NON-CONVENTIONAL LOW COST ADSORBENTS FOR THE REMOVAL OF DYES

DISSERTATION

SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF

i/ ^ . IN I ' • i • . • ' • • ' .

APPLIED CHEMISTRY

By

RAJEEV KUMAR /

Under the Supervision of

Dr. Rais Ahmad

DEPARTMENT OF APPLIED CHEMISTRY 2.H. COLLEGE OF ENGINEERING & TECHNOLOGY

ALIGARH MUSLIM UNIVERSITY ALIGARH ( INDIA)

2008

M iP>^ 1 0 *

DEPARTMENT OF APPLIED CHEMISTRY Z. H. COLLEGE OF ENGINEERING & TECHNOLOGY

ALIGARH MUSLIM UNIVERSITY, ALIGARH - 202 002 (INDIA)

ntcLcL

M.Sc, Ph.D.

r \ Resi. University Fax E-mail

0571-2700920-23 Ext. 3000 9358259832 (0571)2400528 rais45@rediffmail.com

CE^TIfFICME

This is to certify that the work embodied in this dissertation entitled "Non-

conventional low cast adsorbents for the removal of dyes" is the original

research work carried out by Rajeev Kumar, under my guidance and

supervision and is suitable for submission for the award of M. Phil degree.

Dr. Rais Ahmad (Supervisor)

(I>E(DICJl'm<D

To

ACKNOWLEDGEMEiNT

/ am extremely grateful to my supeiyisor Dr. Rais Ahmad for

his invaluable guidance and suggestions, which greatly help me to

come out from difficulties faced during the work.

I gratefully acknowledge the facilities provided by the

chairman, Department of Applied Chemistry, in carrying out the

experimental work. I have deep sense of gratitude for the member

of Department of Applied Chemistry for their cooperation and

inspiration.

My special thank to Dr. Rifaqut Ali Khan Rao, for providing

useful suggestions.

I am thankful to my colleagues and friends for their help,

discussion and encouragement.

I owe a great debt of gratitude to my revered parents for their

affection and blessing. They have been a constant source of

inspiration to me in accomplishing this task. Special mention goes

to my brother for their encouragement and interest in my academic

pursuits.

Kaj^\;foj(V Rajeev Kumar

CONTENTS

Page

List of tables (I)

List of figures (II)

Chapter -1 1- 31

General Introduction 1

1.1. Classification of environmental pollution 4

1.2. Classification of water pollutants 6

1.3. Dyes and its classification 9

1.4. Dyes and its hazardous effects 11

1.5. Wastewater treatment 13

1.6. Theoretical aspects of adsorption 17

1.7. Survey of literature 22

Chapter -2 32-52

Adsorption of crystal violet dye from aqueous solution onto

ginger waste materia! (GWM): Evaluation of equilibrium,

isotherms, kinetics and breakthrough capacity.

1. Introduction 32

2. Materials and methods 33

3. Results and discussion 35

4. Adsorption kinetics 39

5. Column studies 42

6. Comparison of various low-cost adsorbents 42

7. Conclusion 43

References 53-6S

List of Table

Table 1.1. Classification of dyes based on their chemical constitution

Table 1.2. Some important dyes and their hazardous effects

Table 1.3. Factor influencing adsorption from solution

Table 1.4. Survey of literature

Table.2.1. The physical and chemical characteristics of crystal violet dye.

Table.2.2. Thermodynamic parameters of crystal violet adsorption on GWM.

Table.2.3. Langmuir and Freundlich Isotherm model for adsorption of crystal

violet on GWM.

Table.2.4. Comparison of the pseudo-first-order and pseudo-second-order

models for different initial concentration of crystal violet at 30 ^C

Table.2.5. Intra-particle diffusion for different initial concentration of crystal

violet a violet.t 30 °C.

Table.2.6. Comparison of adsorption capacities of various adsorbents for

crystal violet.

List of Figure

Fig. 1. Structure of Crystal Violet.

Fig.2 (a). Scanning electron micrograph (SEM) image of ginger waste material

before adsorption

Fig.2(b). Scanning electron micrograph (SEM) image of ginger waste material

after adsorption

Fig.3. Effect of contact time on adsorption capacity (T=30 ' C, adsorbent

dose=0.05g/50 ml, pH=6.2).

Fig.4. Effect of pH on adsorption capacity (T=30 ' C, adsorbent dose=0.05g/50

ml,conc.=10mg/l).

Fig. 5. Effect of temperature on adsorption capacity (Adsorbent dose=

0.05g/50 ml, pH=6.2).

Fig.6. Plot of log kc versus 1/T.

Fig.7. Effect of adsorbent on adsorption capacity (T=30 ' C, ,conc.=10mg/l,

pH-6.2).

Fig.8. Effect of concentration on adsorption capacity (T=30 ^C, adsorbent

dose=0.05g/50 ml, pH=6.2).

Fig.9, Langmuir isotherm.

Fig. 10. Freundlich isotherm.

Fig. 11. Pseudo- first -order kinetics for adsorption of crystal violet on GWM

at 30 °C.

