbiljpark, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 June 2009 Received in revised form 22 February 2010 Accepted 9 March 2010 Available online 15 May 2010
Pine cone powder surface was treated with potassium hydroxide and applied for copper(II) and lead(II) removal from solution. Isotherm experiments and desorption tests were conducted and kinetic analysis was performed with increasing temperatures. As solution pH increased, the biosorption capacity and the change in hydrogen ion concentration in solution increased. The change in hydrogen ion concentration for lead(II) biosorption was slightly higher than for copper(II) biosorption. The results revealed that ion-exchange is the main mechanism for biosorption for both metal ions. The pseudo-first order kinetic model was unable to describe the biosorption process throughout the effective biosorption period while the modified pseudo-first order kinetics gave a better fit but could not predict the experimentally observed equilibrium capacities. The pseudo-second order kinetics gave a better fit to the experimental data over the temperature range from 291 to 347 K and the equilibrium capacity increased from 15.73 to 19.22 mg g1 for copper(II) and from 23.74 to 26.27 for lead(II). Activation energy was higher for lead(II) (22.40 kJ mol1) than for copper(II) (20.36 kJ mol1). The free energy of activation was higher for lead(II) than for copper(II) and the values of DH* and DS* indicate that the contribution of reorientation to the activation stage is higher for lead(II) than copper(II). This implies that lead(II) biosorption is more spontaneous than copper(II) biosorption. Equilibrium studies showed that the Langmuir isotherm gave a better fit for the equilibrium data indicating monolayer coverage of the biosorbent surface. There was only a small interaction between metal ions when simultaneously biosorbed and cation competition was higher for the Cu-Pb system than for the Pb-Cu system. Desorption studies and the DubinineRadushkevich isotherm and energy parameter, E, also support the ion-exchange mechanism. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Ion-exchange KOH treatment Pine cone powder Equilibrium pH Pseudo-second order model Activation energy
1. Introduction Heavy metal pollution of surface water such as rivers and streams has been largely attributed to disposal of industrial effluents into receiving water bodies (Argun et al., 2008). These heavy metal pollutants are not biodegradable and their presence in surface water may led to bioaccumulation in living organisms, causing health problems in plants, animals and human beings. Intake of some heavy metals in humans has been known to cause serious harmful effects. For example, lead intake in humans causes disruption of biosynthesis of hemoglobin, rise in blood pressure, kidney damage, miscarriages and abortions, brain damage and diminished learning abilities in children (Argun et al., 2008). Copper intake leads to severe mucosal irritation, widespread
* Corresponding author. Tel.: þ27 768202689/þ27 738126830/þ234 80715034. E-mail addresses: [email protected], [email protected] (A.E. Ofomaja). 0301-4797/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2010.03.005
capillary damage, hepatic and renal damage, central nervous problems followed by depression, gastrointestinal irritation, and possible necrotic changes in the liver and kidney (Gündogan et al., 2004). Both copper and lead are widely used industrially. Copper is mainly used for pulp and paper board, wood and leather preserving, petroleum refining and for copper coatings and fittings. Lead on the other hand, is mainly used for insecticide, storage battery, and petrol additive and metal plating/finishing industries and so on. Therefore, efficient and cost effective separation techniques are needed to clean up industrial effluents from the processes before they are discharged into receiving water bodies. Several studies have shown the efficacy of adsorbents of biological origin to remove metal pollutants from aqueous solution (Ho and Ofomaja, 2006) and more recently chemically treated biomass (Ofomaja et al., 2009) have been applied for metal removal from aqueous solution. Min et al. (2004) showed that Sodium hydroxide treatment of lignocellulosic materials could cause swelling which
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
leads to an increase in internal surface area, decrease in the degree of polymerization, decrease in crystallinity, separation of structural linkages between lignin and carbohydrates and disruption of the lignin structure. Base solutions such as sodium hydroxide, potassium hydroxide or calcium hydroxide are also good reagent for saponification or the conversion of an ester group to carboxylate and alcohol functional groups (Min et al., 2004). The potential sources of copper in industrial effluents include metal cleaning and plating baths, pulp, paper board mills, wood pulp production, and the fertilizer industry, etc. In the wastewater of a copper wire mill, an average concentration of copper ions is about 800 mg dm3 (Panday et al., 1985). Lead is introduced into natural waters through various industrial activities such as those from the insecticide, storage battery, and metal plating/finishing industries, etc. In industrial wastewaters, Lead ion concentration is in the range of 200e500 mg dm3, these values are very high in relation to water quality standards, therefore copper and lead concentrations in wastewaters should be reduced (Ucun et al., 2003). Pine cone is an agricultural waste produced when pine tree seeds are removed from matured cones. Pine cone is composed of mainly a-Cellulose (18.8%), Holocellulose (46.5%), and lignin (37.4%) (Nagata et al., 1990). Large quantities of cones are released in pine plantations annually with little or no use. Pine cone powder as biosorbent has the advantage of achieving maximum metal removal at short contact time. For example Ucun et al. (2002) achieve equilibrium for chromium(IV) removal from aqueous solution in 20 min, Malkoc (2006) achieved equilibrium for nickel (II) in 3 min while Ucun et al. (2002) removed copper(II) from solution in 20 min. The use of chemical treatment to improve the biosorption capacity of pine cone powder is scanty in literature and much research has not been carried out in this area. This research therefore seeks to study (i) the application of potassium hydroxide (KOH) treated pine cone powder for the removal of copper(II) and lead(II) from aqueous solution, (ii) Analyze the biosorption kinetic data for the effect of temperature on copper(II) and lead(II) biosorption with the pseudo-first, modified pseudo-first and pseudo-second order kinetic models so as to determine the possible biosorption mechanism (iii) determine the activation energy, enthalpy and entropy of activation from the kinetic data, (iv) Determine the equilibrium isotherm characteristics of copper(II) and lead(II) biosorption using the Langmuir, Freundlich, BET and DubinineRadushkevich isotherm models, (v) To determine the effect of simultaneous biosorption of copper(II) and lead(II) from binary solution and to perform desorption studies. 2. Materials and methods 2.1. Materials Pine tree cones were obtained from a plantation in Sasolburg, Free State, South Africa. Pine tree cones were collected between August and September 2007. The cones were washed to remove impurities such as sand and leaves, the washed cones were then dried at 90 C for 48 h in an oven. The scales on the cones were then removed and blended in a food processing blender. The resultant powder was sieved and particles below 300 mm were collected and used for analysis. A weighed amount (50 g) of the powder obtained was contacted with 500 ml of potassium hydroxide solution of concentration 0.15 mol dm3 and the slurry stirred overnight. The powder was rinsed with distilled water. This procedure was repeated two more times to ensure removal of potassium hydroxide from the powder. The residue was then dried overnight at 90 C.
1675
The stock solution of copper(II) nitrate (Cu(NO3)2) and lead(II) nitrate (Pb(NO3)2) were prepared by dissolving accurately weighed amount of the salts in deionized water. The experimental solutions were prepared by diluting the stock solution with distilled water when necessary.
2.2. Methods The pH at point zero charge (pHPZC) of the pine cone powder was determined by the solid addition method (Mall et al., 2006). Acidic and basic sites on pine cone powder were determined by the acidebase titration method proposed by Boehm (1994). The IR spectra of the Pine cone powder sample were recorded using KBr disk in conjunction with a PerkineElmer infrared spectrophotometer. Iodine number was determined by iodine titration as described by ASTM standards measurements (ASTM D4607-8). A modification of the method of Boehm (1994) developed by Marshall et al. (1999) was used to determine total negative charge. Bulk density was determined by tamping procedure described by Ahmedna et al. (1997). 2.2.1. Effect of initial solution pH The effect of solution pH on the equilibrium uptake of copper(II) and lead(II) from aqueous solution by pine cone powder treated 0.15 mol dm3 KOH was investigated between pH 2 and 6. Experiments were performed by adding a known weight of pine cone powder into eight 500 ml beakers containing 50 ml of 70 mg dm3 of copper(II) and lead(II) solution and the pH of the solution adjusted using 0.10 mol dm3 HCl or NaOH. The flasks were shaken at 160 rpm and 291 K for 15 min and the amount of copper(II) or lead(II) remaining in solution was measured by a PerkineElmer model 2100 atomic absorption spectrometer (AAS). Solution pH profile during this experiment was monitored at different time intervals from 1 to 20 min using a pH meter (Crison Basic 20þ). Blank experiments were also performed in deionized water set at pH 5.0 without the addition of metal ions. 2.2.2. Effect of temperature A range of reaction temperatures (291, 297, 307, 317, 327, 337, and 347 K) was used in this experiment and the flasks were agitated for 15 min. All contact investigations were performed in a 500 ml flask. A 0.4 g sample of KOH treated pine cone powder was added to 100 ml volume of copper(II) and lead(II) solution set at pH 5.0 and agitated at 160 rpm. Experiments were carried out at initial copper (II) and lead(II) concentration of 120 mg dm3. Samples were withdrawn at suitable time interval (Samples were drawn every 1 min in the first 5 min and every 5 min in the next 15 min), filtered through a micro pore filter paper and the filtrate analyzed with AAS. 2.2.3. Equilibrium studies A volume of 100 ml of copper(II) or lead(II) solution with concentration ranging from 60 to 120 mg dm3 was placed in a 250 ml conical flask and set at pH 5.0 and accurately weighed amounts (0.40 g) of the KOH treated pine cone was added to the solutions. The conical flasks were then agitated at a constant speed of 160 rpm in a water bath set at 291 K. After shaking the flasks for 30 min a known quantity of sample was withdrawn, and filtered through a micro pores and the filtrate analyzed with AAS. 2.2.4. Cation competition Isotherm studies carried out as in section 2.2.3 to examine the equilibrium biosorption of lead(II) in the presence of equal concentration of copper(II) and copper(II) in presence of lead(II).
1676
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
2.2.5. Desorption analysis The solid biosorbent residue was filtered off from the biosorption system of 0.4 g KOH treated pine cone powder in contact with 120 mg dm3 of copper(II) or lead(II) ion solution at 291 K. The washed biosorbent was then stirred in 100 ml of each of the desorbing solvents (0.01 mol dm3 of HNO3, HCl and CH3COOH and distilled water). After shaking the flasks for 30 min, the pine cone powders were separated by filtration. The filtrate was analyzed with AAS. 2.2.6. Theory The pseudo-first order kinetic model equation is written as (Ho and Ofomaja, 2006):
dqt ¼ k1 ðqe qt Þ dt
k1 t 2:303
(2)
Plots of log (qe qt) versus t gives a straight line for pseudo-first order kinetics, which allows computation of the biosorption rate constant, k1. If the experimental results do not follow Eqs. (1) and (2) they differ in two important aspects: (i) k1(qe qt) does not represent the number of available sites, and (ii) log (qe) is not equal to the intercept of the plot of log (qe qt) against t. To set up the new model for the pseudo-first order kinetics Eq. (1) was modified by Yang and Al-Duri (2005), Lagergren (1898) and Ho (2004) through the modification of its rate constant, k1. The rate constant in the modified pseudo-first order kinetic model (MPFOM) was denoted by K1 and the following equation was proposed:
qe k1 ¼ K1 qt
h ¼ k2 q2e :
the constant can then be determined experimentally by plotting of t/qt against t. 2.2.6.1. Langmuir (1916) isotherm. At constant temperature, metal ions held onto the biosorbent will be in equilibrium with metal ions in bulk solution. The saturated monolayer isotherm can be represented as:
qe ¼
qm Ka Ce 1 þ Ka Ce
(4)
(5)
Integrating Eq. (5) over time t during which the solid phase concentration increases from zero to qt, the following algebraic equation can be obtained:
qt þ lnðqe qt Þ ¼ lnðqe Þ K1 t qe
(6)
If the biosorption process follows the modified pseudo-first order kinetic model represented by Eq. (6), a plot of qt/qe þ ln(qe qt) against t should be a straight line. The pseudo-second-order chemisorption kinetics may be expressed as:
dqt ¼ k2 ðqe qt Þ2 ; dt
(10)
where Ce is the equilibrium concentration (mg dm3); qe is the amount of metal ion biosorbed (mg g1); qm is qe for a complete monolayer (mg g1); Ka is biosorption equilibrium constant (dm3 mg1). 2.2.6.2. Freundlich (1906) isotherm. The empirical Freundlich isotherm, based on biosorption on heterogeneous surface, can be derived assuming a logarithmic decrease in the enthalpy of biosorption with the increase in the fraction of occupied sites and is given by: 1=n
qe ¼ KF Ce
(11)
where KF and 1/n are the Freundlich constants characteristics of the system, indicating the biosorption capacity and biosorption intensity, respectively. Eq. (11) can be linearized in logarithmic form to give Eq. (12) and the Freundlich constants can be determined.
