O A

5930
Journal of Applied Sciences Research, 9(11): 5930-5940, 2013
ISSN 1819-544X
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLES
Evaluation of natural amendments in minimizing the hazards of potential toxic
elements in contaminated soils technique
1
Sherin Shehata, 2Camilia El-Dewany, 2O.A. El-Hady and 2A.M. Zaghloul
1
2
Soil Chemical and Physical Dept., Desert Research Centre, Mataria
Soils and Water Use Department, National Research Centre, Dokki, Cairo, Egypt
ABSTRACT
Clay minerals and zeolites have large cation exchange capacities, which enable them to be applied as
natural sorption materials for organic and ionic contaminants. In this study, the sorption behavior of Cd, Cu and
Ni applied at 200 ppm onto natural zeolites and bentonite treated soils have been studied in order to evaluate
these materials as natural remediate materials in sandy (Typic Psamments) and calcareous (Typic calcides)
contaminated soils. The kinetic study using electrical Stirred Flow Unit (ESFU) devise method has been used as
an approach to evaluate the minimizing hazards of pollutants in these remediated soils. The rate constants of
Hoerl and Elovich kinetic models were determined for different sorption systems as a function of HM
concentration i.e. 25, 50 and 75 g kg-1, type of clay minerals and soils used. The obtained results indicated that
according to higher coefficient of determinations R2 and lower standard error SE, the rate of potential toxic
elements PTE's in control or treated soils were mach fitted to kinetic models used compared to other models
tested. The numerical values of rate constants indicated that concerning the type of natural materials, zeolite has
a sorption capacity to studied PTE's more than bentonite. It was also found that sorption of pollutants on treated
soils depend on charge density of these pollutants and hydrated ion diameter. According to the kinetic studies,
the selectivity of pollutants on clay minerals take the order Cu2+ > Ni2+> Cd2+. The study suggests also that
using of available natural materials could be economic and promising alternative solution in contaminated soils
to minimize hazards of such PTE's. Different mechanisms take place in removal of HM from the sandy and
calcareous soils were reported.
Key words:
Introduction
Control of heavy metals emission from soils combustor/waste incinerators has been in the limelight for
many years. Different experiments applied revealed that single or multi stages sorption systems can significantly
reduce heavy metals effluent concentrations for the same total amount of sorbent or, alternately dramatically
lower total sorbent consumption for the same effluent concentration.
Soil contamination can have direct consequences, such as deterioration of ecosystem, agricultural
productivity, diminished food chain quality, tainted water resources, economic loss, and human and animal
illness. In extensive areas of industrial regions, people suffer from illnesses associated with elevated levels of
lead in the air, cobalt, arsenic, mercury, and cadmium in the soil, and a food contaminated by metals related to
heavy industry. In some Egyptian regions that contain many polluted environments, these regions must be
remediated to levels that pose negligible human and ecological health risk.
In recent years, attention has focused on the development of in situ immobilization of metals using
inexpensive amendments such as minerals (apatite, zeolite, or clay minerals) or waste by-products (steel shot,
beringite, iron-rich biosolids) these materials represent promising alternative to conduct remediation methods
Wei-Yu et al., (2009). This technique relies on a fundamental understanding of the natural geochemical
processes governing the reactions and bioavailability of metals in the soil systems. In polluted soils, the path
ways of potential toxic elements PTEs can be dissolved in soil solution, sorbed on inorganic soil particles,
complexed with organic soil components such as organic matter, or precipitated as pure or mixed solids
according to residence time of reaction. Soluble contaminants are subject to migration with soil water, loss due
to volatilization into the atmosphere or uptake by plants or aquatic organisms,.
Zeolites are hydrated aluminosilicates of alkaline and alkaline earth cations with three dimensional crystal
structure and a large cation exchange capacity (CEC) of 1000-3000 mmoles (+) / kg (Ming and Dixon, 1987).