Fig. 12. Pseudo- second -order kinetics for adsorption of crystal violet onto

GWM at 30 °C.

Fig. 13. Intra-particle diffusion kinetics at 30 ''C.

Fig. 14. Effect of bed height on breakthrough capacity (T=30 °C,

conc.=10mg/l, pH=6.2,flow ratelml/min).

Cdapter-l

Qeneral introduction

1. Introduction The safety of environment and the prevention of its degradation has become a vita!

issue in this decade. The scare of violence on Indian environment, emanating from the

conditions of poverty and unintentional effects of the process of development, afflicts

the well being of the people. The degradation of environment results in increased

economic inequalities, adversely affects the poor, and causes severe health hazards

including mental degeneration. Pollution, rendering resources unfit for use due to

physical, chemical and biological factors is caused mainly by the release of untreated

sewage, industrial effluents with toxic metals, organic pollutants and careless spraying

of pesticides and insecticides.

Natural environment comprises air, water and soil. Air is one of the three most

important components of natural environment. Fresh air is the primary priority for

healthy living. Due to industrial development and other economic processes,

proliferation of vehicular traffic and also due to agricultural effluents, air pollution

has reached a stage where the public cannot turn blind eye to it any longer.

Phenomena like global warming, green house effect, ozone layer depletion and

photochemical smog are the threats to the environment of this planet. If not addressed,

life would be extinct, within a very short span of time. The situation is acute and

demands urgent action.

Water is abundantly available natural resource on the earth surface comprising 70% of

the earth surface. Water is essential for sustaining life on our planet. Estimates

suggest that nearly 1.5 billion people lack safe drinking water and that at least 5

million deaths per year can be attributed to water borne diseases. Human beings

considering these water bodies as a limitless dumping ground for wastes. Raw

sewage, garbage and oil spills have begun to overwhelm the diluting capabilities of

the oceans, and most costal waters are now polluted. The way human activities

immensely polluting these natural resources is like they are digging their own graxes.

Soil is another element of life, as the life initiated from soil and the forces, which are

sustaining life, are also dependent on soil. Today, the earth is facing many sorts of

environmental threats like soil erosion, misuse and unwise use of chemicals and

fertilizers are the few. Soil erosion is caused due to disappearance of the forests from

the earth. The other source of threat to soil is the misuse of land. The wrong irrigation

of land is the major cause of water logging and salinity. The unsystematic use of

fertilizers is another threat to the land. Along with the loss of land fertility, the

chemicals in the fertilizers go deep into sub soil water, which ultimately play havoc

with the health of the human beings.

Identification and characterization of the pollutants is as important as control of

pollution. As after getting relevant information about the pollutant, it is much easier to

opt the exact process to control pollution. Estimation and characterization of toxic

materials often at trace level in a very complex matrix is a challenging task. Organic

as well as inorganic pollutants are not only toxic but also often carcinogenic and

affect physiological processes, in such a way that there are long run consequences,

which are usually fatal. Moreover, complex organic mixtures are much more difficult

to separate and more difficult to identify.

New challenging task for the environmental chemist is to remove these pollutants,

often found in trace level in various medium of the environment. Today organic

pollutant perhaps become more important as they are not only toxic but also

carcinogenic and affect physiological process of living things. From environmental

point of view, the removal of synthetic dye is a great concern since some dyes and

their degradation product may be carcinogenic and toxic, consequently their treatment

can not depend on biodegradation alone. Therefore the removal of dyes from effluent

becomes enviromnentally important.

Among several chemical and physical methods, such as photoxidation.

electrocogulation, reverse osmosis, membrane filtration and flocculation are applied

for dye removal from textile effluent. These chemical and physical methods are less

effective, costly and produce waste. As a viable alternative, adsoiption process has

received increasing interest due to their cost effectiveness. Adsorption onto activated

carbon has been found to be superior to other technique for removal of dyes from

aqueous solution in term of methodology, its capabilit}- for effective adsorption and

broad range for different type adsorbate and simplicity of design of adsorbent.

Commercially available activated carbon are usually designed from several materials

such as wood, coal, and still considered expensive. This lead to search for another

substitute. Hence, low cost adsorbent are investigated for a long time.

The objective of this study was to find out the possibility of using ginger waste

material, as low cost adsorbent for the removal of Crystal Violet from aqueous

solution. The effect of various parameters like concentration, pH, contact time,

temperature were studies in order to optimize the dye removal process. The

equilibrium and kinetics data of the adsorption process were also studies to

understand the mechanism of dye adsorption.

1.1. Classification of environmental pollution Environmental pollution in generally may be classified as:

• Air pollution

• Soil pollution

• Water pollution

1.1.1. Air pollution

Air pollution is the introduction of chemicals, particulates, or biological materials into

environment by human activities that causes harmfull effect to flaura and fauna. Air

pollution is often identified with major stationary sources, but the greatest source of

emissions is actually mobile sources, mainly automobiles. Gases such as carbon

dioxide, which contribute to global warming, have recently gained recognition as

pollutants by climate scientists, while they also recognise that carbon dioxide is

essential for photosynthesis. Air pollution can be minimised by using high chimneys

in industrial plants, so that smoke, fumes or heated air may not disperse in lower

atmosphere. The fuels used to run automobiles should be free from air pollutants.

