PHYSICO-CHEMICAL STUDIES ON WATER-POLLUTANTS.

DISSERTATION

SUBMITTED fM PARTIAL FULFILMENT OF THE REQUtREMEBITS FOR THE AWARD OF THE DEGREE OF

Mnittv of ^^iloiopl^p m

CHEMISTRY

Uaier the SifM?isk» of

Dr. ANEES AHMAD

By

QASIM ULLAH

DEPAKTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

1994

^ ^S>l'fl ^•i^tn

^-^^Si^

DS2291

PHONE : (0571) 25515

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY ^ A L I G A R H - 2 0 2 0 0 2 M a r c h , 9 . 1 9 9 ^

Dated. „ ^

TO WHOM IT MAY CONCERN

This is to certify that the work embodied in this

dissertation entitled "PHYSICO-CHEMICAL STUDIFS

ON WATER-POLLUTANTS", is the original contribution

of the candidate and is suitable for submission

for the award of M.Phil, degree in Chemistry of

Aligarh Muslim University, Aligarh

(Dr. Anees Ahmad) Supervisor

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17* r^ r- e?- m t:, £5

c o isr T K isi T s A c k n c i w l e d g m e n t ( i )

L i s t o f T a b ! e s ( i i )

List of Figures (i i] )

ChaptfM- I

Int rod net ron ( 1 )

References (22)

Chapter IJ

I ntroduction (26 )

Material and Methods (29)

Result and Discussion (34)

References (64)

ACKNOWLEDGMENT

I feel deep sense of gratitude to Dr. Anees Ahaniad ,

Lecturer, Department of Chemistry, A.M.U. for his constaii*

encouragement-, unflLnching support and excellent supervision

which enabled me to finalize all my work. I sincerely thanl

Prof. A. A. Khan, Chairman, Department of chemistry, f t

providing necessary res<^arch facilities. I am also thankfn'

to Prof.M. A. Beg, ex. Chairman , Department of Chemistr\,

A.M.U. Aligarh,

T must express thanks to my seniors and friends

particularly to M/s Zaheer Khan, Farhat Hasan Khan and I.A.

Ansari, for their kind cooperation.

I am also equally thankful to all of my family members

for thf=ir grea^- affection and care.

Finally, 1 am thankful to Mr. S.Qamar Alam and Mr. Mohd.

Saleem ^1 i for typing the manuscript.

(QASTM ULLAH)

(1)

T TL :FI t:: £^ cz* f^ T* a fc> 1 e^ £^

Table No. 1 .1 Soirif Common Inorganic PoJ lutants .

Table No. 1.2 Sono Common Organ] c PoJ l\3tant s .

Table No. 2.1 Tho Kel.ited Parameters for the Adsorption of

I'd on Saw Dust at Different Temperatures.

Table. No. 2_. 2 Tfie Related Parameters for the Adsorptron of :'n on Saw Dust at Different Temperatures.

Table No. 2.3 The Thermodynamic Parameters for the adsorfit ion of Zn on Saw Dust at Different Temperat\3res .

Table No. 2.4 The Thermodynamic Parameters for the

.i'lsor[)t 1 iin of Cd on Saw Dust at Different

Tempo rat ures.

Page No

( ! i )

IJ JL :3 "tz <o> JF F ± ^ V j^ 3r- ea £3 P a g e Nc

Figure 1.1 : Chemisorption of Hydrogen on Nickel !1)

I'igure 1.2 : Classification of isotherms shape (\^)

Figure 2.1 : Effect of time on removal of Zn and ( 3) + 4

Cd by saw dust + + + +

Figure 2.2 : Effect of dose on removal of Zn and Cd { ', S )

by saw dust

Figure 2.3 : Effect of pH on removal of Zn and Cd (57)

by saw dust

Figure 2.4 : Effect of concentration on removal of (3Q) /n and Cd by saw dust

Figure 2.5 : Adsorption of Zn on saw dust at various (4'~0

t onipeartures

Figure 2.6a: Ereundlich plots for the adsorption on Zn (4(,)

on saw dust

Figure 2.6b: Langmuir pJots for the adsorption of Zn (47)

on saw dust

I'igure 2.6c: The plot of Langmuir and Freundlich constant (4f!)

(Ink) Vs temperature (1/T)

Figure 2.7 : The adsorption of Cd on saw dust at various (4")

temperatures

Figure 2.Ba: Freundlich plots for the adsorption of Cd (50) on saw dust

Figure 2.81): r,angmuir plots for the adsorption of Cd (51 )

on saw dust

Figure 2.<Sc: The plot of T,angmuir and Freundlich constant (52) (Ink) Vs temperature (1/T)

Figure 2.9 : Effect of N a d on removal of Zn and Cd

by saw dust at 40 C

(iil)

(60)

C ! H Z \ E > T E ; E t

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INTRODUCTION

Environmental pollution [1] has been defined

as the unfavorable alternation of our surroundings

by industrialization or by other human activities.

A substance is called a pollutant provided it

interfere with health, comfort, amenities or

property values of people. Generally a pollutant is

introduced into the environment as sewage, waste,

accidental discharge or as a by-product of

manufacturing processes. It is also introduced

into the environment as compounds used to protect

plants and animals.

Pollutants are of different kinds in

surroundings which are found in the form of liquid,

gas or solid. On these bases they may be broadly

classified into following classes - (a) Inorganic

]'ollutants and, (b) Organic Pollutants.

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Environmental pollution is the burning problem

of modern life. Therefore, a number of books [2-9]

have been written and international symposia [10-16]

have been organized on the subject. In developing

countries lil<;e India, there is an immense need of

simple and inexpensive methods for pollution

monitoring and control. Therefor, an attempt havn

been made to develop simple and sensitive

techniques for the detection and determination of

these pollutants. Analytical chemistry plays a very

important role in both dealing and controlling

environmental pollution. It can be thought as

comprising of two branches, qualitative and

quantitative. Qualitative analysis deals with

finding what constituent or constituents are in

analytical sample, and quantitative analysis deals

with the determination of how much of a given

substance is in the sample. With today's

instrumentation and with a large variety of

chemical measurements available, specificity or

sufficient selectivity can often be achieved so

that the quantitative measurement serves as a

(9)

qualitative measurements.

Adsorption and ion-exchange are the two

important conception in analytical chemistry since

the solid-liquid interactions have always been of

interest because of their diversity and immense

applications. Interactions between the components

of liquids or solutions and surfaces of the solids

make, in a wide variety of ways, a momentous

contribution to our everyday life. Its importance

in the petroleum, chemical and pharmaceutical

industries is well established. However, recent

activities in biotechnology, medicine, biomedical,

biochemical, environmental and polymer engineering

have broadened the usefulness of processes.

