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Comparison of adsorption performances of vermiculiteand clinoptilolite for the removal of pyronine Y dyestuff
Mahmut Toprak • Abdullah Salci •
Ali Riza Demirkiran
Received: 1 August 2013 / Accepted: 15 November 2013
� Akademiai Kiado, Budapest, Hungary 2013
Abstract In this study, the adsorption of pyronine Y (PyY) from aqueous solution
on two adsorbents, vermiculite and clinoptilolite, was investigated with respect to
contact time, initial dye concentration, pH, adsorbate concentration and solution
temperature. Moreover, the dye removal performance of vermiculite was compared
with that of clinoptilolite under the same experimental conditions. The adsorption of
dye on adsorbents reached equilibrium in 15–25 min. The dye removal performance
of vermiculite was comparable with that of clinoptilolite at high adsorbent con-
centrations above 5.0 g/L resulting in nearly 91 % dye removal with 10 mg/L initial
dye concentration. The equilibrium experiments were analyzed by the Langmuir
and Freundlich isotherms. As a result, the adsorption of PyY by clinoptilolite fitted
the Freundlich isotherm well, while that by vermiculite fitted the Langmuir isotherm
well. The first order kinetic, pseudo-second order kinetic and intra-particle diffusion
models were used to investigate the kinetic data. The adsorption kinetics of PyY on
adsorbents was described by the pseudo-second order kinetic equation. Moreover,
the activation parameters were also calculated. It was found that the reaction for dye
uptake by vermiculite and clinoptilolite is the presence of an energy barrier.
Keywords Pyronine Y � Vermiculite � Clinoptilolite � Dye
Introduction
Synthetic dyes are widely used in many fields of industry, for example the textile,
cosmetic and pharmaceutical industries. Today, the worldwide productions of
M. Toprak (&) � A. Salci
Department of Chemistry, Bingol University, Bingol 12000, Turkey
e-mail: mahtoprak@gmail.com
A. R. Demirkiran
Department of Agriculture, Bingol University, Bingol 12000, Turkey
123
Reac Kinet Mech Cat
DOI 10.1007/s11144-013-0651-5
synthetic dyes are approximately 8 9 105 tons and most of them are discharged
directly into wastewater. The discharge of dye wastewater is a serious environmental
problem [1–5]. Colored water is harmful to aquatic animals because it contains a
variety of organic compounds and toxic substances [6–8]. Besides, the presence of
dyes in various sources of water diminishes light penetration, preventing photosyn-
thesis of the aquatic plants. In addition, colored water may affect human health
because of the mutagenic and carcinogenic effects of dyes. Furthermore, many of these
dyestuffs are resistant to biological degradation because of their synthetic origins [9–
16]. Therefore, these dyes need to be removed before the wastewater can be released
into the environment. The removal of dyes from wastewater has been conventionally
carried out by physical and chemical methods. Among these methods, adsorption is
one of the effective techniques because it is rapid and relatively easy to use. This
process is based on the principle of transferring the dyes from the wastewater to solid
phase. Activated carbon is an ideal adsorbent for wastewater treatment. However, its
use is restricted owing to the high price and regeneration problems [17, 18]. For this
reason, it is necessary to develop low-cost and easily available alternative adsorbents
for the treatment of effluent. In recent years the use of clinoptilolite, a natural zeolite,
and vermiculite, a mica-type lamellar mineral, has been investigated in terms of the
cost and potential for wastewater treatment [19–21]. Qiu et al. [22] investigated the
adsorption of safranine T and Amido Black 10B from aqueous solution with clin-
optilolite. The maximum adsorption capacity and adsorption affinity of the clinoptilolite
to the two dyes were calculated and predicted using the Langmuir model. Tang et al. [23]
studied the adsorption of methyl orange on vermiculite modified by cetyltrimethylam-
monium bromide (CTMAB) and suggested that the methyl orange removal rate of
CTMAB-vermiculite was better than that of vermiculite. Zhao et al. [24] investigated
the adsorption of methylene blue onto silica nano-sheets derived from vermiculite using
acid leaching. Results showed that the adsorption of methylene blue by silica nano-sheet
fitted the Langmuir equilibrium isotherm very well. Sismanoglu et al. [25] studied the
adsorption of reactive dyes onto clinoptilolite. It was found that the adsorption rate
decreased with increasing dosage of the reactive dyes. As a result, vermiculite and
clinoptilolite have been investigated for a wide variety of effluent applications.