Organic wastes should be treated properly. Finally the most effective way to

overcome the problem of air pollution is the development of green areas, as green belt

development serves as a sink for air pollutants.

1.1.2. Soil pollution

Soil pollution is defined as the introduction of persistent toxic compounds, chemicals,

salts, radioactive materials, or disease causing agents in soil. These contaminates have

adverse effects on plants and animals health. Soil contamination is the presence of

manmade chemicals or other alteration in the natural soil environment. This type of

contamination typically arises from the rupture of underground storage tanks,

application of pesticides, leaching of wastes from landfills or direct discharge of

industrial wastes to the soil. The most common chemicals involved are petroleum

hydrocarbons, solvents, pesticides, dyes, and heavy metals. The occurrence of this

phenomenon is coiTclated with the degree of industrialisation and intensity of

chemical usaue.

Soil pollution has been slightly controlled by putting regulations on the use of

fertilisers, chemicals, radioactive materials etc and introduction of alternatives to it.

Many methods such as chemical reactions to change contaminants into less toxic or

less mobile forms, action of living organisms such as bacteria have been employed to

reduce the effect of these chemicals.

1.1.3. Water pollution

Water is said to be polluted, if its physical and chemical properties are altered due to

the addition of large amounts of waste materials, which makes it unfit for its intended

use. Although natural phenomena such as volcanoes, algae blooms, storms, and

earthquakes also cause major changes in water quality and the ecological status of

water. Water is only called polluted when it is not able to be used for what one wants

it to be used for. Water pollution has many causes and characteristics. Increases in

nutrient loading may lead to eutrophication. Organic wastes such as sewage impose

high oxygen demands on the receiving water leading to oxygen depletion with

potentially severe impacts on the whole ecosystem. Industries discharge a variety of

pollutants in their wastewater including heavy metals, resin pellets, organic toxins,

oils, nutrients, and solids. Discharges can also have thermal effects, especially those

from power stations, and these too reduce the available oxygen. SiU-bearing runoff

from many activities including construction sites, deforestation and agriculture can

inhibit the penetration of sunlight through the water column, restricting

photosynthesis and causing blanketing of the lake or river bed, in turn damaging

ecological systems.

Water pollution can be classified as point source and non point source. Point source of

pollution occurs when harmful substances are emitted directly into a body of water.

The Exxon Valdez oil spill best illustrates point source water pollution. A non point

source delivers pollutants indirectly through environmental changes. An example of

this type of water pollution is when fertilizer from a field is carried into a steam by

rain, in the form of run off which in turn effects aquatic life. The technology exists for

point sources are much more difficult to control. Pollution arising from non point

sources accounts for a majority of the contaminants in streams and lakes.

1.2. Classification of water pollutants Water pollutants can be broadly classified into the following four major categories:

• Organic pollutant

• Inorganic pollutant

• Suspended solids and sediments

• Radioactive material

1.2.1. Organic pollutants

Organic substances comprise a potentially large group of pollutants, particularly in

urban environments. Even at low levels, some of these organic pollutants can be

hazardous to human health, particularly if the exposure is long term. Some organic

pollutants also play an important role in the formation of photochemical smog. Motor

vehicle emissions are a major source of these pollutants together with the petroleum

and chemical industries, emissions from waste incinerators, service stations, domestic

solid fuel and gas combustion, spray painting, dry cleaning and other solvent usage.

and cigarette smoke. The pathogenic microorganisms present in polluted water causes

water bom diseases such as cholera, typhoid, dysentery, polio and hepatitis in

humans.

The pesticides, detergents, insecticides, dyes and other industrial chemicals are toxic

to plants, animals and humans, as these chemicals may enter the hydrosphere either

by spillage during transport and use or by intentional or accidental release of wastes

from their manufacturing establishments.

Oil pollution results in the reduction of light transmission through surface waters,

thereby reducing photosynthesis by marine plants. Further, it reduces the dissolve

oxygen in water and endangers water birds, costal plants and animals. Thus, oil

pollution leads to unsightly and hazardous conditions, which are deleterious to marine

life and seafood.

1.2.2. Inorganic pollutants

Inorganic pollutants comprises of mineral acids, inorganic salts, finely divided metals

or metal compounds, trace elements, cyanides, sulphates, nitrates, organometallic

compounds and complexes of metals with organics present in natural waters. The

metal-organic interactions involve natural organic species. These interactions are

influenced by or influence redox equilibria, acid-base reactions, colloid formation and

reaction involving microorganisms in water and metal toxicity in aquatic ecosystems

are also influenced by these interactions.

Various metals and metallic compounds released from anthropogenic activities add up

to their natural background levels in water. Some of these trace metals play essential

roles in biological processes, but at higher concentrations, they may be toxic to biota.

