Appl Water Sci

DOI 10.1007/s13201-016-0387-2

ORIGINAL ARTICLE

Batch and fixed-bed adsorption of tartrazine azo-dye

onto activated carbon prepared from apricot stones
H. I. Albroomi1 • M. A. Elsayed2 • A. Baraka2 • M. A. Abdelmaged2

Received: 8 October 2015 / Accepted: 27 January 2016

Ó The Author(s) 2016. This article is published with open access at Springerlink.com

Abstract This work describes the potential of utilizing and Thomas models with high coefficient of determination,
prepared activated carbon from apricot stones as an effi- R2 C 94.
cient adsorbent material for tartrazine (TZ) azo-dye
removal in a batch and dynamic adsorption system. The Keywords Adsorption of tartrazine azo-dye  Apricot
results revealed that activated carbons with well-developed stones  Fixed-bed column  Breakthrough curve
surface area (774 m2/g) and pore volume (1.26 cm3/g) can
be manufactured from apricot stones by H3PO4 activation.
In batch experiments, effects of the parameters such as Introduction
initial dye concentration and temperature on the removal of
the dye were studied. Equilibrium was achieved in Azo-dyes as an aromatic molecular structure compound are
120 min. Adsorption capacity was found to be dependent generally resistant to light, biodegradation, temperature,
on the initial concentration of dye solution, and maximum ozonation and oxidation. This significant properties makes
adsorption was found to be 76 mg/g at 100 mg/L of TZ. the dyes to be accumulated in the living organisms and
The adsorption capacity at equilibrium (qe) increased from therefore leading to severe diseases and function disorders
22.6 to 76 mg/g with an increase in the initial dye con- (Gautam et al. 2015b). The issue of the presence of color in
centrations from 25 to 100 mg/L. The thermodynamic effluent has received considerable critical attention for
parameters such as change in free energy (DG0), enthalpy dyestuff manufacturers and textile companies (Annadurai
(DH0) and entropy (DS0) were determined and the positive et al. 2002). This is because increasingly stringent water
value of (DH) 78.1 (K J mol-1) revealed that adsorption quality standards which have been used to controlling and
efficiency increased with an increase in the process tem- reducing discharge of hazardous substances in effluent
perature. In fixed-bed column experiments, the effect of (Yavuz and Aydin 2006; Santhy and Selvapathy 2006).
selected operating parameters such as bed depth, flow rate Nowadays, there is a primary concern of decolorization and
and initial dye concentration on the adsorption capacity treatment of wastewater because many industries depend
was evaluated. Increase in bed height of adsorption col- on dyes to color their products such as textiles, leather and
umns leads to an extension of breakthrough point as well as food processing industries (Robinson et al. 2001). There
the exhaustion time of adsorbent. However, the maximum are various physical and chemical treatment processes for
adsorption capacities decrease with increases of flow rate. organic dyes removals from wastewater have been applied.
The breakthrough data fitted well to bed depth service time The most important treatment processes are coagulation
and flocculation, photo-degradation, biosorption, oxidizing
agents, membrane and ultra-filtration. The advantages,
& M. A. Elsayed
aboelfotoh@gmail.com
disadvantages and limitations of each technique have been
extensively studied by many researchers (Namasivayam
1
Oman Armed Forces, Masqat, Oman and Suba 2001; Robinson et al. 2001; Gurses et al. 2004;
2
Chemical Engineering Department, Military Technical Klán and Vavrik 2006). Due to many draw-backs such as,
College, Egyptian Armed Forces, Cairo, Egypt complexity of the process, low removal efficiencies and

