Banana peel: a green and economical sorbent for Cr (III) removal

Abstract

Banana peel, a common fruit waste has been investigated to remove and preconcentrate Cr(III) from industrial wastewater. It was characterized by FT-IR spectroscopy. The parameters pH, contact time, initial metal ion concentration and temperature were investigated and the maximum sorption was found to be 95%. The binding of metal ions was found to be pH dependent with the optimal sorption occurring at pH 4. The retained species were eluted using 5mL of 2 M HNO 3 . The mechanism for the binding of Cr(III) on the banana peel surface was also studied in detail. The Langmuir and Dubinin-Radushkevich (D-R) isotherms were used to describe the partitioning behavior for the system at different temperatures. Kinetic and thermodynamic measurements of the banana peel for chromium ions were also studied. The method was applied for the removal and preconcentration of Cr(III) from industrial wastewater. Chromium is the common contaminant in wastewater from electroplating, leather tanning and metal-finishing plants. The physiological effects of chromium on the biological system depend upon its oxidation state i.e. Cr(III) and Cr(VI). Cr(III) may be considered as an essential trace element for the proper functioning of living organisms (mammals) e.g. for the maintenance of "glucose tolerance factor"; it is thought to be a cofactor for the insulin action and to have a role in the peripheral activity of this hormone. The toxicity of metal ions comes to play when their concentration values exceed than the threshold value. Chromium is toxic, corrosive and irritant. The maximum allowable limit for total chromium in drinking water as recommended by the World Health Organization (WHO) is 0.05 mg L -1 [1]. The conventional chromium treatment method consists of following three steps.

Full text

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ISSN-1996-918X
Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008) 20 – 25
Banana Peel: A Green and Economical Sorbent for
Cr(III) Removal
Jamil R. Memon*1, Saima Q. Memon2, Muhammad I. Bhanger1
and Muhammad Y. Khuhawar2
1National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan
2Hi Tech Central Resource Laboratories, University of Sindh, Jamshoro, Pakistan.
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Abstract
Banana peel, a common fruit waste has been investigated to remove and preconcentrate Cr(III)
from industrial wastewater. It was characterized by FT-IR spectroscopy. The parameters pH,
contact time, initial metal ion concentration and temperature were investigated and the maximum
sorption was found to be 95%. The binding of metal ions was found to be pH dependent with the
optimal sorption occurring at pH 4. The retained species were eluted using 5mL of 2 M HNO3.
The mechanism for the binding of Cr(III) on the banana peel surface was also studied in detail.
The Langmuir and Dubinin-Radushkevich (D-R) isotherms were used to describe the partitioning
behavior for the system at different temperatures. Kinetic and thermodynamic measurements of
the banana peel for chromium ions were also studied. The method was applied for the removal and
preconcentration of Cr(III) from industrial wastewater.
Keywords:Banana peel; Chromium; Sorption; Kinetics; Adsorption Isotherms; Thermodynamics.
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Introduction
Chromium is the common contaminant in wastewater
from electroplating, leather tanning and metal-finishing
plants. The physiological effects of chromium on the
biological system depend upon its oxidation state i.e.
Cr(III) and Cr(VI). Cr(III) may be considered as an
essential trace element for the proper functioning of
living organisms (mammals) e.g. for the maintenance of
“glucose tolerance factor”; it is thought to be a cofactor
for the insulin action and to have a role in the peripheral
activity of this hormone. The toxicity of metal ions
comes to play when their concentration values exceed
than the threshold value. Chromium is toxic, corrosive
and irritant. The maximum allowable limit for total
chromium in drinking water as recommended by the
World Health Organization (WHO) is 0.05 mg L-1 [1].
The conventional chromium treatment method consists
of following three steps.
1.
2.
3.
The precipitation of Cr(III) as Cr(OH)3 at high pH.
The settling of the insoluble metal hydroxide.
The disposal of the dewatered sludge.
The major shortcoming of conventional
treatment includes the high cost of safely disposing the
sludge. Wastewater containing Cr(III) is usually treated
with ion-exchange resins which offer the advantage of
the recovery of chromic acid but at a high cost brought
about mainly by the use of expensive resins. During the
past two decades, extensive research has been carried
out to identify new sorbents for the removal of
chromium which are both effective and economical. The
following materials have been assessed for chromium
uptake including coconut husk [2], sawdust [3], saltbush
(Atriplex canescens) [4], sunflower stem [5], activated
carbon fibers [6].
In the present work, we describe the use of an
effective and inexpensive banana waste material for the
removal and preconcentration of chromium species
from industrial effluent. The chromium enrichment
capability of the sorbent is ascertained by applying the
method to a commercial wastewater treatment plant.
Experimental
Materials
All chemicals used in the current study were
purchased from Fluka, Germany and were of analytical
*Corresponding Author: memon.jamil@gmail.com

