thermodynamic study of the adsorption of indystrial …

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Abdullah et al. World Journal of Pharmacy and Pharmaceutical Sciences

THERMODYNAMIC STUDY OF THE ADSORPTION OF INDYSTRIAL

DYES BY WESTERN DESERT BENTONITE CLAY

Abdullah Kh. Al-Niemi* and Safwan AS. Al-dbouni

Chem. Dept., College of Educ. for Pure Sci., Univ. Mosul, IRAQ.

ABSTRACT

This research involved studying the adsorption of two dyes (Brilliant

green and Brilliant Yellow) using Western Desert bentonite clay for

the purpose of removing them from their aqueous solutions. The

optimal conditions for the process of adsorption of these two dyes such

as the effect of the amount of adsorbent, initial concentration and

temperature were identified. The results of the study showed that the

forces controlling the adsorption process were of a physical nature, and

that the adsorption process occurs by attaching the dye to the surface of

the adsorption spontaneously to form a less random system. Several

models of isothermic equations such as (Lankmeyer, Frindlach) were

applied on the practical results of adsorption, this study showed their application agreement

with mentioned isotherms, by obtaining a linear relationship and a high correlation coefficient

(R) except the) Brilliant Yellow) dye its practical resells did not agreement to the Lankmeyer

isotherm because its correlation coefficient (R) values are low.

KEYWORDS: Thermodermic, adsorption, bentonite clay, dyes, isotherm.

INTRODUCTION

One of the main environmental problems is the presence of dyes in water sources. This

contaminant must be removed from the water by appropriate methods. Although most of these

methods are effective in treating water contaminated with dye pollutants, they are very

expensive and not commercially feasible.[1]

Industrial dyes are widely used in the textile

industry, as their chemical formulas are characterized by containing aromatic and Aryl rings

and effective groups such as (Azo, SO2, and hydroxyl groups) and other groups. Because of

the inefficiency of the dyeing process, some of the dyes used in the liquid waste of textile units

WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES

SJIF Impact Factor 7.632

Volume 10, Issue 7, 1-21 Research Article ISSN 2278 – 4357

*Corresponding Author

Dr. Abdullah Kh.

Al-Niemi

Chem. Dept., College of

Educ. for Pure Sci., Univ.

Mosul, IRAQ.

Article Received on

24 April 2021,

Revised on 14 May 2021,

Accepted on 04 June 2021

DOI: 10.20959/wjpps20217-19160


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are thrown away. The direct discharge of these liquid wastes leads to the formation of toxic

and carcinogenic substances in the reception medium, and the difficulty of their decomposition

due to their complex composition and solubility in water, so it is necessary to find effective

methods for treating wastewater capable of removing this pollution.[2]

Among the most

important methods used in treatment processes is the adsorption process, which is the most

effective and economical way to remove pollutants in low concentrations. The most commonly

used adsorbent is activated carbon. The reason is due to its high surface area due to its porosity,

as it contains branched inner channels of different diameters. However, its price is relatively

high compared to some adsorbent materials available in nature, such as clay, and it also needs

to be activated with chemicals, so the clay is used as a good alternative to activated carbon.[3]

Different types of clays are available due to their high adsorption property.[4]

Bentonite clay is

mainly composed of montorlonite and other clay minerals such as kaolin and palikorskite, and

bentonite clay has a surface with high charges, has the ability to cation exchange, and has a

high surface area and porosity.[5]

That is why bentonite clay was selected in this study for use

in adsorption of the two dyes (Brilliant green, Brilliant Yellow).

MATERIALS AND METHODS

1- Chemicals

The two dyes (Brilliant green and Brilliant Yellow) used in this research were supplied from

Fluka company.

2- Preparing the solutions

In a 1 liter volume bottle, a solution of Brilliant green and Brilliant Yellow dyes was prepared

at a concentration of (1 × 10-3

) molar using distilled water as a solvent, and from it different

concentrations were prepared ranging between (1 x 10-4

- 1 x 10-6

) M, where (100 ml) of each

concentration was used in the adsorption process in (250 ml) conical flasks (using the dilution

law). For the purpose of carrying out a process that removed these two dyes from their

aqueous solutions by the adsorption process, a one batch method was used), where the conical

flasks were placed in a bath water containing an electric vibrator at a speed (100 cycle /

minute) and for a period of an hour and a half at the laboratory temperature (25 C˚). The

temperature was controlled by using a mercury thermometer for ensuring its stability. The

required water bath temperature for a period of not less than (10 minutes). At each

temperature used, the contents of the flasks were filtered after the adsorption process was

completed using filter paper and the analytical method was used for estimating the residual


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dye concentrations through the spectrophotometry apparatus available in our laboratories.

