Adsorptive Removal of Pb(II) from Aqueous Solution Using NaP Zeolite Synthesized From Coal Fly Ash

Payal Jain1,b), Priyanka Shrivastava1,c), VibhaMalviya1,d), Suresh Jain2,e) and M. K. Dwivedi1,a)

1Department of Chemistry, Govt.Holkar (Model, Autonomous) Science College, Indore, India 2Department of Chemistry, Government Degree College Dhanupu Handia, Allahabad,(U.P)

a)Corresponding author: dwivedimk12@gmail.com b)pjain2308@gmail.com

c)priyanka191189@gmail.com d)vibha220391@gmail.com

e)jainsuresh6730@gmail.com,

Abstract: Zeolite was prepared from coal fly ash obtained from power generation plantwith sodium hydroxide in different concentration ratios at 550 °C with activation time of 12 hours by direct hydrothermal method.The synthesized zeolite was found to have greater removal capabilities for heavy metals than coal fly ash and natural zeolitesIt was characterized by XRF, SEM, XRD and FTIR.Batch studies were performed to study the effect of different parameters like contact time, pH, amount of adsorbent, adsorbate concentration and temperature. The results revealed that the removal of lead was strongly pH dependent and maximum removal metal was observed at equilibrium pH of 5.0, optimum adsorbent dose and contact time were found to be 10 g/l and 120 minutes respectively. It was found that adsorption increased with increase in temperature thereby showing the process exothermic in nature. The experimental data were analyzed by Langmuir, Freundlich, Temkin and Dubnin isotherm models.The adsorption isotherm fitted the Freundlich rather than other isotherms. The maximum removalof Lead was found to be 89.7 % at25 0C. The Kinetic studies were also investigated to know the mechanistic aspect using models pseudo-first-order, pseudo-second-order, Elovich and Intra particle diffusion.

Keywords: Zeolite, Adsorption, Lead, Langmuir, Freundlich, Temkin isotherm.

INTRODUCTION

Water pollution caused by heavy metals and organic pollutants is reaching an alarming situation due to the direct or indirect emission into the environment. Heavy metal discharge into environment due to industrialization and urbanization causes a serious problem to human and plants.Theheavy metals of various industriesinclude lead (Pb), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni) and mercury (Hg)tends to accumulate in the human body causing numerous problems [1].

Lead (Pb) ranks fifth beside Fe, Cu, Al, and Zn in industrial production of metals [2]. About half of the Pb used goes for the manufacture of Pb storage batteries. Other uses include solders, cable covers, bearings, ammunition, pigments, plumbing and caulking. Lead oxide sand hydroxides, ionic lead(Pb2+) and lead-metal oxyanion complexes are main forms of Pb that are released into the soil, groundwater, and surface waters [3].

Ingestion and inhalation are the two routes of exposure and the effects from both are same. Pb accumulates in the body organs (cerebrum), which may lead to poisoning or even causes demise. The gastrointestinal tract, kidneys, and central nervous system are also affected by the presence of lead [4]. Lead can alsodamage the liver and reproductive system, basic cellularprocesses and brain functions. The toxic symptoms are anemia,insomnia, headache, dizziness, and irritability, weakness of muscles,hallucination and renal damages [5].Exposer to lead in

youngsters is at risk for lower IQ, shortened attention span, impaired development, hyperactivity, and mental deterioration. Depending upon the level and duration of exposure to lead can result in a wide range of biological effects [6].

A large amount of fly ash is produced from the combustion of coal in thermalpower stations every year and its small amount is used as ingredient in cement. Most of the fly ash is disposed of by dumping that gives rise to environmental pollution [7]. Therefore,other alternatives are being developed for greater utilization of fly ash. One main use of fly ash is as an adsorbent for the removal of substances such as phenol [8]and heavy metals [9-12] from solution. A new approach for application of fly ash is to convert it into zeolites. A lot of research has been focused on the synthesis of various zeolites by alkaline treatment of the ash [15-17] due to similar chemical composition of fly ash with zeolites. The main constituents of fly ash are aluminosilicate glass, mullite and quartz.The aluminosilicate glass is a readily available source of Si and Al for zeolite synthesis.