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Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)
21
grade. A stock standard solution of Cr(III) was prepared
by dissolving the appropriate amounts of CrCl3. 6H2O
in 0.5 M HCl. pH 4-6 was maintained by the buffer of
acetic acid and sodium acetate, while pH 7-10 was
adjusted by 0.1 M NH3.
Methods
Preparation of sorbent

pieces, dried, crushed and passed through 120 mesh
sieve (125 µm). The banana peel was then washed
thoroughly with de-ionized water to remove physically
adsorbed contamination and dried in an air oven at 100
oC for a period of 8 h. The surface area of the dried
material was measured using the BET method [7] and
was found to be 13 m2 g-1. The dried banana peel was
also analyzed for biological constituents such as: dry
matter, moisture, fat, crude fiber, crude protein and ash
following the procedure reported in the literature [8] and
was found to be 90.4%, 9.6%, 5.0%, 11.0%, 10.1% and
19.0% respectively [9].
Slices of banana peel were cut into small
Esterification
Modification of the carbonyl groups on the
surface of the banana peel (esterification) was achieved
using acidic methanol. 9 g of washed and dried banana
peel was suspended in 633 mL of 99.9% methanol to
which 5.4 mL of concentrated hydrochloric acid was
added (0.1 M HCl final concentration). Then the
solution was heated at 60°C and stirred continuously for
48 h. The solid material was then separated and washed
three times with cold deionized water in order to halt the
esterification reaction [9].
Chemical analysis
A Varian AA-10 atomic absorption
spectrophotometer (AAS) was used to determine the
concentration of chromium in the solution.
The pH measurements were made with a
digital (InoLab pH level I) pH meter equipped with a
calibrated combined pH glass electrode. A Gallenkamp
thermostated automatic shaker model BKS 305–010,
UK was used for the batch experiments.
The dried banana peel was analyzed by FTIR
using a ZnSe SB-ATR accessory. The IR spectra were
acquired using a Thermo Nicolet Avatar 330 FTIR
spectrometer equipped with a deuterated triglycine
sulfate (DTGS) detector and KBr optics and controlled
by OMNIC software (Thermo Nicolet Analytical
Instruments, Madison, WI) with spectra collected by co-
addition of 32 scans at a resolution of 8 cm?1. The
spectrum of sample was rationed against a fresh
background spectrum recorded from the bare ATR
crystal cleaned with propanol to remove any residues
and the residual solvent evaporated in a stream of
nitrogen gas.
Equilibrium metal sorption experiments
The sorption behavior of chromium on the
banana peel surface was investigated using batch
equilibrium experiments. 10 mL aliquot of chromium
solution (1.92 × 10-5 M) adjusted to pH 4 was added to a
polyethylene flask containing 0.1 g of dried and sieved
banana peel. The mixture was then stirred for a
specified time (0-30 min) and temperature (20-40oC) to
allow selective sorption of Cr(III) ions. Finally, the
mixture was filtered and adsorbed metal ions were then
desorbed by shaking with 5 mL of 2 M HNO3 solution
and analyzed by flame
spectrophotometer at 357.9 nm and a slit width of 1 nm
using an air–acetylene flame. Experiments were
conducted in triplicate and the results are the average of
triplicate measurements. Precision in all cases is close to
~ ± 1%.
atomic absorption
Results and Discussions
FT-IR spectra
FT-IR spectra of banana peel were obtained in
order to understand the nature of the functional groups
present in banana peel. FT-IR spectra (Fig. 1a)
displayed a number of peaks, indicating the complex
nature of the adsorbent. Bands appearing at 3313.4,
2920.3, 2850.6, 1734, 1613.6, 1317.4, 1035.2 and 884.6
cm-1 in Fig. 1a were assigned to OH stretching, C-H
stretching of alkane, C-H and C=O stretching of
carboxylic acid or ester, COO- anion stretching, OH
bending, C-O stretching of ester or ether and N-H
deformation of amines respectively [10]. Out of these,
carboxylic and hydroxyl groups played a major role in
the removal of Cr(III) ions. As expected a significant
reduction in the intensity of other groups especially OH
and COOH group peak (absorbance intensity reduced
from 0.0447 and 0.0659 to 0.0266 and 0.0314) along
with peak shifting from 3336 and 1613.6 to 3313.4 and
1622.9 cm-1were recorded in the spectra of esterified
banana peel (Fig. 1b) [9].
Effect of pH
As pH of the system controls the sorption
capacity through its influence on the surface properties
of the adsorbent and species of adsorbate in solution,
sorption experiments were carried out a pH range of 1–
9, whilst maintaining all other parameters as constant.

