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Adsorption of textile dye Reactive Red 120 by the chitosanFe(III)-crosslinked:Batch and fixed-bed studies

Carla Albertina Demarchi, Mayara Campos, Clovis Antonio Rodrigues *

Nucleo de InvestigacoesQu mico-Farmaceuticas (NIQFAR), Universidade do Vale do Itaja (UNIVALI), Itaja 88302-202, Santa Catarina, Brazil

Introduction

Many industries, such as the textiles, leather, cosmetics, paper,

printing and plastics industries, use synthetic dyes as part of their

production processes. Effluents from these industries therefore

contain various kinds of synthetic dye stuffs [1]. Dye contamina-tion in aqueous wastewater from industries is a serious problem

because dyes are not biodegradable, and tend to suppress

photosynthetic activity in aquatic habitats by preventing the

penetration of sunlight [2]. Moreover, most of these dyes cancause

allergy, dermatitis, and skin irritation [3], and can also lead to

genetic mutations in humans[4].

Compared to traditional methods of decontamination of

effluents containing dyes, the adsorption method is the best

alternative, and has been widely used to remove pollutants from

effluents [5], due to its low cost, simplicity of design, availability

and ability to treat dyes in more concentrated form[6,7]. Most

commercial systems use activated carbon as adsorbent to remove

dyes in water, because of its great adsorption capacity. However,

its widespread use is restricted due to its cost. In order to decreasethe cost of treatment, some attempts have been made to find low-

cost alternative adsorbents[1]. Chitosan is derived from a natural

polysaccharide, chitin, which is the second most abundant

polysaccharide in nature. It is relatively cheap and exhibits higher

dye adsorption capacities[8,9].

Absorbents containing iron have received a great deal of

attention, due to their chemical stability and high absorption

capacity[1013]. Chitosaniron complex has been used to remove

oxyanions, such as, Cr (VI)[14,15], As(III)[16]and As (V)[17]from

aqueous solutions, however the uses of chitosaniron complex for

adsorption dyes have not been reported.A great number of publications related to adsorption of textile

dyes by magnetic chitosan and its derivatives have recently been

reported in the literature [10,1822]. However, theuse of magnetic

particles is restricted to the separation process using the batch

method, and it is not appropriate for fixed-bed process. Another

disadvantage of magnetic particles, as compared with the

chitosaniron complex, is related to the fact that their synthesis

involves many steps. On the other hand, the ironchitosan

complex is easily synthesized.

This paper presents a study of the use of chitosaniron(III)

crosslinked with glutaraldehyde (Ch-Fe), as an adsorbent for the

textile anionic dye Reactive Red 120 (RR120). This work involves

studies of equilibrium and kinetics of adsorption in different

conditions of pH and temperature, study of recovery and reuse ofthe adsorbent, and also factorial design in batch studies, and fixed-

bed studies to predict adsorption on an industrial scale.

Experimental

Materials

The chitosan (viscosimetric molecular weight of 2.5 105 g/

mol, and desacetylation degree of 85%) was obtained from

Purifarma (Sao Paulo). The dye Reactive Red 120 (Procion Red

HE-3B; MF: C44H24Cl2N14O20S6Na6; MW: 1469.98) was kindly

Journal of Environmental Chemical Engineering 1 (2013) 13501358

A R T I C L E I N F O

Article history:

Received 16 August 2013

Received in revised form 7 October 2013Accepted 8 October 2013

Keywords:

Reactive Red 120

Chitosaniron(III)

Textile wastewater

Factorial design

A B S T R A C T

This paper presents a study of the use of chitosaniron(III) crosslinked with glutaraldehyde (Ch-Fe) as an

adsorbent for the textile anionic dye Reactive Red 120 (RR120) in batch and fixed-bed systems. The

maximum adsorption capacity was calculated from the adsorption isotherms, and well fitted by the

LangumirFreudlich isotherm model.The process followed the kinetic model of pseudo-second-order. In

fixed-bed studies, the Thomas, Adams-Bahort and Clark models were applied to the breakthrough

curves. The thermodynamic parameters showed that the adsorption process is spontaneous and

favorable. The adsorbent can be easily regenerated and reused. The adsorption of the RR120 was

optimized using a 33 factorial design, and the initial pH of the dye solution had a significant effect.