Similarly, ion-exchange is one of the most

xersatile analytical technique in Separation

Science. Various applications of ion-exchange

procedures are in the field of heterogeneous

catalysis, radiochemical analysis, solid

electrolytes, inorganic ion-exchange membranes,

environmental studies, ion-selective electrodes and

intercalation compounds.

(10)

A. ADSORPTION:

Adsorption may be defined as "the phenomenon

of higher concentration of any molecular species at

the surface than in the bulk of a solid (or a

liquid) is known as adsorption.

Adsorption [17] can be distinguished carefully

from absorption. The latter term implies that a

substance is uniformly distributed throughout the

body of a solid or liquid. The solid that takes up

a yas or vapouror a solute from a solution, is

called the adsorbent, while the gas or the solute,

which is held to the surface of the solid, ]s

called the adsorbate.

Mc Bain [17] suggested that the term sorption

should be used to describe a process in which both

absorption and adsorption take place

simultaneously.

The phenomenon of adsorption, is also known as

surface phenomenon, has been known since 1773 when

ScheeJe 117] discovered the uptake of gases by

charcoal. Sometimes the adsorption can bo

classified as Physical adsorption or physisorption

(11)

and chemical adsorption or chemisorption. The

former is also known as Vander waal's adsorption in

which gaseous molecules are held to the surface o ('

an adsorbent by physical or Vander Waal's forces

i.e. the forces of molecular attraction. Physical

adsorption of a gas is accompanied by a low heat of

adsorption which is of the same order as the heat

of liquefaction of gas.

Chemisorption, in which the gaseous molecules

are more or less completely dissociated into atoms

which combine with the surface atoms of the

adsorbent by valency forces i.e. by the process of

electron sharing as in the formation of chemical

compounds. Chemisorption is accompanied by

evolution of a large amount of heat, Chemisorption

of hydrogen on Nickel is represented as below [18].

ADSORBED HYDROGEN GAS —•• H H H H H H H

I I I I I I I SURFACE ATOMS • -N i — Ni - N'\ - Ni — Ni — Ni — Ni

lihliiiiiiiihiim^^^ Figure No.t.1 : //////////NICKEL METAL/////

In chemisorption, the surface enters into reactions

as a catalyst. This type of catalysis, called

(12)

heterogeneous catalysis, is understandable only on

the basis of some of the informations deduced in

adsorption studies. The photo electron

spectroscopy (ESCA) can be applied to reveal some

of the bonding properties of the adsorbed species.

In surface studies this is normally referred as

photoemission spectroscopy. Adsorption is

essentially a phenomenon of separating surface and

the interfacial tension 119]. It is generally

cjoverned by the thermodynamic relation.

AG = A H - T A S (1 )

AG, AH and AS are taken, respectively, as the free

Energy, heat and entropy changes in the process.

The Process of adsorption is generally exothermic

but endothermic process have also been reported in

case of large ionic-miceller system such as those

of dyes in solution.

The reverse process (i.e. desorption) measures

the resistance of the systems to change, and

manifests itself as a binding force between the

adsorbate and adsorbent. The binding forces

involved may be of several types, such as vander

(13

Waal's Ion exchange, covalent bond formation and

hydrogen bonding, depending on the nature of the

substrate, surface and the adsorbate.

The surface structure of a solid is controlled

to a large extent, by the underlying bulk structure

whach, m turn, is defined by chemical composition

and crystal structure. The various surface groups

on the common polar adsorbents may ionize in the

presence of water or similar solvents leaving a

net charge or so called zeta-potential, on the

surface of the adsorbent. This surface charge has

been claimed by many workers [20,21] to have an

important effect on the sorptive properties of an

ctdsorbent, especially where ion-exchange plays an

important role.

Adsorption Isotherms: Most of the studies on

adsorption from solution have been concerned with

equilibrium conditions, and predominantly with the

adsorption isotherms. An adsorption isotherm

describes the equilibrium relationship between the

adsorbed and unadsorbed sample, at a given

temperature. It is a plot of the concentration of

(14)

"x" in the unadsorbed phase. The interest in

these isotherms lies in the amount of information

they can yield, viz., identification of th(

adsorption mechanism, heat of adsorption, specific

surface area of the porous solid, diagnosis of th<

orientation of the solute molecules at the surface,

and its degree of self associations.

The earlier attempts [22] of classification of

isotherms have served for quite a long time. Four

types of isotherms are identified on the basis of

the shape of the initial part of the isotherms.

This classification of isotherms had been reported

and theoretically explained by Giles et al [20,23]

on the basis of solid solution interface. various

shapes of the isotherms considered are shown in

Fig. 1.2, and can be characterized as follows:

(i) Langrnuir or L-type isotherms

(ii) S-type isotherms

(iii) High affinity or H-type isotherms, and

(iv) Constant partition or C-type isotherms.

The L-type isotherms are most common. They

are characterized by an initial region which is

( J 5 )

0)

" g O ^

§ Q 3 ^ 3

mx

Class L H

y

^^—^

r-

/

_u!--o

r-

^

_^- -o

• ^ ^ ^

/

, ^ 0

concentration of solute in liquid phose

FIGURE 1 .2 :aa»sJficarion of isotherms shopeCGites etal,l960,1974)

(16)

concave to the concentration axis. They are

obtained when there is no strong competition from

the solvent for sites on the surface. The curves

refer to those cases m which the most active sites

are initially covered, but the case with which

adsorption takes place decreases until a monolayer

is completed.

For the S-type Isotherms the initial region is

convex to the concentration axis which is

frequently followed by a point of inflection

leading to an S-shaped curve. These isotherms

indicates that

i) The solvent is strongly adsorbed

Li) There is strong intermolecular attraction

within the adsorbed layer, and

iii) The adsorbate is monofunctional.

The second condition is most likely obtained,

if the major axis of the adsorbed molecules is

I)erpendicular to the surface. By a monof unctional

adsorbate we mean here that the molecule has a

single point of strong attachment in an aromatic

system or an aliphatic system of more than five

(17)

carbon atoms. Further, the adsorbate is not

iniceller. In many cases, the S-curve indicates a

'cooperative adsorption' with solute rnoleculen

tending to be adsorbed, packed in rows or clusters.

The H-curve occurs when there is a high

affinity between the adsorbate and adsorbent, which

is shown even in very dilute solution. Thus, it

can result from the chemisorption or from the

adsorption of polymers or ionic micelles, though

cither special cases are known.

Finally the C-type Isotherm has an initial

linear portion which indicates a constant

partition of the solute between the solution and

the adsorbent and occurs with the microporous

adsorbents.