However, the adsorption process of pyronine Y (PyY) dye which is a xanthine derivative
from aqueous solution on these adsorbents has not been reported so far.
In the current study, we report the ability of natural clinoptilolite and vermiculite
to remove PyY by adsorption from aqueous solution. In addition, this study provides
fundamental information on PyY adsorption capacities and adsorption constants for
clinoptilolite and vermiculite. The PyY removal performance of clinoptilolite was
compared with that of vermiculite under the same conditions. Therefore, this study
chooses to investigate the kinetic, equilibrium and activation parameters of
clinoptilolite and vermiculite to remove basic dye from aqueous solution.
Materials and methods
PyY was purchased from Sigma and used without further purification (chemical
formula: C17H19ClN2O, MW: 302.80 g/mol). The clinoptilolite sample was
Reac Kinet Mech Cat
123
obtained from Goztepe (Istanbul, Turkey). The vermiculite sample used was
obtained from Karamursel (Kocaeli, Turkey). The clinoptilolite and vermiculite
powders of 20–50 mesh were used for adsorption experiments. Some physical
properties and the chemical composition of the adsorbents are shown in Tables 1
and 2. A stock solution was prepared by dissolving precisely 302 mg of PyY in
250 mL distilled water. All working solutions of PyY were prepared by diluting the
stock solution to required concentrations. Isotherm studies were carried out using
different amounts of adsorbents with 10 mL dye solutions of known initial
concentration (10 mg/L) at the desired pH and temperature. To adjust the pH of the
solution, a strong acid (0.1 mol/L HCI) or strong base (0.1 mol/L NaOH) was used.
The pH of the solutions was recorded with a Thermo Scientific pH meter. The
concentration of PyY in aqueous solution was determined by a spectrophotometer
(UV-1600, Shimadzu) at a wavelength of 548 nm. All adsorption experiments were
conducted with 50 mL flasks containing 10 mL of solution at constant temperatures
of 22, 30, 40 and 50 �C and the experiments were performed three times. The
amounts of dye adsorbed on clinoptilolite and vermiculite were calculated from the
concentrations in aqueous solutions before and after adsorption. The solid phase
loading was calculated by Eq. 1:
qe ¼ðC0 � CeÞ:V
1000:mð1Þ
where qe is the amount of dye adsorbed per gram of adsorbent in mg/g, C0 is the
initial dye concentration in mg/L, Ce is the equilibrium (residual) dye concentration
Table 1 Typical physical
properties of adsorbentsClinoptilolite Vermiculite
Bulk density (kg/m3) 650–850 64–160
Cation exchange (meg/g) 1.5–1.9 0.5–1
Water adsorption (%) 42–50 20–45
pH 7–8 6–9
Surface area (m2/g) 39 3.14
Porosity (%) 45–50 25–50
Table 2 Typical chemical
analysis of adsorbentsComposition (%) Clinoptilolite Vermiculite
SiO2 65–72 38–46
AI2O3 10–12 10–16
MgO 0.9–1.2 16–35
CaO 2.5–3.7 0.5–3
K2O 2.3–3.5 2–6
Fe2O3 0.8–1.9 4–12
TiO2 0–0.1 0.7–3
MnO 0–0.08 0.01–2
Na2O 0.3–0.65 0.1–1
Other 4.87–18.2 8.2–17.2
Reac Kinet Mech Cat
123
in mg/L, V is the volume of the solution in mL and m is the mass of the adsorbent in
g.
