Vol.2, No.1, 41-48 (2011) Agricultural Sciences
doi:10.4236/as.2011.2 1007
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Sorption and desorption behavior of lead in four
different soils of India
Sudarshan K. Dutta1,2*, Dhanwinder Singh1
1Department of Soils, Punjab Agricultural University, Ludhiana, Punjab, India;
2Department of Plant and Soil, University of Delaware, Newark, USA; *Corresponding Author: sudarshandutta@gmail.com
Received 20 October 2010; revised 11 November 2010; accepted 20 November 2010
Sorption and desorption mechanisms of lead
(Pb) were determined in four different soils col-
lected from different agro-climatic regions of
India. The soils were classified as: Fine loamy
mixed Typic Dystrudepts, fine sandy loam Typic
Ustochrepts, fine loamy Typic Ustochrept, and
fine sandy loam Udic Haplustalfs. Seven differ-
ent Pb solutions [Pb(NO3)2 dissolved in 0.01M
Ca(NO3)2] in a range of 400 to 2000µgL-1 were
applied to study the sorption amounts at 25-
(±2)oC and 45(±2)oC temperatures. With the in-
crease in application rate and temperature,
sorption amounts of Pb increased; however,
percentages of sorption of applied Pb were de-
creased. Sorptions were positively and signifi-
cantly (p 0.01) correlated with Langmuir ad-
sorption isotherm. Thermodynamic parameters
of sorption (i.e. Ko, Go, Ho, and So) were also
determined at two temperatures, 25(±2)oC and
45(±2)oC. Increase in Ko with the increase in
temperature indicated positive effect of tem-
perature on Pb sorption. High absolute values
of Go, and positive values of Ho, and So
suggested that the sorption reaction was spon-
taneous and endothermic. Sorbed Pb were de-
sorbed in Pb free 0.01 M Ca(NO3)2 solutions at
25(±2)oC and 45(±2)oC. Desorption amounts in-
creased with increase in the Pb application rate,
but not always with the increase in temperature.
Keywords: Desorption; Isotherm; Lead; Sorption;
Lead (Pb) is a widespread non–biodegradable chem-
ical contaminant found in the soil receiving disposal of
city wastes, sewage, and industrial effluents [1]. The
bioavailability of Pb in soil is highly dependent on the
sorption (adsorption + precipitation) and desorption be-
havior of soil [2-4]. Sorption increases the immobility of
Pb while desorption increases the Pb concentration in
soil solution from the sink. Therefore, an understanding
of adsorption and desorption processes and their mecha-
nism is crucial for the assessment of the Pb contamina-
tion and the reclamation of such polluted soils [1]. Con-
siderable research has been done on the adsorption be-
havior of Pb on different soils. Adhikari and Singh [1]
studied the adsorption of Pb by some Indian soils. Aziz
[5] reported the sorption equilibrium of Pb in two dif-
ferent types of Palestine soils. However, Pb sorption
depends on the chemical and mineralogical characteris-
tics of the soils, and therefore varies among soil types
[1]. Therefore, more information related to Pb sorption
in different types of soils with different soil physico-
chemical properties is always helpful to strengthen our
present understanding of sorption.
The sorption of Pb is controlled by the thermody-
namic parameters related to the soil-metal interactions
[1]. Therefore, determination of the thermodynamic pa-
rameters can assist in the prediction of the final state of
metal in the soil system from an initial non-equilib-
rium state [6]. These thermodynamic parameters include
equilibrium constant, Ko; standard free energy, Go;
standard enthalpy, Ho; and standard entropy, So. For
example, Adhikari and Singh [1] reported that the sorp-
tion process can be better expressed by the evaluation of
the free energy change (Go) corresponding to the trans-
fer of element from bulk solution into soil surface. They
also reported that an understanding of the change in en-
thalpy (Ho) and entropy (So) helps in determining the
free energy change and disorders occurred during sorp-
tion process. In the present study, we focused on the
sorption of Pb (II) in four different soils of India, and
evaluated the thermodynamic parameters (Ko; Go; Ho;
and So) related to the interaction of the metal with soils
during sorption.