2013 Elsevier Ltd. All rights reserved.

* Corresponding author at: Universidade do Vale do Itaja , ItajaCEP 88302-202,

SC, Brazil. Tel.: +55 47 3341 7664; fax: +55 47 3341 7600.

E-mail address: [email protected](C.A. Rodrigues).

Contents lists available at ScienceDirect

Journal of Environmental Chemical Engineering

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j e c e

2213-3437/$ see front matter 2013 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.jece.2013.10.005
http://dx.doi.org/10.1016/j.jece.2013.10.005mailto:[email protected]://www.sciencedirect.com/science/journal/aip/22133437http://dx.doi.org/www.elsevier.com/locate/jecehttp://dx.doi.org/10.1016/j.jece.2013.10.005http://dx.doi.org/10.1016/j.jece.2013.10.005http://dx.doi.org/www.elsevier.com/locate/jecehttp://www.sciencedirect.com/science/journal/aip/22133437mailto:[email protected]://dx.doi.org/10.1016/j.jece.2013.10.005


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donated by Trento Brasil Beneficiamento Textil (Nova Trento,

Brazil).All theother reagents used were of analytic grade,and were

used without purification. The adsorbent Ch-Fe was prepared and

characterized as described by Klepka et al. [23]. The average

particle size was determined using SEM (scanning electron

microscopy) and was 4.7 1.7mm [16]. The zero-point of charge(pHzpc) was determined by potentiometric titration [24] and was

found to be 8.5. Thequantityof iron in thesample wasdeterminedby

colorimetric methods using 1.10 phenanthroline and a double beam

UVvis spectrophotometer (Spectrovision mod. DB 188S, China), and

was found to be 80.5 mg/g.

Batch studies

Adsorption kinetics

The adsorption kinetics were performed in the system,

thermostated at 25 8C using 25 mg of adsorbent, 20 mL of

RR120 solution 400 mg/L, under continuous agitation. Ali-

quots were removed at certain time intervals (5, 15, 30, 45,

60, 90 and 120 min), the adsorbent was separated bycentrifugation, and the quantity of dye present in the

supernatant was spectrophotometrically determined based

on an analytical curve (adsorbance at 540 nm vs. dye

concentration), using a UVvis spectrophotometer Spectro-

vision mod. DB 188S, China.

Adsorption isotherms

The adsorption isotherms were obtained using a thermostatic

bath with continuous agitation, with 20 mL of dye solution at

concentrations between 100 and 500 mg/L containing 25 mg of

adsorbent, and agitation time of 60 min. The studies were

conducted in buffer solution with a concentration of 0.05 M:

monochloroacetic acid (pH 2.0), sodium acetate (pH 5.0) and

(tris)hydroxymethyl aminomethane (pH 9.0) to evaluate the pHeffect. To evaluate the effect of temperature, the isotherms were

performed in non-buffered dye solution (pH 3.6) at 25 8C, 40 8C

and 55 8C. After agitation, the solutions were centrifuged and the

dye concentration was determined in a spectrophotometer at

540 nm.

The adsorption capacity (qe) was calculated according to Eq.(1)

[22]:

qe C0 Ce v

m (1)

where C0 and Ce (mg/L) are the initial and equilibrium dye

concentrations in the liquid phase, respectively, v(L) is the volume

of solution and m (g) is the amount of adsorbent.

Regeneration and reuse of the adsorbent

For the regeneration, 100 mg of the adsorbent saturated with a

RR120 solutionwasused. Thedyewas removedwith50 mLof NaOH

0.1 M. The dye concentration was determined as described

previously. The adsorbent was then washed with HCl 0.01 M and

distilled water to neutralize the excess NaOH and recondition theadsorbent. This procedure was repeated three times for each

adsorption/regeneration cycle.

Factorial analysis

The studies using systems of factorial design of experiments

were performed using the variables initial concentration (Ci), pH

solution and agitation temperature. Table 1 shows the levels of the

independent factors and experimental designs. The software

Statistica1 version 6.0 was used to fit the experimental results

from the factorial design, and the main effects and interactions

between the factors were determined.

