Biosorption of palladium(II) and platinum(IV) from aqueous solution using tannin from Indian almond (Terminalia catappa L.) leaf biomass: Kinetic and equilibrium studies

Chemical Engineering Journal 193–194 (2012) 102–111

Contents lists available at SciVerse ScienceDirect

Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej

Biosorption of palladium(II) and platinum(IV) from aqueous solution using tannin from Indian almond (Terminalia catappa L.) leaf biomass: Kinetic and equilibrium studies Prakorn Ramakul a,⇑, Yachanapa Yanachawakul a, Natchanun Leepipatpiboon b, Niti Sunsandee c a b c

Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand Chromatography and Separation Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand

a r t i c l e

i n f o

Article history: Received 21 February 2012 Received in revised form 8 April 2012 Accepted 10 April 2012 Available online 19 April 2012 Keywords: Biosorption Tannin Platinum Palladium Terminalia catappa L.

a b s t r a c t A feasibility study was performed on Indian almond leaf biomass (Terminalia catappa L.) to remove palladium (Pd(II)) and platinum (Pt(IV)) ions from aqueous solution by biosorption. The biosorption characteristics of Pd(II) and Pt(IV) ions were investigated in terms of equilibrium, kinetics and thermodynamics. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature. Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) models were applied to describe the biosorption isotherm. The Langmuir model fitted the equilibrium data better than the Freundlich isotherm. Palladium is more preferable with T. catappa L. than platinum. The maximum biosorption capacity (qm) of T. catappa L. biomass for Pd(II) and Pt(IV) ions were 41.86 and 22.50, respectively. The mean free energy values evaluated from the D–R model indicated that the biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass took place by chemical ion-exchange. The calculated thermodynamic parameters DG0, DH0 and DS0 indicate that the biosorption of Pt(II) and Pd(II) ions onto T. catappa L. biomass is feasible, spontaneous and exothermic. Biosorption kinetics using pseudo-first-order and pseudo-secondorder kinetic models were also examined. Experimental data was found to be in good agreement with pseudo-second-order kinetics. Ó 2012 Elsevier B.V. All rights reserved.

1. Introduction Platinum group metals (PGMs), e.g. Pd and Pt, are precious metals which are widely used in industry because of their specific physical and chemical properties. PGM are of interest due to their high value and catalytic properties [1]. Because of the increasingly heavy industrial demand for these metals [2], their prices are likely to increase in the future [3]. Moreover, they are used as additives to improve the performance of catalysts in catalytic convertors, units that fit into the front part of the exhaust system of a vehicle to reduce the emissions of gaseous pollutants such as carbon monoxide, nitrogen oxide, and hydrocarbons [4]. They act mainly as promoters of the desired catalytic reactions, or serve as stabilizers against deterioration and aging [5]. The effective recovery of PGM from both natural ore and industrial waste is important from the standpoint of full utilization of resources. Solvent extraction [6] is a method traditionally used for PGM recovery. Alternatively, ion exchange [7], chemical precipitation [8], reverse osmosis [9], evaporation [10], membrane ⇑ Corresponding author. Tel./fax: +66 3421 9368. E-mail address: [email protected] (P. Ramakul). 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.04.035

separation [11], adsorption [12] and biosorption have been developed for the recovery of PGM from a solution. Among these methods, biosorption plays an especially important role in the elimination of metal ions from aqueous solutions for water pollution control [13]. The main advantages of this technique are the reusability of biomaterials [14], low operating cost [15], improved selectivity for specific metals of interest [16], removal of heavy metals from effluents irrespective of toxicity [17], short operation time, and no production of secondary compounds which might be toxic [13]. Adsorption seems to be the most suitable method for the recovery of low concentrations of PGM due to its low cost and high efficiency [18]. All of these reasons have stimulated research on the development of methods and adsorbents for effective recovery of these elements from both natural ore and industrial waste. Tannins – natural biomass containing multiple adjacent hydroxyl groups and exhibiting specific affinity to metal ions – can probably be used as an alternative, effective and efficient adsorbent for the recovery of metal ions. Tannins are widely distributed in the roots, bark, stalks and fruits of plants [19]. In recent years, interest in the development of adsorbents prepared from tannins has been increasing [20]. Tannins are an important class of secondary plant

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

103

Fig. 1. (a) Indian almond (Terminalia catappa L.) tree. (b) Leaves of Indian almond (Terminalia catappa L.) tree.

metabolites, water-soluble polyphenolic compounds of molecular weight ranging between 500 to several thousand Da [21]. However, because tannins are water-soluble compounds, when they are used directly as adsorbents for recovery of metals from aqueous systems they have the disadvantage of being leached by water [22]. To overcome this problem, attempts have been made to synthesize tannin to create a water-insoluble adsorbent. The Indian almond tannin used in this research was extracted from the leaves of Terminalia catappa L., also known as Indian almond, a large deciduous tree with smooth gray bark, a porous and fibrous pericarp, a hard endocarp enclosing edible seeds, and whorled branches [23] (Fig. 1). In Thailand, this tree is commonly planted in home gardens for ornamental purposes as well as for the leaves, which are rich in chemicals: the leaves contain several flavonoids, saponins and phytosterols [24], and a high tannin content of around 13% [25]. As far as the authors are aware, no investigation has yet reported on the biosorption of palladium (Pd(II)) and platinum (Pt(IV)) ions by the leaves of Indian almond (T. catappa L.). This material was chosen as a biosorbent for the present study because it is natural, easily available, and thus a low-cost biomass for adsorption of dissolved metal ions. In this work, leaves of Indian almond (T. catappa L.) biomass were used to remove and separate palladium (Pd(II)) and platinum (Pt(IV)) ions from aqueous solution by batch biosorption. Several parameters were investigated, such as pH, biomass dosage, contact time, and temperature. Langmuir, Freundlich, and Dubinin– Radushkevich (D–R) models were used to describe equilibrium isotherms. The mechanisms of biosorption of palladium (Pd(II)) and platinum (Pt(IV)) ions onto Indian almond leaf biomass were also demonstrated in terms of thermodynamics and kinetics.