In our study, we have converted fly ash into zeolite and evaluatedit’s potential for the removal of leadfrom aqueous solution.We have studied the conditions required for zeolite synthesis, the adsorption properties, adsorption isotherms and rate of adsorption of the synthesized zeolite.

MATERIAL AND METHODS

Materials

Coal fly ash was collected from H.E.G. Thermal Power Station, Mandideep, Bhopal, India. It was in the form of small, spherical greyish black particles. The sample collected was sieved to a desired particle size range (100 mesh size) then it was washed with distilled water to remove the adhering organic materials and finally dried in an oven at 1100C for 24 hours, post that it was stored in vacuum desiccator. Most of the reagents used in investigations were analytical grade chemicals.

Zeolite Synthesis

The direct hydrothermal method was used for the synthesis of zeolites since it is fast, economic and less involving than the other fusion and the microwave methods [18-21]. NaOH is added with coal fly ash in different ratios of 1:2, 1:1.5 and 1:1.2 and kept for fusion at varying temperatures of 350oC, 450oC and 550oC for 12 hours. After these fusion mixtures were washed with double distilled water and agitated for 24 hours on magnetic stirrer to wash off excess of alkali, filtered on whatmann filter paper and dried in oven for 12 hours at 110oC and stored in desiccators before use.

Instrumentation

Lead concentration was determined by UV-Visible spectrophotometer (Systronic, Model No. 104), pH of the solution was measured by a systronic pH meter (Model MK-V). X-ray measurements were done by Philips diffractometer (Philips BW 1710 model) employing nickel filtered Cu-Kα radiations. IR spectra of material was recorded on an infrared spectrophotometer (model perkin Elmer-1600 series).The surface area was measured with a model QS-7 Quantasorb surface area analyzer. The specific gravity was determined using specific gravity bottles. The Scanning Electron Microscopy (SEM) was carried out using model LEO 438 VP, UK to study micro structure and qualitative characteristics of the ash of the fly ash.

Sorption method

Batch experiments were performed for the determination of equilibrium time, pH, temperature, amount of adsorbent and initial adsorbate concentration. Synthetic wastewater sample (20 ml) of known concentration (100 mg/l) and pH with desired adsorbent dosage were agitated until the equilibrium was attained. pH was adjusted by adding either 0.1 M HCl or 0.1 M NaOH solution. After adsorption, all samples were filtered through whatmann filter paper (No. 41).

The equilibrium adsorption uptake and percentage removal of adsorbate from the aqueous solution qe (mg g-1) was determined or calculated using the following relationship:

Amount adsorbed 0( )ee

C C VqW

(1)

% removal 0100( )e

eo

C CqC

(2)

Where, Co is initial adsorbate concentration (mg/l), Ce is equilibrium adsorbate concentration (mg/l), V is the volume of solution (l), W is the mass of adsorbent (g).

The fly ash dose was varied from 0.05 to 0.5 g per 20 ml. The effect of pH was studied ranging from 4.0 to 10.0. After the required contact time, the solution was centrifuged. The residue concentration in centrifuged was determined at the wavelength maxima.

Equilibrium Adsorption Isotherm Models

Adsorption in a solid-liquid phase results in the removal of solutes from solution and their concentration at the surface of the solid. As such, the solute remaining in the solution is in dynamic equilibrium with that at the surface. The preferred form for depicting this distribution is to express the quantity qe as a function of Ce at a fixed temperature. The quantity qe being the amount of solute adsorbed per unit weight of adsorbate and Ce, the concentration of solute remaining in solution at equilibrium.

An expression of this type is termed as adsorption isotherm. Several types of isothermal adsorption relations have been proposed, i.e., Langmuir, Freundlich, Dubinin–Radushkevichand Temkin isotherm to find an accurate relationship between dye in the liquid and solid phase.