Fixed-bed studies

The fixed-bed column was made of polyethylene tube with an

inner diameter of 0.75 cm and height of 5.5 cm. A sintered glass

wasattachedto thebottom of the column. A knownquantity of the

material was packed in the column to give the desired bed heights

of the adsorbent: 17 mm, 36 mm and 64 mm. RR120 solution with

concentration of 100 mg/L at non-buffered pH (3.6) was pumped

through the column at a flow rate of 2.0 mL/min controlled by a

peristaltic pump (Spectrovision, mod PP2).

TheRR120 solutions at theoutletof thecolumn werecollected at

regular time intervals. Aliquots were removed at certain time

intervals, and the quantity of dye present in the effluent was

spectrophotometrically determined at a wavelength of 540 nm. The

amount of RR120 adsorbed was calculated based on the difference

between theirinlet concentration(C0) andoutlet concentrations (Ct).The breakthroughcurves,which showed the performance of the

fixed-bed column, were plotted in terms of normalized concen-

tration, Ct/C0, (which is defined as the ratio of effluent dye

concentration, Ct(mg/L), to inlet dye concentration,C0(mg/L)) as a

function of time. The experimental curves were mathematically

modeled using non-linear regression, and the parameters were

estimated using the software OriginPro 8.5.

Results and discussion

Adsorption kinetic

Thekinetic behavior of the adsorption process was studied with

an initial concentration of 400 mg/L, pH 3.6 (non-buffered dye

Table 1

Matrix of factorial design and results of experiments.

Experiment pH (A) Temperature (B) Ci(C) Amount adsorbed (mg/g)

1 0 + 227.5

2 0 0 0 169.6

3 + 0 315.8

4 + + 0 109.3

5 0 + 312.8

6 + 0 81.6

7 0 + 246.48 0 286.4

9 0 235.9

10 + 0 96.0

11 0 0 0 169.6

12 0 0 0 169.6

13 0 + + 255.3

14 + 0 + 112.7

15 0 208.1

pH: 2(), 5(0), 8(); Temperature: 55 8C(+), 40 8C(0), 25 8C(); concentration: 300mg/L(), 400 mg/L(0), 500 mg/L(+).

C.A. Demarchi et al./ Journal of Environmental Chemical Engineering 1 (2013) 13501358 1351


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solution), temperature 25 8C and with 25 mg of Ch-Fe. It can be

observed fromFig. 1that RR120 uptake on Ch-Fe was a very fast

process. The amount of adsorption increased rapidly in the first

5 min, contributing to 80% of the total adsorption. This same

behavior was observed for the adsorption of the acid dyes by a

magnetic chitosanFe(III) hydrogel in alkaline condition[18].

For examination of the controlling mechanisms of the adsorp-

tion process, such as chemical reaction, diffusion control and mass

transfer, several kinetic models were used to test the experimental

data. The pseudo-first-order, pseudo-second-order and intrapar-

ticle models in non-linear forms were used (Fig. 2). The pseudo-

first-order model[25]is represented by Eq.(2):

qt qe1 ek1t (2)

where k1 (1/min) is the constant of the first order adsorption, qe(mg/g) is the amount of dye adsorbed at equilibrium andqt(mg/g)

is the amount of dye adsorbed at time t(min).

The pseudo-second-order model[26], is represented by Eq.(3).

qt k2q

2e t

1 k2q2e t (3)

wherek2(1/min) is the constant of the second order adsorption, qe(mg/g) is the amount of dye adsorbed at equilibrium andqt(mg/g)

is the amount of dye adsorbed at time t(min).

Another kinetic model used was the intraparticle diffusion[27]

(Eq.(4))

qt kit0:5 (4)

where ki (mg/g min1/2) is the intraparticle diffusionconstant and qt(mg/g) is the amount of dye adsorbed at time t(min).

Based on its calculatedqevalue of 254.2 mg/g, which is close to

the experimental values, qex (269.9 mg/g), the pseudo-second-

order equation kinetic was the best kinetic model to explain the

adsorption process, indicating a chemisorption process. The

pseudo-second-order kinetic model was also the best kinetic

model observed for the other adsorbents in the adsorption of acid

dyes[18,2831](Table 2).