3- Analytical method

Since the materials chosen for this study are colored, so the UV-VIS Spectrophotometer (T92

+) was chosen. As a first step, the value of the maximum absorption wavelength (λmax) was

determined for each dye, which then tracks the change of the amount of adsorbed material

over time and according to the nature of eaeh study. To accomplish this work, (Beer`s

lambert Law) was used to create a calibration curve at the value of (λmax) for each dye by

drawing the relationship between absorption and concentration and according to the equation:

A = ε CL ---------------------------------- (1)

As (A) represents absorption, (ε) is the molar absorption coefficient(Liter.mol-1.cm-1), (C) is

the molar dye concentration, and (L) is the width of the cell (L = 1cm). The term adsorption

capacity and adsorption efficiency or (adsorption percentage) were used to express the

amount of adsorbed material by estimating the amount of residual material from the dye in

the adsorption solution. A calibration curve for each dye was adopted to calculate these

concentrations. The adsorption capacity (qe) of the dye adsorbent can be expressed by the

following equation:

Since (Ce) is (residual concentration) and (Ci) is (initial concentration) of the dye and the

value of (M) represents the weight of the adsorbent material in unit (gm) and the value of (V)

represents the volume of the dye solution used when studying the adsorption unit (Liter), and

the percentage of the removed dye can also be calculated (Adsorbed) or what is called

adsorption efficiency using the following equation:

4- Choose an adsorbent

In this research, clay (Western Sahara bentonite) was used as a good adsorbent as it is

naturally available and inexpensive. Where the adsorbent was in the form of a fine powder

and prepared by the Geological Survey in Baghdad.

5- Instruments

a- Ultraviolet spectral measurement: A Spectrophotometer type (T92 +) was used for this.


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The product is from the American company (PG INTERUMENTS), using the purpose

solvent as a (Blank) solution, using quartz and glass cells with a thickness of (1 cm) , and

measurements were made in the range (300 - 800 nm).

b- Water bath with aprogramme vibrator: A programmed vibrator (SW23 Julabo) was

used which contains inside a water bath for the purpose of controlling and regulating the

temperature when studying the adsorption.

c- pH meter: A device of the type (pH 720 WTW 82362 Weilheim) was used in the control

and measurements of the acidic function at the laboratory temperature (25 C˚) and after

calibrating the device with two solutions at an acidity function (4) then (9).

6- Calculation of thermodynamic functions

The values of the adsorption equilibrium constant (K) were calculated at different

temperatures at equilibrium from the ratio between the concentration of the adsorbent and the

residual concentration of the dye solution. The value of (K) and the values of the

ther were calculated at equilibrium state using the

equations following:

Then the previous calculations were re-calculated in the calculation of the thermodynamic

values of the mentioned values based on the values of the Fernelich (Kf) and Langumire (KL)

constants that were found from the application of these isotherms to the practical results for

adsorption, as will be explained later.

7- Adsorption isotherms

The Ferndlich and Lancmayer isotherms were applied on the practical results obtained from

the study of the adsorption system under study, as the values of the Ferendelch constants (Kf,

n) were calculated from the relationship between the value of (log qe and log Ce) according to

the following equation


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Also, Lancmayer constant (b) and the theoretical maximum capacity of adsorption (Qmax)

were calculated from the relationship between (Ce / qe) versus (Ce) and according to the

following equation:

The program (Excel) was used to complete the necessary graphs to calculate the values

mentioned in this paragraph.

The structural formula of the two dyes (Brilliant green and Brilliant Yellow) and their

physical properties Table (1)

dye name Dye Structure M.Wt

g / mol

λ max

(nm)

ε max

L.mol-1

.cm-1

Color M.P C˚

Brilliant green (B.g)

[4-[[4-

(diethylamino)phenyl]-

phenylmethylidene]cycl

ohexa- 2,5-dien-1-

ylidene]-

diethylazanium;hydroge

n sulfate

482.64 624 67315 green

crystalline

210

Brilliant Yellow ( B.y )

sodium 4,4'-bis(p-

hydroxyphenylazo)-2,2'-

vinylenedibenzenesulph

onate

603.6 490 34727 orange 250

RESULTS AND DISCUSSION

Analytical method

The best option for completing this study is to use the Spector photometric method as dyes are

colorants chemical, and as an initial step of this study, a calibration curve for each dye is made

at its (λ max) value by preparing solutions with different concentrations in ranges agreement

with the dye sensitivity and its applicability to the Beer-LamBurt equation , The linear

relationship obtained from the application of the Beer-Lambert equation referred to by the

values of the good correlation coefficients (R2) indicates the possibility of applying this

equation to the ranges of concentrations adopted in the formation of the standard curves of the

dyes under study. Figure (2.1) represents the application of the equation. Beer-Lambert to

perform the calibration curve for the dyes under study.