1 logqe ¼ logKF þ logCe n
(12)
2.2.6.3. DubinineRadushkevich (DeR) isotherm. The DubinineRadushkevich (DeR) isotherm is generally expressed as follows (Dubinin, 1960):
qe ¼ qD exp
Eq. (4) can be rearranged into
qe dqt dqt þ ¼ K1 qe dt ðqe qt Þ
(9)
(3)
As qt < qe, the above equation implies that the rate constant k1 is minimum when equilibrium is reached. The modified pseudo-first order rate equation can be derived as follows:
dqt qe ¼ K1 ðqe qt Þ dt qt
(8)
If the initial sorption rate is
(1)
where qt and qe are the amount sorbed at time t and at equilibrium and k1 is the rate constant of the pseudo-first-order sorption process. The integrated rate law, after applying the initial conditions of qt ¼ 0 at t ¼ 0 is:
logðqe qt Þ ¼ logðqe Þ
t 1 1 ¼ þ t: qt k2 q2e qe
(7)
where k2 is the rate constant of sorption, qe and qt have the same definition as above. This can be separated and integrated to the linear form:
2 ! 1 BD RTln 1 þ Ce
(13)
Radushkevich (1949) and Dubinin (1965) have reported that the characteristic sorption curve is related to the porous structure of the sorbent. The constant, BD, is related to the mean free energy of biosorption per mole of the sorbate as it is transferred to the surface of the solid from infinite distance in the solution and this energy can be computed using the following relationship (Hasamy and Chaudhary, 1996):
1 E ¼ pffiffiffiffiffiffiffiffiffi 2BD
(14)
The linear form of the (DeR) isotherm equation is
lnqe ¼ lnqD BD 32
(15)
where BD is a constant related to the mean free energy of adsorption per mole of the adsorbate (mol2J2); qD, the theoretical saturation capacity and e is the polanyi potential, which is equal to RT ln (1 þ (1/Ce)), where R (Jmol1K1) is the gas constant and T (K), the absolute temperature. Hence by plotting ln qe against 32, it is possible to generate the values of qD (mol g1) from the intercept and the values of BD from the slope.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
2.2.6.4. BET isotherm (Brunauer et al., 1938). The BET model is an extension of the Langmuir model for multilayer biosorption. It is based on the assumption that each adsorbate in the first biosorbed layer serves as biosorption site for the second layer and so on. The original form of the BET equation is given as:
q ¼
KB Ce qm ðCs Ce Þ½1 þ ðKB 1ðCCes
i
(16)
Where Ce is the concentration of solute remaining in solution equilibrium (mg dm3), Cs the saturation concentration of solute (mg dm3), q the amount of solute adsorbed per unit weigh of adsorbent (mg g1), qm the amount of solute adsorbed per unit weigh of biosorbent in forming a complete monolayer on the surface (mg g1) and KB is the constant expressive of energy of intraction with the surface. The equation can be written in the linearized form:
Ce 1 KB 1 Ce þ ¼ ðCs Ce Þq Cs KB qm KB qm
1677
Table 1 Characteristics of KOH treated pine cone powder. Characteristics
Total acid groups (mmol g1) Carboxylic group (mmol g1) Phenolic group (mmol g1) Lactone group (mmol g1) Basic groups (mmol g1) pHPZC Surface negative Charge (mmol g1) Bulk density (g cm3) Iodine number (mg g1)
Values KOH treated
Virgin PCP
2.98 0.51 0.65 1.82 1.02 2.56 2.98 0.41 16.7
3.20 0.80 1.07 1.33 4.25 7.49 3.82 0.50 15.5
Functional groups C]O COOH eOH CeH CeC C-N
(1682.1 cm1) (1647.08 cm1) (3418.47 cm1) (2925.90 cm1) (1058.81 cm1) (559.32 cm1)
(17)
A plot of Ce/(Cs Ce)q against (Ce/Cs) should give a straight line and from the slope and intercept the values of KB and qm can be calculated. 2.2.6.5. Competitive Langmuir model (Yang, 1987). The competitive Langmuir model for two competing ions is applied in other to express the relationship between the quantity of the first component adsorbed and the concentration of the second component. The equation is written as
q1 ¼
qm K1 Ce1 1 þ K1 Ce1 þ K2 Ce2
(18)
q2 ¼
qm K1 Ce2 1 þ K1 Ce1 þ K2 Ce2
(19)
where K1 and K2 are the individual Langmuir constants of the first and second metal ions, and qm1 and qm2 are the maximum amounts of the first and second heavy metal ions. 3. Result and discussion
copper(II) and lead(II) in separate solutions were set to pH 2e6, and results presented in Fig. 1. Biosorption capacity has been shown to be affected by equilibrium pH, although it is not easy to control the equilibrium pH. The equilibrium pH is influenced by initial pH of the solution therefore the effect of initial pH on the removal of copper(II) and lead(II) was employed to discuss the effect of pH. The biosorption capacities for both copper(II) and lead(II) were low at solution pH 2 (copper(II) 5.34 mg g1, lead(II) 5.39 mg g1) and copper(II) biosorption was lower than lead(II) biosorption. As the solution pH increases, the amounts of copper(II) and lead(II) biosorbed from solution increased. This may be due to (i) reduced Hþ competition for biosorption sites, (ii) increased net negative charges on the biosorbent surface as solution pH rises above the pHPZC (pHPZC is 2,56) for KOH treated pine cone powder and (iii) that the dominant species of copper(II) and lead(II) between the pH range of 3e5 are Cu2þ, Cu(OH)þ, Pb2þ and Pb(OH)þ (Larous et al., 2005; Elliot and Huang, 1981; Asmal et al., 1998). Copper(II) biosorption was less than that of lead(II) at each initial solution pH, and both copper(II) and lead(II) biosorption increased as initial solution pH increased up to pH 5.0 after which the amount of metal ions biosorbed reduced. At pH above 2.56, the surface of the biosorbent
3.1. Properties of KOH treated pine cone powder The surface properties of virgin and KOH modified pine cone powder are shown in Table 1 below. Table 1 reveals that KOH washing changed the surface properties to a great extent as can be observed from Table 1. The total negative charge on the biosorbent and the iodine number was increased, while the pHPZC and bulk densities decreased. An increase in surface charge indicates that more biosorption sites were created by KOH washing. This increased amount of sites may be due to the increase in internal surface area as observed by the higher iodine number. A reduction in the bulk density observed after KOH washing shows that some plant components have been leached out of the materials creating pore spaces that lead to increased internal surface. Finally a lower pHPZC after KOH washing indicates that negatively charged sites dominates over positively charged sites even at low pH and that metal biosorption may be effective at pH above 2.56. 3.2. Effect of solution pH Variations in the amount of copper(II) and lead(II) biosorbed were noted in the series of contact time studies, when the pH of the
Fig. 1. Effect of solution pH on copper(II) and lead(II) biosorption on to KOH treated pine cone powder. Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 70 mg dm3; Temp.: 291 K.
1678
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
acquires negative charge and enhances metal biosorption. Therefore further experiments were performed at solution pH 5.0. The values of change in Hþ ion concentration and biosorption capacities at different time periods when 0.4 g of the biosorbent was contacted with 50 mg dm3 of copper(II) or lead(II) ion solution is shown graphically in Fig. 2. Fig. 2 shows that after initial contact, the final solution pH’s were all higher than the initial solution pH (pH 5.0). The change in Hþ ion concentration at a particular time is measured by the difference between the final and initial Hþ ion concentration. These values were negative and the difference increased with time up till 20 min of contact. Results from the blank test revealed that adding the biosorbent alone to deionized water at pH 5.0 led to a slight increase in solution pH. The reason for this can be attributed to the biosorbents ability to retain Hþ on its surface at these pH ranges. Blázquez et al. (2009) observed that between pH 6 and 8, the biosorption of chromium(III) onto olive stone lead to a slight increase in solution pH and attributed this increase to the ability of olive stone to the retention of Hþ on its surface along with chromium(III). Fig. 2 shows that as the metal ion capacity increases with time, the solution pH increased slightly and the change in Hþ concentration increased with time as well. The shape of the biosorption capacity profile is similar and opposite to that of the change in Hþ ion concentration. It was also observed that the change in Hþ ion concentration for lead(II) biosorption was slight higher than for copper(II) biosorption. Han et al. (2006) observed an increase in equilibrium pH with biosorption capacity for chromium(III) on to a microalgal isolate, Chlorella miniata. Mathematical equations were then drawn to show the relationship between the equilibrium pH, time and equilibrium capacity for the contact of 0.4 g of biosorbent with 70 mg dm3 of copper(II) and lead(II) at pH 5.0 at a time interval of 0e20 min:
Lead(II) biosorption
pHequ ¼
t 0:1351t þ 0:0596
(22)
pHequ ¼
qe 0:1036qe þ 0:2386
(23)
These trends suggest that ion-exchange mechanism may be responsible for metal biosorption. 3.3. Effect of temperature Fig. 3a and b shows the effect of temperature on percentage copper(II) and lead(II) uptake rate at different temperatures. It can be observed that the percentage copper(II) and lead(II) uptake increased with contact time and with temperature, and at some point in time reaches an almost constant value. At this point the amounts of copper(II) and lead(II) being removed from aqueous solution onto the solids are in a state of dynamic equilibrium with the amounts of copper(II) and lead(II) desorbed from the KOH treated pine cone powder surface. For the range of contact time under which the experiments were conducted, greater percentage of copper(II) and lead(II) was removed from solution at higher temperatures than at lower
Copper(II) biosorption
pHequ ¼
t 0:1367t þ 0:0711
(20)
pHequ ¼
qe 0:1076qe þ 0:2219
(21)
Fig. 2. Relationship between change in hydrogen ion concentration and metal ion capacities. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 70 mg dm3; Temp.: 291 K.
Fig. 3. Effect of biosorption temperature on percentage (a) copper(II) and (b) lead(II) removal by KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
temperatures. Lead(II) was removed at higher percentage than copper(II) at a particular temperature (See Fig. 3a and b). For a contact time of 15 min, percentage copper(II) removal were 49.86, 51.63, 54.15, 56.64, 59.05, 61.34, and 63.38% and percentage lead(II) removal were 76.52, 77.91, 79.85, 81.76, 83.66, 85.20 and 86.77% as temperature increased from 291 to 347 K. The biosorption rate for the first 1 min was found to be 8.67, 9.96, 11.42, 12.65, 14.24, 15.51, and 16.55 mg min1 for copper(II) biosorption and 15.69, 16.83, 20.09, 21.43, 22.72, and 23.82 mg min1 for lead(II) biosorption as temperature increases from 291 to 347 K. The biosorption reaction at all temperature were found to be extremely rapid for the first 5 min having values between 45.40 and 62.06% for copper(II) and 71.77 and 85.80% for lead(II) as temperature is increased from 291 to 347 K. After this stage, the rate of removal decreased to an almost constant value with time. These observations at reaction temperatures applied revealed that temperature has no effect on equilibrium time. 3.3.1. Pseudo-first and modified pseudo-first order kinetics Pseudo-first order model parameters for the effect of biosorption temperature on the biosorption of copper(II) and lead(II) onto KOH treated pine cone powder are shown in Table 2a and b. The values for equilibrium biosorption capacity as predicted by the pseudo-first order kinetics decreased with increasing temperature while the experimental values increased with reaction temperature. The values were not close to the experimental values for both metals at all temperatures. The pseudo-first order rate constant, k1, increased with temperature for both metals at all temperatures. The values for k1 for lead(II) biosorption were higher than those of copper(II) biosorption. The plots in Fig. 4a and b show that the pattern for the uptake of copper(II) and lead(II) as described by the pseudo-first order model are similar at all temperatures. Although the correlation coefficient, r2, values are relatively high, it will be noticed that there is a deviation from the straight line after 5 min of biosorption in all cases. This deviation has been attributed to the slow biosorption which occurs in the biosorbent pores preceding the very fast initial uptake of copper(II) or lead(II) ions on to the surface of the biosorbent (Ho and McKay, 1999). This slow process tends to continue with smaller change in equilibrium biosorption. The fact that the trends in biosorption capacities are opposite to that observed experimentally, the pseudo-first order predicted capacities were not close to the experimental data and the observed deviation from the straight line at 5 min of contact, suggest that the pseudo-first order kinetics does not sufficiently describe the whole range of whole range of kinetic data.
1679
To eliminate this error, a modified form of the pseudo-first order model was proposed (Yang and Al-Duri, 2005; Lagergren, 1898; Ho, 2004). The modified Pseudo-first order model parameters for the effect of biosorption temperature on the biosorption of copper(II) and lead(II) onto KOH modified pine cone powder are shown in Table 3a and b and Fig. 5a and b. It will be observed that the deviations from the experimental data at 5 min were minimized than in the pseudo-first order model plots. The values for K1 for lead (II) were also higher than for copper(II) and all increased with increasing temperature. The values of equilibrium capacity of copper(II) was found to decrease from 13.88 (291 K) to 7.09 mg g1 (347 K) and lead(II) decreased from 17.94 (291 K) to 6.90 mg g1 (347 K). These observations indicate that although the modified pseudo-first order equation could reduce the deviation of the experimental points from the straight line, the modified pseudofirst order model could not accurately describe the whole range of experimental data. Its predictions of the biosorption capacities are opposite to the observed experimentally. 3.3.2. Pseudo-second order kinetics Analysis of the experimental data with the pseudo-second order kinetic model shows good agreement of the sets of data, which is reflected in the extremely high correlation coefficient of determination, obtained (Table 2a and b and Fig. 6a and b). Thus on increasing the temperature from 291 to 347 K, the biosorption equilibrium capacity, qe, is increased from 15.73 to 19.22 mg g1 for copper(II) and 23.74e26.27 mg g1 for lead(II). The initial biosorption rate, h, and the pseudo-second order rate constant, k2, were also found to increase with temperature variation from 291 to 347 K. The values of initial biosorption rate, h, for both metals were much higher than the pseudo-second order rate constant, k2 as predicted by the pseudo-second order kinetics. The initial biosorption rate, h, and pseudo-second order rate constants, k2, for the lead(II) biosorption were much higher than for copper(II) biosorption. This indicates that rates of lead(II) removal is much faster than copper(II) removal as seen from the percentage removal plots (Fig. 3a and b). These trends in the initial biosorption rate, h, pseudo-second order rate constant, k2, and equilibrium biosorption, qe, with temperature suggests that a chemisorption reaction or an activated biosorption involving valency forces through sharing or exchange of electrons between biosorbent and metal ion occurs. Similar results of the biosorption of copper(II) and lead(II) onto other adsorbents have also been reported in literatures, for example lead (II) on to palm kernel fiber (Ho and Ofomaja, 2005) and copper(II) on to seeds of Capsicum annuum (Özcan et al., 2005).