The removal efficiency was calculated by Eq. 2:
%Q ¼ A0 � Ae
Ao
:100 ð2Þ
where, Q is the removal efficiency, A0 is the absorbency of initial dye, and Ae is the
absorbency of equilibrium dye.
Results and discussion
Effect of experimental conditions on the adsorption process
It is important to be able to estimate the rate at which dyestuff is removed from
wastewater in order to design an adsorption treatment facility. To determine the
equilibration time, the adsorption of PyY dye onto adsorbents was studied as a
function of contact time. The initial PyY concentration was 10 mg/L. An adsorption
experiment was carried out to find the effect of adsorption time on the adsorption of
PyY dye into vermiculite at 22 �C for solid concentration of 5.0 g/L and the result is
displayed in Fig. 1. The result indicated that the percent of adsorption increased
with increasing time. In about 25 min, the adsorbent can reach the adsorption
equilibrium. The amount of adsorbed dye did not show important changes after
15 min. As shown in Fig. 1, when the adsorption time increased, the amount of PyY
dye bound to clinoptilolite at 22 �C for a solid concentration of 3.0 g/L increased
dramatically. In about 10 min, the adsorbent can reach the adsorption equilibrium.
The amount of adsorbed dye did not exhibit important changes after 15 min
compared with the adsorption of PyY on the vermiculite, the clinoptilolite had a
faster adsorption rate. To determine the influence of initial PyY concentration on the
amount of adsorbed dye, the initial PyY concentration varied from 3 to 20 mg/L at
22 �C. It is seen that percent removal efficiency decreased with increasing initial
dye concentrations for both vermiculite and clinoptilolite. The experiments were
carried out against amounts of adsorbent concentrations in the range of 0.5–6.0 g/L
for 30 min at 10 mg/L of initial PyY concentration. The results of the experiments
are shown in Fig. 2. The results given in Figs. 1 and 2 show that the adsorption
capacity of clinoptilolite was higher than vermiculite. For adsorbent concentrations
lower than 5.0 g/L, PyY removal performance of clinoptilolite was better than that
of vermiculite because of the larger specific surface area (m2/g) of clinoptilolite.
However, the PyY removal performance of adsorbents was comparable at high
adsorbent concentrations above 3.0 g/L probably due to the large adsorption area
provided at high vermiculite concentrations. The results indicated that vermiculite
may be as effective an adsorbent as clinoptilolite at high adsorbent concentrations
for the removal of dyestuff. pH is an important factor in dyestuff adsorption. The
removal efficiency as a function of time for PyY on adsorbents at five different pH
values is illustrated in Fig. 3. As shown in Fig. 3, the uptake of dye increased by
increasing the initial pH and the dye adsorption by clinoptilolite was significantly
Reac Kinet Mech Cat
123
affected over the pH range of 2.0–7.0. There was a sharp increase in the removal
when the solution pH increased from 2.0 to 7.0. Vermiculite had the maximum dye
removal (91 %) over a pH of 7, which decreased to 71 % at a pH of 2.0. The
increase in the adsorption with the rise in solution pH may be explained as the
increase in electrostatic force of attraction between the adsorbate and the adsorbent.
Similar studies have also shown that clinoptilolite and vermiculite will have higher
adsorption at higher pH values [22, 24].