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Figure 1: Calibration curve for (B.g) dye. Figure 2: Calibration curve for (B.y) dye.

Effect of adsorbent amount

The purpose of conducting this study is to find an appropriate amount of adsorbent material

that achieves the equilibrium state of the system with an acceptable percentage of it without

the complete removal of color so that we can complete the subsequent study. The concentration

of (4x10-5

) Molar was used for the dyes under study and different quantities of the adsorbent

material represented by the Western Sahara bentonite clay with doses ranging between (0.1-

0.005) grams and at a temperature of (298C˚) absolute degrees with the stabilization of all

other conditions. The results obtained were listed in Table (2).

Table 2: The effect of the amount of clay (Western Sahara bentonite) on the adsorption

capacity, percentage, at temperature (25 C˚) and Concentration (4x10-5 M).

The name of

the dye

Ci

(mg/l)

Ce (mg/l) Dose (g) qe (mg/g) The percentage of

% adsorption

B.g 19.30 0.222 0.1 19.07 98.84

0.250 0.075 25.4 98.70

0.322 0.050 37.95 98.33

0.415 0.025 75.54 97.84

0.846 0.010 184.54 95.61

3.111 0.005 323.88 83.88

B.y 24.14 3.146 0.1 20.994 86.96

2.815 0.075 28.433 88.33

2.398 0.050 43.484 90.06

2.659 0.025 85.924 88.98

2.798 0.010 213.42 88.40

2.972 0.005 423.36 87.68

From the observation of Table No. (2), we find that the adsorption capacity and at the

concentration of (4x10-5

M) molar of the dyes their value decreases, while the percentage of

adsorption increases with the increase in the dose of the adsorbent material represented by the

Western Sahara bentonite. This discrepancy can be explained through two perspectives:


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First: By increasing the amount of adsorbent, the number of sites eligible for adsorption will

increase, and this is accompanied by an increase in the efficiency of adsorption in removing

the dye from the aqueous solution. This can be attributed to the increase in the amount of

adsorbent material causing the introduction of new and additional sites that are eligible for

binding with the dye, thereby increasing the efficiency of adsorption. Moreover, this addition

to the amount of adsorbent makes the ratio of the number of milligrams of adsorbent (for a

specific concentration of dye solution) to the number of grams of adsorbent (adsorption

capacity) less valuable. These results obtained are consistent with other results seen in other

similar studies in the literature.[6][7][8]

The second: which represents another point of view in which the researchers show that the

cause of this change could be through the interactions of implicit molecules between the

adsorbent molecules. Because of these interactions, an increase in the amount of adsorbent

material leads to its clumping and as a result, the total surface area of the adsorbent material

will decrease, which leads to an increase in the length of the adsorbent molecule pathways

through it.[9]

A quantity of adsorbent material estimated at (0.005 g) was chosen for the completion of the

subsequent studies, because it is a moderate amount that achieves an acceptable percentage of

removal of dyes while keeping the color and achieving the equilibrium state of the adsorption

system required to fulfill the requirements of the research for conducting thermodynamic

calculations, and applying adsorption isotherms.

The effect of the initial concertation

The effect of the initial concentration of dyes on the adsorption process was studied in a range

between (1x10-6

M, 1x10-4

M) and at a temperature of (25 C˚) after fixing each of the other

variables affecting the adsorption efficiency. A constant speed (100 cycle / minute), and by

using a constant amount (0.005gm) of the adsorbent (Western Sahara bentonite clay), then

the solutions were filtered, and the residual dye concentration in a solution after the

adsorption process was determined spectrophotometric ally and at (λ max) values for each

dye. The results obtained were listed in Table (3).


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Table 3: The effect of the initial concentration on the percentage of adsorption using)

0.005 g) of Western Sahara bentonite at a temperature of (25 ° C).

