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Kinetics of Adsorption of Pb (II) on Used Tea Leaves and Cr (VI) on Acacia Arabica Bark.

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Dev. Chem. Eng. Mineral Process., 5(In),pp.79-88, 1997.
Kinetics of Adsorption of Pb (11) on Used Tea
Leaves and Cr (VI) on Acacia Arabica Bark
D.P. Tiwari, D.N. Saksena and D.K. Singh"
Departmerit of Chemical Engineerirtg
Harcourt Butler Technological Instilute,
Kaupur - 208 002, INDIA
Adsorption of Pb (II) on used tea leaves mid C r m ) on acacia arabica bark aJer
chemicalpretreatmentexhibit nearlyfirst-orderreversiblereactionkineticsin wastewater
treatment. Adsorption follows Langmuir arid Freundlich isotherni models. Efective
parameters such as initial metal-ion concivilration, adsorption dosage, and size oj'
adsorbent particles have been correlated to enable prediction of the equilibriurti
adsorption of metal ions within a maxiniuni tkviation of 2 10%from experimentaldarn.
Introduction
Due to the severe toxicity of Pb (II) and Cr (VI),it has become necessary to ensure zero
discharge of these metal ions in industrial effluents. The most cost effective method is
adsorption on materials such as tea-leaves carbon, saw dust, human hair, fly ash, peat
moss, barley straw, dry tree leaves and waste lyre rubber [ 1-81. We have previously
investigated used tea leaves [9) and acacia arabica bark [ 101 for removal of lead and
chromium respectively from wastewater streams.This paper studies the adsorption
kinetics and compares data to the predictions of the Langmuir and Freundlich isotherm
models. Effectiveadsorptionparameterssuchasinitial metal-ionconcentration,adsorbent
dosage, and size of the adsorbent particles have been correlated to enable prediction of
the adsorption of metal ions.
*Authorfor correspondence (Dept. of Chwiistry).
79
D. P. Tiwari, D.N. S k e w and D.K. Singh
Experimental Details
Adsorbents Used tea leavesand acacia arabrca bark were washed, dried, pulverisedarid
sieved. These powdered materials were treatcd with formaldehyde and sulphuric acid.
Two parts by weight of the material with 25 parts by volume of 0.5 N %SO, and one part
by volume of 39% HCHO was stirred at 50 'C in a temperature controlled agitator for
4 hours 19, lo]. Formaldehyde insolubilized water soluble polyphenols in the tea leaves
and tannins in the bark particles. These productsafter washingand sun drying were used
as adsorbents.
Chemicals All chemicals were of analytical grade. Standard lead (11) and chroniiuiii
(VI)solutions (1 g/l) were prepared from lead nitrate and potassium dichromate in
distilled water. The base solutions were used to prepare working solutions.
Adsorption Experiments
Batch adsorption experiments were perfortlied at room temperature (28-30 OC) by
agitating 100 ml of the metal ion solutions i n conical flasks with different amounts and
sizesofadsorbentsat 100 rpm inarotary shakeruntil thesystemattainedsaturation state.
The flaskswere then removed from the shakcr and the supernatantwas analysedfor lead
(11) by titration with ethylenediaminetetra acetic acid (EDTA), and for chromium (VI)
by spectrophotometryusing 1,5 diphenylcarbazide.Adsorption of lead and chronuum
was carried out at optimum pH 5.5 and 2.0 respectively. The pH was adjusted using 0. I
N HCI.
Kinetic Studies
A set of operating conditions used for the kiricticstudies is shown in Table I. Adsorption
of Pb (II) and Cr (VI) from the liquid phase to the solid phase is consideredas a reversible
iirst-order reaction [ 1 11, expressed as :
80
Kinetics of adsorption of Pb(I1) on used tea leaves _...
... ( I )
Therefore :
- logc(1 - X,/X,,)
... (2)
= K, (1 + 1KC)
t
where Kc = K,/K, = C,/CAe
-
and X, = (CA0C,)/C,
Table 1. Operating conditionsfor study of kinetics of adsorption.
System
Initial conc.
of metal
ions
(mg/l)
Adsorbent
dosage
Tea leaves/Pb (11)
100
1 .o
BarMCr (VI)
50
I .o
(e/l)
Particle
size
pH of solution
for maximum
adsorption
(-1
0.3
.0.3
5.5
2.0
Equation (2) is satisfied by the experimciital data shown in Figure 1, indicating
confrmity to reversible first-order reactioii kinetics. The rate constants obtained are
given in Table 2.
