International Journal of Science, Engineering and Technology[et_pb_section transparent_background=”off” allow_player_pause=”off” inner_shadow=”off” parallax=”off” parallax_method=”on” custom_padding=”24px|0px|0px|0px” padding_mobile=”off” make_fullwidth=”off” use_custom_width=”off” width_unit=”off” custom_width_px=”1080px” custom_width_percent=”80%” make_equal=”off” use_custom_gutter=”off” fullwidth=”off” specialty=”off” admin_label=”section” disabled=”off”][et_pb_row make_fullwidth=”off” use_custom_width=”off” width_unit=”off” custom_width_px=”1080px” custom_width_percent=”80%” use_custom_gutter=”off” gutter_width=”3″ custom_padding=”5px|0px|0px|0px” padding_mobile=”off” allow_player_pause=”off” parallax=”off” parallax_method=”on” make_equal=”off” column_padding_mobile=”on” parallax_1=”off” parallax_method_1=”on” parallax_2=”off” parallax_method_2=”on” parallax_3=”off” parallax_method_3=”on” parallax_4=”off” parallax_method_4=”on”][et_pb_column type=”4_4″ parallax=”off” parallax_method=”on” column_padding_mobile=”on”][et_pb_text background_layout=”light” text_orientation=”left” header_font_size=”30px”]
Removal of Pb(II) from Aqueous Solution Using Fruits Peel as a Low Cost Adsorbent
Authors- Swarnabala Jena, Rajesh Kumar Sahoo
Author’s details
Department of chemistry, College of Basic Science& Humanities, Odisha University of Agriculture & Technology, Bhubaneswar.
Email:- swarnajena.chem@gmail.com
Copy for Cite this Article- Swarnabala Jena, Rajesh Kumar Sahoo “Removal Of Pb(Ii) From Aqueous Solution Using Fruits Peel As A Low Cost Adsorbent”, International Journal of Science, Engineering and Technology, Volume 5 Issue 1: 2017, pp. 05- 13.
Abstract
Adsorption of Pb(II) ions onto four different fruits peel i.e. orange, lemon, banana, water melon were investigated with the variation in the parameters of pH ,contact time , initial metal ion concentration, adsorbent dose and temperature. Batch adsorption studies indicated maximum of 91%, 94%, 92%, 96% adsorption capacity for orange, lemon, banana, and watermelon respectively. SEM study gives a detailed morphology of the fruits peel. FTIR study of adsorbents at the optimized condition was carried out using JASCO-410 model IR spectrometer to identify the different functional groups that are responsible for the adsorption. The important functional groups like hydroxyl, alkenes, aromatic nitro, carboxyl ate anion, ester, silicon oxide, sulphonic acid etc. present in the fruits peel were responsible for the chemical adsorption. Langmuir adsorption model was used which is confirmed by linear plot of Ce/qe vs Ce. The process is endothermic showing monolayer adsorption of Pb(II) at pH 2.
Keywords: Adsorption, Fruits peel, Langmuir adsorption isotherm, Endothermic, Monolayer adsorption.
Introduction
Global heavy metal pollution in the environment is a serious concern. The discharge of heavy metals from various anthropogenic and technogenic sources into the aquatic system poses a threat to the health of biota. Heavy metals persist in the environment since they cannot be degraded nor destroyed and finally reach the human through food chain. The major sources of lead pollution into waste water include batteries, pigments, paints, petrol, cables, steel, alloys, and plastic industries (Meitei, et al.,2013). Lead poisoning causes damage to the nervous system, reproductive system, kidney and brain. The effect of lead toxicity also include impaired blood synthesis, hypertension, severe stomach ache and even cause miscarriage in pregnant women (Jeyakumar, et al.,2014 ).The permissible level of lead in drinking water is 0.01 mg/l according to World Health Organization. So a very low concentration of lead in water is very toxic. Therefore it is of great relevance to remove Pb(II) ion from aquatic environment using low cost adsorbents.
Several treatment methods have been suggested, developed and used to remove heavy metals from waste waters. These methods include chemical precipitation, ion exchange, solvent extraction, electroplating, electro flotation, membrane filtration, reverse osmosis etc. However these methods proved either inefficient or expensive in case of low concentration (1-100 mg/l) of heavy metals prevailing in the environment and generate huge amount of sludge which are difficult to be disposal off (Sari, et al.,2009; Saeed, et al.,2005).
