BIOSORPTION OF METHYLENE BLUE ON CHEMICALLY MODIFIED ...

Mikati, N.A. Saade, and K.A.Metallurgy, Slim, M.M. 48, El Jamal Journal F.M. of Chemical Technology 1, 2013, 61-71

BIOSORPTION OF METHYLENE BLUE ON CHEMICALLY MODIFIED CHAETOPHORA ELEGANS ALGA BY HCl AND CITRIC ACID F.M. Mikati, N.A. Saade, K.A. Slim, M.M. El Jamal

Chemistry Department, Faculty of Sciences (I), Lebanese University, Hariri Campus, El Hadath, Lebanon E-mail: [email protected]

Received 05 June 2012 Accepted 12 December 2012

ABSTRACT Chemical modification of Chaetophora Elegans algae with HCl and citric acid was undertaken in order to improve the methylene blue adsorption. The modified algae with 1 M HCl showed an increase in the maximum uptake from 143 mg g-1 to 320 mg g-1 due to elimination of carbonate. The modified algae with 1M citric acid showed an important decrease in the uptake from 143 mg g-1 to 20 mg g-1 due to increase in the cross linking degree. Acid concentration used in the chemical modification (0.1 M -1 M) is the major parameter affecting the maximum uptake. The temperature of the chemical modification has a small effect on the uptake. Langmuir-Freundlich isotherm model fitted better the isotherm adsorption data for all samples studied. Pseudo second order model was well in line with the experimental data. The adsorption rate constant (K2) is higher for modified algae with HCl than that of raw algae. The activation thermodynamic parameters Ea, ΔH#, ΔS# and ΔG# were calculated. The maximum uptake is independent of isotherm adsorption temperature in the range studied. Keywords: Modified algae, citric acid, HCl, methylene blue, isotherm adsorption, kinetic.

INTRODUCTION The extensive use of dyes poses pollution problems. They reduce light penetration and photosynthesis; in addition, some dyes are carcinogenic [1]. Several methods exist for reducing the color in textile effluent streams: adsorption, oxidation-ozonation, biological treatment, coagulation-flocculation and membrane processes. The adsorption process is one of the most effective and attractive processes for wastewaters treatment. The most commonly used adsorption agent in industry is activated carbon, which has also been extensively studied for the removal of dyes [2-6]. However; the high operation costs of regeneration prevent the large-scale application of activated carbon. Therefore, a number of other non- conventional adsorbents have been evaluated for the treatment of wastewaters. Natural materials, biosorbents [7-10], and waste materials from industry and agriculture represent potentially more economical

alternative adsorbents [11-16]. Generally, the sorption capacity of a crude biosorbent is low, but chemical modification can improve the sorption capacity of these biomaterials. The chemical treatment increases the number of the active sites or replaces the existing sites by more attractive ones. Many chemical reagents, organic or inorganic are used for this purpose (Table 1). The reagents used for this purpose are citric acid [17 – 22], HCl [23- 26], CaCl2 [25, 27], formaldehyde [25, 28], methanol [24, 27, 29], KMnO4 [30], oxalic acid [31] and NaOH [32]. Citric acid is the mostly reagent used since it introduces carboxylate group at the surface of the biomass, whereas HCl breaks the pectose down to pectin or pectic acid. And also proteins located in cell wall are denaturated by treatment and structural changes occurred [23]. Rubín et al. noted that the adsorption capacity of the Sargassum muticum biomass improved after modification with CHCl3/ CH3OH [24]. The pretreatment of

