adsorption- desorption for some heavy metals in the presence of
TRANSCRIPT
IJRRAS 12 (3) ● September 2012 www.arpapress.com/Volumes/Vol12Issue3/IJRRAS_12_3_26.pdf
536
ADSORPTION- DESORPTION FOR SOME HEAVY METALS IN THE
PRESENCE OF SURFACTANT ON SIX AGRICULTURAL SOILS
Rounak M. Shariff 1
& Lawen S. Esmail 2
1,2 The University of Salahaddin- Erbil, College of Science, Department of Chemistry, Kurdistan Region, Iraq
ABSTRACT
The present work investigate the effects of surfactant on the sorption of some heavy metals as Zinc, Nicle and
Copper at different initial concentrations on six selected soil samples through batch equilibrium experiments. The
pH-adjusted for each metal has been varied from 3 to7. Linear, Freundlich and Langmuir models were used to
describe the sorption processes. The sorption data fitted very well with both Freundlich and Langmuir isotherm
model which gave high correlation coefficients. Freundlich coefficient KF values for adsorption process varied
between 1.582 - 2.121 mlg-1
, 1.781- 2.054 mlg-1
and 1.291- 1.958 mlg-1
for Zinc, Nicle and Copper respectively.
Langmuir coefficient KL values for adsorption process varied between 0.012 - 0.029 mlg-1
, 0.017 - 0.057 mlg-1
and
0.008- 0.021 mlg-1
for Zinc, Nicle and Copper respectively. The pseudo- second order kinetic model was most
agreeable with the experiments. An inionic surfactants sodium dodecyl sulfate (SDS) at critical micelles
concentration (cmc ) were tested for their adsorption-desorption potential, was found to be fairly effective to
removal of more than 61, 64, and 68% of sorbed metals Zinc, Nicle and Copper respectively. The Freundlich
coefficient for desorption processes KFdes values varied between 1.637 - 1.944 mlg-1
, 1.652- 2.311 mlg-1
and 1.546-
2.304 mlg-1
for Zinc, Nicle and Copper respectively. Langmuir coefficient KLdes values for desorption process varied
between 0.025 - 0.080 mlg-1
, 0.083 - 0.117 mlg-1
and 0.041- 0.222 mlg-1
for Zinc, Nicle and Copper respectively.
Keywords: Adsorption- Desorption Isotherms, Zinc, Nicle, Copper, Surfactant.
1. INTRODUCTION
Heavy metals are toxic to our environmental quality, and pose a threat to groundwater through that metal
contaminants can remain on site for long time until they are been removed. Remediation of heavy metal
contaminated soils represents a formidable challenge [1]. The Sorption of heavy metals onto soil particles affects the
movement and fate of heavy metals in soil. Therefore, accurate description of the retention or sorption process of
heavy metal is important. The sorption –desorption of heavy metals from soils can affected by many factors as pH,
temperature, and residence time. The effective remediation of contaminated soils should be explained through the
mechanism of heavy metal interaction with soil and factors that affect their retention and /or release from these
particles [2&3].
Surfactants have shown some potential for remediation of heavy metal from soil. It is possible that surfactant
adsorption may displace adsorbed metals, thereby mobilizing them. Factors affecting soil washing/soil flushing
processes include clay content, humic material, metal concentration, particle size distribution/soil texture, separation
coefficient, and wash solution [4]. The mechanism of surfactant enhanced heavy metal removal from soil surface is
ion exchange, precipitation-dissolution, and counterion binding [5&6]. It is necessary to take into account the
characteristics of the surfactant (e.g., chemical structure, hydrophilic-lipophilic balance [HLB], or its concentration
in the soil-water system, the solubility and hydrophobicity of the characteristics of soil (e.g., OM, clay content)
[7&8]. The concentration at which micelles form is known as the critical micelle concentration (cmc), surfactants
above the cmc level may greatly increase the solubility of less hydrophilic organic pollutants. Surfactants are
classified according to the nature of the hydrophilic portion of the molecule [9&10]. Zinc is the most common
elements in the earth's crust it is highly soluble and therefore very mobile in aquatic system [11]. Nickel is a very
abundant natural element. Pure nickel is a hard, silvery-white metal .Nickel is carcinogenic metal and associated
with reproductive problems and birth defect [12] . Copper is a reddish-colored metal; it has its characteristic color
because of its band structure [13].
2. MATERIALS AND METHODS
2.1. Soils
Fresh soil samples were collected from six main agricultural locations in kurdistan region representing a range of
physico-chemical properties. Subsamples of homogenized soils were analyzed for moisture content, organic matter
content, particle size distribution, texture, pH, loss on ignition and exchangeable basic cations. The detail was
characterized in our previous article[8].
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
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2.2. Metals
Analytical grad substituted heavy metals (Zn, Ni, and Cu) were selected for adsorption studies. Zn(NO3)2.6H2O
(fluka AG, Chemische fabrik, CH-9470 Buchs). NiCl2.6H2O (fluka, Garntie,MG 237.71, Switzend). CuCl2.H2O
(B.D.H.laboratory chemicals, trade mark product No.10088,England). The anionic sodium dodecyl sulphate (SDS),
( B.D.H), formula is C18H29SO4Na, and the molecular weight is 448 g moL-1
, while the cmc is 2.38 gL-1
. All
chemicals used were of analytical grade reagents and used without pre-treatments. Standard stock solutions of the
metals were prepared in deionised water.