In their natural state, the exchangeable ions are predominantly sodium, calcium and potassium. These, together
with their large CEC, wide availability, and low cost make natural and synthetic zeolites potential useful for
Corresponding Author: A.M. Zaghloul, Soils and Water Use Department, National Research Centre, Dokki, Cairo, Egypt.
E-mail: [email protected]
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J. Appl. Sci. Res., 9(11): 5930-5940, 2013
pollution control. In particular, adsorption onto zeolites is an attractive alternative to chemical precipitation for
removing heavy metals from solutions, waste water and behaved like slow release fertilizer in reducing leaching
losses of fertilizers and increasing plant uptake of N and plant yield (Lewis, 1981; Weber et al. 1983). Also,
zeolite characterized by its hydrated aluminosilicate minerals, surface chemistry similar to smectite distributed
cation exchange capacity external, fixed structure with internal channels" and molecular sieve properties.
As for bentonite, it is montmorillonite-rich clay of high sorption capacity and high capacity of cation
exchange. A further property significant of this material to be applied in agriculture is the swelling and bonding
capacity and its plasticity. It occurs in spots with agrillized, rhyolites and rhyolitic tuffs and may be discovered
in any volcanic area near the see-shore (El-Sherif, 1987). Although of these advantages of those important clay
minerals, the utilization of such materials in remediation of heavy metals contaminated soils is limited.
Therefore, the main targets of this research on in situ immobilization of metals were: (1) To evaluate the use of
inexpensive, abundant materials naturally found under Egyptian conditions as stabilizing agents in metalcontaminated soils; (2) To determine the influence of stabilizing agents on the mobility, bioavailability, and
toxicity of metals in soil using kinetic approach; (3) Developing soil quality indices as tools in evaluating the
efficacy of remediation techniques and for monitoring purposes.
Materials and Methods
Soils:
The A horizon (0–30 cm) of two cultivated soil types were used in this study. These soils are classified as
(Typic Calcids) collected from Mariot region and sandy soil classified as (Typic Psamments) collected from
Wadi El-Natron area. Some physical and chemical properties are presented in table1.
Adsorbents remediation materials used:
Two types of clay minerals were tested in this study namely zeolite and bentonite; these materials
characterized by pH 7.54, 7.98 and CEC 48, 155 respectively. The applied clay minerals were added to soils at
three rates i.e. 25, 50 and 75 g/kg beside the control treatment.
Table 1: Some physical and chemical characteristics of the studied soils.
Soil
OM
Particle size distribution
Text
Type
pH
(%)
%
Clay
Silt
sand
Typic
7.24
0.68
35.50
32.0
32.50
Clay loam
Calcid
Typic
8.00
0.41
2.50
3.80
93.70
Sandy
Psam.
Available form of the HM
(ppm)
Cd
Ni
Cu
0.50
nd
1.20
Ca CO3
%
Total
Active
24.6
17.90
1.20
3.00
nd
2.50
-
Experiment procedure:
Three hundred grams of <2 mm air dry soil samples were treated with 200 ppm of Cd, Ni, and Cu salts
applied in chloride form. The treated soils were incubated at 60% of their water holding capacity for 16 weeks
under laboratory conditions. After incubation periods soil samples were kinetically analyzed for heavy metals
desorption.
Kinetic study:
Release experiments were carried out using Electrical Stirred Flow Unit (ESFU) method for all soil samples
and for different incubation times i.e. 2, 8 and 16 weeks. A Diagram of ESFU used in this paper, the
modification of the new set up and mechanism of kinetic working were previously mentioned in more details
(Zaghloul, 2002). Exactly 20g of the Pb treated soil was put in the kinetic part of the device with 100 ml of 0.1
N DTPA solutions. The system was vigorously shaken and the solution samples were received after different
periods ranged between 1 min to 14 days. at 250 C +20 C and analyzed for their concentrations of HM using
atomic absorption as described by Cottenie, et al (1982). The HM released data were fitted to kinetic models
represented empirical equations namely:
• Hoerl eqution in the form:
q=a\t^b\*e^(b\*t)
• The Elovich equation in the form:
qt = 1/b ln ab + 1/b ln t
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J. Appl. Sci. Res., 9(11): 5930-5940, 2013
Where:
q = the amount of HM desorption in time t
b &b\ = constant represents desorption rate coefficient 9ppm)-1.
a &a\ = capacity constant in mg HM kg-1soil.
t = time (min).