Adsorption Isotherms
Adsorption isothermsfor tea IeavedF'b (II) iiitd bark/Cr (VI) are presented in Figures 2
and 3. The data showed a good agreement with the followingforms of the Langmuir and
Freundlich equations, respectively :
81
D.P. Tiwari, D.N. SaGFena and D.K. Singh
... (3)
Values of Langmuir and Freundlich constanis are given in Table 3 .
‘,li
x x
N
0
c
I
ICI
-1;
V
-
m
)o(lea
X
ICOVCS/
MID
W Bork/CrtVI)
1
1
1
1
1
1
1
1
1
Contact time,min
figure 1. First order reversible kinetics
for tea leavedPb OX) and
barWCr (M).
1
10 20 30 40 50 60 70 80 90
2
3
6
5
6
Figure 2. Langmuir isothermsfor tea
IeavesPb @I)andbarWCr (W).
Table 2. First-order reversible rate consimts.
~~~
Rate constants
System
Tea Leaves/Pb (11)
BarWCr (vr)
82
0.033
0.035
1
A x 1 0 2
CAc
0.042
0.018
0.786
1.860
Kinetics of adrorption of Pb(ii) on used tea leaves ....
H Tea l e a v e s / Pb (11)
Bark / Cr I V I )
Y
rn
I
2
3
4
5
loge
6
7
8
CAt
Figure 3. Freundlich isothermsfor tea leows/Pb (71) and.bark/ Cr PI).
Table 3. Langmuir and Freundlich consmnts.
System
Langmuir Constaiits
b s lo’
(mg/g)
(h g )
a
Tea Leaves/Pb (11) 55.55
BarWCr (VI)
142.85
Correlations Developed
Freundlich Constants
K
1
(mg/g)
I1
I .3
7.29
0.46
0.6
11.95
0.50
(a,
The amount of metal ions adsorbed
is found to depend linearly on ( d d p ) for all
concentrationsof metal ions in the solution. This is given by Equation 5 below and also
shown in Figures 4 and 5 for Tea leaves/Pb (11) and BarWCr (VI), respectively.
83
D.P. Tiwari, D.N.Saksena and D.K.Singh
o
5
10 15
(Fil /ap1
20
25
Figure 4. Plots of (q), vs ( d d p )
for tea IeavedPb OI).
1000
-
800
-
V
20
30
Figure 5. Plots of (q),vs
(ddp)
0
10
4
for barWCr (W,).
The slope (s) was also found to change linwly with logc CAogiving the following
relationship (as shown in Figure 6) :
logc CA0= logc p + a s
... (6)
Therefore :
... (7)
s = 1/a ln(CA,/P)
substituting Is' in Equation (5) leads to the ciiipirical correlation :
(Q-
84
=
+
I
a In ('A,/
P 11 (ddp)
... (8)
Kinetics of aakorption of Pb(II) on used tea leaves ....
W Tea leaves/Pb
2
&-&
0
10
(ID
Bark / Cr ( V I I
20
S
Figure 6. Plots of logcCAo
vs S for tea lea\vs/ Pb
30
LO
(II) and barUCr (vl).
Values of the various constants are givcii in Table 4. Figure 7 shows a maxiiiiuiii
deviation of 210 percent for
and (%)..\,, values for tea leaves/Pb (11) and bark/Cr
(VI) systems.
(a,
Table 4. Values of constants in the correlation.
System
Initial
Concentration
of metal
ions
(mgn)
Tea
50-1000
leaves/Pb (11)
Bark/
Cr (VI)
50-1000
Adsorbbent
dosage
(!3m
Panicle
size
(aim)
1-3
2-10
4,
(mg)
Constants
a
(Perurn)
B
(mgn)
0.124.3
16.0
0.10
36.6
0.30-3.0
8.0
0.12
24.5
85
D.P.Tiwari, D.N.Saksena and D.K. Singh
900
-
800
-
700
-
600
-
+ x
+x
+
v
X
:500-
+
0
v
u
c
-82
x +'
Loo-
+\
200 so0
X
X+
+
'X
?p
Tea Icaves/Pb(II)
~ - B1
ark/Cr(VI)
x-$(
X.
v+
100
- #+
o#
1
I
I
I
1
I
I
I
I
Figure 7. Plots o/(q),,,, vs (q), for tea IwvedPb (11) and bark/(.:r(VI)
Conclusions
1.