Langmuir adsorption which was primarily designed to describe gas-solid phase adsorption is also used to quantify and contrast the adsorptive capacity of various adsorbents [22]. The Langmuir equation can be written in the following linear form:

= + (3)

Where Ce is concentration of adsorbate at equilibrium (mg g−1), qm is Langmuir constant related to adsorption capacity (mg g−1), which can be correlated with the variation of the suitable area and porosity of the adsorbent which implies that large surface area and pore volume will result in higher adsorption capacity.

Freundlich isotherm is applicable to adsorption processes that occur on heterogonous surfaces. This isotherm gives an expression which defines the surface heterogeneity and the exponential distribution of active sites and their energies [23]. The linear form of the Freundlich isotherm is as follows: log qe = logKF+ log Ce (4)

Where KF is adsorption capacity (mg g-1) Ce is solution concentration equilibrium and 1/n is adsorption intensity; it also indicates the relative distribution of the energy and the heterogeneity of the adsorbate sites.

Dubinin-Radushkevich isotherm model is an empirical adsorption model that is generally applied to express adsorption mechanism with Gaussian energy distribution onto heterogeneous surfaces.The model is a semiempirical equation in which adsorption follows a pore filling mechanism [24]. It presumes a multilayer character involving Vander Waal’s forces, applicable for physical adsorption processes, and is a fundamental equation that qualitatively describes the adsorption of gases and vapours on microporous sorbents. Dubinin-Radushkevich isotherm is expressed as follows: lnqe = lnqm – βE2 (5) ɛ =RT ln 1 + (6)

E = √

(7)

Where ɛ is Polanyi potential, β is Dubinin-Radushkevich constant, R is gas constant (8.31 Jmol−1 k−1), T is absolute temperature, and E is mean adsorption energy (KJ mol-1). Temkin isotherm model takes into account the effects of indirect adsorbate/adsorbate interactions on the

adsorption process; it is also assumed that the heat of adsorption of all molecules in the layer decreases

linearly as a result of increase surface coverage [25]. The Temkin isotherm is valid only for an intermediate range of ion concentrations [26]. The linear form of Temkin isotherm model is given by the following: qe = ln(A C ) (8)

Where bT is Temkin constant which is related to the heat of sorption (Jmol-1) and AT is Temkin isotherm constant (l g-1) [27].

Adsorption Kinetics

Experiments regarding the adsorption kinetics were performed to determine the rate of adsorption as adsorption is a time dependent process. It is necessary to know the rate of adsorption for the design and evaluation of a treatment system. Kinetic experiments were performed by varying the initial adsorbate concentration, i.e., 25, 75, and 100 mgL−1 over variable time steps.

Specific Rate Constant of Adsorption

The rate constant of adsorption for various adsorbates is determined from the following first order rate expression given by Lagergren.

log (qe-q)= log qe -2.303

adK t (9)

Where q and qe are amounts of metal adsorbed (moles/g) at time‘t’ and at equilibrium respectively and Kad is the rate constant for adsorption (min-1). A straight-line plot of log (qe-q) versus ‘t’ suggested the applicability of Lagergren equation. The rateconstant of adsorption (Kad) was calculated from the slope of the plot. The pseudo-second-order kinetic equation is described as:

=

+ 푡 (10)

Where k2 (g/mg min) is the rate constant and qe and qt (mg/g) are the amount of Lead ion adsorbed on to the coal

fly ash at equilibrium and at time t (min), respectively. Intra particle diffusion is the diffusion mechanism of adsorption, the kinetic results were evaluated using the

intraparticle diffusion model. During the intraparticle diffusion process, the adsorbate species are most probably transferred from the bulk of the solution into the solid phase. The intraparticle diffusion equation is given as: qt = Kᵢt1/2 + C (11)

Where Ki (mg/g min1/2) is the intraparticle diffusion rate constant and C is the intercept. The boundary layer thickness is described by the values of the intercept. The larger the intercept, the greater is the boundary layer effect. From Table 3, it was observed that the intraparticle diffusion rate constant increased with an increase in Lead ion concentrations.