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Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)
22
Figure 1. FT-IR spectra of (a) Banana peel and (b) Esterified
banana peel
Figure 2. Effect of pH for the removal and preconcentration of
Cr(III) ions onto banana peel.
The uptake of metal ions onto banana peel as a
function of pH is shown in (Fig. 2). The maximum
uptake of Cr(III) was achieved at pH 4 and this behavior
can be explained by taking into account the pKa value
of the carboxylic groups which is 3.3–4.8. At pH > 4,
the carboxylic groups is deprotonated and became
negatively charged hence increasing the availability of
binding sites for positively charged metal ions. The
predominant species of Cr(III) at pH 4 are Cr2(OH)2
(~5%), Cr3(OH)4
(~42%) [11]. At pH values below 3, the carboxylic
groups become protonated and thus unavailable for
binding with metal ions in solution.
4+
5+ (~22%), Cr(OH)2+ (~31%) and Cr3+
Sorption of chromium on esterified banana peel
In an attempt to identify the nature of the
functional groups responsible for chromium sorption,
sorption experiments were carried out on esterified
banana peel. Results from the sorption experiments
showed that the amount of Cr(III) bound was reduced
from 99% to 22%. Thus the sorption of Cr(III) was
attributed to complexation with carboxylic groups and
at a lesser extent to interaction with vicinal hydroxyl
groups.
Recovery of chromium
Desorption of chromium ions from Cr(III)
reacted banana peel was studied by shaking the
contaminated material with different concentrations of
HNO3, H2SO4 and HCl. The amount of chromium
recovered is given in Table 1. Elution was found to be
quantitative using 5 mL of 2 M HNO3.
Table 1. Recovery of Cr(III) from the banana peel surface.
*Solvent/Reagent
Concentration
(M)
Recovery
(%)
HNO3
0.117
HNO3
1 31
HNO3
299.3
H2SO4
0.59
H2SO4
1 10
H2SO4
2 14.5
HCl0.56
HCl16
*Volume of each reagent used = 5 mL
Kinetics of sorption

conditions from 0 to 30 min. The sorption was observed
Kinetic study was carried out at optimized
(a)
(b)
0
20
40
60
80
100
02468 10
pH
%Sorption

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Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)
23
to be very fast, equilibrium attained within a 10 min.
The removal was > 95% with very little increase in
sorption after 10 min of contact time. In order to avoid
the experimental error, a reaction time of 30 min was
adopted for further studies. The recorded kinetic data
were fitted to different equations namely, Morris–
Weber and Lagergren. The adsorbed concentration qt
(µmol g-1) at time t, was plotted against
Morris-Weber equation [12] in the following form:
t to test the
tRq
dt=
(1)
Where, Rdis the rate constant of intraparticle transport.
Up to 10 min Eq (1) held well with a regression
coefficient of 0.99 but deviated as the agitation time
increased. From the slope of the plot in the initial stage,
the values of Rd, was found to be 5.13 ± 0.25 µmol g-1
min-1/2. The Lagergren equation [13]
303. 2
log) log(
kt
qqq
ete
−=−
(2)
was tested by plotting log(qe-qt) versus time t, where qe
is the adsorbed concentration of chromium on banana
peel (mol g-1) at equilibrium. The overall value of rate
constant (k) was estimated to be 0.3 ± 0.001 min-1 from
the slope of the plot with a regression coefficient of
0.99.
Sorption isotherms

investigated as a function of concentration at room
temperature in the range of 0.5-100 mg L-1 using 0.1 g
of adsorbent and 10 mL of adsorbate solution, and 30
min shaking time at a shaking speed of 100 rpm. The
uptake of metal ions is 80-99% at lower adsorbate
The sorption of Cr(III) ions was also
concentrations (0.5-8 mg L-1) and 60-79% at higher
adsorbate concentrations (10-100 mg L-1). These results
reflected the efficiency of banana peel for the removal
of chromium ions from aqueous solution over a wide
range of concentrations.