2. Experimental procedures

was crushed and sieved through mesh of different sizes. Adsorbent sizes in a range of 100–150 lm were used in all experiments. This biomass adsorbent preparation method was proposed by Parajuli et al. [26]. 2.2. Reagents and equipment Platinum(IV) and palladium(II) supplied by Merck were used as feed solutions. Other chemicals – hydrochloric acid, sodium hydroxide, sodium bicarbonate, and sulfuric acid – were also purchased from Merck. All chemicals used in this study were analytical grade. Double-deionized water (Milli-Q; Millipore, Billerica MA, USA), 18.2 MO cm1 conductivity, was used for all dilutions. A pH meter with glass-tip electrode (pH Spear; Eutech Instruments, Singapore) was employed to measure pH values in the aqueous phase. Zeta potential values in the aqueous phase were measured using a Zeta Meter System 3.0+ (Zeta-Meter, Staunton VA, USA). In order to study the possible biosorption mechanism, the zeta potential of T. catappa L. biomass particles was measured before and after metal ion adsorption using a Zeta Meter microelectrophoretic apparatus. Inductively coupled plasma– Optical Emission Spectrometer (ICP-OES) (Optima 4300 DV; Perkin-Elmer, Waltham MA, USA) was used to determine the concentrations of platinum (Pt(IV)) and palladium (Pd(II)). Fourier transform infrared (FT-IR) spectra of dried unloaded biomass and Pt(IV)- and Pd(II)-loaded biomass were recorded using an Equinox 55 FT-IR spectrometer (Bruker Optics, Billerica MA, USA). Scanning electron microscopy (SEM) (JSM-5410LV; JEOL, Tokyo, Japan) was used to analyze the surface morphology of the adsorbent after adsorption. X-ray diffractometry (XRD) (D8 Discover; Bruker AXS, Billerica MA, USA) and energy-dispersive X-ray fluorescence spectrometry (EDX) (INCA 300; Oxford Instruments, Concord MA, USA) analysis were carried out to determine the pattern of metals adsorbed onto the adsorbent.

2.1. Biomass preparation 2.3. Batch biosorption procedure Indian almond (T. catappa L.) leaf samples were collected from Silpakorn University, Sanam Chandra Palace, Nakhon Pathom, Thailand. Samples were washed with deionized water and dried in an oven at 343.15 K for 48 h. The dried Indian almond leaf biomass was mixed with concentrated sulfuric acid at 373.15 K for 24 h, then neutralized with sodium bicarbonate solution, washed with distilled water, and dried in an oven at 343.15 K for 48 h. Finally, the adsorbent synthesized from Indian almond leaf biomass

Stock solution (1000 mg/L) of Pd(II) and Pt(IV) was prepared. Biosorption experiments were conducted using solutions of 50 ppm Pd(II) and 50 ppm Pt(IV), with an optimal biomass concentration of 2.5 g/L. Mixtures of platinum and palladium solutions were prepared by dissolving standard platinum and standard palladium solutions in deionized water and then further diluting to the various ppm concentrations used in the experiments. Solution

104

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

samples (20 mL) including the biomass were shaken at 120 rpm for the desired contact times by an electrically thermostatic reciprocating shaker (Selecta Multimatic-55; Barcelona, Spain). Batch studies were performed under a range of conditions: initial metal concentration (20–300 ppm), contact time (5–300 min), pH (1.0–5.0), biomass concentration (0.25–10 g/L), and temperature (293–323 K). The equilibrium time was estimated by drawing samples at regular time intervals until equilibrium was reached. The contents of the flasks were filtered through a 0.25 lm filter (Double-Ring; Hangzhou, China). The concentrations of platinum and palladium in the filtrate were analyzed by ICP-OES. Experiments were done in triplicate, and mean results were used in the analysis. The percentages of biosorption of metal ions were calculated by:

%Biosorption ¼

Cf  Ci  100 Cf

ð1Þ

where Ci and Cf are the initial and final metal ion concentrations, respectively.

In order to investigate the mechanism of the adsorption process, models of intraparticle diffusion, pseudo-first-order adsorption and pseudo-second-order adsorption were used to test adsorption rate data. The intraparticle diffusion model [27] is shown in Eq. (2):

ð2Þ

where qt is the amount of metal ions adsorbed on the adsorbent (mg/g) at time t, and k1 is the intraparticle diffusion rate constant (mg/g min0.5) which is obtained when we plot qt versus t0.5. The pseudo-first-order rate model [27] is expressed in Eq. (3) as:

lnðqe  qt Þqt ¼ ln qe  k2 t

DG0 ¼ RT ln K D

ð6Þ

where R is the universal gas constant (8.314 J/mol K), T is the temperature (K) and KD is the distribution coefficient [29,30]. However, since activity coefficients have not been incorporated, the shifted free energy, DG0, can be calculated. The Gibbs free energy change (DG0) is related to the standard enthalpy and extraction entropy changes (DH0 and DS0) through the Gibbs– Helmholtz equation. The relationship of Gibbs free energy with the enthalpy and entropy is as follows in the following equation:

DG0 ¼ DH0  T DS0

ð7Þ

ln K D ¼ 

DH 0 DS0 þ RT R

ð8Þ

The enthalpy (DH0) and entropy (DS0) are estimated from Eq. (8) by plotting KD against T1. A plot of ln KD versus 1/T should give a straight line, and the standard enthalpy change is calculated from the slope. The equilibrium constant is proportional to KD. Thus, slopes of ln KD versus 1/T plots would yield the standard enthalpy change [33]. 3. Results and discussion 3.1. Influence of initial pH

ð3Þ

where qe and qt are the amounts of metal ions adsorbed on the adsorbent (mg/g) at equilibrium and at time t, respectively, and k2 is the rate constant (min1). The pseudo-second-order rate model [28] is given in the following equation:

t 1 t ¼ þ t qt k3 q2e qe

In order to describe the thermodynamic behavior of the biosorption of Pd(II) and Pt(IV) ions onto T. catappa L. biomass, thermodynamic parameters – including the changing of free energy (DG0), enthalpy (DH0) and entropy (DS0) – were calculated from the following equation:

Substituting Eq. (7) into Eq. (6) results in van’t Hoff’s equation [31,32] in linear form, and is shown as:

2.4. Biosorption kinetics

qt ¼ k1 t 0:5

2.6. Biosorption thermodynamics

ð4Þ

where k3 is the constant of the pseudo-second-order rate (g/ mg min), which is obtained by plotting qtt versus t.

The pH of a solution is the main factor affecting metal adsorption behavior. Experiments were performed using solutions of different pH, ranging from 1.0 to 5.0. Initial metal concentrations were fixed at 50 mg/L, while biomass adsorbent dosages were 0.2 g and solution volumes were 20 mL at room temperature. As shown in Fig. 2, the results demonstrated that the optimum pH for adsorption of palladium and platinum was 2.0. When the pH of the solution was increased from 1.0 to 2.0, the percentage of biosorption of palladium and platinum increased. This can be explained by the chemical mechanism of the adsorption process. In general, the adjacent phenolic hydroxyls of tannins are able to chelate metal ions in solution. The degree of ionization

2.5. Biosorption isotherm models Biosorption equilibrium data were fitted for linear Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The Langmuir model represents one of the first theoretical treatments of nonlinear sorption, and suggests that uptake occurs on a homogeneous surface by monolayer sorption without interaction between adsorbed molecules. The shape of the isotherm curves indicates that they might be described by the Langmuir equation [28]:

Ce Ce 1 ¼ þ qe qmax kqmax

ð5Þ

where qe and Ce are the amount adsorbed (mg/g) at equilibrium and the concentration at equilibrium (mg/L), and qmax and k are Langmuir constants related to adsorption capacity (mg/g) and adsorption energy, respectively. A straight line was obtained by plotting Cqe versus Ce. e

Fig. 2. The influence of pH on the biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass (metal concentration: 50 mg/L; temperature: 303.15 K).

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

105

Table 1 The average zeta potential of palladium and platinum ions obtained at various pH values. pH

1 2 3 4 5

Temperature (K)

303.15 303.15 303.15 303.15 303.15

Zeta potential analysis (mV) Pd(II)

Pt(IV)

26.7 49.8 29.1 27.5 23.4

25.8 42.3 28.5 25.4 20.1

of phenolic hydroxyls increases with increasing pH value, which leads to greater adsorption capacity of metal ions. High ionization degree of phenolic hydroxyls and high cationic charge of metal species favor the reaction. Nevertheless, a decrease in the percentage of biosorption was observed when the pH was higher than 2.0. In this case the charge of metal species is changed from cationic species to neutral species; therefore, the adsorption capacity of metal ions is reduced [34–36]. Fig. 2 also indicates that the optimal pH for biosorption of platinum and palladium biomass adsorbent was 2.0. Zeta potential is one of the most useful parameters to characterize the surface charge of biomaterials; there is a close relationship between zeta potential and biosorption capacity. Zeta potential values were determined at various pH for platinum and palladium ion solutions in deionized water. The zeta potential of T. catappa L. biomass particles at pH 1.0, 2.0, 3.0, 4.0 and 5.0 are shown in Table 1 for platinum and palladium ion solutions. These results demonstrate that the zeta potential of T. catappa L. biomass depends on the pH of the solution, with a negative charge at all pH values. Zeta potential measurement gives an idea of the surface charge associated with the particles. The particle charge is one of the factors that determine the physical stability of emulsions and suspensions. Large negative or positive zeta potentials of particles in suspension will cause them to repel each other; thus there is no tendency to flocculate. However, if the particles have low zeta potential values then there is no force to prevent the particles from coming together and flocculating. The general dividing line between stable and unstable suspensions is generally taken to be either +30 mV or 30 mV. Particles with zeta potentials more positive than +30 mV or more negative than 30 mV are normally considered stable. As can be seen from SEM micrographs and zeta potentials, there is stability on biosorption of T. catappa L. biomass particles obtained at temperature = 303.15 K and pH = 2.0. Hence, the initial pH was fixed at 2.0 for all further adsorption experiments.

Fig. 3. The influence of contact time on the biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass (metal concentration: 50 mg/L; biomass dosage: 2.5 g/L; pH: 2.0; temperature: 303.15 K).

3.3. Influence of initial metal concentration The effect of initial metal concentration on adsorption was investigated for 11 different concentrations of metal (20–220 mg/ L) in aqueous solution. As shown in Fig. 4, when the initial concentrations of palladium and platinum increased from 20 to 70 ppm and from 20 to 80, respectively, the percentage of biosorption increased; this is because when the initial concentration is low, there is a lot of unoccupied surface area [35]. For higher concentrations (80–220 ppm), the increasing of initial concentration of metal led to the maximum capacity of biomass adsorption. All adsorbent sites were occupied by palladium and platinum [39]. Therefore, since there could be no further increase of capacity, the percentage of biosorption decreased. As the results in Fig. 4 indicate, the optimal initial metal concentrations for complete separation of palladium and platinum by 0.05 g biomass adsorbent were 60 and 70 ppm, respectively; the maximum adsorption capacities were 41.23% and 75.12%, respectively, at room temperature. This strongly suggests that T. catappa L. is an effective biomass adsorbent that can selectively adsorb and separate palladium and platinum from a mixture solution.