The name of

the dye

Ci(M) Ce(mg/l) qe(mg/g) The percentage

of adsorption%

B.g 1×10-4

34.66 624 64.64

8×10-5

12.61 520 67.34

6×10-5

6.16 455.8 78.72

4×10-5

3.11 323.88 83.88

2×10-5

1.64 160.2 83.00

1×10-5

0.82 80 82.98

8×10-6

0.71 63 81.60

6×10-6

0.56 46.6 80.62

4×10-6

0.38 31 80.31

2×10-6

0.77 15.4 79.79

1×10-6

0.1 7.6 79.16

B.y 1×10-4

8.265 1042 86.30

8×10-5

5.850 848.6 87.98

6×10-5

4.460 631.4 87.18

4×10-5

2.972 423.36 87.68

2×10-5

1.750 206.4 85.50

1×10-5

0.921 102.1 84.72

8×10-6

0.695 82.5 85.58

6×10-6

0.608 60.2 83.20

4×10-6

0.521 37.7 78.38

2×10-6

0.347 17.06 71.08

1×10-6

0.260 6.87 56.92

The range of concentrations used in this study ranged from (1X10-4

M to 1x10-6

M). The results

obtained indicated that the increase in the concentration of the dyes under study was

accompanied by an increase in the adsorption efficiency (% adsorption) until reaching the

concentration (4X10-5

M), where a decrease the adsorption efficiency after this concentration is

accompanied by a decrease in the adsorption capacity. The results showed that the best

concentration to complete the subsequent study is (4X10-5

M), and we note through the obtained

results that the percentage of adsorption of the two dyes decreases with increasing

concentration and in the range (1x10-4

M to 4x10-5

M) and by using a fixed amount of adsorbent.

The previous statement can be explained to the competition between dye molecules for

adsorption on a fixed number of active sites on the surface of a certain amount of adsorbent

resulting from an increase in concentration, which leads as a result to an increase in the

repulsion between the dye molecules among themselves and the active sites on the surface as

a result of increasing their energy This behavior is consistent with what was obtained in

previous studies.[10][11]


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Effect of the acidic function of an adsorption medium

The test of the effect of the acidic function of the adsorption medium of the dyes was carried

out at a concentration of (4X10-5

M) and a temperature (25 C˚) and a quantity of (0.005) g of

bentonite clay Western Sahara. The obtained results were included in Table (4) and Figure (3)

illustrating that.

Table 4: Shows the effect of the acidic function on the percentage of adsorption of the

dyes under study.

The name of the dye pH Ce(mg/l) qe(mg/g) The percentage of adsorption %

B.g 4 2.80 330 85.49

*6.5 3.111 323.88 83.88

9 3.83 309.4 80.15

B.y 4 2.71 428 88.75

*6.8 3.02 422.4 87.48

9 3.615 410.58 85.02

(*) Represents the natural acidic function of dyes.

Figure 3: Shows the relationship between the percentage of adsorption and the acidity

function of the dyes.

When observing Table (4) and Fig. (3), we find that the adsorption efficiency and capacity are

highest when the acidic function (nature pH) and (pH 4 ) of the dyes in their aqueous solution

and this is due to the nature of the overlap between the dyes under study and the nature of the

surface of the clay used in the process. Adsorption this is positive in terms of the economic

cost of the adsorption process.

Temperature effect

The effect of temperature on the adsorption of the dyes in question was studied at an initial

concentration (4x10-5

M) and a fixed amount of clay adsorbent (Western Sahara bentonite)


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with an amount of (0.005) g and a fixed volume of the dye solution (100 ml) and at temperatures

between (50-15 C˚) as these solutions were shaken for a period of (60) minutes at a constant

speed (100 cycle / minute). The results were included in tables (5):

Table 5: The effect of temperature on the percentage of adsorption of the dye (B.g) and

the weight of (0.005g) of Western Sahara bentonite and at the natural (pH).