The kinetic parameters of the tested equations were calculated for different treatments applied. Different
statistical parameters such as regression analysis applied to test the conformity of used models to describe HM
release from different treated soils, evaluation of significant differences in rate coefficients and cumulative
quantity of metals desorbed after remediation were done using SAS software (SAS institute, 1985).
Results and Discussion
Rate process of Cd, Ni and Cu desorption of used soils as affected by different treatments applied:
Data illustrated in figures 1-3 represent rate of Cd, Cu and Ni desorbed from used soils as affected by
zeolite (A&B) and bentonite (C&D) treatments applied at the rates 25, 50and 75g/kg. As a general output of all
treatments, the rate processes starting with high speed rate trend of HM desorption, followed by decreasing
order to almost steady state condition, this trend was even observed in control treatment. As shown in these
figures, the rate of heavy metals desorption was influenced by soil type, type and rate of sorbate and type of
sorbent. However, all remediation materials applied significantly decrease HM desorption from the treated soil
samples.
Concerning the effect of soil type, data indicated that decreasing order of rate of heavy metals desorbed was
more pronounced in calcareous soil compared to sandy one. For example, in Cd treated soil, the maximum
concentrations desorbed in control treatment was 181 and 152 ppm in sandy and calcareous soils respectively.
The same trend was also observed in both clay minerals treated soils and other heavy metals tested. This result
also observed in figures of calcareous soil with almost narrow trend between control and different treatments of
clay minerals applied in this soil.
The kinetic data represented in these figures clearly indicated that although the studied heavy metals
applied 200 ppm concentration, the variation was observed between different pollutants studied. In this respect,
Cu was retained by soils treated with zeolite more than Ni followed by Cd. For example, in calcareous soil
treated with higher concentration of zeolite 75 mg kg-1, the extracted Cu after 14 days was 47 ppm. At the same
concentration applied, data indicated that the respective values for Cd and Ni were 136 and 62 ppm respectively.
Effect of remediation materials applied at different concentrations on rate of heavy metals release from the
studied soil samples:
Before explaining the results of this study, It should be mentioned that two types of sorption mechanisms
take place, the first concerning with sorption on the soils used in this study especially the calcareous one since
the sandy one is almost structureless or inert material, the second on clay minerals used here with different
mechanisms according to type, nature or charge density of these high accumulator materials. Accordingly, in
previous work (Zaghloul and El-Kharabawy, 2009), indicated that Hoerl model was fitted to explain the data
related with HM released to clay minerals or remediated material applied with especial mechanism, while
Elovich or any other model showed conformity to describe the kinetic data is suitable to describe the release of
pollutants from the soil-remediation material system. Under this experimental condition, Elovich model gave
high conformity to describe the kinetic data under different conditions
Tables 2-4 represent the coefficient of determination R2, Standard error SE, the slope b and the intercept a
of Elovich and Hoerl models. These models showed priority to describe the kinetic data by higher R2 and lower
SE compared to other tested models. In these models, the R2 of Elovich equation ranged between 0.90**- 0.99**
for different pollutants desorbed from sandy or calcareous soils. The respective values of Hoerl equation were
ranged between 0.90** and 0.97**. It should be mentioned here that in calcareous and sandy soils, Elovich
equation was the best to describe a number of reaction mechanisms for various inorganic ions react with
different soil systems (Zaghloul, 1998; Zaghloul and Abou-Seeda 2005; Soad, El-Ashry and Zaghloul, 2007;
and Hellal and Zaghloul 2008). Also, this equation showed priority to describe data of remediation of
contaminated soils as described by Zaghloul and Abou-Seeda, 2003.