3.4. Influence of biomass adsorbent concentration The effect of biomass adsorbent dose on the adsorption capacity of platinum and palladium are shown in Fig. 5. An increase of biomass adsorbent (from 0.0125 to 0.0500 g) generally increases the

3.2. Influence of contact time Experimental studies were carried out with varying contact times. The initial metal concentration was 50 mg/L, with a biomass adsorbent dosage of 0.05 g, 20 mL solution volume, and pH of 2.0 at room temperature. The effect of contact time on the adsorption of platinum and palladium by biomass adsorbent is shown in Fig. 3. It is evident that adsorption occurs very rapidly during the initial contact time. Therefore, we can infer that the biomass adsorbent is mainly located at the outer surface, and thus the diffusion resistance of mass transfer during the adsorption process is negligible due to the rapid adsorption process [37,38]. The results demonstrated that adsorption capacity increased with increasing contact time, and reached equilibrium after 20 h for platinum and 30 h for palladium. When the system is in a state of equilibrium, it is important to establish the capacity of the biomass adsorbent for the metal. Therefore, the optimal contact time for complete separation of platinum and palladium by the biomass adsorbent was 30 h.

Fig. 4. The influence of initial metal concentration on the biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass (biomass dosage: 2.5 g/L; pH: 2.0; temperature: 303.15 K).

106

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

Fig. 5. The influence of biomass adsorbent concentration on the biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass (metal concentration: 50 mg/L; pH: 2.0; temperature: 303.15 K).

amount of metal adsorbed. Due to the increased surface area of the biomass adsorbent, the number of binding sites increases [35]. As the amount of biomass adsorbent increases, the total adsorbed metal increases until ultimately becoming constant. Therefore, the relationship between the amount of biomass adsorbent and metal adsorbed is close to a hyperbolic curve [40]. The maximum selective separation of palladium from platinum was achieved using 1.0 g adsorbent with 1400 ppm of initial metal concentration. Thus this ratio of 1 g to 1400 ppm was used in all experiments.

3.5. Mechanism of reaction between metal and biomass adsorbent 3.5.1. FT-IR analysis and SEM micrographs FT-IR spectra of the biomass adsorbent before and after adsorption are shown in Fig. 6. The adsorption bands of tannin particles at 3600–3000 (OAH), 1620–1610 (C@C), 1460–1440 (C@C) and 1300–1100 (CAH) cm1 are ascribed to the chemical structure of the condensed tannin molecule [30]. From Fig. 6, in the case of the FT-IR spectrum after adsorption, the band at 1720– 1710 cm1 (carbonyl groups) increased. This result suggests that the hydroxyl groups of the biomass adsorbent are oxidized to carbonyl groups [41,42]. SEM micrographs of the biomass adsorbent

Fig. 7. (a) SEM micrograph of biomass adsorbent before adsorption; (b) SEM micrograph of biomass adsorbent after adsorption (metal concentration: 50 mg/L; biomass adsorbent dosage: 2.5 g/L; initial pH: 2.0; operating temperature: 303.15 K; solution volume: 20 mL; contact time: 48 h).

before and after adsorption are shown in Fig. 7. It is evident that the metallic particles were adsorbed by the biomass adsorbent. 3.5.2. XRD and EDX patterns Figs. 8 and 9 show the XRD and EDX patterns of palladium adsorbed at pH 2.0 at room temperature. In the XRD pattern, several peaks are clearly observed at 2h = 12.997°, 26.166°, 37.334°,

Fig. 6. FT-IR spectra of the biomass adsorbent particles before and after adsorption (metal concentration: 50 mg/L; biomass adsorbent dosage: 2.5 g/L; initial pH: 2.0; operating temperature: 303.15 K; solution volume: 20 mL; contact time: 48 h).

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

107

Fig. 8. XRD pattern of palladium adsorbed onto the biomass adsorbent (metal concentration: 50 mg/L; biomass adsorbent dosage: 2.5 g/L; initial pH: 2.0; operating temperature: 303.15 K; solution volume: 20 mL; contact time: 48 h).

39.691° and 46.161°, which means crystallization of reduced metallic palladium on the biomass adsorbent [43]. This indicates that only palladium ions in mixture aqueous solution can be reduced to metallic palladium on the biomass adsorbent during adsorption, as in Eq. (9). The results of FT-IR spectra, XRD and EDX analysis indicate a redox reaction between the biomass adsorbent and palladium ions. This is responsible for the reduction of palladium ions (Pd2+) to metallic palladium (Pd0), and the oxidation of hydroxyl groups of the biomass adsorbent to carbonyl groups [35,43]. The following reactions are proposed:

RAOH ! R@O þ Hþ þ e 2þ

Pd

þ 2e ! Pd

ð9Þ ð10Þ

In fact, it has been reported that the adsorption amount and mechanisms are influenced by speciation of the metals. Anionic  Pd species (PdClÞ42 ; PdCl3 ) are more favorable than cationic species (PdCl+) or the nonionic form (PdCl2) [43], while cationic Pd species are more favorable than anionic Pt species. Thus, biomass adsorbent can selectively separate palladium from platinum in mixture aqueous solution. Furthermore, the maximum adsorption capacity of palladium in binary metal ions tested on biomass

adsorbent was high (17.20 mg/g) compared to the adsorption of single metal ions by nanometer-size titanium dioxide (11.82 mg/ g), Fe3O4 nanoparticles (10.96–11.00 mg/g), modified nanometersized alumina (7.60 mg/g) and crosslinked carboxymethyl chitosan hydrogels (1.053 mg/g) [44,45].

