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European Journal of Applied Sciences – Vol.10, No.5
Publication Date:October 25, 2022
DOI:10.14738/aivp.105.13051.
Olowu, R. A., Osundiya, M. O., Oyewole, T. S., Onwordi, C. T., Yusuff, O. K., Osifeko, O. O., &Tovide, O. O. (2022). Equilibrium and
Kinetic Studies for the Removal of Zn (Ii) and Cr (Vi) Ions from Aqueous Solution Using Pineapple Peels as an Adsorbent. European
Journal of Applied Sciences, 10(5). 34-47.
Services for Science and Education – United Kingdom
Equilibrium and Kinetic Studies for the Removal of Zn(Ii) and
Cr(Vi) Ions from Aqueous Solution Using Pineapple Peels as an
Adsorbent
Rasaq Adewale Olowu
Department of Chemistry, Lagos state University
Ojo, Lagos, Nigeria
Medinat Olubunmi Osundiya
Department of Chemistry, Lagos state University
Ojo, Lagos, Nigeria
Toyib Seun Oyewole
Department of Chemistry, Lagos state University
Ojo, Lagos, Nigeria
Chionyedua Theresa Onwordi
Department of Chemistry, Lagos state University
Ojo, Lagos, Nigeria
Olaniyi Kamil Yusuff
Department of Chemistry, University of Ilorin, Ilorin, Nigeria
Olawale Lawrence Osifeko
Department of Chemistry, Lagos state University
Ojo, Lagos, Nigeria
Oluwakemi Omotunde Tovide
Department of Chemistry, Lagos state University
Ojo, Lagos, Nigeria
ABSTRACT
Adsorption is one of the methods extensively reported to have been successfully
used for the removal of potentially toxic metals (PTMs) from wastewater. In this
study, the equilibrium and kinetics studies of the application of pineapple peels as
an adsorbent for the removal of Zn (II) and Cr (VI) ions from aqueous solutions
was investigated in a batch process. The initial and equilibrium metal ion
concentrations of the solutions were determined by Atomic Absorption
Spectroscopy. The characterization of the adsorbent was done using the Scanning
Electron Microscope and Fourier Transform Infrared Spectroscopy (FTIR). The
FTIRspectra confirmed that there are different functional groups in adsorbents,
which are able to react with metal ions in aqueous solution. Effects of initial pH,
initial metal ions concentrations, shakingtime and solid/liquid ratio on metal ions
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35
Olowu, R. A., Osundiya, M. O., Oyewole, T. S., Onwordi, C. T., Yusuff, O. K., Osifeko, O. O., &Tovide, O. O. (2022). Equilibrium and Kinetic Studies
for the Removal of Zn (Ii) and Cr (Vi) Ions from Aqueous Solution Using Pineapple Peels as an Adsorbent. European Journal of Applied Sciences,
10(5). 34-47.
URL: http://dx.doi.org/10.14738/aivp.105.13051
biosorption were also investigated. Adsorption of metal ions were pH dependent
and the results indicate that the optimum pH for the removal of Zn (II) and Cr (IV)
was found to be 6.0and the maximum percentage removal of Zn (II) and Cr (IV)at
this pH were 86.45% and 92.56% respectively along the whole range of initial
concentrations.Three adsorption isotherm models, Langmuir, Freundlich and
Temkin were used to simulate the equilibrium data. The experimental data were
best fitted to the Langmuir isotherm when compared with other models with the
highest R2 values of 0.937 and 0.987 for Zn(II) and Cr(VI) ions respectively. The
achieved results confirmed that the adsorption of zinc and chromium were in good
compliance with pseudo-first-order reaction kinetic suggesting that the
adsorption is apparently physisorption and the thermodynamics analysis of the
result showed that the process is spontaneous and exothermic.The pineapple
peels investigated in this study showed good potential for the removal of zinc and
chromium from aqueous solutions.
Keywords: Potentially toxic metals, Pineapple peels, Adsorption isotherm, Adsorption
process, pseudo first – order.
