Removal of Heavy Metals from Wastewater Using Crab shells

Removal of Heavy Metals
from Wastewater
Using Crab shells
By
Kenneth Dorris

Water Pollution
Some Sources of water pollution Include
1. Agricultural waste - Nutrients contribute
to water pollution by stimulating
excessive growth of aquatic plants.
2. Sewage
3. Industrial wastes - which include heavy
metals such as Pb, Hg, Cd, Ni, & others

Various technologies have been developed
to remove toxic metal ions from water
1. Filtration
2. Chemical precipitation
3. Adsorption
4. Ion exchange
5. Electrodeposition, and
6. Membrane systems.

All of these technologies have
advantages and limitations
• They are either low cost but not very
effective -
• Or effective and can be expensive –

The Modern Thinking in the area of
Waste Treatment is Increasingly in the
area of SYMBIOTIC RELATIONS
The Use of WASTE
of one Industry by Another
Which in Turn
BENEFITS BOTH

Some Waste Material Might Include
1. Sea Food Industry
- - e.g., Crab Shells
2. Lumber / Timber /
Paper Industry
- - e.g., Sawdust
3. Agricultural waste
producing excessive
plant growth
- - e.g., Water Hyacinth,
duckweed, etc which
inhibit navigation

Crab shells were used to remove heavy
metals in aqueous solutions.
Advantages of crab shell waste include
1. availability
2. low cost and
3. high biocompatibility

Crab shell waste is an abundant
source of chitin
Chitin
[poly-β-(1,4)-N-acetyl-D glucosamine]
Is a Cellulose-like Biopolymer

When chitin is treated with
concentrated alkali, it undergoes
various degrees of deacetylation
and degradation, to give a
product called chitosan
Chitosan is the most important
derivative of chitin

H NHCOCH 3
O
OH H H H
H O O
CH 2 OH
CH 2 OH
O O
OH
H
H NHCOCH 3
H
H NHCOCH 3
OH H
O O
CH 2 OH
Chitin
H NH 2
O
OH H H H
H O O
CH 2 OH
CH 2 OH
O
OH
H NH 2
H
O
H
H NH 2
OH H
O
CH 2 OH
O
Chitosan
O
H
OH
OH
H H H
H O O
CH 2 OH
CH 2 OH
O
OH
H OH
H
O
H
H OH
OH H
O
CH 2 OH
O
Cellulose
Figure 1.1 Chemical Structure of Chitin, Chitosan and Cellulose.
Source: Lin, Shan-Yang; Perng, R. Chem. Pharm. Bull. 1992, 40,
1058-1060

Crab shell Waste
Soaked in 5% HCl for 1 hr (R.T.)
Soaked in 50% NaOH for 1 hr (90 o C)
Rinsed with water and Air Dried
Adsorbent ≡ Treated Crab shells

Instruments & Chemicals
• Varian 220 A A Spectrometer
• Fisher Scientific pH-meter
• Precision Scientific Corporation Shaker
• Reference Solutions for AA measurements
obtained from Fisher Scientific
• All chemicals were ACS reagent grade

Experimental
Initial concentrations of metal ions were
2.5 mg/L, 5 mg/L, 7.5 mg/L, and 10 mg/L
Crab shell quantities were
10 g/L, 25 g/L, and 50 g/L

Typical Experimental Procedure
1. Adsorbent + 100 mL metal ion solution
2. Agitated at 80 rev/min at room temp.
3. Samples taken at 5, 20, 60, 180 & 360 min
4. Analysis by Atomic Absorption

Effect of Crab Shell Loading (10g/L) on
Adsorption with 2.5 mg/L Lead
Time
(min)
Lead
mg/L
0 0.00
5 2.38
20 2.37
60 2.46
180 2.43
360 2.45

Adsorption of Lead vs Time (mins)
3
Adsorption of Lead
2.5
2
1.5
1
0.5
0
0 200 400 600 800 1000 1200 1400

Chitosan interacts efficiently
with transition metal ions

Protonation
CH 2 OH
O
OH
N
H H
Chelation
CH 2 OH
O
OH
O
O
+ H + +
+ 1/nM n+ NO 3
-
CH 2 OH
O O
OH
H
H
H - NO3
N +
CH 2 OH
O O
+ 2H +
+
NO 3
-
H
H
H - NO3
N +
O
N
M/n
H
H
+)
Total reaction
CH 2 OH
O
OH
CH 2 OH
O
O
+ 1/nM n+
O
+ H +
N
H H
O
NH 2
M/n

Chelation Ion Exchange
As opposed to simple ion exchange,
chelation ion exchange takes advantage
of the three dimensional structure of
molecules to chelate and remove ions of
a specific size in the presence of large
quantities of other ions.

Adsorption Kinetics influenced by
• Initial metal ion concentration,
• amount of adsorbent,
• pH value of solution and
• temperature

Effect of Initial Metal Ion Concentration
The initial metal ion concentration was
one of the most important factors that
determined the equilibrium
concentration, but also determines the
uptake rate of metal ion

Effect of pH on Adsorption
Adsorption of metal ions increased with
increases in pH. For lead, the sharpest
increase was obtained between pH 1 and 4,
while around pH 6 a plateau was reached,
and above pH 6, adsorption almost
remained constant. Experiments were
carried out in pH range of 7-8

3
2.5
2
1.5
1
0.5
0
Effect of pH on Adsorption
Cadmium
Lead
Nickel
0 2 4 6 8 10
pH Value
Adsorption of Lead, Cadmium
and Nickel

Percent(%)
120
100
Percent Adsorption vs pH
Concentration of Pb, Cd and Ni 2.5 mg/L
Crab Shell: 10 g/L
80
60
40
Cadmium
Lead
Nickel
20
0
1 2 3 4 5 6 7 8 9

Effect of Crab Shell Loading (10g/L) on Adsorption
with 2.5 mg/L Lead and 1000 ppm Anion Solution
Time
min
Cl - Br - F - CH 3
CO
O - SO 4
2-
NO 3
-
PO 4
-
0 0.0 0.00 0.00 0.00 0.00 0.0 0.0
5 1.99 2.07 2.15 2.15 2.01 2.02 2.37
20 2.04 2.23 2.32 2.28 2.30 2.28 2.36
60 1.86 2.09 2.12 2.31 2.07 2.40 2.42
180 2.30 2.30 2.41 2.41 2.37 2.33 2.42
360 2.27 2.35 2.39 2.45 2.38 2.44 2.19

Effect of Anions on Adsorption
3
Adsorption of Lead
2.5
2
1.5
1
0.5
Chloride
Bromide
Fluoride
Acetate
Sulfate
Nitrate
Phosphate
0
0 50 100 150 200 250 300 350 400
Time(min)

Regeneration of Crab shells
Crab shell samples which had
been exposed to heavy metal
solutions and adsorbed up to
97 percent lead, cadmium and
nickel were stripped with 0.1
M HNO 3
(pH~1.3). The heavy
metal cations were almost
completely removed from the
crab shells.

In Conclusion
• Advantages of the chitosan in parially
converted crab shell waste include
• The Observed Results indicated that the
metal uptake process was successful based
on the ion exchange chelation mechanism

In Conclusion
• pH values influence the adsorption
• No effect of anions on crab shells was
observed
• On changing Crab Shell Quantity and metal
ion concentration, the uptake rate changes