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
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Soil can sorb excessive amount of trace metal ions,
like Pb, from soil solution, and therefore has drawn at-
tention of a lot of researchers [7]. However, only a few
studies are focused on the desorption kinetics of the
sorbed trace metals [8]. The thermodynamics related to
the sorption and desorption assumed to be different as
the sorption reactions involving trace metals are ex-
tremely rapid, and desorption reactions can be slower by
orders of magnitude [7,9,10]. Moreover, adsorption-
desorption reactions are often not completely reversible,
which is known as non-singularity, or hysteresis [7]. On
the contrary, number of studies related to Pb desorption
is very limited, especially for Indian soils. Therefore, in
the present study we also focused on the desorption
characteristics of the sorbed Pb.
Specific questions that were addressed in this study
include: 1) How do the sorption amounts of Pb by the
soil vary with the variation in application rate and soil
temperature, and how well do they fit with Langmuir
adsorption isotherms? 2) How do the thermodynamic
parameters (Ko, Go, Ho, and So) of Pb sorption vary
at two different temperatures? 3) How do the desorptions
of added Pb vary with the initial application rate and soil
temperature, and how well do the desorption data fit
with the Langmuir desorption isotherm?
2.1. Soil Sampling and Analysis
Four surface soil samples (0-15 cm depth) expected to
differ in physicochemical properties, were collected
from four different agro-climatic zones (ACZs) of India
(based on the classification of Gajbhiye and Mandal,
[11]). The samples were collected from Palampur (ACZ
1, Himachal Pradesh; soil type: fine loamy mixed Typic
Dystrudepts), Jalandhar (ACZ 6, Punjab, soil type: fine
sandy loam Typic Ustochrepts ), Purulia (ACZ 7, West
Bengal, soil type: fine loamy Typic Ustochrept), and
Pudukkottai (ACZ 11, Tamil Nadu, soil type: fine sandy
loam Udic Haplustalfs) during summer (April-June) of
2004. The USDA system of soil classification was used
for the determination of soil textural classes. The soil
samples were collected mainly from the agricultural
fields with no history of receiving Pb applications. Sam-
ples were then air dried, crushed in wooden mortar and
pestle, and then passed through a 2 mm sieve. Then the
samples were stored in HDPE (high-density polyethyl-
ene) containers in laboratory until analyzed. The details
of the measurements of the soil physico-chemical proc-
esses were explained elsewhere [12]. Total Pb values
were measured by following the method of Tessier et al.
[13]. The DTPA extractable Pb contents were determined
by DTPA method [14].
2.2. Sorption/Desorption Studies
Batch equilibrium technique was adopted for the Pb
sorption study. Sorption of Pb at soil was determined by
equilibrating the soil samples (2 g of soil samples in
duplicate) with 20ml of 0.01M calcium nitrate [Ca-
(NO3)2] solutions containing seven different concentra-
tions of Pb. The concentrations of Pb used in our study
include 40, 80, 100, 120, 140, 160, and 200 µg ml-1 of
Pb (equivalent to 400, 800, 1000, 1200, 1400, 1600, and
2000 µg Pb g-1 soil, respectively). We used lead nitrate
[Pb(NO3)2] as a source of Pb. Calcium nitrate [Ca(NO3)2]
was used as the supporting electrolyte for reducing the
non-specific adsorption of Pb [15]. Previous studies also
reported a high (> 80%) reduction of non-specific sorp-
tion of heavy metals by using Ca(NO3)2 solution [16].
We preferred nitrate (NO3
-) as the electrolyte anion over
others (like chloride, Cl-) as NO3
- is less likely to form
complexes with metal ions [16,17].
To measure the thermodynamic parameters, sorption
and desorption experiments were carried out at two dif-
ferent temperatures, 25 2
˚C and 45 2˚C. Samples
were allowed to equilibrate at two temperatures (in trip-
licate concentrations as well as temperatures) for 24 hrs
followed by a 2 hrs shaking to attain the sorption equi-
librium; therefore, the total number of sample was 168
(i.e. 4 soils 3 replications 7 concentrations 2 tem-
peratures). The average values of these 3 replications are
presented in this paper. We also performed an initial
study prior to actual experiment to find out the time re-
quired to attain sorption equilibrium at both tempera-
tures (25 2˚C and 45 2˚C) and observed that sorption
did not increase after 2 hrs of shaking. Concentrations of
Pb were measured in these decanted solutions using
Avanta PM Flame Atomic Absorption Spectrophotome-
ter (AAS) (GBC Scientific Equipment, Dandenong,
Australia). The detection limit of the instrument at lower
side was 10 µg L-1 (0.01 ppm). Difference in the mass of
Pb in the solutions before and after equilibrium was con-
sidered as the amount of Pb sorbed per 2 g of soil.
