E-ISSN:2583-2468

Research Article

Treated Eupatorium

Applied Science and Engineering Journal for Advanced Research

2022 Volume 1 Number 3 May
Publisherwww.singhpublication.com

Biosorption Study of Pb(II) Ions onto Treated Eupatorium adinoforum (AEA) and Acer Oblongum (AAO): Thermodynamic and Equilibrium Studies

Vishwakarma MC1*, Hemant KJ2, Sushil KJ3, Narendra SB4
DOI:10.54741/asejar.1.3.1

1* Mahesh Chandra Vishwakarma, Assistant Professor, Department of Chemistry, Govt Post Graduate College Bageshwar Soban Singh Jeena University, Bageshwar, Uttarakhand, India.

2 Kumar Joshi Hemant, Guest Lecturer, Department of Chemistry, Nanhi Pari Seemant Engineering Institute, Pithoragarh, Uttarakhand, India.

3 Kumar Joshi Sushil, Professor, Department of Chemistry, SSJ Campus Almora Soban Singh Jeena University, Almora, Uttarakhand, India.

4 Singh Bhandari Narendra, Professor, Department of Chemistry, SSJ Campus Almora Soban Singh Jeena University, Almora, Uttarakhand, India.

In the present study, dried activated biomass of Eupatorium adinoforum (AEA) and Acer oblongum (AAO) used for removal of Pb (II) from synthetic wastewater. The batch operation was conducted with effect of variation of contact time, biosorbent dose, pH, concentration of metal ions and temperature on biosorption of metal ions on biosorbent. Maximum adsorption was recorded for initial metal ion concentration of 10 mg/l, biosorbent dose of 2.5 gm, at pH 5 with 105 minutes of contact time for activated AEA and AAO biomass. The adsorption equilibrium conditions were well described by Langmuir, Freundlich and Temkin isotherm models. The Langmuir isotherm model has provided a better fit with the experimental data in comparison to that of Freundlich and Temkin isotherm models. Thermodynamic data suggest that the bisorption process was spontaneous, feasible and endothermic. The values of thermodynamic parameters suggest that the biosorption process was spontaneous, feasible and endothermic. The kinetics of the biosorption for the reaction mechanism and types of biosorption process onto activated AEA and AAO biosorbent were also discussed.

Keywords: metal ions, biosorption, isotherm models, kinetics, ageratum conyzoid (TAC) biomass

Corresponding Author How to Cite this Article To Browse
Mahesh Chandra Vishwakarma, Assistant Professor, Department of Chemistry, Govt Post Graduate College Bageshwar Soban Singh Jeena University, Bageshwar, Uttarakhand, India.
Email: 		Vishwakarma MC, Hemant KJ, Sushil KJ, Narendra SB, Biosorption Study of Pb(II) Ions onto Treated Eupatorium adinoforum (AEA) and Acer Oblongum (AAO): Thermodynamic and Equilibrium Studies. Appl. Sci. Eng. J. Adv. Res.. 2022;1(3):1-13.
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Manuscript Received Review Round 1 Review Round 2 Review Round 3 Accepted
2022-04-25 2022-05-09 2022-05-17
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© 2022by Vishwakarma MC, Hemant KJ, Sushil KJ, Narendra SBand Published by Singh Publication. This is an Open Access article licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/ unported [CC BY 4.0].

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Vishwakarma MC et al. Thermodynamic and Equilibrium Studies

Introduction

Water pollution caused by industrial sewage carrying toxic heavy metal ions is a serious environmental issue. The industrial significance of Lead is its use in batteries, paints, pigments and ammunition, petrol, cables, alloys and steels, plastics, the glass industry and the metal industry 1, 2.

Lead has been introduced in the environment from a variety of sources such as, storage battery, lead smelting, tetraethyl-lead manufacturing and mining, plating, ammunition, ceramic and glass industries. industry, plastics, cables, pigments, and a variety of other anthropogenic wells of heavy metals throughout the environment 1.

Lead is found in the environment in an insoluble form that can cause major health concerns in humans. Lead poisoning is mostly caused by inhaling lead-contaminated dust particles or aerosols, as well as ingesting lead-contaminated food, drink, and paints 1.

The kidney absorbs the most lead in the human body, followed by the liver and other soft tissues including the heart and brain; nonetheless, lead in the skeleton makes up the majority of the body 3. Lead poisoning is very dangerous to the nervous system. Early indications of lead exposure on the central nervous system include headache, short attention span, irritability, memory loss, and dullness 3, 4.

