Adsorption of Lead, Zinc and Cadmium Ions

8/2/2019 Adsorption of Lead, Zinc and Cadmium Ions

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ADSORPTION OF LEAD, ZINC AND

CADMIUM IONS ON POLYPHOSPHATE-

MODIFIED KAOLINITE CLAYMohammad W. Amer1, Fawwaz I. Khalili1 and Akl M. Awwad2

1Department of Chemistry, University of Jordan, Amman, Jordan.2Industrial Chemistry Center, Royal Scientific Society, Amman, Jordan.

Accepted 9 November, 2009

A review on

by

Jean Audrey E. Aquinde

MS Environmental Engineering


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DENR Administrative Order 35:

Water Quality Guidelines and General Effluent Standards


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Treatment options for high toxicity WW

1. Chemical precipitation

2. Solvent extraction

leach solution is mixed with an immiscible organic solvent so the desired metal ion in

aqueous phase is transferred to organic phase

The two phases are then allowed to separate.

The process is then reversed by contacting the loaded organic phase with an aqueous

(strip) solution that transfers the desired metal ion back out of the organic.

The aqueous phase obtained is a pure and concentrated solution suitable for metal

recovery while the stripped organic phase is suitable for recycle.


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Treatment options for high toxicity WW

3. Reverse osmosis

4. Adsorption

economical

versatile and simple

applicable for very low concentration of heavy metals

suitable for using batch and continuous processes


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Adsorption

process in which matter is extracted from one phase and

concentrated at the surface of a second phase

PHASE I

PHASE 2

The reverse process of adsorption, i.e. the process in

which adsorbed molecules escape from solid surfaces, is

called Desorption.


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Types of Adsorption

1. Lack of solvent-solute interactions

hydrophobicity surfactants

2. Specific solid-solute interaction

Exchange adsorption: S-Na+ + Ni 2+' S-Ni 2+ + Na+

Physical adsorption

Chemical adsorption


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Kaolinite 1:1

SSA = 10-20 m/g

Non-expansible

Adsorption is typically on

external surfaces

and edges

Na+

O

H

+

-

Slightly

Negative

Limited isomorphous substitution

in octahedra (Al3+ for Si4+ )

CEC = 3-15meq/100g of clay


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Modification of kaolinite using sodium

polyphospate (SPP)

Polyphosphate

commercial dispersant

increases dispersion of clay on aqueous system

improves adsorption by enhancing the exposure of

available sites


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Adsorption Equilibria If the adsorbent and adsorbate are contacted long

enough, an equilibrium will be established between the

amount of adsorbate adsorbed and the amount of

adsorbate in solution.

Equilibrium

Early

Later

Adsorbed Molecule

Diffusing Molecule

Laminar

Boundary

Layer


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Adsorption isotherms on solid surface


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Commonly reported isotherm models

Langmuir

Freundlich

qe = mass of material adsorbed (at equilibrium) per mass of adsorbent

K= constant related to the energy of adsorption

Ce = equilibrium concentration in solution when amount adsorbed equals qe

Qa = maximum adsorption capacity

n, KF - system specific constants


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Langmuir Isotherm


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Objectives

evaluate the adsorption performance of locally modified

kaolinite clay for the removal of Pb (II), Zn (II) and Cd (II)

from single aqueous solution.

explore the possibility of recycling the adsorbents and

recovery of metal resource.


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Methodology

Modification of kaolinite clay

Preparation of adsorbate

Adsorption experiment

Desorption experiment

Establish working temperature

and pH.

Determine effect of contact

time, adsorbent and adsorbatedose


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Figure 1 . XRD of unmodified kaolinite clay

Legend:

K kaolinite

F feldsparH hematite

Q quartz


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Figure2. FTIR spectra of a) unmodified kaolinite clay and b) SPP-modified kaolinite clay


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Figure 3. Langmuir adsorption isotherms for Pb (II), Zn (II) and Cd (II)

sorption by SPP-modified kaolinite clay.

Table 1. Langmuir constants and correlation coefficient at different temperatures.


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92.10 %

74.26 %

55.12 %

Figure 4. Effect of pH on adsorption capacity at temperature 35C.

Figure 5. Sorption isotherm of Pb2+, Zn2+, and Cd2+ ion on SPP-modified kaolinite clay as a

function of initial metal concentration at pH 5.0 and temperature 35C.

Effect of

adsorbatedose


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Figure 6. Variation in the sorption capacity and percent of adsorption versus the

adsorption dose of SPP-kaolinite clay at pH 5.0 and temperature 35C.

Effect of adsorbent dose


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Figure 7. Effect of contact time on the sorption of metal ions at pH 5.0 and temperature 35C.

Effect of contact time


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Desorption study

The total loss amount of metal released from sorbents

varied from 2.0 - 4.0% only.


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Conclusion

SPP-modified kaolinite clay was found to be very goodadsorbent for lead, zinc and cadmium from aqueoussolutions.

The optimal pH for removal of metal ions by the SPP-modified kaolinite clay is 5.0.

The adsorption of Pb, Zn and Cd to SPP-modified

kaolinite follows a monolayer dispersion as best modelledby Langmuir isotherm.

Order of metal binding capacity: Pb2+>Zn2+>Cd2+

Documents

Adsorption of Lead, Zinc and Cadmium Ions