International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
Utilization of Custard Apple (Annona squamosa) Seeds for
Heavy Metal (Ni (II)) Removal
Vishal R. Parate #1, Sukanya S. Waghrulkar *2, Mohammed I. Talib #3
#
Asst. Professor, Department of Food Technology, University Institute of Chemical Technology, North
Maharashtra University, Jalgaon-425001, India
*
M.Tech. Student, Department of Food Technology, University Institute of Chemical Technology, North
Maharashtra University, Jalgaon-425001, India
Abstract—Custard apple processing industries
generate considerable amount of waste specially
seeds. The present study was intended to prepare a
metal adsorbent from these waste custard apple seeds
and to study the metal elimination property of the
developed adsorbent in removing Ni ions from its
aqueous solution. The adsorbent was produced from
custard apple seeds by their carbonization at 500 0C
for 1 hour followed by activation with 10% sulphuric
acid.
The physicochemical characterization of
achieved adsorbent was analysed for different
parameters including crystal nature by XRD and
structural morphology by SEM. The optimum
condition for Ni ions removal was achieved by
altering pH from 2 to 10, agitation speed from 50 to
250 rpm, temperature from 10 to 50°C, adsorbent
dose from 0.1 to 1.25 g and contact time from 30-360
minutes. The work concludes adsorbent prepared from
custard apple seeds had considerable metal
adsorption property and showing maximum activity in
an optimum condition of 8 pH, 200 rpm agitation
speed, 50°C temperature, 240 minutes contact time
and 1 g adsorbent dose. The thermodynamic study
revealed adsorption by the developed adsorbent was
endothermic (positive H0), spontaneous (negative
0
G ) and increasing randomness at the adsorption
sites (positive S0).
Keywords — Adsorption, custard apple seed, nickel,
optimization, thermodynamic.
I. INTRODUCTION
Water pollution by heavy metal contamination due
to rapid industrialization has been a major global
concern. It is well known that the industrial effluents
are loaded with heavy metals and direct disposal of
such effluent without treatment in an aquatic receiving
body lead to adverse effect on aquatic life. The toxic
nature of heavy metal has resulted in the enforcement
of stringent laws for maximum allowable limits in the
water bodies. Heavy metals such as Pb2+, Cd2+, Zn2+,
Ni2+, Cr6+, Cu2+ etc. are prior toxic pollutants in
industrial wastewater, which become common
groundwater contaminants and tend to accumulate in
organisms including human being, causing numerous
diseases and disorders [1], [2].
The chronic toxicity of nickel to humans and the
environment is well known and high nickel
ISSN: 2231-5381
concentration causes gastrointestinal irritation and
lung and bone cancers in human. The safer limit
prescribed by the Indian Environment (Protection)
Rules, 1986 for the disposal of industrial effluent in
inland surface water and public sewer is 3 ppm and in
marine costal area is 5 ppm. Several methods such as
ion exchange, solvent extraction, reverse osmosis,
precipitation and adsorption have been proposed for
treatment of wastewater contaminated with heavy
metals. Among several chemical and physical methods,
the adsorption onto agro-waste adsorbent has been
found to be superior to other techniques because of its
capability of removing a broad range of different types
of adsorbates, high efficiency and its simplicity of
design. Commercially available activated carbons are
still considered expensive and as a result, many
researchers have been developing its cheaper
substitutes from readily, cheaply and abundantly
available food and agro waste [3]-[5].
Studies reveal that various agricultural waste
materials such as bran or husk, saw dust of various
plants, bark of the trees, shells, stone, seed hulls,
waste leaves, cob, deoiled cakes, fruit stalks can be
very well exploited in removing heavy metals. These
promising agricultural waste materials have been used
in the removal of metal ions either in their natural
form or after modification with physical or chemical
treatment [6].
Custard apple (Annona squamosa) plant is a
commonly available hedge plant. The flower of the
plant is thick and fruits are in abundance during the
winter season. The inner core of the ripe fruit is
delicious and of nutritive value. After consumption of
edible core, the obtained seeds are discarded as waste
as are non-edible. Since the Custard apple seeds are
available free of cost therefore development of metal
adsorbent from them may prove cost effective [7].
The aim of the work was to develop low cost metal
adsorbent from Custard apple seed, its characterization
and to study its application in removing Ni ions.