Adsorption isotherms

Isotherm adsorption models are useful for predicting the

adsorption parameters and optimizing the design of an adsorption

system. The adsorption equilibrium isotherm data were studied

using the Langmuir (Eq. (5)) [32], Freundlich (Eq. (6)) [33] and

LangmuirFreundlich (Eq.(7))[34]models (Fig. 2). The non-linear

form of the isotherm models are given as:

qe KLqmCe1 KLCe

(5)

qe KFC1=n

e (6)

qe KLFqmC

ne

1 KLFCne(7)

where Ce (mg/L) is the equilibrium concentration of RR120

adsorbed and qe (mg/g) is the experimental adsorption capacity

of RR120, Langmuir constants qm (mg/g) and KL (L/mg) are the

monolayer adsorption capacity and affinity of adsorbent toward

the adsorbate, respectively. Freundlich constantsKF(L/mg) and n

give information on the extent of adsorption and the degree of

nonlinearity between the adsorption and the solution concentra-

tion, respectively. Absorption intensity is evaluated by the inverse

ofn (1/n).

The Langmuir and LangmuirFreundlich models indicate that

the maximum adsorption capacity of RR120 (Table 3) increases asthe temperature increases, and decreases as the pH decreases. The

adsorption mechanism of adsorption, in this case, is electrostatic

interactions between the adsorption sites of the positively charged

Ch-Fe (Fe3+) and the SO3 groups present in the dye RR120. In Ch-

Fe crosslinked with glutaraldehyde, the free NH2 groups are not

present due to a reaction with glutaraldehyde. As a result, non-

specific interactions between the (NH3+) and sulfonate groups of

[

0 20 40 60 80 100 120

0

50

100

150

200

250

300

pseudo-first order

pseudo-second order

Intraparticle

qt(mg/g)

Time (min)

Fig. 1. Adsorption kinetics of RR120 by Ch-Fe. RR120 concentration 400 mg/L

(20 mL), 25 mg of Ch-Fe, pH 3.6, temperature 258C.

[

Fig. 2. Adsorption isotherms of the RR120 by Ch-Fe, temperature 25 8C, pH 5.0.

Table 2

Kinetic parameters of the adsorption of the dye RR120 by the Ch-Fe.

Pseudo-first order Pseudo-second order Intraparticle

k1(min) qe(mg/g) r2 k2 (g/mg min

1/2) qe(mg/g) r2 C(mg/g) qe (mg/g) r

2

4.25 101 246.69 0.9766 3.85 103 254.20 0.9859 105.95 18.273 0.5938

C.A. Demarchi et al./ Journal of Environmental Chemical Engineering 1 (2013) 135013581352


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the dye reported in the literature [29] are not possible. The

increased adsorption capacity in acid pH can be explained by the

competition between OH (present in a buffered medium) anddye

on the Fe3+ binding sites of the adsorbent. Similar results were

recently reported for the adsorption of anionic dyes [35]. This

behavior usually occurs in adsorbent containing Fe3+ by the

formation of Fe(OH)3 on the adsorbent surface.

Comparing the different adsorption models, the results show

that the model that was best correlated with the adsorptionprocess of RR120 by Ch-Fe was the LangmuirFreundlich model,

because it showed higher correlation coefficients, when compared

with the other two models. The LangmuirFreundlich model is a

combination of the Freundlich and Langmuir models. This model

assumes that at low concentrations of adsorbate, this model

approaches the Freundlich model (which describes heterogeneous

systems) and in high concentrations of adsorbate, provides

monolayer adsorption capacity that is characteristic of the

Langmuir isotherm.

Table 4 shows a comparison of the maximum adsorption

capacity of the dye RR120 of various adsorbents. The qe(mg/g) is

according to the Langmuir model. The adsorbent Ch-Fe has a

higher capacity than other adsorbents reported in the literature.

Thermodynamic parameters

The thermodynamic parameters, like change in Gibbs free

energy (DG8, kJ/mol), enthalpy (DH8, kJ/mol), and entropy (DS8, J/

mol K) were determined using Eqs.(8)(10)[44]:

KD CsCe

(8)

DG RTln KD (9)

ln KD

DS

R

DH

RT (10)

where KD is the equilibrium constant, Cs is the amount of dye

adsorbed (mg/g), Ce is the equilibrium concentration (mg/L), R is

the universal gas constant (8.314 kJ/mol), and T is absolute

temperature (K). By plotting a graph of lnKD versus 1/T, DH8

and DS8values can be determined from the slopes and intercept,

respectively.