The isotherms have a great utility in

diagnosing the mechanism of adsorption, and also in

distinguishing the probable configuration of the

adsorbed molecules [20]. Thus, S-curve indicates a

vertical orientation, L-curve shows the flat

orientation and strong intermolecular interaction,

while H-type isotherm is assumed to be typical of

(18)

sample micelle formation. However, such a

generalization needs great care, as many other

factors also contribute to the isotherm's

shape [24].

The adsorbents which have been commonly

studied earlier are fly ash [25-30], peat [3]

36] clays [37,38] alumina bauxite [39], wool-

astonite [40,41], and sludge [42-48]. Some othef

cidsorbents have been proved quite useful viz.

alumina, silica, carbon and cellulose [49]. In

addition to these, some adsorption studies have

also been reported on tin oxide, titanium oxide,

thorium oxide and zirconium oxide. [50]

Mechanism of adsorption:

Although adsorption from solution by solids is

of great practical importance and a vast number of

papers have been published. Much of the early worl<

was concerned with relatively dilute solutions, and

interpretation of the isotherms was not

unreasonably analogous to that used for adsorption

from the gas phase and experimental results were

fitted to equations of the Langmuir and Freundlich

(19

types. The role of solvent and its competition

with the solute for surfaces sites has now become

recognized as an important factor, particularly as

a result of a large number of studies on the

adsorption from binary liquid mixtures and their

thermodynamic analysis.

The interaction between the surface and

adsorbed species may be either chemical or

physical. Several types of bonding can be

identified as follows [51]:

(1) Chemical adsorption (chemisorption)- stearic

acid from benzene solution on metal powders.

(2) Hydrogen bonding - long-chain alcohols from

hydrocarbon solution on dry oxide surfaces.

(3) Hydrophobic bonding- association of hydro

carbon chains to "escape" from an aqueous

environment, e.g., acids on polystyrene

(4) Vander Waal's forces.

The net interaction of an adsorbate molecule

with a surface might involve more than one type of

interaction, depending on the chemical structure of

both components.

( 2 0 )

The most favoured approar-h to an invest igat i osi

of the adsorption mechanism is a study of the

isotherm [51]. The important aspects are (a) the

rate of adsorption (b) the shape of the isotherms

(c) the significance of the plateau found in many

isofherms (d) the extent of solvent adsorption, (e)

whether the adsorption is mono molecular or extends

over several layers, (f) the orientation of the

adsorbed molecules, (g) the effect of temperature,

(h) 'he nature of the interaction between adsorbate

and adsorbent.

Some Recent Studies on the Adsorption Behaviour of

Saw Dust

'iany workers studied adsorption behaviour of

hea\'y metals on saw dust which are summerised as

fol1ows:

(1) Removal of chromium (vi)- Singh, D.K. Mishra et

6 + .i} [5J] used saw dust for the removal of Cr

f rom aqueous solution by using column packed.

6 + '!'he removal of Cr was max. at pH-2 .

(2) Removal of bead and Copper Ions: Aval ,('..

^iotedaiyen [53 1 have studied the adsorpti( t

(21)

behaviour of Pb Sc Cii on saw dust column.

Thp concentration, of these ions (as measured

via at absorption spectroscopy) could be

reduced to <lppm

Chung. Yongsoon et. al. 154] have also studied

the adsorption behavioiir of heavy metal ions

on saw dust column.

(3) Determination of Copper in industrial effluents

and Receiving Water and Its Removal Begum,

Shak]la [55] estimated Cu by using saw dust in

effluents as well as in water with the help of

l.angmuir adsorption equation. The maximum

adsorption capacity of the adsorbent increased

o

with temperature between 3 0-50 C.

(4) Adsorption of Cu : Vaishya & Prasad [56], have

+ + studied the adsorption of Cu on saw dust of

I'assia latifollia without any pH adjustment.

The sorption equilibrium data were modeled V)v

[lot h Frenndlich and Langmui r isotherm. Copper,

rf'moval was observed and it was found that th.

I'laximum adsorption take place at pH 7.3.

(22)

References

1. A.K. De, and B.K. Pa], J.Indian Chem. Soc. Vol. LrV,:'65, (1 977)

2. Fl.B.n. Jr. Cooper, and A.T. Jr. Rossano, "Sourre

and testing for air pollution control" Mc c,raw

H] I J , N.Y., (1974)

3. "Standard Methods for the Examination of WAter

and waste water", A.P.H.A., W.P.C.F. and

A.W.W.A., 14th ed., N.Y., (1976)

4. 1). E^anerjea, Science and Culture, 42,38 (1976)

5. J.P. Toraany, "Air pollution, the emission, tli

regulations and control", Elsevier, N.Y.,

<1974)

r, . A.c. stern, "Air Pollution", 2nd. ed. , Academic

N.Y.(1968).

7. R.C. Thomas, and L.M. Robert, Meserve "Water and its impurities", 2nd. ed. N.Y. U.S.A., (1973 ) .

R. VV. Strauss, "Air pollution control". Part3,

Chichf^ster Wiley-Inter Sci ence , ( 1 178 ) .

^). (\. Zwi> I g , and J . Sherma , "Ana 1 yt i ca \ Methods for Pesticides and Plant Cirowth Regulators",

Ac. id em I c N . Y . ( 1978 ) .

10. M. Michael, BenruMe, "Pesticides Chemistry m jOth Century", No.37,Elsevier, Amsterdam, (1977).

11 . 1. Michael , B6?norie, "Atmospheric Pollution 1978", F)sevier, Amst erdam, ( 1978) .

12. W.W. Eckenfelder, "Advances in Water Pollution Resf-arch," 2, 1st ed. , (1964).

13. O. Jaaq,"Advances in Water Pollution Research, "l,lst'ed., (1964).

(23)

14. E,A. Pearson, "Advances in Water Pollution

Research,"3, Isted . , {1964) .

]5 . Prague, ".Advances

Research", (1969). m Water poJlut ion

J6. B.A. Southgate,, "Advances in Water PolJuticri

Research", 1, 1st ed., (1964).

17. B.R.Puri, L.R.Sharma "Principle of Physical Chemistry" pp 980, 29th edit (1988).

18. .B.R.Puri,L.R.Sharma"Principle of

Cheirnstry" pp 6.39, 29th edit (1988)

Physica1

19..A.W.Adamson, The physical Chemistry Of

Surfaces, Inter Science (1960).

20. ('.n. Gil PS, T.H. MacEwan, S.N. Nakhwa, and n.Snnth, J.rhem. Soc.(Lonson) 3973 (1960).

21. c.ri. Giles, I.A. Easton and R.R.Mcky, J. Chen.