Table 2a Parameters of kinetic models for Copper(II) biosorption on 0.15 mol dm3 KOH treated pine cone powder at different temperatures. Model
Parameters
291 K
297 K
307 K
317 K
327 K
337 K
347 K
Pseudo-first
qe (Exp) qe1 (Cal) k1 r2 qe K1 r2 qe (Exp) qe2 (Cal) h k2 r2 ki c r2
14.96 7.56 0.3132 0.983 13.88 0.2753 0.997 14.96 15.73 20.32 0.0821 0.994 0.585 12.71 0.982 0.5341
15.49 6.79 0.3224 0.980 13.16 0.2884 0.994 15.49 16.13 26.04 0.1001 0.996 0.493 13.60 0.981 0.4636
16.24 5.86 0.3276 0.974 12.00 0.2995 0.990 16.24 16.75 35.94 0.1281 0.998 0.396 14.72 0.981 0.3701
16.99 5.31 0.3385 0.972 11.30 0.3139 0.987 16.99 17.42 46.22 0.1523 0.993 0.339 15.69 0.980 0.3074
17.32 4.16 0.3408 0.965 9.43 0.3207 0.979 17.32 18.03 67.65 0.2081 0.998 0.253 16.74 0.980 0.2089
18.0 3.53 0.3501 0.964 8.22 0.3355 0.976 18.0 18.65 92.03 0.2646 0.994 0.201 17.63 0.980 0.1462
19.02 2.96 0.3455 0.957 7.09 0.3333 0.968 19.02 19.22 118.99 0.3221 0.992 0.166 18.37 0.979 0.1097
Modified pseudo-first
Pseudo-second
Intraparticle Diffusion
c2 1
qe, qe1 and qe2 ¼ mg g
; k1 ¼ min1; k2 ¼ g mg1 min1; h ¼ mg g1 min1; ki ¼ mg g1 min0.5; ks ¼ min1; Di ¼ cm2 s1
1680
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
Table 2b Parameters of kinetic models for lead(II) biosorption on pine cone powder treated with 0.15 mol dm3 KOH at different temperatures. Model
Parameters
291 K
297 K
307 K
317 K
327 K
337 K
347 K
Pseudo-first
qe (Exp) qe (Cal) k1 r2 qe K1 r2 qe (Exp) qe (Cal) h k2 r2 ki C r2
22.95 8.91 0.3293 0.977 17.49 0.2995 0.992 27.95 23.74 46.25 0.0822 0.995 0.613 20.60 0.981 0.5769
23.37 8.00 0.3339 0.974 16.64 0.3075 0.989 23.37 24.04 56.14 0.0971 0.998 0.526 21.55 0.982 0.4873
23.96 6.50 0.3385 0.968 14.67 0.3158 0.983 23.96 24.46 77.53 0.1296 0.994 0.403 22.41 0.980 0.2295
24.53 5.37 0.3432 0.964 12.24 0.3264 0.977 24.53 24.92 103.72 0.1670 0.996 0.317 23.31 0.980 0.1803
25.10 4.40 0.3501 0.952 10.49 0.3351 0.973 25.10 25.41 136.65 0.2716 0.998 0.252 24.13 0.979 0.1795
25.56 3.45 0.3547 0.959 8.39 0.3440 0.968 25.56 25.79 191.63 0.3701 0.992 0.188 24.84 0.979 0.1121
26.09 2.77 0.3593 0.957 6.90 0.3513 0.965 26.09 26.27 255.44 0.3701 0.997 0.146 25.53 0.979 0.0735
Modified pseudo-first
Pseudo-second
Intraparticle diffusion
c2
qe, qe1 and qe2 ¼ mg g1; k1 ¼ min1; k2 ¼ g mg1 min1; h ¼ mg g1 min1; ki ¼ mg g1 min0.5; ks ¼ min1; Di ¼ cm2 s1
According to Ho et al. (2000), if the Copper(II) and lead(II) uptake is chemically rate controlled, the pseudo-second order constants will be independent of particle diameter and flow rate and will depend on temperature of the metal ion in solution. Increase in temperature will also led to increase in the amounts of metal ions biosorbed at equilibrium for a chemisorption-controlled reaction. The logarithmic plots of initial biosorption rate, h, Pseudosecond order rate constant, k2, and qe versus temperature were made and the plots where found to give straight lines whose correlation coefficients, r2, are extremely high, indicating that copper(II) and lead(II) uptake may be chemically rate controlled. Mathematical expressions of the forms:
where k2 is the pseudo-second order rate constant of biosorption (g mg1 min1), k0 the temperature-independent factor (g mg1 min1), Ea the activation energy of sorption (kJ mol1), R the gas constant (8.314 J mol1 K1) and T is the solution temperature (K). Therefore, the relationship between k2 and T can be represented in an Arrhenius form as represented in Eq. (30):
For Copper(II)
qe ¼ 0:0239T 1:1435
(24)
h ¼ 4:2954 1024 T 10:0180
(25)
k ¼ 7:4645 1021 T 7:7308
(26)
For Lead(II)
qe ¼ 0:9270T 0:5716
(27)
h ¼ 7:7268 1025 T 9:6489
(28)
k ¼ 8:9950 1023 T 8:5057
(29)
The values of rate constant, k2, were found to increase from 0.0821 to 0.3221 g mg1 min1 for copper(II), and from 0.0822 to 0.3701 g mg1 min1 for lead(II), for an increase in the solution temperature of 291e347 K. There is a linear relationship between the pseudo-second order rate constant and temperature with coefficient of determination greater than 0.997 for both metal ions. The biosorption rate constant is usually expressed as a function of solution temperature by the relationship:
lnk2 ¼ lnk0
Ea RT
(30)
Fig. 4. Pseudo-first order kinetics for (a) copper(II) and (b) lead(II) biosorption on to KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
1681
Table 3 Activation energy parameters for copper(II) and lead(II) biosorption on to KOH treated pine cone powder. Sample
Ea (kJ mol1)
Ko (g mg1 min1)
DS* (kJ mol1)
DH* (kJ mol1)
DG*
Copper(II) Lead(II)
20.36 22.40
3.71 103 8.40 102
198.39 197.57
17.73 23.77
73.08 68.45
(kJ mol1)
Copper(II):
k2 ¼ 3:71 103
20:36 103 8:314T
! (31)
Lead(II):
k2 ¼ 8:40 10
2
22:40 103 8:314T
! (32)
From these equations, the rate constant for biosorption, k0, is 3.71 103 g mg1 min1 for copper(II) and 8.40 102 g mg1 min1 for lead(II) and the activation energy for sorption, Ea, 20.36 kJ mol1
Fig. 6. Pseudo-second order kinetics for (a) copper(II) and (b) lead(II) biosorption on to KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
for copper(II) and 22.40 kJ mol1 for lead(II). The value of activation energy for copper(II) is lower than that of lead(II) and both are higher than 20 kJ mol1. The higher activation energy for lead(II) indicates that stronger bonds are formed between lead(II) and KOH treated pine cone powder than copper(II). The change in enthalpy (DH*) and entropy (DS*) of activation for the copper(II) and lead(II) biosorption onto KOH modified pine cone powder were calculated by the Eyring equation (Atun and Sismanoglu, 1996) below:
DS* DH* k k þ ln 2 ¼ ln h R RT T
(33)
Where k2, is the pseudo-second order rate constant, T is the Kelvin temperature, k and h are the Boltzmann’s and Planck’s constants respectively. The change in entropy of activation (DS*) and enthalpy of activation (DH*), for this step have been evaluated from the intercept and slope of each linear plot. The free energies of activation (DG*) for the KOH treated pine cone powder were computed from the equation:
DG* ¼ DH* T DS* Fig. 5. Modified Pseudo-first order kinetics for (a) copper(II) and (b) lead(II) biosorption on to KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
(34)
The corresponding values for change in enthalpy of activation (DH*), enthalpy of activation (DS*) and free energy of activation (DG*) has been calculated and the values for copper(II) and lead(II)
1682
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
on to KOH treated pine cone powder given in Table 3. The entropy of activation (DS*), for copper(II) and lead(II) were found to be smaller than zero. The enthalpy of activation (DH*) obtained from the Eyring equation is lower than TDS*, for both metals, indicating that the reorientation step is mostly entropy controlled at the activation state. The contribution of the reorientation step to activation tends to be higher for lead(II) biosorption than copper(II) as seen from the higher value of enthalpy (DH*), compared with TDS*. The free energy of activated (DG*), was found to be lower for lead(II) indicating that activation is more spontaneous lead(II) than copper (II).
the highest values for correlation coefficient, r2, indicating that it best describes the experimental data than the other isotherm models applied. The Langmuir capacities from this study were compared with those obtained by other biosorbents and were found to be substantially higher (Table 5). The Langmuir constant, Ka, known as the heat of biosorption were 0.0542 dm3 mg1 for copper(II) and 0.1649 dm3 mg1 for lead(II). The bonds formed between lead(II) ions and the functional groups on the biosorbent surface are stronger than those formed between these groups and copper(II) ions as seen from the values of Ka. The free energy, DGo, at 291 K was calculated using Eq. (35)
3.4. Equilibrium isotherm
DGo ¼ RTlnKa :
Isotherm plots were made for the experimental data of the amount of copper(II) and lead(II) biosorbed per unit mass (mg g1) versus equilibrium solution concentration (mg dm3) for the biosorption of copper(II) and lead(II) from solutions of concentration raging from 60 to 120 mg dm3 onto KOH treated pine cone powder at 291 K (Fig. 7). The Freundlich isotherm was then applied to analyze the equilibrium data. The Freundlich constants were calculated along with the coefficient of determination, r2, in Table 4. The results revealed that the values of r2 were fairly high for both copper(II) and lead(II) biosorption. It can also be observed that the constants, n, and KF were found to be higher for lead(II) than copper(II). Freundlich constants KF indicate the biosorption capacity of the biosorbent. The value of KF at equilibrium for copper(II) is 3.733 dm3 g1 and lead(II) is 7.852 dm3 g1. The Freundlich constant n is a measure of the deviation from linearity of the biosorption curve or the biosorption affinity of the biosorbent for the sorbate. The numerical values of n for copper(II) is 2.538 and for lead(II) biosorption 2.558. The values for n were greater than unity, indicating that copper(II) and lead(II) ions are favorably biosorbed by KOH treated pine cone powder. It is also observed that the value for n for lead(II) biosorption was higher than for copper(II) biosorption indicating that lead(II) biosorption is more favorable the copper(II) biosorption. The Langmuir constants, qm and Ka were also calculated and shown in Table 4. The values show that the monolayer capacities of the KOH treated pine cone powder for copper(II) is 26.32 mg g1 and for lead(II) is 32.26 mg g1. The Langmuir isotherm also gave
Fig. 7. Isotherm plots for the biosorption of Copper(II) and lead(II) on to KOH treated Pine cone powder.
(35)
The values of free energy is given as 19.70 kJ mol1 for copper (II) biosorption and 25.26 kJ mol1 for lead(II) biosorption at 291 K. The result indicates that at 291 K, biosorption of both metals are spontaneous but lead(II) biosorption is more spontaneous than copper(II) biosorption. The DubinineRadushkevich (DeR) isotherm parameters are shown in Table 4. The values of the mean free energy, E, for copper (II) was found to be 10.33 kJ mol1 and for lead(II) 11.72 kJ mol1. The parameter E, provides information about the biosorption mechanism as chemical, ion-exchange or physical adsorption. Özcan et al. (2005) and Benhammou et al. (2005) have successfully used this method to determine the copper ions biosorption mechanism by different adsorbents. According to Onyango et al. (2004), mean free energy values greater than 8 kJ mol1 corresponded to biosorption processes controlled by ion-exchange mechanism. The values obtained in this study were greater than 8 kJ mol1, indicating ion-exchange mechanism. The equilibrium isotherm data were finally analyzed using the BET isotherm model. The results revealed that the correlation coefficient, r2, were relatively high (>0.960), the saturation capacity for lead(II) was higher than for copper(II) and the energy of interaction with the surface expressed by the constant, KB, where higher for lead(II) interaction than for copper(II) as predicted by the Langmuir isotherm. The lower values of r2 may indicate that the biosorption of lead(II) and copper(II) onto the KOH treated pine cone powder may not involve a multilayer arrangement of the metal ions on the biosorbent surface. Competition of copper(II) and lead(II) in a binary solution for biosorption sites on KOH treated pine cone powder was determined by contacting equal concentrations of copper(II) and lead(II) in the same solutions and determining their uptake by KOH treated pine cone powder. The equilibrium data was analyzed with both the Langmuir and Competitive Langmuir isotherm models and the isotherm plots shown in Fig. 8a and b. The results as seen from the plot of amount biosorbed at equilibrium versus equilibrium concentration show that the Langmuir isotherm better fitted the experimental data than the competitive Langmuir isotherm. It will also be seen that the competitive Langmuir isotherm gave closer fit to the experimental data for the biosorption of copper(II) in presence of lead(II) plots. This suggests that in the biosorption of both metals simultaneously, there is some interaction of the biosorbed cations at the biosorption sites. Copper (II) biosorption is more affected by the presence of lead(II) than lead (II) is affected by copper(II). The Langmuir monolayer capacity of lead(II) in solution reduced from 32.26 mg g1 with only lead(II) in solution to 30.12 mg g1 in the presence of copper(II). The bonding energy for lead(II) decreased from 0.1649 dm3 mg1 in solution to 0.0849 dm3 mg1 in the presence of copper(II). The monolayer capacity for copper(II) was 26.32 mg g1 and in the presence of lead (II) it became 22.68 mg g1, while bonding energy for copper(II) was 0.0542 dm3 mg1 and the value decreased to 0.0210 dm3 mg1
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
1683
Table 4 Isotherm constants for the adsorption of copper(II) and lead(II) onto KOH treated Pine cone. Metal
Freundlich n
KF 3
1
(dm g Copper(II) Lead(II)
2.358 2.558
Langmuir-1 r2
)
qm (mg g
3.733 7.852
0.994 0.994
BET r2
Ka 1
26.32 32.26
)
3
(dm mg 0.0542 0.1649
1
DubinineRadushkevich (DeR)
qm 1
)
(mg g
0.943 0.935
27.78 34.48
in the presence of lead(II). The capacity and binding energy was strongly affected in the Cu(II)-Pb(II) than the Pb(II)-Cu(II) biosorption. Desorption studies are important in elucidating the mechanism of a biosorption process and its applicability in industrial practice. This characteristic can be evaluated by extracting biosorbed metal ions by different solvents. If the biosorbed metal ion can be desorbed by water, it is believed that the attachment of the metal ion onto the biosorbent is by weak bonds (physical bonds). If a solution of strong acids such as HNO3 or HCl can desorb the metal ion, it is believed that the attachment of metal is by ion-exchange. If a solution of CH3COOH, can desorb the metal, it is believed that the biosorption of metal is by chemisorption. The results of desorption studies are shown in Fig. 9. The percentages of copper(II) and lead(II) desorbed from 0.4 g of the used KOH treated pine cone powder are compared for all four solvents used. From the results presented in Fig. 9, it can be seen that H2O had the least value of percentage desorption as compared with other solvents and water removed more copper(II) than lead (II). Water can desorb copper(II) and lead(II) ions that are weakly bonded to the KOH treated pine cone powder surface. Therefore, only a small fraction of the copper(II) and lead(II) ions held to the biosorbent are attached by weak bonds on biosorption sites. The inorganic acids, HCl and HNO3 were found to desorb quite a high percentage of copper(II) and lead(II) ions from the biosorbent. The desorption of copper(II) and lead(II) ions using HNO3 removed more copper(II) and lead(II) ions from the biosorbent than with HCl. It is believed that the nitrate salts of copper(II) and lead (II) are more soluble than the chloride salts, this may account for the lower desorption percentage observed in the HCl desorption study. High desorption percentages produced by strong acids indicates that the biosorption of copper(II) and lead(II) ions on to
r2
KB )
(kJ mol 0.0466 0.1388
1
qD
BD 1
)
(mmol g 0.974 0.989
)
1.58 104 6.53 105
r2
E 2
(mol kJ
2
)
1.69 109 3.64 109
(kJ mol 10.33 11.72
1
) 0.853 0.806
KOH treated pine cone powder is by ion-exchange mechanism. This is confirmed by repeating the desorption test with increasing concentrations of the HNO3 solution. Fig. 10 shows the different desorption percentages with increasing concentrations of the HNO3 solution. It is observed that the desorption percentage increased with increasing concentrations of HNO3 signifying that increase in hydrogen ion concentration lead to increase in the exchange of hydrogen ion for copper(II) and lead(II) ions. Desorption using CH3COOH solution was also found to remove only a small amount of copper(II) and lead(II) ion from the biosorbent. The percentage copper(II) and lead(II) desorbed was higher for HCl than for CH3COOH (Fig. 9). Therefore ion-exchange
Table 5 Comparison of best isotherm model and monlayer capacities of copper(II) and lead (II) biosorption. Metal ion
Biosorbent Monolayer capacity (mg g1)
Copper(II) 107.52 21.25 0.18 14.90 19.23 26.32 Lead(II)
27.10 196.07 16.14 52.38 29.24 32.26
Reference
Black gram bran Peanut hull Wheat straw NaOH-treated Rubber leaves powder Pine cone biomass
Nadeem et al. (2009) Zhu et al. (2009) Dang et al. (2009) Ngah and Hanafiah (2008) Nuhoglu and Oguz (2003) KOH treated pine cone This Study powder Mushrooms Vimala and Das (2009) Cotton waste Riaz et al. (2009) Seed of Strychnos Jayaram et al. (2009) potatorum L. NaOH-treated sawdust Meena et al. (2007) (Acacia arabica) Fenton oxidized pine Argun et al. (2008) cone biomass KOH treated pine cone This Study powder
Fig. 8. Cation competition for (a) Pb-Cu and (b) Cu-Pb competition on to KOH treated Pine cone powder.