2.
3.
4.
5.
6.
86
Tea leaves/Pb (II) and barWCr (VI)are effective adsorption systems for
wastewater treatment.
Formaldehyde and sulphuric acid lreatment of the adsorbents prevent their
colour leaking tendency in aqueous systems.
Adsorption kinetics shows the reaction to be of first-order reversible.
Adsorption follows both the Langiiiuir and Freundlich isotherm equations.
Effective adsorption parameters ( CAo,m and dp) are correlated to give the
amount of metal ions adsorbed at cquilibrium.
A maximum deviation of 510 percciit in (qJ- and (Q, for tea leaves/Pb (11)
and barWCr (VI) is observed.
Kinetics of adsorption of Pb(II) on used tea leaves ....
Acknowledgement
Finaricial assistance provided by Ministv of Human Resource and Development.
GovernmentofIndia; and researchfacilitiesprovided by theDirector, H.B. Technological
Institute, Kanpur are gratefully acknowledged.
Notations
Initial concentration of metal ion i n solution (mg/l)
Concentration of metal ion in solution at any time (mg/l)
Equilibrium concentration of metiil ion in solution (mg/l)
Equilibrium concentration of metiil ion on the sorbent
Fractional conversion of metal ion
Fractional conversion of metal ion at equilibrium
First order forward rate constant (inin-')
First order backward rate constant (inin-')
Equilibrium constant (mid)
Amount of metal ions adsorbed at equilibrium (mg/g)
Langmuir constant (nig/g)
Langmuir constant (Vg)
Freundlich constant (mg/g)
Freundlich constant
Amount of metal ions adsorbed, dcrermined esperimentally (mg)
Value of intercept in plot of (e),, \ s. ( d d p ) (mg)
Adsorbent dosage (g/l)
Average particle &a (mm)
Slope of plot (qJ, vs ( d d p ) (mg/g I mm)
A constant in plot logc CAovs s (n@)
A constant in plot logc CAovs s (g/iiig/Vmm)
Amount of metal ions adsorbed, dclermined fromcorrelation (mg)
(mu)
87
D.P.Tiwari, D.N.Saksena and D.K. Singh
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
1 1.
Sin& D.K.and Lal, J. 1992. Removal ofCr(M) f h r aqueous solutions wingwaste tea leaves carbon. Ind.
J. Environ. Health, 34,108-1 13.
Sin& D.K., Mishra, N.K. and Saksenp D.N. 1990. Ikmoval ofCr (Vl) kom aqueous solutions using low
cost sarbent. J. Institution of Engineers (India) Chari. Engg., 70,90-91.
Tan, T.C.. Chip C.K. and Teo, C.K. 1985. Uptake ol'metal ions by chemically treated human hair. Water
R-h,
19, 157-162.
Pan&, K.K.. Prasad, G . and Sin& V.N. 1984. Fly ;ash China clay for removal of Cr (VI)from aqueous
Solutions. Ind. J. Chem., 234,514-515.
Coupel, B.and Lalencette, J.M. 1976. The treatmelit of wastewaters with peat moss. Water Research, LO,
1071-1076.
Lamen, V.J. and Schirierup, H. 1981. The use of siriiw for removal of heavy metals from wastewaters. J.
Environ. Qual., 10, 188-193.
Sin& D.K.,Tiwari. D.P. and Saksena, D.N. 1993. Kcinoval ofCr(V1) by Man&era indica leaves. Pollution
R12,223-228.
Rowley, AG., Husband,F.M.and Cunningham AH. 1984. Mechanism of metal adsorption fiom aqueous
solutions by waste tyre mbber. Water Research, 18.981-984.
Sin& D.K.,Tewari, D.P. and Saksma, D.N. 1993. Rmoval of lead fram aqueous solutions by chemically
treated wed tea leaves. Ind J. Environ.. Health, 35. 169.177.
SinghD.K..Saksena,D.N.andTiwari,D.P. 1994. Removal ofCr(VI)ftomaqueoussolutions. Ind. J. Environ.
Health., 36.272-277.
bvenspiel 0..1972 Chemical Reaction Engineering. Indedition,p. 62, John Wiley &Sons, Inc., New Yo&.
-
Received: 15 February 1996 ;Accepledafier revision : 0 December 1996
88
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