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Removal of Heavy Metals from Aqueous Solutions Using modified Irish potato leaf as Low Cost Biosorbent (kinetic and thermodynamic studies). Abimbola A. Ogundiran1,2, N. A. Adesola Babarinde2
1Department of Chemical Sciences, Tai Solarin University of Education, Ijagun, Ogun-State.
2Department of Chemical Sciences, Olabisi Onabanjo University, Ago- Iwoye, Ogun- State.
*Corresponding Author E-mail: ogundiranaa@tasued.edu.ng
Abstract
This study deals with the kinetic of biosorption, equilibrium and thermodynamic of six metal ions (Cd2+, Zn2+, Ni2+, Cr3+,
Pb2+& Co2+) from synthetic wastewater unto base modified Irish potato leaf. The biosorbent was characterised using
Fourier transform infrared spectroscopy. The effects of parameters such as initial concentration of metal ions, pH, contact
time, mass of biosorbent and temperature were investigated. Batch kinetic data were subjected to the pseudo first-order,
pseudo second-order, intraparticle diffusion and Elovich kinetic models The maximum adsorption capacity was found at pH
6, 10 mg/L concentration, adsorbent dosage at 1.0 g/L and 2 h contact time. The adsorption capacity was found to be
highest for Nickel metal ion (mg/L) in the order Ni > Zn > Pb > Cd > Cr > Co. The adsorption capacity also increased as
temperature of experiment increased. Biosorption kinetics study showed that pseudo second order model was suitable to
explain the experimental data having correlation coefficient (R2) ranges from (0.998- 0.999). Intraparticle diffusion model
showed that the adsorption process develops in stages, as fast, moderate and slow stages. Conclusively, the study showed
that the prepared biosorbent can be a preferable biosorbent for the removal of toxic metal ions being a cheap and eco-
friendly alternative adsorption materials.
1. Introduction
to population explosion, increased
years the quest to find solution to the
persistence of heavy metals in the environment
has been a global issue. Large quantity of
wastewater containing organic and inorganic
contaminants are been generated. Heavy metals
such as Ni, As, Cd, Pb, Cr, etc are some of the
wastewater pollutants. The presence of heavy
metals in industrial wastewater being discharged
into surface waters is becoming a serious
environmental global issue. Subsequently their
non-biodegradability and their potential to
accumulate in the food chain pose an important
risk to human wellbeing (Mani and Kumar,
2014). Therefore, it become necessary to
sequester these metals from the environment
(Mohamed et al., 2016). Several techniques have
been employed for efficient and effective
removal of heavy metals from aqueous solutions
95
techniques include; coagulation-flocculation,
2014; Barsbay et al., 2017; Choi, 2015b; Feizi and
Jalali, 2015; Ihsanullah et al., 2016). Most of
these methods are costly, and are inept in
controlling the concentration of heavy metal
ions in industrial wastewater especially in small
scale industries. Biosorption has been studied
over the years to be suitable for the removal of
heavy metals because it is cheap and easier to
operate than other processes (Kim et al., 2015;
Wang and Chen, 2009). Some of the industries
which release heavy metals contaminants are
metal plating, tanneries, car radiator
manufacturing, pharmaceutical, and mining
low-cost adsorbents. Many materials have been
investigated, they include microbial biomass,
peat, compost, leaf mould, palm press fibre,
coal, sugarcane bagasse, straw, wool fibre and
by products of rice mill, soybean and cottonseed
hulls etc.
This study, is aimed at confirming the possibility
of the removal of Cr, Ni, Zn, Co, Pb, and Cd from
aqueous solution using base modified irish
potato leaves. Accordingly, irish potato leaves
are by-products of irish potato plant and are
natural biosorbents that can easily be obtained
from local farms in the northern part of Nigeria.
The leaves contain a large amount of tannin, a
polyphenol compound that can binds to metal
ions by chelation (Xie et al., 2015).
2. Materials and Methods
2.1 Preparation of adsorbate
were of analytic reagent grade. Adequate
amounts of the metal salts were dissolved in de-
ionized water (DIW) to yield the stock solutions
of concentration 1000 mg/L. Concentrations
used in the adsorption studies were obtained by
dilution of stock solution with DIW. All glassware
was washed with soap, followed by 10% HNO3
and then rinsed many times with DIW before
use. Adjustment of pH was done using either 0.1
M HCl or 0.1M NaOH, and pH was measured with
a pocket pH meter.
biomass were collected from a local agriculture
farmland after harvest in Jos Nigeria. The
biomass was washed with tap water to remove
organic substances and contaminants on the
surface of the leaves and dehydrated under the
sunlight for 3 days. It was then activated with 0.2
M NaOH. The base modified Irish potato leaves
(bIPL) leaves were dried and stored in a
desiccator for the experiment.