3.6. Biosorption kinetics Fig. 10 shows the adsorption rates of Pt(IV) and Pd(II) on biomass adsorbent at different temperatures. A fast adsorption rate was observed at the beginning of the adsorption period. After that it slowed down and approached equilibrium. It was found that the adsorption equilibrium at 303.15 K was attained in about 60 min for Pt(IV) and 240 min for Pd(II). As temperature increased, the adsorption capacity also increased, but the time to attain adsorption equilibrium was prolonged. This might be due to the fact that a part of the adjacent phenolic hydroxyls of tannin, which associate with collagen fiber through hydrogen bonds, were released at higher temperature, and therefore more adsorption sites were available. Table 2 lists the results of rate constants investigated by the models. The correlation coefficient (R2) for the pseudosecond-order adsorption model has higher values (>0.980), and

Fig. 9. EDX pattern of palladium adsorbed onto the biomass adsorbent (metal concentration: 50 mg/L; biomass adsorbent dosage: 2.5 g/L; initial pH: 2.0; operating temperature: 303.15 K; solution volume: 20 mL; contact time: 48 h).

108

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

equilibrium adsorption capacities of Pd(II) and Pt(IV) were 41.86 and 22.50 mg/g, respectively. The parameters of the Langmuir Equation in Eq. (5) for experimental data are presented in Table 3. The correlation coefficients (R2) are 0.9911 for Pd(II) and 0.9914 for Pt(IV). The calculated values of qmax are close to those actually determined. These results imply that the adsorption mechanism might be monolayer coverage of Pd(II) or Pt(IV) on the outer surface of the adsorbent. 3.8. Biosorption thermodynamics In order to describe the thermodynamic behavior of the biosorption of Pd(II) and Pt(IV) ions onto T. catappa L. biomass, thermodynamic parameters – including the change in free energy (DG0), enthalpy (DH0) and entropy (DS0) – must be calculated. According to Eq. (8), when 1T is plotted as a function of ln KD for different temperatures (shown in Fig. 12), a straight line is obtained 0

Fig. 10. Adsorption rates of (a) Pd(II) and (b) Pt(IV). Initial concentrations of Pd(II) and Pt(IV): 50 mg/L and 50 mg/L; solution volume: 100 mL.

the adsorption capacities calculated by the model are close to those determined by experiments. Moreover, the correlation coefficients (R2) of pseudo-first-order and intraparticle diffusion models were not satisfactory. Thus, it can be concluded that the pseudosecond-order adsorption model could be used to describe the adsorption rates of Pt(IV) and Pd(II) on biomass adsorbent. Based on the adsorption kinetics data shown in Table 2, the activation energy of the adsorption process can be determined according to the Arrhenius equation for Pd(II) and Pt(IV) were 24.6 and 35.7 kJ/moll, respectively. Therefore, the adsorption of Pd(II) and Pt(IV) on the biomass adsorbent can easily take place since their activation energies are less than 47 kJ/mol [34]. Looking at the behavior over the whole adsorption process, it is likely to agree with an adsorption mechanism being the rate-controlling step [28,46]. 3.7. Biosorption isotherm models Fig. 11 illustrates the adsorption isotherms of Pd(II) and Pt(IV) on biomass adsorbent at 303 K and optimal pH value. The

0

with a slope of  DHR and an ordinate of DRS . The values of DH0 and DS0 can be calculated from the slope and ordinate, respectively. Gibbs free energy change (DG0), as calculated by Eq. (6), was found to be 16.8, 15.0, 13.7, and 12.1 kJ/mol for Pd(II) biosorption and 20.7, 19.6, 18.6, and 17.9 kJ/mol for Pt(IV) biosorption at 293.15, 303.15, 313, and 323.15 K, respectively. The negative DG0 values indicate the thermodynamically feasible and spontaneous nature of the biosorption. The decrease in DG0 values with an increase in temperature shows a decrease in feasibility of biosorption at higher temperatures. The DH0 parameters were found to be 48.3 and 52.5 kJ/mol for Pd(II) and Pt(IV) biosorption, respectively. The negative DH0 indicates the exothermic nature of the biosorption processes at 293.15–323.15 K. The DS0 parameters were found to be 97.8 J/mol K for Pd(II) biosorption and 105.2 J/mol K for Pt(IV) biosorption. The negative DS0 value suggests a decrease in randomness at the solid/solution interface during the biosorption process. 3.9. Binary metal adsorption studies The effect of the presence of the competing ions on Pd(II) and Pt(IV) removal was observed using kinetic and equilibrium experiments. Pd(II) and Pt(IV) ion concentrations were 50 and 50 mg/L, respectively, for the binary kinetic experiment. As shown in Fig. 13, removal rates from the experimental results for the binary component system were slightly lower than those for singlecomponent solutions. Biosorptive removal in binary solutions was reduced to 74.40% and 21.40% for Pd(II) and Pt(IV), respectively. Binary ion isotherm studies were carried out using nine adsorbate concentrations that varied from 1 to 5 g/L for each metal. Fig. 14 shows the results of binary metal ion isotherm studies. Each isotherm experiment consisted of both metals at the same