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 Appl Water Sci

relatively high operating costs using the above-mentioned On the basis of the previous discussions, the focus of this
techniques, dyestuff manufacturers and paper industries research was to evaluate the adsorption potential of the
seldom apply these methods to treat their wastewater Apricot stone-based activated carbon in removing Tartrazine
effluents (Robinson et al. 2002; Kadirvelu et al. 2003). azo-dye from aqueous solutions through batch and fixed-bed
However, regarding to initial operating costs, ease of experiments. Batch adsorption experiments were conducted
operation, simplicity of equipments design, adsorption onto using synthetic aqueous solutions of tartrazine and the
activated carbon process has been found to be an efficient effects of initial dye concentration and temperature were
and economic process to remove dyes and other pollutant investigated. Thermodynamics of the adsorption process has
from wastewater (Annadurai and Lee 2002; Grégorio Crini also been studied and the changes in Gibbs free energy,
2010; Algidsawi 2011). enthalpy and the entropy have been determined. In column
Although batch adsorption studies provide useful data experiments, effects of parameters such as flow rate, initial
and parameters on the application of specific adsorbents for concentration of TZ, and fixed-bed height on TZ adsorption
the removal of dyes or specific pollutant, continuously using; Thomas, bed depth service time (BDST) and Adams–
fixed bed or column experiments are also necessary to Bohart kinetic models were considered.
provide practical operational information with respect to
the adsorption of constituents with the use of a particular
adsorbent (Ahmad and Hameed 2010; Dutta and Basu Experimental
2014). Fixed-bed columns can be operated singly, in series
or in parallel. Small-scale column tests can be employed to Materials and apparatus
simulate the potential performance of the adsorbent and the
results obtained extrapolated in the design of full-scale Tartrazine dye supplied by Morgan Chemical Company
reactors (Walker and Weatherley 1997; Futalan et al. 2011; was used without further purification to prepare all syn-
Mulgundmath et al. 2012). thetic wastewater solutions. It was kept in a tightly sealed
Tartrazine is a synthetic lemon yellow azo-dye autho- bottle to prevent any contaminations and assure the
rized in many countries in food processing manufacture material quality. Other reagents include phosphoric acid
with maximum permitted use levels of 50–500 mg/kg- (H3PO4), dilute HCl and NaOH solutions. All reagents
food for various food processing. It is also known as E were of analytical grade. Deionized water was used
number E102, C.I. 19140, FD&C Yellow 5, Acid Yellow throughout the experiments. The dyes concentrations were
23, and Food Yellow 4. Reduction of Tartrazine may determined using Agilant UV–Vis Cary 60 PC scan
produce sulphonated aromatic amines compounds, which double beam recording spectrophotometer using (1) cm
have low toxicity potential (Aguilar et al. 2009). Tar- glass cells. The measurement of Tartrazine concentration
trazine is considered to be toxic to humans as it acts as was conducted at kmax = 425 nm. A digital pH meter,
hyperactivity and causes asthma, migraines, eczema, type 720 WTW 82362 was used to adjust the pH. Sche-
thyroid cancer and other behavioral problems (Gautam matic structure of Tartrazine and its properties are shown
et al. 2015a). in Table 1.

Table 1 Schematic structure of Tartrazine and its properties

Properties

Chemical structure

Chemical name Trisodium (4E)-5-oxo-1-(4-sulfonatophenyl)-4-[(4-sulfonatophenyl)hydrazono]-3-pyrazolecarboxylate

Molecular formula C16H9N4Na3O9S2
Molecular weight (g/mol) 534.3 g/mol
Tartrazine purity (%) C98 %
Maximum wavelength k (nm) 427 ± 2 nm
Solubility Soluble in cold water, hot water

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Appl Water Sci

Adsorbent preparation For the chemical characterization, the analyses were

limited to determination of C, H, N, O elements, ash
In this study, activated carbon was prepared from apricot analysis and FTIR; to provide information with respect to
stones by chemical activation technique using phosphoric elemental composition and functional groups, respectively.
acid (H3PO4) as activating agent. Chemical activation is The proximate analysis of the prepared activated carbon
known by its advantage compared to physical activation was performed according to ASTM standards (Aygun et al.
in crosslinking and protective of carbon skeleton and its 2003). A carbon/hydrogen/oxygen/nitrogen/sulfur (C/H/O/
participation in the creation and expansion of the pores N/S) content of activated carbon used in this experimental
(Deng et al. 2009). In addition, chemical activation using work was analyzed by elemental analyzer (model CHNO-
phosphoric acid is known to prevent excessive sample RAPID, Heraeus Co., Germany). Table 2 shows the prox-
burn-off, resulting in high yield and well-developed imate and elemental analyses of the prepared activated
internal porosity. Firstly, the apricot stones were dried at carbon from apricot stones.
room temperature then crushed with a jaw crusher. The Perkin Elmer Spectrum Infrared Spectrometer with reso-
resulting particles were sieved and the particles having lution of 4 cm-1 in the range of 4000–500 cm-1 was used
sizes between 1–2 mm were used in the rest of the for the FTIR analysis of prepared active carbon. The adsor-
experimental work. Then samples were treated with the bent and potassium bromide (KBr) were dried in an oven and
50 % (vol) H3PO4 solution at 25 °C at ratio of 2.5:1 then ground together in a ratio of 20:1 (KBr:AC) for FTIR
(weight) for 24 h. measurement using disk sample method (Gupta et al. 2011).
After impregnation, solution was filtered to take the
residual acid. Subsequently impregnated samples were air Batch equilibrium studies
dried at room temperature for 3 days. Impregnated apricot
stones samples containing %18 H3PO4 were obtained after Adsorption tests were performed in a set of Erlenmeyer
drying. To produce activated carbon, acid impregnated flasks (250 mL) where 100 mL of TZ solutions with initial
samples were heated; at a heating rate of 20 °C/min to the concentrations of 25–100 mg/L were placed in these flasks.
final carbonization temperatures, 700 °C, for 180 min. Equal mass of 0.1 g of the prepared activated carbon with
Before the characterization, products were crushed to the particle size of 0.595–0.212 mm was added to each
obtain small particles (30–70 mesh or 0.595–0.212 mm) flask and kept in an isothermal shaker of 100 rpm at 25 °C
and rinsed with boiling distilled water to decrease the pH to reach equilibrium. The pH of the solutions was natural
value of the activated carbon. (pH 6.5). Aqueous samples were taken from the solution
and the concentrations were analyzed. All samples were
Physicochemical characterization of the adsorbent filtered prior to the analysis to minimize the interference of
the carbon fines with the analysis. The concentrations of
BET surface area and micropore volume of each activated TZ in the supernatant solution before and after adsorption
carbon were determined from the N2 adsorption experi- were determined using Agilent UV–Vis Cary 60 PC scan
ments. Approximately 0.12 g samples were heated to double beam recording spectrophotometer using (1) cm
250 °C to remove all the adsorbed species. Nitrogen glass cells. Each experiment was duplicated under identical
adsorption and desorption isotherms were then taken using conditions. The amount of adsorption at equilibrium, qe
Quantrachrome Autosorb I-CLP Surface Area Analyzer (mg/g), was calculated by:
(Micromeritics Instrument Corp.). According to the V
resulting isotherm, the BET surface area (SBET), micropore qe ¼ ðC0  Ce Þ ð1Þ
W
volume (Vmic), micropore surface area (Smic), mesopore
volume (VBJH), mesopore surface area (SBJH), and pore size where C0 and Ce (mg/L) are the liquid phase concentrations
of the samples were analyzed by BET (Brunauere Emmette of dye at the initial and equilibrium conditions, respec-
Teller) theory, t-plot theory and BJH (Barrette Johnere tively. V is the volume of the solution (l) and W is the mass
Halendar) theory, respectively. of dry adsorbent used (g).