Desorption was determined by measuring the Pb con-
centrations in the extracted solutions. Four to six extrac-
tions based on a pre-study were performed with pure (Pb
free) 0.01 M Ca(NO3)2 solution for the same soil sam-
ples used for sorption studies. Ca(NO3)2 solution was
used for the extraction of the heavy metals (like Pb) as
this could be a good indicator of the bioavailability of Pb
[1]. The number of extraction required for maximum
desorption was decided based on initial experiments
performed at both 25 and 45˚C (described in [12]).
2.3. Analysis of Sorption and Desorption
Data Using Langmuir Adsorption
To further our understanding of sorption and desorp-
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
tion processes, we fitted our Pb sorption and desorption
data to Langmuir adsorption and desorption isotherms.
The details of data analyses steps were described in
Adhikari and Singh [1]. In short, Langmuir adsorption
isotherm was used to calculate the adsorption parameters,
such as: Adsorption maxima ‘b’, and bonding energy
coefficient, ‘K’. The conventional form of the Langmuir
adsorption isotherm of Pb can be written as: Ce/(x/m) =
1/(K.b) + Ce/b (Eq. 1).
Where, Ce is the equilibrium Pb concentration (mg
L-1), x/m is the amount of Pb adsorbed by soil (mg kg-1),
‘b’ and ‘K’ are Langmuir constants. The constant ‘K’ is
related to the bonding energy of the adsorbent for the Pb
(L mg-1).
The Langmuir isotherm (Eq. 1) is a straight line
where Ce/(x/m) were plotted against Ce. The best fit val-
ues of the coefficients ‘b’ and ‘K’ were derived using the
isotherm equations, where b = 1/slope, and K = slope/
Cumulative Pb desorption data were fitted to a modi-
fied Langmuir desorption isotherm, which can be written
as: De/R = 1/Kd Dm + De/Dm (Eq. 2).
Here, De is the concentration of Pb desorbed (mg L-1),
and Dm is the desorption maxima (mg kg-1 soil). R is the
amount of Pb desorbed per gram of soil (µgg-1 soil), Kd
is the constant related to the mobility of lead. Dm and Kd
were calculated from the linear plots of De versus De/R.
Previous studies [18] also applied this equation in their
Pb desorption studies in different soils of Punjab, India.
2.4. Analysis of Thermodynamic
The Pb sorption data obtained at two different tem-
peratures (25 2˚C and 45 2˚C) were used to measure
the thermodynamic properties of the reactions. Among
the different thermodynamic parameters, the variation of
thermodynamic equilibrium constant (Ko) were com-
puted following the procedure described by Adhhikari
and Singh [1].
The value of Ko for the adsorption reaction can be ex-
pressed as: Ko = as/ae = s Cs/e Ce (Eq. 3).
Where, as denotes activity of adsorbed metal, ae is the
activity of metal in equilibrium solution. Cs is the
amount (milligrams) of metal adsorbed per unit volume
(liter) of solution in contact with the adsorbent surfaces,
Ce is the amount (milligrams) of solute per unit volume
(liter) of solution in contact with the adsorbent surfaces
at equilibrium, s is the activity coefficient of the sorbed
metals, and e denotes the activity coefficient of metal at
equilibrium. In physical chemistry it is assumed that
with the lowering of concentration (Cs and Ce), the ac-
tivity coefficients (s and e) approach unity. Therefore,
the equation becomes: Ko = Cs/ Ce (Eq. 4).
The Ko values were determined by plotting ln (Cs/ Ce)
versus Cs and extrapolating to Cs = 0. The standard free
energy (ΔGo) was determined by using the following
equation: (ΔGo) = –R T ln Ko (Eq. 5).
The standard enthalpy (Ho) was obtained by using
the integrated Vant Hoff equation:
ln K2
o = Ho/R [1/T1 – 1/T2] (Eq. 6).
The standard entropy (So) was measured as:
So = (Ho ΔGo)/T (Eq. 7).