2.3 Batch Biosorption Experiments
system using boiling tube in a thermostatic
shaker 25 unless otherwise stated. Each tube
was filled with 25 mL of solution and 0.5 g
biosorbent as appropriate. The influence of
several parameters on the biosorption
characteristics of the metals such as pH of the
aqueous solution (1–7), contact time (0−300
min), initial metal ion concentration (10−100 mg
L−1), and temperature (25−50). After the
reactions residual concentration of the heavy
metals in the aqueous phase was analysed. The
amount of the metal ions remaining in the
solutions was measured by using Atomic
96
by centrifugation. The amount of metal
adsorbed per gram of the biosorbent at
equilibrium, (mg g−1), was calculated from the
difference of the metal concentration in the
aqueous phase before and after biosorption as
follows:
concentration of metal ions in the solution
(mg/L), respectively, is the volume of metal
solution (L), and is the mass of the dry
biosorbent (g). The percentage of metal removal
(, %) from the solution was calculated as
follows:
triplicate results.
kinetic models applied in this study are as
follows: pseudo-first-order (PFO) equation (3),
pseudo-second-order (PSO) equation (4), Elovich
equation (5), and intraparticle diffusion (IpD)
equation (6).
)1( 1tk
et eQQ
mechanism of binding of metal ions to the
surface of the biosorbent. Most researchers
apply the pseudo-first-order kinetics of
(Lagergren, 1898), the pseudo-second-order
McKay 1999), Elovich model as described by
(Chien and Clayton 1980; Roginsky and
Zeldovich, 1934) and the intraparticle diffusion
model as shown in (Liu, Sun, and Li, 2011; Weber
and Morris, 1963) to describe kinetic data. These
models are used to investigate the controlling
mechanism of biosorption process.
analysis was carried out to determine the
possible functional groups present in the dried
biomass of modified sweet potato leaf. Infrared
spectra of the raw and metal-loaded biomass
were obtained using a Fourier transform infrared
(FTIR) spectrophotometer
for a pH range of 1-7 and the results are
presented in Figure 1. Hydrogen ion
concentration (pH) is one of the most important
parameter which has to be investigated in the
removal of heavy metals from aqueous solution
(Kosmulski, 2014). The results showed that the
removal of the metal ions from the solution
increased as the pH increased from pH 1 to pH 6.
At low pH below 4 the concentration of
hydrogen ion was high and competed with the
metal ions for the binding sites which lead to
repulsion of the metal ions thereby inhibiting the
97
removal of the metal ions by the surface of the
biosorbent. However as the pH increased
exchangeable cations on the adsorbent surface
become less competitive with the adsorption of
H+ ion and the adsorption of the metal ions
increased considerably (Barsbay et al., 2017). As
the pH increased the surface of the biosorbent
become deprotonated and thus lead to the
increased removal of metal ions.
3.2 Effect of Contact Time
The influence of contact time on the sorption of
metal ions onto bIPL, at room temperature
(25°C), constant adsorbent mass (0.5 g), initial
solution pH of 6 and initial heavy metal ions
concentration 100 mg/L, is illustrated in (Figure
2). The results showed that the amount of heavy
metal ion removed from the solution increased
with increase of contact time which range from
5-300 min and reached maximum after 120 min.
The adsorption curves showed a slow increase
until equilibrium and, in the next phase, a
plateau. After 120 min, adsorption of the metal
ions approached equilibrium.
suggested to take place in two distinct steps: a
relatively rapid phase of significant absorption
followed by a slower and quantitatively
insignificant one, and this type of behaviour has
been reported by (Babarinde et al., 2013) , the
rapid stage lasts from several minutes to an
hour, while the slow stage continues for several
hours. Biosorption is rapid initially due to the
availability of abundant active binding sites on
the biosorbent, however, with the gradual
occupancy of these sites, sorption becomes less
proficient, leading to the slow stage and
inefficiency of biosorbent to remove the metal
ions (Costa and Leite, 1991; Adebayo et al.,
2012).
effect of metal ion concentration is shown in
Figure 3. The study revealed that the uptake of
metal ions is dependent on initial concentration
and it increases with increasing in initial
concentration of metal ions. At lower
concentration the ratio of the binding active
sites to metal ion concentration is high which
enable all metal ions to interact with the sorbent
surfaces (Reddy et. al., 2010). However, as the
concentration increased, there were a greater
driving force to transport the metals ions but the
adsorption removal rate become less. As the
concentration of metal ions become extremely
high the binding sites were saturated, thus
causing the reduction in the percentage of metal
ion removed from the solution.