2.3. Adsorption Experiments
Kinetic studies indicated that metal ion adsorption were characterized by a rapid adsorption processes, for Zn, Ni,
and Cu were carried out through batch method[14&15]. Duplicate air-dried soil samples were equilibrated with
different metal initial concentration (50, 100, 150 and 200) μgml-1
, were for each metal alone at the soil solution
ratios 1:10 gml-1
, in 18 ml glass tube fitted with Teflon-lined screw caps. The samples plus blanks (no metal) and
control (no soil). The samples were shaken continuously at temperature controlled (25 0C) water bath shaker (185
rpm) for different contact time intervals (15, 30, 60, 120, 180, 240, 480 and 600) hours. The tubes were centrifuged
for 20 min. at 3500 rpm. The clear supernatant was removed and analyzed for the metal ion of Zn, Ni, and Cu
solution with by atomic absorption spectrophotometer AAS. The initial pH solution values were adjusted at 6.0 for
Zn, 5.6 for Ni, and 5.9 for Cu using 0.1M NaOH and 0.1M HCl. The total amount of metal adsorbed in the
adsorption processes was calculated from the difference between the amount added initially and that remaining in
solution after equilibration. The measured liquid phase concentrations were then used to calculate the adsorption
capacity. Desorption experiments were done as each test tube was placed in a thermostated shaker at 25ºC after
equilibration for 24 h with different metals concentrations (50, 100, 150, and 200) µg ml-1
, the samples were
centrifuged, 5ml of supernatant was removed from the adsorption equilibrium solution and immediately replaced by
5ml of SDS and was this repeated for four times. The resuspended samples were shaken for (15, 30, 60, 120, 180,
240, 480 and 600) min for the kinetic study. Desorption of the metal that remained on soil at each desorption stage
was calculated as the difference between the initial amount adsorbed (the amount of metal sorbed at equilibrium
concentration corresponding to the initial concentration) and the amount desorbed (after each removing), all
determinations were carried out in duplicate.
Competitive metal ion adsorption-desorption between soil and surfactant in the soil-metal-water-surfactant system,
in the presence SDS, at concentrations of 0.1cmc, cmc, and 10cmc were conducted adsorption-desorption
isotherms[12&16]. The same procedure were repeated in the presence of SDS for the three metals alone and for the
same agitation time, and the desorption done by removing 5ml from the adsorption equilibrium solution and
immediately replaced by 5ml of water and was this repeated for four times.
3. DATA ANALYSIS
3.1. Kinetic Model
The amount of metals adsorbed (qt) per gram of soil (μgg-1
) at time t, was calculated as follows[14]:
(1)
(2)
(3)
Co and Ct are the metal concentration in liquid phase at the initial and time t (in μg.ml-1
) respectively, M is the
weight of the soil (g), and V is the volume of the solution (ml). For the desorption intestate of (Co : Ce is used
which means the equilibrium metal concentration), equation 2 calculate the sorption capacity, and equation 3
calculate the recovery or percent of metal removal. Fig. 1-a,b, and c plotted the R% vis pH for 100 µgml-1
for a-
Zinc b-Nicle, and c- Copper.
3.1. 1. Pseudo-First Order Equation
The pseudo-first order rate expression known as Lagergren equation which describes the adsorption rate based on
the adsorption capacity, generally expressed as [17&18]:
M
VCCq tot *)(
1000**)(
M
VCeCq oe
0
100*)(%
CCeCR o
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
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)(1 tet qqK
dt
dq (4)
Where qe and qt are the adsorption capacities at equilibrium and at time t, respectively (µgg-1
) and K1 is the rate
constant of pseudo-first order adsorption (min-1
). After integration and applying boundary condition t=0 to t=t and
qt=0 to qt=qt, the integrated form of equation (4) becomes as follows:
tK
eLogqtqeqLog303.2
1)( (5)
When the values of log (qe-qt) were linearly correlated with t, the plot of log (qe-qt) versus t will give a linear relation
ship from which K1 and qe can be determined from the slope and intercept of the graph respectively all the results
shown in table 1-a, b, and c.
3.1. 1. Pseudo-Second Order Equation
pseudo–second order kinetic expression for the adsorption system of divalent metal ions. This model has since been
widely applied to a number of metal/adsorbent adsorption system to investigate the mechanism of adsorption and the
rate constants for the adsorption of metal ions on to soil samples the pseudo- second order equation given below was
used[19&20]:
eet q
t
qKq
t
2
2
1 (6)
in which K2 is the rate constant for the pseudo second order adsorption (g.μg-1
min-1
). The initial rate can be obtained
as qt/t approaches zero:
2
2 eqKh (7)
Where h is the initial adsorption rate (μgg-1
min-1
). The results were also analyzed using the pseudo second order
model. The linear variation of t/qt vise t for the selected soil samples at different initial metal ion concentration Zn,
Ni, and Cu, the values of qe and K2 are determined from the slope and intercepts respectively. The initial adsorption
rate (h ) , the pseudo second order regression of coefficients of determination (R2) and amount of metal ions
adsorbed at equilibrium (qe) obtained from the kinetic experiments were all given in Table 1 a, b, and c.
3.2. Adsorption-Desorption Isotherms
3.2.1. Linear Adsorption-Desorption Isotherms
In the linear adsorption model, adsorption is described with distribution coefficient or Kd(ml/g) as [21]:
(8)
Where Cs (μg/g) is the concentration of the metal on the solid and Ce (μg/ml) is the concentration of the metal in the
aqueous phase. Kd is the distribution coefficient, which obtained from the slope of plot of Cs versus Ce and it
indicates the mobility of the metal. Values of R2
revealed that adsorption isotherms were non linear under all
conditions tested so our data were not fit the linear distribution model. The values of Kd and R2 obtained are listed in
Table 2,3,4.
.
3.2.2. Frendlich Adsorption-Desorption Isotherms
The Freundlich isotherm is the most widely used non linear adsorption model. Freundlich isotherm is often used for
heterogeneous surface energy systems. A linear form of the Freundlich equation is given as [22]:
(9)
eds CKC
eF Cn
KLogqe log1
log
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
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Where KF is the Freundlich distribution coefficient (ml/g) related to adsorption capacity and n the exponent
(correction factor) related to adsorption intensity. KFa nd n can be determined from the linear plot of Log qe versus
Log Ce, as shown in Fig. 2 and 4.The model is an empirical equation based on the distribution of solute between the
solid phase and aqueous phase at equilibrium[23]. Values of KF were in Table 2,3,4.revealed that our experimental
data fit to Freundlich model rather than to Linear model. Adsorption isotherm parameters were calculated using the
linearized form of Freundlich equation.
