Journal of Scientific & Industrial Research
Vol. 64, September 2005, pp 674-678
Separation of lead ions from aqueous solutions by adsorption at talc surface
Navin Chandra*, Nitin Agnihotri, Priya Sharma, Sanjeev Bhasin and S S Amritphale
Regional Research Laboratory (CSIR), Habibganj Naka, Hoshangabad Road, Bhopal 462 026
Received 04.January 2005; accepted 20 June 2005
Separation of lead ions from aqueous solutions containing 5, 10, 20, 50, 100, 200 and 500 ppm lead was studied by
adsorption at the surface of talc mineral of Indian origin. The effect of temperature (20, 30, 40, 50, 60, 70oC) on adsorption
phenomena was studied and the data was analyzed using Langmuir isotherm. The changes in enthalpy (∆H), free energy
(∆G) and entropy (∆S) were evaluated. The negative values of ∆G and ∆H indicate the adsorption of lead ions on talc
surface to be spontaneous and exothermic under the experimental conditions.
Keywords: Talc surface, Adsorption, Lead ion, Temperature effect, Langmuir isotherm, Thermodynamic parameters,
Ions separation
IPC Code: B 01 D 15/00
Introduction
Lead is widely used in storage battery, hot-dip
galvanizing, ceramic glazing, petroleum refining,
printing, paper and pulp, electrochemical, chemical
and paint industries1-3. About 5 million tons of the
metal is produced annually all over the world4.
However, it is potentially toxic and has the tendency
to accumulate in blood, soft tissues and mineralizing
tissues like bones, and poses serious health hazards
such as anemia and damage to kidney, lung, brain and
central nervous system5. It has an approx half-life of
25-40 d in blood and soft tissues and more than 25 y
in non-labile portion of bones5.
For the separation of heavy metal ions such as lead
ions from aqueous media, techniques like
precipitation, ion exchange, solvent extraction,
reverse osmosis, distillation and adsorption have been
found to be effective6. In the adsorption process for
the attenuation of heavy metal ions, substrate
materials such as activated carbon, synthetic
hydroxyapatite, high grade rock phosphate, clays and
clay minerals have been tried7-9. To explore the
possibility of utilizing inexpensive minerals for the
removal of lead and other heavy metal ions from
aqueous solutions, sorption studies were carried
out10-15. Talc, a hydroxyl magnesium silicate
Mg3Si4O10(OH)2, is another inexpensive mineral of
________________
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E-mail: [email protected]
pyrophyllite family16 occurring widely in India17,18. Its
structure comprises of a magnesium-oxygen-hydroxyl
tri-octahedral brucite layer, sand-witched between
two sheets of silicon-oxygen tetrahedral layers19,20.
The adjacent layers are held together by weak van der
Waals forces and hence give rise to a soapy feeling in
the talc21. However, unlike pyrophyllite, where –OH
groups are located at the edges, here –OH groups are
sand-witched between the layers in talc22. This paper
reports the adsorption of lead ions on talc surface
from aqueous solutions.
Experimental Details
Chemicals and Reagents
Merck A R grade lead nitrate was used to prepare
test solutions. The stock solution (1000 ppm lead ions
by weight) was prepared by dissolving appropriate
quantity of lead nitrate in double distilled water. The
test solutions were prepared by serial dilution of the
stock solution. The pH of the test solutions was
adjusted to 6.0 by addition of dilute HNO3.
The samples of talc mineral were collected from
the mines in Jabalpur district, MP. Representative
sample of the mineral, prepared by coning and
quartering method, was manually crushed followed by
grinding in a Ball Mill. The sieve analysis of powder
showed mineral size as follows: + 400 µ, 1.8; -400
+150 µ, 90.2: -150+75 µ, 7.9; and -75 µ, 0.1 %.
The surface area of the powder, determined by
Quantachrome (model - Nova 1000) BET surface area
analyzer, was 3.4 m2/g. Silica and alumina were
CHANDRA et al: LEAD IONS FROM AQUEOUS SOLUTIONS BY ADSORPTION AT TALC SURFACE
Fig. 1 Effect of contact time on % separation of lead ions on 1 g
talc from100 ml test solutions containing different concentration
of lead ions at 20oC
estimated by wet chemical analysis method23, while
iron, magnesium and calcium were determined by
Inductively Coupled Plasma Spectrometer (Jobin
Yvon, model JY-2000), and sodium and potassium
were estimated by Flame Photometer (Systronic
model - Medi Flame). The results of the chemical
analysis are as follows: SiO2, 60.35; Fe2O3, 0.22;
Al2O3, 1.86; MgO, 29.20; CaO, 0.12; Na2O, 1.20;
K2O, 0.80; and loss on ignition at 950 oC, 4.0 wt %.
