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Badawy, N.A., El-Bayaa, A.A. and AlKhalik, E.A. Vermiculite as an exchanger for copper (II) and Cr (III) ions, kinetic studies. Ionics, 16(8), 2010, pp.733-739. [24].

International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 4, April 2017, pp. 837-845, Article ID: IJCIET_08_04_098 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication

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REMOVAL OF COPPER FROM AQUEOUS SOLUTION USING GROUND GRANULATED BLAST FURNACE SLAG AS ADSORBENT Vinith PG Student, Department of Civil Engineering, Manipal Institute of Technology, Manipal, Karnataka, India Sridevi H Assistant Professor, Department of Civil Engineering, Manipal Institute of Technology, Manipal, Karnataka, India ABSTRACT This work aims to evaluate the effectiveness of ground granulated blast furnace slag (GGBS) in removing copper from aqueous solutions. Batch adsorption studies were done to optimize conditions for the removal of copper. Factors affecting adsorption such as pH, GGBS dosage, contact time, copper concentration and temperature were determined. The kinetics and isotherm models were studied for the obtained data. It was found that removal efficiency increased with the GGBS dosage and the optimum dose was 2.5g/L. The removal was increased to 90% when the pH of the solution was 5 and contact time of 120 minutes The results revealed that adsorption was endothermic and spontaneous in nature. Key words: Copper, Adsorption, GGBS, Isotherms, Kinetics. Cite this Article: Vinith and Sridevi H, Removal of Copper from Aqueous Solution using Ground Granulated Blast Furnace Slag as Adsorbent. International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 837-845. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4

1. INTRODUCTION The increased use of heavy metals has resulted in an increased flow of metallic substances into water courses. Industrial wastewater from industries such as electroplating, metal finishing, coal combustion, chemical, tanneries and battery manufacturing contains high amount of heavy metals that causes pollution when discharged to water. Copper is a widely used metal because of its excellent physical and mechanical properties [1]. If copper is present in excess it may cause toxic and harmful effects to the living organisms, such as hemolysis, hepatotoxic and nephrotoxic effects, stomach upset, headache, dizziness and respiratory distress[2].Therefore, it is of great significance to remove copper from wastewater.

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The treatment methods to remove copper from wastewater include membrane filtration chemical precipitation, floatation, ion exchange, electro dialysis, reverse osmosis, evaporative recovery and adsorption[3].But sometimes these methods have technical and economical constraints. Adsorption is the most widely used treatment process because of its low cost and good efficiency in removing contaminants from waste water . Activated carbon is widely used as adsorbent but the application of this material is limited due to the high cost and the difficulty in regeneration. Thus, there is recent trend to use agricultural or industrial solid wastes as adsorbents for the removal of metals from aqueous solutions. The adsorbents like rice husk ash, sawdust, sugarcane biogases [4], waste biomass, and activated sludge [5], and Lignite [6], chitosan [7] have been used for treatment of wastewater. In this study, GGBS is used to remove copper from the aqueous solution. GGBS is the by-product of steel manufacturing process. It is obtained when molten iron is tapped for the production of steel and the slag is made to pass through a granulator. In granulator, the slag is rapidly mixed with large quantities of water to minimize crystallization and forms granulated slag, primarily composed of calcium alumina silicate glass. Finally, the slag is grinded to fine powder and forms ground granulated blast furnace slag (GGBS).

2. MATERIALS AND METHODS 2.1. Materials GGBS was collected from Shivally industrial area, Manipal. All the chemicals utilized in the experiment were of reagent grade. Copper sulphate pentahydrate (CuSO4.5H2O) was dissolved in distilled water for preparing stock solution of 100mg/L of copper solution. The solution pH was adjusted by Hcl and NaOH.

2.2. Instrumentation X-ray diffractometer was used for the phase identification of the GGBS. The scanning range of 2θ was between 0 and 80.0, with a scan speed of 2º/minute. The pH measurements were done using a digital pH meter which was standardized using buffers with pH values 4 and 7.Batch sorption studies were carried in a rotary shaker at 150 rpm. UV spectrophotometer was used for the measurement of copper concentrations in aqueous solution.

2.3. Adsorption Experiment Batch sorption tests were carried to study the effect of pH, GGBS dose, contact time and copper initial concentration. 50mL of copper solution with concentration varying from 10 mg/L to 100 mg/L, pH varying from 2 to 6 was added with GGBS varying from 0.4g/L to 3 g/L and agitated using a shaker for a specified contact time varying from 10 minutes to 180 minutes at temperature 25º to50ºC and 150 rpm. The solution was then filtered and the copper concentration was measured using an UV spectrophotometer (Hach DR5000). The percentage removal efficiency was calculated using the equation: Co  Ce % removal = x 100 Co Where Co is the copper initial concentration in mg/L and ‫ܥ‬e is the equilibrium copper concentration in mg/L. The adsorption capacity of copper was determined by:

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Removal of Copper from Aqueous Solution using Ground Granulated Blast Furnace Slag as Adsorbent

(Co  Ce )V m qe = where m is the adsorbent mass (g) and V is the solution volume (L).