Desorption isotherm parameters were calculated using the linearized form of Freundlich equation[19]:
(10)
The values of KFdes and 1/n calculated from this regression equation showed that Freundlich adsorption
model effectively describes isotherms for the metalses in all cases. Cs and Ce were defined previously, KFdes is
Freundlich desorption coefficients, and n is a linearity factor, it is also known as desorption intensity [20-22]:
(Table2,3,4.)
3.2.3. Langmuir Adsorption isotherm
Data from the batch adsorption conform to Langmuir equation[24&25]:
(11)
Cm is the maximum amount of metal adsorbed (adsorption maxima, µg ml-1
), it reflects the adsorption strength and
KL is the Langmuir adsorption coefficient, binding energy coefficient. The results were summarized in (Table 2, 3,
4) and shown in Fig. 3, and5.
4. RESULTS AND DISSCUSSION
The most important parameter in the adsorption processes is the initial pH value of the solution, which influences
both the adsorbent surface metal binding sites and the metal chemistry in water[26]. Fig. 1-a, b, and c represents the
influence of pH on the adsorption of 100 μgml-1
for a- Zinc b-Nicle c- Copper on selected soils. At pH less than 3.0,
H+
ions compete with Zn+2
, Ni+2
and Cu+2
ions from reaching binding site on the surface of the adsorbent by
repulsive forces. At pH higher than 5 formation of hydroxide ions causes’ precipitation, for this reason the
maximum pH value were selected to be 6.0 for Zi+2
, 5.6 for Ni+2
, and 5.9 for Cu+2
ions[27]. The non-linear
adsorption isotherms might be expected for the compounds for which competition for a limited number of cation
exchange sites contributes significantly to adsorption process.
eFdess Cn
KLogC log1
log
m
e
Lms
e
C
C
KCC
C
1
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Figure 1. The influence of pH on the adsorption of 100ppm for a-Zinc
b-Nicle, and c- Copper on selected samples.
Kinetic studies showed that the sorption rates could be described by both pseudo first-order and pseudo second-
order models. Data in table 1-a, b, and c summarized the K1 values ranged between 0.001-0.005 min- with R
2 0.790-
0.996, 0.002-0.009 min- with R
2 0.723-0.996, and 0.002-0.008 min
-1 with R
2 0.856-0.944 for Zinc, Nicle, and
Copper respectively. The pseudo-second order model showed a better fit with a rate constant K2 value ranged
between 2.82x10-6
-8.13x10-5
g.μg-1
min-1
with R2 value 0.906-0.998 and h value ranged between 0.542-2.257 μgg
-
1min
-1for Zinc. K2 value ranged between 2.74x10
-6-1.13x10
-4 g.μg
-1min
-1 with R
2 value 0.943-0.999 and h value
ranged between 0.613-3.985 μgg-1
min-1
for Nicle. K2 value ranged between 2.98x10-6
-2.24x10-4
g.μg-1
min-1
with R2
value 0.856-0.944 and h value ranged between 0.455-7.438 μgg-1
min-1
for Copper[19&28].
a-
b-
c-
020406080
3 4 5 6 7 8
R%
pH
0
20
40
60
3 4 5 6 7 8
R%
pH
0
20
40
60
3 4 5 6 7 8
R%
pH
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
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Table 1-a. The kinetic parameters of Adsorption process of Zinc using Pseudo-first order Lagergren model K1
and Pseudo-second order model K2 on the selected soil samples.
Soil
Initial
Conc.
μgml-1
Pseudo-first order Pseudo-second order model.
K1 (min-1) R2 K2( g.μg-1min-1) h(μgg-1min-1) R2
S1 50 0.003 0.987 7.36x10-6 0.773 0.991
100 0.004 0.790 5.12x10-6 1.078 0.998
150 0.003 0.919 3.21x10-6 1.611 0.997
200 0.003 0.994 3.02x10-6 1.651 0.936
S2 50 0.003 0.975 6.69x10-6 0.819 0.972
100 0.004 0.987 4.71x10-6 1.323 0.958
150 0.004 0.938 3.58x10-6 1.753 0.955
200 0.003 0.977 2.84x10-6 1.906 0.970
S3 50 0.005 0.964 6.48x10-6 0.858 0.980
100 0.005 0.987 5.16x10-6 1.024 0.987
150 0.004 0.988 3.26x10-5 1.358 0.974
200 0.003 0.980 2.89x10-6 2.257 0.906
S4 50 0.003 0.976 9.27x10-6 0.486 0.994
100 0.004 0.985 5.47x10-6 1.044 0.965
150 0.005 0.957 3.76x10-5 9.115 0.979
200 0.003 0.957 3.30x10-6 1.575 0.987
S5 50 0.001 0.950 1.02x10-5 0.542 0.914
100 0.004 0.976 5.04x10-6 1.018 0.983
150 0.002 0.996 8.13x10-5 2.077 0.989
200 0.002 0.991 3.39x10-6 1.457 0.980
S6 50 0.003 0.977 8.89x10-6 0.784 0.907
100 0.003 0.984 4.63x10-6 1.151 0.974
150 0.003 0.941 3.77x10-5 1.320 0.975
200 0.002 0.962 2.82x10-6 1.773 0.978
Table 1-b. The kinetic parameters of Adsorption process of Nicle using Pseudo-first order Lagergren model K1
and Pseudo-second order model K2 on the selected soil samples.
Soil
Initial Conc. μgml-1
Pseudo-first order Pseudo-second order model.