II. MATERIALS AND METHODS
Custard apple seeds were obtained from local seed
supplier of Jalna (Maharashtra State, India). The seeds
which were sorted out as waste such as shrunken, unfit
for germinating were selected for the present research
project. Stock solution of Ni (II) ion (500 ppm) was
made by dissolving 1.1193 g of Nickel Sulphate
(NiSO4.6H2O) in 500 ml of double distilled water. The
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prepared stock solution was used to prepare desired
concentration of fresh Ni solution by suitable dilution.
The metal adsorbent from the Custard apple seeds
was prepared as per the method given in Fig. 1 [8].
TABLE I:
ANALYSIS METHODS AND INSTRUMENTS FOR
PHYSICOCHEMICAL CHARACTERIZATION OF
ADSORBENT
Parameters
Moisture (%)
Water soluble
content (%)
pH
Electrical
Conductivity
(mS/m)
Ash (%)
Bulk density
(g/cm3)
Yield (%)
Adsorbent
nature and
shape of
crystals
Surface
morphology
Fig. 1 Method of preparation of adsorbent from Custard apple seeds
The yield of adsorbent was calculated as follows
given in equation (1):
(1)
Where, Wo = Mass of the raw custard apple seeds and
Wc= Mass of the adsorbent obtained from Wo.
Characterization of Adsorbent
The prepared adsorbent was analyzed for various
physicochemical parameters, crystallography and
morphological structure by standard methods and
instruments given in TABLE I.
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Specific
Surface Area
Total Pore
Volume
Average Pore
Diameter
Acid soluble
content (%)
(Mass basis)
Volatile
matter
content (%)
(Dry basis)
Fixed carbon
content (%)
(Dry basis)
Sulphated ash
(%) (Dry
basis)
Zero Point
Charge (pzc
value)
Equipments/Instruments
Hot air oven
Weighing balance (AND,
Model HR-200)
pH Meter (Deluxe 101(EI))
Methods
Bureau of
Indian
Standards
method (IS 877:
1989) [9]
Conductivity Meter (Systronic,
Bureau of
Model 304)
Indian
Standards
method (IS
14767: 2000)
[10]
Muffle furnace (Tempo
European
Instruments and Equipment
Chemical
Pvt. Ltd.)
Industry
Council
Bulk Density apparatus (DBK
(CEFIC)
5028-7)
methods, 1986
[11]
Weighing balance (AND,
El-Ashtoukhya
Model HR-200)
et al., 2008 [12]
X-Ray Diffraction (XRD) (BRUKER, Germany,
Model: D8 ADVANCE)
Scanning Electron Microscope (SEM) (HITACHI,
Model: S- 4800TypeII), Coupled with Energy
Dispersive X-ray Spectroscopy (EDS) of
BRUKER
NOVA-1000
Nitrogen
QUANTACHROME
sorption
instrument (version 3.70), at
measurement
77.4 K.
method
Bureau of Indian Standards, 1989 [13]
International Organization for Standardization,
1981 [14]
American Society for Testing and Materials, 1997
[15]
Food and Agriculture Organization/ World Health
Organization, 2010 [16]
Arlette et al., 2012 [17]
Initial Adsorption Study
Initially the rough trial was taken under the
conditions given in TABLE II.
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TABLE II
ROUGH TRIAL CONDITION
Parameters
Concentration of Ni ion
solution
Volume of Ni ion solution
pH of Ni ion solution
Adsorbent dose
Particle size of Adsorbent
Agitation speed
Temperature
Time
Condition
50 ppm
50 ml
6.50
0.1g, 0.25g, 0.5g and 1g
150-250µm
150
30°C
120, 240 and360 minutes
Where, R = ideal gas constant, T = temperature in K
The KC is related to C∂ and Ce by the equation (4):
(4)
Where, C∂ is mg of Adsorbate adsorbed per liter
(mg/L) and Ce is the equilibrium concentration of
solution in mg/L. C∂ was calculated on the basis of
following relation given in equation (5):
(5)
The Ni solution and adsorbent was taken in 100 ml
capped conical flasks and agitated in orbital shaking
incubator (REMI) for 6 hours. After each contact
period the suspension was passed through Whatman
No.42 filter paper to separate the adsorbent and the Ni
solution. The filtrate was then diluted to desired
dilution with double distilled water for the analysis of
residual Ni concentration using Atomic Absorption
Spectrophotometer (SL 176, ELICO Ltd., Hyderabad,
India). The % Removal or Adsorption of Ni was
calculated as follows shown in equation (2):
Van’t Hoff equation 6 relate ∆G° with ∆H°
(change in standard enthalpy) and ∆Sº (change in
standard entropy).