Soc, ( London ), 449"^ ( 1964 ) .

22 . lA'.Ostw,! Id and F . Izaggurra , Ko 1 1 oi d , 7,. , 30 , 27')

(19 2 3) .

2'y. (••. H .c i les , D.Smith and A.Huitson, J.Colloid Interface Sci., 47 755 (1974)

24. I .R.Snyder, "Principles Of Adsorption Chromato­

graphy", Marcel Uekker, New York, pp.lf:' i

(196 8).

25. R. M. James and G.L. Richard, J. Wat. Pollut,

Cont. Fed., 58, 242 (1986).

26. P.P. Vishwakarma, K.P. Yadav and V.N. Singh,

Pertainka, 12, 3 (1989).

27. A.K. Sen and A.K.De, Water Research, 21, 885 ( 1 )8 7 ) .

28. K.P. Y.^dnve, B.S. Tyagi, K.K.Pandey, and V.N., Smyh, Environ. Technol . Lett., 8, 225 (1987).

(24)

29. C.P.Haung and W.J. Stumin, J.CoJloid interfaro Sri. , 43 409 (1973) .

30. R.R. Gadde- and H.A. Laitinen, Anal. Chfm., 4ji ,

2022 (1974).

31. P.R.Bloom and M.B. Mc Bride, Soil Sci., Sor. Am. J., 43, 687 (1979).

32. R.L. Chaney and P.T. Hundeinann, J. Water

Pol H u t . Control. Fed. 51, 17 (1979).

33. C.B.nissanayake, and S.V.R.Weera Sooriya, J.

Environ. Stud., 17 233 (1981).

34. E.P. Smith, P. Mac Carthy, T.C. Yu and H.B.

Mark. .1. Water Pollut. Control F'ed. , 49, 63^.

' I 477) .

!5. A.Wolf, K.Bunzl, F'.Dietl and W.F.Schmidt,

(Miomospher, 5 207 ( 1977) .

36. T.c.oRset, J. Ij. Trancart and 0. R. The Vanot,

Water Res., 20, 1 (1986).

37. H.R.Frost and R.A. Griffin, Soil sci., Soc. Am.

Proc. , 41 53(1977) .

''8. M.Ajmal, A.A.Nomani and A.Ahmad, Water,Air and

Soil Pollution, 23, 119, (1984).

39. S.K. Gupta and K.Y. Chem, J.Water Pollution.

Cont. Fed., 50 49 3 (1978).

40. f>.K.Jain, V.N.Sing and G.Prasad, Proc.7th inter-natlonal Clay Conf. 137 (1982).

41. K.K Pandey, G.Prasad and V.N. Singh, "Water,

A 1r and So i 1 Po1 lution", 27,287 (1986).

42. S.F.Fee, H.S.Shin and B.C.Paink, Wat.er Res., 23, 67 (1989).

43. B.G.Oliver and E . G . Cosgrove , T,eH , 9,75 (197S).

(25)

45. R.D.Neufeld, J.Gutierrez and R.A. Novak, ,T.

Water Pollut. Contr Fed., 49 489 (1977).

46. M.H. Cheng, J.W.Patterson anJ R.A.Minear,

J.Water Pollut. Control fed., 47 562 (1975).

47. P.O.Nelson, A.K. Chung and M.C.Hudson, J,,

Water Pollut. Control Fed., 53, 1323 (1981).

48. S.Tom, S.L. Patricia, R. Thomasj.n, M.S. Robert

and N.lj. John, J.Envir., Engg. n j 1074 (1987).

49. E.Heftman, "Chromatography" Reinhold Pub. Cort^.

pp 53, (1963).

50. H. Kitagawa, Carbon ,1^8, 448 (1980).

51. (J.l). Partfitt and C.H. Rochester, "Adsorption

fron Solutin at the Sol id-Li njuid Interface",

j)pU) ( 1983) .

52. P.K. S]ng, N.K. Mishra, D.N. Saksena, J. Inst. Engg. (India), Chem. Eng. Div., ?JH3),90-I, (1990) (Eng.).

53. G. Aval, Motedayen Iran. J. Chem. Eng. 1991, IJl

(2), 21-3 (Eng).

54. Chung, Yong Soon, Lee, Kang Woo, Yoon, Yeo Seong, Kwon, Soohan, Lim, Kwang Soo Bull Korean Chen. Soc. y (2), 212-14,(1992) (Eng).

55. S. Begum, (PCSIR Lab, Peshawar, Pak.). Sci.

Inst. (Lahore) 4(1), 67-8, (1992) (Eng).

56. R.C. Vaishya, S.C Prasad, Indian J. Enviro. Prot. 11(4), 284-9 (1991) (Eng).

O H Z V ^ f T E T R X T

(26)

INTRODUCTION

The environmental pollution in general and

water pollution in particular is the burning

problem of modern life. Therefore, a number of

books [1-6] have been written and international

symposia have been organized on the subject. Water

is polluted by the industrial waste and effluents.

Industrial waste includes heavy metals such as Zn,

Cd, Hg, Cu etc. and other impurities.

Zinc IS discharged into the waste streams of

many industries such as steel works with

galvanizing lines, zinc and brass metals works,

zinc and brass plating, viscose rayon, yarn and

fiber production, ground wood pulp production and

news print paper production. The zinc salts ar.

also used in the pigment industries. The safety

limit of zinc for aquatic life is given as 5 mg/L.

Cadmium is introduced into aquatic system

through discharge of their untreated effluents int.)

various water bodies by industrial process such as

electroplating process. Cd has been proven to be

a non essentia] and non beneficial elements. It

(27

causes a number of acute and chronic disorders,

causing cancer of various parts of the body, the

fatal 'itai-itai' disease, cyanosis, anemia,

weakening of bones etc. [7], Therefore, the

induslrial effluents/ waste waters containing

cadmium should be treated to eliminate/reduced the

cd-contents prior to their discharge into the

receiving water bodies. A number of process are

known which are employed for the removal of heavy

met.ils. The major of them are neutralization,

precipitation, adsorption, ion-exchange etc.

Adsorption process using activated carbon has been

a popular choice Jn developed countries like U.S.A

but the high cost of activated carbon limits its

use in the developed nations only.

The adsorption phenomenon has still been found

economically appealing for the removal of toxic

metals from waste waters, by choosing some

adsorbents under optimum operation conditions.

Several adsorbents have been used earlier for

+ + + + treatment of these metal ions (Zn , Cd ). It

lias been reported that some aquatic plants [8-11],

(28)

agricultural by products [12], waste tea leaves

113], and sawdust []4], have tine capacity to adsorb

and acciirrivi 1 ated heavy metals.