Elovichmodel is based on a kinetic principle which assumes that adsorption sites increase exponentially with adsorption; this implies a multilayer adsorption [28-29]. The equation was first developed to describe the kinetics of chemisorption of gas onto solids [30-31]. The linear forms of the Elovich model are expressed as follows: qt = β ln (αβ) + β ln t (12)

where qt is the amount of adsorbatesorbed by zeolite at time t, α is initial adsorbate sorption rate (mmol g-1 min-1) and β desorption constant (g mmol-1) during an experiment. Thus, constants can be obtained from the slope and intercept of linear plot of qtversus ln t. Table 3 lists the kinetic constants obtained from the Elovich equation. It will be seen that applicability of the

simple Elovich equation for the present kinetic data indicates that the Elovich equation was able to describe properly the kinetics of Lead ion adsorption on to coal fly ash.

RESULT AND DISCUSSION

Characterization of Fly ash and Zeolite

X Ray Fluorescence Analysis

XRF analysis of untreated Coal fly ash and synthesized Zeolite is shown in Table 1. TABLE 1. XRF analysis of Coal Fly Ash and zeolite (CFA: NaOH 1:1.5)

Constituents SiO2 Al2O3 Fe2O3 CaO TiO2 K2O P2O5 SO3 Na2O MgO LOI CFA Wt% 55.26 22.75 7.12 4.1 2.95 2.14 1.65 1.58 1.23 0.63 4.1 CFA:NaOHWt% 49.13 17.43 7.06 3.8 2.89 2.04 1.57 1.53 6.19 0.61 -----

FTIR Analysis

IR spectra of coal fly ash and alkali activated fly ash (AAF) as shown in Fig. 1 and Fig. 2 indicated significant changes in the intensities and the width of various bands due to interaction of fly ash with alkali.

It was noticed that there was an increase in intensity and broadness of the stretching frequency OH band at 3452 cm-1 after the treatment. This could be attributed to an increase in hydrated products due to the reaction between amorphous silicate and the alkali. Further the shift in the frequency to lower values indicated change in acidic character of the terminal Si-OH group.

Moreover, asymmetrical stretching of TO4 (SiO4 and AlO4) band corresponding to the variation in frequency from 1076 to 1000 cm-1 and the increase in its sharpness confirmed synthesis of silicates and change in its acidic characteristics (Fig. 2). This could be attributed to substitution of Si+4 by Al+3 in some of the tetrahedral framework of the primary building units of the aluminosilicates and their external linkage with the Na+ ions due to their interaction with the alkali. The band at 434 cm-1 indicated the increased crystallization of product.

Based on FTIR spectrum, it could be observed that there was presence of pore opening corresponding to frequency range from 420-400 cm-1 in the AAF which could be attributed to the dissolution of minerals present in the fly ash and precipitation of zeolite [32].

FIGURE1. FTIR spectra of coal fly ash FIGURE2.FTIR spectra of alkali activated coal fly ash

SEM Analysis

The morphological structure of the raw fly ash, treated fly ash and synthesized zeolitic materials were obtained by using scanning electron microscope. The bulk composition was also estimated from SEM/EDXS by indirect method. The elemental composition of the samples was first determined from the SEM/EDXS, and from these data, the percentages of oxides were calculated (Fig. 3). The results were further verified by X-ray fluorescence (XRF) data.Most of the particles found in the fly ash were sub-angular and spherical in shape. The image also showed that the particles present in the fly ash were covered with relatively smooth grains of quartz, clusters of iron (Fe-oxide). Irregular surface of glass matrix so observed might be due to an increase in adsorbent pore volume (Fig 3a). Fig. 3c

showed a significant transition in morphology from lumps to crystalline form which is attributed to chemical reaction between Si4+, Al3+and Na+ions and their nucleation and precipitation of zeolite Na-P crystals.