Statistical operations were performed using the statis-
tical software JMP (Version 8, SAS Institute Inc., Cary,
3.1. Physicochemical Properties of the
Experimental Soils
The physicochemical properties of the four experi-
mental soils have been described in Ta bl e 1 . The pH of
the soils ranged from 5.6 to 6.2; EC values were from
0.08 to 0.15 dSm-1; CEC varied from 11.5 to 23.4 cmol
(p+) per kg soil; clay contents were from 15 to 22%, and
% organic C ranged from 0.29 to 0.91%. The experi-
mental soils were non-calcareous and therefore did not
have any CaCO3. Total native Pb content of the soils
varied from 16.8 to 34.8 µg g-1 soil; whereas, the DTPA
Pb content ranged from 0.21 to 1.48 µgg-1 (Table 1). The
percentage of labile Pb, i.e. amount of Pb over total na-
tive Pb varied from 1.3 to 7.4%. Overall, the soils varied
in their physicochemical characteristics; and expected to
show variation in sorption and desorption amounts of
3.2. Variation of Pb Sorption with Pb
Application Rate and Temperature
All the soil samples exhibited high capacities to sorb
Pb at both 25(±2)˚C and 45(±2)˚C. The amounts of Pb
sorption with varying application rates (400, 800, 1000,
1200, 1400, 1600, and 2000 gg-1 soil) have been re-
ported in Table 3. We observed that, with increase in Pb
concentrations from 400 to 2000 gg-1 soil, the amount
of Pb sorption also increased in all the four soils (Table
This was expected because more Pb was available for
sorption on soil with the increase in application. However,
the percentage of Pb sorbed on soils decreased. This was
also expected because the availability of the binding sites
decreased with the increase in concentration. Previous
studies also reported an increase in Pb sorption with the
increase in application rate. Shaheen et al. [19] observed
Pb sorption in 11 different types of soils. They found
increase in Pb sorption with the increase in Pb applica-
tion rate from 1 to 4 m ML-1; however, they reported de-
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Table 1. Physicochemical properties and total (Pb) contents of the collected soil samples.
Sampling Loca-
/Soil type
(dS m-1)
Carbon (%)
Total Pb
(µg g-1 )
(µg g-1 )
Pb (%)
(Fine loamy
mixed Typic
6.2 0.08 0.91 ND*22.9 64.5 12 22 34.8 1.31 3.8
(Fine sandy loam
Typic Usto-
5.6 0.08 0.60 ND 23.4 80.9 5 15 20.1 1.48 7.4
(Fine loamy Typic
6.1 0.15 0.48 ND 17.9 47.8 33 19 24.9 0.94 3.8
(Fine sandy loam
Udic Haplustalfs)
6.1 0.09 0.29 ND 11.5 73.0 6 20 16.8 0.21 1.3
*ND = Non detectable
Tab le 2. Amount and percentage of Pb sorbed (g g-1) at four different soils receiving seven different initial Pb treatments at two
different temperatures (25 ± 2˚C and 45 ± 2˚C).
Amount of Pb applied per gram soil (g g-1) at 25 (±2)˚C
locations 400 800 1000 1200 1400 1600 2000
Palampur 381.6 (96.5) 757.6 (94.7) 927.1 (92.7)1100.1 91.7) 1268.9 (90.0)1427.8 (89.1) 1763.4 (88.2)
Jalandhar 368.2 (92.05) 732.0 (91.5) 889.6 (89.1)1057.8 (88.1) 1221.1 (87.2)1349.5 (84.3) 1670.0 (83.5)
Purulia 386.6 (96.7) 758.1 (94.8) 921.8 (92.2)1066.3 (88.9) 1179.1 (84.2)1334.1 (83.4) 1629.8 (81.5)
Pudukkottai 355.4 (88.9) 678.9 (84.9) 803.8 (80.4)934.3 (77.9) 991.6 (70.83)1054.6 (65.3) 1216.3 (60.8)
Amount of Pb applied per gram soil (g g-1) at 45 (±2)˚C
Palampur 395.6 (98.9) 786.6 (98.5) 965.0 (96.5)1154.4 (96.3) 1320.9 (94.4)1480.6 (92.5) 1845.1 (92.3)
Jalandhar 397.7 (94.9) 755.2 (94.4) 930.2 (93.0)1115.1 (92.9) 1283.1 (91.7)1455.6 (91.0) 1802.8 (90.1)
Purulia 389.1 (97.3) 766.3 (95.8) 929.5 (93.0)1111.8 (92.6) 1271.2 (90.8)1435.6 (89.7) 1668.8 (83.4)
Pudukkottai 367.5 (91.8) 689.6 (86.2) 830.8 (83.1)993.5 (82.8) 1055.0 (77.1)1155.0 (72.2) 1269.4 (63.2)
(Figures within parentheses denote percent of Pb sorption)
Table 3. Langmuir adsorption isotherms, correlation coefficients, and Langmuir parameters for four experimental soils at two
different temperatures.