Adsorption isotherm models
The applicability of adsorption on an adsorbent for the removal of dyes can be
explained by adsorption isotherms. In this study, the Langmuir model and the
0 10 20 30 40 50 60 70 80 90
1.50
1.65
1.80
1.95
2.10
2.25
2.40
2.55
Time (minute)
qe
(mg
/g)
Clinoptilolite Vermiculite
Fig. 1 Effect of adsorption time on the adsorption of dye on adsorbents
0 1 2 3 4 5 60
20
40
60
80
100
Rem
oval
Eff
icie
ncy
(%)
Adsorbent Concentration (g/L)
ClinoptiloliteVermiculite
Fig. 2 Effect of sorbent concentration on the adsorption of dye on adsorbents
Reac Kinet Mech Cat
123
Freundlich model were used to define the adsorption of PyY on clinoptilolite and
vermiculite. The Langmuir model is based on the assumption that the adsorption
takes place at particular homogenous sites in the adsorbent and supposes a uniform
surface, a monolayer adsorbing adsorbate at constant temperature. The linear form
of the Langmuir model can be given by Eq. 3:
Ce
qe
¼ 1
q0KL
þ Ce
q0
ð3Þ
where Ce is the equilibrium (residual) adsorbate concentration in mg/L, q0 (mg/g) is
the maximum amount of adsorbate per unit weight of adsorbent to form a complete
monolayer on the surface bound at high Ce, KL (L/mg) is a constant related to the
energy of adsorption, q0 and KL are the Langmuir constants. The adsorption capacity
q0 and adsorption constant KL can be determined from the slope and intercept of a
linearized plot of Ce/qe against qe. The essential characteristics of the Langmuir
isotherm can be described in terms of a dimensionless constant separation factor
(RL), which is described by Eq. 4:
RL ¼1
1þ KLC0
ð4Þ
Here, KL is the Langmuir constant and C0 is the highest initial PyY concentration.
The value of RL demonstrates the type of isotherm to be either favorable
(0 \ RL \ 1), unfavorable (RL [ 1), linear (RL = 1) or irreversible (RL = 0). A
basic assumption of the Freundlich theory is that the adsorption takes place on a
heterogeneous surface. The Freundlich isotherm is valid for multilayer adsorption
on adsorbent surfaces as well as non-ideal adsorption. The linear form of the
Freundlich model can be given by the following Eq. 5:
2 4 6 8 10 1220
30
40
50
60
70
80
90
100
Rem
oval
Eff
icie
ncy
(%)
pH
Vermiculite Clinoptilolite
Fig. 3 Effect of initial solution pH on the removal of PyY on adsorbents
Reac Kinet Mech Cat
123
logqe ¼ logK þ 1
nlogCe ð5Þ
Here, K and n are the mono-component Freundlich constants related to the
adsorption capacity and adsorption intensity of the adsorbent, respectively. For the
adsorption isotherm experiments done with each of the adsorbents, the isotherm
constants were obtained after fitting the data to the respective equations through
linear regression analysis. Each isotherm consisted of eight adsorbate concentrations
which varied from 3 to 20 mg/L. The Langmuir and Freundlich adsorption
isotherms of PyY on adsorbents are shown in Figs. 4 and 5, respectively. The results
of fitting experimental data with the Langmuir and Freundlich isotherms for the
adsorption of PyY on adsorbents are represented in Table 3. The suitability of
isotherms for the system was compared by utilizing the correlation coefficients, R2
values. For PyY adsorption on vermiculite, as shown in Table 3, the R2 obtained
from the Langmuir isotherm model (R2 = 0.9976) was higher than that obtained
from the Freundlich isotherm model. The low values of RL for the adsorbent confirm
the favorable uptake of PyY process. Therefore, the Langmuir equation better
exhibits the adsorption process. For PyY adsorption on clinoptillite, the R2 obtained
from the Freundlich isotherm model (R2 = 0.9825) was higher than that obtained
from the Langmuir isotherm model. Therefore, the Freundlich adsorption model is
suitable for modeling the adsorption of PyY on clinopitlolite.