The most popular adsorbent is activated carbon, widely used but it is expensive. Based on both environmental and the economical points of view ,special attention has been focused on the use of natural adsorbents obtained from natural materials and waste agricultural products as an alternative to replace commercial activated carbon . The abundance and availability of agricultural by products make them good sources of raw materials for natural sorbents. A low cost adsorbent is one which is abundant in nature or is a byproduct of waste material from another industry. Some low cost adsorbents have capable of concentrating metal species from dilute aqueous solutions and accumulating them within their cell structure. The cell walls are porous and allow the free passage of molecules and ions in aqueous solutions. The constituents of the cell wall provide an array of ligands with different functional groups capable of binding various heavy metals (Aktha,et al.,1995; Gong, et al.,2005).
Agricultural waste is a rich source for activated carbon production due to its low ash content and reasonable hardness. The abundance and availability of agricultural by products make them good sources of raw materials for natural sorbents. The basic components of the agricultural waste materials include hemicelluloses, lignin, lipids, proteins, simple sugars, water, hydrocarbons and starch, containing a variety of functional groups. In particular agricultural materials containing cellulose show a potential sorption capacity for various pollutants (Bhatnagar, et al.,2010; Ahmedna,et al.,2000) . If these wastes could be used as low cost adsorbents ,it will provide a two fold advantage to environmental pollution. Firstly , the volume of waste materials could be partly reduced and secondly the low cost adsorbent if developed ,can reduce the treatment of waste waters at a reasonable cost (Bhatnagar ,et al 2005;9 Jain,et al.,2010).
In this study, different fruit peels i.e. Orange, lemon, banana and watermelon were subsequently used to treat the Pb(II) ion concentration from aqueous solution . Emphasis was laid on the effect of contact time adsorbent dose, pH, temperature variation, agitation speed and effect of concentration.
Materials and Methods
Preparation of Adsorbents
Agricultural wastes used in this study are orange , lemon , banana and watermelon peel. The fruits were obtained from fruit selling source in Bhubaneswar, Odisha state and peeled off to obtain the outer skin of the fruit and then removal of the inner fleshy layer after squeezing off the juice. The peels were washed with tap water to remove possible foreign materials present (dirt and sands). Then with deionized water. Washed sample materials were sun dried for 5-7 days and then cut into small pieces, ground by a mechanical blender upto a size of nearly 200-400µm and used in adsorption test (Bennard,et al.,2013; Feng,et al.,2012; Gueu,et al.,2007).
Preparation of Metal ion Solution
All the chemicals used in this study are AR grade. A stock solution of Lead(II) ions concentration 1000ppm was prepared by dissolving an accurate quantity of 1.6 gm Pb(NO3)2 (NICE) in deionized water. Other concentrations prepared from stock solution by dilution varied from 10 to 80 ppm i.e 10, 20 ,40, 60 ,80 ppm. The pH of working solution was adjusted to desired values with 0.1 N HCl or 0.1 N NaOH. Fresh dilutions were used for each experiment.
Batch adsorption studies
Batch adsorption equilibrium experiments were conducted for the adsorption of lead on fruits peel as a function of initial pH, initial Pb(II) concentration, adsorbent dose, contact time and temperature. Adsorption experiments were carried out in 100 ml stoppered reagent bottles at a constant shaking speed of 150 rpm. All the experiments were carried out at room temperature (28°C ± 2°C). For studying the influence of pH on the adsorption of Pb(II) , the experiments were conducted at various initial pH values of 2 to 7. The concentrations of Pb(II) ions in solution before and after adsorption were determined using atomic adsorption spectrophotometer(Perkin Elmer-A Analyst-200) by monitoring the absorbance for metal ion used. The equilibrium and kinetics data were obtained from batch experiments.
During the adsorption a rapid equilibrium established between adsorbed metal ions on the active cites of adsorbent (qe) and unabsorbed metal ion in the solution. The amount of adsorption at equilibrium (qe) (mg/g) and the percentage adsorption (%) were computed as follows.
qe =
Percentage adsorption (%) =
Where Co and Ce are represented the initial and equilibrium concentrations (mg/L), V is the volume of solution and X weight of adsorbent (gm).
Result and Discussion
Effect of pH on Pb(II) adsorption
The pH of aqueous solution is an important factor and influences on metal speciation in aqueous solution as well as the surface properties of adsorbent and therefore can affect the extent of adsorption. Thus the adsorption behavior of Pb(II) on the surface of fruits peel has been investigated over a pH range of 2 to 7 at room temperature with 50ml of Pb(II) ion concentration (10 mg/L) containing 1.0 gm of the adsorbent and contact time 2hrs with agitation speed of 150 rpm. The pH was adjusted from 2-7 using 0.1N HCl. The solution was filtered using WHATMAN-40 filter paper and the residual metal ions concentration analyzed (Oxyeji, et al.,2011; Sreejalekshmi, et al.,2009).Table 1 shows the maximum uptakes for different fruits peel.