INTRODUCTION
Potentially toxic metals (PTMs)are produced in enormous magnitude during industrial
activities and pollute the environment. PTM contamination of the aquatic environment has
become an important issue with respect to environmental and human health. Metal ions are
non-biodegradable and many of them are soluble in aqueous media and easily available for
living things[1]. Toxicity of PTMs result into a number of disorders in animals and plants and
their removal from aqueous media is a crucial and challenging task [1-2]. The extensive
industrial use of low-cost adsorbents that have metal-binding capacities for wastewater
treatment is strongly suggested presently, due to their local availability,cost effectiveness
engineering applicability and technical feasibility. The application agricultural by-product as
biosorbent material tocleanse up PTM contaminated water has become increasinglyaccepted
through the past decade because they areeco-friendly, abundant and efficient [3]. Agricultural
by-products are mostly made up of cellulose and lignin and usually contain some active
functional groups, such as hydroxyl, carboxyl and ether groups[4].
Zinc is an essential element in bio-molecules and its uptake by living organisms is important.
Conversely, excessive concentration of zinc from metal refining and manufacturing processes
wastewaters result in damages to human health causing interference in metabolism and
arteriosclerosis [5]. To circumvent oxidation zinc is generally coated with ion and other
metals as well salts containing zinc are used as preservatives, ceramics, fertilizes, pigments,
and batteries [6]. Chromium subsists in aqueous media in two various oxidation state, Cr (VI),
and Cr (III) and the toxicity of chromium usually depends upon its oxidation state. In solution,
the Cr (VI) occurs in various forms depending upon the pH, such as hydro chromate (HCrO4-),
chromate (CrO42 -) , or dichromate (Cr2O72-
) [7]. In human blood the chromium only exist as
chromium (III) where it is responsible for maintenance of blood metabolism. The
recommended daily dietary intake (DDI) of chromium for human is 50 -200 μg/day [8].
Industrial activities like metal cleaning, dyeing processing, electroplating, cement and leather
tanning contribute to a great extent in releasing chromium into the environment and
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European Journal of Applied Sciences(EJAS) Vol.10, Issue 5, October-2022
Services for Science and Education – United Kingdom
chromium in the hexavalent form Cris very toxic. It is quite mysterious that contaminated
field by industrial effluent show a mobilization ratio of less than 5 (potentially toxic) for
specific plant species. Unexpectedly, the mobilization ratio for weeds becomes greater than 5,
which have healthy morphology in the early flowering stage [9].
Different processes are in recent times used in industry for the removal of PTMs from
aqueous butthe most commonly used methods include: filtration, electro dialysis, adsorption,
reverse osmosis, chemical precipitation and sedimentation [10-11]. Several works have been
reported on the adsorption of heavy metal onto solid surface, taking separation or
preconcentration into account, where complex mixture, a single element or a series can be
separated and quantitatively determined [12].
Adsorption method of removal of PTMs has demonstrated its economic feasibility, easy
handling and efficiency when compared with other methods and this has gained significance
in industrial applications [13]. Adsorption emerged to be good for the treatment of effluents.
The first thing for an efficient adsorption process is the search for a low cost adsorbent with
high adsorption capacity and secondly, its biodegradability [14]. Many workshave
demonstrated that agricultural wastes represent a new and promising class of adsorbent
materials for adsorption processes [15-34].
This study therefore investigates the optimal conditions for the use of pineapple peels as an
effective adsorbent for the removal of chromium and zinc ions from aqueous solution.
MATERIALS AND METHODS
Collection and Preparation of Adsorbent Sample
Pineapple peels (PP) were collected from fruit sellers in Iyana-Iba market, Ojo area, Lagos
State. The peels were washed first with tap water to remove dirt and mud and finally washed
with distilled water. After washing, they were air-dried, pulverized with an electric blender
and then sieved with mesh screens. The precursor obtained was finally transferred into a
cleaned plastic.
Preparation of Stock Solutions
All the chemical reagents used in this study were of analytical grade and taken from the
repository of the Chemistry department, Lagos State University, Ojo, Lagos, Nigeria.
Chromium dichromate (K2Cr2O7) and zinc sulphate (ZnSO4.7H2O) were used for the
preparation of stock solution. Stock solution of 1000 mg/L of Cr (VI) ion was prepared by
dissolving 2.8269 g of potassium dichromate (K2Cr2O7) in distilled water in 1L volumetric
flask. Stock solution of 1000 mg/L of Zn (II) was prepared by dissolving 4.4154 g of zinc
sulphateheptahydrate (ZnSO4.7H2O) in distilled water in 1 L volumetric flask. The solutions
for the experiments were prepared by appropriate dilution of the stock solution with distilled
water to obtain solution of concentrations 200 – 1000 mg/L.