Sampling locations
At 25(±2)˚C
Linear Langmuir equations Correlations of
equations (R)
Adsorption maxima
(b) (mg kg-1)
Bonding energy coeffi-
cient (k) (L/mg)
Palampur y = 0.442x + 5.165 0.97* 2.26 0.086
Jalandhar y = 0.379x + 8.731 0.93* 2.39 0.043
Purulia y = 0.697x + 2.682 0.99* 1.44 0.259
Pudukkottai y = 0.701x + 11.207 0.99* 1.43 0.063
At 45(±2)˚C
Palampur y = 0.508x + 1.397 0.98* 1.97 0.360
Jalandhar y = 0.335x + 4.797 0.98* 2.99 0.070
Purulia y = 0.501x + 3.059 0.99* 1.99 0.164
Pudukkottai y = 0.692x + 7.797 0.99* 1.54 0.088
* Statistically significant at p 0.01.
crease in Pb sorption percentage due to less availability
of binding space.
Although we observed increase in Pb sorption with
increase in application rates for all the four experimental
soils, there were variations in the sorption amounts. The
sorption trend was Typic Dystrudepts > Typic Usto-
chrepts (loamy sand) > Typic Ustochrept (loamy) >
Typic Haplustalfs (i.e. Palampur soil > Jalandhar soil >
Purulia soil > Pudukkottai soil) at all concentrations.
This variation might be a consequence of the variation in
the % organic C, and CEC values of the soils. The %
Organic C and CEC values were also higher for Palam-
pur and Jalandhar soils as compared to that of Purulia
and Pudukkottai soils (Table 1). Previous studies also
reported that % organic C, and CEC played important
roles in Pb sorption [2,4,20,21]. Singh and Sekhon [18]
observed a significant correlation of sorption maxima
with CEC, clay contents, and % organic C for some of
the Punjab soils. Adhikari and Singh [1] reported that
variations in sorption maxima were correlated with the
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
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pH, CEC, and organic carbon contents of the soils.
The effect of temperature on the amount of Pb sorp-
tion can also be observed in Ta b l e 2. We found that Pb
sorption and percentage of applied Pb sorbed increased
with increase in temperature from 25˚C to 45˚C at all the
levels of Pb application (Table 2). Adhikari and Singh [1]
also reported an increase in Pb sorption with increase in
temperature from 25˚C to 45˚C. They concluded that the
Pb sorption reaction was endothermic which resulted in
an increase in Pb sorption with the increase in the tem-
We also compared the sorption isotherms at the two
different temperatures with the different solute sorption
isotherms based on the classification of Giles et al. [22].
According to Giles et al. [22], there are four different
solute sorption isotherms: namely ‘S’, ‘L’, ‘H’, and ‘C’
curves; and each of them corresponds to a different sol-
ute/sorbent interaction. They mentioned that the shape of
these isotherms also provide information related to the
strength by which the sorbate is held/attached to the soil.
The Pb sorption isotherms of our four experimental soils
were presented in Figures 1(a)-(d). By comparing our
present graphs with Giles et al. [22], we observed ‘L’
type of curve for all the four soils at 25˚C temperature
(Figure 1(a)-(d)). However, in 45˚C, the curve types
varied among the soils. In Palampur and Jalandhar soils,
the sorption isotherms were approaching to be ‘H’ type
(Figure 1(a), (b)); whereas, for Purulia and Pudukottai
soils, the sorption isotherms were ‘L’ type (Figure 1(c),
(d)). According to Giles et al. [22], ‘L’ type of curves
corresponds to a strong affinity between metallic cations
and the sorbent surface, which favors specific sorption.
On the other hand, ‘H’ type of curve indicates strong
sorbate-substrate attraction force and may lead to pre-
cipitation. Martı́nez-Villegas et al. [17] also observed the
same Pb sorption isotherm pattern with the increase in
Pb concentrations from 10 to 400 mg L-1 in different
Mexican soils.