Ci (M) Tem(K Ce (mg) qe (mg/g) The percentage of

adsorption %

8× 10-5

288 11.40 544.2 70.47

293 11.61 540 69.93

298 12.61 520 67.34

303 13.12 509.8 66.01

308 14.12 489.8 63.42

313 14.62 479.8 62.13

323 15.41 464 60.08

6× 10-5

288 5.44 470.2 81.20

293 5.55 468 80.82

298 6.15 456 78.75

303 6.45 450 77.72

308 9.96 379.8 65.59

313 10.39 371.2 64.11

323 10.96 359.8 62.14

288 2.11 343.8 89.06

4× 10-5

293 2.40 338 87.56

298 2.68 332.4 86.11

303 2.81 329.8 85.44

308 3.01 325.8 84.40

313 3.22 321.6 83.31

323 3.80 310 80.31

2× 10-5

288 1.32 166.6 86.32

293 1.50 163 84.45

298 1.54 162.2 84.04

303 1.65 160 82.90

308 1.85 156 80.82

313 1.95 154 79.79

323 2.14 150.2 77.82

1× 10-5

288 0.72 82 85.06

293 0.77 81 84.02

298 0.79 80.6 83.60

303 0.82 80 82.98

308 0.92 78 80.91

313 1.02 76 78.83

323 1.12 74 76.76


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Table 6: The effect of temperature on the percentage of dye (B.y) and weight of 0.005g

of Western Sahara bentonite and the natural (pH).

Ci (mg/L) Tem(K ) Ce (mg) qe (mg/g) The percentage of

% adsorption

8× 10-5

288 4.27 880.2 91.15

293 4.48 876 90.72

298 5.28 860 89.06

303 5.48 855.8 88.62

308 5.99 845.8 87.59

313 6.86 828.4 85.79

323 7.30 819.6 84.87

6× 10-5

288 3.71 650 89.75

293 4.20 640.2 88.40

298 4.62 631.8 87.24

303 5.02 623.8 86.13

308 5.71 610 84.23

313 6.01 604 83.40

323 6.22 599.8 82.82

4× 10-5

288 2.15 439.8 91.09

293 2.34 436 90.30

298 2.64 430 89.06

303 2.74 428 88.64

308 3.04 422 87.40

313 3.14 420 86.99

323 3.84 406 84.09

288 1.47 212 87.82

293 1.52 210 87.40

2× 10-5

298 1.66 208.2 86.24

303 1.65 208.4 86.32

308 1.77 206 85.33

313 1.87 204 84.50

323 2.08 199.8 82.76

1× 10-5

288 0.73 106 87.89

293 0.88 103 85.40

298 0.93 102 84.57

303 0.97 101.2 83.91

308 1.04 99.8 82.75

313 1.14 97.8 81.09

323 1.19 96.8 80.26

When looking at the two previous tables carefully, we notice the following

1- Within the single dye, by using a fixed concentration, we find that increasing the

temperature in the aforementioned range reduces the adsorption capacity (qe) and its

efficiency (percentage) and this can be attributed to the fact that the controlling force on

the adsorption process is a weak force and that increasing the temperature in the


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mentioned range serves to break down the forces That binds the dye to the adsorbent

surface, which stimulates the return of the dye molecules to the solution, thus the

adsorption efficiency decreases and the number of molecules associated with the

adsorption surface decreases, so the adsorption capacity decreases relative to the fixed

mass of the adsorbent used (g). This pattern of change can give an indication that the

bonding forces between the dye molecules and the surface of the clay used are of the type

of weak forces such as Vandervals forces, and that the adsorption process in the studied

system is of a physical nature.

2- At a constant concentration and temperature, the adsorption efficiency and capacity of the

different dyes under study vary depending on many variables related to the type of active

groups associated with the aromatic rings in the molecule in terms of electron propulsion,

as well as the nature of the static body that the dye molecules take and the movement of

electrons in them by the resonance process, which may go along The molecule or its part,

depending on the equatorially of the molecule and the nature of the sequence of double

bonds in it, as well as the spatial disability in it.[12][13][14]

.

The thermodynamic study

The thermodynamic study of the adsorption system is necessary to know the nature of the

adsorption system under study and to know the nature of the forces that control the

adsorption process as well as to know the type of molecular interferences affecting the

process of transferring the dye molecules from the solution to the surface of the slurry that

can occur during the adsorption process, which has a major role in Determine its efficiency.

The values of thermodynamic functions were calculated through equations[4,5,6,7,8]

The

calculated results (∆H, ∆G, ∆S, ∆S , K) have been included in Tables (7,8) and Fig. (4,5)

shows the linear relationships resulting from drawing LnK versus 1/T when applying

VantHoff equation. Used to calculate the values of change in enthalpies.

Figure 4: The relationship between lnK versus 1 / T to calculate the desorption

involution value of the) B.g dye).


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Figure 5: The relationship between lnK versus 1 / T to calculate the adsorption

involution value of the) B.y dye).