K1 (min-1) R2 K2( g.μg
-1min-1) h(μgg-1min-1) R2
S1 50 0.005 0.944 7.57x10-6 0.656 0.955
100 0.008 0.948 5.18x10-6 0.915 0.993
150 0.003 0.869 7.40x10-5 3.584 0.996
200 0.009 0.792 3.19x10-6 1.569 0.943
S2 50 0.005 0.939 6.83x10-6 0.701 0.997
100 0.007 0.921 4.26x10-6 1.108 0.999
150 0.004 0.995 1.08x10-4 3.907 0.999
200 0.008 0.787 2.74x10-6 1.714 0.999
S3 50 0.006 0.939 6.38x10-6 0.739 0.999
100 0.009 0.876 4.46x10-6 1.078 0.999
150 0.005 0.964 1.09x10-4 3.821 0.999
200 0.004 0.994 2.71x10-6 1.711 0.999
S4 50 0.004 0.996 1.33x10-5 0.344 0.999
100 0.006 0.723 4.80x10-6 0.967 0.999
150 0.002 0.949 1.10x10-4 3.729 0.999
200 0.004 0.991 3.08x10-6 1.510 0.999
S5 50 0.002 0.731 7.58x10-6 0.613 0.990
100 0.004 0.879 4.70x10-6 0.979 0.995
150 0.005 0.919 1.13x10-4 3.985 0.999
200 0.003 0.907 3.07x10-6 1.512 0.990
S6 50 0.006 0.862 8.47x10-6 0.548 0.997
100 0.007 0.879 3.99x10-6 1.165 0.999
150 0.006 0.941 1.10x10-4 3.816 0.999
200 0.008 0.809 2.98x10-6 1.558 0.999
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Table 1-c. The kinetic parameters of Adsorption process of Copper using Pseudo-first order Lagergren model K1
and Pseudo-second order model K2 on the selected soil samples.
Soil
Initial Conc. μgml
-1
Pseudo-first order Pseudo-second order model.
K1 (min-1) R2 K2( g.μg
-1min
-1) h(μgg-1
min-1)
R2
S1 50 0.003 0.983 1.76x10-5
1.357 0.905
100 0.004 0.995 5.82x10-6
0.958 0.951
150 0.003 0.989 4.65x10-5
2.093 0.935
200 0.003 0.990 2.98x10-6
1.458 0.934
S2 50 0.005 0.973 7.65x10-6
0.735 0.955
100 0.004 0.947 6.13x10-6
1.471 0.856
150 0.004 0.952 8.87x10-6
2.683 0.953
200 0.005 0.992 3.32x10-6
1.866 0.948
S3 50 0.009 0.995 7.75x10-6
0.764 0.972
100 0.007 0.991 5.95x10-6
0.931 0.986
150 0.003 0.963 2.26x10-5
6.732 0.944
200 0.007 0.995 3.60x10-6
1.817 0.944
S4 50 0.002 0.995 8.65x10-5
0.522 0.994
100 0.002 0.994 7.05x10-6
0.774 0.953
150 0.002 0.837 3.80x10-5
7.057 0.963
200 0.003 0.923 4.17x10-6
1.238 0.980
S5 50 0.004 0.979 1.11x10-5
0.455 0.987
100 0.004 0.965 5.66x10-6
0.862 0.936
150 0.004 0.994 1.37x10-4
2.195 0.989
200 0.003 0.995 3.63x10-6
1.328 0.994
S6 50 0.006 0.899 1.89x10-4
1.474 0.948
100 0.007 0.956 7.54x10-5
1.474 0.967
150 0.006 0.966 2.24x10-4
7.438 0.932
200 0.008 0.987 4.62x10-5
2.404 0.987
Data demonstrated in table 2,a and b represents the values of partition coefficient Kd for adsorption of Zinc on
selected soil sample. The Kd , standard error S.E , and R2 ranged from 6.696 -12.57 mlg
-1, 0.139-0.192, and 0.705-
0.946 for adsorption of Zinc respectively. While Kd, S.E , and R2 ranged from 2.816 -3.948 mlg
-1, 0.102-0.188, and
0.740-0.780 for desorption of Zinc in presence of SDS respectively. To investigate the effect of surfactants on
adsorption behavior of metals[11], batch equilibrium experiments performed. The presence of anionic surfactant
SDS in adsorption of Zinc Kd, S.E , and R2 ranged from 4.762 -8.825 mlg
-1, 0.123-0.159, and 0.735-0.895
respectively . While Kd, S.E , and R2 ranged from 6.342 -10.52 mlg
-1, 0.132-0.164, and 0.635-0.765 for desorption
of Zinc respectively.
Data demonstrated in table 3, a, and b represents the values of partition coefficient Kd for adsorption of Nicle on
selected soil sample. The Kd, standard error S.E, and R2 ranged from 8.386 -11.09 mlg
-1, 0.129-0.161, and 0.706-
0.765 for adsorption of Nicle respectively. While Kd, S.E, and R2 ranged from 2.915 -8.382 mlg
-1, 0.138-0.150, and
0.627-0.688 for desorption of Nicle in presence of SDS respectively. The presence of anionic surfactant SDS in
adsorption of Nicle Kd, S.E, and R2 ranged from 4.804 -7.240 mlg
-1, 0.121-0.158, and 0.684-0.870 respectively.
While Kd, S.E, and R2 ranged from 7.466 -14.77 mlg
-1, 0.110-0.171, and 0.708-0.840 for desorption of Nicle
respectively.
Data demonstrated in table 4, a and b represents the values of partition coefficient Kd for adsorption of Copper on
selected soil sample. The Kd, standard error S.E, and R2 ranged from 5.293 -9.325 mlg
-1, 0.125-0.143, and 0.709-
0.766 for adsorption of Copper respectively. While Kd, S.E, and R2 ranged from 2.107 -4.377 mlg
-1, 0.119-0.164,
and 0.711-0.962 for desorption of Copper in presence of SDS respectively. The presence of anionic surfactant SDS
in adsorption of Copper Kd, S.E, and R2 ranged from 2.630 -6.529 mlg
-1, 0.116-0.188, and 0.708-0.786 respectively.
While Kd, S.E, and R2 ranged from 7.942 -17.89 mlg
-1, 0.109-0.186, and 0.605-0.731 for desorption of Copper
respectively.
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
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A smaller Kd value indicates that a smaller amount of the soil-borne element is needed to produce 1mlg-1
of
the element in solution phase thus potentially higher exposure risks[13&29].