Table 2 Adsorption kinetic parameters of T. catappa L. biomass to Pt(IV) and Pd(II). Temperature (K)

a b

qea

Intraparticle diffusion model 2

First-order kinetic model

k1

R

k2  10

2

2

Second-order kinetic model

R

k3  104

R2

qeb

Pd(II) 293.15 303.15 313.15 323.15

30.60 40.90 47.20 56.17

2.09 3.05 3.65 4.49

0.9420 0.9020 0.8840 0.8513

1.42 2.63 3.17 4.16

0.9510 0.9630 0.9580 0.9643

9.36 10.00 14.10 15.89

0.9930 0.9980 0.9970 0.9970

35.60 45.50 54.60 64.23

Pt(IV) 293.15 303.15 313.15 323.15

22.50 28.80 36.00 45.20

1.24 1.44 1.83 2.22

0.9840 0.9860 0.9660 0.9846

1.46 0.76 0.59 0.42

0.9380 0.9490 0.9440 0.9490

3.67 4.57 4.85 5.13

0.9800 0.9940 0.9970 0.9970

28.00 30.30 37.30 44.30

Experimental data. Pseudo-second-order model.

109

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

a

50 45 40

qe (mg/g)

35 30 25 20 15

Pd

10 Pt

5 0 0

10

20

30

40

50

Ce (mg/L)

qe/Ce (g/L)

b

1.8 1.6

Pd

1.4

Pt

1.2

y = 0.0361x + 0.1355 2 R = 0.9979

Fig. 13. Binary removal of Pd(II) and Pt(IV) on T. catappa L. biomass (metal concentration: 50 mg/L; biomass adsorbent dosage: 2.5 g/L; initial pH: 2.0; operating temperature: 303.15 K; solution volume: 20 mL; contact time: 48 h).

Linear

1 0.8 y = 0.0212x + 0.0401

0.6

2

R = 0.9996

0.4 0.2 0 0

10

20

30

40

50

Ce (mg/L) Fig. 11. Adsorption isotherms of Pd(II) and Pt(IV) on T. catappa L. biomass: (a) adsorption isotherms and (b) Langmuir fitting. Temperature: 303.15 K; adsorbent dose: 2.5 g. Table 3 Langmuir parameters of Pt(IV) and Pd(II) adsorbed by T. catappa L. biomass.

Pd(II) Pt(IV) a b

qea

qmaxb

k

R2

40.90 28.80

47.17 27.70

0.57 0.27

0.9996 0.9979

Experimental data. Langmuir Equation.

9 8.5

ln KD

8

y = 6326.2x - 12.744 Pd

Fig. 14. Binary adsorption isotherms of Pd(II) and Pt(IV) on T. catappa L. biomass (metal concentration: 50 mg/L; biomass adsorbent dosage: 2.5 g/L; initial pH: 2.0; operating temperature: 303.15 K; solution volume: 20 mL; contact time: 48 h).

Table 4 Selected properties of metal ions.

2

R = 0.9951

Pt

Metal property

Pd(II)

Pt(IV)

Linear

Atomic number Atomic weight (g/mol) Ionic radius (nm) Hydrated radius (nm) Electronegativity (Pauling scale) Ionic potential (charge (–)/radius (nm)) Hydration enthalpy (kJ/mol) Electron configuration

46 106.42 0.137 0.163 2.20 14.60 48.30 [Kr]4d105s0

78 195.09 0.096 0.175 2.28 41.67 52.50 [Xe]4f145d96s1

7.5

y = 5804.3x - 11.492 2

R = 0.9976

7 6.5

6 0.00305 0.0031 0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 0.00345

(1/T) (1/K) Fig. 12. Plot of ln KD versus 1/T for the estimation of thermodynamic parameters for biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass.

concentrations. The maximum adsorbed amount of Pd(II) and Pt(IV) ions by T. catappa L. biomass in binary solutions was significantly reduced (37.20 and 10.70 mg/g for Pd(II) and Pt(IV), respectively) when compared to single metal sorption studies. Adsorption was constrained by the presence of other metal ions. The decrease of the adsorbed amount of metal ions in binary solutions can be attributed to the competition of each metal ion. The different affinity of certain metal ions to adsorption sites can be explained by their ionic properties such as ion radius, charge, ionic potential, electronegativity, and electron configuration. These properties of metal ions are given in Table 4. Ionic potential gives

the sense of how strongly or weakly an ion will be electrostatically attracted to ions of opposite charge, and is given as the ratio of electric charge to the radius of an ion. Electronegativity is a chemical property that describes the ability of an atom (or, more rarely, a functional group) to attract electrons (or electron density) toward itself in a covalent bond. Metal adsorption capacity on the T. catappa L. biomass surface was increased with metal electronegativity. The electronegativity and ionic potential for Pd(II) were slightly higher than for Pt(IV). This means that Pd(II) ions interact more strongly electrostatically with the surface groups present on the surface of the adsorbent. On the other hand, the tendency to lose water molecules from the cations must be stronger for Pd(II) since the single ion hydration enthalpies (DH0) are 48.3 and 52.5 kJ/ mol for Pd(II) and Pt(IV) biosorption, respectively. This also facilitates the interaction between Pd(II) and the T. catappa L. biomass surface. Another factor, which may determine the metal adsorption

