Removal of Heavy Metals from Wastewater Using Crab shells

ByKenneth Dorris

Water PollutionSome Sources of water pollution Include1. Agricultural waste - Nutrients contribute

to water pollution by stimulating excessive growth of aquatic plants.

2. Sewage3. 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. Filtration2. Chemical precipitation3. Adsorption4. Ion exchange5. Electrodeposition, and6. 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

2. Lumber / Timber / Paper Industry

3. Agricultural waste producing excessive plant growth

- - e.g., Crab Shells

- - e.g., Sawdust

- - 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 include1. 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

O

H

OHH

OH

CH 2OH

OHCH 2OH

H

OH

O

OH

HO

OHCH 2OH

H

OH

O

OH

HO H H

O

H

NHCOCH 3H

OH

CH 2OH

OHCH 2OH

H

OH

O

NHCOCH 3

HO

OHCH 2OH

H

OH

O

NHCOCH 3

HO H H

O

H

NH 2H

OH

CH 2OH

OHCH 2OH

H

OH

O

NH 2

HO

OHCH 2OH

H

OH

O

NH 2

HO H H

C h i ti n

C h i t o s a n

C e l lu l o s e

F i g u r e 1 . 1 C h e m i c a l S t r u c t u r e o f C h i t i n , C h i t o s a n a n d C e l l u l o s e .

S o u rc e : L i n , S h a n - Y a n g ; P e r n g , R . C h e m . P h a r m . B u l l . 1 9 9 2 , 4 0 , 1 0 5 8 - 1 0 6 0

Adsorbent ≡ Treated Crab shells

Crab shell Waste

Soaked in 5% HCl for 1 hr (R.T.)

Soaked in 50% NaOH for 1 hr (90oC)

Rinsed with water and Air Dried

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 LeadTime (min)

Leadmg/L

0 0.00

5 2.38

20 2.37

60 2.46

180 2.43

360 2.45

0

0.5

1

1.5

2

2.5

3

0 200 400 600 800 1000 1200 1400

Adsorption of Lead

Adsorption of Lead vs Time (mins)

Chitosan interacts efficiently with transition metal ions

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O

N

OH

CH2OH

H H

O+ H + +

O

N+

OH

CH2OHO

Protonation

Chelation

O

N

OH

CH2OH

H H

O

HHHNO3

-

O

N+

OH

CH2OHO

HHHNO3

-

+ 1/nM n+

NO3-

O

NO

CH2OHO

H

H

NO3-++ 2H+

M/n

+)

+ 1/nM n+O

NH2O

CH2OHO

M/n

+ H +

Total reaction

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

Effect of pH on Adsorption

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10

pH Value

Adsorption of Lead, Cadmium

and Nickel

Cadmium

Lead

Nickel

Percent Adsorption vs pHConcentration of Pb, Cd and Ni 2.5 mg/L

Crab Shell: 10 g/L

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9

Percent(%)

Cadmium

Lead

Nickel

Effect of Crab Shell Loading (10g/L) on Adsorption

with 2.5 mg/L Lead and 1000 ppm Anion SolutionTimemin

Cl- Br- F- CH3COO-

SO42- NO3

- PO4-

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

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250 300 350 400

Time(min)

Adsorption of Lead

ChlorideBromideFluorideAcetateSulfateNitratePhosphate

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 HNO3 (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