Characterization of the Adsorbent Material
FT-IR Analysis
The chemistry of the surface of the pineapple peels were probed by determining the
functional groups present using Fourier Transform Infra Red (FT-IR) Spectroscopy analysis.
Page 4 of 14
37
Olowu, R. A., Osundiya, M. O., Oyewole, T. S., Onwordi, C. T., Yusuff, O. K., Osifeko, O. O., &Tovide, O. O. (2022). Equilibrium and Kinetic Studies
for the Removal of Zn (Ii) and Cr (Vi) Ions from Aqueous Solution Using Pineapple Peels as an Adsorbent. European Journal of Applied Sciences,
10(5). 34-47.
URL: http://dx.doi.org/10.14738/aivp.105.13051
The FT-IR spectra of the sample before and after the adsorption processes were recorded
within 650 - 4000 cm-1 using the Fourier Transform spectrophotometer; SHIMADZU FT-IR- 8400S model.
Scanning Electron Microscopy
The surface morphology of the pineapple peels were analyzed using Scanning Electron
Microscope (SEM). Surface topographical information was obtained by a surface
morphological study using phenonprox Scanning Electron Microscope JEOL-JSM-35CF model.
Adsorption Experiment
Batch adsorption experiments of zinc and chromium ions were carried out to investigate the
effect of pH, initial metal ion concentration, adsorbent dose, time and temperature on the
adsorption capacity of pineapple peels. The pH range of 2 – 10, initial metal ion concentration
range of 200 – 1000 mg/L, adsorbent dose range of 0.1 – 1.0 g, time range of 20 – 100 minutes
and temperature range of 27 – 670C were used respectively. A constant amount (0.8 g) of
pineapple peels in order to calculate the adsorption constant using different isothermsand
50mLof different concentration of zinc (II) and chromium (VI) solution ranging from 200-
1000 mg/L were used. The fixed mass of the pineapple peels were added to flasks and
agitated at 27oC and 120 rpm for 120 minutes. The samples were tested for their initial and
final concentrations with Atomic Absorption Spectrophotometer (AAS). The maximum
adsorption wavelength and the adsorption capacities of the adsorbent were calculated. After
equilibrium was attained, the metal uptake capacity for each sample was calculated according
to a mass balance on the metal ion using equation (1):
�!=
"($!%$")
' -------------- (1)
Where � is the mass of the adsorbent (g), � is the volume of the solution (L), �( is the initial
concentration of metal (mg/L), �! is the equilibrium metal concentration (mg/L) and �! is the
metal quantity adsorbed at equilibrium (mg/g).
The experiments were carried out at different initial pH values. The initial pH of the solutions
was adjusted with either HCl or NaOH. The percentage removal of metal ions from the
solution was calculated using equation (2):
%������� = ($!%$")
$!
�100-------------- (2)
Where �( (mg/L) is the initial metal ion concentration and �! (mg/L) is the final metal ion
concentration in the solution.
Adsorption Kinetics
The kinetic study of adsorption plays an important role because it affords an essential insight
into reaction pathways and into the mechanism of the reaction. Kinetic have been proposed to
describe the mechanism of a solute sorption from aqueous solution onto an adsorbent. The
Lagergren’s pseudo first order kinetics model was used to describe the kinetic studies of this
experiment. The pseudo first order kinetic model has been widely used to predict the metal
adsorption kinetics [25]. The integral form of the model is express as:
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European Journal of Applied Sciences(EJAS) Vol.10, Issue 5, October-2022
Services for Science and Education – United Kingdom
���(�! − �)) = ����!
*#
+.-(-
�-------------- (3)
By plotting ���(�! − �)) against �, the adsorption rate can be calculated
Equilibrium Isotherm Modeling
In this present work three isotherm models were applied to investigate the adsorption
process of Zn (II) and Cr (VI) on pineapple peels at different conditions of process parameters.
The adsorption equilibrium study was carried out for metal concentration varying from 200 -
1000 mg/L.
Langmuir Isotherm
The Langmuir adsorption Isotherm model [26]has been effectively applied in many
adsorption processes. The Langmuir equation is express as:
�! = .$/%$"
01/%$"
-------------- (4)
Linearization of equation (4) gives:
$!
.!
=
0
.$/%
+ $"
."