Encephalopathy, cognitive impairment, behave aural problems, kidney damage, and anemia are all symptoms of excessive lead (Pb) buildup 5. Lead is a toxic metal that can harm the neurological system and cause mental illness. Long-term exposure to lead can result in nephropathy, gastrointestinal aches, and is especially damaging to women's reproductive function 6, 7.

Lead compounds are poisonous in all forms, but Pb(II) salts and organic lead compounds are the most dangerous. Although Chemical precipitation, filtration, ion exchange, chromatography, and carbon adsorption are some of the methods for removing heavy metals from wastewaters 8-12. These approaches have a number of drawbacks, including secondary pollutants, high costs, excessive energy usage, and so on 13.

Biosorption is an environmentally acceptable method for removing heavy metal ions from wastewater. In recent years, a variety of biosorbents such as soyabean 14, Algerian pine, beech and fir sawdust's 15, modified Cocoa (Theobroma cacao) Pod husk residue 16, Activated Carbon derived from Sugarcane bagasse 17, banana (Musa paradisaca)18, Rubus ellipticus 19, Pyras pashia 20, and Urtica dioica 21 have been employed to remove heavy metal ions from wastewaters.

FT- IR is an important tool for determination of functional group present in biomass. The main objective of this study is to investigate the possibility of activated biomass Eupatorium adinoforum (AEA) and Acer oblongum (AAO) leaves as an alternative low-cost biosorbents for removal of Pb(II) metal ions from synthetic wastewaters.

Materials and Methods

Preparation of Adsorbent

The leaves of Eupatorium adinoforum (AEA) were collected from Almora city area and Eupatorium adinoforum (AEA) leaves were obtained in Almora and Acer oblongum (AAO) leaves were collected in Chopta (Rudraprayag) in Uttarakhand, India. These leaves are professionally cleansed with double distilled water to remove dust and solvent chemicals. The leaves were dried at room temperature for 24 hours before being baked at 60°C (Model: SN-1680, Popular Trader).

The dried biomass is crushed into a fine powder in an electric processor. This fine mass was incubated with hot air at 60°C for two days after being treated with N/10 HNO3 at room temperature for 24 hours. In the oven, it was heated and dried.

This treated biomass was sieved to a molecule size of 63 µm in view of smashing and subsequently placed in water/airtight containers for use as an adsorbent. Fourier-transform infrared spectroscopy (FT-IR) spectroscopy was used to detect surface functional groups of the treated adsorbent (Model: spectrum 10 version, PerkinElmer).

Preparation of Adsorbate

The chemicals used were of analytical reagent quality. In distilled water, a stock solution of Pb(II) in 1000 mgL-1 of their different salts as Pb (NO3)2 was created.


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The pH of these solutions was tuned to four using N/10 NaOH or N/10 HNO3 solutions and a digital pH meter (Model: Systronic 361). These stock solutions were utilized to deliver synthetic wastewater. In synthetic wastewater, lead ionic concentrations vary from 10 to 50 mgL-1.

Biosorption Experiments

The biosorption experiments were carried out with 100 mL of standard solution in 250 mL conical flask. The experimental conditions employed to investigate the effects of adsorption dose, agitation period, pH, beginning metal ion concentration, and temperature on metal ion biosorption are listed in Table 1.

The solution was shaken at 170 rpm for 45 min and then filtered by using Whatman No. 42 filter paper. The filtrate was digested with conc. HNO3. The digested solution was analyzed by atomic absorption spectrophotometer (Optima 4300DV ICP, Perkin Elmer Boston, MA). The adsorption efficiency of mixed ions was calculated using eqn. 1:

where Ci is the initial concentration of metal ion (mgL-1) and Ce is the equilibrium concentration of metal ion (mgL-1).

Table 1: Batch adsorption experimental conditions

Experimental parameterMs (g /100ml)t (min.)pHInitial metal ion in equimolar concentration C0 (mgL-1)Temperature (0C)
Effect of adsorbent mass (g)0.5-2.53041022
Effect of contact
time, t (min.)		1.0015-10541022
Effect of pH1.00301-91022
Effect of metal
concentration, C0 (mgL-1)		1.0030410-5022
Effect of temperature, (0C)1.003041015-75

Results and Discussion

FT-IR and SEM used for the changes in biosorbent before and after biosorption.