1.2.3. Suspended solids and sediments

Sediments are mostly contributed by soil erosion by natural processes, agricultural

development, strip mining and construction activities. Suspended solids in water

mainly comprise of silt, sand and minerals eroded from the land. Soil erosion by

water, wind and other natural forces are very significant for tropical countries like

India leading to qualitative and quantitative degradation of the soil in land area. Thus,

soil may be getting removed from agricultural land to the areas where it is not at all

required, such as water reservoirs. Soil particles eroded by running water ultimately

find their way into water reservoirs and such a process is called 'siltation'. Reservoirs

and dams are filled with soil particles and other solid materials, because of siltation.

This reduces the water storage capacity of the dams and reservoirs and thus shortens

their life. Apart from the filling up the reservoirs and harbours, the suspended solids

present in water bodies may block the sunlight required for the photosynthesis by the

bottom vegetation. This may also smother shellfish, corals and other bottom life

forms. Deposition of solid in quiescent stretches of streams impairs the nonnal

aquatic life in the streams. Further, sludge blankets containing organic solids

decompose, leading to anaerobic conditions and formation of obnoxious gases. The

tremendous problem of soil erosion can be controlled by proper cultivation practices

and efficient soil and forest management techniques.

The organic matter content in the sediments is generally higher than that in soils.

Sediments and suspended particles exchange cations with the surrounding aquatic

medium and act as repositories for trace metals such as Cu, Co, Ni, Mn, Cr and Mo.

Suspended solids such as silt and coal may injure the gills of the fish and causes

asphyxiation.

1.2.4. Radioactive materials

Radioactive pollution can be defined as the release of radioactive substances or high

energy particles into the air, water, or earth as a result of human activity, either by

accident or by design. The sources of such waste are nuclear weapon testing or

detonation, the nuclear fuel cycle, including the mining, separation, and production of

nuclear materials for use in nuclear power plants or nuclear bombs and accidental

release of radioactive material from nuclear power plants. The radioactive isotopes

found in water include Sr^°, l'^', Cs'^^ Cs"", Co^°, Mn^\ Fe^^ Pu^^^ Ba'^^ K ",

Ra^^ . These radioactive isotopes are toxic to life forms.

1.3. Dyes and its classification

A coloured substance can act as a dye only when it fulfills following conditions:

• It must have suitable colour.

• It must be able to attach itself permanently to the fabric.

• The fixed dye must have fastness properties. Its colour should not fade in

light. It should have resistance to the action of water, dilute acid, alkalies,

detergents and organic solvents used in dry cleaning.

Table!.1: Classincation of dyes based on their chemical constitution

S.No. Class of dye Example Remark

Nitroso Fast Green,

Napthol Green Y

Nitro group as chromophore,

phenolic as auxochromein

in o-position

2- Nitro Martins Yellow,

Napthol Yellow-S

Nitro group as

chromophore

3- Anthraquinone Alizarin Red S,

Alizarin Rlue

Presence of chromophore

-C=0 and ==C=C arrange in

anthraquinone complex

Triphenylmethane Malachite Green,

Methyl Violet

Quinonoid group as

chromophore and acidic -OH

and basic -NH2, -NHR, etc

group as auxochrome

Diphenylmethane Auraine-0 NH=C=group as,

cliromophore also contain a

diphenylmethane nucleus

6- Phthaleins Phenolphthalein Regarded as derivative of

triphenyhnethane

Xanthene Eosin =C=0= or =C=N- as

chromophore

Thiazole Premuline >C=0, S-C etc as

chromophore

Azo dye

(a)Acidic Methyl Orange

-N=N- as chromophore

Acidic group as -COOH

-S03H, -OH as

auxochrome

(b) Basic Aniline Yellow Amino or substituted

amino guroup as

auxochrome

1.4. Dyes and its hazardous effects

Dyes have a synthetic origin and complex aromatic molecular structures, and widely

used in industries such as textiles, rubber, paper, plastics, cosmetics etc. to colour

their products, these dyes are invariably left in the industrial wastes (about 8 to 20%

of the total pollution load due to incomplete exhaustion of the dye). Effluents

discharged from dyeing industries are highly coloured and low BOD and high COD.

These coloured effluents pollute surface water and ground water system. They also

pose a problem because they may be mutagenic and carcinogenic and can cause

severe damage to human beings, such as dysfunction of kidney, reproductive system,

liver, brain and central. Due to the large degree of organics present in these molecules

and the stability of dyes, conventional physicochemical and biological treatment

methods are ineffective for their removal

Tablel.2: Some important dyes and their hazardous effects

Dye Hazardous effects

Methylene Blue

Rhodamine B

Fast Green

Fast Ponceau disazo dye

Fast Red Salt B

Malachite Green

Crvatal Violet

Toxic to blood, reproductive system, liver, upper

respiratory tract, skin& eye contact (irritant),

central nervous system

Causes respiratory tract irritation, eye and skin

irritation digestive tract irritation, adverse

reproductive and fetal effects in animals,

vomiting and diarrhea

Tumours of the liver, testes, thyroid.