1684
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
reorientation to the activation step was higher for lead(II) than copper(II). Biosorption Equilibrium studies revealed that KOH treated pine cone powder had a higher capacity for lead(II) than copper(II) and a monolayer surface coverage was formed over the biosorbent surface. There was only a small interaction between metal ions when simultaneously biosorbed and cation competition was higher for the Cu-Pb system than for the Pb-Cu system. Desorption studies and DubinineRadushkevich, energy parameter, E, also supports ion-exchange mechanism. References
Fig. 9. Desorption efficiencies of copper(II) and lead(II) from KOH treated pine cone powder by various solvents. Temp. ¼ 291 K, time ¼ 1 h, Co (desorbing solvent) ¼ 0.01 mol dm3, m ¼ 1.0/100 ml.
Fig. 10. Effect of HNO3 concentration on the desorption efficiencies of copper(II) and lead(II) from KOH treated pine cone powder. Temp. ¼ 291 K, time ¼ 1 h, dose ¼ 1.0/ 100 ml.
mechanism was more involved in the bonding of copper(II) and lead(II) ions on to KOH treated pine cone powder than chemisorption mechanism. This confirms the applicability of pseudosecond order model to the biosorption process. 4. Conclusion Biosorption of copper(II) and lead(II) ions on to pine cone powder treated with 500 ml 0.15 mol dm3 KOH solution has been studied. Biosorption capacity of the two metal ions was shown to be dependent on initial and final solution pH. The trend in the change in Hþ concentration with biosorption capacity and time where similar and indicating that Hþ biosorption occurred in the pH range studied and ion-exchange mechanism predominates. Both the pseudo-first and modified pseudo-first order kinetic models were applied to analyze the biosorption kinetics but provided poor fitting to the experimental data. The pseudo-second order model on the other hand gave better fit and was able to describe the experimental data sufficiently suggesting that ionexchange is the dominating mechanism. Activation energies where higher for lead(II) than for copper(II), and the contribution of
Ahmedna, M., Johns, M.M., Clarke, S.J., Marshall, W.E., Rao, R.M., 1997. Potential of agricultural by-product based carbons for use in raw sugar decolorization. Journal of the Science of Food and Agriculture 75, 117e124. Argun, M.E., Sukru, D., Karatas, M., Gürü, M., 2008. Activation of pine cone using Fenton oxidation for Cd(II) and Pb(II) removal. Bioresource Technology 99, 8691e8698. Asmal, M., Khan, A.H., Ahmad, S., Ahmad, A., 1998. Role of sawdust in the removal of copper(II) from industrial wastes. Water Research 32, 3085e3091. ASTM, standard test method for determination of iodine number of activated carbon, D 4607-86, pp. 384e387. Atun, G., Sismanoglu, T., 1996. Adsorption of 4,40 -isopropylidenediphenol and diphenylolpropane 4, 40 dioxyaceticacid from aqueous solution on kaolinite. Journal of Environmental Science and Health A31 (8), 2055e2069. Blázquez, G., Hernáinz1, F., Calero, M., Martín-Lara, M.A., Tenorio, G., 2009. The effect of pH on the biosorption of Cr (III) and Cr (VI) with olive stone. Chemical engineering journal 148, 473e479. Boehm, H.P., 1994. Some aspects of the surface chemistry of carbon black and other carbons. Carbon 32, 759e769. Brunauer, S., Emmett, P.H., Teller, E., 1938. Adsorption of gases in multimolecular layers. Journal of American Chemical Society 60, 309e319. Dang, V.B.H., Doan, H.D., Dang-Vu, T., Lohi, A., 2009. Equilibrium and kinetics of biosorption of cadmium(II) and copper(II) ions by wheat straw. Bioresource Technology 100 (1), 211e219. Dubinin, M.M., 1960. The potential theory of adsorption of gases and vapours for adsorbent with energetically nonuniform surface. Chemical Review 60, 235e266. Dubinin, M.M., 1965. Modern state of the theory of volume filling of micropore adsorbents during adsorption of gases and steam on carbon adsorbents. Zhurnal Fizcheskoi Khimii 39, 1305e1317. Elliot, H.A., Huang, C.P., 1981. Adsorption characteristics of some copper(II) complexes on aluminosilicates. Water Research 15, 849e855. } Freundlich, H.M.F., 1906. Uber die adsorption in lösungen. Zeitschrift für Physikalische. Chemie (Leipzig) 57A, 385e470. Gündogan, R., Acemioglu, B., Alma, M.H., 2004. Copper (II) adsorption from aqueous solution by herbaceous peat. Journal of Colloid and Interface Science 269, 303e309. Han, R., Li, H., Li, Y., Zhang, J., Xiao, H., Shi, J., 2006. Biosorption of copper and lead ions by waste beer yeast. Journal of Hazardous Materials 137, 1569e1576. Hasamy, S.M., Chaudhary, M.H., 1996. Sorption potential of hare river sand for the removal of antimony from acidic aqueous solution. Applied Radiation and Isotopes 47, 467e471. Ho, Y.S., McKay, G., 1999. Pseudo-second order model for sorption processes. Proc. Biochem 34, 451e456. Ho, Y.S., Ng, J.C.Y., Mckay, G., 2000. Kinetics of pollutant sorption by biosorbents: review, Sep. Purif. Methods 29, 186e232. Ho, Y.S., 2004. Citation review of Lagergren kinetic rate equation on adsorption reactions. Scientometrics 59 (1), 171e177. Ho, Y.S., Ofomaja, A.E., 2006. Biosorption thermodynamics of cadmium on coconut copra meal as biosorbent. Biochemical Engineering Journal 30, 117e123. Ho, Y.S., Ofomaja, A.E., 2005. Kinetics and thermodynamics of lead ion sorption on palm kernel fiber from aqueous solution. Process Biochemistry 40, 3455e3461. Jayaram, K., Murthy, I.Y.L.N., Lalhruaitluanga, H., Prasad, M.N.V., 2009. Biosorption of lead from aqueous solution by seed powder of Strychnos potatorum L. Colloids and Surfaces B: Biointerfaces 71, 248e254. Lagergren, S., 1898. Kungliga Svenska Vetenskapsakademiens. Handlingar, Band 24 (4), 1e39. Langmuir, I., 1916. The constitution and fundamental properties of solids and liquids. Journal of American Chemical Society 38, 2221e2295. Larous, S., Menai, A.H., Lehocine, M.B., 2005. Experimental study of the removal of copper from aqueous solutions by adsorption using sawdust. Desalination 185, 483e490. Mall, I.D., Srivastava, V.C., Agarwal, N.K., 2006. Removal of Orange-G and methyl violet dyes by adsorption onto bagasse fly ash kinetic study and equilibrium isotherm analyses. Dyes Pigments 69, 210e223. Malkoc, E., 2006. Ni(II) removal from aqueous solutions using cone biomass of Thuja orientalis. Journal of Hazardous Materials B137, 899e908. Marshall, W.E., Wartelle, L.H., Boler, D.E., Johns, M.M., Toles, C.A., 1999. Enhanced metal adsorption by soybean hulls modified with citric acid. Bioresource Technology 69, 263e268.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685 Meena, A.K., Kadirvelu, K., Mishra, G.K., Rajagopal, C., Nagar, P.N., 2007. Adsorptive removal of heavy metals from aqueous solution by treated sawdust (Acacia arabica). Journal of Hazardous Materials 150, 604e611. Min, S.H., Han, J.S., Shin, E.W., Park, J.K., 2004. Improvement of cadmium ion removal by base treatment of juniper fiber. Water Research 38, 1289e1295. Nadeem, R., Hanif, M.A., Mahmood, A., Jamil, M.S., Ashraf, M., 2009. Biosorption of Cu(II) ions from aqueous effluents by blackgram bran (BGB). Journal of Hazardous Materials 168, 1622e1625. Nagata, K., Salagami, H., Harada, H., Monoyama, M., Ishihama, A., Konno, K., 1990. Inhibition of influenza virus infection by pine cone antitumor substances. Antiviral Research 13, 11e21. Ngah, W.S.W., Hanafiah, M.A.K.M., 2008. Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review. Bioresource Technology 99, 3935e3948. Nuhoglu, Y., Oguz, E., 2003. Removal of copper(II) from aqueous solutions by biosorption on the cone biomass of Thuja orientalis. Process Biochemistry 38, 1627e1638. Ofomaja, A.E., Naidoo, E.B., Modise, S.J. 2009. Removal of copper(II) from aqueous solution by pine and base modified pine cone powder as biosorbent; 168: 909e917. Özcan, A., Özcan, A.S., Tunali, S., Akar, T., Kiran, I., 2005. Determination of the equilibrium, kinetic and thermodynamic parameters of adsorption of copper(II)
1685
ions onto seeds of Capsicum annuum. Journal of Hazardous Materials B124, 200e208. Panday, K.K., Gur, P., Singh, V.N., 1985. Copper (II) removal from aqueous solutions by fly ash. Water Research 19 (7), 869e873. Radushkevich, L.V., 1949. Potential theory of sorption and structure of carbon. Zhurnal Fizcheskoi Khimii 23, 1410e1420. Riaz, M., Nadeem, R., Hanif, M.A., Ansari, T.M., Rehman, K.U., 2009. Pb(II) biosorption from hazardous aqueous streams using Gossypium hirsutum (cotton) waste biomass. Journal of Hazardous Materials 161, 88e94. Ucun, H., Bayhan, Y.K., Kaya, Y., Cakici, A., Algur, O.F., 2002. Biosorption of chromium (VI) from aqueous solution by cone biomass of Pinus sylvestris. Bioresource Technology 85, 155e158. Ucun, H., Bayhan, Y.K., Kaya, Y., Cakici, A., Algur, O.F., 2003. Biosorption of lead (II) from aqueous solution by cone biomass of Pinus sylvestris. Desalination 154, 233e238. Vimala, R., Das, N., 2009. Biosorption of cadmium (II) and lead (II) from aqueous solutions using mushrooms: a comparative study. Journal of Hazardous Materials 168, 376e382. Yang, R.T., 1987. Gas Separation by Adsorption Processes. Butterworths, Boston, MA. Yang, X., Al-Duri, B., 2005. Kinetic modeling of liquid-phase adsorption of reactive dyes on activated carbon. Journal of Colloid and Interface Science 287, 25e34. Zhu, C.S., Wang, L.P., Chen, W.B., 2009. Removal of Cu(II) from aqueous solution by agricultural by-product: peanut hull.