110

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111

capacity, is the ionic radius itself. Smaller ions with the same valence have higher charge densities and attract more water molecules, resulting in a larger hydrated radius [46,47]. Because of this, Pd(II) ions have a larger ionic radius and consequently a smaller hydrated radius than Pt(IV) ions. Therefore, it can be said that Pd(II) ions can penetrate into smaller pores, and thus have greater access to the T. catappa L. biomass surface. As a result, single metal ion adsorption interfered with the uptake of another ion in the system, and the overall total uptake for each metal was slightly lower than that in the single-ion system. This indicated that Pd(II) ions had a relatively stronger affinity than Pt(IV) ions. 4. Conclusion A low-cost biosorbent, Indian almond leaves (T. catappa L.), can selectively adsorb palladium and platinum from aqueous solution. Palladium reacts more preferably with T. catappa L. than platinum. The operating parameters – pH of solution, biomass dosage, contact time, and temperature – affected biosorption efficiency. The monolayer biosorption capacity of T. catappa L. biomass was found to be 22.50 and 41.86 mg/g for Pd(II) and Pt(IV) ions, respectively. Mean free energy values evaluated from the D–R model indicated that the biosorption of Pd(II) and Pt(IV) onto T. catappa L. biomass took place by chemical ion-exchange. The interactions between metal ions and functional groups on the biomass surface were estimated by FT-IR spectroscopy analysis. Kinetic evaluation of the equilibrium data showed that the biosorption of platinum and palladium ions on T. catappa L. biomass fit well with the pseudosecond-order kinetic model. Thermodynamic calculations indicated the feasibility as well as the spontaneous and exothermic nature of the biosorption process at 293.15–323.15 K. Acknowledgements The authors greatly appreciate financial support from the Thailand Research Fund (TRF) and the Commission on Higher Education (Grant No. MRG5380236), as well as the Silpakorn University Research and Development Institute (SURDI). We also wish to thank the Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Thailand, for chemical and apparatus support. References [1] K. Ravindra, L. Bencs, R. van Grieken, Platinum group elements in the environment and their health risk, Sci. Total Environ. 318 (2004) 1–43. [2] A.B. Boricha, H.C. Bajaj, P.K. Ghosh, R.V. Jasra, Recovery of palladium from palladium phthalocyanine complex adsorbed on silica, Hydrometallurgy 87 (2007) 140–147. [3] J. Kielhorn, C. Melber, D. Keller, I. Mangelsdorf, Palladium – a review of exposure and effects to human health, Int. J. Hyg. Environ. Health 205 (2002) 417–432. [4] C. Melber, D. Keller, I. Mangelsdorf, Palladium: Environmental Health Criteria, World Health Organization, Geneva, 2002. p. 222. [5] K.H. Ek, G.M. Morrison, S. Rauch, Environmental routes for platinum group elements to biological materials – a review, Sci. Total Environ. 334–335 (2004) 21–38. [6] J.R. Kumar, H.I. Lee, J.Y. Lee, J.S. Kim, J.S. Sohn, Comparison of liquid-liquid extraction studies on platinum(IV) from acidic solutions using bis(2,4,4trimethylpentyl) monothiophosphinic acid, Sep. Purif. Technol. 63 (2008) 184– 190. [7] E.R. Els, L. Lorenzen, C. Aldrich, The adsorption of precious metals and base metals on a quaternary ammonium group ion exchange resin, Min. Eng. 13 (2000) 401–414. [8] M. McDonald, I. Mila, A. Scalbert, Precipitation of metal ions by plant polyphenols: optimal conditions and origin of precipitation, J. Agric. Food Chem. 44 (1996) 599–606. [9] J.E. Hoffman, Recovering platinum-group metals from auto catalysts, J. Met. 40 (1988) 40–44. [10] C.S. Brooks, Metal Recovery from Industrial Waste, Lewis Publishers, Chelsea, MI, 1991. p. 267.