Table 7: Values of equilibrium constants and thermodynamic functions for the

adsorption of the compound (B.g) and under ideal adsorption conditions.

Ci (M) emp( ) K ∆H ( Kj.mol-1

) ∆ ( Kj.mol-1

) ∆ (j.mol-1

.K-1

) ∆ (j.mol-1

.K-1

)

8× 10-5

288 2.38 -10.982 -2.05 -31.01 -38.13

293 2.32 -2.04 -30.51 -37.48

298 2.06 -1.78 -30.87 -36.85

303 1.94 -1.66 -30.76 -36.24

308 1.73 -1.40 -31.11 -35.65

313 1.64 -1.27 -31.02 -35.08

323 1.50 -1.07 -30.68 -34.00

6× 10-5

288 4.32 -25.599 -3.49 -76.76 -88.88

293 4.21 -3.48 -75.49 -87.36

298 3.70 -3.24 -75.03 -85.90

303 3.48 -3.12 -74.12 -84.48

308 1.90 -1.63 -77.82 -83.11

313 1.78 -1.50 -76.99 -81.78

323 1.64 -1.31 -75.19 -79.25

4× 10-5

288 8.14 -5.00 -32.51 -49.87

293 7.04 -4.75 -32.81 -49.02

298 6.20 -14.364 -4.50 -33.10 -48.20

303 5.86 -4.43 -32.78 -47.40

308 5.41 -4.30 -32.67 -46.63

313 4.99 -4.16 -32.60 -45.89

323 4.07 -3.75 -32.86 -44.47

2× 10-5

288 6.31 -12.914 -4.40 -29.56 -44.84

293 5.43 -4.116 -30.02 -44.07

298 5.26 -4.112 -29.53 -43.33

303 4.84 -3.95 -29.58 -42.62

308 4.21 -3.66 -30.04 -41.92

313 3.94 -3.56 -29.88 -41.25

323 3.50 -3.35 -29.60 -39.98

1× 10-5

288 5.69 -12.317 -4.14 -28.39 -42.76

293 5.25 -4.04 -28.24 -42.03

298 5.10 -4.01 -27.87 -41.33


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303 4.87 -3.98 -27.51 -40.65

308 4.23 -3.68 -28.04 -39.99

313 3.72 -3.40 -28.48 -39.35

323 3.30 -3.19 -28.25 -38.13

Table 8: Values of equilibrium Constants and Thermodynamic functions for the

adsorption of compound (B.y) at ideal adsorption conditions.

Ci (M) emp( ) K ∆H (Kj.mol-1) ∆ (Kj.mol-1) ∆ (j.mol-1.K-1) ∆ (j.mol-1.K-1)

8× 10-5

288 10.30

-14.35

-5.57 -30.48 -49.82

293 9.77 -5.55 -30.03 -48.97

298 8.14 -5.17 -30.80 -48.15

303 7.81 -5.16 -30.33 -47.35

308 7.06 -4.99 -30.38 -46.59

313 6.03 -4.65 -30.99 -45.84

323 5.61 -4.61 -30.15 -44.42

6× 10-5

288 8.76

-13.93

-5.19 -30.34 -48.36

293 7.62 -4.94 -30.68 -47.54

298 6.83 -4.75 -30.80 -46.74

303 6.21 -4.58 -30.85 -45.97

308 5.34 -4.27 -31.36 -45.22

313 5.02 -4.18 -31.15 -44.50

323 4.82 -4.21 -30.09 -43.12

4× 10-5

288 10.22

-13.89

-5.55 -28.95 -48.22

293 9.31 -5.43 -28.87 -47.40

298 8.14 -5.17 -29.26 -46.61

303 7.81 -5.16 -28.81 -45.84

308 6.94 -4.942 -29.05 -45.09

313 6.68 -4.944 -28.58 -44.37

323 5.28 -4.45 -29.22 -43.00

2× 10-5

288 7.21

-8.84

-4.71 -14.34 -30.69

293 6.94 -4.70 -14.12 -30.17

298 6.27 -4.53 -14.46 -29.66

303 6.31

-4.63 -13.89 -29.17

308 5.81 -4.50 -14.09 -28.70

313 5.45 -4.39 -14.21 -28.24

323 4.80 -4.18 -14.42 -27.36

1× 10-5

288 7.26

-12.13

-4.74 -25.65 -42.11

293 5.85 -4.28 -26.79 -41.39

298 5.48 -4.21 -26.57 -40.70

303 5.21 -4.15 -26.33 -40.03

308 4.79 -3.99 -26.42 -39.38

313 4.28 -3.77 -26.70 -38.75

323 4.06 -3.75 -25.94 -37.55

Figures (4 and 5) show good linear relationships, and this is inferred from the values of the

correlation coefficient (R2) and at most of the different temperatures and primary