The values of KF, n, S.E and R2 demonstrated in table 2, a, and for adsorption of Zinc on selected soil
sample. The KF, n, S.E, and R2 ranged from 1.582 - 2.121 mlg
-1, 1.727-2.801, 0.148-0.163, and 0.813-0.994 for
adsorption of Zinc respectively. While KFdes, n, S.E, and R2 ranged from 0.943 -1.362mlg
-1, 1.645-1.961, 0.135-
0.147, and 0.878-0.925 for desorption of Zinc in presence of SDS respectively. The presence of anionic surfactant
SDS in adsorption of Zinc KF, n, S.E, and R2 ranged from 1.337-1.839mlg
-1, 1.605-2.342, 0.136-0.153, and 0.751-
0.980 respectively. While KFdes, n, S.E, and R2 ranged from 1.637- 1.944mlg
-1, 1.869-2.681, 0.149-0.162, and 0.763-
0.930 for desorption of Zinc respectively.
The values of KF, n, S.E and R2 demonstrated in table 3, a, and b for adsorption of Nicle on selected soil
sample. The KF, n, S.E, and R2 ranged from 1.781- 2.054 mlg
-1, 1.968-2.597, 0.149 -0.159, and 0.886-0.999 for
adsorption of Nicle respectively. While KFdes, n, S.E, and R2 ranged between 0.897-1.906 mlg
-1, 1.347-2.203, 0.138 -
0.154, and 0.857-0.964 for desorption of Nicle in presence of SDS respectively. The presence of anionic surfactant
SDS in adsorption of Nicle KF, n, S.E, and R2 ranged from 1.422 -1.725mlg
-1, 1.194-2.020, 0.145-0.157, and 0.781-
0.941respectively. While KFdes, n, S.E, and R2 ranged from 1.652- 2.311mlg
-1, 2.074-5.780, 0.154-0.166, and 0.749-
0.975 for desorption of Nicle respectively.
The values of KF, n, S.E and R2 demonstrated in table 4, a, and b for adsorption of Copper on selected soil
sample. The KF, n, S.E, and R2 ranged from 1.291- 1.958 mlg
-1, 1.494-2.545, 0.143-0.157, and 0.815-0.997 for
adsorption of Copper respectively. While KFdes, n, S.E, and R2 ranged from 0.832-1.308mlg
-1, 0.772-1.727, 0.132-
0.145, and 0.886-0.987 for desorption of Copper in presence of SDS respectively. The presence of anionic surfactant
SDS in adsorption of Copper KF, n, S.E, and R2 ranged from 0.865-1.920 mlg
-1, 1.279-2.778, 0.134-0.148, and
0.716-0.872 respectively. While KFdes, n, S.E, and R2 ranged from 1.546- 2.304mlg
-1, 1.751-5.587, 0.156-0.172, and
0.817-0.980 for desorption of Copper respectively. Our result agreed with literature. The results reveal that the
model parameters are largely dependent on the initial sorbate concentration value. The KF indicates the binding
affinity between the sorbate and sorbent[30].
The values of KL, Cm, S.E and R2 demonstrated in table 2, a, and for adsorption of Zinc on selected soil
sample. The KL, Cm, S.E, and R2 ranged from 0.012 - 0.029 mlg
-1, 1000μgg
-1, 0.146-0.153, and 0.877-0.974 for
adsorption of Zinc respectively. While KL, Cm, S.E, and R2 ranged from 0.003 -0.013mlg
-1, 500μgg
-1, 0.135-0.144,
and 0.750-0.808 for desorption of Zinc in presence of SDS respectively. The presence of anionic surfactant SDS in
adsorption of Zinc KL, Cm, S.E, and R2 ranged from 0.008-0.017mlg
-1, 1000 μgg
-1, 0.149-0.157, and 0.740-0.944
respectively. While KL, Cm, S.E, and R2 ranged from 0.025 - 0.080 mlg
-1, 500μgg
-1, 0.133-0.141, and 0.827-0.961
for desorption of Zinc respectively.
The values of KL, Cm, S.E and R2 demonstrated in table 3, a, and b for adsorption of Nicle on selected soil
sample. The KL, Cm, S.E, and R2 ranged from 0.017 - 0.057 mlg
-1, 1000 μgg
-1, 0.147 -0.245, and 0.878-0.987 for
adsorption of Nicle respectively. While KL, Cm, S.E, and R2 ranged between 0.008-0.038 mlg
-1, 500 μgg
-1, 0.136 -
0.141, and 0.838-0.976 for desorption of Nicle in presence of SDS respectively. The presence of anionic surfactant
SDS in adsorption of Nicle KL, Cm, S.E, and R2 ranged from 0.007 -0.019mlg
-1, 1000 μgg
-1, 0.152-0.156, and 0.724-
0.939 respectively. While KL, Cm, S.E, and R2 ranged from 0.083 - 0.117mlg
-1, 500μgg
-1, 0.132-0.143, and 0.855-
0.996 for desorption of Nicle respectively.
The values of KL, Cm, S.E and R2 demonstrated in table 4, a, and b for adsorption of Copper on selected soil
sample. The KL, Cm, S.E, and R2 ranged from 0.008- 0.021 mlg
-1, 1000 μgg
-1, 0.147-0.157, and 0.841-0.966 for
adsorption of Copper respectively. While KL, Cm, S.E, and R2 ranged from 0.003-0.018mlg
-1, 500μgg
-1, 0.138-0.146,
and 0.715-0.948 for desorption of Copper in presence of SDS respectively. The presence of anionic surfactant SDS
in adsorption of Copper KL, Cm, S.E, and R2 ranged from 0.004-0.012 mlg
-1, 1000 μgg
-1, 0.153-0.162, and 0.825-
0.957 respectively. While KL, Cm, S.E, and R2 ranged from 0.041- 0.222mlg
-1, 500μgg
-1, 0.134-0.139, and 0.912-
0.986 for desorption of Copper respectively. The Langmuir sorption model served to estimate the maximum metal
adsorption values Cm. The constant KL represents the affinity between the sorbate and the sorbent and it indicate the
binding capasity[31].