For identification of the phases present in the
representative talc mineral sample, X-ray diffraction
studies were carried out and lattice constants were
calculated as follows: a, 5.15; b, 9.29; and c, 18.89.
The corresponding lattice constant values of 5.28,
9.158 and 18.90 are reported24 for the tri-layer
monoclinic form of talc and it was inferred that the
talc used in the present study is a tri-layer monoclinic
form.
Lead Ion Separation Studies
For optimization of contact time required for the
sorptive separation of lead ions at talc surface from
aqueous lead solutions, talc powder (1.0 g) was
equilibrated with test solution (100 ml thermo-stated
at 20oC) containing lead ions (5.0, 10.0, 20.0, 50.0,
100, 200 & 500 ppm) for contact times of 10, 20, 30,
40 and 50 min. The contact time comprised of 10 min
by stirring of the talc powder with the test solution
using a mechanical shaker followed by equilibration
for the remainder period under quiescent conditions.
At the end of equilibration time, talc powder was
separated by filtration using Whatman 42 filter paper
and concentration of the remaining lead ions in
solutions was estimated using Atomic Absorption
Spectrometer (GBC Model-902) following the
procedures adopted earlier11. From these data,
675
Fig. 2 Effect of the initial concentration of lead ions in solution
on the % separation and quantity (mg) of lead ions separated from
100 ml test solutions containing 100 ppm lead at 1 g of talc
at 20 oC
separation of lead ions at talc surface was evaluated.
From the plot (Fig. 1), a contact time of 40 min was
found satisfactory and the same was used in all further
studies.
For studying the effect of quantity of adsorbent on
separation of lead ions, test solution (100 ml)
containing lead ions (100 ppm) was equilibrated for
40 min at 20oC with different quantities of talc
powder (0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0,
3.5, 4.0 & 5.0 g). Similarly for studying the effect of
temperature on the separation of lead ions, talc
powder (1.0 g) was equilibrated at 20, 30, 40, 50, 60
and 70oC.
Results and Discussion
Effect of Initial Concentration on Sorptive Separation of Lead
Ions
For studying the effect of initial concentration of
lead ions in solution on separation percentage and
quantity of lead ions separated per unit weight of
adsorbent talc (mg/g), talc powder (1.0 g) was
equilibrated at 20oC for 40 min in solutions containing
5, 10, 20, 50, 100, 200 and 500 ppm lead ions (Fig. 2).
In dilute solutions (5-20 ppm), lead ion separation
was 100 percent. However, with increase in
concentration, the separation percentage decreased.
The quantity of lead ions separated from talc sample,
initially increased rapidly with increase in the lead ion
concentration in solution, but in solutions of higher
concentrations, it became practically constant (8
mg/g). This may be attributed to the fact that at low
concentrations of lead ions in solution, surface
coverage (θ) is small and hence almost all the
available lead ions are removed. However, at higher
concentrations, all sites available for adsorption get
occupied.
676
J SCI IND RES VOL 64 SEPTEMBER 2005
Fig. 3 Plot of % separation of lead ions vs quantity of
adsorbent talc from 100 ml test solutions containing 100 ppm lead
ions at 20oC
Fig. 5 Langmuir isotherm plot for the adsorption of lead ions at
different temperatures
Fig. 6 Plot of ln b vs 1/T for the adsorption of lead ions on the
talc surface
Fig. 4 Effect of temperature on quantity (mg) of separated lead
ions at 1 g talc from test solutions containing different initial
concentrations of lead in solutions at 20oC
Adsorption Isotherms
Effect of the Quantity of Adsorbent on the Separation of Lead
Ions
(1/qe ) = (1/θο b) . (1/Ce) + (1/θο )
The separation of lead ions from test solution
(100 ml) containing lead ions (100 ppm) at 20 oC
increased almost linearly as the amount of adsorbent
increased gradually from 100 mg to 2.5 g and can be
attributed to increase in the availability of adsorption
sites (Fig. 3). A further increase in the quantity of
adsorbent leads to a complete removal of lead ions
from the solution and hence the quantity of separated
lead ions remains constant.
Effect of Temperature on the Separation of Lead Ions
In general, the quantity of separated lead ions from
100 ml solutions containing 5, 10, 20, 50, 100, 200
and 500 ppm lead ions per unit weight of adsorbent
decreased with increase in temperature, indicating that
the sorption of lead on talc surface is exothermic in
nature (Fig. 4).