3. RESULTS AND DISCUSSION 3.1. Characterization of GGBS XRD analysis was done for the characterization of the GGBS. The analysis revealed that there were no significant peaks indicating crystalline phases and hence it can be concluded that GGBS used in the study has amorphous structure. The XRD pattern of GGBS is shown in Figure 1. The main components of GGBS include silica, calcium oxide and magnesium oxide which represent 77.33% of the sample mass. The physical and chemical characteristics of GGBS are shown in Table 1. Table 1 Physical and chemical characteristics of GGBS Characteristics

Values

Physical form

Off white powder

Specific gravity

2.88

2

400

Surface area(m /kg) SiO2(%)

32.50

CaO(%)

37.05

MgO(%)

7.81

SO3(%)

0.54

MnO(%)

0.11

3.2. Effect of pH The effect of varying initial pH (2-6) was studied at 25°Cwith adsorbent dosage of 2.5g/L for a contact time of 120 minutes. The copper concentration was kept constant at 10mg/L. The results showed that there was increase in removal efficiency as pH of the solution was increased (Figure 2). There was 90% removal of copper at pH 5. This trend was expected because adsorption increases with rise in pH upto certain value and decreases with further increase [8]. pH values higher than 6 were not considered in the study because they result in precipitation of copper as Cu(OH)2 [9].

3.3. Effect of Adsorbent Dosage This was studied at 25ºC with pH 5, contact time of 120 minutes, agitation speed of 150rpm and adsorbent dosages varying from 0.4 to 3 g/L. The initial concentration of the solution was 10mg/L. The results show that the removal efficiency increases with the adsorbent dosage. The copper removal was 90.6% when the dose was 2.5 g/L (Figure 3). It can be observed that the available sites at low adsorbent dose are not sufficient to take all available ions in the solution resulting in poor removal efficiency [10]. Therefore it can be concluded that optimum adsorbent dosage for maximum copper removal was 2.5g/L.

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Collected Data-1 800

600

400

200

0

20

40 Theta/2-Theta[deg]

60

80

Figure 1 XRD patterns of GGBS 100

% removal

80 60 40 20 0 0

1

2

3

4

5

6

7

pH

Figure 2 Effect of pH on copper adsorption

3.4. Effect of Initial Copper Concentration This was studied at 25ºC with adsorbent dosage of 2.5g/L for a contact time of 120 minutes and pH 5. The initial copper concentration was varied from 10 to 100mg/L. It was observed that as the initial copper concentration was increased there was decrease in removal efficiency [20].When the initial copper concentration was 10mg/L, the removal efficiency was about 90.6% and when the initial concentration was increased to 100mg/L, the removal efficiency was decreased to 55.1%(Figure 4) As the initial copper concentration increases, the accessible sites are not adequate to adsorb them and major part of the copper ions remain in the solution without being adsorbed by the adsorbent[11].

3.5. Effect of Contact Time This is one of the main factors for batch adsorption tests because it gives an idea on the minimum time needed for the good amount of adsorption to take place [23]. The study was done by varying the contact time from 15 to 240 minutes. The initial concentration of the copper solution was fixed at 10mg/L, initial pH of the solution was 5 and the adsorbent dosage was 2.5g/L. There was 50% removal after 30 minutes of contact time and for a contact time of 120 minutes, there was 90.6% removal (Figure 5). Hence, the optimum contact time of 120 minutes was applied for the tests in the study.

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Removal of Copper from Aqueous Solution using Ground Granulated Blast Furnace Slag as Adsorbent

80

80

% removal

100

% removal

100

60 40

60 40

20

20

0

0 0

1

2

3

0

4

40

60

80

100

120

Initial concentration (mg/l)

Adsorbent dosage (g/l)

Figure 3 Effect of adsorbent dosage on copper adsorption

Figure 4 Effect of initial concentration on copper adsorption

100

100

80

98

% removal

60

% removal

20

40 20

96 94 92

0 0

50

100

150

200

90

250

20

Contact time( min)

30

40

50

60

Temperature(°C)

Figure 5 Effect of contact time on copper adsorption

Figure 6 Effect of temperature on copper adsorption

3.6. Effect of Temperature This was studied at 25, 30,35,40,45 and 50°C with pH 5, adsorbent dosage of 2.5g/L and contact time of 120 minutes. It was found that as the temperature was increased the removal efficiency was increased and maximum removal efficiency was 96.50% at 50°C(Figure 6).The increase in removal efficiency with temperature may be due to surface coverage, expansion and due to the reactive and active sites[24]. It has been found by the researchers that generally as the temperature is increased metal ion removal is enhanced [12, 13].