Data in table (2) showed that the slope values of constant b which represents the rate of Cd desorbed were
significantly influenced by soil type and rate of zeolite applied. Concerning the effect of soil type, in control
treatment, the rate values of Cd release was 19.21 in calcareous soil, decreased to 12.65 in sandy soil. Addition
of zeolite in both soils, led to decrease these values with the same above mentioned trend. For example,
addition of 50 g/kg, soil led to decrease the rate constant from 19.20 in control to 15.40, the same trend was
observed in different concentrations applied of zeolite. The a constant, represents the capacity factor, of the
same equation almost gave the same trend.
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J. Appl. Sci. Res., 9(11): 5930-5940, 2013
(A)
Sandy soil
Cd concentration (ppm)
200
160
cont
C1
C2
C3
120
80
40
0
0
5000
10000
15000
20000
25000
Time (min)
(B)
Calcareous soil
Cd concentration (ppm)
200
160
cont
120
C1
C2
C3
80
40
0
0
5000
10000
15000
20000
25000
Time (min)
(C)
Sandy soil
Cd concentration (ppm)
200
160
cont
120
C1
C2
80
C3
40
0
0
5000
10000
15000
20000
25000
Time (min)
(D)
Calcareous soil
Cd concention (ppm)
200
160
120
cont
C5
80
C6
C7
40
0
0
5000
10000
15000
20000
25000
Time (min)
Fig. 1: Kinetics of Cd release from used soils as affected by different rates of Zeolite (A&B) and Bentonite
(C&D) application.
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J. Appl. Sci. Res., 9(11): 5930-5940, 2013
(A)
Sandy soil
Ni concentration (ppm)
200
160
cont
120
C1
C2
80
C3
40
0
0
5000
10000
15000
20000
25000
Time (min)
(B)
Calcareous soil
Ni concentration (ppm)
200
160
co nt
120
C1
C2
C3
80
40
0
0
5000
10000
15000
20000
25000
Time (min)
(C)
Sandy soil
Ni concentration (ppm)
200
160
cont
C5
C6
120
80
C7
40
0
0
5000
10000
15000
20000
25000
Time (min)
(D)
Calcareous soil
Ni concenetration (ppm)
200
160
co nt
C1
C2
120
80
C3
40
0
0
5000
10000
15000
20000
25000
Time (min)
Fig. 2: Kinetics of Ni release from used soils as affected by different rates of Zeolite (A&B) and Bentonite (C &
D) application.
5935
J. Appl. Sci. Res., 9(11): 5930-5940, 2013
(A)
Sandy soil
Cu concentration (ppm)
200
160
120
cont
C1
80
C2
C3
40
0
0
5000
10000
15000
20000
25000
Time (min)
(B)
Calcareous soil
Cu concentration (ppm)
200
160
cont
C1
C2
C3
120
80
40
0
0
5000
10000
15000
20000
25000
Time (min)
(C)
Cu concentration (ppm)
Sandy soil
200
160
cont
120
C5
80
C6
C7
40
0
0
5000
10000
15000
20000
25000
Time
(D)
Calcareous soil
Cu concentration (ppm)
200
160
cont
120
C5
C6
80
C7
40
0
0
5000
10000
15000
20000
25000
Time (min)
Fig. 3: Kinetics of Cu release from used soils as affected by different rates of Zeolite (A&B) and Bentonite
(C&D) application.
5936
J. Appl. Sci. Res., 9(11): 5930-5940, 2013
The same values of Cd in calcareous polluted soil were decreased from 15.61 in control to 14.70, 14.50 and
14.36. These values were less than the values of sandy soil. In other words, although 200 ppm Cd was add to
both types of soil, this pollutant was retained in calcareous soil more than sandy soil.