(6)
The values of ∆H° and ∆S° were calculated from the
slope and intercept of the plot of lnKC versus 1/T [19],
[20].
(2)
Where, Ci = initial concentration of Ni ion solution
and Ce = final or equilibrium concentration of Ni ion
solution in mg/L [18] .
Optimization of Adsorption Condition and
Thermodynamic study
The batch adsorption study was carried out to
optimized pH, agitation speed, temperature and
adsorbent dose, keeping the other parameter of
adsorption such as initial concentration of Ni solution
(50 ppm), volume of solution (50 ml), particle size
(150-250 µm) and contact time (4 hr.) constant. The
pH was optimization by varying it from 2 to 10,
keeping agitation speed 150 rpm, temperature 30 oC,
time 4 hr. and adsorbent dose 0.75 gram. In the
optimization of agitation speed the agitation speed
varied from 50- 250 rpm by keeping pH at optimized
condition and other parameters constant. The
temperature was optimized by changing it from 10ºC
to 50°C keeping pH and agitation speed at optimized
level and other parameters constant. For the
optimization of contact time it was varied from 0.5 to
6 hr.
maintaining pH, agitation speed, and
temperature at optimized point and adsorbent dose
0.75 g.
The thermodynamic analysis was done from the data
obtained from optimization of temperature.
The Gibb’s Free Energy ∆G° (J/mol) was obtained
using thermodynamic equilibrium constant (KC) given
in equation (3):
(3)
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Where, Ci is the initial concentration of solution
(mg/L) and Ce is the equilibrium concentration of
solution (mg/L).
In the optimization of adsorption dose 0.1 g, 0.25
g, 0.5 g, 0.75 g, 1.0 g, and 1.5 g dose was tried at all
the obtained optimized condition. The adsorption
capacity (qe milligram per gram) was determined by
the equation (7):
(7)
Where, Ci is initial concentration of Ni ions solution
and Ce is final or equilibrium concentration of Ni ions
solution in mg/L, V is the volume of the solution in L
and W is the mass of the prepared adsorbent from
Custard apple seeds in gram [21], [22].
III. RESULTS AND DISCUSSIONS
TABLE III is showing the result of analysis of
various physicochemical parameter for prepared
Custard apple seeds adsorbent (CASA). The moisture
in CASA was found to be 2.45%, ash 6.75%, water
soluble content 0.29%, acid soluble content 0.95%.
The pH of CASA solution was 6.73 and yield of
CASA from dried seeds was 32.52%. The bulk density
and conductivity of adsorbent was 0.405 g/cm3 and
152 mS/m respectively. The fixed carbon content and
sulphated ash was observed to be 67.74% and 4.31%
respectively. The specific surface area of adsorbent
was found to be 52.31 m2/g giving rough idea
regarding the capability of adsorbent for metal
removal. The adsorbent had pores of average diameter
54.176 ºA with pore volume 0.0708 cc/g. The
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adsorbent found to posses zero point charge at pH
6.98.
TABLE III
RESULT OF PHYSICOCHEMICAL ANALYSIS OF CASA
Parameters
Yield (%)
Moisture (%)
Ash (%)
Sulphated Ash (%) (Dry basis)
pH
Water Soluble Content(%)(Mass basis)
Acid Soluble Content (%)(Mass basis)
Bulk Density (g/cm3)
Fixed Carbon Content (%) (Dry basis)
Zero Point charge (pzc value)
Conductivity (mS/m)
Volatile Matter Content (%)(Dry basis)
Surface Area (m2/g)
Total Pore Volume (cc/g)
Average Pore Diameter (°A)
Results
32.52 ± 0.46
2.45 ± 0.07
6.75 ± 0.10
4.31 ± 0.03
6.73 ± 0.15
0.29 ± 0.02
0.95 ± 0.11
0.405 ± 0.31
67.74 ± 0.08
6.98
152 ± 0.02
23.08 ± 0.02
52.31
0.0708
54.176
Fig. 2 is showing the X-Ray Diffraction (XRD)
result of prepared adsorbent CASA. The standard
XRD peak for carbon was found to be matching with
XRD peak obtained for developed adsorbent and
implies the produced material was carbon. The XRD
result also confirmed the obtained adsorbent was a
mixture of 60.7% amorphous and 39.3% crystalline
crystals.