The effect of the variation of amount of biosorbent, contact time, temperature, pH and concentration of metal ions in removing the Pb(II) metal ions from synthetic wastewater using AEA and AAO biomass have been studied by batch operations.

Characteristics of the AEA and AAO Biomass

FT-IR Analysis (Characterisation of Functional Groups)

The FT-IR study reveals a number of functional group present in the Eupatorium adinoforum and Acer oblongum. In order to determine, the main functional groups of activated AEA and AAO biosorbents that participate in Pb (II) ion sorption, FT-IR spectra were recorded before and after sorption of Pb (II) ions onto activated AEA and AAO biomass Figure 1A.

The sharp absorption bands of activated AEA biomass at 3743, 2363, and 2922 cm-1 are attributed to stretching vibration bands of N-H, aliphatic C-H, and NH2 22, respectively. The presence of the O-H group in biosorbent is indicated by the absorption bands at 3836, 3615, and 3515. The bending vibrations C-O, C-O-H, and C-C are ascribed to the peaks at 1461, 1239, and 1023, which are all connected to saccharide structure 23, 24.

After biosorption of the Pb (II) ion onto activated AEA (AEA-Pb) biomass, these absorption bands change. In Figure 1B for activated Acer oblongum, the broad peaks in the region of 2916 and 2949 cm−1 are characteristic of C-H group in the aliphatic compound. The peaks at 1611, 1516 and 1439 cm-1 are related to the N-H stretching vibrations in tertiary amine.

The formation of –CH2–O–CH2– linkage is appeared at 1085–1104 cm−1 25These shifts may be due to the changes in counter ions associated with the ether and amine group suggesting that these groups are predominant contributors in metal ion uptake 26.

The absorption band of –C–O was decreased due to the formation of complex between atom oxygen and Pb (II) 27. Obvious changes in the FT-IR spectra were found at the wave numbers of 3810, 3742 and 3280 cm-1 that appeared after Pb (II) adsorption 28. Which indicate that the metal ions adsorption affected the chemical bonds in biosorbent.


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asejar_13_01.JPG
Figure 1: SEM Analysis (Characterisation of Surface Morphology)

Scanning electronic microscopy (SEM) analysis is one of the useful characterization techniques applied for the analysis of surface morphology, properties, porosity and texture morphology of biosorbent 29, 30.

The irregular, rough and porous structure of the activated Eupatorium adinoforum (AEA) and Acer oblongum (AAO) biomass is shown in Figure 2 A and Figure 2 C, which are one of the criteria of high adsorption capacity and favourable for adsorption process.

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Figure 2: SEM image of (A): unloaded Eupatorium adinoforum (AEA) (B): Lead loaded Eupatorium adinoforum (AEA) biomass. (C) unloaded Acer oblongum (AAO) biomass (D) Lead loaded Acer oblongum (AAO) biomass

Biosorption of Pb (II) Metal Ions

Biosorption study of Pb (II) metal ions onto activated AEA and AAO biomass is carried out by batch experiments and process parameters used were pH, contact time, biosorbent dose, initial metal ion concentration and temperature.

Effect of solution pH

In Figure 3, For activated AAO biosorbent, the removal percentage increased pH from 1 to 5. The removal percent of Pb(II) ions was 25.7 % and 10.1% for AEA and AAO biosorbent respectively at pH 1. It increased to 58 % and 38% for AEA and AAO respectively at pH 3. For AEA, the maximum removal percent of Pb(II) ion was found to be 92.4 % and for AAO 85% at pH 5. After pH 7 a steady decrease to 81% for AEA and 65% for AAO. It decreased to 78 % for AEA 60.1% for AAO at pH 9..

The maximum adsorption of lead ions is obtained at pH 5.0. It was show that the activated AEA biomass was more efficient biosorbent as compared to activated AAO biomass for the removal of Pb(II) ion from synthetic waste water and the optimum pH 5.

Experimental results exhibited that the percentage removal and adsorption capacity of the Pb(II) ions increases with an increase in solution pH from 1 to 5. After pH 5 the percentage removal and adsorption capacity decreases..

The minimum biosorption at low pH is due to high concentration and high mobility of hydrogen ions. The hydrogen ions are preferentially adsorbed rather than the metal ions.