3.7. Adsorption Kinetics To study the mechanism of the adsorption, the kinetic data were fitted to the pseudo first order and pseudo second order kinetic models [14, 15, 23]. The expressions are listed below:  k1  log (qe - qt) = log qe -  t  2.303  t 1 t   qt k 2 qeqe qe

Where qe and qt are the values of amount sorbed per unit mass at equilibrium and time t respectively. k 1 and k 2 are the first order and second order constants respectively[27, 28]. http://www.iaeme.com/IJCIET/index.asp

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The data fit well with the second order model much better than the first order model. The R 2 value for the second order model was 0.9516 whereas for the first order model it was 0.9057. The rate constants for first order and second order model found to be 0.0385/min and 0.00383g/mg/min respectively.

3.8. Adsorption Isotherms Adsorption isotherms are necessary to study the interaction between the copper ion and GGBS and to optimize it [16,18]. Langmuir and Freundlich isotherm was used in this study to determine adsorption capacity of the GGBS. y = -0.016x + 1.045 R² = 0.905

1

y = 0.2078x + 11.275 R² = 0.9516

60 0

50

100

150

200

250

40

t/qt

log(qe-qt)

50

-1 -3

30 20

-5 -7

10 0 0

Time(min)

Figure 7 Pseudo first order kinetic model for copper

adsorption

50

100

150

Time(min)

200

250

Figure 8 Pseudo second order kinetic model for copper adsorption

3.8.1. Langmuir Adsorption Isotherm It is based on the assumptions like surface of the adsorbent is in contact with the adsorbate and it contains a number of active sites on which the adsorbate adsorbed and the adsorption consists the attachment of only one molecular monolayer on surface of the adsorbate [9,19]. Langmuir isotherm is given by the following expression: Ce 1 Ce   qe qmKL qm Where Ce is the copper concentration at equilibrium in mg/L, KL is Langmuir constant and qm is the maximum monolayer adsorption capacity. The results showed that the Langmuir isotherm had R2 value of 0.9568, adsorption capacity (qm) was 22.321 mg/g and value of KLwas 0.108mg/L.

3.8.2. Freundlich Adsorption Isotherm Freundlich isotherm describes adsorption in aqueous systems involving adsorption surface with heterogeneity and active sites with varied energies [9,25]. Freundlich isotherm is given by the following expression: 1 ln qe  ln KF  ln Ce n Where Ce is the copper concentration at equilibrium, KF and n are the constants. The plot of lnqe versus lnCe will lead to the slope of 1/n and intercept of ln KF [29] . The results showed that Freundlich model had R2 value of 0.9852 which is a better fit than Langmuir adsorption isotherm model. The Freundlich constants KF and n were 26.533 mg/g and 2.534 L/mg respectively. Generally, if the value of n is between 2 to 10 indicates good adsorption [21]. The calculated n value was 2.534 showing good efficiency for copper adsorption by GGBS. http://www.iaeme.com/IJCIET/index.asp

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3.9. Thermodynamic Parameters The parameters like enthalpy (ΔH), free energy (ΔG) and entropy (ΔS) for copper adsorption by GGBS was determined by following expressions [17]: S H ln Kd   R RT Where R is the gas constant and T is temperature in Kelvin. The plot of ln Kd versus 1/T will yield a straight line (Figure 11). The values of (ΔH/R) and (ΔS/R) will be obtained from the slope and intercept of the straight line. ΔG can be calculated by [22,26]: G  H  TS The results show that the values of ΔH and ΔS are positive and value of ΔG reduces with the increase in temperature. This indicates the adsorption is endothermic. ΔG values are negative at all temperatures suggesting the spontaneous nature of copper adsorption [22]. y = 0.0448x + 0.4138 R² = 0.9568

3.000

3.000

2.500

2.500

2.000 1.500

ln qe

Ce/qe

y = 0.3945x + 1.4238 R² = 0.9852

3.500

1.000

2.000 1.500 1.000

0.500

0.500

0.000 0

10

20

30

40

50

0.000

60

0

Ce

1

2

ln Ce

3

4

5

Figure 10 Freundlich plot for copper adsorption

Figure 9 Langmuir plot for copper adsorption

y = -4427x + 16.926 R² = 0.941

3.500 3.000 2.500

ln Kd

2.000 1.500 1.000 0.500 0.000 0.00305

0.00310

0.00315

0.00320

0.00325

0.00330

0.00335

1/T

Figure 11 Vanthoff’s plot of lnKd versus 1/T for copper adsorption

4. CONCLUSION The present study shows that the GGBS is an efficient adsorbent in copper removal from aqueous solution. The optimum pH and contact time was found to be 5 and 120 minutes respectively. It was found that as the initial concentration of copper was increased, there was decrease in removal efficiency. With a small GGBS dosage of2.5 g/L there was 90% removal of copper from the aqueous solution and also the sorption increases with the increase in

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temperature. The adsorption kinetics showed that the adsorption followed second order model with R2 value of 0.9516. The data was fitted to isotherm models and was found that the data fitted best with Freundlich isotherm .Thermodynamic parameters of adsorption indicated that the adsorption is endothermic in nature.

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