International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
BIOSORPTION OF Cr(VI) FROM AQUEOUS SOLUTION USING NEEM LEAF
SARITHA .B1, PRAYASH PRADHAN2 , SOUGAT PATNAIK3, NISHANT KISHEN4
1
Assistant Professor, Department of Civil Engineering, Bharath University
173, Agaram Road, Selaiyur, Tambaram,Chennai-73,India.
2,3,4
Department of Civil Engineering, Bharath University
173, Agaram Road, Selaiyur, Tambaram,Chennai-73,India.
ABSTRACT
In this article, Azadirachta indica ( neem ) leaf powder is used as an adsorbent for the removal of
chromium from aqueous solution. The experimental tests were carried out in the laboratory covering
various parameters which include adsorbent dosage, contact time, pH of the aqueous solution.
KEYWORDS : Adsorption, Chromium, dosage, Neem leaf.
INTRODUCTION
In recent times, science and technology brought tremendous progress in many spheres of development,
but in the process has caused the degradation of environment due to negligence of the treatment of
industrial effluents. Industrial pollution is a major threat affecting the water. The release of nonbiodegradable heavy metals into water stream is dangerous because the consumption of polluted water
causes various health problems. The waste water released from the industries contain heavy metals such
as Cu, Zn, Cd, Cr. Among these metals pollution by chromium is a major concern as the metal is used in
electroplating, leather tanning, metal finishing. Chromium occurs in trivalent and hexavalent forms, But
the latter form is of particular concern due to its greater toxicity.
Various methods have been adopted for the removal of heavy metals from industrial effluents which
include precipitation, membrane separation, ion exchange and adsorption. In case of adsorption,
popularly used adsorbents like activated carbon, silica, alumina etc- are expensive. This has prompted
the use of various materials as adsorbents in order to develop cheaper alternatives. Natura materials
available in large quantities or waste products may have the potentiality of high uptake of metals. They
can be disposed off without regeneration due to their lower cost. The present investigation looks into a
specific process, for the removal of toxic element, chromium by adsorption using low cost adsorbent
developed from abundantly available neem leaf powder, a plant material (Venkata et al., 2005).
MATERIALS AND METHODS
Preparation of the adsorbent
The neem belongs to meliaceae family and is native to Indian sub-continent. Its seeds and leaves have
been in use since ancient times to treat a number of human ailments and also as a household pesticide.
The medicinal and germicidal of the neem tree have been put to use in a variety of applications. The
neem leaves used in the present investigation are collected from the available trees in Engineering
college area of Bharath University, Chennai. They are washed thrice with distilled water to remove dust
and water soluble impurities and are dried until the leaves become crisp. Then the leaves are crushed in
powder and sieved with the help of 1.18mm and 600 microns sieve. The resulting neem leaf powder are
ISSN: 2231-5381
http://www.ijettjournal.org
Page 8
International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
preserved in glass bottles for use as an adsorbent. The presence of niacin, proline, glutamic acid, aspartic
acid, glutamine, tyrosine and alanine which contain polar groups like –NH2, -COOH, -OH etc. in neem
powder (Battacharya and Sarma, 2004; Neem foundation, http://www.neemfoundation.org, 1997)
contribute to thenegative surface charge.
Preparation of stock solution
The stock solution is prepared by dissolving 141.4 mg of dry potassium dichromate(K 2Cr2O7) in
distilled water and dilutiong it upto the mark in 100ml volumetric flask. 20 ml of the stock solution is
then taken and diluted against distilled water in a 100ml volumetric flask ( 100mg/l ).
Experimental procedure
After preparing the stock solution samples of 100 ml of 50 mg/l concentration of chromium were
prepared and placed in the jar test apparatus and the adsorbent loading is varied. The samples were then
mixed continuously at a constant speed of 150 r.p.m for 30 mins. The sample is allowed to settle and
then it is filtered through a Whatman filter paper. Since Chromium ions combine with DPC in acidic
condition to produce red – violet colour, the pH of the sample were found out using pH meter and the
pH was brought to 2-2.4 by adding diluted H2SO4. 250 mg of 1,5 Diphenylcarbazide is dissolved in 50
ml of acetone and stored in a coloured bottle to prepare the DPC ( Diphenylcarbazide ) solution. 2ml of
the Diphenyl carbazide solution was added to the samples and the OD value were noted down from the
spectrophotometer. The percentage removal of chromium (VI) is calculated as (Co-Ct) x 100/Co. The
same experimental procedure is repeated for different agitation times and also for the other adsorbent
sizes. The effects of other parameters such as pH, adsorbent dosage, initial concentration of Chromium
in aqueous solution are obtained by following the procedure.