15


concentrations selected for this study. In addition, when checking the values of the

thermodynamic functions (∆S, ∆S ,∆G ,∆H) and the values of the equilibrium constants

shown in tables (8.7), we find that they change as follows:

1- We note that the values of the equilibrium constant (K) decrease with increasing the

temperature of one dye and at a constant concentration and this is consistent with the

results obtained in Table (7), which indicate that the adsorption efficiency decreases with

increasing the temperature and is an indication that the forces responsible for the

adsorption process of a physical nature.

2- The values of the change in enthalpy (∆H), which were calculated in a range of

temperatures between (323-288 absolute) and at different initial concentrations, were all-

negative, indicating that the adsorption process is a heat emitter. The fact that its value is

less than (40 kJ / mol) indicates that the forces responsible for the process of bonding

dyes on the surface of the clay are of a physical nature.[15][16]

3- For the purpose of tracking the change in the entropy value, two values have been

calculated for it:

The first: It is the value of (∆S) calculated at equilibrium, that is, when (∆G = 0), and its

value is all-negative at all the selected thermal temperatures and the different concentrations

and in all the dyes under study, this indicates an increase in the regularity state in the studied

systems at equilibrium. on the other hand, we find that the values of (∆S) and at a constant

concentration increase the randomness with increasing temperature, which indicates that the

increase in temperature increases the randomness of the system under study due to the

increase in the return of adsorbed particles to the solution and this is consistent with what was

previously concluded that the studied system is of a physical nature.

Second: To follow the values of (∆S˚) calculated at different conditions for the adsorption

process, we find the following: The negative values of (∆S˚) increase with increasing

temperature in one dye, and thus the automaticity of the studied system will increase with the

temperature.

As for the value (∆H˚) for both dyes, we note that it carries a negative signal, and this

indicates that the adsorption process occurs automatically. The value of (∆H˚) decreases with

its negative value with increasing temperature. This confirms the nature of the heat-emitting

adsorption, and thus it is consistent with the value of (∆S˚) obtained in the same calculations.


16


Adsorption isotherms

Isotherms are mathematical relationships that are derived and adapted to describe a specific

adsorption system through specific assumptions, which are a good source for obtaining

results related to the nature of different systems by computing some constants specific to each

isotherm[17]

In this study, three isotherms models were chosen for the purpose of their

application to the experimental results. For the adsorption process, they are the Ferendallach

isotherms, Lancmeier and Tekkan.

Isotherm lancemire

This isotherm was applied to the practical results for adsorption of the dyes under study on the

adsorbent material and at equilibrium by drawing the relationship between (Ce / qe) versus

(Ce) and at different temperatures and in the aforementioned range.

Figure 6: Illustrates the Lancmair isotherm of dye adsorption (B.g) on the surface of

Western Sahara bentonite.

Figure 7: Illustrates the Lancmair isotherm for dye adsorption (B.y) on the surface of

the Western Sahara bentonite.


17


Table 9: Shows the Lancemire reward (Qmax and b) and the correlation coefficients for

my dye adsorption process (B.g, B.y).

The name of the dye Temp(K°) b (L/mg) Qmax (mg/g) R

B.g 288 0.228 769 0.9565

293 0.181 833 0.9474

298 0.191 769 0.9644

303 0.180 769 0.9640

308 0.176 666 0.9597

313 0.159 666 0.9526

323 0.137 666 0.9538

B.y 288 -0.070 -2000 0.7454

293 -0.072 -1666 0.7279

298 -0.056 -2000 0.7233

303 -0.044 -2500 0.5874

308 -0.031 -3333 0.4603

313 -0.029 -3333 0.3993

323 -0.033 -2500 0.7503

Through Table (9), we can include the following points:

1- The Lancemire isotherm equation model applies well to the experimental results for (B.g)

dye. In addition, this is through the accepted linear relationship obtained from the drawing

of (Ce / qe) versus (Ce), where we notice that the value of (R) varied between (0.9538 -

0.9565) and at all temperatures of the studied system, which is an acceptable value.