Mutagen and a potential carcinogen, highly toxic,

skin and eye irritant, must never be handled

during pregnancy

Potential carcinogen, irritant to eyes and the

respiratory tract

Accumulates in the tissues, liver, thyroid gland

and bladder.

Mutagen and mitotic poison

U

Eosin

Congo Red

Diamond Black

Carcinogenic, estrogenic and clastogenic

properties

Mutagenic, hazardous in case of skin contact, eye

irritant

Thyroid cancers, mutagenic effects,

DNA-damaging

12

1.5. Wastewater treatment Various methods used in sewage and industrial wastewater treatment are as follows:

1.5.1. Preliminary treatment

The primary aim of preliminary treatment is the removal of gross solids such as large

floating and suspended solid matter, grit, oil and grease if present in considerable

quantities. Large quantities of floating rubbish such as cans, cloth, wood and other

objects present in wastewater are usually removed under preliminary treatment.

1.5.2. Primary treatment

Primary treatment involves the removal of gross solids, gritty materials and excessive

quantities of oil and grease, the next step is to remove the remaining suspended solids

as much as possible. This is aimed at reducing the strength of the wastewater and also

to facilitate secondary treatment.

The suspended matter can be removed effectively and economically by sedimentation.

This process is particularly useful for treatment of wastes containing high percentage

of settleable solids or when the waste is subjected to combined treatment with sewage.

Finely divided suspended solids and colloidal particles cannot be removed by simple

sedimentation by gravity. In such cases, mechanical flocculation or chemical

coagulation is employed. Coagulation is the most effective and economical means to

remove impurities.

Sometimes, in addition to the coagulants, other chemicals called "coagulant aids" are

also used in very small quantities to promote the formation of large and quick settling

floe and thereby enhancing coagulation. Activated silica and polyelectrolytes such as

polymers of cyanamide, acrylic acids and their derivatives, and hydrolysed high

molecular weight polymers having molecular mass lO"* to 10^ of acrylamide or

acrylonitrile are the most commonly used coagulant aids.

Some industries produce different type of wastes, having different characteristics at

different intervals of time. Hence, uniform treatment is not possible. In order to

obviate this problem, different streams of effluents are held in big holding tanks for

specified periods of time. Each unit volume of the waste is mixed thoroughly with

other unit volumes of other wastes to produce a homogenous and equalised effluent.

Highly acidic and highly alkaline wastes should be properly neutralised before being

discharged. Acidic wastes are usually neutralised by treatment with lime stone or lime

slurry or caustic soda, depending upon the treatment and quality of the waste

.Alkaline wastes may be neutralised by treatment with sulphuric acid or CO2 or waste

boiler flue gas.

1.5.3. Secondary treatment

Biological processes involving bacteria and other microorganisms remove the

dissolved and colloidal organic matter present in wastewaters. These processes ma}'

be aerobic or anaerobic.

In aerobic processes, bacteria and other microorganisms consume organic matter as

food causing coagulation and flocculation of colloidal matter, oxidation of dissolved

organic matter to CO2 and degradation of nitrogenous organic matter to ammonia,

converted to nitrite and eventually to nitrate. Thus, secondary treatment reduces BOD

and it also removes appreciable amounts of oil and phenol. However, commissioning

and maintenance of secondary treatment systems are expensive.

Anaerobic treatment is mainly employed for the digestion of sludge. However,

organic liquid wastes from dairy, slaughterhouses etc., were treated by this method

economically and effectively. The efficiency of this process depends upon pH,

temperature, waste loading, absence of oxygen and toxic materials.

14

1.5.4. Tertiary treatment

It is the final treatment, meant for "polishing" the effluent from the secondary

treatment processes to improve the quality further. The main objectives of tertiary

treatment are the removal of fine suspended solids, bacteria, dissolved inorganic

solids and final traces of organics.

Depending upon the required quality of the final effluent and the cost of treatment that

can be afforded in a given situation, any of the following treatment methods can be

employed

a. Evaporation

This is an expensive process. It is used only when the recovered solids or the

concentrated solutions are reused, e.g., some electroplating wastes. This method is

also employed for concentrating radioactive liquid wastes.

b. Ion-exchange:

The use of ion exchange for demineralisation of water is well known. It is widely used

for obtaining deionized water for use in high pressure boilers. This process is now

extended to wastewater treatment for the removal and recovery of toxic materials

from wastewater. Ion exchange process is economical only when the recovered salts

are reused in the process, as in electroplating industry. Despite the simplicity of its

operation, the method may not be economical if the objective of the treatment is only

the removal of dissolved solids from wastewater. Special ion exchangers are available

for the retrieval of toxic metal ions from industrial wastewater.

c. Reverse osmosis

When a wastewater containing dissolved solids is allowed to pass through a semi­

permeable membrane, at a pressure over and above the osmotic pressure of tlr;

wastewater only the water from the waste permeates through the membrane, leaving

behind concentrated liquor, containing the dissolved solids. This process is

particularly suitable and effective for the removal of dissolved solids fro;n

wastewater. The cost of the membranes and the fouling of the membranes are tl,;

major limitations of this process.

d. Chemical precipitation

The dissolved solids in the wastewater, particularly the heavy metal ions, can be

removed by precipitation as their hydroxides with cheap precipitating agent like lime.