Table 2 Proximate and elemental analyses of prepared active carbon

Sample Proximate analysis (wt%) Elemental analysis (wt%)
Moisture Ash Volatile matter C H N S O by diff.

AC 5.1 3.36 82.8 83.12 3.87 0.91 0.56 11.54

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 Appl Water Sci

Fixed-bed adsorption experiment conditions (concentration and flow rate) is determined by

computation of area under the plot from the integral of
The experiment was conducted in a 2 cm diameter and adsorbed concentrations expressed as;
15 cm length encased Pyrex glass tube having an embed- Cad ðCad ¼ Co  Ct Þ mg=L for a given time t:
ded stainless steel mesh for supporting layer of adsorbent. QA Q t¼ttotal
A schematic of the experimental setup used for column qtotal ¼ ¼ r Cad dt ð3Þ
1000 1000 t¼0
study is shown in Fig. 1. The experiments were conducted
by varying the weight of activated carbon and different where ttotal, is the total flow time, Q and A are the
initial solutions concentration of TZ. The height of the volumetric flow rate (mL/min) and the area under the
activated carbon bed was measured before the tests to breakthrough curve, respectively. The equilibrium uptake
monitor the variation cause by bed height. The Activated (qeq(exp)) (mg/g) can be evaluated using Eq. (4)
carbon 5.6, 7 and 8.4 g adsorbent corresponding to 8, 10 (Karunarathne and Amarasinghe 2013);
and 12 cm bed heights, respectively, were measured into qtotal
qeqðexpÞ ¼ ð4Þ
the column. Fluidization and bypass flow of the system m
were retarded by good packing of the adsorbent. Influent
where m (g) is the mass of adsorbent in the column.
flow rate of 2.7, 4.2 and 5.7 mL/min in an upward direction
with the aid of peristaltic pump (Master-flex, Cole-Parmer
Instrument Co.) were used for 10, 15, and 20 mg/L initial
Result and discussion
concentrations of TZ. The effluent TZ concentration was
measured at intervals at kmax = 425 nm UV–Vis spec-
Adsorbent characterization
trophotometer. Experiments were continued until the col-
umn reached equilibrium concentration. All experiments
The nitrogen adsorption–desorption isotherms of activated
were carried out under room temperature (25 ± 2 °C).
carbon prepared from Apricot stone is depicted in Fig. 2,
where the amount of N2 adsorbed at 77 K is plotted against
Fixed-bed column data analysis
the relative pressure.
Figure 2 showed that the adsorption–desorption iso-
Several bed parameters are important for the characteri-
therm resemble a combination of types I and IV isotherms
zation of any adsorption process. They were determined for
(in accordance with the International Union of Pure and
each column from the breakthrough curves using previ-
Applied Chemistry (IUPAC) classification), which is cor-
ously published calculation methods (Crhribi and Chlendi
responding to micro-mesoporous solid. The type IV iso-
2011; Casas et al. 2012; Chen et al. 2012).
therm usually originates from mesoporous solids. It
The adsorption breakthrough profiles were obtained
describes a multilayer adsorption process where complete
from Ct (mg/L) or Ct/Co vs. Vt (mL) or t plots; where Ct is
filling of the smallest capillaries has occurred. Whilst type I
effluent concentration, Co influent concentration, Vt volume
isotherm is typical of microporous solids where only
of effluent treated and t is the service time. The treated
monolayer adsorption occurs. In these micropores, filling
effluent volume Vt is determined.as:
Vt ¼ Q t e ð2Þ
900
Volume Adsorbed [cm (STP)/g ]