The results are shown in Table 5. The positive DS8 value

indicates the increased degree of freedom of the system,

suggesting randomness at the solid/liquid interface. The negative

value ofDH8shows the adsorption to be exothermic. The negative

values ofDG8demonstrate that the dye adsorption is spontaneous

and that the system is not gaining energy from any external source

[28].

Regeneration and reuse of the adsorbent

The regeneration of the adsorbent is important for lowering the

cost of the adsorption process and for possibly recovering the

pollutant extracted from wastewater [18]. Table 6 shows the

results of RR120 desorption and adsorbent reuse. With the

exception of the first cycle, there was no significant difference

in the ability to remove the dye in cycles of adsorption/desorption.

These results show that the adsorbent is stable when subjected to

the process of removing and reconditioning by adding NaOH 0.5 M

and HCl 0.01 M. The capacity of adsorption reduces slightly in each

cycle, and in the last cycle, the reduction was 30%. Therefore, Ch-Fe

can be easily regenerated and reused.

Factorial analysis

Thegoal of the factorial designwas to findthe parameters of the

process that have a significant influence on the process, and to find

Table 3

Study of temperature and pH variation on the adsorption isotherms of the dye RR120.

Langmuir Freundlich LangmuirFreundlich

KL(L/g) qm(mg/g) r2 KF(L/g) n r

2 KLF(L/g) qm(mg/g) n r2

T(8C)a

25 0.3920 290.70 0.8117 111.10 0.219 0.8417 0.3102 433.84 0.427 0.8473

40 0.3747 331.35 0.7547 131.67 0.207 0.6800 0.0033 309.94 7.241 0.8487

55 0.5224 361.96 0.8543 230.68 0.095 0.7465 0.0135 350.42 3.250 0.9882

pHb

2.0 0.4657 336.77 0.7972 192.38 0.120 0.9579 0.7198 380.57 0.486 0.8946

5.0 0.4387 230.08 0.9399 100.16 0.177 0.9605 0.4403 283.57 0.493 0.9908

9.0 0.0503 135.69 0.8484 36.635 0.229 0.9382 1.393 14.756 0.0381 0.9353

a pH 3.6 non-buffered dye solution.b Temperature 25 8C.

Table 4

Comparison of different sorbents in the adsorption of textile dye RR120. Maximum

adsorption capacity calculated with the Langmuir model.

Adsorbent qe(mg/g) Reference

Ch-Fe 361.9 In this study

Chitosan/modified montmorillonite 5.6 [36]

Commercial activated carbon 293.1 [37]

Jatropha curcasshells 42.5 [38]

Chara contraria 112.8 [39]

Activated carbonaceous Brazilian pine-fruit-shell 275.0 [40]

nanoparticles of Fe3O4 166.67 [41]

Cetylpyridiniun-Bentonite 81.97 [42]

Pistachio husk 324.88 [43]

Table 5

Thermodynamic parameters for the adsorption of RR120 on the Ch-Fe.

DS8(J/molK) DH8 (kJ/mol) DG8(kJ/mol)

248.32 71.2 2.80 (25 8C)

6.46 (408C)

10.26 558C

Table 6

Desorption of RR120 and reuse of Ch-Fe. Dye concentration 500 mg/L; volume of

solution 80 mL, 100 mg of adsorbent; temperature 55 8C, pH 3.6, contact time

60min.

Cycle RR120 adsorbed (mg/g) Desorption (%)

1 361.2 57.7

2 321.8 81.4

3 304.1 83.4

4 249.3 84.8



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the setting valuesof the principal parameters forsetting theresults

of the process on the desired values [45].

The matrix codes used for the factorial design, and the results,

are shown inTable 1. The effects, standard error, tvalue,p value,

errors of coefficients and regression coefficient are shown in

Table 7.

The quadratic model was used for the initial calculation of the

regression

Qe b0 b1xA b2x2

A b3xB b4x2B b5xC b6x

2C

b7xAxB b8xAxC b9xBxC (11)

where b0 is the global mean, bi represents the regression

coefficient relating to the main factor effects and interactions,

and A, B and C represent the pH, temperature and initial

concentration, respectively.

