Indian Journal of Chemical Technology
Vol. 3, January 1996, pp. 55-57
Adsorption of Pb(II) on polyacrylamide grafted tin(IV). oxide gel from
aqueous solution
K P Shubha ~ T S Anirudhan
Department
of Chemistry, University of Kerala, Kariavattom,
Received 20 February
Thiruvananthapuram
695 581, India
1995; accepted 22 May 1995
Polyacrylamidegrafted hydrous tin(IV)oxidegelhas been studiedas a sorbent for removal ofPb(II) from
aqueous solutions. Effectsof contact time, initialconcentration, pH and temperature have been studied. The·
adsorption followsfirstorder kinetics.The uptake ismaximumaround pH 5.5and it has beenexplainedon the
basisof the surfact:complexationinvolving H + exchange.The adsorption isotherms ofPb(II) were found to
follow the Langmuir adsorption model. The adsorption rate constants and thermodynamical parameters
werealso presentedto predict the nature of adsorption. The spentadsorbent can be regeneratedand reusedby
acid treatment.
Adsorption of Pb(II) ions has- been studied by a
variety of materials such as activated charcoal,
polymeric synthetic resins, clays, oxide solids 1-4. It
appears to be an important means of controlling the
Pb(II) concentration in water and wastewater. In
recent years, considerable attention has been devoted
to the study of hydrous metal oxide gel and to its
multipurpose uses in high performance liquid
chromatography, pre-concentration and separation.
process. Only a few studies on hydrous tin(IV) oxide
as an ion exchanger have been reported and very little
work has been done with Pb(II) ions. Moreover,
surface modifications by chemical treatment of these
materials usually increase the sorption capacity. In
the present investigation, adsorption characteristics
for the removal ofPb(II) ions from aqueous solutions
onto polymer grafted hydrous tin{IV) oxide gel have
been studied.
Experimental' Procedure
Sorbent - The starting material, hydrous tin{IV)
oxide gel of relatively uniform and narrow:~ particle
size distribution was first prepared by the reported
methods. The gel was grafted with polyacrylamide by
using the procedure described by Shigetomi and
Kojima6• The polymerised product wasrefluxed with
ethylene diamine (75.0 mL) continuously for 8 hat
lOO·C.To convert into (;ation exchanger, one part by
weight of the above material was refluxed with equal
part by weight of succinic anhydride at pH 4.0 for 6 h.
The excess succinic anhydride was washed out with
I A-dioxane and finally with ethanol and then dried.
The dried polyacrylamide grafted gel (PGG) was
sieved to get -120 + 230 mesh size.
Characterisation - The IR spectra of PGG was
recorded on a Perkin Elmer IR-180 Spectrophotometer. The sharp asymmetric absorption band
observed at 3422 em -1 is attributed to the
exchangeable OH group. The ban~s at 1655 cm-1
(vC=O) and 1458 cm-1 (VC-O) indicate the
presence of - COOH group in PGG. The characteristics of the sorbent are: apparent density, 1.93 g/mL;
moisture content, 4.15%; cation exchange capacity,
0.47 meq!g; surface area, 133.0 m2/g and pHzpc, 6.5.
Adsorption experiments- One hundred milligrams
of PGG was agitated in duplicate with 20.0 mLof
aqueous solution oflead at desired concentration, pH
and temperature using shaking machine for different
time intervals. At the end of predetermined time
intervals, the sorbate was separated by filtration and
the supernatant was analysed for the remaining lead
concentration using Perkin-Elmer 2380 Atomic
Absorption Spectrophotometer.
The pH of the
solution oflead nitrate of desired concentratio~ was
adjusted with 0.1 N HN03 and 0.1 N NaOH.
Batch desorption and regeneration studies - After
the attainment of equilibrium the supernatants were
carefully decanted and desorption experiments were
carried out in aqueous medium of 0.5 M HCl. To
regenerate, the same procedure was followed for
three cycles. After each desorption cycle, the spent
adsorbent was washed with distilled water to remove
any Pb(II) ions which may be weakly sorbed on the
surface and dried at 80·C.