Important aspect to be considered is the interaction of surfactant with soil, since it may, on one hand, alter
the surfactant concentration in solution, thereby decreasing its efficiency for desorption, and on the other, alter the
soil surface, where surfactant molecules may be adsorbed in the form of monomer or forming hemicelles or
admicelles. Thus surfactant adsorption increases the organic C content of the soil and increased hydrophobic
surfaces, which may contribute to decrease in the organic compound desorption. Of all the above processes, the
study of surfactant-enhanced desorption for organic pollutants adsorbed on soil has been addressed by many
investigators in recent years although such information can only be considered a beneficial effect in the context of
major engineered remediation processes. In the study of surfactant- enhanced desorption , enhanced solubility of
pollutants has been clearly indicated by several authors at surfactant concentrations higher than the cmc. However,
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
544
at surfactant concentrations below the cmc competitive adsorption of organic compound by soil and/or by a
surfactant in solution may occur, and hence an increase or decrease in desorption of compound from soil, depending
on the characteristics of soil and organic compound[32].
Desorption of the neutral form was completely reversible, however, the charged species exhibited
desorption-resistance fraction. The difference in sorption and desorption between the neutral and charged species is
attributed to the fact that the neutral form partition by the hydrophobic binding to the soil, while anionic sorbs by a
more specific exothermic adsorption reaction[33]. Desorption of soil-associated metal ions and possible mechanisms
have received considerable attention in literature[34]. Desorption rates of metal ions can be characterized by three
types of processes, rapid desorption, rate-limited desorption, and a fraction that does not desorbed over experimental
time scale. Many factors affect the adsorption-desorption of metalion type; soil properties, organic matter, clay
content, soil pH and environmental conditions[35]. The main effect of surfactant at concentrations close to cmc is to
increase the affinity of metal ion for the soil with, except for soils high in clay content where the surfactant effect is
to enhance the affinity of metal ion for aqueous phase.
Table 2-a. The characteristic parameters of linear, Freundlich and Langmuir models
isotherms for Adsorption-desorption process of Zinc on the selected soil samples.
Mo
dels
Pa
ram
eter
Soils
S1 S2 S3 S4 S5 S6
(ad
sorp
tion
)
linea
r
.
D
istr.
Kd (calc) 10.43 12.57 12.41 6.696 6.802 9.697
S.E 0.148 0.164 0.183 0.192 0.185 0.139
R2 0.708 0.802 0.946 0.855 0.751 0.705
Fre
un
dlic
h co
ffi.
KF(mL/g) 1.944 2.049 2.121 1.607 1.582 1.873
S.E 0.159 0.163 0.162 0.148 0.149 0.157
nF 2.242 2.415 2.801 1.783 1.727 2.096
R2 0.920 0.994 0.813 0.954 0.944 0.976
La
ng
mu
ir. coffi.
KL (ml/g) 0.023 0.029 0.023 0.012 0.013 0.020
S.E 0.146 0.152 0.145 0.153 0.152 0.147
Cm(μg/g) 1000 1000 1000 1000 1000 1000
R2 0.914 0.974 0.877 0.917 0.923 0.929
(deso
rptio
n)
Des.D
i
str.
coffi
Kd (calc) 3.386 3.434 3.834 2.816 3.168 3.948
S.E 0.188 0.102 0.143 0.184 0.134 0.181
R2 0.747 0.740 0.780 0.754 0.763 0.759
Fre
un
dlic
h co
ffi.
KFdes(mL/g) 0.943 1.027 1.073 1.103 1.302 1.297
S.E 0.141 0.142 0.146 0.135 0.137 0.143
nF 1.944 1.754 1.484 1.645 1.961 1.855
R2 0.925 0.908 0.910 0.912 0.895 0.878
La
ng
mu
i
r. coffi.
KL (ml/g) 0.009 0.010 0.010 0.010 0.003 0.013
S.E 0.138 0.137 0.135 0.144 0.143 0.136
Cm(μg/g) 500 500 500 500 500 500
R2 0.763 0.765 0.746 0.808 0.798 0.750
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
545
Table 2-b. The characteristic parameters of linear, Freundlich and Langmuir models isotherm for Adsorption-
desorption process of Zinc in the presence of SDS at cmc concentration, on the selected soil samples.
Mo
dels
Pa
ram
ete
r
Soils
S1 S2 S3 S4 S5 S6
(ad
sorp
tion
)
linea
.
Distr
.
Kd (calc) 4.884 8.825 6.877 4.871 4.762 7.349
S.E 0.123 0.136 0.138 0.129 0.159 0.124
R2 0.735 0.759 0.785 0.769 0.763 0.895
Freu
nd
lich
co
ffi.
KF(mL/g) 1.689 1.838 1.839 1.377 1.492 1.689
S.E 0.142 0.136 0.149 0.143 0.142 0.153
nF 2.247 2.083 2.342 1.605 1.808 1.879
R2 0.776 0.980 0.858 0.818 0.751 0.943
La
ng
m
uir
.
co
ffi.
KL (ml/g) 0.011 0.017 0.013 0.008 0.008 0.014
S.E 0.153 0.149 0.154 0.156 0.157 0.154
Cm(μg/g) 1000 1000 1000 1000 1000 1000
R2 0.740 0.932 0.779 0.754 0.944 0.862
(deso
rp
tion
)
Des.D
ist
r. co
ffi
Kd (calc) 9.995 9.276 10.52 8.826 6.342 9.117
S.E 0.164 0.142 0.143 0.153 0.143 0.132
R2 0.635 0.741 0.765 0.709 0.644 0.655
Freu
nd
lich
co
ffi.
KFdes(mL/g) 1.944 1.671 1.709 1.889 1.784 1.637
S.E 0.159 0.159 0.162 0.155 0.149 0.158
nF 2.653 2.008 1.946 2.681 2.625 1.869
R2 0.907 0.848 0.930 0.878 0.763 0.792
La
ng
m
uir
.
co
ffi.
KL (ml/g) 0.063 0.051 0.080 0.049 0.025 0.041
S.E 0.139 0.133 0.135 0.138 0.141 0.134
Cm(μg/g) 500 500 500 500 500 500
R2 0.961 0.916 0.876 0.920 0.827 0.892
Table 3-a. The characteristic parameters of linear, Freundlich and Langmuir models
isotherms for Adsorption-desorption process of Nicle on the selected soil samples.
Mod
els
Pa
ra
met
er
Soils
S1 S2 S3 S4 S5 S6
(ad
sorp
tion
)
linea
r.
D
istr.