where Q (mL/min) and te are the influent flow rate and time 800
of exhaustion. Fixed-bed capacity qtotal (mg) at set influent
700
3

600

500

400

300

200

100
0 0.2 0.4 0.6 0.8 1
Relative Pressure (P/P )
0

Fig. 2 Adsorption profiles of N2 at 77 K on the activated carbon

prepared from apricot stone. Open keys indicate adsorption whilst
Fig. 1 Experimental setup for the fixed-bed adsorption process closed keys indicate desorption

123
Appl Water Sci

occurs significantly at relatively low partial pressure \0.1 Knowledge on surface chemistry characteristics of the
p/po, the adsorption process being complete at p/po &0.5. produced activated chars would give insight to its adsorp-
The main feature of such isotherm is the long plateau tion capability and behavior (Elsayed and Zalat 2015).
which is indicative of a relatively small amount of multi- FTIR analysis was conducted for qualitative characteriza-
layer adsorption on the open surface. On the other hands, tion of surface functional groups of porous carbons acti-
the nitrogen uptake occurs mostly at (p/po [ 0.9). This vated by H3PO4. The IR spectrum of AC prepared by
indicates that the meso- or macropore structure in the H3PO4 activation is shown in Fig. 3. The FTIR spectra
sample significantly developed. The isotherm is charac- show a number of significant peaks, indicating the complex
terized by hysteresis loop, which appear in the multilayer structure of the chemical activated carbon sample.
rang of physical sorption isotherm. This kind of loop is According to the spectrum, the appearance of bands at
generally associated with capillary condensation. It is well 3448.5–3421.5 cm-1 refers to (O–H) stretching vibrations
known that most mesoporous adsorbents give distinctive in the hydroxyl, carboxylic or phenolic groups. The band
and reproducible hysteresis loops. appears at 2854.5 cm-1 can be assigned to C–H group
In Table 3 are given some textural parameters obtained stretching. The band appears at 1635.5 cm-1 can be
from nitrogen adsorption isotherms at 77 K of the carbons assigned explained to the olefinic C=C stretching. In fact,
samples prepared by H3PO4 chemical activation. The the C=C stretching absorption frequently occurs at
results revealed that activated carbons with well-developed approximately nearby 1600 cm-1 for carbonaceous mate-
porosity and high surface area can be manufactured from rials (Aygun et al. 2003), The band shift from 1600 cm-1
apricot stones. These superior properties could provide may be due to conjugation with another C=C bond, or a
high concentration of active sites for adsorption of TZ dye C=O bond. The band located at 1384.8 cm-1 could be
to occur. attributed to C–H deformation vibration in alkenes that
frequently occurs at approximately at 1381 cm-1. The

Table 3 The characteristic pore properties of resulting activated carbon

SaBET (m2/g) Vbt (cm3/g) Vcmic (cm3/g) Vdmes (cm3/g) Dep (nm)
±10 ±0.02 ±0.02 ±0.02 ±0.02

Activated carbon (AC) 774 1.26 0.30 0.95 7.48

a
Specific surface area determined from the BET equation
b
Total pore volume, calculated from the amount of vapor adsorbed at a relative pressure of (0.99)
c
Micropore volume determine by Horvath-Kawazoe model, calculated from the amount of nitrogen adsorbed at relative pressure (p/po) of 0.20
d
Mesopore volume, calculated by subtracting the amount adsorbed at a relative pressure of 0.2 from that adsorbed at relative pressure of 0.99
e
Mean pore diameter, calculated from (4 Vt/SBET). Note; the number of significant figures quoted in the table an indication of precision