3.4 Effect of biosorbent dosage
The amount of metal ions biosorbed by bIPL is
influenced by its dosage. The effect of
biosorbent dosage is represented in Figure 4.
The percentage of metal ion biosorbed increased
as the mass of biosorbent increased (Tasar,
Kaya& Özer 2014) this is because the biosorption
process is dependent on the number of available
active sites as observed when the dose of
adsorbent was increased from 0.1- 1g/25 mL.
Further increase in the adsorbent dose did not
cause any significant change in the adsorption of
the metal ions. This may be due to overlapping
of adsorption site as a result of overcrowding of
adsorbent particles which eventually resulted in
the reduction of effectiveness of the biosorbent.
98
thermodynamic studies
biosorption of heavy metals. The biosorption of
metal ions onto base modified Irish potato
leaves (bIPL) increased with increase in
temperature from 298 to 323 K. This is indicative
of an endothermic process. The increase in
adsorption efficiency with increase in
temperature may be indicative of a
chemisorption process (Kara et al., 2003).
The thermodynamic behaviour of the
biosorption of the metal ions onto bIPL was
described using thermodynamics parameters
enthalpy change (Ho) and entropy change (So).
These parameters were evaluated from the
equations (7) below:
J/Mol/K), T is temperature in Kelvin and Kc is the
thermodynamic equilibrium constant and is
obtained from the below equation:
=
⁄ (8)
and Ce is equilibrium concentration of solution
(Sarin and Pant, 2006). According to
thermodynamics, the Gibb’s free energy is also
related to enthalpy change (H° ) and entropy
change (S°) at constant temperature by the
Van’t Hoff equation:
The values of Ho and So were evaluated from
the slope and intercept of Van’t Hoff’s plot of In
Kc against 1/T (Figure 6.).The positive value of
Ho of biosorption indicates that the process is
endothermic while positive value of So shows
increased randomness at solid solution
interphase (Dang et al., 2009). Also, the increase
in negative value of the change in Gibb’s free
energy (Δo) as temperature increased is an
indication of feasibility and spontaneous nature
of the biosorption process.
biosorption of metal ions onto bIPL
Figure 2: Time profile for the adsorption of metal
ions onto the leaf biomass of bIPL
1 2 3 4 5 6 7
35
40
45
50
55
60
65
70
75
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
99
the biosorption of metal ions onto bIPL
Figure 4: Effect of adsorbent dose on the
biosorption of metal ions onto bIPL
Figure 5: Effect of temperature on the
biosorption of metal ions onto bIPL
0.00305 0.00310 0.00315 0.00320 0.00325 0.00330 0.00335 0.00340 0.00345
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
biosorption of metal ions using base modified
irish potato leaf
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
10
20
30
40
50
60
70
55
60
65
70
75
80
100
Table 1: Thermodynamic parameters for biosorption using acid modified Irish potato leaves.
Temperature Cr3+ Pb2+ Ni2+ Co2+ Zn2+ Cd2+
293 -1305.89 -733.367 -1181.17 -1286.04 -1040.61 -1101.95
298 -1816.48 -1162.54 -1477.28 -1695.43 -1275.13 -1521.74
G°(kJ/mol) 303 -2122.48 -1500.96 -2071.2 -2192.31 -2439.53 -2375.49
308 -2414.68 -1986.91 -2254.39 -2305.27 -2880.59 -3374.27
313 -2788.59 -2641.35 -2398.67 -2653.36 -3429.05 -3739.65
318 -3333.92 -3406.71 -2974.12 -2918.69 -3746.88 -3814.76
323 -3790.43 -3636.34 -3623.19 -3460.27 -4637.13 -4407.35
H°(kJ/mol) 20.359 28.321 18.462 17.744 32.569 30.885
S° J/Kmol) 73.45 98.196 66.43 64.523 113.93 108.85
101
Table 2: Kinetic model parameters for the metal ions biosorption onto base modified Irish potato
leaves (bIPL).