The study of the feasibility of these metal-

+ f +- + ions (Zn Cd ), by sawdust, an unconventional

adsoibent is describe here. Much attention has

been paid to optimizes the effective abatement

conditions in a cost effective fashion. Saw dust,

one of the cheapest and abundantly available

adsorbent has been tried for the uptaVce of these

metaJs from aqueous solution. The effect of

equilibrium time, pH, temperature, concentration,

dose and salinity on the removal of these metals by

saw dust Jiave been studies. The adsorption

isotherm and the probable mechanism have been

explained. The appropriate thermodynamic

parameter, viz., change in free energy, entropy and

enthalpy have been calculated and described here.

(29)

MATERIAL AND METHODS

1.1. Adsorbent:

Saw dust was used as an adsorbent for the

removal of these metal-ions from aqueous solution.

Tt was collected from the timber workshop situated

neai the university campus. Saw dust was treated

with HCl and washed with distilled water thoroughly

to clean the adhering dirt, and finally dried in an

air oven at 100 C and then used.

1.2 Adsorbent so]uti on:

The stock solution of metal-ions was prepared

(.005M) by dissolving their corresponding salts in

distilled water and standardized coroplexometrically

with FDTA (disodium salt) using EBT (Eriochrome

Black-T). All other reagents used were of

analytical grade.

1.3. Batch Adsorption Studies: Batch

adsorption experiments were carried out by shaking

0.5 gra of the saw dust with 50 ml aqueous solution

of metal ions solution of desired concentration at

various pH and at different temperatures (22"C to

o 60 C) in different stoppered bottles for different

(30)

retention times using a temperature controlled

shaker. At the end of the predetermined time

inteival the adsorbent was removed by filtration

and the equilibrium concentration was estimated

with EDTA. Blanks were also prepared to find out

the adsorption on to the internal surface of the

bottles, if any. The effect of pH on th<

adsorption phenomenon was studied by adding either

1.0 N HCl or NaOH in metal-ions solution.

To study the effect of salinity on the removal

+ + + + of these metal ions (Zn , Cd ), the experiment

o was also conducted in presence of NaCl at 40 C

only. The concentration of the NaCl was maintained

at 0.1 M by adding 5 ml of a 1.0 M NaCl stock

Bolut ion.

1.4 Adsorption Model:

To quantify, the adsorption capacity of saw

dust for the removal of metal-ions solutions from

vvater, the Langmuir and Freundlich equations were

app]led.

a) Langmuir Model: Langmuir proposed the

following model:

(31

Ce/ Am = 1/K 1/b + (1/b) Ce (1)

where 'Ce' is the equilibrium concentration

(mole/1) and 'Am' is the amount adsorbed per-

specified amount of adsorbent (mg/g). 'K' is the

equilibrium constant and 'b' is the amount of

adsorbate required to form a monolayer. Hence, a

plot of Ce/Am vs. Ce should be a straight line witli

a slope 1/b and intercept as 1/Kb.

b) Freundlich Model: According to this model

1/n Am = K.Ce

or in (Am) = In K + 1/n [In (Ce)] (2)

wher(= all the terms have the usual significance and

'n' is an empirical constant. Thus a plot of In

(Am) Vs. In (Ce) should be a straight line with .i

slopi^ ']/n' and intercept In K. This model deals

with the multilayer adsorption of the substance oti

the ,-idsorbet . The points indicate the observed

data and the line corresponds to the fitted data.

A computer simulation technique have been

applied to fit the Freundlich and Langmuir

equations, for the adsorption data. The

coefficients of least square fitting to a straight

(32)

link (R) were computed for these two models.

The thermodynamics parameter AG, AH and A S .

were computed from the equations given below and

listed in table. The free energy change (AQ) was

calculated from the relations,

AG = - R T l n K (3)

Similarly, the enthalpy change/iH between 22

to 60 C was computed from the following equation:

In K = - AH/RT + C (4)

and the entropy change was calculated from the

e q u a t i o n .

A G = AH - T AS (5)

(33)

0 5 10 15 20 30 40 50 60 70 80 90 100 110 120

Time (Minutes)

FIGURE 2 . 1 ' Effect of time on removal of Zn*"^ and Cd"*"^ by sow dust.

(34)

RESULT AND DISCUSSION

1.5 Time of Equilibrium:

+ + + + The percent adsorption of Zn and Cd was

studied with time and results are shown in Fig.

+ + 2.1. It is observed that the adsorption of Zn is

a rnultistep process and reaches to a final plateau

after 70 minutes. The maximum uptake after this

time is constant at a value of 61.5% adsorption.

+ + On the other hand, the behavior of Cd is entirely

-t + different from that of Zn . It shows just a two

step process and the final plateau is obtained

+ + after 15 minutes where the uptake of Cd reaches

+ + to a value of 60%. Thus the adsorption of Cd on

saw dust IS more and faster in comparison to that

+ + of Zn . However, the time of equilibrium used in

all the following studied was set to 1.5 hour for th(?

sake of simplicity as well as to ensure the

complete process of adsorption in both cases.

( 3 5 )

7 0

6 0

50 c o i 40 o VI

^ 30

^ 2 0

10

0

- ^ - Zn"

Cd -•- -•-

^ ^

- • • -

__G O -O O O 0 - -

Q--Qf

p-—(y

•--cr

-1 1 1 1 1 1 L. _» I I L.

O .1 .2 3 4 5 .6 7 .8 .9 1 12 1.3 1.4 1.5

Dose (gm)

FIGURE 2 . 2 .* Effect of dose on removal of Zn"'""^and Cd'*""'"by saw dus

(36

1.6 Effect of dose of saw dust :

The effect of the dose of saw dust on the

+ + + + adsorption of Zn and Cd has been depicted in

Fig. 2.2. The percent adsorption increases with

increase in the dose of adsorbent. But the

adsorption increases in a stepped fashion. In case

+ + of Zn ions, the final plateau is attained at 62%

adsorption for a dose of ). 0.7 gni of saw dust. On

+ + the other hand Cd ions show a three step

adsorption process which is initially very fast as

+ + compared to Zn ions and reaches to a final

plateau equivalent to 70% adsorption. This plateau

observed at a dose of >/ 0.8 gm of saw dust.

1.7 Effect of pH:

+ + The effect of pH on adsorption of Zn and

+ + +

Cd ions are shown in Fig. 2.3. The H ion

concentration seems to play an important role in

(37)

FIGURE 2 . 3 : Effect of pH on removal of Zn'*'*ond Cd' ' by

sow dust .

(38)

the adsorption of these ions. Further, the

adsorption of two ions are affected in an entirely

+ different manner by the concentration of H ions.