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Figure 3: Effect of solution pH on adsorption of Pb (II), metal ions onto activated AEA and AAO biomass: (experimental conditions: initial concentration of metal ions 10 mg/L; 1 g AEA and AAO; contact Time 30 min.; temperature 295 K; agitating speed:170 rpm)


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At higher pH values, the lower number of hydrogen ion and greater number of ligands with negatives charges results in greater metal ions biosorption 31. The maximum adsorption of metal ions is obtained at pH 5.0 31. Above pH 5 a steady decrease of adsorption of metal ions can be related to the precipitation of metal hydroxide 32, 33.

Effect of Biosorbent Dose

For AEA biosorbent, the removal efficiency of Pb(II) ions is found to be 81% at 0.5 g of biosorbent dose. This removal efficiency reaches 92.4 % at biosorbent dose 1 g. It increases to 95.7 % at biosorbent dose 2.0 g. The removal efficiency attains maximum value of 96.01 % at 2.5 g of biosorbent dose. The amount of lead ion adsorbed per unit mass qe from 1.62 mg/g to 0.364 mg/g for 0.5 g and 2.5 g of AEA biosorbent dose respectively.

The removal efficiency of lead ion onto activated AAO biosorbent, is 75 % at 0.5 g of biosorbent dose. On increasing biosorbent dose to 1g, it becomes 86 %. It increases to 90.02% at 1.5 g of biosorbent. It is observed that after 1.5g of biosorbent dose gradually increases the removal efficiency.

The removal percent obtained was 92.32 % for 2.0 g and 93.31 % for 2.5 g of biosorbent dose. Adsorption capacity qe decreases from 1.5 to 0.373 mg/g with increase of the biosorbent dose from 0.5 to 2.5 g. It was observed that the Pb (II) ion removal efficiency increases with increase biosorbent dose from 0.5 to 2.5 gm of activated AAO biomass.

The percentage removal and adsorption capacity of Pb(II) onto activated AEA and AAO biosorbent with different doses of biosorbent are shown in Figure 4 (A)and Figure 4(B) which indicated that the activated AEA is more efficient in comparison to activated AAO biosorbent for the removal of lead.

Initially the removal efficiency rapidly increased with biosorbent dos4e after 1.5 g of biosorbent dose it increases gradually, this is due to the availability of more active sites 34, 35. However, for the same dose the adsorption capacity qe of Pb(II) ions decreases with increase in metal biosorbent ratio. It may be due to aggregation resulting from high sorbent dose. The aggregation would lead to a decrease in total surface area of the sorbent and results to increase in diffusional path length 36.

asejar_13_04.JPG
Figure 4: Effect of biosorbent dose of Pb (II), metal ions onto activated AEA and AAO biomass: (experimental conditions: initial concentration of metal ions 10 mg/L; pH 5.0; contact Time 30 min.; temperature 22 oC; agitating speed 170 rpm)

Effect of Initial Metal Ion Boncentration

For 10 mg/L of Pb (II) ion biosorption, the maximum removal efficiency was found 92.2 % and 83% for AEA and AAO biomass respectively. It decreased to 76.65% and 69.45 % onto AEA and AAO for 20 mg/l of lead ion concentration. For 50 mg/L, it becomes 63.3 % and 55.32% for AEA and AAO biosorbent respectively. At the same time absolute amount of Pb (II) ions absorbed per unit of adsorbent increases from 0.92 mgg-1 to 3.16 mgg-1 when metal ion concentration increases from 10 to 50 mgL-1. The adsorption capacity (mgg-1) reverse trend of removal efficiency. In 50 mgL-1 lead ion concentration adsorption capacity was 3.168 and 2.766 for AEA and AAO respectively. It was observed that the Pb (II) ion removal efficiency increases with increase biosorbent dose from 0.5 to 2.5 gm of activated AAO biomass.

It is evident that on increasing metal ion concentration from 10 to 50 mg/l, percentage removal of Pb (II) ions decreases. This is due to fact that for a given adsorbent dose the total number of available adsorption sites is fixed thereby adsorbing almost same amount of adsorbate. Thus resulting in a decrease in removal of adsorbate corresponding to an increase in initial adsorbate concentration i.e. saturation of the adsorbent 37. The equilibrium uptake has been increased with increase in initial metal ion concentration from 10 to 50 mg/l (Table 6.7 and Table 8.8). This is due to increasing concentration gradient which acts as increasing driving force to overcome the resistances to mass transfer of metal ions between aqueous phase and solid phase 38.


