INTRODUCTION:
One of the major issues faced today is
pollution of the biosphere by heavy metals that are released as a result of
man-made activities. These have been shown to have adverse effects on the
environment as well as human health.[1] Heavy metals include any metallic element
that has a relatively high density and is toxic even at low concentrations.
Some heavy metals are lead (Pb), cadmium (Cd), zinc (Zn),
mercury (Hg), arsenic (As), silver (Ag) chromium (Cr), copper (Cu) iron (Fe),
and the platinum group elements. Heavy metals can be commonly found in
industrial applications such as the manufacture of pesticides, batteries,
mining operations, alloys, metal plating facilities, textile dyes, tanneries.
Contamination by chromium is commonly seen
in agricultural soils and industrial sites. Cr
(VI) has the tendency to move readily through soils and aquatic environments
and is a strong oxidizing agent that can be absorbed through the skin[2].
Chromium and its compounds
are widely employed in electroplating, leather tanning, cement, dyeing, metal
processing, wood preservatives, paint and pigments, textile, steel fabrication
and canning industries and these industries tend to produce large quantities of
toxic wastewater effluents.[3] The maximum
concentration limit for Cr (VI) can be finalized as 0.1mg/ml for discharge into
inland surface waters and is 0.05mg/ml
in potable water.
Various techniques can be
employed for the removal of heavy metals. Some of those techniques are precipitation,
reduction, ion exchange and adsorption. Adsorption over solid
adsorbents being one of the most convenient methods. Adsorption is the
process of accumulation of a gas or liquid on the surface of a solid or a
liquid (adsorbent), forming a molecular or atomic film (the adsorbate).
One other approach is use of chitin and its deacytelated
form, chitosan that have the ability to fix a great variety of heavy metals.[4]
Chitin is
a structural polysaccharide, a homopolymer of 1-4
linked 2-acetamido-2-deoxy-
-D-glucopyranose. It
is commonly found in fungi, yeast and marine vertebrates. They
are commonly exploited from two marine crustaceans, shrimp and crabs. [5] Sand is a naturally occurring granular material
that can be used for the adsorption of heavy metals. This can be done by the
use of slow sand filters.[6,7]
In this current paper, preparation of chitosan from prawn shells and chitosan
coated sand (CCS) was done. The adsorption of chitosan,
sand and chitosan coated sand by varying different
parameters like adsorbent dose, adsorbate
concentration; contact time and temperature were done.
EXPERIMENTAL:
5kg of prawn wastes were collected from Tambaram fish market. The obtained prawn shells were washed
to remove the adhering sand and sun dried the shells for 72 hours.
PREPARATION
OF CHITIN:
The prawn shells were grounded to get
uniform size. For demineralization of
prawn shell, 40g of prawn shell was taken and mixed with 400ml of 10% HCl (1:10) ratio (w/v) and allowed for continuous mixing
for 24 hours.
PREPARATION
OF CHITOSAN:
The obtained chitin was added with 60% of
concentrated NaOH (1:15) (w/v) to remove the acetyl
groups from chitin. The mixture was kept in microwave oven for 5min. It was
filtered using Wattman filter paper and dried in hot
air oven to get the chitosan.
PREPARATION
OF CHITOSAN COATED SAND:
5 grams of chitosan
was mixed with 100g of sand, and 300ml of 5% HCl
(pH1.5) was added. The acid was added to chitosan in
order for the uniform distribution on sand particles. The mixture was stirred
for 5 hours at room temperature. The resulting solution was neutralized with NaOH (1N, pH 13), which was added drop by drop until chitosan-coated sand was formed by precipitating the mixture . The solution was filtered, washed and dried in hot
air oven. After grinding and sieving, the particles were passed through ASTM
sieve size #35. Particles whose size greater than 0.5mm were
collected and used as the adsorbent for the adsorption studies. Coated
sand increases the surface area of chitosan. All pH
values were measured with pH meter.
ADSORPTION
STUDIES FOR CHITOSAN, CHITOSAN COATED SAND AND SAND
EFFECT
OF ADSORBATE CONCENTRATION:
0.5g of adsorbent was added to 100ml each
of 5, 10, 20, 30, 40,50mg/l potassium dichromate in
250ml conical flask (pH 5 and room temperature).The samples were kept in shaker
for 2 hours.10ml of supernatant solution was taken from each sample treated
with adsorbent. Supernatant of each sample was taken to Atomic Adsorption
Spectrophotometer (AAS) and the absorbance of the samples
were noted. Absorbance at 426 nm Vs concentration (mg/l) was plotted.
EFFECT
OF ADSORBENT DOSE:
The adsorbent dose varied as 0.5, 1, 1.5,
2, 3g (whereas adsorbate concentration was kept
constant as 20mg/l, pH5 and room temperature). The samples were kept in shaker
for a contact time of 2h.10ml of each sample was taken for AAS. Absorbance of
the samples was noted at 426 nm. Absorbance at 426 nm vs
concentration (mg/l) was plotted.
EFFECT
OF CONTACT TIME:
2g of adsorbent dose and 20mg/l of adsorbate concentration was taken and the maximum
adsorptions of samples under varied contact times were identified. The samples
taken in the flask were kept in shaker for 1, 2, 3, 4, 5 hours. After
incubation, the supernatant of each sample was taken to AAS. Maximum absorbance
of the samples were noted at 426 nm and plotted against concentration (mg/l).