61

Journal of Chemical Technology and Metallurgy, 48, 1, 2013

Peniccillum chrysogenum with polyethylenimine using glutaraldehyde increased significantly the adsorption capacities of the biomass toward metal ions [33]. Batzias and Sidiras treated beech sawdust using CaCl2 and they found that the adsorption capacity of the adsorbent towards dye compounds was greatly increased after the chemical modification [34]. In the environmental field, methylene blue is frequently used as a model of organic cation in the search of new adsorbent biomass based materials, which can be used as an alternative for activated carbon [35]. This work deals with the adsorption of methylene blue by chemically modified biomass of the Chaetophora algae by HCl and citric acid ( with 3- COOH). EXPERIMENTAL Chemical modification of algae was studied in order to improve the adsorption uptake of raw algae. Several operating conditions affecting the dye uptake were studied in order to optimize the overall adsorption process. Thus the experiments were carried out with different chemical reagents, different reagent concentration, and temperature of the chemical reaction. The reagents used for this purpose were citric acid and HCl. The concentrations of the acid were 0.1, 0.5 and 1 M. The chemical reaction between the acid and the raw algae (RG) in the water bath was occurred at 25, 40, 50 and 60oC. The general procedure applied for this purpose was according to that mentioned in ref. 19. Dye solution preparation The dye used in this study is methylene blue (C.I. 52015, BDH, 82 %), a cationic thiazine dye. Stock solutions of methylene blue, were prepared without further purification, by dissolving accurately weighed dye in distilled water at a concentration of 500 mg dm-3. Eight working solutions (62.5, 125, 250, 300, 350, 400, 450, 500 mg dm-3) were prepared in order to draw the adsorption isotherm and calculate its parameters. Surface modification Chaetophora elegans algae (collected in June 2010, and prepared as described in a previous work was mixed with various concentrations of acid (HCl or Citric acid) [36]. 5.0 g biomass to 50 mL of a selected acid concentration (0.1, 0.5 and 1M) and stirred for 4 h at a selected

62

water bath temperature (25, 40, 50, 60 oC). The acid/ biomass was then heated at 110 oC for 4 h, afterward; the dried powder was washed and filtered several times with distilled water (~ 500 ml) until the pH of water became neutral and the drain water became clear. The washed biomass was finally dried in an oven at 110 oC for 16 h. and preserved for future use. The biomass weight loss was determined after each treatment. For simplicity the samples treated with citric acid are called x Cit y, where x and y represent the concentration of the acid used and y the temperature of the first step in the chemical reaction. Three samples of raw algae was treated in the same manner at 40, 50 and 60 oC by replacing the acid solution with distilled water in order to use them as references. Batch mode adsorption studies Batch adsorption experiments were conducted to evaluate the MB adsorption capacities of the raw and modified biomasses. The different parameters affecting the adsorption such as pH, mass of algae, equilibrium time, …) are already determined in a previous work [37]. 0.1 g of modified biomass was added to 100 ml plastic erlnmeyer, containing 50 mL of MB solutions of different concentration and agitated in the water bath shaker at 200 rpm at 25±1oC for 3h 30 min, which was sufficient to attain equilibrium. Eight concentrations of MB ranging from 60 to 500 mg/L were used in order to draw the adsorption isotherm and deduce qmax. After equilibrium being attained, the samples were centrifuged and the remaining concentration in the supernatant solution were analyzed at 666 nm, λmax of MB, using a double beam UV – Visible spectrophotometer (Specord 200, Analytical Jena), after appropriate dilution with distilled water. Isotherm experiments were carried out in duplicate. For the kinetic study, several samples are prepared in the same conditions (0.1 g of biomass, 50 mL of MB of fixed concentration). Then 2 ml is withdrawn at a selected time in order to determine the adsorption rate constant and the order of adsorption. The amount of dye adsorbed per unit weight of alga at equilibrium; qe (mg g-1) or at time t; qt (mg g-1) were calculated according to the following relations

V m V qt = (Co − Ct ) × m

qe = (Co − Ce ) ×

(1) (2)

F.M. Mikati, N.A. Saade, K.A. Slim, M.M. El Jamal

Co and Ce: The initial and equilibrium concentrations of dye (mg dm-3), respectively. V is the volume of the dye solution (L) and m is the amount of the adsorbent used (g). To determine the percentage of dye removal equation (3) is used: (Co − Ce ) % removed = ×100 Co

120

T% 100 80 60

(3)

1 HCl 40 40

Raw algae Carbonate

20

Characterization of the modified algae The raw and the modified algae were analyzed and characterized by FTIR (spectrophotometer Thermo, Nicolet IR 200, dilution with KBr) to know the functional groups that might intervene in the adsorption process. XR diffraction is carried out with D8 Focus Bruker (Cu Kα 1.54 Ao at 50 KV) to observe any change in the modified biomass with respect to raw algae.