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Figure 5: Effect of initial metal ion concentration on adsorption of Pb (II) metal ion onto activated AEA and AAO biomass: (experimental conditions: pH 5; 1gm dose of biomass; contact time 30 min; temperature 22 0C; agitating speed 170 rpm)

Effect of Contact Time

The effect of contact time on the adsorption of Pb (II) ions onto AEA and AAO was investigated with different initial Pb (II) ion concentration (10–50 mg/L), and shown in Figure 6 and Figure 6.10. The effect of contact time from 15 to 105 minutes in the removal of Pb(II) ion has been examined with 1 g of biosorbent dose at 22 0C. The initial concentration of lead ion was kept 10, 30 and 50 mg/L keeping the agitation speed to 170 rpm.

asejar_13_06.JPG
Figure 6: Effect of contact time and initial Pb (II) ion concentration adsorption biosorption onto (A) activated AEA biomass: (experimental condition: biosorbent dose 1gm/100 ml; temperature 22 oC; pH 5), (B) activated AAO biomass: (experimental condition: biosorbent dose 1gm/100 ml; temperature 22 0C, pH 5; agitation speed 170 rpm).

For 10 mg/L of Pb(II) ion with AEA, the removal percent was found to be 76% at contact time of 15 minutes. This reaches 89% at 30 minutes and 93.77% at 60 minutes. The metal uptake by biosorbent also increases from 0.76mg/g to 0.922mg for 15 minutes to 105 minutes. At a contact duration of 15 minutes, the removal efficiency of 30 mg/L of Pb(II) ion onto AEA biosorbent was 49.33 percent. After 45 minutes of contact time, the biosorption percentage climbed to 83.67 percent.

The removal efficiency increased gradually from 87.85 percent to 89.33 percent. when the interaction time is raised from 75 minutes to 105 minutes. For 50 mg/L of Pb (II), the removal percentage achieved on AEA biosorbent was 48 percent after 15 minutes of contact time and climbed to 63.3 percent after 30 minutes. At 45 minutes, the removal efficiency climbed to 73.56 percent, progressively increasing to 75.58 percent at 60 minutes. It reached to 77.58 % at 75 minutes of contact time and it increased to 78.62 at 90 minutes. Finally, removal efficiency reached to 79.8% at 105 minutes.

In case of 10 mg/L of Pb (II) onto AAO biosorbent, the removal efficiency is increased 0.69 mg/g at 15 min to 0.9901 mg/g at 105 min. The adsorption capacity and% removal efficiency increase with increasing the contact time which reached to equilibrium within 105 minutes. After 90 minutes, the surface pores of biosorbent may be occupied and the Pb(II) ion requires more driving force to enter into the interior of the adsorption site after equilibrium [310]. The equilibrium adsorption capacity of the have increased with an increase initial Pb (II) ion concentration, while the percentage removal of Pb (II) ion showed the opposite trend. The values of qe increased from 0.48 to 0.771 mg/g for AAO biosorbent of contact time from 15 to 105 minutes.

This may be attributes to the initial concentration which provides an important driving force to overcome all mass transfer resistances of Pb(II) ions between the aqueous and solid phase, hence a higher initial concentration of Pb (II) ions will enhance the adsorption process 39. The result shows that for all of initial metal ion concentrations the equilibrium is reached in the same time. The time required to attain the equilibrium time and the amount of metal adsorbed at that equilibrium time reflected the maximum metal adsorption capacity under these particular conditions 40. AEA have better removal efficiency of Pb(II) as compared to AAO biosorbent.

Effect of Temperature

Biosorption of Pb (II) ion onto AEA and AAO biomass as biosorbent was investigated at five different temperatures ranging from 15 0C to 75 0C. Experiments with AEA biosorbent showed that the removal efficiency of Pb (II) ion decreased after 45 0C.


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The removal efficiency was 76.9 % at 15 0C which reaches to 85.8 % at 30 0 C. The maximum removal percent achieved was 94.3 % at 45 0C, which decreased to 67.5 % at 60 0C and further removal percent decreased to 45.8 % with increase in reaction temperature at 75 0C. The data obtained from adsorption of Pb (II) ion onto the AAO showed that removal efficiency decreases after 15 0 C, maximum percentage removal is achieved at 150 C, which is 90.2 %, which further decreases to 78.8 % at 30 0 C.

The removal efficiency was 69.9 % at 45 0C which reaches to 90.1 % at 450 C; however, it decreases to 22.8% at 750 C. The removal efficiency of 53.5 % for Pb (II) ion is recorded at 60 0C, finally it achieved a minimum removal percent of 40.1 % at 75 0C. The optimum temperature should be kept at 45 0C for activated AEA and 15 0C for AAO biomass.