-------------- (5)
Where Ce is the equilibrium metal concentration, �' and �2 are the Langmuir constants
related to maximum adsorption capacity (mg/g), and the relative energy of adsorption
(1/mg), respectively.
Freundlich Isotherm Model
The Freundlich adsorption Isotherm model [27] is one of the most broadly used mathematical
models which fit the experimental data to a multilayered adsorption over a wide range of
concentration. This isotherm is based on heterogeneous surface, distribution of active sites
and their energies and enthalpy changes logarithmically [28]. The Freundlich equation is
expressed as:
�! = �3�!
#
&-------------- (9)
The logarithmic form of the equation is:
ln �! = In �3 + 0
4 ���!-------------- (10)
Where�! is the amount of metal ion adsorbed after per specific amount of adsorbent (mg/g),
�!is the equilibrium concentration (mg/L), �3 and n are Freundlich equilibrium constants.
Temkin Isotherm Model
The Temkin isotherm model [29] contains a factor that clearly takes the account of adsorbent- adsorbate interaction. The model assumes that heat of adsorption (function of temperature)
of all molecules in the layer would decrease linearly rather than logarithmic with coverage on
ignoring the extremely low and large value of concentration [10- 11]. The Temkin isotherm is
given by the following expression:
�! = 6'
7
��(��!)-------------- (11)
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39
Olowu, R. A., Osundiya, M. O., Oyewole, T. S., Onwordi, C. T., Yusuff, O. K., Osifeko, O. O., &Tovide, O. O. (2022). Equilibrium and Kinetic Studies
for the Removal of Zn (Ii) and Cr (Vi) Ions from Aqueous Solution Using Pineapple Peels as an Adsorbent. European Journal of Applied Sciences,
10(5). 34-47.
URL: http://dx.doi.org/10.14738/aivp.105.13051
The linear form of equation (11) gives;
�! = � + ����!-------------- (12)
Where �! is the amount of metal ion adsorbed per specific amount of adsorbent (mg/g), �! is
the equilibrium concentration (mg/L), � is the equilibrium binding constant (g-1) and � is
related to heat of adsorption (Jmol-1) which are the Temkin constants.
Thermodynamic Parameters
The thermodynamic parameters such as change in Gibbs free energy (∆G0), enthalpy (∆H0)
and the entropy (∆S0) can be determine from the equilibrium constant K which is temperature
(T) dependent. All the thermodynamic parameters that are associated with adsorption
process can be determined by using the equation below [10-11]:
∆� = −�����-------------- (13)
Where � is the Langmuir constant, � is the Absolute temperature and � is the Universal gas
constant (R = 8.314 Jmol-1.K-1).
Also,
��� = ∆9
6 − ∆:
6;-------------- (14)
The plot of��� as a function of 0
; gives a straight line graph from which ∆� and ∆� can be
calculated from the slope and the intercept respectively.
RESULT AND DISCUSSION
Fourier Transform Infra-Red Spectrophotometer
Fig. 2 shows FT-IR spectra for the adsorbents before and after adsorption process. Variations
of peaks were observed on the adsorbents in this study. The broad band occurring at 3339.7
cm-1- 3291.2 cm-1 are due to the presence of –OH group in aliphatic alcohol on the adsorbents
materials. The band peaks at 2918.5 cm-1 and 2922.2 cm-1 may be attributed to C – H stretch
in alkenes. The peak at 1722.0 cm-1 is due to C=O stretch in aliphatic ketone. The FT-IR
spectral reveals the abundance of hydroxyl group in the adsorbent materials.
Page 8 of 14
41
Olowu, R. A., Osundiya, M. O., Oyewole, T. S., Onwordi, C. T., Yusuff, O. K., Osifeko, O. O., &Tovide, O. O. (2022). Equilibrium and Kinetic Studies
for the Removal of Zn (Ii) and Cr (Vi) Ions from Aqueous Solution Using Pineapple Peels as an Adsorbent. European Journal of Applied Sciences,
10(5). 34-47.