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Biosorption of copper(II) and lead(II) onto potassium hydroxide treated pine cone powder A.E. Ofomaja*, E.B Naidoo, S.J. Modise Department of Chemistry, Vaal University of Technology, Vanderbiljpark, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 June 2009 Received in revised form 22 February 2010 Accepted 9 March 2010 Available online 15 May 2010
Pine cone powder surface was treated with potassium hydroxide and applied for copper(II) and lead(II) removal from solution. Isotherm experiments and desorption tests were conducted and kinetic analysis was performed with increasing temperatures. As solution pH increased, the biosorption capacity and the change in hydrogen ion concentration in solution increased. The change in hydrogen ion concentration for lead(II) biosorption was slightly higher than for copper(II) biosorption. The results revealed that ion-exchange is the main mechanism for biosorption for both metal ions. The pseudo-first order kinetic model was unable to describe the biosorption process throughout the effective biosorption period while the modified pseudo-first order kinetics gave a better fit but could not predict the experimentally observed equilibrium capacities. The pseudo-second order kinetics gave a better fit to the experimental data over the temperature range from 291 to 347 K and the equilibrium capacity increased from 15.73 to 19.22 mg g1 for copper(II) and from 23.74 to 26.27 for lead(II). Activation energy was higher for lead(II) (22.40 kJ mol1) than for copper(II) (20.36 kJ mol1). The free energy of activation was higher for lead(II) than for copper(II) and the values of DH* and DS* indicate that the contribution of reorientation to the activation stage is higher for lead(II) than copper(II). This implies that lead(II) biosorption is more spontaneous than copper(II) biosorption. Equilibrium studies showed that the Langmuir isotherm gave a better fit for the equilibrium data indicating monolayer coverage of the biosorbent surface. There was only a small interaction between metal ions when simultaneously biosorbed and cation competition was higher for the Cu-Pb system than for the Pb-Cu system. Desorption studies and the DubinineRadushkevich isotherm and energy parameter, E, also support the ion-exchange mechanism. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Ion-exchange KOH treatment Pine cone powder Equilibrium pH Pseudo-second order model Activation energy
1. Introduction Heavy metal pollution of surface water such as rivers and streams has been largely attributed to disposal of industrial effluents into receiving water bodies (Argun et al., 2008). These heavy metal pollutants are not biodegradable and their presence in surface water may led to bioaccumulation in living organisms, causing health problems in plants, animals and human beings. Intake of some heavy metals in humans has been known to cause serious harmful effects. For example, lead intake in humans causes disruption of biosynthesis of hemoglobin, rise in blood pressure, kidney damage, miscarriages and abortions, brain damage and diminished learning abilities in children (Argun et al., 2008). Copper intake leads to severe mucosal irritation, widespread
* Corresponding author. Tel.: þ27 768202689/þ27 738126830/þ234 80715034. E-mail addresses: [email protected], [email protected] (A.E. Ofomaja). 0301-4797/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2010.03.005
capillary damage, hepatic and renal damage, central nervous problems followed by depression, gastrointestinal irritation, and possible necrotic changes in the liver and kidney (Gündogan et al., 2004). Both copper and lead are widely used industrially. Copper is mainly used for pulp and paper board, wood and leather preserving, petroleum refining and for copper coatings and fittings. Lead on the other hand, is mainly used for insecticide, storage battery, and petrol additive and metal plating/finishing industries and so on. Therefore, efficient and cost effective separation techniques are needed to clean up industrial effluents from the processes before they are discharged into receiving water bodies. Several studies have shown the efficacy of adsorbents of biological origin to remove metal pollutants from aqueous solution (Ho and Ofomaja, 2006) and more recently chemically treated biomass (Ofomaja et al., 2009) have been applied for metal removal from aqueous solution. Min et al. (2004) showed that Sodium hydroxide treatment of lignocellulosic materials could cause swelling which
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
leads to an increase in internal surface area, decrease in the degree of polymerization, decrease in crystallinity, separation of structural linkages between lignin and carbohydrates and disruption of the lignin structure. Base solutions such as sodium hydroxide, potassium hydroxide or calcium hydroxide are also good reagent for saponification or the conversion of an ester group to carboxylate and alcohol functional groups (Min et al., 2004). The potential sources of copper in industrial effluents include metal cleaning and plating baths, pulp, paper board mills, wood pulp production, and the fertilizer industry, etc. In the wastewater of a copper wire mill, an average concentration of copper ions is about 800 mg dm3 (Panday et al., 1985). Lead is introduced into natural waters through various industrial activities such as those from the insecticide, storage battery, and metal plating/finishing industries, etc. In industrial wastewaters, Lead ion concentration is in the range of 200e500 mg dm3, these values are very high in relation to water quality standards, therefore copper and lead concentrations in wastewaters should be reduced (Ucun et al., 2003). Pine cone is an agricultural waste produced when pine tree seeds are removed from matured cones. Pine cone is composed of mainly a-Cellulose (18.8%), Holocellulose (46.5%), and lignin (37.4%) (Nagata et al., 1990). Large quantities of cones are released in pine plantations annually with little or no use. Pine cone powder as biosorbent has the advantage of achieving maximum metal removal at short contact time. For example Ucun et al. (2002) achieve equilibrium for chromium(IV) removal from aqueous solution in 20 min, Malkoc (2006) achieved equilibrium for nickel (II) in 3 min while Ucun et al. (2002) removed copper(II) from solution in 20 min. The use of chemical treatment to improve the biosorption capacity of pine cone powder is scanty in literature and much research has not been carried out in this area. This research therefore seeks to study (i) the application of potassium hydroxide (KOH) treated pine cone powder for the removal of copper(II) and lead(II) from aqueous solution, (ii) Analyze the biosorption kinetic data for the effect of temperature on copper(II) and lead(II) biosorption with the pseudo-first, modified pseudo-first and pseudo-second order kinetic models so as to determine the possible biosorption mechanism (iii) determine the activation energy, enthalpy and entropy of activation from the kinetic data, (iv) Determine the equilibrium isotherm characteristics of copper(II) and lead(II) biosorption using the Langmuir, Freundlich, BET and DubinineRadushkevich isotherm models, (v) To determine the effect of simultaneous biosorption of copper(II) and lead(II) from binary solution and to perform desorption studies. 2. Materials and methods 2.1. Materials Pine tree cones were obtained from a plantation in Sasolburg, Free State, South Africa. Pine tree cones were collected between August and September 2007. The cones were washed to remove impurities such as sand and leaves, the washed cones were then dried at 90 C for 48 h in an oven. The scales on the cones were then removed and blended in a food processing blender. The resultant powder was sieved and particles below 300 mm were collected and used for analysis. A weighed amount (50 g) of the powder obtained was contacted with 500 ml of potassium hydroxide solution of concentration 0.15 mol dm3 and the slurry stirred overnight. The powder was rinsed with distilled water. This procedure was repeated two more times to ensure removal of potassium hydroxide from the powder. The residue was then dried overnight at 90 C.
1675
The stock solution of copper(II) nitrate (Cu(NO3)2) and lead(II) nitrate (Pb(NO3)2) were prepared by dissolving accurately weighed amount of the salts in deionized water. The experimental solutions were prepared by diluting the stock solution with distilled water when necessary.
2.2. Methods The pH at point zero charge (pHPZC) of the pine cone powder was determined by the solid addition method (Mall et al., 2006). Acidic and basic sites on pine cone powder were determined by the acidebase titration method proposed by Boehm (1994). The IR spectra of the Pine cone powder sample were recorded using KBr disk in conjunction with a PerkineElmer infrared spectrophotometer. Iodine number was determined by iodine titration as described by ASTM standards measurements (ASTM D4607-8). A modification of the method of Boehm (1994) developed by Marshall et al. (1999) was used to determine total negative charge. Bulk density was determined by tamping procedure described by Ahmedna et al. (1997). 2.2.1. Effect of initial solution pH The effect of solution pH on the equilibrium uptake of copper(II) and lead(II) from aqueous solution by pine cone powder treated 0.15 mol dm3 KOH was investigated between pH 2 and 6. Experiments were performed by adding a known weight of pine cone powder into eight 500 ml beakers containing 50 ml of 70 mg dm3 of copper(II) and lead(II) solution and the pH of the solution adjusted using 0.10 mol dm3 HCl or NaOH. The flasks were shaken at 160 rpm and 291 K for 15 min and the amount of copper(II) or lead(II) remaining in solution was measured by a PerkineElmer model 2100 atomic absorption spectrometer (AAS). Solution pH profile during this experiment was monitored at different time intervals from 1 to 20 min using a pH meter (Crison Basic 20þ). Blank experiments were also performed in deionized water set at pH 5.0 without the addition of metal ions. 2.2.2. Effect of temperature A range of reaction temperatures (291, 297, 307, 317, 327, 337, and 347 K) was used in this experiment and the flasks were agitated for 15 min. All contact investigations were performed in a 500 ml flask. A 0.4 g sample of KOH treated pine cone powder was added to 100 ml volume of copper(II) and lead(II) solution set at pH 5.0 and agitated at 160 rpm. Experiments were carried out at initial copper (II) and lead(II) concentration of 120 mg dm3. Samples were withdrawn at suitable time interval (Samples were drawn every 1 min in the first 5 min and every 5 min in the next 15 min), filtered through a micro pore filter paper and the filtrate analyzed with AAS. 2.2.3. Equilibrium studies A volume of 100 ml of copper(II) or lead(II) solution with concentration ranging from 60 to 120 mg dm3 was placed in a 250 ml conical flask and set at pH 5.0 and accurately weighed amounts (0.40 g) of the KOH treated pine cone was added to the solutions. The conical flasks were then agitated at a constant speed of 160 rpm in a water bath set at 291 K. After shaking the flasks for 30 min a known quantity of sample was withdrawn, and filtered through a micro pores and the filtrate analyzed with AAS. 2.2.4. Cation competition Isotherm studies carried out as in section 2.2.3 to examine the equilibrium biosorption of lead(II) in the presence of equal concentration of copper(II) and copper(II) in presence of lead(II).
1676
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
2.2.5. Desorption analysis The solid biosorbent residue was filtered off from the biosorption system of 0.4 g KOH treated pine cone powder in contact with 120 mg dm3 of copper(II) or lead(II) ion solution at 291 K. The washed biosorbent was then stirred in 100 ml of each of the desorbing solvents (0.01 mol dm3 of HNO3, HCl and CH3COOH and distilled water). After shaking the flasks for 30 min, the pine cone powders were separated by filtration. The filtrate was analyzed with AAS. 2.2.6. Theory The pseudo-first order kinetic model equation is written as (Ho and Ofomaja, 2006):
dqt ¼ k1 ðqe qt Þ dt
k1 t 2:303
(2)
Plots of log (qe qt) versus t gives a straight line for pseudo-first order kinetics, which allows computation of the biosorption rate constant, k1. If the experimental results do not follow Eqs. (1) and (2) they differ in two important aspects: (i) k1(qe qt) does not represent the number of available sites, and (ii) log (qe) is not equal to the intercept of the plot of log (qe qt) against t. To set up the new model for the pseudo-first order kinetics Eq. (1) was modified by Yang and Al-Duri (2005), Lagergren (1898) and Ho (2004) through the modification of its rate constant, k1. The rate constant in the modified pseudo-first order kinetic model (MPFOM) was denoted by K1 and the following equation was proposed:
qe k1 ¼ K1 qt
h ¼ k2 q2e :
the constant can then be determined experimentally by plotting of t/qt against t. 2.2.6.1. Langmuir (1916) isotherm. At constant temperature, metal ions held onto the biosorbent will be in equilibrium with metal ions in bulk solution. The saturated monolayer isotherm can be represented as:
qe ¼
qm Ka Ce 1 þ Ka Ce
(4)
(5)
Integrating Eq. (5) over time t during which the solid phase concentration increases from zero to qt, the following algebraic equation can be obtained:
qt þ lnðqe qt Þ ¼ lnðqe Þ K1 t qe
(6)
If the biosorption process follows the modified pseudo-first order kinetic model represented by Eq. (6), a plot of qt/qe þ ln(qe qt) against t should be a straight line. The pseudo-second-order chemisorption kinetics may be expressed as:
dqt ¼ k2 ðqe qt Þ2 ; dt
(10)
where Ce is the equilibrium concentration (mg dm3); qe is the amount of metal ion biosorbed (mg g1); qm is qe for a complete monolayer (mg g1); Ka is biosorption equilibrium constant (dm3 mg1). 2.2.6.2. Freundlich (1906) isotherm. The empirical Freundlich isotherm, based on biosorption on heterogeneous surface, can be derived assuming a logarithmic decrease in the enthalpy of biosorption with the increase in the fraction of occupied sites and is given by: 1=n
qe ¼ KF Ce
(11)
where KF and 1/n are the Freundlich constants characteristics of the system, indicating the biosorption capacity and biosorption intensity, respectively. Eq. (11) can be linearized in logarithmic form to give Eq. (12) and the Freundlich constants can be determined.