+ + The Zn ions show negligible adsorption upto pH 6

and the adsorption increases abruptly at a pH of

6.35. It remains constant upto pH 7.3 which is

equivalent to 23% of uptake. From pH 7.3 to 9.5, it

increases linearly and then reaches to a plateau

which is equivalent to 70% adsorption. On the

+ + other hand the Cd ions show negligible adsorption

upto pH 2. Only a 10% adsorption is observed

between pH 2.8 to 3.4 and then rise, in a non

linear fashion, upto 60% at pH 6.7 and it remains

constant at this level at higher pH values.

The role of pH in the process of adsorption of

+ + + + Zn and Cd ions are entirely different and seems

to follow two different types of the mechanism:

a) With increase in pH of the solution the

extent of removal was found to range from zero to

+ + + +

60% in Cd and zero to 70% in Zn

b) At a neutral pH value, the maximum uptake

( 3 9 )

0 OOl .002 .003 004 J005 .006 .007

Concn (M /L i t te r )

FIGURE 2 . 4 : Effect of concentration on rennoval of

Zn"^ " and Cd* "*" ty sow dust .

(40)

+ + of Zn is only 24% while it is upto 10% in case of

+ + Cd ions.

1.8 Effect of Concentration:

The effect of concentration on the adsorption

of these metal ions are shown in Fig 2.4. The

adsorption start from concentration .001 M and

+ + remains constant onwards in case of Cd as well a:

+ + Zn ions. No effect of concentration has been

observed in either case. However, the total

+ + adsorption in case of Zn is only 23% while in

+ + case of Cd it is upto 60%. The difference in the

extent of adsorption is actually the effect of pH

(as explained above) which is maintained between 6-

7 to make an ideal situation.

1.9 Mechanism of Adsorption:

+ Actually at lower pH value, the H ions

compete with metal cation for the exchange sites in

the system, thereby partially releasing the latter.

The heavy metal cations are completely released

under circumstances of extreme acidic conditions

115]

The reason of the maximum adsorption at pH > 6

(41

+ + in case of Cd are as follows. The pH of the

solution, has been termed as 'Master variable'

115,16,17] in adsorption process, controlling the

surface charge of the adsorbent as well as degree

of ionization and speciation of aqueous adsorbates.

The pH has been documented to control the surface

properties of several adsorbents [18,19] In

present studies maximum uptal^e was observed around

pH 6.5.

+ In aqueous environments, adsorption of H and

OH ions is, thus, based on protonation and

deprotonation of surface hydroxyls.

-R0H2^ > -ROH + H > -RO + H (6)

The chemical interactions of primary importance are:

(i) the interaction of solute with the surface

(ii) the interaction of the solute with the solvent

They may be classified as :

(i) The long range columbic forces: These forces

dominate when the adsorbent surface and the

adsorbate possess opposite charges in the process

of adsorption.

(ii) Short range chemical interactions: These

(42)

forces dominate when in the process of adsorption,

the surface of adsorbent is neutral or bears a

charge similar to that of adsorbate.

(iii) Surface complexation: It is generally invoked

to describe the reactions at solid-solution

interface [14]. The surface hydroxides donate or

accept hydrogen ions which leads to the formation

of surface charge. These reactions involving

molecules on the surface of the adsorbent are

analogous to the solution reactions. The metal ion

on the surface of the adsorbate can form complexes

with iigands, just as a metal in solution does.

The surface complex formation results in specific

adsorption and does not depend on electrostatic

+ + attraction [20]. The maximum removal of Cd on saw

dust is observed at pH > 6.5. The variation of

adsorption with change in pH of the system

undertaken shows three distinct regions of

interest:

(1) Between pH 2.5 - 3.5, the adsorption in

this range is only 10%

(2) Between 3.5 - 6.5, there is a significant

(43)

+ + increase in the removal of Cd with the rise in

pH.

(3) Beyond pH 6.5 an adsorption edge is

observed equivalent to 60% only. The possible

+ + mechanism of adsorption of Cd on saw dust is as

follows:

In the first region, ion exchange mechanism

may be operative due to interactions at constant

charge sites.

Cd* * + 2R Na > R2 Cd + 2 Na^ (7)

This type of mechanism has also been suggested

by Huang and Rhoads I 21]. The second region, which

is greater than pU^-gf. is very much influenced by

pH. This region involves the interaction of solutn

with constant potential sites of the adsorbents.

Apart from the weak columbic attractions the

possible surface reactions accounting for specific

adsorption are as follows:

Ion exchange;

-ROH + Cd^^ > -R0~ Cd^^ + H^ (8)

-ROH + CdOH > -RO~ Cd OH + H (9)

(44)

Adsorption:

-RO + Cd > -RO Cd (10)

-R0~ + CdOH > -R0~ CdOH* (11)

Though both the metal ions show an almost

similar adsorption behavior with the variation of

pH but the effective pH ranges are entirely

different (see Fig. 2.3). The pH 6-7 is the range

+ + where the adsorption of Zn starts on the other

+ + hand it is the range of maximum adsorption for Cd

ions. It can be attributed to the effective

hydrated ionic radii of the two metal ions which

+ + + +

are 6 A" and 5 A" for Zn and Cd ions

respectively.

1.10 Isotherms:

The related parameters for the fitting of

Freundlich and Langmuir equations at different

+ + temperatures are summarized in Table 2.1 (for Cd )

+ + & 2.2 (for Zn ) and isotherms plots shown in Fig.

2.5-2.6 (for Zn" " ) & 2.7-2.8 (for Cd^ ) respecti­

vely. The thermodynamic parameters calculated on

the basis of the two models are summarized in

Tables 2.3 (for Zn ) & 2.4 (for Cd^^).

(45)

0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 x 10 Ce (M-/Lirrer)

r 3

4--J-FIGURE 2 . 5 * Adsorpfion of Zn"^ " on sow dusf of various femperatures

"n o c

m

en

Q a «

§

N + +

ex

m Am O - K) w ^ en

u

CD

3

<n •

In Am O - • r\3 oJ A ui

00

o

(46)

o^

O (J,

(Ti •

In Am w w A

o

0=^

O c m

o

o

o Q.

s •o

o' 3 a

o 3

Q. C M

8h b 8

o

Ce Am

(sj 2 $ S

( 4 7 )

"T 1 1 I r-

- K) OJ

O

ro e

O

Am o o b b (2 jt ro ^ en ® o ro

(48

c

10

9

8

7

6

5

4

3

2

1

0

Zn

1 2 3 4

1 / T (K~^)

FIGURE 2 . 6 C • The plot of Longmuir and Freundlich

consfont (Ink) Vs temperature (1 / T ) .