0 400

900

1400

1900

2400

2900

3400

3900

Wavenumber (cm-1)

Fig. 1. FTIR of raw algae (RG) and of modified algae with 1 M HCl treated at 40oC. 120 100

FTIR and XR diffraction analysis The infrared spectrum of raw algae (RG), shown in Fig. 1, displays a number of absorption peaks, indicating its complex nature. Several bands were found at 3350 cm-1 (-OH or –NH2), 2915 cm-1 (-CH or COOH), 1620 cm-1 (>C=O), and 1060 cm-1 (C-O or >S=O). Effervescence is observed immediately after addition of HCl and citric acid to raw algae, but it is stronger with HCl. Chemical reaction occurred between the acid and the carbonate already presents in the protective wall of algae, leading to the formation of CO2 and a dramatic decrease in algae weight. The weight loss is more affected by the concentration and the nature of the acid used rather than by the temperature of the chemical treatment: ~ 20 % with 0.1 M HCl, ~ 40 % with 0.5 M HCl and ~ 70 % with 1 M HCl. Similar decreases in the amount of biomass were found after HCl wash and formaldehyde cross-linking by Lodeiro et al. [38]. The authors explained the decrease by the replacement of Ca2+, and Mg2+ bound to active sites in the raw biomass by H+. The FTIR spectrum of HCl modified algae is similar to that of raw algae with few differences: decrease in the strong peak at 1430 cm-1 and in the medium peak at 866 cm-1 (Fig. 1). These two peaks are characteristic bands of carbonate. The decrease in the peak’s heights

80

RG

I%

RESULTS AND DISCUSSION

60

1HCl 40

40 20 0 10

15

20

25 2 θ

30

35

40

Fig. 2. XR diffraction of raw algae (RG) and of modified algae with 1 M HCl treated at 40oC.

and in the weight of algae remained after chemical treatment is proportional to HCl concentration used. So the chemical modification with HCl decreases the amount of carbonate in the raw biomass and let the algae more pure. Thermal analysis (TG-DSC) on Carolina algae showed a sharp decrease at 786oC (endothermic) attributed to the conversion of CaCO3 to CaO (s) and CO2 (g) [28]. The crystalline state of raw algae is good as shown by its XR diffraction spectrum. The XR diffraction spectra of algae before and after treatment with HCl are completely different (Fig. 2). Three peaks at 2q:14.64, 17.1, and 22.92 became more intense after chemical treatment with HCl, but the intense peak in RG and in CaCO3 (2q: 29.54, 100 %) decreased. We attributed the

63


120

120 1AC 62 RG

100

100 1Cit 62 RG Citric Acid

80

T%

I%

80

60

60

40

40

20

20

0

0 400

900

1400

1900

2400

-1

2900

Wavenumber (cm )

3400

10

3900

15

20

2θ

25

30

35

Fig. 3. FTIR spectra of raw algae and modified algae with 1 M citric acid treated at 62oC.

