JCBPS; Section D; February 2016 – April 2016, Vol. 6, No.2; 312-320.
E- ISSN: 2249 –1929
Journal of Chemical, Biological and Physical Sciences
An International Peer Review E-3 Journal of Sciences
Available online at www.jcbsc.org
Section D: Environmental Sciences
CODEN (USA): JCBPAT
Research Article
Adsorption Studies on Waste of Vegetable
Methi(Fenugreek) For Removal of Heavy Metal Ions from
Aqueous Solution
Kiran Pakhale*, Chandranayan Waghmare and Milind Ubale
*
Dept. of applied Chemistry,CSMSS College of polytechnic,Aurangabad,M.S.(India)
Post Graduate Dept. of Chemistry, VasantraoNaik College of Arts, Commerce and Science,
Aurangabad, M.S. (India),
Received: 05 April 2016; Revised: 14 April 2016; Accepted: 17 April 2016
Abstract: In the present work the waste of vegetable Methi (Fenugreek) was used as
adsorbent for removal of heavy metals like Fe (III), Cu (II), and Cr(III) from aqueous
solution. The adsorption of all three metals on waste of Methi was evaluated as a
function of varying adsorbent dose, temperature and time. The percentage removal of
Fe(III), Cu(II), and Cr(III) by waste of vegetable Methi carried under different
conditions,during these findings were significant. The order of adsorption of metals ions
on vegetable waste of Methi was Cu>Fe>Cr during the findings.The adsorption data
fitted well into Freundlich and Langmuir adsorption models. The results shows that
waste of Methi vegetable holds a great potential in removal of metal ions from
aqueous solution. The thermodynamic study has showed that the Fe(III), Cu(II), Cr(III)
ions adsorption on the surface of waste of vegetable Methi was physical adsorption and
the process was spontaneous and exothermic.The study also showed that waste of
vegetable Methi can be efficiently used as low cost alternative for removal of metal ions.
Keywords: Waste of vegetable Methi(WVM), Heavy metal ions, Freundlich
Isotherm, Langmuir Isotherm.
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Kiran Pakhale et al.
INTRODUCTION
A metal is classified as a heavy metal when its density is five times that of water. Heavy metal pollution
because of industrial wastewater is a common environmental threat in recent years. At least 20 metals
are considered to be toxic, and approximately half of these metals are emitted to the environment in
quantities that are hazardous to the environment, in addition to the human health. 1
Since heavy metals such as Fe, Cr, Cu,Cd, Ni, Zn and Pb are present in industrial wastewater, these
heavy metals in wastewater are not biodegradable and their existence in receiving lakes and streams
causes bioaccumulation in living organisms, the toxic metal ions dissolved can eventually reach the top
of the food chain which leads to several health problems in animals, plants and human beings such as
cancer, kidney failure, metabolic acidosis, oral ulcer, renal failure and damage for stomach of the
rodent.2 The conventional technologies for the removal of heavy metal ions from aqueous solution are
precipitation, filtration, coagulation3, ion-exchange, chemical oxidation4, liquid-liquid extraction5,
magnetic fields, fluidized bed reactor, flue gas purification6, electrochemical treatment 7-8and
adsorption. 9-11 These methods have their advantages; however, to choose the suitable method, the
disadvantages need to be compared.
Among the different treatments described above, adsorption technology is attractive due to its merits of
efficiency, economy and simple operation. Adsorption has been used as a suitable process to remove
heavy metals from aqueous solution. Many studies have been conducted to remove these heavy metals
by using different materials.12-15
In recent past development of efficient and eco-friendly methods for removal of heavy metals
arereceiving attention by agro wastes as adsorbent by various researchers. 16-17 Recently efforts have
been made to use cheap and available agricultural wastes such as coconut shell, orange peel, rice husk,
peanut husk and sawdust as adsorbentsto remove heavy metals from wastewater.18-20
In the present investigation an attempt has been made to study the feasibility of waste of
vegetable Methi as a cheap, locally available material for the adsorption of Iron, Copper and
Chromium. The adsorption of heavy metal ions from aqueous solution was carried to study
varying adsorbent dose, temperature & time.
EXPERIMENTAL
2.1 Adsorption experiments: Laboratory batch experiments were carried out to study the adsorption of
heavy metals Fe,Cu,Cr using waste of vegetable Methi (WVM) to analyze how the adsorbate and
adsorbent perform under various conditions. These conditions include temperature, contact time,
concentration of adsorbent, initial concentration of metal solution. The adsorbent selected for the present
work was waste of locally available vegetable Methi (Fenugreek).
2.2 Preparation of Adsorbent: The dried waste of vegetable Methi (WVM) were grinded into powder
and was boiled in distilled water to remove the suspended matter and dust for one hour and filtered.