The data obtained for the adsorption of lead ions at
talc surface were analyzed using Langmuir isotherm:
…(1)
where qe = the amount of lead ion adsorbed per unit
weight of adsorbent (mg/g), Ce = the equilibrium
concentration of lead ions in test solution (mg/l), θο is
the adsorption capacity and b is the equilibrium
constant of adsorption.
The dependence of (1/qe) on (1/Ce) with varying
concentration of lead ions in test solution at different
temperatures is observed to be linear indicating the
applicability of the Langmuir model to the adsorption
of lead ions on talc surface (Fig. 5). From the values
of slope and intercept, θο and b were calculated for
isotherms obtained at 20, 30, 40, 50, 60 and 70oC
(Table 1). The values of b so obtained were plotted
against 1/T (Fig. 6) following the Eq. (2):
ln b = - (∆H/RT) + Constt
…(2)
CHANDRA et al: LEAD IONS FROM AQUEOUS SOLUTIONS BY ADSORPTION AT TALC SURFACE
677
Table 1  Langmuir constants and thermodynamic parameters for the adsorption of lead ions on talc at different temperatures
Parameters
Temperature°C
20
7.9936
0.1352
-4.8777
7.564
Langmuir constant, θo, mg/g
Langmuir constant, b, L/mg
∆G, KJ/mole
∆S, J/mole
30
6.1462
0.1658
-4.5298
6.166
40
6.3051
0.1541
-4.8699
7.05
50
5.3590
0.1793
-4.6184
6.05
60
4.7236
0.1231
-5.8033
9.43
70
4.2553
0.1240
-5.9568
9.60
Table 2  Dimensionless equilibrium parameter, (R),; quantity(mg) of lead adsorbed/g of talc, (qe) and rate constant for
adsorption of lead on talc
Intial conc. of lead
ions in solution(ppm)
5
10
20
50
100
200
500
20°C
R
0.5966
0.4251
0.2699
0.1288
0.0688
0.0356
0.0145
qe
0.5
1.00
2.00
4.20
6.00
8.00
7.95
30°C
R
0.5467
0.3762
0.2316
0.1076
0.0568
0.0292
0.0119
qe
0.41
0.6
1.6
3.93
5.497
5.508
6.332
40°C
R
0.5648
0.3935
0.2449
0.1148
0.0609
0.0314
0.0128
The value of change in enthalpy was calculated
from the slope of the straight line and was observed to
be -2.6614 kJ m-1 indicating the process to be
exothermic in nature25. The change in free energy of
the system25,26 due to adsorption at different
temperatures of study was calculated using Eq. (3):
ln (b ) = - ∆G/RT
…(3)
As expected, the values of ∆G obtained for
different temperatures of study are observed to be
negative (Table 1). The change in entropy of the
system25,26 due to adsorption at different temperatures
was calculated using Eq. (4):
∆S = ( ∆H - ∆G ) / T
…(4)
The values of ∆S (Table 1) at different
temperatures are positive indicating the affinity of
lead ions for talc, similar to the observation for
adsorption of lead ions on tea leaves26. The essential
characteristics of the Langmuir isotherm are
embodied in a dimensionless equilibrium parameter
R25,26 expressed as
R = 1/(1 + bCo)
…(5)
Accordingly, values of R at different temperatures,
calculated at different concentrations of lead ions in
test solution (Table 2), were positive (0-1).
Conclusions
Talc minerals were effectively used for the
separation (> 98%) of lead ions from its dilute
50°C
qe
0.33
0.57
1.44
3.928
5.496
6.06
6.141
R
0.5272
0.3580
0.2180
0.1003
0.0528
0.0271
0.0110
qe
0.375
0.57
1.285
3.75
4.536
5.075
5.75
60°C
R
0.6190
0.4482
0.2888
0.1397
0.0751
0.0390
0.0159
qe
0.375
0.536
1.308
3.55
4.118
4.616
4.546
70°C
R
0.6152
0.4464
0.2873
0.1388
0.0746
0.0387
0.058
qe
0.346
0.529
1.175
3.00
3.947
3.949
4.139
aqueous solutions containing up to 20 ppm lead but
decreases in more concentrated solutions. The
adsorption of lead at talc surface is spontaneous and
exothermic as evidenced by negative values of the
changes in free energy (∆G) and enthalpy (∆H).
Acknowledgements
The authors thank Dr N Ramakrishnan, Director
RRL, Bhopal, for interest in this work and Mr B
Kujur and Mr M K Ban for help in the chemical
analysis.
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