The efficiency of bentonite applied on Cd release is presented in table (2). The rate constant of Elovich
equation showed that bentonite applied at different rates, led to decrease Cd release from used soils. In this
respect, application of 25 g kg-1 decreases a constant from 19.21 in control to 16.94. As shown in the same table,
a reverse trend was observed in capacity constant a. Under the same rate of application, the capacity constant of
Elovich equation was increased from13.30 to 14.63. In calcareous soil enriched with bentonite at the same rate
the respective values of a rate constant were 15.61 and 13.66 in control and treated soil. The comparison
between sandy and calcareous soil, data revealed that a higher capacity to minimize the rate of Cd release was
observed in both control and bentonite enriched soils compared to sandy one, which represents the role of
CaCO3 in retention heavy metals pollutants to unavailable form. The same trend was documented by Zaghloul
and Abo Seeda, 2005, they found that the presence of CaCO3, led to minimize Pb desorption under varied
conditions.
In Hoerl model, unlike Elovich equation, there is a reverse trend represented in tendency of increasing the
rate constant of Cd release with increasing rate of remediation material applied in both soils with high rate
observed in sandy soil compared to calcareous one. This increasing could be explained by increasing the
remediation materials applied to adsorb pollutants. A reverse trend, however, was observed in capacity factor in
both soils and with increasing the rate of bentonite applied by increasing the capacity factor by increasing the
rate of remediation materials applied. Concerning Cu release from treated soils, data in table (3) showed that
zeolite decreased significantly the rate of Cu desorption. In percentage expression, application of 25g kg-1
zeolite, for example, led to decrease a constant of Elovich equation by about 60%. Increasing the application
rate to 50 and 75 g kg-1, increased this constant to 62 and 64% compared to control treatment. In calcareous soil,
the effect of zeolite was more pronounced than in sandy soil. For example, application of low rate of the added
material led to increase a constant by about 97% under control treatment, by increasing the rate of application
the percentage value was increased to about 99%. The capacity factor, b constant, data showed that application
of zeolite led to increase this constant compared to control.
Table 2: Rate constants of Cd release from soils treated with zeolite and bentonite.
Sandy soil
Treat.
b
a
R2
SE
b\
Zeolite
Elovich equation
Cont.
19.21
13.30
0.99**
7.12
15.61
C1
16.73
13.26
0.97**
8.64
14.7
C2
16.1
14.53
0.97**
8.54
14.49
C3
15.4
14.9
0.97**
8.7
14.36
Hoerl model
Cont.
4.58
2.74
0.97**
0.002
5.24
C1
4.71
2.06
0.97**
0.013
5.34
C2
4.85
1.90
0.96**
0.014
5.64
C3
5.36
1.71
0.97**
0.015
6.23
Bentonite
Elovich equation
Cont.
19.21
13.30
0.99**
7.12
15.61
C1
16.94
14.63
0.97**
8.81
13.66
C2
16.92
14.77
0.98**
8.81
13.06
C3
16.04
16.13
0.94**
13.91
12.92
Hoerl model
Cont.
4.58
2.74
0.96**
0.001
5.24
C1
3.99
2.26
0.98**
0.002
5.67
C2
4.93
1.97
0.97**
0.001
5.90
C3
5.19
1.77
0.97**
0.001
6.48
Calcareous soil
a\
R2
SE
7.69
7.65
8.16
8.19
0.99**
0.98**
0.98**
0.99**
0.70
0.68
0.58
0.57
2.72
2.57
2.33
2.04
0.93**
0.92**
0.92**
0.93**
0.016
0.018
0.002
0.002
7.69
7.79
8.32
8.72
0.99**
0.97**
0.98**
0.93**
0.70
0.78
0.87
1.19
2.72
2.55
2.41
2.21
0.93**
0.93**
0.93**
0.92**
0.016
0.017
0.002
0.002
According to table (3), application of bentonite led to decrease Cu desorption from both treated soils. Data
showed that in Elovich equation, application of 25 g kg-1, led to decrease Cu desorption from 17.85 to 7.61 in
sandy soil and from 6.81 to 6.04 in calcareous one. Increasing the application rate of Bentonite also led to
decrease this constant to 7.23 and 7.09 in sandy soil. In Hoerl model data, increasing the application rate of
bentonite led to decrease constant values from 5.19 in control to 2.45, 2.84 and 2.98 by application low, medium
and high rate of bentonite respectively. Although the same trend was observed in calcareous soil, the values of
capacity factor in calcareous were higher that that in sandy soil.