(a) (b)

(C) (d)

FIGURE 3.(a) Untreated CFA (b) CFA:NaOH (1:1.2)(c) CFA:NaOH (1:1.5)(d) CFA:NaOH (1:2)

X Ray Diffraction

The X-ray diffraction patterns (XRD) of different fly ash samples and synthetic zeolitic materials were obtained using a Philips diffractometer (Philips BW1710). Operating conditions involved the use of Cu-Kα radiation at 4 kV and 30 mA. The samples were scanned from 10–90° (2θ, where θ is the angle of diffraction). To complement the technique, crystalline phases present in the samples were identified with the help of JCPDS (Joint Committee on Powder Diffraction Standards) files for inorganic compounds. Quantitative measure of the crystallinity of the synthesized zeolite was made by using the summed heights of major peaks in the X-ray diffraction pattern [33]. The major peaks were selected specifically because they are least affected by the degree of hydration of samples and also by others.

FIGURE4.XRD of Coal fly ash FIGURE5.XRD of CFA: NaOH (1:1.2) at 550oC The XRD pattern of CFA revealed the presence of crystalline quartz and mullite phases. The pattern hub seen in

the background at lower diffraction angles of CFA was attributed to amorphous phases. After CFA treatment sharp edges of diffraction peaks of greater intensity emerges confirmed the formation of zeolite. The peak pattern of zeolite was dominant with higher concentration of NaOH, which showed slight decrease of quartz and mullite phases indicating stable phase generated during hydrothermal treatment (Fig. 4-5). The results correlate with observation reported by Kiti [34] and Scott et.al.[35].Data obtained from XRD shows that the quartz and mullitehave changed their mineral phases reflected by their intensity count/seconds. Zeolite from alkali activated flyash(1:1.5) was identified as Na-P type as confirmed by JCPDF software corresponding to maximum peak intensity of 390counts per second and diffraction angle (2 theta) equal to28oIt is observed that due to its alkali activation, there is reduction in the silica and alumina contents associated withthe crystalline particles of the fly ash. This can be accredited to the dissolution of the metal oxides and release ofcorresponding soluble ions Na+. The Si/Al ratio of the zeolite crystals present in alkali activated fly ash is around one which corresponds to a tetrahedral framework structure of the zeolite Na-P where there is presence of the Al3+ which has been replaced equal number of Si4+.

Surface area analysis

Surface area for fly ash and the prepared zeolite material were found to be 2.89m2 /g and 60.36m2/g respectively. The increase in surface area might be attributed to the formation of zeolite structure.

Adsorption studies

Effect of contact time

The effect of contact time of Lead ion on adsorption behaviour was performed at two concentrations of 100 and 500 mgL-1 with a fixed adsorbent dose of 10 gL-1 at 298 K and at a natural pH. The contact time was performed from 15 min to 180 min for both the concentrations studied. The percentage removal of metal ion was calculated and plotted in (Fig.6). An examination of figure demonstrated that the uptake of metal was rapid in initial stage up to 120 min but due to saturation of the active site it further decreased. It was also observed that at the lower concentration 100 mgL-1, the adsorption efficiency was high (81.8 %) in comparison to the maximum efficiency (71.4 %) for 500 mgL-1 after 120 min of contact time. Thus, the maximum contact time to attain equilibrium was experimentally found to be about 120 min.

FIGURE6.Influence of contact time on uptake of Lead FIGURE7.Influence of pH on uptake of Lead

Effect of pH

To decide the optimum pH for adsorption of Lead onto zeolite material, the studies were conducted at adsorbate concentration of 100 mgL-1, contact time 120 min and adsorbent dose 10 gL-1 at 250C. pH was adjusted by 0.1M HCl or 0.1M NaOH. The results obtained were shown in (Fig.7), which showed that adsorption of metal increases with increase in pH from 2.0 to 5.0 and after that a decrease in adsorption capacity has been observed till pH 7 and still further a slight decrease is observed on increase in pH to 10.0. Maximum adsorption of cadmium metal was 89.7% at an optimum pH of 5.0. Keeping initial pH was too high, metal ion could precipitate out and this deflects the purpose of employing the sorption process as the sorption process was kinetically faster than the precipitate. The adsorption of lead ion becomes slower because of competitive adsorption between H+ ions and heavy metal cation.