Table 1: Amount of adsorption (mg/g) at different pH
Although pH controls the surface properties of the adsorbent it also controls the functional groups and ionic state of metals species. The adsorption capacities of Pb from water onto fruit peel were strongly affected by the pH (Fig. 1). The maximum adsorption capacities for orange, lemon, banana, watermelon was found to be 97.78%, 98.36%, 88.30%, 97.78% respectively. The maximum uptake for orange, lemon, banana, and watermelon are 0.488mg/gm, 0.493 mg/gm, 0.441 mg/gm, 0.489 mg/gm respectively. Except banana, other fruits peel shows nearly 100% removal of Pb(II) ion and was obtained at a low pH of 2, but for banana it is at pH 4. This can be explained as Pb(II), Pb(OH)+ and Pb(OH)2 species are available for adsorption at pH 2 for orange, lemon , watermelon and at pH 4 for banana. (Hossain , et al.,2012).
Figure 01: Effect of pH on the Pb(II) removal: Initial Pb(II) 10 ppm, adsorbent dose 1gm/50 ml, contact time 2hr
At high pH, the binding site may not be activated because of high concentration of OH– ions in the solution and lead started precipitating as Pb(OH)2+ . So the removal was not complete by adsorption (Wang, et al.,2005; Sheng,et al.,2004; Memon,et al.,2008). At lower pH of banana, H3O+ ion completes with metal ion for binding and surrounded hydronium ions (H+) preventing the lead ions from approaching the binding sites and could be responsible for low adsorption capacities (Karthikeyan, et al.,2008).Further adsorption experiments were carried out an optimum pH 2 for orange, lemon and watermelon and pH 4 for banana.
Effect of contact time
The effect of contact time on adsorption was studied between 0 to 120 min. The experiments were carried out using 50 ml of Pb(II) concentration (10 mg/L) containing 0.2g adsorbent at maximum pH for adsorbents with agitation speed 150 rpm at room temperature. The maximum uptake capacities are given in Table 2. Fig. 2 showed the % of removal of lead at their optimum pH.
Table 2: Amount of adsorption (mg/g) on variation of time
Figure 02: Effect of contact time on the Pb(II) removal, pH 2 for orange, lemon, watermelon and pH 4 for banana, initial Pb(II) conc. 10 ppm, adsorbent dose 0.2gm/50 ml.
It is evident from the figure that the rate of adsorption of Pb(II) by orange, lemon, banana and watermelon was rapid and the equilibrium was reached within 40 minutes and thereafter the rate of metal removal remained almost stable. There were no significant increase found after 60 minutes. Initially there were large number of vacant active binding sites available at the first phase of experiment and large amount of lead ions were bound rapidly on the adsorbents at a faster adsorption rate. The binding site was shortly become limited and the remaining vacant surface sites were difficult to be occupied by metal ions due to formation of repulsive forces between the lead on the solid surface and the liquid phase (Anwar,et al.,2010). Highest uptake for orange is 2.291mg/g, for lemon 2.350mg/g, banana 2.303mg/g and watermelon is 2.401mg/g . The maximum adsorption capacities for orange, lemon, banana, watermelon was found to be 91.66%, 94.01%, 92.11%, 96.07% respectively.
Initial Pb(II) concentration
Lead adsorption at different initial concentrations by the adsorbents were carried out using 50ml of Pb(II) concentration varying from 10 to 80mg/L at the maximum pH , 0.2 gm of adsorbent was used for each adsorption experiment and contact time 2hr with agitation speed 150 rpm.
Figure 03: Effect of initial Pb(II) concentration on the Pb(II) removal: pH 4 for banana and pH 2 for orange, lemon, watermelon, adsorbent dose 0.2 gm/50 ml and contact time 2 hr.
The percentage of removal of Pb(II) ion was shown in (Fig. 3). Indicating adsorption increases with the increase in equilibrium concentration at a low metal ion concentration. Which suggested that these metal ions are adsorbed accordingly to the Langmuir adsorption and tend to approach a constant values at their high concentrations. The fixed number of active sites eventually limits the adsorption of metal ions.
Table 3: Amount of adsorption (mg/g) on variation of initial concentration
Table 3 shows the maximum uptake of lead at varying concentration. Maximum uptake capacities are 19.146mg/g, 19.318mg/g, 19.180mg/g and 19.392mg/g and % removal are 95.72,96.59,95.89,96.96 for orange, lemon, banana and watermelon respectively.