Chromates in the electroplating waste are highly toxic and can be removed by

treatment with FeS04 first to reduce the chromates to Cr (III), followed by

precipitation with lime.

e. Adsorption

Adsorption is one of the promising processes for the removal of organic and inorganic

pollutants from water particularly if the pollutants are present in low concentrations.

Conventional and Non-conventional adsorbents are used in this approach. Activated

carbon, a conventional adsorbent used efficiently for the treatment of industrial

effluents and it is marketed in both powdered and granular form. The drawback of

using activated carbon, as an adsorbent is its higher regeneration cost. To make

adsorption an economically feasible process non-conventional adsorbents have come

into application. Non-conventional adsorbents include inorganic adsorbents, organic

adsorbents and biosorbents.

The non-conventional adsorbents may be classified as:

1. Inorganic adsorbents

They may be natural minerals, ores, clay and waste materials from various industries

like fly ash, metallurgical solid wastes like bauxite and red mud etc.

2. Organic adsorbents

A large number of waste materials of organic origin like dead leaves of trees, bar':.

roots, seed shells and saw dust from various plants in the form of powder have been

utilised for the removal of heavy metals and their adsorption properties have beej;

explored.

3. Biosorbents

They include biomass of algae, fungi, and peat moss. The advantages of biosoi7)tJ!.i:

are low cost, high efficiencN- of heavy metals and dyes removal from dilute soluiior:,

regeneration and possible nicla! and dye recovery.

' A;

1.6. Theoretical aspects of adsorption

1.6.1. Adsorption

The term Adsorption was first used by "Kayser" in 1881 and it refers strictly to the

existence of higher concentration of any particular component at the surface of the

liquid or solid phase than in the bulk. The Adsorption may be of two types namely

physical and chemical. The physical Adsorption occurs mainly due to weak forces

like ion-dipole, dipole-dipole, polarization or induced dipole, Vander Wall's force etc.

The physical adsorption is reversible, temporary in character. It usually involves

lesser heat exchange (Adams, 1973). While chemical Adsorption is due to the

formation of chemical linkages between adsorbate and adsorbent surface. The

chemical adsorption is non reversible and is carried out at high temperature. It is

characterized by a large heat change during Adsorption

1.6.2. Mechanism of adsorption

A solid surface in contact with a solution has the tendency to accumulate a layer of

solute molecules at the interface due to imbalance of surface forces. This

accumulation of molecules is a vectorial sum of the forces of the attraction and

repulsion between the solution and the adsorbent. Majorities of the solute ions or

molecules, accumulated at the interface are adsorbed onto the large surface area

within the pores of adsorbent and relatively a few are adsorbed on the out side surface

of the adsorbent. Adsorption from an aqueous solution is influenced largely by the

competition between the solute and solvent molecules for adsorption sites. The

tendency of a particular solute to get adsorbed is determined by the difference in th :

adsorption potential between the solute and the solvent when the solute-solver ;

affinity is large .The low adsorption capacity of polar adsorbents like zeolite fc;

solute in a polar solvent like water is an example of this phenomenon. In general, th;

lower the affinity of adsorbent for the solvent, the higher will be adsorption capacit

for solutes. A polar (or non polar) adsorbent will preferentially adsorb the more pola •

(or non polar) component of a non- polar (or polar) solute. Activated carbon an.\

polymeric adsorbents have high adsorption capacities in water primarily because of r

low potential.

The following distinct steps take place for adsorption to occur:

i /

• The adsorbed molecules must be transferred from the bulk phase of solution to

the surface of the adsorbent particle. In doing so, it must pass through a film of

solvent that surrounds the adsorbent particle. This process is referred as "film

diffusion".

• The adsobate molecule must be transferred to an adsorption site on the inside

of the pore. This process is referred as "pore diffusion ".

• The particle must become attached to the surface of the solute

Many factors influence the rate of adsorption and extant to which a particular solute

can be adsorbed. The effects of various important factors like nature of adsorbent and

adsorbate, concentration, extent of agitation, pH, temperature, contact time, etc., are

summarized in table 1.3.

Tablel.3. Factor influencing adsorption from solution

Agitation/relative velocity

Adsorbent characteristics

At low agitation film diffusion is rate

controlling. At high agitation pore

diffiision is rate limiting

Adsorption rate increases with

decreasing particle size of adsorbent,

presence of surface charges.

Size and shape of adsorbate Adsorption usually decreases, as

the size of the molecule become

large.

Concentration Rate of adsorption increases with

increase in concentration. Rate

constant is directly proportiona! to

concentration.

pH Strong influence on adsorDtion due

to change in ionic concentrations of

water and solutes.