The biosorption capacity of Pb (II) ion onto AEA which is decreased with increase in reaction temperature may be due to rising metal desorption tendency from interface to the solution. The experimental result showed that adsorption capacity decreases with increase in solution temperature. This indicates that adsorption of metal ions on AAO is exothermic in nature.

The decrease in the rate of adsorption with increase in temperature may be attributed to weakening of adsorptive forces between the active sites of biosorbents and adsorbate species and also between adjacent molecules of adsorbed phases 41. The variation in extent of adsorption with respect to temperature has been explained on basis of thermodynamic parameters. This effect proposed that a description of biosorption mechanism 42, 43.

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Figure 7: Effect of temperature on Pb (II) ion adsorption on to activated AAO and AEA biomass: (experimental condition: Initial metal ions concentration 10 mg/l; biosorbent dose 1gm/100 ml; contact time 30 min; pH 5; agitation speed 170 rpm)

The biosorption of Pb(II) onto AAO biosorbent involves a physical process, in which biosorption arises from the electrostatic interaction, which is usually associated with low adsorption heat 43.

Thermodynamic Study of Biosorption

At five different temperatures ranging from 288 to 348 K, the biosorption of lead ion onto AEA and AAO biomass as a biosorbent was examined. The initial concentration of Pb (II) ions was 10 mg/L. For adsorption of Pb(II) ion onto AEA and AAO biomass, the thermodynamic parameters enthalpy change (H0), free energy change (G0), and entropy change (S0) describe the effect of temperature on the biosorption process. Whether the biosorption process is spontaneous or not, the variation in the process with regard to temperature has been described using thermodynamic factors. The Gibbs free energy change (G0) is a measure of a chemical process' spontaneity, and it is affected by changes in enthalpy, entropy, and reaction temperature.

The ΔH° and ΔS° were obtained from the slope and intercept of the Van't Hoff plot of ln Kc versus 1/T. The value of ∆G0, ∆S0 and ∆H0 are listed in Table 2.

Table 2: Thermodynamic parameters for adsorption of Pb (II) onto activated AEA and AAO biomass

Temperature (K)AEAAAO
ΔG0(kJ/mole)KcΔH0 (kJ/mole)ΔS0 (kJ/mole)ΔG0(kJ/mole)KcΔH0 (kJ/mole)ΔS0 (kJ/mole)
288-7.973.33+44.773+0.157-5.279.02-35.47-0.105
303-15.226.04-3.313.72
318-43.9816.64-2.232.32
333-5.752.08-0.391.15
348-2.440.841.160.67

The Kc values calculated for the adsorption of Pb (II) for activated AEA and AAO biomass are given in Table 2. As seen from the tables, the Kc values increase with increase in temperature which results in a shifting of equilibrium to the right i.e., adsorption lead ion is favored at higher temperatures. The low enthalpy values of ΔH° is 20 kJ/mole indicates that the physical sorption is involved in the process of adsorption 44.


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The estimated values of ΔH° for the present system were greater than 20 kJ/mole and hence, the process may involve a spontaneous sorption mechanism as ion exchange where chemical bonds are not of strong energies. According to given data in activated AEA biosorbent the chemisorption takes place while in activated AAO biosorbent physical sorption takes place. The negative value of entropy change (ΔS°) corresponds to a decrease in degree of freedom of the adsorbed species and suggests the decrease in concentration of adsorbate in solid–solution interface indicating there by increase in adsorbate concentration onto the solid phase. This is the normal effect of the chemical adsorption phenomenon, which takes place through ion exchange interactions.

In Table 2, ΔG0 values are -7.97, -15.22, -43.98, -5.75 and -2.44 kJ/mole at 288, 303, 318, 333 and 348 K for activated AEA biosorbent. It indicates that increase of spontaneity on rise in temperature till 45 0C. After 45 0C the free energy change became negative and decreases the spontaneity of biosorption process. The ΔG0 values were found to be positive at temperature 288 K and became more negative at higher temperature 333K.

In Table 2, ΔG0 values are -5.27, -3.31, -2.23, -0.39 and 1.16 kJ/mole at 288, 303, 318, 333 and 348 K respectively with activated AAO biosorbent. It indicates that the spontaneity decreases with rise in temperature. The ΔG0 values were found to be high negative value at lower temperature 288 K and become more positive at higher temperature 348 K. The value of enthalpy change is -35.47 indicate that the reaction is exothermic in nature. The randomness decreases with rise in temperature.