1 logqe ¼ logKF þ logCe n
(12)
2.2.6.3. DubinineRadushkevich (DeR) isotherm. The DubinineRadushkevich (DeR) isotherm is generally expressed as follows (Dubinin, 1960):
qe ¼ qD exp
Eq. (4) can be rearranged into
qe dqt dqt þ ¼ K1 qe dt ðqe qt Þ
(9)
(3)
As qt < qe, the above equation implies that the rate constant k1 is minimum when equilibrium is reached. The modified pseudo-first order rate equation can be derived as follows:
dqt qe ¼ K1 ðqe qt Þ dt qt
(8)
If the initial sorption rate is
(1)
where qt and qe are the amount sorbed at time t and at equilibrium and k1 is the rate constant of the pseudo-first-order sorption process. The integrated rate law, after applying the initial conditions of qt ¼ 0 at t ¼ 0 is:
logðqe qt Þ ¼ logðqe Þ
t 1 1 ¼ þ t: qt k2 q2e qe
(7)
where k2 is the rate constant of sorption, qe and qt have the same definition as above. This can be separated and integrated to the linear form:
2 ! 1 BD RTln 1 þ Ce
(13)
Radushkevich (1949) and Dubinin (1965) have reported that the characteristic sorption curve is related to the porous structure of the sorbent. The constant, BD, is related to the mean free energy of biosorption per mole of the sorbate as it is transferred to the surface of the solid from infinite distance in the solution and this energy can be computed using the following relationship (Hasamy and Chaudhary, 1996):
1 E ¼ pffiffiffiffiffiffiffiffiffi 2BD
(14)
The linear form of the (DeR) isotherm equation is
lnqe ¼ lnqD BD 32
(15)
where BD is a constant related to the mean free energy of adsorption per mole of the adsorbate (mol2J2); qD, the theoretical saturation capacity and e is the polanyi potential, which is equal to RT ln (1 þ (1/Ce)), where R (Jmol1K1) is the gas constant and T (K), the absolute temperature. Hence by plotting ln qe against 32, it is possible to generate the values of qD (mol g1) from the intercept and the values of BD from the slope.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
2.2.6.4. BET isotherm (Brunauer et al., 1938). The BET model is an extension of the Langmuir model for multilayer biosorption. It is based on the assumption that each adsorbate in the first biosorbed layer serves as biosorption site for the second layer and so on. The original form of the BET equation is given as:
q ¼
KB Ce qm ðCs Ce Þ½1 þ ðKB 1ðCCes
i
(16)
Where Ce is the concentration of solute remaining in solution equilibrium (mg dm3), Cs the saturation concentration of solute (mg dm3), q the amount of solute adsorbed per unit weigh of adsorbent (mg g1), qm the amount of solute adsorbed per unit weigh of biosorbent in forming a complete monolayer on the surface (mg g1) and KB is the constant expressive of energy of intraction with the surface. The equation can be written in the linearized form:
Ce 1 KB 1 Ce þ ¼ ðCs Ce Þq Cs KB qm KB qm
1677
Table 1 Characteristics of KOH treated pine cone powder. Characteristics
Total acid groups (mmol g1) Carboxylic group (mmol g1) Phenolic group (mmol g1) Lactone group (mmol g1) Basic groups (mmol g1) pHPZC Surface negative Charge (mmol g1) Bulk density (g cm3) Iodine number (mg g1)
Values KOH treated
Virgin PCP
2.98 0.51 0.65 1.82 1.02 2.56 2.98 0.41 16.7
3.20 0.80 1.07 1.33 4.25 7.49 3.82 0.50 15.5
Functional groups C]O COOH eOH CeH CeC C-N
(1682.1 cm1) (1647.08 cm1) (3418.47 cm1) (2925.90 cm1) (1058.81 cm1) (559.32 cm1)
(17)
A plot of Ce/(Cs Ce)q against (Ce/Cs) should give a straight line and from the slope and intercept the values of KB and qm can be calculated. 2.2.6.5. Competitive Langmuir model (Yang, 1987). The competitive Langmuir model for two competing ions is applied in other to express the relationship between the quantity of the first component adsorbed and the concentration of the second component. The equation is written as
q1 ¼
qm K1 Ce1 1 þ K1 Ce1 þ K2 Ce2
(18)
q2 ¼
qm K1 Ce2 1 þ K1 Ce1 þ K2 Ce2
(19)
where K1 and K2 are the individual Langmuir constants of the first and second metal ions, and qm1 and qm2 are the maximum amounts of the first and second heavy metal ions. 3. Result and discussion
copper(II) and lead(II) in separate solutions were set to pH 2e6, and results presented in Fig. 1. Biosorption capacity has been shown to be affected by equilibrium pH, although it is not easy to control the equilibrium pH. The equilibrium pH is influenced by initial pH of the solution therefore the effect of initial pH on the removal of copper(II) and lead(II) was employed to discuss the effect of pH. The biosorption capacities for both copper(II) and lead(II) were low at solution pH 2 (copper(II) 5.34 mg g1, lead(II) 5.39 mg g1) and copper(II) biosorption was lower than lead(II) biosorption. As the solution pH increases, the amounts of copper(II) and lead(II) biosorbed from solution increased. This may be due to (i) reduced Hþ competition for biosorption sites, (ii) increased net negative charges on the biosorbent surface as solution pH rises above the pHPZC (pHPZC is 2,56) for KOH treated pine cone powder and (iii) that the dominant species of copper(II) and lead(II) between the pH range of 3e5 are Cu2þ, Cu(OH)þ, Pb2þ and Pb(OH)þ (Larous et al., 2005; Elliot and Huang, 1981; Asmal et al., 1998). Copper(II) biosorption was less than that of lead(II) at each initial solution pH, and both copper(II) and lead(II) biosorption increased as initial solution pH increased up to pH 5.0 after which the amount of metal ions biosorbed reduced. At pH above 2.56, the surface of the biosorbent
3.1. Properties of KOH treated pine cone powder The surface properties of virgin and KOH modified pine cone powder are shown in Table 1 below. Table 1 reveals that KOH washing changed the surface properties to a great extent as can be observed from Table 1. The total negative charge on the biosorbent and the iodine number was increased, while the pHPZC and bulk densities decreased. An increase in surface charge indicates that more biosorption sites were created by KOH washing. This increased amount of sites may be due to the increase in internal surface area as observed by the higher iodine number. A reduction in the bulk density observed after KOH washing shows that some plant components have been leached out of the materials creating pore spaces that lead to increased internal surface. Finally a lower pHPZC after KOH washing indicates that negatively charged sites dominates over positively charged sites even at low pH and that metal biosorption may be effective at pH above 2.56. 3.2. Effect of solution pH Variations in the amount of copper(II) and lead(II) biosorbed were noted in the series of contact time studies, when the pH of the
Fig. 1. Effect of solution pH on copper(II) and lead(II) biosorption on to KOH treated pine cone powder. Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 70 mg dm3; Temp.: 291 K.
1678
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
acquires negative charge and enhances metal biosorption. Therefore further experiments were performed at solution pH 5.0. The values of change in Hþ ion concentration and biosorption capacities at different time periods when 0.4 g of the biosorbent was contacted with 50 mg dm3 of copper(II) or lead(II) ion solution is shown graphically in Fig. 2. Fig. 2 shows that after initial contact, the final solution pH’s were all higher than the initial solution pH (pH 5.0). The change in Hþ ion concentration at a particular time is measured by the difference between the final and initial Hþ ion concentration. These values were negative and the difference increased with time up till 20 min of contact. Results from the blank test revealed that adding the biosorbent alone to deionized water at pH 5.0 led to a slight increase in solution pH. The reason for this can be attributed to the biosorbents ability to retain Hþ on its surface at these pH ranges. Blázquez et al. (2009) observed that between pH 6 and 8, the biosorption of chromium(III) onto olive stone lead to a slight increase in solution pH and attributed this increase to the ability of olive stone to the retention of Hþ on its surface along with chromium(III). Fig. 2 shows that as the metal ion capacity increases with time, the solution pH increased slightly and the change in Hþ concentration increased with time as well. The shape of the biosorption capacity profile is similar and opposite to that of the change in Hþ ion concentration. It was also observed that the change in Hþ ion concentration for lead(II) biosorption was slight higher than for copper(II) biosorption. Han et al. (2006) observed an increase in equilibrium pH with biosorption capacity for chromium(III) on to a microalgal isolate, Chlorella miniata. Mathematical equations were then drawn to show the relationship between the equilibrium pH, time and equilibrium capacity for the contact of 0.4 g of biosorbent with 70 mg dm3 of copper(II) and lead(II) at pH 5.0 at a time interval of 0e20 min:
Lead(II) biosorption
pHequ ¼
t 0:1351t þ 0:0596
(22)
pHequ ¼
qe 0:1036qe þ 0:2386
(23)
These trends suggest that ion-exchange mechanism may be responsible for metal biosorption. 3.3. Effect of temperature Fig. 3a and b shows the effect of temperature on percentage copper(II) and lead(II) uptake rate at different temperatures. It can be observed that the percentage copper(II) and lead(II) uptake increased with contact time and with temperature, and at some point in time reaches an almost constant value. At this point the amounts of copper(II) and lead(II) being removed from aqueous solution onto the solids are in a state of dynamic equilibrium with the amounts of copper(II) and lead(II) desorbed from the KOH treated pine cone powder surface. For the range of contact time under which the experiments were conducted, greater percentage of copper(II) and lead(II) was removed from solution at higher temperatures than at lower
Copper(II) biosorption
pHequ ¼
t 0:1367t þ 0:0711
(20)
pHequ ¼
qe 0:1076qe þ 0:2219
(21)
Fig. 2. Relationship between change in hydrogen ion concentration and metal ion capacities. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 70 mg dm3; Temp.: 291 K.
Fig. 3. Effect of biosorption temperature on percentage (a) copper(II) and (b) lead(II) removal by KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
temperatures. Lead(II) was removed at higher percentage than copper(II) at a particular temperature (See Fig. 3a and b). For a contact time of 15 min, percentage copper(II) removal were 49.86, 51.63, 54.15, 56.64, 59.05, 61.34, and 63.38% and percentage lead(II) removal were 76.52, 77.91, 79.85, 81.76, 83.66, 85.20 and 86.77% as temperature increased from 291 to 347 K. The biosorption rate for the first 1 min was found to be 8.67, 9.96, 11.42, 12.65, 14.24, 15.51, and 16.55 mg min1 for copper(II) biosorption and 15.69, 16.83, 20.09, 21.43, 22.72, and 23.82 mg min1 for lead(II) biosorption as temperature increases from 291 to 347 K. The biosorption reaction at all temperature were found to be extremely rapid for the first 5 min having values between 45.40 and 62.06% for copper(II) and 71.77 and 85.80% for lead(II) as temperature is increased from 291 to 347 K. After this stage, the rate of removal decreased to an almost constant value with time. These observations at reaction temperatures applied revealed that temperature has no effect on equilibrium time. 3.3.1. Pseudo-first and modified pseudo-first order kinetics Pseudo-first order model parameters for the effect of biosorption temperature on the biosorption of copper(II) and lead(II) onto KOH treated pine cone powder are shown in Table 2a and b. The values for equilibrium biosorption capacity as predicted by the pseudo-first order kinetics decreased with increasing temperature while the experimental values increased with reaction temperature. The values were not close to the experimental values for both metals at all temperatures. The pseudo-first order rate constant, k1, increased with temperature for both metals at all temperatures. The values for k1 for lead(II) biosorption were higher than those of copper(II) biosorption. The plots in Fig. 4a and b show that the pattern for the uptake of copper(II) and lead(II) as described by the pseudo-first order model are similar at all temperatures. Although the correlation coefficient, r2, values are relatively high, it will be noticed that there is a deviation from the straight line after 5 min of biosorption in all cases. This deviation has been attributed to the slow biosorption which occurs in the biosorbent pores preceding the very fast initial uptake of copper(II) or lead(II) ions on to the surface of the biosorbent (Ho and McKay, 1999). This slow process tends to continue with smaller change in equilibrium biosorption. The fact that the trends in biosorption capacities are opposite to that observed experimentally, the pseudo-first order predicted capacities were not close to the experimental data and the observed deviation from the straight line at 5 min of contact, suggest that the pseudo-first order kinetics does not sufficiently describe the whole range of whole range of kinetic data.
1679
To eliminate this error, a modified form of the pseudo-first order model was proposed (Yang and Al-Duri, 2005; Lagergren, 1898; Ho, 2004). The modified Pseudo-first order model parameters for the effect of biosorption temperature on the biosorption of copper(II) and lead(II) onto KOH modified pine cone powder are shown in Table 3a and b and Fig. 5a and b. It will be observed that the deviations from the experimental data at 5 min were minimized than in the pseudo-first order model plots. The values for K1 for lead (II) were also higher than for copper(II) and all increased with increasing temperature. The values of equilibrium capacity of copper(II) was found to decrease from 13.88 (291 K) to 7.09 mg g1 (347 K) and lead(II) decreased from 17.94 (291 K) to 6.90 mg g1 (347 K). These observations indicate that although the modified pseudo-first order equation could reduce the deviation of the experimental points from the straight line, the modified pseudofirst order model could not accurately describe the whole range of experimental data. Its predictions of the biosorption capacities are opposite to the observed experimentally. 3.3.2. Pseudo-second order kinetics Analysis of the experimental data with the pseudo-second order kinetic model shows good agreement of the sets of data, which is reflected in the extremely high correlation coefficient of determination, obtained (Table 2a and b and Fig. 6a and b). Thus on increasing the temperature from 291 to 347 K, the biosorption equilibrium capacity, qe, is increased from 15.73 to 19.22 mg g1 for copper(II) and 23.74e26.27 mg g1 for lead(II). The initial biosorption rate, h, and the pseudo-second order rate constant, k2, were also found to increase with temperature variation from 291 to 347 K. The values of initial biosorption rate, h, for both metals were much higher than the pseudo-second order rate constant, k2 as predicted by the pseudo-second order kinetics. The initial biosorption rate, h, and pseudo-second order rate constants, k2, for the lead(II) biosorption were much higher than for copper(II) biosorption. This indicates that rates of lead(II) removal is much faster than copper(II) removal as seen from the percentage removal plots (Fig. 3a and b). These trends in the initial biosorption rate, h, pseudo-second order rate constant, k2, and equilibrium biosorption, qe, with temperature suggests that a chemisorption reaction or an activated biosorption involving valency forces through sharing or exchange of electrons between biosorbent and metal ion occurs. Similar results of the biosorption of copper(II) and lead(II) onto other adsorbents have also been reported in literatures, for example lead (II) on to palm kernel fiber (Ho and Ofomaja, 2005) and copper(II) on to seeds of Capsicum annuum (Özcan et al., 2005).