(49)

0 ZZ-C

• 4 0 " C

X 60« C

.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x 10 ^

Ce ( M / Lifter)

RGURE 2 . 7 • The adsorption of Cd"*"*" on sow dust

of various temperatures .

In Am O -» ro w .b yi 0>

2] o c :o m ro bo Q

J

3 -

I +

8

I

7 o n

ro

•t>,

y i

m

» — 1 » 1 1 1

\.o

\

ro ^3

O

CD

o

o -

• > ! •

a> •

3

m Am ro w j i u" (T

In Am

— TO <Jl U <J' <f>

( 5 0 )

o

o

c JO

m ro

« o

r o o 3 c

( 5 1 )

!

C«/Am

o a

•o 5 3

o Q. +

a c C«/ftfn

o o 6 b 2 o ic ro A 0> 05 O r\3

8

3 O o

0 O

(52

Cd -•"•-

6

5

4

2

1

0 2 3 4 5

1/ T ( K"^)

F I G U R E 2 8 C ' ^ ^ P*® °^ Longmuir and Freundlich constant (Lnk) Vs temperature ( 1 / T )

(53)

rH •

CN

• 0 z a;

i-H Xi to E-i

+ +

U

<w 0

c 0

•H 4-1 ^ V 0 m (0

dJ X 4-)

b 0

<W

CO u dJ

a; £ n u

T3

4J 0 0) ex

03

3 +J (C u 0) a E CJ E-i

+J C <u h <u

tw >w •H o

+J fC

+J to 3 D

(C w c 0

-p c IT) -p [fl c 0

o

1 i 1 1 o 1 00 i 00 ! ^ j r s

a^ n i n rH .—I

•

r~-i n r og rH

• ^ Xi

m

0

c

a.' —

c ft

4-' CO

c 0 u c

c

(LI o u

0.1 a

e u 0)0

04 • *

00 lO • ^

(N i n o CM <H >,C

r~-fN <-( 'X) i n

r -ro c .H .H

00 <N (^ CN ^

CN i n G^ r-ro

r - l

o CO' • ^ 00

oo CTi O O^ CN

0^

r--0 0

>x) rs

CTN o •>* ^ • < *

^ r-{ O •cf OO

<N cn •^ U3 CM

OD rg 00 CM • < *

CN i n •* c i n

• *

rsi <N i n ' i '

CN o o

(54)

CN

• f N

• 0 z (U w

Xi (T3 H

C N

M-J 0

c 0

•H +J 04 u 0 m

T3

o; ^ -P

b 0

U-l

m ;-! d)

t e (C ^

T3

(t ^ K

Oi 4? t '

M

3 4J (T3 ^ o; Ol

w d) H

-P C <u u <u

VM iw • r "

Q

4J t

4J EC 3

(B IC

c 0

4J C (Ti

-P 03 C 0

u

c

i£:

0 O

0.1 — a OS

c (T!

-P TO C 0

13 C

tc 4-1

o

0.1 ^

K OS

OJO

00 0^ O m o

[ ^

o CT^ I D O

r r VD t ^ O

o c CO r-A

a •

o

0 0 CTi i D <Ti

v

r~-0 0 •5t • ^

1 ^

• o

< — 1

ro CM OD CTN

»* • ^

(Ti

^ I ^

• O

r-o 0 0

r-(T>

CO

"* r r~-o

r on ^ CN CM

ro a i H CO CM

00 CO 00 i n

^

c 00 'X>

r~ ^

CT^

r-r-fv| CM

CO 1 ^ 0 0 CN i n

0 0 'S" 0 0 CM

a

cr. CO

-* in a

CM C•^l

o o

(55)

+ + The adsorption of Zn between pH 6-7 follow

both Freundlich as well as Langmuir type isotherm.

However, the Langmuir equations is better obeyed by

the system than the Freundlich one as is evident

from the values of regression coefficients which

are very close unity at 40 and 60 °C whereas they

are far from unity in both the cases at 22 °C.

The Freundlich type adsorption isotherm is

indicative of surface heterogeneity of the

adsorbent while Langmuir isotherm hints towards its

surface homogeneity. This leads to the conclusion

that the surface of saw dust is made up of small

heterogeneous adsorption patches which are very

much similar to each other in respect of adsorption

phenomenon.

The overall adsorption increases with the

increase in temperature at all the concentrations

and no cross over is seen, that is, there is no

reversal in the process of adsorption or

selectivity. However, at all the temperatures, a

minima is seen. At 22 C corresponding to Am=

-3 .015 m moles/g at Ce = 4.75 xlO M. At 40 and

(56)

+ + c

^5

M

• CN

• 0 z CJ

p ^

£i (t3 H

C 0

•H

04 u 0 CO

co <U h I t

4J ft) t^ OJ

TS ft (Cj g

OJ OJ E-<

• i : ! + j +J

SH

0 M

CO X 0)

4J aj £ rC ! tC

u £ nj

c

c OJ u (U

IM U-l •H C

4J CI

+J CO

a

? nj

CO

T( 0

0)

c 0

£ 1

1 0)1

Xi E-

e 0)

-p 0

c o

•H

-p

o < CO

<: • H

e c fC

c

u 0,1

-p o CO

c 0

• H

+J

o CO

<: x; u

• iH t—I

C

<D

c

e u 0.10

on 00 o o

• o t H

r-r i n T H

o •

o '

CN o r i n fO

• i n 1

C\ o CTi on i H

• cr>

m <x> CD

• i H

*^ i D <N O O

0 E " t>S

• \

^H ro

t—1

0 E

^^ 1—1

fO 0 »

1

r~-r-i r r H O

• o

o ^ <N t n •X)

• 1

•^ r~-00 • ^

• ^

• r>

CN i n CN o o

^ t ^ i n i H O

• O

^ cn o IX) r «

1

CN

'^ ^ CTi rH

• r-

>X) i,D CN O o

o CO o

o on

CO

CN i n r-r--o

i-H O <T. r ON

•rr i n CN m [ ^

o X ) (T. r ^

CN CN

O C 1X1

4-> 0 W

c 0

<

0 E

o :>i c \ ,

• 0

o

(57)

00

O O

• CN

0 z

E2I

+ +

c 0 W|

•H a;

a 31 0 to

(T3

0)

j j

s^ 0

m u (U

4-) 0)

e )H

(T3

& 0

•H

£ c > •

0

x:

fo! ^ 1 a B o; E^

+J

c Ul (D

VH IW •iH Q

4-1 (C

+-I 03

Q

3 (t W

c 0

Oi CTJ

0 ^

<:

3 g o

c

c

a:

E

0,1

c CO

c 0

& 1

o

O

c

00

I

0 B

VC r—( • 03

I 1 ^

o I—I o

o

CO IT)