Fig. 3 IR spectrum of prepared

activated carbon sample

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 Appl Water Sci

appearance of bands between 1033.8 and 1037.6 cm-1 and when the initial dye concentration increases, the
could be assigned to C–O stretching vibrations in phenolic active sites required for adsorption of the dye molecules
and carboxylic groups. The bands at 680–700 cm-1 may will occupy and disappear (Gautam et al. 2013). How-
refer to C–H vibration. The data mentioned above show the ever, the increase in the initial dye concentration leading
presence of phenolic, carboxylic and hydroxylic groups, to the high driving force for mass causes an increase in
which may be responsible for the potential adsorption of the loading capacity of the adsorbent. In other words, the
TZ dye onto the prepared AC sample (Baraka 2012). number of dye molecules in the solution will be higher
than active sites available on the adsorbent surface for
Effect of contact time and initial dye concentration higher initial dye concentrations. In contrast, at the case
on adsorption equilibrium of lower initial dye concentrations, the ratio of initial
number of dye molecules in the solution to the available
Figure 4 shows the adsorption capacity vs. the adsorption adsorption active sites on the surface of the adsorbent is
time at various initial TZ concentrations at 25 °C. It indi- low and subsequently the fractional adsorption becomes
cated that the contact time needed for TZ solutions with independent of initial concentration (Gautam et al.
initial concentrations of 25–100 mg/L to reach equilibrium 2014a).
was 120 min. As can be seen from Fig. 3, the amount of
TZ adsorbed onto the activated carbon increased with time Effect of temperature on adsorption equilibrium
and, at some point in time, it reached a constant value and thermodynamic parameters
beyond which no more TZ dye was further removed from
the solution. At this point, the amount of the TZ dye des- Figure 5 shows the adsorption equilibrium vs. tempera-
orbing from the activated carbon was in a state of equi- ture at initial TZ concentrations 100 ppm. It is shown that
librium with the amount of the TZ dye being adsorbed onto the adsorption capacity increases with temperature, indi-
the activated carbon. The amount of dye adsorbed at the cating an endothermic process. It had been investigated
equilibrium time reflects the maximum adsorption capacity from the experiment that with the rise of temperature from
of the adsorbent under those operating conditions. In this 288 to 303 K the amount of dye uptake increases from 57
study, the adsorption capacity at equilibrium (qe) increased to 80 mg/g. As the rate of diffusion of the dye molecules
from 22.6 to 76 mg/g with an increase in the initial dye is a temperature controlled process, variation in temper-
concentrations from 25 to 100 mg/L. The effect of the ature alters the equilibrium capacity of the adsorbent for a
initial dye concentration depends on the immediate relation particular adsorbate. In the present study, an increases of
between the dye concentration and the available binding the adsorption temperature leads to fast diffusion of dye
sites on an adsorbent surface (Gautam et al. 2014b). molecules across the external boundary layer and internal
Generally, the adsorption capacity of activated carbon pore structure of the adsorbent particles. This may be due
samples and the percentage of dye removal decrease with to less resistance offered by viscous forces in the solutio.
an increase in initial dye concentration, which may be due In addition, in some cases the solubility of the dye
to the saturation of adsorption sites on the adsorbent molecules is affected with the increase of the temperature
surface. At low initial dye concentration, there will be which finally has a significant impact on the removal
unoccupied active sites on the activated carbon surface, efficiency.

80
90
70 80
60 70
50 60
qt (mg/g)

100 mg/g
qe (mg/g)

40 50
75 mg/g 40
30
50 mg/g 30
20
25 mg/g 20
10 10
0 0
0 50 100 150 285 290 295 300 305
Time (min) T (K)

Fig. 4 Adsorption capacity vs. adsorption time at various initial TZ Fig. 5 Effect of temperature on adsorption equilibrium at initial TZ
concentrations at 25 °C concentrations (100 ppm)

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Appl Water Sci

The thermodynamics of the adsorption process were Fixed-bed adsorption column study
studied at three different temperatures in a thermostated
incubator. Thermodynamic parameters such as the Gibbs Effect of bed height on breakthrough curve
free energy change (DG), enthalpy changes (DH) and
entropy change (DS) can be used for the characterization of An effect of bed height on the adsorption of TZ by acti-
temperature effect on the adsorption process. These vated carbon samples is shown in Fig. 6. In this experiment
parameters were calculated using the following equations: the bed heights were 8, 10 and 12 cm with fixed flow rate
DG ¼ RTLnKL ðGibbs equationÞ ð5Þ of 2.7 mL/min, 15 mg/L TZ concentration and pH = 6.8.
Increase in bed height of adsorption columns leads to
DH DS longer breakthrough point as well as the exhaustion time of
LnKL ¼  þ ðVant’ Hoff equationÞ ð6Þ
RT R adsorbent. This is due to increase in the amount of adsor-
where KL ¼ Cqee , R is the molar gas constant (8.314 J/mol K) bent in the column which leads to increase in surface area
and T is the absolute temperature. KL is the equilibrium (Khoo et al. 2012). The shape and gradient of the break-
constant obtained for each temperature from the Langmuir through curves were slightly different for different bed
model. DH and DS were obtained from the slopes and height.
intercepts of the linear plots of In KL against 1/T (Fig- It was also observed that, the sorption capacity and
ure not shown). The values of the thermodynamic param- breakthrough time increased with an increase in the bed
eters are given in Table 4. height as shown in Table 5. This increase can be attributed
sitive value of (DH) 78.1(K J mol-1) revealed that to sufficient residence time of TZ dye in the column
adsorption efficiency increased with an increase in the adsorption region which provided sufficient time for dif-
adsorption temperature; this implies that each TZ molecule fusion or interaction of the dye molecules with the adsor-
had to displace more than one water molecule from the bent. An increase in adsorption capacity of TZ from 1.61 to
adsorbent surface before it is adsorbed. Generally, most of 2.41 mg/g was recorded.
the adsorption studies substantiate the assumption that the The BDST model proposed by Bohart and Adams offer
adsorption of dye on the active carbon surface is the simplest approach and most rapid prediction of column
endothermic. Significantly, these high values of (DH) adsorption performance (Vaňková et al. 2010). The model
indicate a strong chemical interaction between the active gives a linear relationship between the time required to
carbon and TZ dye. The negative value of DG reflects the
feasibility and spontaneity of the adsorption process. In
addition, the value of DS (285 J mol-1 k-1) had been 1.2
expected to be so large which indicated an increase of
entropy as a result of adsorption process (Gautam et al. 1