Effect of adsorbent dose

To explore the impact of mass of adsorbent dose on the adsorption of Lead, a series of adsorption experiments was carried out with different adsorbent dosage of 5 to 30 gml-1. Fig.8 showed the effect of adsorbent dosages on the removal of Lead. The percentage removal of Lead increased with the increase in adsorbent dose initially from 5 to 10 mgL-1. This can be attributed to increased adsorbent surface area and availability of more adsorption sites resulting from the increased adsorbent dosage. With the increase in the amount of adsorbent, the sites for adsorption increase initially, but on increasing it further the adsorption efficiency was reduced which was due to overcrowding of metal ions which prevents diffusion on actual adsorption sites.

FIGURE 8. Influence of adsorbent dose on uptake of Lead metal

0

20

40

60

80

100

0 50 100 150 200

% R

emov

al

Time (min)

100 ppm

500ppm

74767880828486889092

4 5 6 7 8 9 10

% A

dsor

ptio

n

pH scale

0

20

40

60

80

100

0 10 20 30

% a

dsor

ptio

n

Amount of zeolite in g/l

100 ppm300 ppm500 ppm

Adsorption Isotherms

Langmuir Isotherm

The adsorption of Lead ion at equilibrium with increase in initial dye concentrations at temperatures of 250Cwas fitted in Langmuir, Freundlich, Temkin and D-R isotherms. In Langmuir isotherm, 1/qe has been plotted against 1/Ce and a straight line with slope 1/bQmwas obtained as shown in (Fig. 9). Langmuir constants Qm and b were calculated, and the values of these constants along with coefficient of correlation (R2) were given in Table 2. The maximum adsorption capacity (Qm) was found to be 50mg-g-1.

FIGURE 9. Langmuir isotherm plot of Lead at 250C FIGURE 10. Freundlich Isotherm plot of Lead at 250C

Freundlich Isotherm

The equilibrium adsorption data has been also fitted in the linear form of Freundlich isotherm model and the plots of log qeagainst log Ce shown in (Fig. 10), were linear. The values of Kf and 1/n, calculated from intercept and slope of the plot respectively, were shown in Table 2. The obtained value of 1/n was less than 1, which concludes for favorable adsorption of metal onto the zeolite material.

Temkin Isotherm

Temkin isotherm was plotted between qeand lnCeas shown in (Fig. 11), were linear. Table 2 gives the value of B and AT as calculated from slope and intercept of graph which relates sorption heat.

FIGURE 11. Temkin Isotherm plot of Lead at250C FIGURE 12.D-R plot of Lead at 250C

0

10

20

30

40

50

0 2 4 6

qe

ln Ce

0

1

2

3

4

0 200000000 400000000

ln q

e

Є²

Dubinin-Radushkevich

D-R model was plotted between lnqeand ϵ2 as shown I n (Fig. 12), were linear. Table 2 gives the value of slope mean adsorption energy (β) and mean free energy (E) were calculated whereas intercept gave maximum adsorption capacity qDR.

The values of the regression coefficients indicate that the experimental data satisfactorily follow isotherms in order of Freundlich >D-R>Langmuir >Temkin at 250C

TABLE 2. Langmuir, Freundlich, Temkin, Dubinin-Radushkevich isotherm parameters at 298K S. No. Isotherm Model Parameters Value R2

1. Langmuir

b qm (mg/g) RL

2.22 50

0.0431

0.991

2. Freundlich Kf (mg/g) 1/n

36.81 0.588

0.996

3. 4.