Kd (calc) 8.904 10.37 11.09 8.386 8.398 9.216
S.E 0.133 0.146 0.161 0.133 0.129 0.131
R2 0.765 0.710 0.701 0.706 0.761 0.755
Freu
nd
lich
co
ffi.
KF(mL/g) 1.792 1.944 2.054 1.817 1.781 1.819
S.E 0.155 0.158 0.159 0.153 0.154 0.149
nF 1.968 2.247 2.597 2.070 1.980 2.000
R2 0.886 0.975 0.945 0.998 0.999 0.905
La
ng
m
uir
.
co
ffi.
KL (ml/g) 0.057 0.023 0.024 0.017 0.017 0.020
S.E 0.149 0.147 0.147 0.245 0.149 0.148
Cm(μg/g) 1000 1000 1000 1000 1000 1000
R2 0.878 0.934 0.901 0.974 0.987 0.959
(deso
rp
tion
)
Des.
Dist
r.
co
ffi
Kd (calc) 3.598 3.752 3.876 3.556 2.915 8.382
S.E 0.111 0.118 0.118 0.121 0.162 0.165
R2 0.685 0.647 0.688 0.674 0.692 0.627
Freu
nd
lich
co
ffi.
KFdes(mL/g) 1.176 1.141 1.190 1.391 0.897 1.906
S.E 0.139 0.143 0.145 0.150 0.138 0.154
nF 1.642 1.579 1.667 2.203 1.357 1.347
R2 0.955 0.932 0.908 0.964 0.962 0.857
La
ng
m
uir
.
co
ffi.
KL (ml/g) 0.013 0.013 0.018 0.010 0.008 0.038
S.E 0.139 0.138 0.137 0.140 0.141 0.136
Cm(μg/g) 500 500 500 500 500 500
R2 0.954 0.918 0.861 0.838 0.976 0.848
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
546
Table 3-b. The characteristic parameters of linear, Freundlich and Langmuir models isotherm for Adsorption-
desorption process of Nicle in the presence of SDS at cmc concentration, on the selected soil samples.
Mod
els
Pa
ra
met
er
Soils
S1 S2 S3 S4 S5 S6
(ad
sorp
tion
)
linea
r.
D
istr.
Kd (calc) 6.868 7.240 5.593 5.751 4.804 5.128
S.E 0.128 0.124 0.121 0.123 0.142 0.158
R2 0.734 0.752 0.799 0.772 0.870 0.684
Freu
nd
lich
co
ffi.
KF(mL/g) 1.725 1.708 1.603 1.642 1.422 1.516
S.E 0.152 0.151 0.145 0.146 0.149 0.157
nF 2.020 1.194 1.908 1.976 1.678 1.795
R2 0.901 0.839 0.797 0.781 0.941 0.866
La
ng
m
uir
.
co
ffi.
KL (ml/g) 0.012 0.016 0.019 0.009 0.007 0.008
S.E 0.152 0.152 0.154 0.155 0.156 0.156
Cm(μg/g) 1000 1000 1000 1000 1000 1000
R2 0.873 0.939 0.855 0.907 0.724 0.725
(deso
rp
tion
)
Des.
Dist
r.
co
ffi
Kd (calc) 7.466 14.44 14.77 13.78 11.28 11.97
S.E 0.132 0.110 0.166 0.112 0.171 0.161
R2 0.717 0.708 0.780 0.754 0.840 0.795
Freu
nd
lich
co
ffi.
KFdes(mL/g) 1.652 2.058 1.917 2.311 1.995 1.991
S.E 0.154 0.166 0.167 0.162 0.161 0.162
nF 2.074 3.300 2.217 5.780 2.881 2.762
R2 0.900 0.795 0.910 0.975 0.943 0.749
La
ng
m
uir
.
co
ffi.
KL (ml/g) 0.044 0.100 0.154 0.143 0.083 0.117
S.E 0.137 0.135 0.132 0.143 0.137 0.137
Cm(μg/g) 500 500 500 500 500 500
R2 0.969 0.954 0.855 0.996 0.991 0.958
Table 4-a. The characteristic parameters of linear, Freundlich and Langmuir models
isotherms for Adsorption-desorption process of Copper on the selected soil samples.
Mo
dels
Pa
ram
ete
r
Soils
S1 S2 S3 S4 S5 S6
(ad
sorp
tion
)
linea
r.
D
istr.
Kd (calc) 9.325 9.428 8.521 8.578 5.293 7.818
S.E 0.139 0.143 0.125 0.137 0.133 0.129
R2 0.755 0.709 0.773 0.733 0.766 0.757 Freu
nd
lich
coffi.
KF(mL/g) 1.807 1.945 1.958 1.417 1.418 1.291
S.E 0.157 0.156 0.153 0.143 0.145 0.152
nF 2.000 2.347 2.545 1.494 1.618 2.053
R2 0.913 0.949 0.815 0.997 0.889 0.938 La
ng
mu
ir.
co
ffi.
KL (ml/g) 0.018 0.021 0.015 0.008 0.009 0.015
S.E 0.147 0.149 0.151 0.157 0.156 0.151
Cm(μg/g) 1000 1000 1000 1000 1000 1000
R2 0.865 0.904 0.860 0.956 0.966 0.841
(deso
rp
tion
)
Des.D
istr.
co
ffi
Kd (calc) 2.107 2.183 4.168 2.978 2.645 4.377
S.E 0.154 0.159 0.119 0.164 0.157 0.149
R2 0.901 0.962 0.875 0.712 0.755 0.711
Freu
nd
lich
co
ffi.
KFdes(mL/g) 0.846 0.832 1.296 0.968 0.935 1.308
S.E 0.132 0.136 0.145 0.136 0.134 0.144
nF 1.459 1.433 0.772 1.401 1.431 1.727
R2 0.960 0.987 0.915 0.934 0.886 0.977
La
ng
mu
ir.
co
ffi.
KL (ml/g) 0.006 0.003 0.013 0.009 0.018 0.008
S.E 0.141 0.142 0.139 0.145 0.146 0.138
Cm(μg/g) 500 500 500 500 500 500
R2 0.863 0.794 0.733 0.871 0.715 0.948
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
547
Table 4-b. The characteristic parameters of linear, Freundlich and Langmuir models isotherm for Adsorption-
desorption process of Copper in the presence of SDS at cmc concentration, on the selected soil samples.