3.3. Pb Sorption and Langmuir Adsorption
The Pb sorption data were fitted to the Langmuir and
Freundlich adsorption isotherms. In the case of Lang-
muir adsorption isotherm, we observed that the sorption
data fitted significantly (p 0.01) in the isotherms for all
the experimental soils and at both 25˚C and 45˚C tem-
peratures (Table 3). The observed correlations were also
high (R = 0.93 to 0.99) (Ta b le 3). Previous studies also
reported significant correlations of their sorption data
and the Langmuir adsorption isotherms [18,23]. For
example, Singh and Sekhon, [18] described that their Pb
sorption in alkaline soils fitted significantly (p 0.05)
with Langmuir adsorption isotherm. In all of our ex-
(a) (b)
(c) (d)
Figure 1. (a) Lead sorption isotherms for Palampur soil. At 25˚C the sorption isotherm is ‘L’ type, and
at 45˚C the isotherm trends towards ‘H’ type. (b) Lead sorption isotherms for Jalandhar soil. At 25˚C
the sorption isotherm is ‘L’ type, and at 45˚C the isotherm is ‘H’ type. (c) Lead sorption isotherms for
Purulia soil. At both 25˚C and 45˚C the sorption isotherm is ‘L’ type. (d) Lead sorption isotherms for
Pudukkottai soil. At both 25˚C and 45˚C the sorption isotherm is ‘L’ type.
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
Copyright © 2011 SciRes. Openly accessi ble at http://www.scirp.org/journal/AS/
perimental soils, we observed that the Langmuir adsorp-
tion maxima (‘b’) increased with the increase in tem-
perature from 25˚C to 45˚C (Table 3). The ‘b’ values
were in the order of Jalandhar soil > Palampur soil >
Purulia soil > Pudukkottai soil at both the temperatures.
The physicochemical properties of the Jalandhar soil and
the Palampur soil were almost similar and might have
resulted in similar ‘b’ values (2.26 and 2.39µgml-1, re-
spectively). The higher 'b’ values for Palampur and
Jalandhar soils compared to Purulia and Pudukkottai soil
can be attributed to the higher % organic C, and CEC
values of these soils. Soil CEC and % organic C play
important role in Pb sorption [4,12]. Adhikari and Singh
[1] also reported highest Pb sorption maxima for the soil
which had the highest CEC, and % organic C contents
among their experimental soils. The bonding energy
coefficient (k) of experimental soils varied from 0.043 to
0.259 L mg-1 at 25˚C; and with the increase in tempera-
ture to 45˚C, the ‘k’ values also increased (Table 3).
Adhikari and Singh [1] also studied sorption of Pb in
four different soils of India at 25 and 45˚C and reported
the range of bonding energy coefficient (k) from 0.094
to 0.135 L mg-1.
3.4. Thermodynamic Parameters of
Pb Sorption in Soils
The thermodynamic parameters which include ther-
modynamic equilibrium constant (Ko), standard free
energy (Go), standard enthalpy (Ho), and standard
entropy (So), provide an insight into the Pb sorption
mechanism in the soils [1]. We calculated all these men-
tioned parameters at both 25˚C to 45˚C (Table 4). We
observed that, ‘Ko’ increased with a rise in the tempera-
ture from 25˚C to 45˚C for all the four soils. The calcu-
lated free energy (Go) values were negative. Since the
negative ‘Go’ denotes the amount of energy diminished
or required before reaching equilibrium, therefore, more
negative ‘Go’ value indicates more Pb sorption [1]. We
also observed the highest amount of Pb sorption in our
Palampur soil which had the highest absolute value of
Go’. Moreover, in all the experimental soils, the ‘Go
values were more negative at a higher temperature,
which suggested more spontaneity of the sorption reac-
tion at a higher temperature [6]. The values of isosteric
heat or enthalpy (Ho) of Pb sorption were positive
ranging from 27.5 to 92.9 KJ mol-1. This suggests that
the Pb sorption reactions are endothermic in nature. Pre-
vious studies [1] also found good correlation between
the thermodynamic parameters (Go, and Ho), and the
soil physico-chemical properties (pH, CEC, and % or-
ganic C) of the soils. The standard entropy (So) values
for all the four soils at both the temperatures were posi-
tive ranging from 112.61 to 348.12 J mole-1 K-1 at 25˚C
and 107.42 to 334.68 J mole-1 K
-1 at 45˚C (Table 4).