DESORPTION
STUDIES
For desorption of chromium ions, from the CCS
was done by leaching. The chromium adsorbed CCS was treated with solutions at
various pH. For leaching HCl,
water and acetic acid was used. (HCl at pH 2.9,
acetic acid at pH 4 and water at pH 7 was contacted with chromium adsorbed CCS
for 2 hours). The concentration of chromium recovered and percentage recovery
was found.
RESULTS AND
DISCUSSION:
EFFECT
OF ADSORBATE CONCENTRATION:
Figure 1: Effect of initial Chromium ion
concentration on Chitosan SAND and CCS (Chromium ion
concentration = 10-50 mg/L, Adsorbent dose= 0.5 g, volume of sample=100 mL, pH=5.0 and temperature= 300C)
The effect of adsorbate concentration is found by varying concentration
in the range from 5, 10, 20, 30, 40, 50mg/l and adsorption was investigated
under room temperature, pH 5 and the contact time is 1hour. For all these runs,
sand and chitosan coated sand was fixed as 2g.In
graph CCS shows the amount of chromium
ions were decreasing rapidly in the supernatant with the increasing
concentration of adsorbent dose due to greater availability of CCS surface
area. The maximum adsorption value of 20mg/l can be taken to be the optimum. For sand,the
absorbance increases with increasing adsorbate concentration.
On comparison
between CCS and sand, the adsorption of chromium is much more higher in CCS
than that of sand.For
chitosan, The absorbance increases with
increasing adsorbate concentration.On comparison between CCS, sand and chitosan
the adsorption of chromium was much higher in CCS than that of sand and
chitosan due to maximum surface area and free amino groups.
EFFECT
OF ADSORBENT DOSE:
The effect of adsorbent dose
is found by varying the range from 0.5, 1, 1.5, 2, 3 g for adsorption under
specific conditions like room temperature, pH 5 and contact time was 2 hours.
For all these runs, the adsorbate concentration is
taken as 20mg/l. In
the case of CCS, in the above graph,
by increasing the adsorbent dose, the absorbance of the supernatant decreases. For sand
and chitosan, the absorbance
seems to be constant for all the different adsorbent doses. On comparing CCS, chitosan and sand, the adsorption of chromium is much more higher in CCS than that of sand and chitosan.Therefore the maximum adsorption value of
2g can be taken to the optimum.
Figure
2. Effect of adsorbent dose on Chromium removal (Chromium ion
concentration = 20 mg/L, volume of sample=100 mL, pH
= 5.0, and temperature= 300C)
EFFECT
OF CONTACT TIME:
The adsorbate
concentration and adsorbent dose were kept as constant 20mg/l and 2gfrom the
above results..
Effect of contact time was found by varying time 30, 60, 120, 180, 300
minutes. For CCS, by increasing the
contact time, the absorbance of the supernatant was decreased and maximum
adsorption was found to be 300 minutes. For Sand, The absorbance seems to be
constant for varying contact time. The absorbance
increases with increasing the contact time for chitosan.
On comparing CCS, chitosan and sand; the adsorption
of chromium was much higher in CCS than that of sand and chitosan.
Increasing the contact time, the absorbance of supernatant was decreased, which
shows the maximum adsorption was attained at equilibrium condition.
Figure 3. Effect of contact time on Chromium ions
by Chitosan, sand and CCS (Chromium ion concentration
= 20 mg/L, Adsorbent dose= 2 g, volume of sample=100 mL,
pH=5.0 )
(a)SEM IMAGES OF CHITOSAN COATED SAND
BEFORE AND AFTER ADSORPTION
(b)SEM
IMAGE OF CHITOSAN
The Scanning Electron microscopic images of chitosan and chitosan coated sand are picturised
in figure 3.5 (a) and (b) and shows the better availability of surface
for the adsorption of chromium ions. The images are with striated and wrinkled
surface which could allow the surface for adsorption of chromium ions.
CONCLUSION:
Chitosan, a natural biopolymer was derived from
chitin. Chitosan coated sand (CCS) was used as an
effective low cost adsorbent for the removal of chromium metal ions. Synthetic
metal solution used was potassium dichromate. Chitosan,
CCS and sand were the three systems taken for the adsorption studies and then
the absorbance of the system was found using Atomic Adsorption
Spectrophotometer. The morphology of CCS before and after adsorption was done
using Scanning Electron Microscope (SEM). CCS shows effective adsorption due to
greater surface area availability than Chitosan and
sand alone, hence it is also advantageous that CCS is cost effective.CCS could
be very useful in creating permeable reactive barrier for the recovery of
metals. The recovery of chromium ions from the adsorbent was also done for the
reuse of adsorbent.
REFERENCES:
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Dube. A, Zbytniewski. R, Kowalkowski. T, Cukrowska. E, Buszewski. B,
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Baig.M.A, Bilal Mehmood and asifmatin.(2003),‘Removal of
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3.
Nassereldeen
Ahmed Kabbashi, Jamal I. Daoud,
Suleyman Aremu Muyibi and Isam Y. Qudsieh.(2011)’ Statistical Optimization of for Chromium
(IV) Removal on Aqueous Solution Using Chitosan’, Australian
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McKay.G,
J.C.Y. Ng, W.H. Cheung. (2003), ‘Equilibrium studies for the adsorption of lead
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PradipkumarDutta, JoydeepDutta and V S Tripathi. (2004),‘Chitin and Chitosan: Chemistry, properties and Application’, Journal
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Masud Aslam1, Ishtiaq
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Received on 20.09.2013 Accepted on 01.10.2013
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Asian J. Pharm.
Tech. 2013; Vol. 3: Issue 4, Pg 185-188