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J. Appl. Sci. Res., 9(11): 5930-5940, 2013
Table 3: Rate constants of Cu release from soils treated with Zeolite and Bentonite.
Sandy soil
Treat.
b
a
R2
SE
b\
Zeolite
Elovich equation
Cont.
17.85
6.43
0.98**
0.78
6.811
C1
7.1
4.86
0.97**
0.46
0.167
C2
6.85
6.67
0.96**
0.42
0.158
C3
6.6
6.61
0.96**
0.44
0.093
Hoerl model
Cont.
5.19
1.78
0.95**
0.016
3.86
C1
3.06
1.53
0.98**
0.009
4.49
C2
3.40
1.26
0.98**
0.001
4.79
C3
4.24
1.02
0.97**
0.002
4.84
Bentonite
Elovich equation
Cont.
17.85
6.43
0.98**
0.78
6.811
C1
7.61
0.97
0.98**
0.41
6.04
C2
7.23
2.25
0.98**
0.39
5.75
C3
7.09
3.78
0.97**
0.42
5.67
Hoerl model
Cont.
5.19
1.78
0.95**
0.016
3.86
C1
2.45
2.05
0.97**
0.009
4.35
C2
2.84
1.84
0.97**
0.006
5.08
C3
2.98
1.68
0.97**
0.001
5.37
Calcareous soil
a\
R2
SE
0.68
17.3
15.6
11.56
0.99
0.91
0.93
0.94
0.23
0.05
0.06
0.03
1.74
1.40
1.18
0.87
0.96**
0.96**
0.96**
0.95**
0.012
0.013
0.014
0.018
0.68
1.11
2.69
3.48
0.99**
0.98**
0.98**
0.97**
0.23
0.22
0.24
0.25
1.74
1.52
1.15
0.98
0.96**
0.96**
0.95**
0.95**
0.012
0.013
0.016
0.017
The effect of zeolite applied at different rates on Ni desorption from used soils is presented in Table 4. Data
indicated that according to R2 values, the conformity of Elovich equation in describing the kinetic data is higher
than Hoerl equation. Also, the effect of applied zeolite was more efficient in sandy soil compared to calcareous
one.
The rate constant of Ni desorption decreased by about 50% compared to control at low concentration of
applied zeolite, however, increasing the rate of zeolite did not influence the rate of Ni release. In calcareous soil,
although the zeolite decreased the rate constant of Ni release compared to control treatment, the decreasing
order was not the same like sandy soil treated with the same amended material used. The application of
bentonite almost gave the same results of zeolite in relation to the effect of soil type. As presented in table (4),
again the decreasing order of Ni desorption was more pronounced in sandy soil compared to calcareous one. At
low concentration applied from bentonite, Ni desorption was decreased by about 35% compared to control
treatment.
Table 4: Rate constants of Ni release from soils treated with Zeolite and Bentonite.
Sandy soil
Treat.
a
b
R2
SE
a\
Zeolite
Elovich equation
Cont.
18.5
4.31
0.99**
0.57
8.02
C1
9.99
3.7
0.97**
0.56
6.88
C2
9.81
2.26
0.97**
0.54
6.76
C3
9.13
0.66
0.96**
0.59
6.63
Hoerl model
Cont.
4.98
2.53
0.96**
0.013
2.53
C1
5.35
2.16
0.92**
0.018
4.35
C2
5.61
2.01
0.91**
0.011
4.45
C3
6.09
1.76
0.91**
0.022
4.98
Bentonite
Elovich equation
Cont.
18.5
4.31
0.99**
0.57
8.02
C1
12.31
0.06
0.98**
0.83
5.81
C2
11.42
1.56
0.99**
0.58
5.57
C3
11.02
2.22
0.98**
0.59
4.95
Hoerl model
Cont.