2013). This can be explained as that, before adsorption 0.8

occurs, the dyes ions near the active carbon boundary were
Ct/CO

0.6
in ordered form than in the subsequent adsorbed state and Bed height 8 Cm
the ratio of free dye ions to the captured dye ions with the 0.4 Bed height 10 Cm
active carbon will be higher than in the adsorbed state. As a Bed height 12 Cm
0.2
result of adsorption, there will be an increased randomness
at solid–liquid interface and the distribution of translational 0
0 200 400 600 800 1000
and rotational energy will increase, producing a positive Time (min)
entropy value. In the present study, at high operating
temperature, adsorption is likely to occur spontaneously Fig. 6 Effect of bed height on adsorption of TZ by activated carbon
because DH [ 0 and DS [ 0. (flow rate of 2.7 mL/min, Initial TZ concentration of 15 mg/L, and
temperature of 25 °C)

Table 5 Experimental constants of BDST model for TZ adsorption

Table 4 Values of thermodynamic parameters for the removal of onto activated carbon (TZ concentration = 15 ppm, pH = 6.8 and
Tartrazine onto AC flow rate = 2.7 mL/min)
Temperature (K) DG (K J mol-1) DH (K J mol-1) DS (mol-1k-1) Bed depth qe (mg/g) tb (min) te (min) R2

288 -4.49 78.4 285 8 cm 1.61 52 425 0.99

298 -6.16 10 cm 1.78 82 550
303 -9.8 12 cm 2.41 115 790

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 Appl Water Sci

reach the desired breakthrough concentration and the bed In conducting packed-bed sorption experiments, normally
height. The equation can be expressed as follows: the results are presented in terms of concentration time
  profile or breakthrough curve. The process of calculation is
No Z 1 Co
t¼  ln 1 ð4Þ complicated and time consuming. Prediction of the
Co Q Ka Co Ct
adsorption rate and the maximum sorption bed capacity can
where Ct is the breakthrough dye concentration (mg/L), CO be determined by applying certain mathematical models
is influent or initial solute concentration (mg/L), N0 the (Vaňková et al. 2010; Unuabonah et al. 2010).
sorption capacity of bed (mg/L), Q the linear velocity (mL/ Thomas model is widely used in predicting column
min), Z is the depth of adsorbent bed and Ka is the rate performance modeling. Its derivation assume Langmuir
constant (L/mg min). isotherm for equilibrium, plug flow behavior in the bed and
The plot of service time against bed height at a flow rate second-order reversible reaction kinetics. This model is
of 2.7 mL/min was linear indicating the validity of BDST suitable for studying fixed-bed adsorption processes where
model (Fig. 7). The results of different bed height showed the internal and external diffusion limitations are negligi-
the validity of BDST model to study adsorption of TZ with ble. The linearized form of Thomas model can be expres-
the regression coefficient (R2) of 0.99, (Table 4). The value sed as follows (Sidiras et al. 2011):
of adsorption capacity of the bed per unit of bed volume,  
C0 kTh qe W
No and the rate constant, Ka were computed from the slope ln 1 ¼  kTh C0 ðtÞ ð5Þ
Ct Q
and intercept of BDST plot assuming initial concentration,
Co and the linear velocity, as constant. The rate constant, where qe (mg/g) is the equilibrium dye uptake per g of the
Ka is a measure of the rate transfer of dye solution from the adsorbent; kTh (mL/min mg) is the Thomas rate constant;
fluid phase to the solid phase. For TZ adsorption the values Co (mg/L) is the inlet concentration; Ct (mg/L) is the outlet
of No and Ka were 637.8 mg/L and 0.002 L/mg h, The concentration at time t; Q (mL/min) the flow rate; W (g) the
parameters obtained from BDST plot can be used to scale- mass of adsorbent, and (t) stands for flow time. The value
up the process (Walker and Weatherley 1997). of C0/Ct is the ratio of inlet and outlet dye concentrations.
A higher bed height indicates a larger amount of binding A linear plot of ln[(Co/Ct) - 1] against time (t) was
sites available. Similar observations also have been employed to determine values of kTh and qe from the
reported by several researchers (Unuabonah et al. 2010; intercept and slope of the plot as shown in Figs. 8 and 9 for
Mulgundmath et al. 2012; Noreen et al. 2013). The longer TZ adsorption.
exhaustion time (te, the time that the effluents reach the The Thomas model gave a good fit of experimental data
influent concentration) was observed by increasing the bed with high coefficient of determination, R2 is greater than
height from 8 to 12 cm. The exhaustion time also increased 0.92. The values of Thomas model show that the maximum
from 425 to 790 min for TZ adsorption. After breakthrough adsorption capacities increases with increasing initial
time (tb, the time that the effluents concentration start to be concentrations. However, the maximum adsorption capac-
detected), the concentration of effluent of dyes TZ rapidly ities decrease with increases of flow rate. Table 6 shows
increases. the coefficient of determination values were varied from
0.92 to 0.98 with relative errors (RE) variation from 2.8 to
Validity of kinetic models of fixed-bed column adsorption