Results and Discussion
Effect of agitation time and initial Pb(ll)
concentration - The per cent adsorption ofPb(II) on
PGG increases with increase of contact time upto 5 h,
INDIAN 1. CHEM. TECHNOL.,
56
-f
Sorb.n'
100
JANUARY
1996
I.S
dose
1.0
tonic ItrenQth
pH
O.S
~
-
80
CT
c:
5..
o
I 0.0
..
.!!
0-
CT
60
r-o.s.
'0
<
"': 50.0 mg/L
•• : 100·0 mQ/L
C : 250.0 mQ/L
X : 500.0 mQ/L
o : 1000.0 mQ/L
20
o
1
1
IS
50
pH
:S.S
-2:0
30
IS
4~
If,io
~O
Time,
Fig. I-Effect
Sorbent do••
:S.O Q/L
Initial Pblil) concn:100.0 mQ/L
Ionic .t"nQt"
:0.01 M
-1.0
-f~
40
360
240
480
min
10
oS
Tim. ,min
Fig. 3-Lagergren
of time and concentration,. on Pb(II) removal by
adsclrption .on POO
plot for the adsorption of Pb(Il) on POO at
different temperatures
100
100
90
80
70
Sarbent d.,.e
Initial Pb(1I) canen
Agitation time
Ionic .trength
-
c:
20
Initial Pb(ll)cancn
Sorbent da.e
Ionic .trength
100.0 m~/L
5· 0 Q/L
0·01 M
pH
5.5
.!!
5.0 Q/L
IOO.omQ/L
5h
0.01 M
so
eo
•.
~
40
30
o
o
!lO
100
ISO
200
ISO
!OO
3!lO
~
20
Time,min
Fig. 2-Effect
of time and temperature
PGG
on Pb(II) removal by
afterwards no significant change was found (Fig. 1).
Equilibrium time was independent ofPb(II) concentration. The removal ofPb(II) decreases from 85.4 to
47.3 % by increasing Pb(II) concentration from 10.0
to 1000.0 mg/L. The removal curves are single,
smooth and continuous indicating the possibility of
the formation of monolayer coverage ofPb(lI) at the
outer interface of PGG.
Effect of temperature and adsorption dynamics The effect of agitation time and temperature on Pb(II)
removal by PGG are shown in Fig.2. The sorption
capacity increases from 78.8 to 90.0% with increase in
temperature of solution from 30 to 60°C indicating
the process to be endothermic. The equilibrium time
was found to be 5 h for the temperatures studied. The
increase in uptake of metal ions with temperature
may be due to the desolvation of the sorbing species
and change in the size of the pores. The kinetics of
sorption of Pb(II) on PGG was studied and rate
constant kr of the process was determined using
Lagergren? equation. Using this equation the
10
o
I
2
~
4
S
pH
6
7
8
9
\0
Fig. 4-Effect of initial pH on the removal ofPb(lI) by adsorption
on PGG [(0) Adsorption, (x ) Hydroxide precipitation]
straight lines obtained from the plots oflog (qe-q) vs t
(Fig.3) at different temperatures indicate that the
process follows first order kinetics. The values of kr
were determined from the slope of the plots and found
to be 4.15 x 10-2,6.68 X 10-2,8.52 X 10-2 and
10.60 x 10-2 min-1 at 30, 40, 50 and 60°C
respectively.
The activation energy,Ea, was determined using
Arrhenius equation8. A plot of In kr vs 11 T was found to
be linear. The activation energy as calculated from
the slope of the plot is equal to 31.5 kllmol which was
comparable with reported values8 indicating that this
adsorption was due to chemical rather than physical
adsorption.