Fig. 2 XRD Result of CASA
Fig. 3 and 4 is showing the Scanning Electron
Microscope (SEM) images of raw Custard apple seeds
powder and prepared adsorbent CASA respectively.
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The structure of raw Custard apple seeds shows a
highly rigid and stiff morphology and CASA shows
the porous structure which expecting CASA to be
more efficient adsorbent as compare to Custard apple
seeds in raw form.
TABLE IV
ROUGH ADSORPTION TRIALS OF Ni ADSORPTION
Dose
(gm)
Time
(minutes)
Initial Conc.
(ppm)
0.1
120
240
360
120
240
360
120
240
360
180
360
50
50
50
50
50
50
50
50
50
50
50
0.25
0.5
1
Final Conc.
%
(ppm)
Removal
45
39.8
38.8
40.4
37.6
36.6
38.8
34.2
32.6
31.8
30.6
10
20.4
22.4
19.2
24.8
26.8
22.4
31.6
34.8
36.4
38.8
Fig. 5 is showing the optimization result for pH.
92 91.8
100
90
Fig. 3 SEM image of raw Custard apple seeds
80
% Removal of Ni ions
70
70
54.4
60
50
40
30.6
30
19.6
13.6
20
10
1.2
4.2
0
2
3
4
5
6
7
8
9
pH
Fig. 5 Optimization of pH
Fig. 4 SEM image of prepared adsorbent CASA
TABLE IV is showing the result of rough trial for
the removal of Ni by prepared adsorbent. The
maximum Ni removal obtained was 38.8 % and
required the need to optimize adsorption conditions
for improving the removal efficiency.
It can be observed that the % removal was
increasing with increasing pH. Beyond 8 pH the
drastic removal was observed but it was not due to
adsorption alone, it was a combine effect of adsorption
as well as precipitation of Ni ion due to formation of
metal complex (hydroxide). Shukla and Pai, 2005 [23]
were obtained the similar result while adsorbing Ni
ion on modified Jute fibers. Therefore to obtain the
removal of Ni ion only by adsorption and not by
precipitation, the optimum pH for the adsorption was
fixed at 8.0.
The result of optimization of agitation speed is given
in Fig. 6. The result shows as the agitation speed
increased the removal % also increased until it
reached maximum value 79 % and then further
increase in agitation had no considerable impact on %
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
removal. Therefore the agitation speed was optimized
at 200 rpm.
90
80
70.4
70
% Removal of Ni ions
79.4
79
negative for all the temperature and conclude that the
considered adsorption process was spontaneous.
TABLE V
STANDARD GIBB’S FREE ENERGY AT DIFFERENT
TEMPERATURE
Temp.
(°C)
61
60
50
45.2
10
20
30
40
50
40
30
20
Initial Final C∂
Conc. Conc.
(Ci)
(Ce)
ppm
ppm
49.6
20.6
29
49.6
16.2
33.4
49.6
12.7
36.9
49.6
9.4
40.2
49.6
7.3
42.3
Kc
∆G
1.41
2.09
2.9
4.27
5.79
-799.97
-1802.64
-2670.29
-3773.31
-4699.49
10
0
50
100
150
200
Agitation Speed (rpm)
250
Fig. 8 is the plot of lnKc versus 1/T for determining
the values of ∆H° and ∆S°. The line data points were
found to fit well as coefficient of determination (R2)
was nearer to unity (0.997).
Fig. 6: Optimization of agitation speed
2
Fig. 7 is presenting temperature optimization in
removing Ni by CASA.
90
81.2
% Removal of Ni ions
1.75
1.45
1.6
1.4
y = -0.353x + 2.127
1.06
R² = 0.997
1.2
lnKc
74.6
80
70
85.4
1.8
1
67.6
0.74
0.8
58.8
60
0.6
50
0.4
40
0.2
30
0
0.34
0.0031
20
0.0032
0.0033
0.0034
0.0035
1/T
10
Fig. 8 Plot lnKc versus 1/T
0
10
20
30
40
50
Temperature (°C)
TABLE VI is showing values of calculated enthalpy
change (∆H°) and entropy change (∆S°) for the said
study.