Table 2a Parameters of kinetic models for Copper(II) biosorption on 0.15 mol dm3 KOH treated pine cone powder at different temperatures. Model
Parameters
291 K
297 K
307 K
317 K
327 K
337 K
347 K
Pseudo-first
qe (Exp) qe1 (Cal) k1 r2 qe K1 r2 qe (Exp) qe2 (Cal) h k2 r2 ki c r2
14.96 7.56 0.3132 0.983 13.88 0.2753 0.997 14.96 15.73 20.32 0.0821 0.994 0.585 12.71 0.982 0.5341
15.49 6.79 0.3224 0.980 13.16 0.2884 0.994 15.49 16.13 26.04 0.1001 0.996 0.493 13.60 0.981 0.4636
16.24 5.86 0.3276 0.974 12.00 0.2995 0.990 16.24 16.75 35.94 0.1281 0.998 0.396 14.72 0.981 0.3701
16.99 5.31 0.3385 0.972 11.30 0.3139 0.987 16.99 17.42 46.22 0.1523 0.993 0.339 15.69 0.980 0.3074
17.32 4.16 0.3408 0.965 9.43 0.3207 0.979 17.32 18.03 67.65 0.2081 0.998 0.253 16.74 0.980 0.2089
18.0 3.53 0.3501 0.964 8.22 0.3355 0.976 18.0 18.65 92.03 0.2646 0.994 0.201 17.63 0.980 0.1462
19.02 2.96 0.3455 0.957 7.09 0.3333 0.968 19.02 19.22 118.99 0.3221 0.992 0.166 18.37 0.979 0.1097
Modified pseudo-first
Pseudo-second
Intraparticle Diffusion
c2 1
qe, qe1 and qe2 ¼ mg g
; k1 ¼ min1; k2 ¼ g mg1 min1; h ¼ mg g1 min1; ki ¼ mg g1 min0.5; ks ¼ min1; Di ¼ cm2 s1
1680
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
Table 2b Parameters of kinetic models for lead(II) biosorption on pine cone powder treated with 0.15 mol dm3 KOH at different temperatures. Model
Parameters
291 K
297 K
307 K
317 K
327 K
337 K
347 K
Pseudo-first
qe (Exp) qe (Cal) k1 r2 qe K1 r2 qe (Exp) qe (Cal) h k2 r2 ki C r2
22.95 8.91 0.3293 0.977 17.49 0.2995 0.992 27.95 23.74 46.25 0.0822 0.995 0.613 20.60 0.981 0.5769
23.37 8.00 0.3339 0.974 16.64 0.3075 0.989 23.37 24.04 56.14 0.0971 0.998 0.526 21.55 0.982 0.4873
23.96 6.50 0.3385 0.968 14.67 0.3158 0.983 23.96 24.46 77.53 0.1296 0.994 0.403 22.41 0.980 0.2295
24.53 5.37 0.3432 0.964 12.24 0.3264 0.977 24.53 24.92 103.72 0.1670 0.996 0.317 23.31 0.980 0.1803
25.10 4.40 0.3501 0.952 10.49 0.3351 0.973 25.10 25.41 136.65 0.2716 0.998 0.252 24.13 0.979 0.1795
25.56 3.45 0.3547 0.959 8.39 0.3440 0.968 25.56 25.79 191.63 0.3701 0.992 0.188 24.84 0.979 0.1121
26.09 2.77 0.3593 0.957 6.90 0.3513 0.965 26.09 26.27 255.44 0.3701 0.997 0.146 25.53 0.979 0.0735
Modified pseudo-first
Pseudo-second
Intraparticle diffusion
c2
qe, qe1 and qe2 ¼ mg g1; k1 ¼ min1; k2 ¼ g mg1 min1; h ¼ mg g1 min1; ki ¼ mg g1 min0.5; ks ¼ min1; Di ¼ cm2 s1
According to Ho et al. (2000), if the Copper(II) and lead(II) uptake is chemically rate controlled, the pseudo-second order constants will be independent of particle diameter and flow rate and will depend on temperature of the metal ion in solution. Increase in temperature will also led to increase in the amounts of metal ions biosorbed at equilibrium for a chemisorption-controlled reaction. The logarithmic plots of initial biosorption rate, h, Pseudosecond order rate constant, k2, and qe versus temperature were made and the plots where found to give straight lines whose correlation coefficients, r2, are extremely high, indicating that copper(II) and lead(II) uptake may be chemically rate controlled. Mathematical expressions of the forms:
where k2 is the pseudo-second order rate constant of biosorption (g mg1 min1), k0 the temperature-independent factor (g mg1 min1), Ea the activation energy of sorption (kJ mol1), R the gas constant (8.314 J mol1 K1) and T is the solution temperature (K). Therefore, the relationship between k2 and T can be represented in an Arrhenius form as represented in Eq. (30):
For Copper(II)
qe ¼ 0:0239T 1:1435
(24)
h ¼ 4:2954 1024 T 10:0180
(25)
k ¼ 7:4645 1021 T 7:7308
(26)
For Lead(II)
qe ¼ 0:9270T 0:5716
(27)
h ¼ 7:7268 1025 T 9:6489
(28)
k ¼ 8:9950 1023 T 8:5057
(29)
The values of rate constant, k2, were found to increase from 0.0821 to 0.3221 g mg1 min1 for copper(II), and from 0.0822 to 0.3701 g mg1 min1 for lead(II), for an increase in the solution temperature of 291e347 K. There is a linear relationship between the pseudo-second order rate constant and temperature with coefficient of determination greater than 0.997 for both metal ions. The biosorption rate constant is usually expressed as a function of solution temperature by the relationship:
lnk2 ¼ lnk0
Ea RT
(30)
Fig. 4. Pseudo-first order kinetics for (a) copper(II) and (b) lead(II) biosorption on to KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
1681
Table 3 Activation energy parameters for copper(II) and lead(II) biosorption on to KOH treated pine cone powder. Sample
Ea (kJ mol1)
Ko (g mg1 min1)
DS* (kJ mol1)
DH* (kJ mol1)
DG*
Copper(II) Lead(II)
20.36 22.40
3.71 103 8.40 102
198.39 197.57
17.73 23.77
73.08 68.45
(kJ mol1)
Copper(II):
k2 ¼ 3:71 103
20:36 103 8:314T
! (31)
Lead(II):
k2 ¼ 8:40 10
2
22:40 103 8:314T
! (32)
From these equations, the rate constant for biosorption, k0, is 3.71 103 g mg1 min1 for copper(II) and 8.40 102 g mg1 min1 for lead(II) and the activation energy for sorption, Ea, 20.36 kJ mol1
Fig. 6. Pseudo-second order kinetics for (a) copper(II) and (b) lead(II) biosorption on to KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
for copper(II) and 22.40 kJ mol1 for lead(II). The value of activation energy for copper(II) is lower than that of lead(II) and both are higher than 20 kJ mol1. The higher activation energy for lead(II) indicates that stronger bonds are formed between lead(II) and KOH treated pine cone powder than copper(II). The change in enthalpy (DH*) and entropy (DS*) of activation for the copper(II) and lead(II) biosorption onto KOH modified pine cone powder were calculated by the Eyring equation (Atun and Sismanoglu, 1996) below:
DS* DH* k k þ ln 2 ¼ ln h R RT T
(33)
Where k2, is the pseudo-second order rate constant, T is the Kelvin temperature, k and h are the Boltzmann’s and Planck’s constants respectively. The change in entropy of activation (DS*) and enthalpy of activation (DH*), for this step have been evaluated from the intercept and slope of each linear plot. The free energies of activation (DG*) for the KOH treated pine cone powder were computed from the equation:
DG* ¼ DH* T DS* Fig. 5. Modified Pseudo-first order kinetics for (a) copper(II) and (b) lead(II) biosorption on to KOH treated pine cone powder. Solution pH: 5.0; Biosorbent mass: 0.4 g; Agitation speed: 160 rpm; Initial Conc.: 120 mg dm3; Temp.: 291 K.
(34)
The corresponding values for change in enthalpy of activation (DH*), enthalpy of activation (DS*) and free energy of activation (DG*) has been calculated and the values for copper(II) and lead(II)
1682
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
on to KOH treated pine cone powder given in Table 3. The entropy of activation (DS*), for copper(II) and lead(II) were found to be smaller than zero. The enthalpy of activation (DH*) obtained from the Eyring equation is lower than TDS*, for both metals, indicating that the reorientation step is mostly entropy controlled at the activation state. The contribution of the reorientation step to activation tends to be higher for lead(II) biosorption than copper(II) as seen from the higher value of enthalpy (DH*), compared with TDS*. The free energy of activated (DG*), was found to be lower for lead(II) indicating that activation is more spontaneous lead(II) than copper (II).
the highest values for correlation coefficient, r2, indicating that it best describes the experimental data than the other isotherm models applied. The Langmuir capacities from this study were compared with those obtained by other biosorbents and were found to be substantially higher (Table 5). The Langmuir constant, Ka, known as the heat of biosorption were 0.0542 dm3 mg1 for copper(II) and 0.1649 dm3 mg1 for lead(II). The bonds formed between lead(II) ions and the functional groups on the biosorbent surface are stronger than those formed between these groups and copper(II) ions as seen from the values of Ka. The free energy, DGo, at 291 K was calculated using Eq. (35)
3.4. Equilibrium isotherm
DGo ¼ RTlnKa :
Isotherm plots were made for the experimental data of the amount of copper(II) and lead(II) biosorbed per unit mass (mg g1) versus equilibrium solution concentration (mg dm3) for the biosorption of copper(II) and lead(II) from solutions of concentration raging from 60 to 120 mg dm3 onto KOH treated pine cone powder at 291 K (Fig. 7). The Freundlich isotherm was then applied to analyze the equilibrium data. The Freundlich constants were calculated along with the coefficient of determination, r2, in Table 4. The results revealed that the values of r2 were fairly high for both copper(II) and lead(II) biosorption. It can also be observed that the constants, n, and KF were found to be higher for lead(II) than copper(II). Freundlich constants KF indicate the biosorption capacity of the biosorbent. The value of KF at equilibrium for copper(II) is 3.733 dm3 g1 and lead(II) is 7.852 dm3 g1. The Freundlich constant n is a measure of the deviation from linearity of the biosorption curve or the biosorption affinity of the biosorbent for the sorbate. The numerical values of n for copper(II) is 2.538 and for lead(II) biosorption 2.558. The values for n were greater than unity, indicating that copper(II) and lead(II) ions are favorably biosorbed by KOH treated pine cone powder. It is also observed that the value for n for lead(II) biosorption was higher than for copper(II) biosorption indicating that lead(II) biosorption is more favorable the copper(II) biosorption. The Langmuir constants, qm and Ka were also calculated and shown in Table 4. The values show that the monolayer capacities of the KOH treated pine cone powder for copper(II) is 26.32 mg g1 and for lead(II) is 32.26 mg g1. The Langmuir isotherm also gave
Fig. 7. Isotherm plots for the biosorption of Copper(II) and lead(II) on to KOH treated Pine cone powder.
(35)
The values of free energy is given as 19.70 kJ mol1 for copper (II) biosorption and 25.26 kJ mol1 for lead(II) biosorption at 291 K. The result indicates that at 291 K, biosorption of both metals are spontaneous but lead(II) biosorption is more spontaneous than copper(II) biosorption. The DubinineRadushkevich (DeR) isotherm parameters are shown in Table 4. The values of the mean free energy, E, for copper (II) was found to be 10.33 kJ mol1 and for lead(II) 11.72 kJ mol1. The parameter E, provides information about the biosorption mechanism as chemical, ion-exchange or physical adsorption. Özcan et al. (2005) and Benhammou et al. (2005) have successfully used this method to determine the copper ions biosorption mechanism by different adsorbents. According to Onyango et al. (2004), mean free energy values greater than 8 kJ mol1 corresponded to biosorption processes controlled by ion-exchange mechanism. The values obtained in this study were greater than 8 kJ mol1, indicating ion-exchange mechanism. The equilibrium isotherm data were finally analyzed using the BET isotherm model. The results revealed that the correlation coefficient, r2, were relatively high (>0.960), the saturation capacity for lead(II) was higher than for copper(II) and the energy of interaction with the surface expressed by the constant, KB, where higher for lead(II) interaction than for copper(II) as predicted by the Langmuir isotherm. The lower values of r2 may indicate that the biosorption of lead(II) and copper(II) onto the KOH treated pine cone powder may not involve a multilayer arrangement of the metal ions on the biosorbent surface. Competition of copper(II) and lead(II) in a binary solution for biosorption sites on KOH treated pine cone powder was determined by contacting equal concentrations of copper(II) and lead(II) in the same solutions and determining their uptake by KOH treated pine cone powder. The equilibrium data was analyzed with both the Langmuir and Competitive Langmuir isotherm models and the isotherm plots shown in Fig. 8a and b. The results as seen from the plot of amount biosorbed at equilibrium versus equilibrium concentration show that the Langmuir isotherm better fitted the experimental data than the competitive Langmuir isotherm. It will also be seen that the competitive Langmuir isotherm gave closer fit to the experimental data for the biosorption of copper(II) in presence of lead(II) plots. This suggests that in the biosorption of both metals simultaneously, there is some interaction of the biosorbed cations at the biosorption sites. Copper (II) biosorption is more affected by the presence of lead(II) than lead (II) is affected by copper(II). The Langmuir monolayer capacity of lead(II) in solution reduced from 32.26 mg g1 with only lead(II) in solution to 30.12 mg g1 in the presence of copper(II). The bonding energy for lead(II) decreased from 0.1649 dm3 mg1 in solution to 0.0849 dm3 mg1 in the presence of copper(II). The monolayer capacity for copper(II) was 26.32 mg g1 and in the presence of lead (II) it became 22.68 mg g1, while bonding energy for copper(II) was 0.0542 dm3 mg1 and the value decreased to 0.0210 dm3 mg1
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
1683
Table 4 Isotherm constants for the adsorption of copper(II) and lead(II) onto KOH treated Pine cone. Metal
Freundlich n
KF 3
1
(dm g Copper(II) Lead(II)
2.358 2.558
Langmuir-1 r2
)
qm (mg g
3.733 7.852
0.994 0.994
BET r2
Ka 1
26.32 32.26
)
3
(dm mg 0.0542 0.1649
1
DubinineRadushkevich (DeR)
qm 1
)
(mg g
0.943 0.935
27.78 34.48
in the presence of lead(II). The capacity and binding energy was strongly affected in the Cu(II)-Pb(II) than the Pb(II)-Cu(II) biosorption. Desorption studies are important in elucidating the mechanism of a biosorption process and its applicability in industrial practice. This characteristic can be evaluated by extracting biosorbed metal ions by different solvents. If the biosorbed metal ion can be desorbed by water, it is believed that the attachment of the metal ion onto the biosorbent is by weak bonds (physical bonds). If a solution of strong acids such as HNO3 or HCl can desorb the metal ion, it is believed that the attachment of metal is by ion-exchange. If a solution of CH3COOH, can desorb the metal, it is believed that the biosorption of metal is by chemisorption. The results of desorption studies are shown in Fig. 9. The percentages of copper(II) and lead(II) desorbed from 0.4 g of the used KOH treated pine cone powder are compared for all four solvents used. From the results presented in Fig. 9, it can be seen that H2O had the least value of percentage desorption as compared with other solvents and water removed more copper(II) than lead (II). Water can desorb copper(II) and lead(II) ions that are weakly bonded to the KOH treated pine cone powder surface. Therefore, only a small fraction of the copper(II) and lead(II) ions held to the biosorbent are attached by weak bonds on biosorption sites. The inorganic acids, HCl and HNO3 were found to desorb quite a high percentage of copper(II) and lead(II) ions from the biosorbent. The desorption of copper(II) and lead(II) ions using HNO3 removed more copper(II) and lead(II) ions from the biosorbent than with HCl. It is believed that the nitrate salts of copper(II) and lead (II) are more soluble than the chloride salts, this may account for the lower desorption percentage observed in the HCl desorption study. High desorption percentages produced by strong acids indicates that the biosorption of copper(II) and lead(II) ions on to
r2
KB )
(kJ mol 0.0466 0.1388
1
qD
BD 1
)
(mmol g 0.974 0.989
)
1.58 104 6.53 105
r2
E 2
(mol kJ
2
)
1.69 109 3.64 109
(kJ mol 10.33 11.72
1
) 0.853 0.806
KOH treated pine cone powder is by ion-exchange mechanism. This is confirmed by repeating the desorption test with increasing concentrations of the HNO3 solution. Fig. 10 shows the different desorption percentages with increasing concentrations of the HNO3 solution. It is observed that the desorption percentage increased with increasing concentrations of HNO3 signifying that increase in hydrogen ion concentration lead to increase in the exchange of hydrogen ion for copper(II) and lead(II) ions. Desorption using CH3COOH solution was also found to remove only a small amount of copper(II) and lead(II) ion from the biosorbent. The percentage copper(II) and lead(II) desorbed was higher for HCl than for CH3COOH (Fig. 9). Therefore ion-exchange
Table 5 Comparison of best isotherm model and monlayer capacities of copper(II) and lead (II) biosorption. Metal ion
Biosorbent Monolayer capacity (mg g1)
Copper(II) 107.52 21.25 0.18 14.90 19.23 26.32 Lead(II)
27.10 196.07 16.14 52.38 29.24 32.26
Reference
Black gram bran Peanut hull Wheat straw NaOH-treated Rubber leaves powder Pine cone biomass
Nadeem et al. (2009) Zhu et al. (2009) Dang et al. (2009) Ngah and Hanafiah (2008) Nuhoglu and Oguz (2003) KOH treated pine cone This Study powder Mushrooms Vimala and Das (2009) Cotton waste Riaz et al. (2009) Seed of Strychnos Jayaram et al. (2009) potatorum L. NaOH-treated sawdust Meena et al. (2007) (Acacia arabica) Fenton oxidized pine Argun et al. (2008) cone biomass KOH treated pine cone This Study powder
Fig. 8. Cation competition for (a) Pb-Cu and (b) Cu-Pb competition on to KOH treated Pine cone powder.