The values of variables studied in this investigation are shown in Table 1.
Table 1. Experimental conditions investigated
Parameters
Values investigated
Adsorbent dosage (w) gm
0.2,0.4,0.6,0.8,1.0,1.2,1.4,1.6
Contact time (min)
20,30,40,50,60,70,80
pH of the aqueous solution
2,4,6,8,10,12
Initial concentration of Cr(VI) in Aqueous solution
Co, mg/l
10,20,30,40,50,60,70,80
RESULTS AND DISCUSSIONS
ISSN: 2231-5381
http://www.ijettjournal.org
Page 9
International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
Effect of adsorbent dosage
The % removal of chromium increases from 55.08 (1.65 mg/g) to 81.44% (1.77 mg/g) for 1 g
of dosage. This phenomenon is expected as the decrease in the size of the adsorbent results in
the increase of the surface area of it, thereby the number of active sites are better exposed to
the adsorbate.
Effect of contact time
The contact time is determined by plotting the % removal of chromium against agitation time for
different adsorbent sizes as shown in Figure 2. The % removal of chromium increases upto 40
minutes of agitation time and there after no further increase is recorded as reported earlier (Sarma and
Battacharya, 2005) for chromium removal by neem leaf powder. Adsorption equilibrium time is defined
as the time required for heavy metal concentration to reach a constant value.
94
% REMOVAL OF CHROMIUM
92
90
88
86
84
% REMOVAL OF CR.
82
80
78
76
74
20
30
40
50
60
70
AGITATION TIME (in mins.)
80
90
Figure 2. Effect of agitation time on % removal of chromium.
Effect of pH of the aqueous solution
pH controls the process of adsorption as it affects the surface charge of the adsorbents, the degree of
ionization and species of adsorbate. The effect of pH on adsorption of chromium is shown in Figure 4.
The % removal of chromium increases from 88.96 to 93.52% with 1g of adsorbent with an increase in
pH from 2 to 4.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 10
International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
96
% REMOVAL OF CHROMIUM
94
92
90
88
% removal of chromium
86
84
82
80
78
2
4
6
pH
8
10
12
Figure 4. Effect of pH on % removal of chromium.
Adsorption isotherms
The theoretical adsorption capacity of the neem leaf adsorbent for Cr(VI) removal can be determined
by developing its adsorption isotherm.
The adsorbent phase concentration data is computed using the equation
Qe=(Co-Ce)*V/M
where Qe=adsorbent phase concentration after equilibrium.
Co=initial concentration of adsorbate (mg/l).
Ce=final equilibrium concentration of adsorbate after
absorption has occurred (mg/l).
M=mass of adsorbent ,g.
V= volume of sample taken in litres.
The Freundlich equation was also employed for the adsorption of Cr(total) ions on the adsorbents. The
Freundlich isotherm have represented as in equation(1):
1
log 𝑄𝑒 = log 𝐾𝑓 + log 𝐶𝑒
𝑛
where Qe is the amount of Cr(total) ions adsorbed (mg g−1), Ce is the equilibrium concentration of
Cr(total) ions in solution (mg L−1) and Kf and n are constants incorporating all factors affecting the
adsorption capacity and intensity of adsorption, respectively. A graph is plotted between log Qe versus
log Ce which follows the Freundlich isotherm which is shown if Figure 5.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 11
International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
7
ADSORBENT CAPACITY (mg/g)
6
5
4
ADSORBENT CAPACITY (mg/g)
3
2
1
0
10
20
30
40
50
60
70
80
90 100
EQUILIBRIUM CONC.(mg/l)
Figure 5. Langmuir adsorption of chromium using neem leaf powder
CONCLUSION
From the present study, it can be concluded that the neem has a moderate potential to remove chromium
(VI). The percentage removal of Cr (VI) depends on adsorbent dose, pH, contact time, and initial Cr
(VI) concentration. At 60 minutes contact time and initial metal concentration of 50 mg/L, 70.2% Cr
(VI) removal was observed but when the metal concentration was increased to 50 mg/L the removal
efficiency dropped to 30.8%. Neem adsorbed chromium ions best at lower Cr (VI) concentration in the
range of 40 to 50 mg/L but the removal efficiency dropped to 19% when the metal concentration was
increased to 70 mg/L.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 12