Fig. 4. XR diffraction spectra of raw algae and modified algae with 1 M citric acid treated at 62oC.

decrease of this peak in HCl 40 to decrease in CaCO3 amount. According to XR diffraction, the chemical modification with HCl affects strongly the chemical composition of algae. After chemical modification with 1 M citric acid, the broad band of OH at 3365 cm-1 is divided into several

bands (OH of COOH and OH of alcohol). The intensity of the band at 2914 cm-1 which corresponds to C-H increases dramatically. New bands appeared after reaction with citric acid at 1615 and 1336 cm-1, which can be assigned to C=O stretching, indicating the introduction of a new COOH sites (Fig. 3) [ 19]. The same behavior

Table 1. Comparison of the uptake of pollutants by modified and unmodified algae. Biomass

Sargassum muticum

Pollutant

MB

Q max (mg g-1) Raw Modified

HNO3

-----

279 ± 4

CHCl3/MeOH Me2CO reflux

---------

841 ± 81 860±100

Me2CO MeOH CH3OH/H+ CaCl2 HCl

----------------------

402 ± 8 416 ± 10 358 ± 8 237 279

Sargassum Muticum

MB

Corynebacterium Glutamicum

BB3

Citric acid

25±0.9 50.4±0.7

MB

H2CO

55

64

MG

HCl Citric acid Citric acid

143 143 -----

320 20 256.4

Pinus Merkusii (wood)

Pb(II)

Citric acid

7.71

82.64

2.56

23.70

Cladophora Glomerata

Pb(II) Cu (II)

26.5 15.5

36.6 22.5

Carolina

Chaetophora Elegans MB Rice Straw

64

Treatment

Cu(II) HCl

Sources

Pilar et al. [17]

Vincente et al. [24] Y,-S,Yun et al. [19] Hammud et al. [28] This work Gong et al. [18] Low et al. [21] Yalçın et al. [23]


is observed with the other treated samples (0.1 M and 0.5 M), but it is more pronounced with 1 M of citric acid or 1 M of HCl. The XR diffraction spectra of algae before and after treatment with citric acid are also very different (Fig. 4). For example, the sample 1Cit 62 showed the appearance of new intense peaks (2q: 16.48, 21.16, 31.36) and the disappearance of that at 29.54 (100 % in the raw algae). We thought that an important chemical reaction occurred between the raw algae and the acid added. The chemical modification occurred with HCl is different from that occurred with citric acid. The weight loss of samples treated with 0.1 M, 0.5 M citric acid is the 8 %, and 2 %. It’s much lower than that obtained with HCl due to introduction of citric acid to wall cells. Isotherm modeling analysis Several isotherm models are used in the literature to find the relationship between qe and Ce .The experimental data related to the adsorption of MB molecules onto the algal biomass at different temperatures were fitted using Langmuir [39], Freundlich [40], Temkin [41], and combined Langmuir-Freundlich equations [42]. In this study, the theoretically predicted isotherm data were determined using a non-linear regression analysis via the Origin 7 software (in order to avoid the error induced using the lineriazed forms). (i) The Langmuir model: The Langmuir isotherm suggests that MB adsorption is limited with monolayer coverage and there is no significant interaction among adsorbed species.

qe =

qmax × b × Ce 1 + b × Ce

with

b=

K ads K des

(4)

with qmax (mg g-1) is the maximum sorbate uptake under the given conditions and b (dm3 mg-1) is the adsorption equilibrium constant, related to the affinity between the adsorbent and sorbate. (ii) The Freundlich model : The Freundlich relationship is an exponential one expressed as follows: n (5)

qe= k × Ce

where k is the Freundlich constant. The Freundlich isotherm exponent n is considered as a heterogeneity factor. (iii) Temkin isotherm: The Temkin isotherm deals with the heat of adsorption and the involved sorbent/

sorbate interactions.

qe =

RT (ln KT + ln Ce ) = A + B × ln Ce b

(6)

where B is a factor related to the heat of adsorption and KT is Temkin equilibrium constant (dm3 mg-1). (iv) Combined Langmiur-Freundlich : Basically, it is an equation combining the previously mentioned Langmuir and Freundlich isotherms

qe =

qmax × b × Cen 1 + b × Cen

(7)