00 CO

00

c: I

• in IX)

o 00

• 1

CN in o (N

^ •

UJ

r r--rr r-l

r^ • 1

<-j

r-r rH »J0

• in

c

o I

o

LD

o

o I

00 in o 00 CO

CJ in CD r o

in 00

o ro 00

e o QJO o o

(58

60 C the minima is observed at Ce = 3.15 x 10 M

-3 and Ce=2.6 xlO corresponding to Am = 0.045 and

.05 m rao]es/g respectively. The overall behavior

of the system indicates that it is a multilayer

endothermic adsorption process. This statement

contradicts to the earlier statement that Langmuir

adsorption isotherm is better obeyed. It can be

justified as follows:

(1) The multilayer adsorption process is not

possible in case of Langmuir model. It is only

possible in Freundlich adsorption model where the

surface of the saw dust is assumed to be made up of

heterogeneous patches which are homogenous m

themselves (As explained above)

(2) The application of van't Hoff type

equation for the calculation of thermodynamic

parameters (Tables 2.3 & 2.4) shows that the

Enthalpy of adsorption is positive in case of

Freundlich adsorption model whereas it is negative

for the Langmuir one. The positive A H value of

the former model corresponds to endothermic process

which we have observed. Hence it is proved that

(59)

Freundlich adsorption model is obeyed in the

+ + adsorption of Zn on the saw dust.

To find out the reason of appearance of the

minima in the adsorption isotherm, the pH of tho

system is noted and it is found to be 5.8, which is

less than 6.5, a value to which the system was

preset by adding NaOH. The ion exchange seems to

be possible mechanism of this minima. With the

increase in concentration, the aggregation of the

metal ions at the surface of the saw dust increases

which results to the exchange reactions with the

already protonated sites, resulting thereby an

+ increase in H concentration and hence a decrease

in pH. The latter effect decreases the adsorption

of the metal ions leading to a minima in the

adsorption isotherm. With the rise in temperature,

this minima shifts to a lower value of the

concentration of metal ions. The increased

temperature increases the aggregation of ionic

species and hence brings about the ion exchange

process at lower equilibrium concentration.

The adsorption studies were also conducted in

+ + + + c -o N O

r I

O

Xi

0 6-

•o X

10

in - .

~JO

V-. ' •" * — —

CM

CD O

in o o O

CVJ O

( U J 6 / S 9 | 0 L U UU) L U V

o

(60)

o o o

o

+ + O

T3 C o

+

N

N ID Q O

in o ^ to o o

00

o

'o X

in

o

o > o E 2? c o

u o

t

ro

CVl

O

a>

_ j N 2 0) O

o 0 ) >*-

H -LU

0) c\i

IL.

l i .

( U J 6 / S 8 | 0 U J UJ ) \JJ\f

(61)

presence of 0.1 M NaCl at 40 C only. Both the metal

+ + + + ions (Zn , Cd ) show a minima at Am=0.005 m.

-3 moles/g corresponding to Ce= 3.6 x 10 and Ce= 1.2

-3 X 10 M respectively (see Fig. 2.9). These values

of Am are very low as compared to the values noted

in absence of NaCl. The reason of this minima has

already been discussed.

+ + Adsorption of Cd on saw dust at different

temperatures is shown in Table 2.1 . It is clear

from the values of regression coefficients that

neither it follows Langmuir nor Freundlich type

isotherm. Initially, the extent of adsorption

increases with the rise in temperature which

indicates that the process is endothermic. After

an equilibrium concentration of 0.5 M, a cross over

in adsorption isotherms is observed which result to

o a decrease in the extent of adsorption at 60 C

resulting thereby to a minima at Ce = 1 M.

However, the adsorption at 40 C and 22 C become;i

almost equal between Ce = 0.6 to 2 M. With the

increase in equilibrium concentration so many cros-s

overs are observed among the three adsorption

(62)

isotherms and finally the order of the extent of

adsorption becomes 40 > 22 > 60 C.

According Giles classification [22] the

+ + adsorption of Cd on saw dust shows 'S' type

isotherm. This class of adsorption isotherm is

indicative of the composite isotherm where there is

a competition between the solute and solvent

molecules for the adsorption on the adsorbent

The following may be the possible mechanism of over

+ + all process of Cd adsorption.

+ + Initially the adsorption of Cd ion at all

the temperatures occur in the unhydrated form i.e.

the dehydration of both the ions and the adsorption

site occurs first and then they get adsorbed. On

increasing the concentration of the ions in

solution, the aggregation of these ions increases

on the surface leading to their access to the less

accessible sites. This tends to an increase in the

adsorption through the opening of the pores of

adsorbent. The latter effect facilitate the entry

of water molecules too into the pores. On the entry

of water, the adsorbed ions/sites gets hydrated

(63)

leading to a decrease/reversal in the extent of

adsorption. Thus it causes a minima in the

adsorption process.

(64)

REFERENCES

1. T.R. Camp & R.L.M. Meserve, "Water and its

impurities", 2nd Edition, U.S.A. (1973).

2. W.W. Eckenfelder, "Advances in water pollution Research", 1st Edition, vol.2 (1964).

'^. O. Jaag, "Advances in water pollution

Research", 1st Edition, vol.] (1964).

4. E.A. Pearson. "Advances in water pollution

Reasearch", 1st Edition, vol.3. (1964).

5. N.V.R. Rao & S.N. Tandon, "Prague Advances in

water pollution Reasearch", (1977),

Application Of Mixed anhydride reagent for the

detection of some alkaloids on thin layer

plates. Forensic Sci., 9, 103-104. (1969).

6. B.A. Southgate ' "Advances in water pollutio

Reasearch",1st edition, vol.1. (1964).

7. A.G. Mukherjee, "Environmental pollution and

Health- Hazards, causes and control" (Galgotia

Pub., New Delhi 1986).

8. G. Fajardo and C. Alberto, Rev. Colomb. Quim.,

14,1-2, 89-97,(1987).

9. S. Trideeh, A.J. Englande, M.J. Hebert, R.F.

Wilkinson, "Chemistry in Water reuse",

Vol.2,(1981); W.J. Cooper (ed.) Ann. Arbor Sci.

Publishers Inc., U.S.A. 521,.

10. G.L. tayon, P.J. Peterson, R.R. Brooks, G.W. Butler, J. Ecol. 59, 421,(1971).

11. A.K. De, A.K.Sen, D.P. Modak, S. Jana, Water, Air and Soil Pollution, 24, 351,(1985).

12. P.Kumar, S.S. Dara, Water Sci. and Tecnol.,lJ( 7), 353-61, (1981).