Dynamic adsorption is a complex process and its perfor- 6

mance is controlled by many variables (Chen et al. 2012). Inial conc. 10 ppm
4 Inial conc. 15 ppm
140 Inial conc. 20 ppm
120 y = 15.75x - 74.5 2
ln(Co/Ct - 1)

R² = 0.9992
Service me (min)

100
0
80
0 100 200 300 400 500 600
60 -2
40
20 -4
0
6 8 10 12 14 -6 Time (min)
Bed height of acvated carbon (cm)
Fig. 8 Thomas model for adsorption of TZ on activated carbon at
Fig. 7 BDST model plot for TZ adsorption onto activated carbon bed different initial concentration (flow rate of 2.7 mL/min, bed height of
(Co = 15 mg/L, pH = 7, flow rate = 2.7 mL/min.) 10 cm, temperature of 25 °C)

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Appl Water Sci

6 intercept and slope of a linear plot of ln [(Ct/C0)] against tb

Flow rate 2.7 ml/min as shown in Figs. 10 and 11 for TZ adsorption.
4 Linear regression results (Table 7) shown that adsorption
Flow rate 4.2 ml/min
capacity of the adsorbent (N0) and kinetic constant of the
Flow rate 5.7 ml/min
2 model (kAB) increased with increasing initial dye concen-
tration. However, because of more saturation of active carbon
ln(Co/Ct-1)

0 sites, adsorption capacity of the adsorbent (N0) decreased

0 50 100 150 200 250 300 350 with increasing flow rate. In addition, kinetic constant of the
-2 model (kAB) decrease with increasing flow rate. The lower R2
values relative to the other model can be interpreted that the
-4 Adams–Bohart model is not as appropriate a predictor for the
breakthrough curve (Rozada et al. 2003).
-6
Time (min)
Adsorption performance of prepared activated
Fig. 9 Thomas model for adsorption of TZ on activated carbon at carbon
different flow rates (bed height of 10 cm, Initial TZ concentration of
15 mg/L, and temperature of 25 °C) The adsorption capacities of tartrazine over a variety of
adsorbents are compared and reported in Table 8. The
adsorption capacity of apricot stones based activated car-
8.9 which indicate a good agreement between the experi- bon prepared in this study was found to be larger than
mental data and the column data generated using the adsorption capacity accounted by several researcher from
Thomas model. The rate constant, KTh is observed to batch studies. Therefore, the activated carbon prepared in
increase and decrease with the same pattern with qe (mg/g) this work could be used as an effective adsorbent for
(the calculated equilibrium dye uptake per gram of the removing azo-dye from aqueous solutions. However, the
adsorbent) (Futalan et al. 2011). TZ adsorption capacity obtained from the column experi-
Bohart–Adams model which describes the initial part of ments was lower than the values obtained from the batch
a breakthrough profile is assumed to have rectangular experiments for the same initial dye concentrations used.
shape isotherm. The model equation can be expressed as: This might be due to the insufficient contact time between
  the dye ions in the solution and the adsorbent in the col-
Ct kAB N0 Z
ln ¼ kAB C0 ðtÞ  ð6Þ umn. The difference between the batch and continuous
C0 L
capacity could also be attributed to the channeling of the
where Co and Ct are the initial and breakthrough concen- flowing stream. Besides, the effective surface area of the
trations (mg/L), No is fixed-bed sorption capacity per unit activated carbons adsorbent packed in the column was
volume (mg/mL), kAB (mL/mg min) is Bohart–Adams lower than that in the batch process. Therefore, the per-
model’s constant, Z is the bed height, L (mL/min) is the formance of the activated carbon bed could be enhanced by
linear or superficial velocity and tb is the breakthrough applying a lower solution flow rate and/or using a higher
time. The model’s parameters are obtained from the bed height.