[11] W. Patthaveekongka, N. Vijitchalermpong, U. Pancharoen, Selective recovery of palladium from used aqua regia by hollow fiber supported with liquid membrane, Korean J. Chem. Eng. 20 (2003) 1092–1096. [12] A. Uheida, M. Iglesias, C. Fontas, M. Hidalgo, V. Salvado, Y. Zhang, M. Muhammed, Sorption of palladium(II), rhodium(III), and platinum(IV) on Fe3O4 nanoparticles, J. Colloid Interface Sci. 301 (2006) 402–408. [13] X.Q. Chen, K.F. Lam, K.L. Yeung, Selective removal of chromium from different aqueous systems using magnetic MCM-41 nanosorbents, Chem. Eng. J. 172 (2011) 728–734. [14] X.Q. Chen, K.F. Lam, Q.J. Zhang, B.C. Pan, M.N. Arruebo, K.L. Yeung, Synthesis of highly selective magnetic mesoporous adsorbent, J. Phys. Chem. C 113 (2009) 9804–9813. [15] K.F. Lam, H. Kassab, M. Pera-Titus, K.L. Yeung, B. Albela, L. Bonneviot, MCM-41 ‘‘LUS’’: alumina tubular membranes for metal separation in aqueous solution, J. Phys. Chem. C 115 (2011) 176–187. [16] K.F. Lam, K.L. Yeung, G.D. McKay, An investigation of gold adsorption from a binary mixture with selective mesoporous silica adsorbents, J. Phys. Chem. B 110 (5) (2006) 2187–2194. [17] K.F. Lam, C.M. Fong, K.L. Yeung, G. McKay, Selective adsorption of gold from complex mixtures using mesoporous adsorbents, Chem. Eng. J. 145 (2008) 185–195. [18] X.Q. Chen, K.F. Lam, S.F. Mak, K.L. Yeung, Precious metal recovery by selective adsorption using biosorbents, J. Hazard. Mater. 186 (2011) 902–910. [19] H.M. Burkill, The useful plants of west tropical Africa, Families A–D, vol. 1, University of Virginia Press, Charlottesville, VA, 1985. [20] J.K. Francis, Terminalia catappa L., Combretaceae: Indian Almond, Almendra, Combretum Family, Institute of Tropical Forestry, Rio Piedras, San Juan, Puerto Rico, 1989. [21] H.P.M. Gunasena, Kottamba: Terminalia catappa L., in: D.K.N.G. Pushpakumara, H.P.M. Gunasena, V.P. Singh (Eds.), Underutilized Fruit Trees in Sri Lanka, World Agroforestry Centre, South Asia Office, New Delhi, India, 2007, pp. 437–451. [22] D.K.N.G. Pushpakumara, H.P.M. Gunasena, V.P. Singh (Eds.), Underutilized Fruit Trees in Sri Lanka, World Agroforestry Centre, South Asia Office, New Delhi, India, 2007. pp. 437-451. [23] D.F. Hayward, The phenology and economic potential of Terminalia catappa L. in south-central Ghana, Vegetation 90 (1990) 125–131. [24] T.C. Lin, F.L. Hsu, Tannin and related compounds from Terminalia catappa and Terminalia parviflora, J. Chin. Chem. Soc. 46 (1999) 613–618. [25] Y.L. Lin, Y.H. Kuo, M.S. Shiao, C.C. Chen, J.C. Ou, Flavonoid glycosides from Terminalia catappa L, J. Chin. Chem. Soc. 47 (2000) 253–256. [26] D. Parajuli, H. Kawakita, K. Inoue, K. Ohto, K. Kajiyama, Persimmon peel gel for the selective recovery of gold, Hydrometallurgy 87 (2007) 133–139. [27] M.S. Chiou, H.Y. Li, Adsorption behavior of reactive dye in aqueous solution on chemical cross-linked chitosan beads, Chemosphere 50 (2003) 1095. [28] Y.S. Ho, G. McKay, Pseudo-second-order model for sorption processes, Process Biochem. 34 (1999) 451–465. [29] A.D. Westland, E.O. Otu, The thermodynamics of extraction of some lanthanide and other ions by 2-ethylhexylhydrogen-p-phenylphosphonate, Solvent Extr. Ion Exch. 9 (1991) 607–621. [30] E.O. Otu, A.D. Westland, The thermodynamics of extraction of some lanthanides and other ions by dinonylnaphthalene sulfonic acid, Solvent Extr. Ion Exch. 8 (1990) 827–842. [31] W. Greiner, L. Neise, H. Stöcker, Thermodynamics and Statistical Mechanics, Springer-Verlag, Berlin and Heidelberg, 1995. p. 101. [32] F. Angulo-Brown, L. Arias-Hernández, Van’t Hoff’s equation for endoreversible chemical reactions, J. Phys. Chem. 100 (1996) 9193–9195. [33] E.O. Otu, The thermodynamics of synergistic extraction of bismuth by 2ethylhexyl phenylphosphonic acid and micelles of dinonyl naphthalene sulfonic acid, Thermochim. Acta 329 (1999) 117–121. [34] C. Mack, B. Wilhelmi, J.R. Duncan, J.E. Burgess, Biosorption of precious metals, Biotechnol. Adv. 25 (2007) 264–271. [35] N. Das, Recovery of precious metals through biosorption – a review, Hydrometallurgy 103 (2010) 180–189. [36] H. Ma, X. Liao, X. Liu, B. Shi, Recovery of platinum(IV) and palladium(II) by bayberry tannin immobilized collagen fiber membrane from water solution, J. Membrane. Sci. 278 (2006) 373–380. [37] I.A. S ß engil, M. Özacar, H. Türkmenler, Kinetic and isotherm studies of Cu(II) biosorption onto valonia tannin resin, J. Hazard. Mater. 162 (2009) 1046– 1052. [38] X. Huang, X. Liao, B. Shi, Hg(II) removal from aqueous solution by bayberry tannin-immobilized collagen fiber, J. Hazard. Mater. 170 (2009) 1141–1148. [39] K. Fujiwara, A. Ramesh, T. Maki, H. Hasegawa, K. Ueda, Adsorption of platinum(IV), palladium(II) and gold(III) from aqueous solutions onto Llysine modified crosslinked chitosan resin, J. Hazard. Mater. 146 (2007) 39–50. [40] A. Nakajima, T. Sakaguchi, Uptake and recovery of gold by immobilised persimmon tannin, J. Chem. Technol. Biotechnol. 57 (1993) 321–326. [41] T. Ogata, Y. Nakano, Mechanisms of gold recovery from aqueous solutions using a novel tannin gel adsorbent synthesized from natural condensed tannin, Water Res. 39 (2005) 4281–4286. _ [42] M. Özacar, I.A. Sßengil, H. Türkmenler, Equilibrium and kinetic data, and adsorption mechanism for adsorption of lead onto valonia tannin resin, Chem. Eng. J. 143 (2008) 32–42. [43] Y.H. Kim, Y. Nakano, Adsorption mechanism of palladium by redox within condensed-tannin gel, Water Res. 39 (2005) 1324–1330.

P. Ramakul et al. / Chemical Engineering Journal 193–194 (2012) 102–111 [44] A. Ramesh, H. Hasegawa, W. Sugimoto, T. Maki, K. Ueda, Adsorption of gold(III), platinum(IV) and palladium(II) onto glycine modified crosslinked chitosan resin, Bioresour. Technol. 99 (2008) 3801–3809. [45] A. Sari, D. Mendil, M. Tuzen, M. Soylak, Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies, J. Hazard. Mater. 162 (2009) 874–879.

111

[46] Y.S. Ho, G. McKay, The sorption of lead(II) ions on peat, Water Res. 33 (1999) 578–584. [47] O. Etci, N. Bektasß, M.S. Öncel, Single and binary adsorption of lead and cadmium ions from aqueous solution using the clay mineral beidellite, Environ. Earth Sci. 61 (2010) 231–240.