Adhikari and Singh, [1] also reported a decrease in So
with increase in temperature and suggested that, the dis-
order in the sorption process was lower at higher tem-
3.5. How does Pb Desorption Vary with
Initial Application Rate and
The cumulative desorption of sorbed Pb increased with
the increase in the rate of application in all the experi-
mental soils (Table 5). The percentage of the Pb de-
sorbed from the amount sorbed also increased with Pb
application rate (Table 5). Padmanabham [24] suggested
that, with the increase in Pb concentrations, the available
sites for Pb binding become lower and the required
bonding energies for the Pb sorption become higher;
therefore, a larger amount of applied Pb become avail-
able for desorption. The Pb desorption data followed the
pattern of Pudukkottai soil > Purulia soil > Jalandhar soil
> Palampur soil. Therefore, we observed an overall op-
posite trend between the sorption and desorption data for
our four experimental soils; i.e. the soils having higher
sorption of Pb, desorbed less and vice-versa. It empha-
sizes that, sorption and desorption does not follow the
same patterns [7,8]. However, we did not observe any
certain pattern in Pb desorption with the increase in
We hypothesize that, at high application rates some of
the Pb might get physically precipitated instead of
chemically bonded and therefore, a portion of sorbed Pb
did not show any certain desorption pattern.
3.6. Pb Desorption Isotherm
We fitted Pb desorption data with Langmuir desorption
equations for the experimental soils at both 25˚C and
45˚C (Table 6). We found the desorption data fitted well
with the Langmuir desorption isotherms. We found high
and significant correlation (p 0.01) among the Pb de-
Table 4. Thermodynamic parameters for Pb sorption in four experimental soils at two different temperatures (25 ± 2˚C and 45 ± 2˚C).
Ko Go (kJ mol-1) So (J mol-1 K-1)
Sampling locations 25(±2)oC 45(±2)oC 25(±2)oC 45(±2)oCHo (kJ mol-1) 25(±2)oC 45(±2)oC
Palampur 152.24 161.04 –10.75 –13.44 92.9 348.12 334.68
Jalandhar 72.99 73.63 –10.03 –11.37 38.5 163.76 156.82
Purulia 23.42 25.52 –7.81 –8.56 33.8 139.63 133.21
Pudukkottai 25.97 26.47 –6.07 –6.66 27.5 112.61 107.42
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
Copyright © 2011 SciRes. Openly accessi ble at http://www.scirp.org/journal/AS/
Table 5. Amount of Pb desorbed (g g-1) and percentage of desorbed Pb over sorption at four different soils receiving seven
different initial Pb treatments at two different temperatures (25 ± 2˚C and 45 ± 2˚C).
Amount of Pb applied per gram soil (g g-1) at 25 (±2)˚C
400 800 1000 1200 1400 1600 2000
Palampur 4.1 (1.1) 75.8 (10) 103.9 (11.2)136.5 (12.4)184.2 (14.5)289.9 (20.3) 360. 8 (20.5)
Jalandhar 7.8 (2.1) 88.3 (12.1) 122.8 (13.8)163.9 (15.5)217.7 (17.8)262.8 (19.5) 376.1 (22.5)
Purulia 7.9 (2) 92.2 (12.2) 164.4 (17.8)257.1 (24.1)320.2 (27.2)424.5 (31.8) 500.4 (30.7)
Pudukkottai 11.9 (3.3) 123.2 (18.1) 234.2 (29. 2)304.9 (32.6)339.3 (34.2)379.1 (35.9) 460.4 (37.9)
At 45 (±2)˚C
Palampur 4.8 (1.2) 42.8 (5.4) 82.8 (8.6) 106.5 (9.2) 161.4 (12.2)202.1 (13.6) 311.7 (16.9)
Jalandhar 22.9 (5.8) 72.2 (9.6) 106.8 (11.5)166.8 (14.9)240.2 (18.7)308.4 (21.2) 484.6 (26.9)
Purulia 13.2 (3.4) 60.1 (7.8) 100.9 (10.9)147.5 (13.3)223.1 (17.6)306.3 (21.3) 411.6 (24.7)
Pudukkottai 23.9 (6.5) 126.1 (18.3) 205.5 (24.7)287.4 (28.9)339.9 (32.2)394.9 (34.2) 486.2 (38.3)
(Figures within parentheses denote percent of Pb desorbed from the Pb sorbed during sorption study)
Table 6. Langmuir desorption equations, correlation coefficients and Langmuir parameters for various soils at 25 (±2)˚C and
45 (±2)˚C.