Table 6 Thomas model parameter of TZ adsorption on AC

Inlet conc. (mg/L) Bed height, H Flow rate (mL/min) Parameters
kTh (mL/min mg) qe (mg/g) R2 qe(exp) RE

Effect of initial concentration

10 10 2.7 1.05 1.70 0.934 1.56 8.97
15 10 2.7 1.12 1.86 0.973 1.78 4.49
20 10 2.7 1.81 1.98 0.963 1.84 7.61
Effect of flow rate
15 10 2.7 1.23 2.53 0.970 2.46 2.80
15 10 4.2 1.11 2.35 0.948 2.28 3.07
15 10 5.7 1.06 1.88 0.968 1.76 6.81

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 Appl Water Sci

1 Table 8 Comparison of the adsorption capacity of Apricot stone-

based activated carbon with various adsorbents
0
0 100 200 300 400 Adsorbent Maximum adsorption References
-1 capacity (mg/g)

-2 Jute processing 22.47 Banerjee and

ln(Ct/Co)

wastes Dastidar (2005)

R² = 0.7819 Flow rate 5.7 ml/min
-3 Chitin 30 Dotto et al. (2012)
R² = 0.8593 Flow rate 4.2 ml/min
Polyaniline nano layer 2.47 Ansari et al. (2011)
-4
R² = 0.9349 Flow rate 2.7 ml/min composite
-5 Bottom ash 12.6 Mittal et al. (2006)
Deoiled soya 24.6 Mittal et al. (2006)
-6
Time (min) Amberlite IRA-900 49.88 Wawrzkiewicz and
Hubicki (2009)
Fig. 10 Adam’s–Bohart model for adsorption of TZ onto activated Amberlite IRA-910 49.96 Wawrzkiewicz and
carbon at different flow rate (bed height of 10 cm, Initial TZ Hubicki (2009)
concentration of 15 mg/L, and temperature of 25 °C) Commercial activated 4.48 Jibril et al. (2013)
carbon
Sawdust 4.71
1
Apricot stone-based 76 This study
0 activated carbon
0 200 400 600
-1
ln(Ct/Co)

-2

-3 adsorption–desorption isotherm was a combination of types

R² = 0.9052 Inial conc. 10 ppm I and IV isotherms, which is corresponding to micro-me-
-4 R² = 0.942 Inial conc. 15 ppm soporous solid. Studies on continuous adsorption using a
-5 R² = 0.822 Inial conc. 20 ppm series of column experiments revealed that activated car-
bon prepared from apricot stones by H3PO4 activation has
-6
Time (min) high ability to remove Tartrazine dye from aqueous solu-
tions. The continuous adsorption system represented by the
Fig. 11 Adam’s–Bohart model for adsorption of TZ on activated breakthrough curves was dependent on the initial dye
carbon at different initial concentration (flow rate of 2.7 mL/min, bed
height of 10 cm, temperature of 25 °C) concentration, bed height and the solution flow rate used.
The results of different bed height showed the validity of
Table 7 Adam-Bohart model parameter of TZ adsorption on AC
BDST model to study adsorption of TZ with the regression
coefficient (R2) of 0.99. Comparison of Thomas and
Dye inlet Bed Flow rate Parameters Adams–Bohart kinetic models with experimental data was
conc. (mg/L) height, (mL/min)
H kAB (mL/ N0 (mg/ R2 performed and model parameters were determined by lin-
mg. min) mL) ear regression analysis for TZ adsorption under various
Effect of initial concentration
operating conditions. The experimental data fit well with
10 10 2.7 0.50 1.57 0.90
Thomas, but the Adams–Bohart model predicted poor
15 10 2.7 0.67 1.79 0.94
performance of fixed-bed column.
20 10 2.7 0.81 2.19 0.82
Open Access This article is distributed under the terms of the
Effect of flow rate Creative Commons Attribution 4.0 International License (http://
15 10 2.7 0.62 2.83 0.93 creativecommons.org/licenses/by/4.0/), which permits unrestricted
15 10 4.2 0.41 2.57 0.86 use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
15 10 5.7 0.30 1.78 0.78 link to the Creative Commons license, and indicate if changes were
made.

Conclusions
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