Temperature Affect rate and extent of adsorption

1.6.3 Adsorption isotherm

The Freundhch equation may be expressed as:

Inx/m =In Kf + 1/nlnCe

Where x/m is the amount of adsorbate (mgL"') adsorbed per unit weight of the

adsorbent, Kf and n rare Freundlich constants and Ce is the equiUbrium concentration

(mg L "' ) of dyes (adsorbate). The linear plot of In x/m versus In C e indicates that

adsorption process follows Freundlich isotherm.

The Langmuir equation may be described as:

l / (x /m)=l /e°bl /Ce+l /e°

Where x/m is metal uptake per unit weight of the adsorbent, Ce is the equilibrium

concentration of metal ion (mg L "'), 9° and b are Langmuir constants relating to

adsorption capacity and adsorption energy respectively. The Langmuir isotherm is

valid for monolayer adsorption onto the surface of the adsorbent containing a finite

number of identical sites. The linear pot of l/(x/m) Vj. 1/Ce indicates that adsorption of

follows Langmuir isotherm. The essential feature of the Langmuir isotheiTn can be

expressed in terms of a dimensionless constant separation factor or equilibrium

parameter (RL, which is defined as:

RL=l/(l+bCo)

19

Where b is the Langmuir constant, Co is the initial dye concentration (mgL').

If,

RL > 1 Unfavorable type of isotherm

RL = 1 Linear isotherm

0< RL < 1 Favorable type of isotherm

RL = 0 Irreversible.

1.6.4. Thermodynamics of adsorption

Thermodynamic parameters such as standard free energy change (AG°), enthalpy

change (AH ) and entropy change (AS ) are calculated using the following equations

Ce

Where, Kc is the equilibrium constant. Cac and Ce are the equilibrium constants

(mg/L) of the dye on the adsorbent and in the solution respectively. AG° was

calculated from the equation

AG' '=-RTlnKc

Where, T is the temperature in Kelvin and R is gas constant (8.314 J/mol K). AH'^ was

calculated from the following equation

AS° A//° logKc

2.3037? 2.303RT

AH° and AS" were obtained from the slope and intercept of Van't Hoff plot of log Kc

versus 1/T Positive value of AH° shows the endothermic nature of adsorption. The

negative values of AG° indicate the spontaneous nature of adsorption. The positive

value of AS shows the increased randomness at the solid/solution interface during the

adsorption

20

1.6.5. Adsorption Kinetics

The pseudo- first-order, pseudo second order and intra-particle diffusion equation are

used to find out the adsorption mechanism.

Pseudo-first-order kinetic model

A simple kinetic analysis of adsorption is the pseudo-first -order equation in the form

log (qe - q,) = log qe '— /

2.303

Where qe and qt are the amount of dye adsorbed (mg/g) at equilibrium and at any

time t, ki is the rate constant (min ' '). The plot of log (qe-qO versus t gives a straight

line for the pseudo first order adsorption kinetics.

Pseudo- second- order model

The Pseudo- second- order model can be represented in the following form

t 1 1 — = +—/ q, kiq.2 q.

Where, ka (min g/mg) is the rate constant for the Pseudo- second- order adsorption

kinetics. The slopes of the plots t/qt versus t give the value of q^ and from the

intercept ka can be calculated.

Diffusion rate constant study

The adsorption can be described by three consecutive steps:

• The transport of adsorbate from bulk solution to the outer surface of the

adsorbent by molecular diffusion, known as external or film diffusion.

• Internal diffusion, i.e. the transport of adsorbate from the particle surface into

interior sites.

• The adsorption of solute molecules from the active sites into the interior

surfaces of pores.

Weber and Morris equation can be used to explain the diffusion mechanism

q = KdirVT + C

Where, Kjjf is the intra-particle diffusion rate constant. The adsorption rates for intra-

particle diffusion (Kaif) under different conditions were calculated from the slopes of

the linear portions of the respective plots with units of mgg'' min' .

1.7. Survey of literature During the past three decades, several physical, chemical and biological

decolourization methods have been reported, few however, accepted by the textile

industries. Amongst numerous techniques, adsorption is the best choice and gives the

best result as it can be used to remove the different type of colouring materials. If the

adsorption system designed correctly it will provide high quality treated effluent.

Most commercial system currently use activated carbon as sorbent to remove dye in

waste water because of it excellent adsorption ability. However although activated

carbon is preferred sorbent, its use restricted due to high cost. In order to decrease the

cost treatment, attempts have been made to search inexpensive alternative adsorbent.

Resent literature survey on adsorption of removal of dyes from aqueous solution and

wastewater using various low cost adsorbent is summarized in table 1.4

Tablel.4. Survey of literature Adsorbent Dyes Remark Reference

Polyacrylic Acid-Bound Magnetic Nanoparticles

Crystal Violet Langmuir adsorption isotherm with a maximum adsorption amount of 116 mgg' ' .

Liao et al., 2005

Agricultural wastes carbon

Methylene Blue Follow first- and second-order kinetic equations and intraparticle diffusion model.