Modified algae with HCl The experimental isotherm adsorption data of raw algae fitted better Langmiur-Freundlich isotherm than Langmiur model (See Table 2).The untreated raw algae (collected two years ago) and the treated with distilled water at 40, 50 and 62oC showed an average of qmax equal to 143 ± 5 mg g-1. The raw biomass (organic compound) looses its adsorption property with storage time. In a previous work, the maximum uptake of MB onto fresh collected algae was much higher (300 mg g-1) [37]. The decrease in qmax is related to deterioration of the external surface. The HCl modified algae showed an increase in the qmax. (Fig. 5 and 6). The increase in the maximum uptake is more related to HCl concentration than to the reaction temperature (Fig. 6, Table 2). According to R2 values and qmax, Langmuir- Freundlich model is more realistic than Langmuir model (Table 2). The maximum uptake passed from 143 mg g-1 (for RG) to 320 mg g-1 for 1 HCl 25. The difference in the uptake is manifested for (4) high initial MB concentration ([MB]o > 150 mg dm-3). The remained concentration of MB in contact with 500 mg dm-3 of MB is 15.5 mg dm-3 for 1HCl 40 against 144.4 mg dm-3 for RG. Modified algae with citric acid Concerning, the isotherm adsorption of modified algae with citric acid, Langmiur - Freundlich model remained the best model in line with the experimental data, but all the samples showed a decrease in the uptake (Table 3, Fig. 5). The lowest qmax is obtained with 1 M of citric acid (1Cit 62). The chemical modification with citric acid has a negative effect on the MB uptake. The concentration of citric acid is the important factor which

65


350

q th 1HCl 40

q 1 HCl 40

q (RG)

q 1Cit 25

1 Cit 62

300

350

250 -1

q (mg g )

300

q (mg g-1)

250

200 150

200

100

150

50

100

0

50

0.1 M HCl 0.5 M HCl 1 M HCl

0 0

50

100

150 200 [MB] (mg L-1)

250

24 oC

40 oC

50 oC

60 oC

190 240 320

180 250 322

210 253 315

202 227 303

300

T (oC)

Fig. 5. Isotherm adsorptions of MB (at 25 oC) for modified algae with 1M HCl and 1M citric acid.

Fig. 6. Effect of HCl concentration and temperature, used in the chemical modification of algae on the maximum uptake according to non linear Langmuir- Freundlich model.

governs the decrease in the uptake. The qmax of 0.1Cit 25 (134 mg g-1) is near to qmax of RG (143 mg g-1) but that of 1Cit 25 is much lower (47 mg g-1) (Table 3). The decrease in qmax may be due to increase in the cross-linking degree which would hamper the adsorption of MB or to denaturation of some active sites.

Kinetic modeling analysis In the present study, non-linear regression method has been used to predict the best sorption kinetic model and also to obtain reliable kinetic parameters. Lagergren first order kinetic expression was used mostly in the literature to show adsorption capacity on

Table 2. Isotherm modeling parameters at 25 oC related to the biosorption of MB onto modified Chaetophora elegans with 1 M HCl treated at several temperatures (non-linear approach). Models R2 Langmuir

Freundlich

Temkin

Lang- Freund.

66

24 oC

40 oC

50 oC

60 oC

0.967

0.99

0.946

0.99

623

420

Qmax (mg g-1) 57.67 386.40 b

0.64

0.11

0.044

0.074

R2

0.98

0.96

0.975

0.96

K

46

52.9

21.86

26.8

n

0.77

0.977

0.96

0.81

R2

0.95

0.96

0.98

0.988

A

45.9

32.3

-25

-13.22

B

80

73

91.42

84.9

R2

0.992

0.994

0.96

0.995

Qmax

320

322

315

303

B

0.013

0.11

0.047

0.068

n

1.35

1.2

1.7

1.35


different adsorbents [43]. Pseudo-first first order equations are: Non Linear form:

qt = qe (1 − e − K1t )

(8)