Replacing the bi coefficients with their respective values

(Table 6), it was possible to derive an equation model linking

the parameters to the adsorption of the dye RR120.

Qe 207:2 187:4pH 8:15pH2 17:9T 40:3T2

43:2Ci 24:4Ci2 8:25pHT

22:3pHCi 5:25CiT

(12)

The values of the effects of principal factors are shown in the

Pareto graph in Fig. 3 (horizontal columns). To indicate the

minimum statistically significant effect, for p= 0.05, a vertical line

was drawn. The linear factors pH (A), quadratic factor temperature

(B2), initial concentration (C) and quadratic factor initial concen-

tration (C2) are the most significant. The graph shows that the

effect of pH is the most important effect, followed by the

temperature.

Fig. 4shows the graphs, constructed using the surface response

method that correlates with the initial concentration factors

temperature pH (Fig. 4A), (Ci) pH (Fig. 4B) and Ci tempera-

temperature (Fig. 4C). The experiments that resulted in Fig. 4A

were conducted with an initial concentration of 400 mg/L, and the

pH in this condition is an essential factor in determining the

amount of dye adsorbed. In the case ofFig. 4B, the experiments

were conducted at a constant temperature of 40 8C, and pH was

also a major factor responsible for the adsorption of the dye. Theexperiments that resulted inFig. 4C were conducted at pH 5.0 and

in this case, Ci and temperature had no significant effect on

adsorption of the dye.

Fixed-bed studies

The objective of using a fixed-bed system is to reduce the

concentration of a substance that is considered, by the government

agencies, to be polluting up to a predetermined value. At the

beginning of the adsorption operation, when the sorbent material

is still unused, thefinalconcentrationis actually lower than what is

permitted by the regulatory agencies, but as adsorption proceeds

and the sorbent material gradually becomes saturated, the effluent

concentration increases and reaches the so-called breakthroughpoint, or breakdown of the efficiency of the column [46].

The desired breakthrough volume (Vb) was determined at 5% of

the inlet solution concentration. The flow through the tested

column was continued until the RR120 concentration of the

column effluent approached 95% of the influent solution concen-

tration, indicating the exhaustion volume (Ve).

The capacity at exhaustion was determined by calculating the

total area below the breakthrough curve (plot of Ct/C0 against t

(min)). The column capacity was estimated by Eq.(13)[47].

qtotal

Z ve

vb

CECBdQ

x (13)

where qtotalis the column capacity adsorption (mg),CBand CEare

breakthrough and exhaustion RR120 concentration (mg/L) respec-tively,Qis the flow rate in (mL/min) and x is the Ch-Fe mass (g).

The value of adsorption capacity, determined experimentally,

qe(exp)(mg/g) is calculated as follows[48]:

qeexp qtotal

x (14)

wherex(g) is the total dry weight of the adsorbent in the column.

The breakthrough curves of the (Ct/C0) versus time for various

bed depth of 17, 34 and 66 mm (150, 100 and 150 mg), at a

constant flow rate of 2 mL/min and RR120and initial concentration

of 100 mg/L, areshownin Fig. 5. From Fig. 5, thebreakthrough time

and exhaustion time increased with the increase in bed depth. As

the bed depth (Ch-Fe mass) and number of active sites of

adsorption (Fe

3+

) increased, RR120 had more time to contact with

Table 7

Effect estimated coefficients for the adsorption of the dye RR120.

Effect Standard error Effect Tvalue Pv alue Coefficient Standa rd e rro r of coefficient

Interactions media 207.18 2.823407 73.380 0.000000 207.18 2.823407

pH 187.47 6.915906 27.108 0.000001 93.738 3.457953

pH2 8.150 5.089969 1.6012 0.170234 4.0750 2.544984

T 17.900 6 .915906 2.5882 0.048941 8.9500 3.457953

T2 40.325 5.089969 7.9224 0.000516 20.1625 2.544984

Ci 43.225 6.915906 6.2501 0.001537 21.6125 3.457953

Ci2

24.200 5.089969 4.7544 0.005084 12.1000 2.544984pH T 8.250 9.780567 0.8435 0.437425 4.1250 4.890284

pH Ci 22.300 9.780567 2.2800 0.071535 11.1500 4.890284

T Ci 5.250 9.780567 0.5368 0.614435 2.6250 4.890284

R2 = 0.99431;R2 adjusted 0.98406.