1684
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685
reorientation to the activation step was higher for lead(II) than copper(II). Biosorption Equilibrium studies revealed that KOH treated pine cone powder had a higher capacity for lead(II) than copper(II) and a monolayer surface coverage was formed over the biosorbent surface. There was only a small interaction between metal ions when simultaneously biosorbed and cation competition was higher for the Cu-Pb system than for the Pb-Cu system. Desorption studies and DubinineRadushkevich, energy parameter, E, also supports ion-exchange mechanism. References
Fig. 9. Desorption efficiencies of copper(II) and lead(II) from KOH treated pine cone powder by various solvents. Temp. ¼ 291 K, time ¼ 1 h, Co (desorbing solvent) ¼ 0.01 mol dm3, m ¼ 1.0/100 ml.
Fig. 10. Effect of HNO3 concentration on the desorption efficiencies of copper(II) and lead(II) from KOH treated pine cone powder. Temp. ¼ 291 K, time ¼ 1 h, dose ¼ 1.0/ 100 ml.
mechanism was more involved in the bonding of copper(II) and lead(II) ions on to KOH treated pine cone powder than chemisorption mechanism. This confirms the applicability of pseudosecond order model to the biosorption process. 4. Conclusion Biosorption of copper(II) and lead(II) ions on to pine cone powder treated with 500 ml 0.15 mol dm3 KOH solution has been studied. Biosorption capacity of the two metal ions was shown to be dependent on initial and final solution pH. The trend in the change in Hþ concentration with biosorption capacity and time where similar and indicating that Hþ biosorption occurred in the pH range studied and ion-exchange mechanism predominates. Both the pseudo-first and modified pseudo-first order kinetic models were applied to analyze the biosorption kinetics but provided poor fitting to the experimental data. The pseudo-second order model on the other hand gave better fit and was able to describe the experimental data sufficiently suggesting that ionexchange is the dominating mechanism. Activation energies where higher for lead(II) than for copper(II), and the contribution of
Ahmedna, M., Johns, M.M., Clarke, S.J., Marshall, W.E., Rao, R.M., 1997. Potential of agricultural by-product based carbons for use in raw sugar decolorization. Journal of the Science of Food and Agriculture 75, 117e124. Argun, M.E., Sukru, D., Karatas, M., Gürü, M., 2008. Activation of pine cone using Fenton oxidation for Cd(II) and Pb(II) removal. Bioresource Technology 99, 8691e8698. Asmal, M., Khan, A.H., Ahmad, S., Ahmad, A., 1998. Role of sawdust in the removal of copper(II) from industrial wastes. Water Research 32, 3085e3091. ASTM, standard test method for determination of iodine number of activated carbon, D 4607-86, pp. 384e387. Atun, G., Sismanoglu, T., 1996. Adsorption of 4,40 -isopropylidenediphenol and diphenylolpropane 4, 40 dioxyaceticacid from aqueous solution on kaolinite. Journal of Environmental Science and Health A31 (8), 2055e2069. Blázquez, G., Hernáinz1, F., Calero, M., Martín-Lara, M.A., Tenorio, G., 2009. The effect of pH on the biosorption of Cr (III) and Cr (VI) with olive stone. Chemical engineering journal 148, 473e479. Boehm, H.P., 1994. Some aspects of the surface chemistry of carbon black and other carbons. Carbon 32, 759e769. Brunauer, S., Emmett, P.H., Teller, E., 1938. Adsorption of gases in multimolecular layers. Journal of American Chemical Society 60, 309e319. Dang, V.B.H., Doan, H.D., Dang-Vu, T., Lohi, A., 2009. Equilibrium and kinetics of biosorption of cadmium(II) and copper(II) ions by wheat straw. Bioresource Technology 100 (1), 211e219. Dubinin, M.M., 1960. The potential theory of adsorption of gases and vapours for adsorbent with energetically nonuniform surface. Chemical Review 60, 235e266. Dubinin, M.M., 1965. Modern state of the theory of volume filling of micropore adsorbents during adsorption of gases and steam on carbon adsorbents. Zhurnal Fizcheskoi Khimii 39, 1305e1317. Elliot, H.A., Huang, C.P., 1981. Adsorption characteristics of some copper(II) complexes on aluminosilicates. Water Research 15, 849e855. } Freundlich, H.M.F., 1906. Uber die adsorption in lösungen. Zeitschrift für Physikalische. Chemie (Leipzig) 57A, 385e470. Gündogan, R., Acemioglu, B., Alma, M.H., 2004. Copper (II) adsorption from aqueous solution by herbaceous peat. Journal of Colloid and Interface Science 269, 303e309. Han, R., Li, H., Li, Y., Zhang, J., Xiao, H., Shi, J., 2006. Biosorption of copper and lead ions by waste beer yeast. Journal of Hazardous Materials 137, 1569e1576. Hasamy, S.M., Chaudhary, M.H., 1996. Sorption potential of hare river sand for the removal of antimony from acidic aqueous solution. Applied Radiation and Isotopes 47, 467e471. Ho, Y.S., McKay, G., 1999. Pseudo-second order model for sorption processes. Proc. Biochem 34, 451e456. Ho, Y.S., Ng, J.C.Y., Mckay, G., 2000. Kinetics of pollutant sorption by biosorbents: review, Sep. Purif. Methods 29, 186e232. Ho, Y.S., 2004. Citation review of Lagergren kinetic rate equation on adsorption reactions. Scientometrics 59 (1), 171e177. Ho, Y.S., Ofomaja, A.E., 2006. Biosorption thermodynamics of cadmium on coconut copra meal as biosorbent. Biochemical Engineering Journal 30, 117e123. Ho, Y.S., Ofomaja, A.E., 2005. Kinetics and thermodynamics of lead ion sorption on palm kernel fiber from aqueous solution. Process Biochemistry 40, 3455e3461. Jayaram, K., Murthy, I.Y.L.N., Lalhruaitluanga, H., Prasad, M.N.V., 2009. Biosorption of lead from aqueous solution by seed powder of Strychnos potatorum L. Colloids and Surfaces B: Biointerfaces 71, 248e254. Lagergren, S., 1898. Kungliga Svenska Vetenskapsakademiens. Handlingar, Band 24 (4), 1e39. Langmuir, I., 1916. The constitution and fundamental properties of solids and liquids. Journal of American Chemical Society 38, 2221e2295. Larous, S., Menai, A.H., Lehocine, M.B., 2005. Experimental study of the removal of copper from aqueous solutions by adsorption using sawdust. Desalination 185, 483e490. Mall, I.D., Srivastava, V.C., Agarwal, N.K., 2006. Removal of Orange-G and methyl violet dyes by adsorption onto bagasse fly ash kinetic study and equilibrium isotherm analyses. Dyes Pigments 69, 210e223. Malkoc, E., 2006. Ni(II) removal from aqueous solutions using cone biomass of Thuja orientalis. Journal of Hazardous Materials B137, 899e908. Marshall, W.E., Wartelle, L.H., Boler, D.E., Johns, M.M., Toles, C.A., 1999. Enhanced metal adsorption by soybean hulls modified with citric acid. Bioresource Technology 69, 263e268.
A.E. Ofomaja et al. / Journal of Environmental Management 91 (2010) 1674e1685 Meena, A.K., Kadirvelu, K., Mishra, G.K., Rajagopal, C., Nagar, P.N., 2007. Adsorptive removal of heavy metals from aqueous solution by treated sawdust (Acacia arabica). Journal of Hazardous Materials 150, 604e611. Min, S.H., Han, J.S., Shin, E.W., Park, J.K., 2004. Improvement of cadmium ion removal by base treatment of juniper fiber. Water Research 38, 1289e1295. Nadeem, R., Hanif, M.A., Mahmood, A., Jamil, M.S., Ashraf, M., 2009. Biosorption of Cu(II) ions from aqueous effluents by blackgram bran (BGB). Journal of Hazardous Materials 168, 1622e1625. Nagata, K., Salagami, H., Harada, H., Monoyama, M., Ishihama, A., Konno, K., 1990. Inhibition of influenza virus infection by pine cone antitumor substances. Antiviral Research 13, 11e21. Ngah, W.S.W., Hanafiah, M.A.K.M., 2008. Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review. Bioresource Technology 99, 3935e3948. Nuhoglu, Y., Oguz, E., 2003. Removal of copper(II) from aqueous solutions by biosorption on the cone biomass of Thuja orientalis. Process Biochemistry 38, 1627e1638. Ofomaja, A.E., Naidoo, E.B., Modise, S.J. 2009. Removal of copper(II) from aqueous solution by pine and base modified pine cone powder as biosorbent; 168: 909e917. Özcan, A., Özcan, A.S., Tunali, S., Akar, T., Kiran, I., 2005. Determination of the equilibrium, kinetic and thermodynamic parameters of adsorption of copper(II)
1685
ions onto seeds of Capsicum annuum. Journal of Hazardous Materials B124, 200e208. Panday, K.K., Gur, P., Singh, V.N., 1985. Copper (II) removal from aqueous solutions by fly ash. Water Research 19 (7), 869e873. Radushkevich, L.V., 1949. Potential theory of sorption and structure of carbon. Zhurnal Fizcheskoi Khimii 23, 1410e1420. Riaz, M., Nadeem, R., Hanif, M.A., Ansari, T.M., Rehman, K.U., 2009. Pb(II) biosorption from hazardous aqueous streams using Gossypium hirsutum (cotton) waste biomass. Journal of Hazardous Materials 161, 88e94. Ucun, H., Bayhan, Y.K., Kaya, Y., Cakici, A., Algur, O.F., 2002. Biosorption of chromium (VI) from aqueous solution by cone biomass of Pinus sylvestris. Bioresource Technology 85, 155e158. Ucun, H., Bayhan, Y.K., Kaya, Y., Cakici, A., Algur, O.F., 2003. Biosorption of lead (II) from aqueous solution by cone biomass of Pinus sylvestris. Desalination 154, 233e238. Vimala, R., Das, N., 2009. Biosorption of cadmium (II) and lead (II) from aqueous solutions using mushrooms: a comparative study. Journal of Hazardous Materials 168, 376e382. Yang, R.T., 1987. Gas Separation by Adsorption Processes. Butterworths, Boston, MA. Yang, X., Al-Duri, B., 2005. Kinetic modeling of liquid-phase adsorption of reactive dyes on activated carbon. Journal of Colloid and Interface Science 287, 25e34. Zhu, C.S., Wang, L.P., Chen, W.B., 2009. Removal of Cu(II) from aqueous solution by agricultural by-product: peanut hull.