Effect of adsorbent dose
To find out the effect of adsorbent dose for the adsorption of Pb(II) from aqueous solution, adsorption studies were carried out by varying the amount of adsorbents(0.2,0.4,0.6,0.8,1.0 gm ) while keeping the maximum adsorption pH 2 for all except banana having pH 4. Initial metal concentration (10 mg/L) 50 ml, shaking speed of 150 rpm for 2hrs at room temperature. The percentage of adsorption increases for an increase in adsorbent dose as shown in (Fig. 4).
Figure 04: Effect of adsorbent dose on the Pb(II) removal: pH 4 for banana and pH 2 for orange, lemon, watermelon, initial Pb(II) conentration 10 ppm, contact time 2 hr.
Table 4: Amount of adsorption on variation of adsorbent dose
(Table 4) represents the maximum adsorption uptake capacity. Higher percentage of adsorption with increase of adsorbent concentration can be attributed to increase in surface area and the availability of more binding sites for adsorption. This suggests that after a certain dose of adsorbent, the maximum adsorption sets in and hence the amount of ions bound to the adsorbents and the amount of free ions remains constant even with further addition of the dose of adsorbent (Kartkeyan,et al.,2009). The maximum adsorption capacities for orange, lemon, banana, and watermelon are 2.187mg/g, 2.330 mg/gm, 2.050 mg/g and 2.387 mg/g and % of adsorption are 97.6, 98.36, 88.30,97.78 respectively showing watermelon , lemon, orange are the superior adsorbent than banana.
Effect of temperature and thermodynamics parameters
The effect of temperature on the adsorption of lead ion on different fruits peel was investigated by conducting experiments for 10mg/L of initial metal ion concentration (50 ml), 0.2gm adsorbent dose at 303, 313, 323 K with agitation speed of 150rpm for 1 hr.
Table 5: Amount of adsorption (mg/g) on variation of temperature
(Table 5) shows maximum uptake of metal adsorption at varying temperatures. Which are 0.4560mg/g, 0.4668mg/g, 0.40511mg/g, 0.4386mg/g and percentage of removal are 87.29, 91.21, 69.32, 93.36 for orange, lemon, banana and watermelon respectively. (Fig. 5) shows that the percentage of removal increases with increase of temperature indicating that the adsorption process was endothermic in nature.
Figure 05: Effect of temperature on the Pb(II) removal: initial Pb(II) concentration 10 ppm, pH 4 for banana and pH 2 for orange, lemon, watermelon, adsorbent dose 1gm/50 ml and contact time 1 hr.
The thermodynamic parameters Gibb’s free energy (∆Go), enthalpy (∆H0) and entropy (∆So) were calculated using the following equations.
ln(qem/ce)=
Where “m” is the adsorbents dose (g/L), Ce is the Concentration of metal ion (mg/L),
qe is amount of metals ion at equilibrium in unit mass of adsorbent (mg/g), qem/ce is the adsorption affinity.∆H0, ∆So, ∆Go are change in enthalpy (KJ/mol), entropy (J/mol K) and free energy (KJ/mol) respectively. ‘R’ is the gas constant (8.314 J/mol K) and T is the temperature (K).
The values of ∆Ho and ∆So were obtained from the slopes and intercepts of the Van‘t Hoff plots of ln(qem/ce) vs 1/T respectively, thereafter ∆Go values were determined by using equation 2. As the % of removal increase with increasing in temperature, it indicated that the ∆Go values are –ve and increased in their absolute values with temperature (Baser,et al.,2005). The high temperature is favoured for the adsorption of heavy metals indicated a spontaneous adsorption process. The positive value of ∆H0 indicated that the adsorption process was endothermic.
Adsorption isotherms
Adsorption isotherm expresses the relation between the amount of adsorbed metal ions per unit mass of biosorbent (qe) and metal concentration in solution (Ce) at equilibrium. The data of sorption equilibrium in this work was tested with Langmuir adsorption isotherm as follows.
qe =
Where qe is the amount adsorbed at equilibrium (mg/g), Ce is the equilibrium concentration (mg/L), ‘b’ is a constant related to the energy or net enthalpy of adsorption (L/mg) and Q0 the mass of adsorbed solute required to saturate a unit mass of adsorbent (mg/g).
The Langmuir adsorption model is based on the assumption of surface homogeneity such as equally available adsorption sites monolayer surface coverage and no interaction between adsorbed species (Arica,et al.,2004). The Langmuir equation can be describred by the linearized form as follows.
By putting Ce/qe vs Ce, , Q0 and b can be determined from slope and intercepts respectively.