increasing temperature was also observed indicating the
nature of process to be endothermic. The sorption data
was followed the Langmuir and Dubinin-Radushkevich
(D-R) isotherms. The sorption data was analyzed using
the Langmuir ((Ce/Cads) = (1/Qb) + (Ce/Q)) and D-R (ln
Cads =lnXm - ??2) and ? = RT ln[1 + (1/Ce)] equations,
where Cads is the amount of metal ions adsorbed per unit
mass of sorbent and Ce is the amount of metal ions in
the liquid phase at equilibrium. Q, b, Xm and ? are
Langmuir and D–R constants, respectively [14]. The
Langmuir and D–R constants were evaluated from the
slopes and intercepts of the linear plots studied at
different temperatures. The results are listed in Table 2.
The essential characteristic of the Langmuir isotherm,
separation factor (RL) was calculated using equation RL
= 1/(1 + bCi), where Ci is the initial concentration of
metal ions and b is Langmuir constant. RL describes the
type of Langmuir isotherm [15] to be irreversible (RL =
0), favorable (0 < RL < 1), linear (RL = 1) or unfavorable
(RL > 1). The values of RL calculated were between 0.07
and 0.99 (Table 2), indicating highly favorable sorption
of chromium on banana peel at all temperatures. The
values of E evaluated from the slope (?) of the D–R
curve using the equation (
E
An increase in the uptake of Cr(III) with
β
2
1
−
=
) lied in between
9.10–9.43 kJ mol-1 and were out of the range (8–16 kJ
mol?1) indicated the ion exchange mechanism of
sorption for Cr(III) [16]. It was observed that the values
of the sorption capacities increased with the rise of
temperature. This is because of the endothermic nature
of the reaction.
Table 2. Langmuir and D-R constant of Cr(III) ions onto sorbent surface at different temperatures.
R2regression coefficient, RL dimensionless constant
Langmuir
b ×103
(L g-1)
Dubinin-Radushkevich
? ×10-3
(kJ2 mol-2)
T
(oC)
Q
(mmol g-1)
RL
R2
Xm
(mmol g-1)
E
(kJ mol-1)
R2
20 1.31 ± 0.09 4.2 ± 0.34 0.11 - 0.96 0.98 10.10 ± 1.11 -6.19 ± 0.10 9.10 ± 0.10 0.99
25 1.53 ± 0.09 5.55 ± 0.39 0.09 - 0.95 0.98 10.73 ± 1.62 -6.18 ± 0.25 9.10 ± 0.20 0.99
30 1.70 ± 0.05 6.01 ± 0.36 0.08 - 0.94 0.99 11.50 ± 1.66 -5.74 ± 0.19 9.10 ± 0.20 0.99
35 1.79 ± 0.06 6.63 ± 0.40 0.07 - 0.94 0.99 15.1 ± 2.92 -5.81 ± 0.16 9.10 ± 0.20 0.99
40 2.22 ± 0.07 6.42 ± 0.26 0.08 - 0.94 0.99 24.42 ± 4.21 -5.67 ± 0.21 9.43 ± 0.19 0.99