The change in enthalpy ΔH0, during biosorption of Pb (II) was found to be +44.77 and -37.47 kJ/mole for activated AEA and AAO biomass, respectively. The entropy change ΔS0 for activated AEA biomass was +0.157 kJ/mole and that for the activated AAO biomass was -0.105 kJ/mole. The values of ΔH0 obtained shows that the adsorption of Pb (II) onto both biosorbents was endothermic. The positive values of entropy may be due to some structural changes in the adsorbate and biosorbents during the adsorption process from aqueous solution onto the biosorbents. In addition to this, positive value of ΔS0 indicates the increasing randomness at the solid–liquid interface during the adsorption of Pb (II) onto activated AEA biosorbents.

The variation in biosorption process with respect to temperature has been explained on basis of thermodynamic parameters, whether process is spontaneous or not. The Gibbs free energy change (ΔG0) is an indication of spontaneity of a chemical process and depends on enthalpy change (ΔH0) and entropy change (ΔS0) 45. In the biosorption of Pb (II) onto activated AEA biomass, the free energy range is -2 kJ/mole to -43.984 kJ/mole. It reveals that physical adsorption takes place with rise in given temperature shown in Table 6.21. Generally for physical adsorption free energy change (ΔG0) ranges from (-20 to 0) kJ/mole and for chemical adsorption it ranges between (-80 and -400) kJ/mole 46. At 318 K the ΔG0 value is in range of -43.59 which indicates that chemisorption at this temperature.

Adsorption Isotherm

An adsorption isotherm is characterized by certain constant values, which have to be investigated to understand biosorption process. The surface properties and affinity of biosorbent can also be used for comparative study of biosorbent for different pollutants 47. Adsorption isotherm is important to describe how adsorbate ions interact with active site of biosorbent. The equilibrium data of biosorption of Pb (II) ion onto activated AEA and AAO biomass were subjected to Langmuir, Freundlich and Temkin isotherm models.

Langmuir Isotherm

According Langmuir isotherm model all-adsorption sites are homogeneous and does not dependent on adjacent active sites are occupied or not, meaning monolayer. The Qe and Ce correspond to mg of metal adsorbed per g of activated AEA and AAO biomass and residual metal concentration in solution when in equilibrium. KL (L/mg) and Qmax are Langmuir constant and maximum capacity of adsorption (mg/g), respectively. Values of Langmuir parameters Qmax and KL were calculated from slope and intercept of linear plot of Ce/Qe versus Ce and given in Figure 8(A). The values of Qmax, KL and correlation coefficient R2 are listed in Table 3. The monolayer adsorption capacity Qmax is also calculated from Langmuir equation. The maximum biosorption capacity Qmax of Pb(II) ion was found to be 2.915 mg/g for AEA biosorbent and 3.002 mg/g for AAO biosorbent. High value of Qmax for AAO in comparison to AEA biosorbent was obtained.


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Freundlich Isotherm

This model proposes heterogeneous distribution of active sites, accompanied by interaction between adsorbed molecules and based on adsorption of metal ions on a heterogeneous surface of biosorbent. The logarithmic values of Qe and Ce for Pb(II) ion onto AEA and AAO leaf are given in Table 3. KF and 1/n can be determined from linear plot of log Qe versus log Ce. The linear plots log Qe versus log Ce of Pb(II) ions on to AEA and AAO leaves are illustrated in Figure 8(B). Maximum adsorption capacity of Pb (II) ion was 1.16 and 0.96 mg/g with AEA and AAO biosorbent respectively. The regression coefficient R2 values are recorded 0.993 and 0.9751 for AEA and AAO respectively. The values of ‘n’ at equilibrium are 3.878 and 2.365 for Pb (II) ion.

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Figure 8: (A) Langmuir isotherm, (B) Freundlich isotherm, (C) Temkin isotherm, model for biosorption of Pb (II) onto activated AEA and AAO biomass

Temkin Isotherm

The Temkin isotherm model gives an idea of equal distribution of binding energies over a number of exchange sites on surface. The equilibrium values of Qe and ln Ce for Pb(II) ion onto AEA and AAO biosorbents are given in Table 6.24. The constant A is related to equilibrium binding constant (maximum binding energy), whereas constant B is related to heat of adsorption, in this pattern AAO biosorbent shows more binding energy with lead ion as comparison with AAO biosorbent.

