cadmium removal from aqueous solution by prosopis...

Journal of Environmentally Friendly Processes: Volume 4. Issue 1. June 2016

Petrotex Library Archive

Journal of Environmentally Friendly Processes

Journal Website: http://www.petrotex.us/

Cadmium Removal from Aqueous Solution by Prosopis Cineraria Leaf Ash

(PCLA)

F.Eshraghi

1, M.Motavassel

1, B.Roozbehani

1, N.Jaafarzadeh Haghighi Fard

2

1Department of Chemical Engineering, Petroleum University of Technology, Abadan, Iran

2Department of Environmental Health Engineering, School of Public Health, Jundishapur University of Medical Sciences, Ahvaz,

Iran

Abstract:

Sorption ability of Prosopis Cineraria Leaf Ash (PCLA) was investigated for removal of cadmium (II) from aqueous solution. The

effect of different factors such as sorbent dose (1-3 g/L), pH (4-10) and initial concentration of cadmium (20-100mg/L) was studied

in batch experiments. The experimental equilibria data were analyzed by Freundlich, Langmuir, Temkin and Brunauer-Emmett-

Teller isotherm models. The Freundlich isotherm model provided a best fit with the equilibrium sorption data. Using Langmuir

isotherm model the calculated maximum binding capacity was 24.6 mg of cadmium (II) per gram of PCLA. The maximum

percentage of removed cadmium was 96% at pH of 7, with 3 g/L PCLA from solution containing 20 mg/L of Cd (II).

Keyword: Cadmium, PCLA, sorption, isotherms

1. Introduction

Recently, the contamination of water with toxic heavy metals has been one of the great problems, mainly due to the very large

discharge from industrial processes into environment [1]. Heavy metals are hazardous for health, if the amount of they exceed

permissible limits, because of their bioaccumulation tendency [2]. Cadmium is one of the highly toxic heavy metals and a nuisance

element [3]. Cadmium is introduced into the environment from electroplating, alloy manufacturing, smelting, plastic, pigments,

refining and mining industries [4]. The injurious effects of cadmium in humans include liver damage, bone degeneration,

hypertension, renal dysfunction, lung insufficiency and Itai-Itai disease [5, 6]. The maximum acceptable concentration of cadmium

is 0.003 mg/L in drinking water, as recommended by the World Health Organization [7]. So, it is essential to remove Cd (II) from

industrial wastewater.

Many types of method are used to remove cadmium and other heavy metals from wastewater such as chemical precipitation,

chemical oxidation, ion-exchange, ozonation, reverse osmosis and membrane filtration, that these methods are extremely expensive,

ineffective when the solutions are dilute with initial heavy metal ions concentration of 1 to 100 mg/L and not eco-friendly [8, 9].

Among the various methods, adsorption is effective technique due to low production of refuses, feasibility for the use of the sorbent

again, low cost and ease of process [10].

Many natural sorbents have been used for the removal of cadmium such as tree fern, beech leaves, lignin, peat, coconut copra, rice

husk, grains, waste bagasse, algae, biomass, activated carbons, woods and fly ash [11].

Prosopis cineraria trees are native to arid portions of Western Asia and the Indian Subcontinent, including Iran [12]. In Khuzestan

coastal areas, especially in Abadan and Khorramshahr cities, it is estimated that there are over millions of prosopis cineraria trees. In

this study, because of the abundance, low cost and being safe for human health, prosopis cineraria tree leaf will be used as a low-

cost absorbent. Though Prosopis Cineraria Leaf Powder (PCLP) has successfully been used for the removal of Methyl Orange Dye,

reactive Red dyes 198 and Blue 19 and some heavy metal from contaminated water [13, 14, 15, 16, 17, 18], but the impact of

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Eshraghi et al / Journal of Environmentally Friendly Processes 4 (2016) 4 - 11

5

Prosopis Cineraria Leaf Ash (PCLA) on Cd (II) sorption has not been unraveled to date. In this study, the ability of prosopis tree

leaf is examined in removal of cadmium and then adsorption isotherm of it will be determined.

2. Materials, Experimental and Calculations

2.1. Chemicals

Appropriate amount of Cd (No3)2.4H2O (MW =308.47

, Merck) was dissolved in distillated water for preparation of cadmium

(II) stock solution. 0.1N HNO3 or NaOH solutions were used to adjust the solution pH.

2.2. Apparatus

Residual concentration of cadmium (II) in the filtered solution was determined using an Atomic adsorption flame Spectrometer

(Analytic Jena AAS 5FL, Germany). In all experiments mixing rate and pH were measured respectively by using a plat form shaker

(yellow line- MSEB model- Germany) and a jenway model 3510, UK pH-meter.