Figure 06: Langmuir adsorption isotherm at 303 K
Based on further analysis of Langmuir equation, the essential features of the Langmuir isotherm can be expressed in terms of a dimensionless constant, separation factor or equilibrium parameter RL which is given by (Malkoc,et al.,2007; Ozer,et al.,2004).
RL=1/1+bc0
Where C0 (mg/L) is the initial amount of adsorbate and b (L/mg) is the Langmuir constant.
Table 6: Langmuir adsorption isotherm constants
|
Metal |
Q0(mg/gm) |
b (L/mg) |
RL |
|
Pb(II) |
1.231 |
0.541 |
0.2 |
The RL parameter is considered as a more reliable indicator of the adsorption. RL values between 0 to 1 indicate favourable adsorption. The RL value here is 0.2 which indicated that Langmuir isotherm holds good to explain adsorption of Pb(II).
Adsorbent characterization
SEM analysis
ZEISS (JEEOL-JSM-6510) Scanning electron microscope (SEM), Operating in variable pressure mode at 0.3 Tor and 20 KV accelerating voltage was used for studying the surface morphology of the fruits peel. Fig. 7 (a, b, c and d) shows the original SEM images of watermelon, banana, lemon and orange peels in (500 X) and (1500X) electron beam. This images revealed the combination of small and large particles size (nearly 10 to 20), heterogeneous rough and porous surfaces with crater-like pores [19]. In banana images there is agglomeration in comparison to watermelon. Orange shows needle like structure. So the efficiency to bind metal ions is lesser in comparison to watermelon and lemon. More porous surfaces in watermelon and lemon could promote the adherence of lead (Annaduari,et al.,2002). The exposure and availability of binding sites depends on particle shapes and sizes of adsorbent. Although all are good adsorbents but the removal efficiency of watermelon is more in comparison to others. This behavior can be attributed to the effective surface area increased as the particle size decreased (Sengil,et al.,2008).
Figure 07: Scanning Electron micrographs of the fruit peel of
(a) watermelon (500×) (b) watermelon (1500×)
(c) Banana (500×) (d) Banana (1500×)
Figure 08: Scanning Electron micrographs of the fruit peel of (a) Lemon (500×) (b) Lemon (1500×) (c) Orange (500×) (d) Orange (1500×)
FT-IR analysis
Figure 09: FTIR Spectra of fruits peel (a) Watermelon (b) Banana (c) Lemon (d) Orange
To understand the nature of functional groups present, the FT-IR spectra were obtained by using a JASCO-410 model FT-IR spectrometer having wave number range 400-4000 cm-1 (Fig. 9) displayed a number of peaks. Bands appearing at 3321, between 2906-2936, 1607-1617, 1048-1057, 996, 935, 944 cm¬-1 were assigned to OH stretch, CH stretch(alkanes), N-H Bend (Primary amines), CO stretch(acids and alcohols) ,O-H bend (carboxylic group and ester) respectively. The O-H stretching vibrations includes cellulose, pectin, absorbed water, hemicelluloses, and lignin. C-H stretching vibrations include methyl, methylene, and methoxy groups. Among the active groups, carboxylic acid and hydroxyl groups could play major role for lead adsorption.
Fruits peel is a low cost and readily available material for preparing bio-sorbents. In this study the use of fruits peel were tested as adsorbents for removal of Pb(II) ions from aqueous solution. The batch study parameter, pH of solution, contact time, initial Pb(II) concentration and adsorbent dose were found to be effective on the adsorption efficiency of Pb(II). The Langmuir isotherm model is used for mathematical description of the adsorption of Pb(II) onto peel of fruits and isotherm constant is evaluated. Results indicated that the adsorption equilibrium data fitted well to the Langmuir model. The negative values of ∆G0 suggested that the adsorption process was spontaneous in nature. The positive value of ∆H and ∆S indicated endothermic adsorption process and increased randomness at surface solution interface respectively. The adsorption mechanism is mainly based on ion exchange between divalent cation in solution chelated or linked to carboxylic groups in the polymeric structure of pectin. The study revealed that watermelon has much potential as an adsorbent for the removal of Pb(II) ions from aqueous solution. This is due to more negatively charged binding sites present in the adsorbent .Other than adsorptive capacity these adsorbents have medicinal character with antibacterial activity (Nisha,et al.,2013; Tumane, et al.,2014).
Acknowledgement
The authors are very thankful to Director, IMMT, Bhubaneswar for providing research facilities and special thank to Dr. Sushant Kumar Pattanayak, Prof and Head, Department of soil chemistry, College of agriculture, OUAT, Bhubaneswar for giving laboratory facilities throughout the period of research work.
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