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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

537

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


538

)(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


539

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


540

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


541

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


Soil

Initial Conc. μgml-1


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


542

Table 1-c. The kinetic parameters of Adsorption process of Copper using Pseudo-first order Lagergren model K1


Soil

Initial Conc. μgml

-1


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.


543

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,


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


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


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


546


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


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


547


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


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


549

Figure 3. Fitted adsorption isotherm Languir

model for a- Zinc b-Nicle c- Copper


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)


550

Figure 4. Fitted adsorption isotherm Ferundlich

model for a- Zinc b-Nicle c- Copper in the presence of cmc SDS


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


551

Figure5. Fitted adsorption isotherm Langmiur model for a- Zinc b-Nicle c- Copper in the presence of cmc SDS


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)


552

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