4.98
2.53
0.96**
0.013
2.53
C1
6.36
1.99
0.91**
0.022
3.93
C2
5.53
1.97
0.93**
0.019
4.54
C3
6.27
1.77
0.92**
0.021
4.76
Calcareous soil
b\
R2
SE
1.166
0.65
2.04
3.27
0.99**
0.99**
0.98**
0.99**
0.28
0.23
0.24
0.23
1.97
1.70
1.53
1.29
0.97
0.95**
0.96**
0.95**
0.82
0.014
0.015
0.016
1.166
1.41
1.6
1.7
0.99**
0.99**
0.99**
0.98**
0.28
0.28
0.24
0.23
1.97
1.79
1.65
1.47
0.97**
0.96**
0.95**
0.96**
0.82
0.39
0.48
0.48
5938
J. Appl. Sci. Res., 9(11): 5930-5940, 2013
Comparison between rate constants of Elovich equation for different pollutants as affected by zeolite and
Bentonite applied in soils:
Figure (4) represents the comparison between Elovich rate constants of Cd, Ni and Cu desorbed from sandy
soil as affected by zeolite and bentonite applied at three rates. Generally, according to the standard deviation
(SD) it should be mentioned that clay minerals applied in both soils significantly minimize the rate of HM
release. However, no significant difference was observed between different rates of applied materials. Also, data
referred that both clay minerals used significantly reduced HM concentration in the order Cd<Ni<Cu. Finally,
the effect of zeolite in decreasing the rate of heavy metals studied was more pronounced than bentonite.
Although the same trend was observed in calcareous soils, the percent of decrease in rate of pollutants
release in this soil was significantly less than the sandy soil. Compared to control treatment data represented in
figure 4 showed that at low rate of application, zeolite decreased the rate of Cd desorbed from calcareous soil by
about 6% under control, increasing the application rate of zeolite to 50 and 75 g/kg only decreased the rate of
desorption by about 7 and 9% respectively, almost the same trend was observed in bentonite treatment. The
effect of the same clay minerals was varied with Ni compared to Cd. At low concentration of zeolite, the
decreasing order of the rate was 14.2% under control at low concentration applied of zeolite, increasing the
application rate of the mineral, led to decrease the rate of Ni desorption by about 16 and 18% at medium and
high concentration respectively. In the case of Bentonite, the corresponding values of decreasing order were
about 5, 9 and 11% compared to control treatment. The decreasing of the rate of Cu was drastically affected by
soil type and clay minerals used and were more pronounced compared to Cd and Ni. Numerically, data indicated
that rate constants of Cu were decreased by about 60-63% in zeolite and 58-60% according to the concentration
of remediation material applied in sand y soil. The corresponding values of calcareous soil were 14-28 % and
12-19 % in zeolite and bentonite respectively. It should be mentioned that the decreasing order of pollutants
applied is agreed with the charge density and hydrated ion diameter of the studied pollutants.
As a conclusion, attention has focused on the development of in situ immobilization methods that are
generally economic and promising tool in minimizing hazards of HM in soils. The obtained results showed the
advantage and suitability of using such technique in the polluted soils especially the sandy one. The application
of 50g kg-1 of zeolite or bentonite in the soil is an economic concentration. Also, these remediation materials
could be suitable under specific condition of contamination with Copper or Nickel because of significant
minimizing of these pollutants.
Sandy Soil:
Zeolite
rate constants of Elovich equation
25
20
15
con
c1
10
c2
c3
5
0
Cd
Ni
Cu
Pollutants studied
Bentonite
Rate constants of Elovich
equation
25
20
con
15
c1
c2
10
c3
5
0
Cd
Ni
Pollutants studied
Cu
5939
J. Appl. Sci. Res., 9(11): 5930-5940, 2013
Calcareous soil:
zeolite
rate constants of Elovich
equation
25
20
con
c1
15
c2
10
c3
5
0
Cd
Ni
Cu
Pollutants studied
Bentonite
Rate constants of Elovich
equation
25
20
con
c1
c2
c3
15
10
5
0
Cd
Ni studied
Pollutants
Cu
Fig. 4: Rate constant of Elovich equation represents heavy metals release from sandy and calcareous soils as
affected by remediation materials applied at different rates.
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