2.3. Adsorbent preparation

Prosopis Cineraria Leaves were obtained from Abadan (Iran) region prosopis cineraria trees. They were washed repeatedly by

double distilled water to remove dust and soluble impurities and then dried in oven for 48 hours at 105 ºC and burned at 500 ºC for

10 min. Then leaves were crushed into small particles by mechanical grinder and the powder was sieved to 8, 18, 30, 80, 100 and

200 mesh sizes. After sieving, micro powder kept in bottle in desiccator. Powders of mesh size of 200 (75 μm) were used in all

experiments throughout this work.

2.4. Batch adsorption experiments

Batch adsorption studies were conducted in 250ml glass beaker to study the effect of parameters pH of solutions (4-10), PCLA

dosages (1-3 g/L), initial cadmium concentration (20-100 mg/L) and at room temperature (25±2˚C). All experiments were carried

out in a platform shaker (yellow line-mseb model, Germany) at a constant shaking rate of 250 rpm. In order to assess optimized

adsorption pH, the pH values changed (4-10) at different initial cadmium concentration (20, 60, 100 mg/L), while the PCLA dosage

was fixed at 3 g/L in the solution. To do this, a 0.3g PCLA was added to glass beaker (250ml) containing 100 ml of cadmium

solution with various concentrations. Before adding adsorbent, solutions were adjusted to given pH value with 0.1 N nitric acid or

0.1 N sodium hydroxide solutions. Then the beaker was put on a platform shaker at 250 rpm at room temperature (25±2˚C) for 1 hr.

Afterwards, solution was filtered through a 0.45 µm pore size filter paper and the concentration of cadmium was determined using

an atomic adsorption flame spectrometer.

2.5. Theory and calculations

2.5.1. Removal percentage

After determination of final cadmium concentration, the removal percentage was calculated as follows:

⁄ (1)

Where, R% is the percentage removal of cadmium; C0 and Ct are the initial and final concentrations of cadmium in the solution

(mg/L), respectively.

2.5.2. Adsorption isotherms

Equilibrium time was obtained from the kinetic results to be 2 hr and 120 min was considered as contact time for isotherms

experiments. Isotherm studies were performed at different cadmium concentrations in the rang 10 to 100 mg/L. A 0.3 of adsorbent

was added to glass beaker containing 100 ml of metal solution. The pH of solution was 7 and the all samples were agitated at speed

250 rpm for 120 min. Then, the adsorbent in all samples was separated by filtration through filter paper. Finally, the cadmium

concentrations in the filtrates were measured with an Analytic Jena AAS 5FL atomic adsorption spectrometer.

In this study, the adsorption data has been analyzed with Langmuir, Freundlich, BET and Temkin isotherm models. The linearized

form of Langmuir model equation is expressed as [19]:

(2)


6

Where qe is the amount of cadmium sorbed at equilibrium time (mg/g), Ce is the equilibrium concentration of cadmium in solution

(mg/L), qm is the maximum adsorption capacity of PCLA (mg/g) and KL is also the Langmuir constant (L/mg).

The Freundlich isotherm is based on the assumption that the surface of an adsorbent is heterogeneous. The linear form of this model

can be written as [20]:

+

(3)

Where n and KF are indicative intensity and capacity of sorption, respectively.

The assumption in BET isotherm model is the adsorbate molecules can be adsorbed in several layer [21].The linearized form of

BET model is given by:

=

+{[

].

} (4)

Where Cs is the concentration at which all sites are saturated and KB is the BET constant.

Temkin model considers that heat of adsorption of all molecules in the layer would decline linearly [22]. Linear form of Temkin

model is shown as follows:

(5)

In this equation, R is the gas constant (8.314 J/mol.K), T is the absolute temperature (K), is the Temkin isotherm constant (L/g) and bT is the Temkin constant regarding adsorption heat (J/mol).

3. Result and Discussion

3.1. Effect of pH

The pH parameter is one of the important controlling variables in the sorption process, thus, the effects of it was investigated at

different pH ranging from 4.0 to 10.0 (Figure 1). According to Figure 1 the maximum adsorption of cadmium to PCLA occurred at

initial pH = 7. A main reason for low adsorption at low pH is competition for the adsorption sites on PCLA surfaces between higher

concentration of H+

and Cd (II) ions, so 𝐻+ ions prevent from attraction of cadmium ions on PCLA surfaces because of electrostatic repulsion. Increase of removal efficiency of cadmium was observed with increasing solution pH from 4 to 7, because the PCLA

surfaces are more negatively charged and competition decreases. Above initial pH 7, removal efficiency was decreasing due to the

precipitation of cadmium as Cd (OH)2.


7

Figure 1. Effect of pH on Cd (II) removal efficiency by PCLA sorbent at different initial Cd (II) concentrations,

25˚C temperature, and mixing at 250 rpm

3.2. Effect of adsorbent dosage on Cd (II) removal

The effect of a change of PCLA dosage on the sorption of cadmium in the range of 1.0 to 3.0 g/L at different initial concentrations

and initial pH = 7 for 60 min contact time is represented in Figure 2. The results show that by increasing the PCLA amount, removal

efficiency of cadmium increases. In fact, with increasing weight of PCLA the residual Cd (II) concentrations decrease, that it may

be attributed to access of more active sites and more surface area.