Q(cal)(mg/g) 3.266 3.811 3.613 3.298 4.811 4.017
PSEUDO-FIRST-ORDER Q(exp)(mg/g) 3.008 3.239 3.306 3.094 3.312 3.162
k1(min-1) 0.0323 0.039 0.0033 0.0234 0.0435 0.0031
SSE% 0.01818 0.03532 0.01985 0.01408 0.07343 0.04987
R2 0.958 0.978 0.983 0.981 0.975 0.963
Q(cal)(mg/g) 2.956 3.131 3.091 2.927 3.149 2.995
PSEUDO-SECOND
k2 (g/mg min) 0.014 0.099 0.011 0.013 0.033 0.022
SSE% 0.005 0.008 0.016 0.014 0.013 0.014
R2 0.977 0.983 0.981 0.982 0.981 0.983
α (mg/g min) 0.431 0.637 0.421 0.344 0.501 0.418
Elovich β (g/mg) 1.654 1.608 1.506 1.554 1.543 1.594
R2 0.921 0.987 0.978 0.982 0.977 0.981
Kp( mg/g min½) 0.793 0.969 0.817 0.717 0.893 0.785
Intra particle diffusion C 0.164 0.171 0.178 0.168 0.177 0.174
R2 0.922 0.914 0.954 0.951 0.943 0.954
3.6 Kinetic of biosorption
Figures 7-10 and as shown in Table 2 the high
value of the correlation coefficient of the
pseudo-first-order model suggests that the
experimental data accurately support the PFO
model to describe adsorption kinetics of the
metal ions. But the differences between the
experimental values, , were higher than the
modelled values . It refers to the fact that
both the metal ions and adsorbent were
involved in the process of biosorption.
Therefore, it is assumed that the pseudo-first-
order model may not be suitable to explain the
kinetic for the experimental metal ions sorption
by base modified Irish potato leaves. Therefore
among the studied kinetic models, the
experimental values for pseudo second order
matched well with the calculated data (Table 2).
102
of the PSO model for the adsorption of the metal
ions. Hence, chemisorption is the rate-limiting
step which involves valence forces through the
sharing or exchange of electrons between the
metal ions and different functional groups in the
sorbent. The behaviour of Elovich constant
shows that the process of biosorption is more
than one mechanism. Similar results have been
reported for the sorption kinetic of different
metal ions onto different adsorbents (Ksakas et
al 2018; Farnane et al 2018; Sayedur and
Kathiresan 2015, Arshadi et al 2014; Meitei and
Prasad 2014).
of metal ions using base modified Irish potato
leaf.
biosorption of metal ions using base modified
Irish leaves
ions using base modified Irish potato leaf.
Q t(
103
biosorption of metal ions using base modified
Irish potato leaf
3.7 FTIR Characterization
indicative of the presence of hydroxyl groups of
macromolecular association (cellulose, pectin,
stretching around 3,000 cm–1 and the –CH
deformation modes around 1,460 cm-1 and 1,365
cm-1 . The atoms directly attached to the
aliphatic groups may result in significant shifts
from the standard frequencies. In particular
adjacent atoms with high electro negativity will
shift the band locations to higher frequencies.
The CH3 asymmetric stretching vibration
occurred at 2,978–2,950 cm-1. Carboxylic acid
salts typically show a strong, characteristic
asymmetric stretching absorption from the CO2-
group in the 1,655–1, 550 cm–1 region. The
corresponding symmetric stretching absorption
occurs at around 1,440–1,335 cm–1. The peak at
1,468 cm–1 can be attributed to the methylene C–
H bend (Baraka et al. 2007). The comparison
showed that the bands characteristic to hydroxyl
groups at 3475.07 cm–1, alkyl group at 2978cm-1
and that characteristic to unsaturated carbonyl
at 1651 cm-1 frequencies were slightly shifted
due to the attachment of the metal ions.
Figure 11: FTIR spectra of free and metal bound
modified sweet potato leaf
of Ni(II), Cr(III), Co(II), Cd(II), Pb(II) and Zn(II)
Conclusion
(III), Co(II), Zn(II), Ni(II), Pb(II) and Cd(II) by Irish
potato leaf biomass was influenced by the
solution pH, biosorbent dose, contact time,
temperature and initial metal ion concentration.
The metal ions biosorption process is best
described by a Pseudo-second order model
based on the assumption that the rate limiting
step may be a chemical sorption process. The
study of the thermodynamic parameters showed
104
is feasible and spontaneous and therefore
industrially applicable while the positive value of
enthalpy change (H°) indicates an endothermic
process. The FT-IR studies of the biosorbent
before and after being loaded by the metals
revealed that hydroxyl, carboxylate, functional
groups may be involved in the sorption process
as the intensities and wave numbers of these
bands changed after the biosorption. Hence the
use of the leaf biomass of Irish potato can be
employed as good biosorbent for the removal of
metal ions from aqueous solutions and as an
alternative sorbent of their removal from
industrial effluent.
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