Theresidues left was treated with formaldehyde and finally with very dilute solution
of
sulphuric acid. It was then stirred for half an hour using mechanical stirrer. Then it was filtered and
washed with distilled water repeatedly to remove free acid. After chemical treatment the residue was
dried first in air and finally in oven at
90-100oc for 8-10 hours and powdered using electric
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Kiran Pakhale et al.
grinder.The homogeneous powder was pass through mesh for desired particle size (9.8-41.8 micron).The
adsorbent once prepared was used throughout the experimental work. The particle size of the adsorbent
was of the same mesh size(9-8-41-8 micron).The particle size of adsorbent selected for these
experiments were on the basis of their settlement at the bottom of the system, so that the portion of the
solution could be taken out conveniently from the supernatant liquid.
2.3 Preparation of Adsorbate Solution: Iron, Copper and Chromium were the metal ions selected
for the present investigation. The aqueous solution containing metal ions was artificially prepared in
the laboratory. This was due to the fact that the effect of studying each metal alone was required. Each
sample that was tested had only one metal solution dissolved. The water used to dissolve the metal
crystals was doubly distilled water to eliminate the disturbances of other soluble substances present in
regular tap or drinking water. CuSO4.5H2O was used to obtain copper solution, K 2Cr2O7 was used to
obtain chromium solution and FeSO4.7H2O was used to obtain Iron solution. Chemicals used were all of
Analytical grade and used without further purification. Wherever necessary the prepared solutions were
standardized as per literature.21
2.4 Batch Adsorption Experiments: Each batch adsorption study was carried out by contacting WVM
with the ions Fe(III),Cu(II),Cr(III) under different conditions for 60 minutes in glass tube.
o
The s t u d y o f uptake of metal on WVMwas carried systematically at temperature 30 C to evaluate
effect of adsorbent dose, contact time, initial concentration of metal ions on adsorption of metal
ions. The effect of temperature on the adsorption was carried out in order to study the
thermodynamics of the process. Each study was conducted in thermostated water bath and the
residual metal ions were analyzed. The amount of metal ions adsorbed fromsolution was
determined by difference. 21 The concentration of metal ion solution was determined from
calibration curve spectrophotometrically (shimatzu-1211) at their respective wavelength i.e.
Iron (λmax = 515 nm).
RESULT AND DISCUSSION
3.1 Effect of Temperature: Temperature can change the adsorption equilibrium depending on the
exothermic or endothermic nature of a process. Enthalpy, entropy and Gibbs free energy are such
parameters that need to be determined before the spontaneity of the process can be inferred. Gibbs free
energy ( G°) is considered as the spontaneity indicator of a chemical reaction.22 The relation between
Gibbs free energy change, ( G°), temperature and equilibrium constant, Kc, is given by Equation 1,
G° = – RTlnKc
-------1
The other thermal parameters such as enthalpy change ∆H, and entropy change ∆S may be determined
using the Equation 2 ,
∆S
∆H-
------- 2
−
lnkc=
R
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RT
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Kiran Pakhale et al.
The percentage of Fe, Cu, Cr adsorption by WVM that decreases with the increasing temperature from
283 to 313°K have been investigated. The negative values of free energy change ( G°) indicate the
spontaneous nature of the adsorption
The adsorption experiments were performed at different temperatures from 283 to 313°K.The
temperature was maintained constant with an accuracy of ± 0.5º C.The magnitude of the temperature
effects for the adsorption process is one of the most important criteria for the efficient removal of heavy
metals from the waste water.23 The data of heavy metal ions adsorption onto WVM at different
temperature indicates decrease in adsorption with rise in temperature.24 These effects may attributes to a
negative temperature co-efficient of solubility of the solute or to a steep simultaneous decrease of real
adsorption of solvent. Similar findings are also reported by other researchers.25 The decrease in
adsorption with increase in temperature is due to the increase in solubility of the adsorbate with increase
in temperature, or the mobility of the large ions increases with increasing temperature.26 The effect of
temperature on adsorption of metal ion on WVM is given in Figure 1.
70
Amount Adsorbed
60
50
40
Cr
30
Fe
20
Cu
10
0
283 293 298 303 308 313
Temperature0K
Figure: 1
3.2 Effect of Contact Time:Adsorptions can be assumed to be complete when equilibrium is achieved
between the solute of solution and the adsorbent. However, specific time is needed to maintain the
equilibrium interactions to ensure that the adsorption process is complete. The effect of contact time on
WVM for adsorptive removal of Fe(II),Cu(II) and Cr(III) ions from aqueous solutions is observed.
The experiment measures the effect of contact time under batch adsorption’s initial concentration and pH
of 25 mg/L and pH 5 for Fe(II) 25 mg/L and pH 5 for Cu(II), while 20 mg/L and pH 6 for Cr(III) under
contact time varied from 0 to 35min. For the first 20min, the increased contact time enhanced the
adsorption of both ions. However, the rapid adsorption initially affected the time needed to reach an
equilibrium. For WVM, the equilibrium time was 2 hr for Fe (II) and Cu(II) adsorption and 2hr were
needed to reach the equilibrium for the adsorption of Cr(III) respectively.The similar observations were
also observed by other researchers.27, 28 The effect of contact time on adsorption of metal ion on WVM is
given in Figure 2.