Temkin Dubinin Radushkevich

B (J/mole) AT (L/mg) bt qDR(mg/g) B (mol g-1L)2 E (KJ mol-1)

12.72 0.1583 194.77

115.353 9 x10-9

7.453

0.960

0.995

Kinetic Studies

Pseudo First Order

The linear nature of the plots of log(qe-q) versus time for Lead at 250C were shown in (Fig. 13) which showed the applicability of the first order rate expression equation of Lagergren. The values of rate constant of adsorption (Kad) were also calculated and were presented in Table 3.

FIGURE 13.Legergren plot of Lead FIGURE 14.Pseudo second order plot for adsorption of Lead

-1

-0.5

0

0.5

0 50 100 150

log(

qe-q

t)

Time (min)

0

5

10

15

0 50 100 150

t/qt

Time(min)

Pseudo second order

The pseudo second order equation was based on adsorption capacity at equilibrium. From the slope and intercept of the (t/qt) as a function of t, the plot provided excellent linearity R2> 0.99. K and qe values for Lead at 250C was mentioned in Table 3. Fig. 14 showed the applicability of the pseudo second order rate expression equation.

Elovich Kinetics

Elovich equation was mainly applicable for chemo adsorption kinetics. The equation was often valid for systems in which the adsorbing surface was heterogenous. Figure 15 showed plot of (qt) vs. (ln t) with a linear slope of 1/β and intercept of 1/β ln (α β). The results of Elovich plot at various concentrations of Lead was cited in Table 3.

FIGURE 15.Elovich plot for adsorption of Lead FIGURE 16. Intra particle diffusion plot for adsorption of Lead

Intra Particle Diffusion

This model was applied to describe the competitive adsorption. The initial rate of diffusion was obtained by linearization of the curve (qt) Vs (t0.5). The plot of (qt) against (t0.5) for Lead showed competitive adsorption occurring in solution (Fig. 16). The linear portion of plot for wide range of contact time between adsorbent and adsorbate did not pass through the origin. The variation from the origin or near saturation might be due to the variation of mass transfer in the initial and final stage of adsorption. The values are given in Table 3.

TABLE 3.Kinetic Model Parameters S. No. Isotherm Model Parameters Value R2

1. Pseudo First Order

kad (min-1) qe (mg/g)

2.07 X 10-2 2.22

0.892

2. Pseudo Second Order K2 (g/mg) qe (mg/g)

1.953 X 10-2 9.259

0.998

3. 4.

Intra- particle diffusion Elovich Kinetics

Kad

C α (mg/g) β (g/mg)

0.198 6.78

3.757 X 103

1.522

0.9805

0.9291

0

2

4

6

8

10

0 2 4 6

qt

ln t

7

7.5

8

8.5

9

9.5

0 5 10 15qt

√푡

CONCLUSION

The studies revealed that zeolite synthesized from coal fly ash can be fruitfully employed as adsorbent for the removal of Lead metal ion. The pH was found to be significant factor which affects the adsorption capacity of dye. The removal of Lead metal is about 89.7 % at 100 mg/l with a dose of adsorbent of 10 mg/l and pH 5.0 at 250C. The optimum contact time was found to be 120 min. The adsorption data was analyzed by Langmuir and Freundlich models and fitted well. The fitness of Langmuir’s model indicated the formation of monolayer coverage of the adsorbate on the outer surface of the adsorbent.

The characteristic parameter and mechanism of adsorption were also investigated using isotherms and kinetic models. The adsorption data reflected best fits in the following order based on coefficient of determination:Freundlich >D-R>Langmuir >Temkin. The adsorption data obeyed Pseudo-second order>Intra particle diffusion>Elovich> pseudo first order.The developed adsorbent is quite cheaper than commercially available activated carbon, while their performance is comparable.

ACKNOWLEDGMENTS

The authors (Payal Jain, Priyanka Shrivastava and Vibha Malviya) are grateful to Govt. Holkar Science College Indore, for providing all facility to carry out measurements.

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