Figure 2. Effect of PCLA dosage on Cd (II) removal efficiency at different initial Cd (II) concentrations, pH = 7,

25˚C temperature and 250 rpm

3.3. Effect of initial cadmium (II) concentration

Figure 3 indicates the effect of initial cadmium (II) concentrations ranging from 20 to 100 mg/L at 3 g/L of PCLA dosage and pH =

7. This figure represents that percentage of cadmium uptake decreased as a result of increasing of initial cadmium concentration,

because of saturation of active sites. For example, in this range the removal efficiency decreased from 96% to 62%. In fact at low

20

40

60

80

100

120

4 5.5 7 8.5 10

% C

ad

miu

m (

II)

rem

ov

ed

pH

Cd = 20 mg/L Cd = 60 mg/L Cd = 100 mg/L

20

40

60

80

100

1 1.5 2 2.5 3

% C

ad

miu

m (

II)

rem

ov

ed

PCLA dosage (g/L)

Cd = 20 mg/L Cd = 60 mg/L Cd = 100 mg/L


8

concentrations cadmium, Cd (II) ions can be uptake by certain sites on the surface of PCLA, so there is more adsorption, but with

increasing of initial Cd (II) concentration, metal uptake decreases because of lack of available binding sites for adsorption cadmium

on adsorbent.

Figure 3. Effect of initial Cd (II) concentration on the removal efficiency of Cd (II) by PCLA at pH = 7, 250 rpm

agitation and 25˚C

3.4. Sorption isotherms

Biosorption isotherms are important to optimize the design factors of future designing purposes. This isotherm models indicate the

relationship between the amount of metal ions adsorbed on adsorbent surface and the concentration of residual ions in liquid phase

[23]. In this study, the equilibrium data has been analyzed with Langmuir, Freundlich, BET (Brunauer- Emmett- Teller) and Temkin

isotherm models.

Figure 4 shows the linear form of these four models. The constant parameters for various models are presented in Table 1 with their

correlation coefficients, R2, that calculated for Cd (II) removal by using linear regression analysis. The R

2 values obtained in Table

1, indicate that adsorption data were fitted onto all the investigated isotherm models (Langmuir, BET, Temkin), although, the

Freundlich isotherm exhibited a better fit to the equilibrium data than other models. As obvious from the regression coefficient

values in Table 1, the highest R2 was found related to the Freundlich isotherm model. The determined results from the intercept and

slope of the plot log (qe) versus log (Ce) are Freundlich coefficient (KF = 4.54) and n parameter (n =2.38), respectively.

40

60

80

100

20 40 60 80 100% C

ad

miu

m (

II)

rem

ov

ed

Initial Cd (II) concentration

0.40

0.60

0.80

1.00

1.20

1.40

1.60

-1.00 -0.50 0.00 0.50 1.00 1.50 2.00

Lo

g q

e

Log Ce

A) Freundlich Isotherm Model


9

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25 30 35

Ce/

qe

Ce (mg/l)

B) Langmuir Isotherm Model

0.00E+00

2.50E-06

5.00E-06

7.50E-06

1.00E-05

1.25E-05

1.50E-05

0.0000 0.0001

Ce/

((C

s-C

e) q

e)

Ce/Cs

C) BET Isotherm Model


10

Figure 4. Sorption isotherm of Cd (II) on PCLA

Table 1. Parameters of Freundlich, Langmuir, BET and Temkin for adsorption of Cd (II) on PCLA

Isotherm models

Isotherm parameters

KF N q m KL KB bT aT R2

Freundlich 5.338 2.38 _ _ _ _ _ 0.9941

Langmuir _ _ 24.63 0.202 _ _ _ 0.9677

BET _ _ 24.63 _ 101501 _ _ 0.9678

Temkin _ _ _ _ _ 615.18 0.780 0.9874

4. Conclusion

In this work, PCLA were studied for the adsorption of cadmium from aqueous solution by investigate the effects of some

parameters. This study showed that PCLA could be used as an effective natural adsorbent for the cadmium removal from aqueous

solution and wastewater. The percentage of cadmium removed increased with the increasing PCLA dosage from 1 to 3 g/L, while the removal efficiency decreased with increasing adsorbate concentrations. Also, the cadmium uptake enhanced by increasing the

pH up to 7.0 and at higher pH this value decreased due to precipitaton of cadmium. We observed a 96% cadmium removal

efficiency at pH 7.0, where the initial cadmium concentration was 20 mg/L at 3 g/L of PCLA dosage. The Freundlich biosorption

isotherm model had the best correlation coefficient (R2) compared to other models.

5. Acknowledgement I would like to thank the Petroleum University of Technology. I also thank Mr. Ali Rastegar for his help during experimental

conduction.

0.0

5.0

10.0

15.0

20.0

25.0

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

qe

(mg

/l)

Ln Ce

D) Temkin Isotherm Model


11

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