Adsorption kinetic models
In order to predict the kinetic mechanism that governed the adsorption process,
pseudo-first order, pseudo-second order, and intra-particle diffusion models were
applied to analyze the experimental data at different temperatures. The pseudo-first
order equation has often been used to define the adsorption of an adsorbate from an
aqueous solution. This equation is based on the supposition that the change of solute
0 1 2 3 4 5 6 7 8 90.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
y = 0.114x + 0.5018
R² = 0.9514
y = 0.466x + 0.2649
R² = 0.9976
Ce
Ce/
q e
Vermiculite Clinoptilolite
Fig. 4 The Langmuir isotherm plots for clinoptilolite and vermiculite
Reac Kinet Mech Cat
123
uptake with time is dependent on the difference in satiety concentration and the
amount of solid uptake with time. The linear form of the pseudo-first order model is
given by Eq. 6 [26]:
logðqeq � qtÞ ¼ logqeq �kpf t
2:303ð6Þ
Here, qeq (mg/g) and qt (mg/g) are the amounts of dye adsorbed on the adsorbent
at equilibrium and at time t, respectively, and kpf (/min) is the first order adsorption
rate constant. The values of log(qeq-qt) were calculated from the kinetic data. The
plot of log(qeq-qt) against t should give a straight line with slope -kpf and intercept
logqeq. The results of fitting the experimental data with the pseudo-first order
(Fig. 6) for the adsorption of the dye on clinoptilolite and vermiculite are presented
in Table 4. As can be seen, the linear regression R2 values for PyY adsorption on
clinoptilolite and vermiculite changed in the range of 0.8894–0.9268 and
0.9195–0.9533, respectively. These results show that the experimental data are
not described by the pseudo-first order model. The pseudo-second order equation is
based on the assumption that the change of solute uptake with time is directly
proportional to the amount of solute adsorbed on the surface of adsorbent and the
amount of dye adsorbed at equilibrium. The linear form of pseudo-second order
model is given by Eq. 7 [27]:
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
y = 1.3728x - 0.2564
R² = 0.9825
y = 0.2871x + 0.0714
R² = 0.9344
log Ce
logq
e
Vermiculite Clinoptilolite
Fig. 5 The Freundlich isotherm plots for clinoptilolite and vermiculite
Table 3 Values of the constans in Langmuir and Freundlich models
Adsorbent Langmuir Freundlich
qmax
(mg/g)
KL
(L/mg)
RL r2 n K (mg/g)
(L/mg)1/nr2
Clinoptilolite 8.772 0.227 0.595–0.1805 0.9514 1.389 1.564 0.9825
Vermiculite 2.145 1.75 0.159–0.0277 0.9976 3.483 1.787 0.9344
Reac Kinet Mech Cat
123
t
qt
¼ 1
kpsq2eq
þ t
qeq
ð7Þ
Here, kps (g/mg/min) is the pseudo-second order rate constant and qeq is as
defined above. The pseudo-second order rate constant (kps) and the equilibrium
adsorption capacity (qeq) can be calculated experimentally from the slope and
intercept of the plot of t/qt versus t. The results of fitting experimental data with the
pseudo-second order model (Figs. 7, 8) for the adsorption of PyY on clinoptilolite
and vermiculite at different temperatures are given in Table 4. As can be seen, the
linear regression R2 values for PyY adsorption on clinoptilolite and vermiculite
changed in the range of 0.9993–0.9999 and 0.9912–0.9999, respectively. The above
0 5 10 15 20 25 30 35 40 45 50 55 60 65-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
y = -0.0524x + 0.2697R² = 0.9195
y = -0.0351x - 0.0306R² = 0.8864
Clinoptilolite Vermiculite
log
(qe-
q t)
t(minute)
Fig. 6 Pseudo-first order kinetic plots for the adsorption of PyY on clinoptilolite and vermiculite
Table 4 Adsorption kinetic parameters of PyY on adsorbents
T Pseudo-first order Pseudo-second order Intraparticle diffusion
kpf qae r2
1 qbe
kps qae r2
2kid c r2
3
PyY-clinoptilolite
22 0.0808 2.325 0.8864 2.3963 0.195245 2.325 0.9993 0.1706 1.327 0.528
30 0.0598 2.540 0.8642 2.5974 0.200093 2.540 0.9998 0.1092 1.7543 0.5654
40 0.0594 2.594 0.8216 2.6511 0.221626 2.594 0.9996 0.1142 1.7798 0.4990
50 0.0580 2.458 0.9268 2.4801 0.307654 2.458 0.9999 0.0382 2.1652 0.5046
PyY-vermiculite
22 0.1674 1.559 0.9195 1.7540 0.159291 1.559 0.9912 0.1602 0.4505 0.7129
30 0.1552 1.570 0.9522 1.6257 0.287040 1.570 0.9995 0.0931 0.9395 0.63
40 0.1545 1.570 0.9809 1.6069 0.436986 1.570 0.9998 0.0714 1.0894 0.613
50 0.1398 1.579 0.9533 1.6020 0.668231 1.579 0.9999 0.0488 1.248 0.6009
a Experimentalb Calculated
Reac Kinet Mech Cat
123
results show that the pseudo-second order model fitted the equilibrium data better
than pseudo-first order model. Therefore, the adsorption kinetics of PyY by
clinoptilolite and vermiculite could be described by the pseudo-second order model.