Sampling locations Linear Langmuir equationCorrelation of equations
Desorption maxima
Dm (mg kg-1 )
Desorption coefficient
Kd (L/mg)
At 25 (±2)˚C
Palampur y = 0.005x + 0.045 0.95* 182.62 0.116
Jalandhar y = 0.005x + 0.058 0.96* 192.31 0.10
Purulia y = 0.006x + 0.059 0.95* 166.67 0.101
Pudukkottai y = 0.007x + 0.087 0.95* 136.99 0.084
At 45 (±2)˚C
Palampur y = 0.005x + 0.032 0.96* 204.08 0.152
Jalandhar y = 0.005x + 0.066 0.99* 222.22 0.068
Purulia y = 0.005x + 0.047 0.98* 192.31 0.111
Pudukkottai y = 0.007x + 0.085 0.97* 149.25 0.080
* Statistically significant at p 0.01
sorption values and the Langmuir desorption equation (R
= 0.95-0.99) at both the temperatures. Desorption pa-
rameters i.e. desorption maxima (‘Dm’), and desorption
coefficient (‘Kd’) were also reported (Table 6). Previous
studies [23] also reported a significant (p 0.05) corre-
lation between Pb desorption and Langmuir desorption
Interestingly, although we observed higher amount of
‘Dm’ values for the Palampur as well as Jalandhar soils
compared to that of Purulia and Pudukkottai soils, the
desorption was higher for the last two soils. Less Go
values for Purulia and Pudukkottai soil signifies that the
sorption process was less spontaneous for them as com-
pared to the other two soils.
In our Pb sorption and desorption study, performed in
four different soils of India, we observed an increase in
Pb sorption at all of these soils with an increase in Pb
application. Thermodynamic parameters revealed that Pb
sorption was an endothermic reaction. We observed an
increase in the sorption amount with the increase in
temperature. On the basis of isotherm classification de-
scribed by Giles et al. [22], we observed that our Pb
sorption data followed the ‘L’ type of curve, which sig-
nifies a strong affinity between metallic cations and the
sorbent surface. The sorption data fitted well with Lang-
muir adsorption isotherms. At both 25˚C and 45˚C
(R2 = 0.96-0.99). In all the soils, Langmuir sorption
maxima ‘b’ and bonding energy coefficient ‘k’ increased
with the increase in temperature. Desorption of sorbed
Pb showed that sorption and desorption did not follow
the same pattern. Desorption data also fitted well to
Langmuir desorption isotherms (R2 = 0.91-0.98) for all
the experimental soils.
The sorption and desorption studies performed to date
were mostly in laboratory scale with sampled soil and
therefore have disturbed soil profile. On the contrary,
field scale study with undisturbed soil column is missing
although in-situ study is extremely important, especially
for remediation aspects. This is especially true as the
factors controlling the sorption and desorption behavior
of Pb in the soil are more varied, less human controlled,
and act simultaneously. However, the in-vitro studies
S. K. Dutta et al. / Agricultural Sciences 2 (20 11) 41-48
Copyright © 2011 SciRes. Openly accessi ble at http://www.scirp.org/journal/AS/
determining the fate of heavy metals like Pb could be an
initial step to understand the environmental processes.
Therefore, with the knowledge and concept of laboratory
analyses, in-situ field study related to heavy metal sorp-
tion is required under various environmental conditions.
Grateful acknowledgement is extended to Punjab Agricultural Uni-
versity, India, for providing laboratory facility. Indian Council of Ag-
riculture Research provided fellowship to the graduate student (Sudar-
shan Dutta) to complete the research. Authors show special gratitude to
H. S. Hundal, PhD, Department of Soils, and S. S. Bhardwaj (Phd),
Department of Chemistry, Punjab Agricultural University; Pritha Dey,
Department of Bioinformatics, Sikkim Manipal University of Health
Science & Technology, and Obaidur Rahaman, Chemistry Department,
University of Delaware for their overall support.
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