[

Fig. 3. Pareto graph of the effects.



6/9

Ch-Fe, resulting in higher removal efficiency of RR120 in the

column. The higher bed depth therefore resulted in a decrease in

the effluent concentration at the same service time. The

parameters shown inTable 8 Vband Ve depend on the higherof the bed and increased with bed depth. High adsorption capacity

in breakthrough (qb) and adsorption capacity in exhaustion (qe)

were observed at the highest bed depth, due to an increase in the

surface area of adsorbent, providing more binding sites for the

adsorption.

The success of the column design for the adsorption process

requires predicting the effect profile concentration-time curves of

the effluents. Over the years, various mathematical models have

been developed to analyze the column studies in the laboratory, inorder to plan columns on an industrial scale. This study applies the

mathematical models of Thomas, Adams-Bohart and Clark in non-

linear forms.

The Adams-Bohart model is used to describe the initial part of

the breakthrough curve. This model assumes that the adsorption

rate is proportional to both the residual capacity of the adsorbent

and the concentration of the adsorbing species, and is expressed as

[49]

CtC0

exp kABC0t kABN0Z

F

(15)

where C0 is the inlet concentration (mg/L), Ct is the exit outlet

concentration (mg/L), kAB is the mass transfer coefficient (L/

[

Fig. 4.Surface response amount adsorbed (mg/g). (A) Effect of temperature and pH. (B) Effect of the initial concentration ( Ci) and pH. (C) Effect ofCiand temperature. In all

experiments, the agitation time (1 h) and the amount of adsorbent (25 mg) and volume of solution (20 mL) were kept constant.

Table 8

Column data and parameters obtained at different bed heights on the adsorption of

the dye RR120. Initial concentration 100mg/L, flow rate 2 mL/min.

Bed height (mm) 17 36 64

Vb(mL) 60 80 350

Ve (mL) 340 600 850

qb(mg/g) 60 80 350

qe (mg/g) 250 510 680



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mg min), N0 is the saturation concentration (mg/L), Z is the bedheight (cm) and F is the linear velocity (1/cm).

Plotting Ct/C0 against t also gave the breakthrough curves

predicted by the Bohart-Adams model (Fig. 5C), and the

experimental points. For all breakthrough curves using non-

linear regression analysis, respective values of KAB and N0were calculated and are presented in Table 9, along with

the correlation coefficients (r2). Table 9 also shows that the

values of KAB and N0 increased with increasing bed depth.This shows that the overall system kinetics was dominated

by external mass transfer in the initial part of adsorption in

the column [48].

Another model that was employed is the Thomas model, which

is one of the most widely used models in column performance

theory. The Thomas model is based on the assumption that the

process follows Langmuir kinetics with no axial dispersion.

[

-50 0 50 100 150 200 250 300 350 400 450

-0,1

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

(A)

50 mg

100 mg

150 mg

C

t/C

0(mg/L)

Time (min)

-50 0 50 100 150 200 250 300 350 400 450

-0,1

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

(B)

50 mg

100 mg

150 mg

Ct/

C0

(mg/L)

Time (min)

-50 0 50 100 150 200 250 300 350 400 450

-0,1

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

1,2

(C)

50 mg

100 mg

150 mg

Ct/

C0

(mg/L)

Time (min)

Fig. 5. Comparison of fitted curves and experimental data, Thomas (A), Clark (B), Adams-Bahort (C). Initial concentration 100 mg/L, flow rate 2 mL/min.

Table 9

Thomas, Adams-Bahort and Clark models constants at different bed heights. Initial concentration 100 mg/L, flow rate 2 mL/min.