The pseudo-second order model is based on the assumption that the adsorption follows second order chemisorption [44]. The pseudo-second order model can be expressed as: (9) 2

q × K2 × t qt = e 1 + K 2 × qe × t

were t is the contact time (min), qe (mg g-1) and qt (mg g-1) are the amount of dye adsorbed at equilibrium and at any time. K1 and K2 are the first and the second rate adsorption constant respectively. For low initial MB concentrations (62.5 mg dm-3 - 150 mg dm-3), the uptake of modified algae with HCl and the raw algae as a function of time is quit similar (Table 4). The adsorption rate of both kinds of algae is very fast in the first five minutes, then decreases to become negligible after 30 minutes (Fig. 7). The dynamic sorption behavior of MB onto Chaetophora elagans’ surface under several initial dye concentrations was monitored and modeled. The related kinetic parameters and error derivation values are presented in Table 4. The first and the second adsorption models can be used to interpret the results, but according

to R2 values, the pseudo-second order model fit better the kinetic data. Effect of Temperature (8) activation parameters associated with the adThe sorption of 62.5 mg dm-3 MB onto RG and 1HCl40 are calculated as follow: plot of ln K2 vs. 1/T gives the value of the activation energy (Ea), according to Arrhenius equation:

with R : 8.3 J K −1 mol −1(10)

ln K 2 = − Ea / RT + cte

(9)

The ΔH≠ and ΔS≠ value can be calculated from Eyring plot:

ln(

K2 k ∆S ≠ ∆H ≠ ) = (ln B + )− T h R R ×T

(11)

where kB = Boltzmann’s constant (1.381x10-23 J·K-1), h = Plank’s constant (6.626x10-34 J·s) and ln (kB/h) = 23.76 The free activation enthalpy ΔG≠ is equal to:

∆G ≠ = ∆H ≠ − T × ∆S ≠

(12)

−5.03

The linear equation of ln (K2) vs. 103/T is + 15.05 T for modified algae with 1 M HCl (Fig. 8). The activation energy and the others kinetics parameters in the range of temperature studied (23 oC - 32 oC) are listed in Table 5.

Table 3. Isotherm modeling parameters at 24oC related to the biosorption of MB onto modified Chaetophora elegans algae with citric acid treated at 25oC and 60oC.

Sample

Langmuir

Langmuir - Freundilch

R2

qmax

b

R2

RG

0.93

160

0.21

0.96

143

0.076

1.98

0.1Cit 25

0.957

166.7

0.11

0.99

134

0.06

1.61

0.1Cit 60

0.98

142

0.15

0.99

127.6

0.15

1.3

0.5Cit 25

0.96

111

0.03

0.996

87.4

0.006

1.07

0.5Cit 60

0.986

64.7

0.08

0.994 60.47

0.044

1.3

1Cit 25

0.98

42

0.041

0.985

47.4

0.064

0.78

1Cit 60

0.95

19.4

0.073

0.983

19.85

0.077

1.06

qmax

b

n

67


Table 4. Pseudo first and pseudo second order adsorption kinetic parameters at 24 oC and error estimation at different initial dye concentrations for 1HCl40 and raw algae (given in brackets). Pseudo-first order (Non linear) [MB]o (mg dm-3)

62.5

100

150

qe calc.

K1

(mg g-1)

(min−1)

30.02

Pseudo-second order (Non linear) qe

K2

(mg g-1)

(g mg-1.min-1)

0.47

30.83

(0.98)

(1.79)

1.79

0.9977

(47)

(1.4)

72.73 (72.29)

R2

χ2

R2

χ2

1.739

0.996

0.148

1

0.015

(28.55)

(1.52)

(29.65)

(0.111)

0.998

(0.2)

48.36

0.77

49.1

0.149

1

0.06

(0.983)

(3.93)

(47.97)

(0.077)

(0.995)

(1.11)

2.185

0.996

2.1

73.73

0.1

0.999

0.34

(0.79)

(0.993)

(3)

(73.76)

(0.024)

(0.999)

(0.31)

Table 5. The activation kinetic parameters for modified algae with 1M HCl (1HCl40) and raw algae (given in brackets).