URL: http://dx.doi.org/10.14738/aivp.105.13051
Fig.: 1 SEM images for the adsorbent (a) raw pineapple peels, (b) pineapple peels after Zn(II)
adsorption and (c) pineapple peels after Cr(VI) adsorption
Effect of Parameters
Effect of pH
Fig. 4(a) illustrates that pH obviously influenced the removal efficiency of the zinc ions in the
aqueous solution. The result showed that removal of Zn(II) and Cr(VI) increase as the pH
increases to a maximum value at pH 6 and later decrease with pH from 7 to 10 at 27 0C. The
maximum % removal of Zn(II) and Cr(VI) were 86.45 and 92.56 respectively at pH 6. Cr(VI)
exists in solution as HCrO4-
, Cr2O72- and CrO42- at lower pH. The adsorbents material surface is
also protonated and there is a strong electrostatic attraction between the positively charged
surface of the adsorbent with oxyanions of Cr(VI). The interaction between these ions HCrO4-
,
Cr2O72- and CrO42- with adsorbent surface decreases at higher pH because at higher pH the
surface of adsorbent becomes negatively charged and also there is abundance of hydroxyl
ions in aqueous solution which causes repulsion..
Effect of Adsorbent Dose
The effect of varying the adsorbents dose on the adsorption of Zn (II) and Cr (VI) ions was
studied by varying the adsorbent dose from 0.1 – 1.0 g and keeping other parameters
constant. Fig. 4(b) indicates that the % removal of Zn (II) and Cr (VI) ions increases on
increasing adsorbent doses. This is expected to occur as a result the higher adsorbent dose in
the solution provides the greater availability of exchangeable sites for the ions. From the
figure it is clear that the maximum % removal of Zn (II) and Cr (VI) ions were 89.0 % at the
dosage of 0.8 g and 91.20% at 1 g dosage respectively. This result suggests that adsorption
equilibrium efficiency depends on adsorbent dosage. This may be due to the fact the higher
dose of adsorbents in the solution provides more availability of exchangeable sites for the ions
[16-17].
Effect of Initial Metal Ion Concentration
The effect of initial zinc concentration on the adsorption rate was studied in the range (200 -
1000 mg/L). The result in Fig. 4(c) shows that the % removal of the metal ions decreases with
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European Journal of Applied Sciences(EJAS) Vol.10, Issue 5, October-2022
Services for Science and Education – United Kingdom
increasing in the initial concentrations. The poorer uptake at higher metal concentration may
be attributed to the increased ratio of initial number of moles of the metal ions to the vacant
sites available. This result indicates that the adsorption of Zn(II) and Cr(VI) ions is affected by
the initial concentration of the ions until equilibrium is attained.
Effect of Contact Time
The effect of contact time on the adsorption of Zn(II) and Cr(VI) ions were determined by
varying the contact time between the adsorbate and adsorbent in the range of 20 – 100
minutes. Fig. 4(d) indicates that % removal of Zn(II) and Cr(VI) ions from aqueous solution
increases before the equilibrium was established as the contact time increases.
Effect of Temperature
The temperature dependence of the adsorption process is related with several
thermodynamic parameters. The effect of temperature was studied by varying the
temperature within the range (27-67 0C) and keeping other parameter constant. The result in
fig. 4(e) indicates that with increase in temperature from 27-67 0C, the % removal of Zn(II)
and Cr(VI) ions decreases. It is clear that low temperatures favor the removal of the Zn(II) and
Cr(VI) ions and this may be attributed to the tendency of the ions to escape from the solid
phase to the bulk phase with an increased in temperature of the solution. The result indicates
that the adsorption process is physical in nature and this implies that the process was
exergonic in nature with low adsorption heat.
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43
Olowu, R. A., Osundiya, M. O., Oyewole, T. S., Onwordi, C. T., Yusuff, O. K., Osifeko, O. O., &Tovide, O. O. (2022). Equilibrium and Kinetic Studies
for the Removal of Zn (Ii) and Cr (Vi) Ions from Aqueous Solution Using Pineapple Peels as an Adsorbent. European Journal of Applied Sciences,
10(5). 34-47.
URL: http://dx.doi.org/10.14738/aivp.105.13051
Fig.4 : Effects of (a) pH, (b) Adsorbent dose (c) Initial metal ion concentration, (d) Time and (e)
Temperature on adsorption of Zn (II) and Cr (VI) from aqueous solution
Adsorption Kinetics
The adsorption kinetics of the adsorption experiments were determined by pseudo-first order
reaction. The contact time ranging from 30-150 minutes was used and the result in fig.5
indicates that the experimental data was fitted for pseudo- first order kinetic model due to R2
value that is closer to unit.
Fig. 5: Pseudo first order kinetics plot for (a) Zn (II) and (b) Cr (VI).