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80
Amount Adsorbed
70
60
50
40
Fe
30
Cu
20
Cr
10
0
0
5
10
15
20
25
30
35
Time in minutes
Figure: 2
Amount Adsorbed
3.3 Effect of Adsorbent dose: Adsorbent dose is another parameter used to determine the capacity of
adsorbent at a given concentration of the adsorbate. The effects of adsorbent dosage were varied from 5
to 25g/L under room temperature (30°C). Result obtained from this study describes the adsorption of
Fe(II),Cu(II)and Cr(III) which increases rapidly when the dose WVM is increased further explaining the
large availability of the surface area at higher concentration of adsorbent. Any further addition of the
adsorbent beyond this would not cause any significant change in the adsorption due to the overlapping
adsorption sites of adsorbent particles.29-31 The increase in adsorption with increasing amount of
adsorbent is given in figure 3,
90
80
70
60
50
40
30
20
10
0
Cr
Fe
Cu
1
2
3
4
5
Adsorbent dose in gms
Figure: 3
3.4 Effect of Initial Concentration: Initial concentration of metal ions can alter the metal removal
efficiency through a combination of factors such as the availability of specific surface functional groups
and the ability of surface functional groups to bind metal ions. Initial concentration of solution can
provide an important driving force to overcome the mass transfer resistance of metal between the
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Kiran Pakhale et al.
aqueous and solid phases.As the initial concentration of Fe(II),Cu(II) and Cr(III) increased from 10 to
100 ppm the adsorption removal had decreased which was probably due to the fact that at lower
concentration, almost all metal ions were adsorbed very quickly on the outer surface. However, further
increase of the initial concentration of metal ions leads to the fast saturation of adsorbent.The adsorption
of all three metal ions onto the surface of WVM were rapid initially, slow down later on and finally
reached towards equilibrium (figure-4) indicating saturated adsorption as also reported by several
researchers.32
70
Amount Adsorbed
60
50
40
Cr
30
Fe
20
Cu
10
0
10
20
40
60
80
100
Initial concentration in ppm
Figure: 4
ADSORPTION ISOTHERMS
The adsorption isotherm data were fitted to the classical Freundlich and Langmuir isotherm equations.
33
The linearized forms of isotherm equations used are Freundlich equation 3:
1
logQe = logK +
logCe
------ 3
n
Where Qe is the equilibrium metal ion uptake capacity and Ce the residual metal ion concentration at
equilibrium. The constant K is a measure of adsorption capacity and 1/n is the intensity of adsorption. A
plot of log Qe versus log Ce gives a straight line indicates the confirmation of the Freundlich adsorption
Isotherm. The Langmuir model represents monolayer adsorption on as set of distinct localized
adsorption sites having the same adsorption energies.
The essential characteristics of Langmuir isotherm is expressed in terms of dimensionless constant
separation factor or equilibrium factor RL which is indicative of the isotherm and is indicative of the
nature of the isotherm and is enlisted below as given in Table 1.34
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Kiran Pakhale et al.
RLvalue
Types ofIsotherm
RL >1
Unfavorable
RL =1
Linear
0 <RL<1
Favorable
R =0
Irreversible
Table 1
The adsorption was favorable onto the surface WVM as RL value in the present study falls in the
type0<RL<1 our findings are in good agreement with other researchers.25
THERMODYNAMIC PARAMETERS
Thermodynamic parameters such as free energy, enthalpy and entropy of adsorption for adsorption of
metals on WVM were calculated and found that ∆G was negative and showed spontaneous nature
of adsorption process, ∆H was negative and showed exothermic nature of adsorption process, ∆S was
positive and showed the increasing randomness at solid/liquid interface during the adsorption of metal
ions which are displayed by adsorbed species gain more translational entropy than was lost by the
adsorbate ions. All these values demonstrate a spontaneous and exothermic adsorption process which is
favorable. The findings are well supported by the other researchers.35
CONCLUSION
It has been proved that activated WVA is an excellent adsorbent for removal of heavy metal ions from
aqueous solution under certain physiochemical conditions. The results indicate the potentially practical
value of WVA as adsorbent. The dimensionless equilibrium parameter RL found to be in the range
between 0to1 is indicative of favorable adsorption on to the surface of WVA. Thermodynamic
parameters ∆ G,∆ H,∆S shows spontaneous process.
The conventional technologies for the removal of heavy metal ions from aqueous solution like
precipitation, filtration, coagulation, ion-exchange can be substituted by adsorption on WVA for removal
of Heavy meal ions from aqueous solution. It is also applicable for removing trace amount of metal ions
in water treatment of drinking water. This technique can be applicable for removal of heavy metals from
industrial waste water as a remedial action against pollution control because of its efficiency and
economy.
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Corresponding author: KiranPakhale
Dept. of applied Chemistry,CSMSS College of
polytechnic,Aurangabad,M.S.(India)
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