Ea (kJ.mol-1)

ΔH≠ (kJ.mol-1)

ΔS≠ (kJ.mol-1.K-1)

∆G#298 (kJ.mol-1)

41.8 (48.6)

41.9 (46.1)

-0.12 (-0.11)

77.7 (78.3)

Chemical modification of Chaetophora Elegans algae with HCl and citric acid has opposite action with respect to the MB uptake. The modified algae with HCl showed an increase in the maximum uptake, proportional to HCl concentration used due to elimination of carbonate. Modified algae with 1 M HCl gave the best uptke (qmax increased from 143 mg g-1 to 320 mg g-1). The modified algae with citric acid showed an important decrease in the uptake due to increase in the cross linking degree. The decrease in qmax is inversely proportional to citric acid concentration used (0.1 M - 1 M). Modified algae with 1 M citric acid gave the worst uptake (qmax decreased from 143 mg g-1 to 20 mg g-1). Acid concentration used in the chemical modification is the major parameter affecting the maximum uptake. The temperature of the chemical modification has a small effect on the uptake

68

80 70 60 50 -1

CONCLUSIONS

(25oC-60oC). Langmuir-Freundlich isotherm model fitted better the isotherm adsorption data for all samples studied. Pseudo-first and pseudo-second order kinetic models were applied to the adsorption dynamic data. Pseudo second order model was well in line with the experimental data. The adsorption rate constant (K2) is higher for modified algae with HCl than that of raw al-

q(mg g )

The chemical modification by HCl did not affect strongly the activation thermodynamic parameters.

40 30 150 mg L-1 100 mg L-1 62.5 mg L-1

20 10 0 0

20

40 Time(s) 60

80

100

Fig. 7. Variation of the MB uptake as a function of time for modified algae with HCl (1HCl40).


-1 3.24 -1.2 -1.4

3.26

3.28

3.30

3.32

3.34

3.36

3.38

y = -5.03x + 15.05 2 R = 0.989 (1HCl 40) ln K2 (1HCl40) Ln K (RG)

Lnk2

-1.6 -1.8 -2 -2.2 -2.4

y = -5.85x + 17.47 R2 = 0.993 (RG)

3

10 /T

Fig. 8. Plot of lnk2 versus 1/T for the raw and modified algae with HCl.

gae. The activation thermodynamic parameters Ea, ΔH#, ΔS# and ΔG# were calculated. The equilibtium uptake is independent of isotherm adsorption temperature in the range studied (25oC – 35oC). Acknowledgements The authors wish to thank the “Ecole Doctorale de Sciences et Technologie” in Lebanese University for financial support. REFERENCES 1. K. C. Chen, J. Y. Wu, C. C. Huang, Y. M. Liang, and S. C. J. Hwang, Decolorization of azo dye using PVA-immobilized microorganisms, J. Biotechnol., 101, 2003, 241-252. 2. E. S Abechi, C. E Gimba, A. Uzairu, J. A. Kagbu, Kinetics of adsorption of methylene blue onto activated carbon prepared from palm kernel shell, Archives of Applied Sci. Res., 3, 1, 2011, 154-164. 3. Y. Guo, S. Yang,W. Fu, J. Qi, R. Li, Z. Wang, H. Xu, Adsorption of malachite green on micro- and mesoporous rice husk-based active carbon, Dyes Pigments, 56, 2003, 219-229. 4. P. K. Malik, Use of activated carbons prepared from sawdust and rice-husk for adsorption of acid dyes: a case study of acid yellow 36, Dyes Pigments, 56, 2003, 239-249. 5. M. Dutta, S. Mishra, M. Kaushik, J. K. Basu, Application of Various Activated Carbons in the Adsorptive Removal of Methylene Blue from Aqueous Solution, Research J. Env. Sci., 5, 2011, 741-751.

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