Effect of pH The influence of pH on the
adsorption ofPb(II) by PGG is shown in Fig.4. For
II 1111I~'m
ill'~
'"
"''')
t
'I'
I
SHUBHA & ANIRUDHAN:
conen. metal
Light
ADSORPTION
OF Pb(II) POLYACRYLAMIDE
14.1
14.3
14.9
14.7
15.3
15.4
14.2
15.7
16.2
16.2
14.6
K+effect
Na+
(77:1)
(71.0)
(73.2)
(77.3)
(73.6)
Ca2+
(70.6)
(71.5)
Table I-TheMg2+
(81.1)
(78.5)
of Pb(II)
various
light metal
concentration
(81.1
(74.5)
)15.7
Pb(II) concentration,
absorbed,
mg/g,
% mg/L
Initial
100.0
mg/L
Pb(II) sorption by POO
on
GRAFfED
TIN(IV) OXIDE GEL
57
was investigated with lead salts. Experiments were
conducted with 100.0 mg/L ofPb(II) solution at pH
5.5. The results showed that maximum adsorption
from solution was 83.5% for acetate whereas in the
case of chloride and nitrate it was 81.1 % and 79.6%.
The higher adsorption in acetate medium is possibly
due to the formation of organic leads complexes9 that
may adsorb more strongly than the hydrated
cation10• The adsorption was found to be minimum in
sulphate solution (73.2%). The S041igand is strong
enough to form a neutral and stable sulphate Pb
complex which prevent the uptake of Pb(II) by
sorbent11•
comparison lead hydroxide precipitation by NaOH is
also given .. Precipitation curve shows a sharp
decrease in concentration of Pb(II) ions in solution
suggests that lead is precipitating from solution at this
concentration, well before adsorption is complete.
However, at any pH Pb(II) removal by adsorption is
greater than by hydroxide precipitation. It can be
observed that maximum adsorption of Pb(In is
recorded at pH 5.5. The possible sites on PGG for
specific adsorption in acidic pH includes H + ions in
- COOH functional group. The perusal of Pb(II)
speciation diagram3 clearly indicates that in the range
of highest sorption efficiency, the dominant species
were Pb2 + and PbOH +. In PGG the H + from the
peripheral - COOH group can be exchanged for
cations in solutions. It has been shown that the final
pH is always less than the initial pH. This indicates that
as the metal ions are bound on the sorbent, hydrogen
ions ate released into the solution and it leads to the
conclusion that PGG probably acts as an acid form
ion exchanger.
Effect aflight metal ions- In order to examine the
effect of different light metal ions such as Na, K, Ca,
Mg on Pb(II) uptake by PGG, experiments were
conducted
with 100.0 mgjL Pb(lI) solution
containing light metal ions (Table 1). Each value is a
mean of triplicate determinations and statistically
significant- at 1% level. As the PGG is an acid ion
exchanger, competition from cations for sites on the
surface was expected. However, it will be noted that
the presence of these cations did not. reduce the
amount of Pb lost from solutions. The influence of
cations was relatively small, and changed only
marginally when the concentration was increased
from 50.0 to 500.0 mgjL.
Effect of anions - The effect of acetate, sulphate,
nitrate and chloride in the uptake ofPb(lI) by PGG
Regeneration - Experiments were carried out by
shaking 1.0g spent adsorbent with 200.0 mL of 0.5 M
HCI. The regeneration was completed within 2 h.
From the adsorbed quantity of 30.3 mgjg of Pb(II)
from the initial concentration of 250.0 mgjL, 29.3
mgjg was desorbed in 0.5 M HC1, constituting a net
regeneration of96.7% of the total adsorbed in a single
step. After three cycles the sorption capacity ofPGG
was reduced by 10.4% and on the other hand,
regeneration of Pb(lI) ions in 0.5 M HCI was
decreased from 96.7% in the first cycle to 91.3 % in the
third cycle'. So spent PGG can be regenerated for
further use by acid treatment.
Acknowledgement
The authors are thankful to the Head, Department
of Chemistry, University ofKerala, Trivandrum for
providing the laboratory facilities.
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