The best fit of the pseudo-second order expression suggest that the chemisorption
mechanism is involved in the adsorption. The adsorbate species are most likely
transported from the solution phase to the solid surface of adsorbent particle through
an intra-particle diffusion process. The transport of adsorbate species onto the
surface of the adsorbent is often the rate limiting step in the adsorption. In the intra-
particle diffusion model, it is assumed that the adsorption capacity varies almost
proportionally with t1/2 and the model is commonly given by Eq. 8 [28]:
0 10 20 30 40 50 60 70 80 900
3
6
9
12
15
18
21
24
27
30
33
36
y = 0.4032x + 0.3081R² = 0.9999
y = 0.3772x + 0.6413R² = 0.9996
y = 0.385x + 0.6674R² = 0.9998
y = 0.413x + 1.1163R² = 0.9993
t/q t
t (minute)
22°C
30°C
40°C
50°C
Fig. 7 Pseudo-second order kinetic plots for the adsorption of PyY on clinoptilolite
0 10 20 30 40 50 60 70 800
10
20
30
40
50
y = 0.6242x + 0.583R² = 0.9999
y = 0.6223x + 0.8862R² = 0.9998
y = 0.6151x + 1.3181R² = 0.9995
y = 0.5701x + 4.099R² = 0.9912
t/q
t
t (minute)
22°C30°C40°C50°C
Fig. 8 Pseudo-second order kinetic plots for the adsorption of PyY on vermiculite
Reac Kinet Mech Cat
123
qt ¼ kidt1=2 þ C ð8Þ
where t (min) is the contact time, kid (mg/g min1/2) is the intra-particle diffusion
constant, and C is the constant. Plots between qt versus t1/2 are shown in Fig. 9. The
values of the parameters and the correlation coefficients obtained by using exper-
imental data are listed in Table 4. As can be seen, the low R2 values determined for
the intra-particle diffusion model show that adsorption of PyY on clinoptillite and
vermiculite does not occur in the pores of a solid in accordance with surface
adsorption.
