Prof. Dr. Salah Eldin EIMofty Prof. of Mining & Environmental Engineering,

Faculty of Engineering,

Cairo University, Egypt

October/2011

4th Kuwait Waste Management Conference 2011

USE OF ELECTROPHORESIS TECHNIQUE TO STUDY REMOVAL OF TOXIC METAL IONS

FROM WASTE WATER BY ADSORPTION ON MINERAL SURFACE

Introduction Introduction

Large quantities of toxic metals and Large quantities of toxic metals and pollutantspollutants

Entering the EnvironmentEntering the Environment

Different Areas of ResearchDifferent Areas of Research

Adsorption on Mineral Surfaces such as ClayAdsorption on Mineral Surfaces such as Clay

Clay structure

  EXPERIMENTS RESULTS

MaterialsMaterials The Clay Sample from Alex, Egypt The surface area of Clay was found to be 155m2/g

Compound % by weight

SiO2

Al2O3

MgO L.O.I

55.5 19.4 1.34 11.2

Electro Kinetic Characterization

Double-layer showing the surface of clays particles (left side), and the distribution of the adsorbed cations and anions within the double layer (right side).

Surface Charge Results

The surface charge patterns of Clay mineral particles in the absence and presence of the chloride salts of the heavy metals

Zeta potential of clay particles in absence and presence of different heavy metal cations

-30-25-20-15-10

-505

101520

0 2 4 6 8 10pH

Zeta

Pot

entia

l mV

pb++ C d++ C o++ K aolin Ni++

Effect of equilibrium time on adsorption density of M2+ onto Clay. (S/L 50g/L, Ci =10-3 M/L, temperature 200C).

0

0.005

0.01

0.015

0.02

0.025

0 1 2 3 4 5

Equilibrium time(min)

Ad

sorp

tio

n d

eniis

ty

(mg

/m2)

Pb2+ Cd2+Co2+ Ni2+

The adsorption density at equilibrium qe (g/m2) was calculated according to eq. (1)

(1)(1)

The pseudo first-order and pseudo second-order models were used. The first-order model is generally expressed as follows :

 

(2)(2)

Integrating eq.(2), at the following boundary conditions, t = 0 and qt =0 to t = t and qe = qt eq. (2) becomes:

(3)(3)

On the other hand, the second-order equation was used to predict the behavior over the whole range of adsorption. The second-order rate equation is described by:

(4)(4)

Where K2 is the rate constant of pseudo-second-order sorption (g/mg min). Integrating eqn (4) at the boundary conditions t=0 and qt =0 to t = t and qe = qt eq. (4) becomes:

(5)(5)

The constants qe and k2 can be determined using Excel Solver. The values of constants qe and k2 for second-order sorption.

Kinetic Models Constants For Heavy Metals Adsorption On Clay

Model type

Model constant

s

Heavy metalsPb Cd Co Ni

First order

qe

k1

0.0218.196

0.0118.196

0.00618.196

0.00618.196

Second order

qe

k2

0.0228200

0.0124200

0.008200

0.008200

Effect of solid to liquid ratio on the adsorption of M2+ onto Clay (Conditioning time of 15 min, Ci = 10-3

M/L, Temperature 20o C, and pH 5-8)

0

5

10

15

20

25

30

35

40

0 0.05 0.1 0.15 0.2 0.25

Solid-Liquid ratio

Ad

sorp

tion

den

sity

1X

10-3

, mg/

m2

Pb2+

Cd2+

Co2+

Ni2+

Effect of pH on adsorption density of M2+, onto Clay (S/L ratio 50g/L, Ci= 2x10-3 M/L, T=

20oC, and conditioning time 2 h)

0

10

20

30

40

50

60

0 2 4 6 8 10 12

pH

Ad

sorp

tion

den

sity

1X10

-3, m

g/m

2Pb2+

Cd2+

Co2+

Ni2+

Effect of heavy metal concentration on adsorption density of M2+ onto clay. (S/L ratio 50g/L, T=

20Co, and conditioning time 2 h, and pH 4.8-7.6)

Schematic of treatment plane for waste water with dissolved heavy metal ions, including adsorption of heavy metal using clay particles.

Conclusion

Electrophoresis measurements (Zeta potential) of these studies indicated the adsorption of the hydrolysable metal toxic ions on the Clay surfaces.

The sorption study indicated that the heavy and toxic metals Pb (II), Ni (II), Co (VI) and Cd (II) could be adsorbed and thus removed significantly by Clay from aqueous solutions.

The batch adsorption tests showed that the removal of metal ion by Clay is a fast process which can reach the equilibrium after 30 seconds.

The adsorption increases with increasing the initial ions concentration and pH. Kinetic modeling showed that the first-order model was appropriate for the description of this type of adsorption.

The experiment of heavy metal ion uptake by adsorbents showed a marked trend as follows: Pb2+ < Cd2+ <Co2+ ≥ Ni2+.

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