Thomas

Bed height (mm) KTh(mL/mgmin) qe (mg/g) r2 x2 SSE

17 0.4384 136.48 0.9463 0.00631 0.17663

36 0.1338 363.65 0.9019 0.00633 0.29138

64 0.1524 671.79 0.9802 0.00136 0.08857

Adams-Bahort

Bed height (mm) kAB(L/mg/min) N0 (mg/L) r2 x2 SSE

17 0.0920 73.11 0.7413 0.85121 0.07187

36 0.0592 150.15 0.8009 0.59148 0.04666

64 0.0837 200.39 0.9438 0.25171 0.08698

Clark

Bed height (mm) A KC(1/min) n r2 x2 SSE

17 43.84 0.0639 2.1 0.9782 0.00104 0.04666

36 34.47 0.0294 2.4 0.9843 0.00266 0.07187

64 185.81 0.0160 2.1 0.9806 0.00136 0.08698



8/9

The Thomas model has the following form[50]:

CtC0

1

1 expKThqex=Q C0t (16)

where Qis the flow rate in (mL/min),x the adsorbent mass (g), qe is

the maximum adsorption capacity (mg/g) and KTh is the velocity

constant (mL/mg min).


predicted by the Thomas model (Fig. 5A), and the experimentalpoints. It can be clearly seen in Table 9 that as the bed depth

increased, the value ofKThdecreased and the value ofqeincreased.

The high values of correlationr2 (>0.90) calculated for the tested

parameters suggest that the Thomas model can satisfactorily

describe the adsorption of RR120 in the fixed bed column Ch-Fe.

The Thomas model is suitable for adsorption processes where the

external and internal diffusions are not the limiting step [48].

Adsorption capacity depended mainly on the amount of adsorbent

available for adsorption. The breakthrough time and exhaustion

time increased with the increase in bed height, since more time

was required to exhaust more adsorbent.

Another model developed by Clark was based on the use of a

mass-transfer concept, but in the form of the Freundlich

adsorption equation[51]:

CtC0

1

1 AeKct

1=n1(17)

where n is the Freundlich adsorption constant,A is the Clark model

constant, andKCis the adsorption rate (mg/L min). Based on a plot

of Ct/C0 against t at a given bed height, and flow rate using

nonlinear regressive analysis, the values of A and KC can be

obtained[51]. In bath studies, the adsorption does not follow the

Freundlich model (poor correlation coefficients), and the Freun-

dlich constantnwas estimated by nonlinear regression along with

the parameters A and KC in the Clark model.


predicted by the Clark model and the experimental points, as

shown in Fig. 5B. As shown in Table 9, the values of the rate of masstransferKcdecreased as the bed depth increased. This is due to the

increase in the amount of adsorbent available for interactions,

resulting in a reduction in the mass transfer rate [52]. From the

experimental results and data regression, the model proposed by

the Clark model provided good correlation on the effects of bed

depth.

Comparison of the Bohart-Adams, Clark and the Thomas models

The coefficient of determination (r2), non-linear chi-square test

x2 (Eq.(18)), and sum square errors (SSE) (Eq. (19)), were used to

determine the best-fit model:

x2

Xn1l

qe;calc qe;exp

qe;meas

2

(18)

SSEXnil

qe;calc qe;exp2i (19)

whereqe,calis the amount of dye adsorbed in equilibrium (mg g1)

calculated by the mathematical model and qe,expis the amount of

dye adsorbed in equilibrium (mg g1).

Among the Bohart-Adams, Clark and the Thomas models, the

values ofr2 from the Clark model andthe Thomas model are higher

than those of the Bohart-Adamsmodel. The SSEandx2 forthe Clark

model was the lowest for all the experimental conditions shown in

Table 9. In all the conditions examined, the predictedbreakthrough

curves from the Clark model showed reasonably better agreement

with the experimental curves than the Thomas and Bohart-Adams

models, as shown inFig. 5. Thus, it was concluded that the Clark

model was better able to predict the RR120 adsorption on CH-Fe

column than the Thomas and Bohart-Adams models.

Conclusions

Ch-Fe has high capacity for adsorption of the dye RR120, both

batch (380 mg/g) and fixed-bed (680 mg/g). The adsorption wasimproved by decreasing the pH and increasing temperature. The

adsorption kinetics follows the pseudo-second-order. In bath

studies follows the LangmuirFreundlich model and in fixed-bed

studies, can be explainedby the Clark model. The adsorbent proved

to be stable enough to enable its regeneration and reuse. The

results of thefactorial designshowed that pH is theprincipal factor

in the process of adsorption of the RR120 by the Ch-Fe.

Acknowledgements

The authors would like to thank CAPES (Brazilian Agency for

Improvement of Graduate Personnel) and CNPq (National Council

of Science and Technological Development) for the financial

support.

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