Fig. 7 Optimization of temperature
The % removal observed was 58.8%, 67.6%, 78.6%,
81.2% and 85.4% at 10, 20, 30, 40 and 50°C
respectively. The Ni removal was observed to be
increasing with increasing temperature. This indicate
that the removal of Ni by CASA was endothermic in
nature. The temperature thus optimized was 50°C.
TABLE V is showing the Standard Gibb’s free
energy at various temperature. The ∆G° was found to
be -799.97, -1802.64, -2670.29, -3773.31 and 4699.49 J/mol for the temperature 10, 20, 30, 40 and
50ºC respectively. The ∆G° was observed to be
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TABLE VI
STANDARD ENTHALPY CHANGE (∆H°) AND
ENTROPY CHANGE (∆S°) OF ADSORPTION
Equation of line with
Correlation Coefficient
y = -0.353x + 2.127
R² = 0.997
∆H°
(J/mol)
2.9348
∆S°
(J/mol K)
17.6838
The value of ∆H° and ∆S° was found to be 2.9348
J/mol and 17.6838 J/mol K respectively. Both ∆H°
and ∆S° were observed to be positive for the said
adsorption and confirms adsorption to be endothermic,
unfavorable for enthalpy but favorable for entropy,
increase randomness at the solid/solution interface and
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the system became
adsorption process.
more
disordered
through
Fig. 9 is showing the result of the optimization of
contact time. The maximum removal was found at 240
minutes and beyond this no appreciable improvement
in removal was observed, therefore time optimized
was 240 minutes.
Fig. 9: Optimization of contact time
IV. CONCLUSIONS
The work concludes that the Custard apple seeds
with physical treatment (heating at 5000C in air free
atmosphere) plus chemical treatment (H2SO4) can be
transformed into metal adsorbent. The effectiveness of
the prepared adsorbent in removing Ni ions from their
aqueous solution however depends on the initial pH of
the solution, agitation speed, temperature, contact time
and adsorbent dose. The adsorption of Ni ions on
Custard apple seeds adsorbent was endothermic and
spontaneous and system became more disordered
through adsorption process. In an optimum condition
of 8.0 pH, 200 rpm, 500C and 240 minutes contact
time the minimum amount of Custard apple seeds
adsorbent require to remove almost all the Ni ions
from its 50ml, 50 ppm aqueous solution was found to
be 1 gram. The outcome of the present work can be
used to develop model for large scale removal of
metal ion Ni from the industrial waste. The work thus
suggest the way to utilize food waste of Custard apple
as value added product.
The effect of adsorbent dose on Ni removal by
adsorption is expressed in Fig. 10.
[1]
85
90
80
% Removal of Ni ions
85.4 85.6
68.2
70
60.4
52.6
60
42.8
50
40
30
25.2
20
10
0
30
60
90
120 180 240
Time (min.)
300
360
120
6
99.6
5.45
% Removal
60
5
85.6
4.56
80
99.8
45.6
71.4
4
3.57
3
qe in mg/g
100
2.85
40
2
2.49
21.8
1.99
20
1
0
0
0
increasing with increase dose of adsorbent whereas the
adsorption capacity qe found to be decreasing with
increasing dose of adsorbent. The % removal
increased with increasing level of adsorbent due to the
availability of large surface area which increased more
numbers of adsorption sites.
0.5
Dose (g.) 1
1.5
Fig. 10: Effect of adsorbent dose
The % removal was found to be 21.8 %, 45.6 %,
71.4 %, 85.6 %, 99.6 % and 99.8 % for adsorbent dose
0.1 g, 0.25 g, 0.5 g, 0.75 g, 1.0 g, and 1.5 g
respectively. The adsorbent capacity (qe) of 5.45 mg,
4.56 mg, 3.57 mg, 2.85 mg, 2.49 mg and 1.99 mg of
Ni per g of adsorbent were observed for adsorbent
dose 0.1 g, 0.25 g, 0.5 g, 0.75 g, 1.0 g and 1.5 g
respectively. The % removal of Ni was found to be
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