As for the value of (R) for the (By) dye, we find it decreased from that obtained for the (Bg)

dye, where the quantity ranged between (0.7454 - 0.7503), which is an unacceptable value.

On the values and constants of this isotherm in describing the adsorption system for this dye.

2- The value of (b), which represents a constant value to describe the relationship of the

strength of the dye's binding to the adsorbent surface, as we note that this value in the

(Bg) dye decreases with increasing temperature, and this in turn indicates a decrease in the

strength of the dye's binding to the adsorbent surface due to the increase of the molecular

vibrations of the resulting molecule By increasing its kinetic energy, then it will lead to its

disengagement and return to the solution. This confirms that the studied system for

adsorption of this dye is of a physical nature and that the bonding force between the

surface of the adsorbent material and the dye is of the type Vandervals.

3- The value of (Qmax), which represents the theoretical total adsorption capacity, is greater

than the value of (qe) the process obtained in Table (7), where we note that this value does


18


not change in a specific typical way with the change of temperature, and this can be

interpreted as the value of (Qmax) It is affected by many factors, including due to the

nature of the adsorbent material, such as the surface area, the method of distributing the

active sites eligible for the adsorption process and their homogeneity on the surface, the

size of the gaps or pores on it, as well as the type of active groups present within their

surface structures or the nature of the adsorbent material, the type of active groups (the

steric shape) and the method of interaction with The adsorption surface and its surface,

these factors together limit the adsorption efficiency and capacity.

Frendlich isotherm

The Ferendallch isotherm equation was applied to my dyes (B.g, B.y) and at different

temperatures (323-288 K°), and by using Western Sahara bentonite as an adsorbent.) and (Kf)

from the slope of straight lines and segments respectively. The values of the constants

calculated from the application of this isotherm were included in Table No. (10) and they

were as follows.

Figure 8: Fernandlech isotherm for adsorption of the (B.g) dye on Western Sahara

bentonite.

Figure 9: Fernandlech isotherm for adsorption of B.y dye on Western Sahara bentonite.


19


Table 10: The values of the Wernelich constants (Kf, n) and the correlation coefficients

obtained for the adsorption process of my dye (B.g, B.y).

The name of the dye Temp C° n Kf R

B.g 288 1.498 136.77 0.9304

293 1.427 124.33 0.9414

298 1.480 119.64 0.9469

303 1.483 114.63 0.9465

308 1.629 105.36 0.9334

313 1.597 97.94 0.9297

323 1.552 87.35 0.9428

B.y 288 0.842 151.04 0.9913

293 0.802 126.85 0.9889

298 0.839 115.69 0.9927

303 0.861 113.08 0.9894

308 0.887 103.75 0.9873

313 0.896 95.58 0.9856

323 0.881 83.02 0.9970

By noting the values of the results obtained in Table (10), we find the following:

1- The Fernandelch isotherm model applies to the practical results of the studied systems for

both dyes (bg, by), where we notice that the values of the correlation coefficient (R) that

were obtained gave good linear relationships by drawing the relationship between (log qe)

versus (log Ce). Where the value of (R) ranged between (0.9304 - 0.9970) and at all

temperatures, and this indicates the possibility of applying the Frendelsh mathematical

model to these dyes and taking advantage of the values of the constants obtained and

explaining the nature of the studied system.

2- The value of (Kf), which has a relationship with the adsorption capacity, its value

decreases with increasing temperature, and for both dyes under study, this leads to a

reduction in the binding energy of the dye molecules and returns them from the

adsorption surface to the aqueous solution, thus reducing the adsorption capacity. This is

in agreement with what has been observed in studying the effect of temperature on

adsorption capacity. It also supports the physical nature in the process of the studied

system.

3- We note the value of (n), which has a relationship to the intensity of adsorption, that its

value is between decrease and increase with increasing temperature. Also, the value of (n)

for the (B.g) dye is more than (1) and this indicates that adsorption is preferred and good

and indicates that the adsorption system of the studied dye is of a physical nature. It is

known that the value of adsorption intensity (n) is preferred when its value is in the


20


range.[1-10]

which indicates the occurrence of physical adsorption of the adsorbed material

on the surface of the adsorbent material. However, the values of (n) obtained for (B.y)

dye were less than one and ranged in a range (0.802 - 0.896) These values do not in

conformity with the requirements of the physical adsorption process and are not favorable

in adsorption systems when the values (n) are less than one,[18]

which may refer to implies

(chemisorption) in the adsorption system.[19]

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