Mo
dels
Pa
ram
ete
r
Soils
S1 S2 S3 S4 S5 S6
(ad
sorp
tion
)
linea
r.
D
istr.
Kd (calc) 6.385 6.529 4.684 2.630 3.322 5.128
S.E 0.138 0.135 0.123 0.163 0.188 0.116
R2 0.749 0.719 0.754 0.708 0.756 0.786 Freu
nd
lich
coffi.
KF(mL/g) 1.920 1.868 1.712 0.865 1.069 1.516
S.E 0.147 0.148 0.141 0.134 0.148 0.144
nF 2.778 2.532 2.364 1.279 1.418 1.795
R2 0.816 0.872 0.860 0.879 0.716 0.866 La
ng
mu
ir.
co
ffi.
KL (ml/g) 0.011 0.012 0.008 0.004 0.005 0.009
S.E 0.156 0.156 0.159 0.162 0.161 0.153
Cm(μg/g) 1000 1000 1000 1000 1000 1000
R2 0.957 0.837 0.848 0.912 0.903 0.825
(deso
rp
tion
)
Des.D
istr.
co
ffi
Kd (calc) 7.942 11.18 17.89 13.45 12.57 13.90
S.E 0.126 0.153 0.186 0.112 0.109 0.190
R2 0.605 0.718 0.651 0.731 0.714 0.722
Freu
nd
lich
co
ffi.
KFdes(mL/g) 1.546 1.850 2.094 2.304 2.186 2.114
S.E 0.156 0.167 0.172 0.161 0.161 0.165
nF 1.751 2.369 2.710 5.587 4.048 3.424
R2 0.817 0.821 0.936 0.962 0.980 0.764
La
ng
mu
ir.
co
ffi.
KL (ml/g) 0.041 0.053 0.100 0.111 0.111 0.222
S.E 0.138 0.137 0.134 0.142 0.139 0.137
Cm(μg/g) 500 500 500 500 500 500
R2 0.912 0.986 0.922 0.957 0.996 0.968
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
548
Figure 2. Fitted adsorption isotherm Ferundlich
model for a- Zinc b-Nicle c- Copper
on selected soils samples (♦ S1, ■ S2, ▲ S3, x S4, * S5, ●S6).
a-
b-
c-
22.22.42.62.8
3
1.1 1.4 1.7 2 2.3
log
Cs
log Ce
2.1
2.3
2.5
2.7
2.9
1.1 1.3 1.5 1.7 1.9 2.1 2.3
log
Cs
log Ce
2
2.2
2.4
2.6
2.8
3
1.1 1.3 1.5 1.7 1.9 2.1 2.3
log
Cs
log Ce
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
549
Figure 3. Fitted adsorption isotherm Languir
model for a- Zinc b-Nicle c- Copper
on selected soils samples (♦ S1, ■ S2, ▲ S3, x S4, * S5, ●S6).
a-
b-
c-
0
0.05
0.1
0.15
0.2
0.25
0 50 100 150
Ce
/Cs
Ce(mg/L)
0
0.05
0.1
0.15
0.2
0.25
0 50 100 150
Ce
/Cs
Ce(mg/L)
0
0.05
0.1
0.15
0.2
0.25
0.3
0 50 100 150 200
Ce
/Cs
Ce(mg/L)
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
550
Figure 4. Fitted adsorption isotherm Ferundlich
model for a- Zinc b-Nicle c- Copper in the presence of cmc SDS
on selected soils samples (♦ S1, ■ S2, ▲ S3, x S4, * S5, ●S6).
a-
b-
c-
2
2.2
2.4
2.6
2.8
3
1.2 1.5 1.8 2.1
log
Cs
log Ce
2.1
2.3
2.5
2.7
2.9
1.3 1.5 1.7 1.9 2.1 2.3
log
Cs
log Ce
2
2.2
2.4
2.6
2.8
3
1.3 1.5 1.7 1.9 2.1 2.3
log
Cs
log Ce
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
551
Figure5. Fitted adsorption isotherm Langmiur model for a- Zinc b-Nicle c- Copper in the presence of cmc SDS
on selected soils samples (♦ S1, ■ S2, ▲ S3, x S4, * S5, ●S6).
5. OVERALL CONCLUSIONS Surfactants work as a remediation tool by lowering the contaminant-water interfacial tension and thereby causing a
degree of contaminant mobility, and enhanced contaminant solubility in water, so responsible for increasing the
solubility. The potential of anionoic surfactant to desorb the studied heavy metals from the contaminated matrix
was also investigated. Results showed that anionic surfactant significantly decreased the retention of heavy metals
6. ACKNOWLEDGEMENTS The authors wish to thank all the chemistry staff in Salahaddin University. We express my gratitude to Assit proff
Dr. Kasim.
a-
b-
c-
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 50 100 150 200
Ce
/Cs
Ce(mg/L)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 50 100 150 200
Ce
/Cs
Ce(mg/L)
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150 200
Ce
/Cs
Ce(mg/L)
IJRRAS 12 (3) ● September 2012 Rounak & Esmail ● Adsorption- Desorption for Some Heavy Metals
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7. REFERENCES [1] Mulligan, C.N., Yong, R.N., and Gibbs, B.F., " Rremoval of heavy metals from soil and sediments using the biosurfactant surfactin".
Journal of Soil Contamination. 8,231-254 (1999).
[2] Peters, R. W., and Shem, L., "Adsorption/desorption characteristics of lead on various types of soil"., Environ Prog, 11,234-240. (1992).
[3] Ray. A. B., Ma, J.H., and Borst, M., "Adsorption of surfactants on clays". Hazardous wast and hazardous materials. 12, 357-364 (1995). [4] Peters, R. W., "Chelant extraction of heavy metals from contaminated soils". J. hazard. Materi., 66, 151-210 (1999).
[5] Rosen, M.J. "Surfactants and interfacial Phenomena, 2nd". Wiley – Intersciencs: NowYork (1989).
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