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Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)
24
Thermodynamics of sorption
The effect of temperature on the sorption of
Cr(III) ions onto banana peel was studied in the range of
20–40oC at the optimized conditions. ln Kc = Fe/(1 - Fe)
where Fe is the fraction sorbed at equilibrium, was
plotted against 1/T (Fig. 3). The values of ?H, ?S and
?G were estimated using the relationships from the
slope and intercept of the linear plot.
S
RT
and
R
Kc
∆
+
∆Η
−=
ln
(3)
?G = - RT ln Kc (4)
The values of ?H= 46 ± 2.82 kJ mol-1, ?S = -
0.13 ± 0.01 kJ mol-1 K-1 and ?G = [-(6.9-4.4) kJ mol-1]
were estimated with a regression coefficient
0.99..The positive value of ?H indicated the
endothermic and the negative values of ?G were
obtained showing the spontaneous nature of the sorption
process.
of
Figure 3. Effect of temperature on the sorption of Cr(III) ions
onto banana peel.
Reusability of banana peel
In order to check the reusability of sorbent,
banana peel was subjected to several loading and elution
experiments. The capacity of the sorbent was found to
be practically constant (variation of 1-3%) after 10
times repeated use; thus multiple use of sorbent was
seen to be feasible.
Interference study
The sorption of metal ions in the presence of
common ions or complexing agents may be affected due
to precipitation, complex formation or competition for
sorption sites. The sorption of Cr(III) ions onto banana
peel in the presence of different cations and anions have
been investigated under optimized conditions. The
sodium salts of anions and nitrates or chlorides of
cations were added with the sorbate in solution in the
concentration ratios of 1:50 and 1:10, respectively. The
results are given in Tables 3. In case of anions, PO4
and C6H5O7
56%. The interferences of these ions can be tolerated
using concentration ratios of 1:10. With cations, Al(III),
Cd(II), Bi(III), Ni(II) and Mn(II) impede the sorption in
the range of 50-70%. The interferences of these ions can
be tolerated using concentration ratios of 1:1. The ions
which cause hindrance in the sorption of Cr(III) ions
onto the solid surface may be explained in terms of their
stronger affinity for anionic complexes of Cr(III) and
other cations which may replace Cr(III) ions sorbed
already on the sorbent surface.
3-
3- impede the sorption in the range of 53-
Table 3. Interferences of cations and anions on the sorption of
Cr(III) onto banana peel
Cr:Cation
(Tolerance
Limit = 1:10)
Sorption
(%)
Cr:Anion
(Tolerance
Limit = 1:50)
Sorption
(%)
Al(III)25 PO4
3-
39
Cd(II)32 C6H5O7
3-
42
Bi(III)34 CO3
2-
83
Ni(II) 41 HCO3
-
85
Mn(II) 45 Br-
87
Tl(III)85 CH3COO-
90
Hg(II)87 HPO4
2-
90
Fe(II)89 Cl-
90
Ca(II) 90 C4H4O6
2-
90
Pb(II)90 NO3
-
91
Cu(II)91 SO4
2-
91
K(I) 91 HSO4
-
92
Tl(I) 91 C2O4
2-
93
Co(II) 92 SCN-
93
Fe(III)92 F-
94
Zn(II) 93 NO2
-
94
Mg(II)94 SO3
2-
94
Nil95 Nil 95
1.5
1.8
2.1
2.4
2.7
3
3.153.21 3.27
1/T × 103 (K)
3.33 3.393.45
lnKc

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Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)
25
Analytical application
The analytical applicability of banana peel was
tested for removal and preconcentration of chromium
ions from industrial wastewater samples collected from
Karachi, Pakistan. A 50mL aliquot of water sample was
filtered and adjusted to required pH. Another 50mL
aliquot of water sample was spiked with Cr(III) at pH 4.
The solutions were then agitated at optimum shaking
speed for a period of 30 min. The metal ions were eluted
and determined. The results are given in Table 4. The
RSD was always within 2% which showed the
suitability of banana peel for the removal of Cr(III) ions
from industrial wastewater.
Table 4. Determination and recovery of chromium ions from
industrial wastewater
Cr(III) (?g mL-1)
Sample
SAa Found %Recovery
0.0 5.72 100
Mian M. Shafee Leather
Tanning
5 10.7 99.81
0.0 NDb
-
Fasto Leather Workers
5 4.96 99.2
0.0 4.06100
Alma Leathers
5 9.0 99.34
0.0 4.33100
Leather Tanning
5 9.3 99.68
0.0 ND-
National Oil Refinery
5 4.9599
a SA = Standard addition
b ND = Not detected
Conclusion
The present work explores a new cheaper,
economical and selective adsorbent as an alternative to
costly adsorbents for the removal of Cr(III) ions. The
main advantages of procedure are:
1.
2.
3.
4.
Cost of process.
Ease and simplicity of preparation of the sorbent.
Sensitivity.
Rapid attainment of phase equilibration and good
enrichment.
FT-IR analysis of banana peel showed the
presence of various functional groups indicating the
complex nature of the banana peel. The kinetics of
sorption for chromium follows a pseudo first order rate
equation. The positive value of ?H and negative values
of ?G indicate the endothermic and spontaneous nature
of the sorption process. For the sorption of Cr(III) ions,
most of the cations and anions can be tolerated up to
1:10 and 1:50 concentration ratios except with Al(III),
Cd(II), Bi(III), Ni(II), Mn(II), PO4
which can be tolerated up to ratios of 1:1 and 1:10.
Study shows that the banana peel has the ability to
extract Cr(III) from industrial wastewater.
3-and C6H5O7
3- ions,
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