Activation parameters
The activation parameters of the adsorption process will help us to understand the
adsorption mechanisms and to improve the practical application of adsorbents to
wastewater treatment. The k2 constants of the second order kinetic equation for
adsorption of PyY on adsorbents at different temperatures listed in Table 4
(C0 = 10 mg/L, pH = 7.0) have been used to determine the activation energy of
PyY adsorption on adsorbents using the Arrhenius equation (Eq. 9):
lnk2 ¼ �Ea
RgTþ lnA ð9Þ
Here, A is the Arrhenius factor, Rg is the gas constant (8.3145 J/mol K) and Ea is
activation energy (J/mol). The plot of lnk2 against 1/T should give a straight line
with slope -Ea/Rg and intercept lnA. The results are shown in Fig. 10. According to
the results calculated in Fig. 10, the Ea values were found to be 12.3 kJ/mol for
clinoptilolite, and 40.2 kJ/mol for vermiculite. The positive values of activation
energy show the presence of an energy barrier in the adsorption process. Parameters
including free energy (DG*), enthalpy (DH*) and entropy (DS*) of activation can be
obtained using the Eyring equation (Eq. 10):
0 2 4 6 8 100.0
0.5
1.0
1.5
2.0
2.5
qt
t1/2
Clinoptilolite Vermiculite
Fig. 9 Intrapaticle diffusion plots for the adsorption of PyY on clinoptilolite and vermiculite
Reac Kinet Mech Cat
123
lnk2
T¼ ln
kb
hþ ln
DS�
Rg
� DH�
RgTð10Þ
Here, kb and h. e Boltzmann’s constant (1.38 9 10-23 J/K) and Planck’s constant
(6.626 9 10-34 J s), respectively, and T is the absolute temperature. The values of
activation parameters including enthalpy (DH*) and entropy (DS*) for PyY-
clinoptilolite and PyY-vermiculite systems have been obtained from the slope and
the intercept of the Eyring plots in Fig. 11. The Gibbs free energies of activation
have been calculated using Eq. 11:
DG� ¼ DH� � TDS� ð11Þ
0.0031 0.0032 0.0033 0.0034
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
y = -4842x + 14.617R² = 0.9821
y = -1489x + 3.3501R² = 0.8103
lnk
2
1/T
Clinoptilolite Vermiculite
Fig. 10 Arrhenius plots for the adsorption of PyY on clinoptilolite and vermiculite
0.00306 0.00315 0.00324 0.00333 0.00342
-7.6
-7.2
-6.8
-6.4
-6.0y = -4531.6x + 7.8781R² = 0.9793
y = -1178.5x - 3.3885R² = 0.7346
1/T
ln(k
2/T
)
Clinoptilolite Vermiculite
Fig. 11 Plots of ln k2
Tversus 1
Tfor the adsorption of PyY on clinoptilolite and vermiculite
Reac Kinet Mech Cat
123
As listed in Table 5, the values of DG* and DH* are positive, confirming again
the presence of an energy barrier in all the systems. The negative value of DS*
points out the diminishing randomness at the solid/liquid interface during the
adsorption of dye on vermiculite and clinoptilolite. In addition, the second order rate
constants increased with the rise in temperature. Therefore, the adsorption of PyY
on adsorbents was more favorable at a high temperature in the investigated range.
Similar results have been recorded on the adsorption of methylene blue onto silica
nanosheets derived from vermiculite.
Conclusions
Dyestuff removal performances of vermiculite and clinoptilolite were compared at
different initial adsorbent concentrations (3.0–5.0 g/L) and a constant initial PyY
concentration of (10 mg/L). The adsorption performance of clinoptilolite was better
than that of vermiculite at low adsorbent concentrations below 4.0 g/L. However,
the performances of vermiculite and clinoptilolite were comparable in terms of the
rate and the extent of PyY removal at high adsorbent concentrations above 4.0 g/L.
More than 91 % dyestuff removal efficiencies were obtained for both vermiculite
and clinoptilolite after 30 min. with adsorbent concentrations above 3.0 g/L. Two
adsorption isotherms were investigated to correlate the equilibrium adsorption data
and the isotherm constants were calculated for both adsorbents. As a result, the
adsorption of PyY by vermiculite was a good fit for the Langmuir isotherm, while
that by clinoptilolite was a good fit for the Freundlich isotherm. The adsorption
kinetics of PyY by clinoptilolie and vermiculite could be better described in the
pseudo-second order model. The positive values of activation energy show the
presence of an energy barrier. This study shows that vermiculite and clinoptilolite
are effective adsorbents for the removal of PyY from aqueous solutions. In this
sense, it could be suggested that could be utilized as simple and low-cost alternative
adsorbents for the removal of PyY from wastewater.
Acknowledgments We are grateful to the Research Fund of Bingol University (Project Number:
BUBAP199-121-2013) for their financial support.
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Table 5 The activation parameters for the adsorption process of dye on clinoptilolite and vermiculite
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