The value of A and B are given in Table 6.2 The binding energy for Pb(II) ion in terms of Temkin isotherm model is 0.48 and 0.646 for activated AEA and AAO biosorbent respectively. High binding energy value for activated AAO biomass reveals that activated AAO biomass has more binding energy for Lead in comparison activated AAO biosorbent. The regression coefficient R2 values are recorded 0.994 and 0.993 for activated AEA and AAO biosorbent respectively.

Table 3: Biosorption isotherm constants for sorption of Pb (II) onto activated AEA and AAO biomass

BiosorbentLangmuir isothermFreundlich isothermTemkin isotherm
Qmax
(mg/g)		KL
(L/mg)		R2KF (mg/g)(L/mg)1/nNR2bT (mg/g)AR2
AEA2.9152.0240.990.6517.550.9920.4812.1340.994
AAO3.0019.960.990.1247.830.930.6462.0460.993

The isotherm constants and correlation coefficient R2 of Langmuir, Freundlich and Temkin isotherm models are listed in Table 6.25. The correlation coefficients for Langmuir isotherm are highest in comparison to value obtained for Freundlich and Temkin isotherms. Therefore, Langmuir isotherm is followed in biosorption of Pb (II) ion onto AEA and AAO biomass. Qmax is monolayer saturation at equilibrium. KL which corresponds to concentration at which amount of Pb (II) ion bound to AEA and AAO biomass is equal to 2.024 L/mg and 9.96 L/mg respectively. The affinity of Pb (II) ion with AEA and AAO biomass is very high. Show higher monolayer adsorption capacity. KF and 1/n indicate adsorption capacity and adsorption intensity, respectively. The higher value of 1/n indicates that the higher affinity and heterogeneity of adsorption sites. The linear plots for Temkin adsorption isotherm (Figure 6.15), which consider chemisorption of adsorbate onto biosorbent, fit quite well with correlation coefficients (R2> 0.99).

RL Values at Different Initial Metal Ion Concentrations

RL values can be used to predict whether an adsorption system is favourable or unfavourable 48. The essential feature of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter RL48.


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C0 is initial concentration of metal ions (mg/L) and is Langmuir constant (L/mg).

Table 4: The RL value for AEA and AAO biomass

BiosorbentRL Value
10 mg/L20 mg/L30 mg/L40 mg/L50 mg/L
AEA0.0470.0240.0160.0120.01
AAO0.020.010.0070.0050.004

The parameter, R­L indicates the adsorption nature to be either irreversible if (RL=0), favourable if (0<RL<1), linear if (RL=1) and unfavourable if (RL>1) 48. In this study, the values of RL obtained for Pb (II) ions onto AEA and AAO biomass at 293K are given in Table 6.26 and are greater than 0 and less than 1. This indicates that the adsorption of metal ions onto AEA and AAO biomass is favourable. In this study, all R­L values fall between zero and one as shown in Table 4.

Conclusion

The findings of biosorption of Pb(II) ions onto AEA and AAO biomass make it clear that the biosorbent is quite effective for the removal of metal ions from synthetic waste water. It is observed that the removal efficiency (%) increases with increase in biosorbent dose and adsorption capacity (qe) decreases with increase in biosorbent dose. Removal percent of Pb (II) ion onto AEA and AAO biomass decreases with the increase of the metal ion concentration while metal biosorption capacity (mg/g) increases with increasing metal ion concentration. The maximum removal is achieved at pH 5. The adsorption increases with increase in biosorbent dose and adsorption capacity decreases with increase in biosorbent dose. The thermodynamic parameters ΔH0, ΔG0 and ΔS0 give information about spontaneity of adsorption process. The results indicated that Pb (II) biosorption onto AEA was spontaneous, endothermic and irreversible and for AAO biosorbent biosorption process was spontaneous, exothermic, reversible chemisorption process. Langmuir, Freundlich, and Temkin adsorption models were used to represent the experimental data. The Langmuir adsorption isotherm was best correlation coefficient for biosorption of Pb (II) ions onto activated AEA and AAO biomass, this indicating that the applicability of monolayer coverage of Pb (II) on activated AEA and AAO biomass surface. The biosorption capacity of AAO is greater than AEA biomass.

The equilibrium data are also well described by the Temkin equation further supporting Pb (II) biosorption onto AAO as a chemisorption process.

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