Maiti et al., 2005

Palm kernel shell activated carbon

Basic Blue 9 The isotherm data were well described by the Redlich-Peterson isotherm mode.

Jumasiah et al 2005

Carbon Pyrazolone Dyes Kinetics and mass transfer studies were studied

Sarawy et al., 2005

Unbumed carbon Methylene Blue Adsorption increases with the initial dye concentration, solution pH, and temperature.

Wang et al., 2005

! i

Hybrid silica/chitosan

Anionic Dyes Follow first-order Lagergren kinetic model and pore diffusion mechanism.

Antonio et al., 1 2005

!

j

De-oiled soya Malachite Green Maximum adsorption at pH-9.

Mittal et al., j 2005 '

Peanut hulls Basic Dyes Adsorption increase with increase temperature and follow Langmuir adsorption isotherm.

Allen et al., 2005

1

i Sepiolite Acid Dyes The adsorption isotherm

data can be fitted well known Langmuir isotherm.

Ozcan et al., i 2005

Activated clay, montmorillonite, and activated carbon

Basic Green 5 The activated carbon was suitable for BG5 but not forBVlO.

Shiau et al., 2005

Activated carbons

Malachite green The pH of dye solution in the range of 6-10,was found favorable for adsorption.

Ba§ar et al, 2005

Peanut hull Methylene Blue Brilliant Cresyl Blue, Zeutral Red, Amaranth

Carboxyl group inliibited the adsorption of anionic dyes.

Gong et al., 2005

Chitosan beads Reactive D\e 1 Adsorption isotherm 1 follow Langmuir model.

Kim et n!., 2005

Adsorbent Dyes Remark References

Rubber wood sawdust

Bismark Brown Adsorption capacities of 2000 and 1111 mg g"' were obtained for steam and chemical followed by steam-activated carbons.

Prakash et al., 2005

Unburned carbon Rhodamine B Adsorption is endothermic reaction with AH° at 25kJmor'.

Shaobin et al., 2005

Jute wastes Methylene Blue A maximum removal of 81.7% was obtained.

Banerjee et al., 2005

Biopolymers Reactive, Acidic, and Basic Dyes

Chemisorption mechanism. Chang et al., 2005

Iron humate Methylene Blue, Malachite Green, Rhodamine B, Crystal Violet

Diffusion mechanisms controlling the rate of the dye sorption.

Smidova, 2005

Bagasse fly ash and activated carbon

Congo Red The effective pHo was 7.0 for adsorption on BFA.

Mall et al., 2005

Polyester C.l. Disperse Orange 30

The pseudo-second-order kinetic model fitted well.

Ozcanand et al., 2005

1

Activated Carbon

Acid Blue Dye The adsorption capacities obtained from different carbons are in the range of 15-358 mg/g.

Valix et al., 2006

Acrylamide/ N-vinylpyrrolidone/ 3(2-hydroxyet-hylcarbamoyl) acrylic acid]

Crystal Violet, Malachite Green and Methylene Blue.

The uptake of dyes within the hydrogel increased as MG>MB>CV.

Dadhaniyaet al., 2006

Montmorillonite Crystal Violet Erytlirosine-B

100% adsorption for crystal violet.

Rytwo et al., i 2006 i

i

Rice husk ash Methylene Blue The highest adsorption capacity achieved is found to be 690 mg/g.

Chandrasekliar ( et al.,2006

Ulva lactuca Methylene Blue The maximum adsorption capacity was about 40.2 mg of dye per gram of dry green algae at pH 10.

Sikaily et al., 2006

Silica Methylene Blue MCM-41,MCM48 display reversible adsorption after reaching equilibrium while MCM-50 exhibits iiTeversiblc adsoiption.

Wang et al., i 2006 1

24

Adsorbent Dyes Remark References

Sporopollenin Crystal violet Cation-exchange is suggested as an effective process for removal and recovery of CV.

Gezici et al, 2006

Egg shell Direct Red 80, Acid Blue 25

Maximum desorption of 81.8% was achieved for both dyes in aqueous solution at pH 12.

Arami et al., 2006

Hen feathers Erythrosine The adsorption follows first-order kinetics at all the temperatures.

Gupta et al., 2006

Sepiolite Methyl Violet and Methylene Blue

Amount of MV and MB dyes on sepiolite increased with increasing pH, ionic strength and temperature.

Ozdemir et al., 2006

Coke waste Reactive Red 4 The maximum adsorption capacities of the coke waste were 70.3 ± 11.1 and 24.9±1.8mg/gatpH 1 and 2.

Won et al., 2006

Mesoporous hybrid gels

Methyl Orange, Methyl Red, Bromo cresol Purple, Phenol Red, Neutral Red, and Brilliant Blue FCF.

Adsorption sequence NR > MR ~ BBF > MO > BP ~ PR.

Wu et al., 2006

Aminopropyl-silica

Anionic Dyes A rise of temperature accelerates the mass transfer of the red dye into the Sil-NH2 surface, der Waals forces

Cestari et al., 2006

Sepiolite Maxilon Blue GRL Intra-particle diffusion was rate-limiting step.

Dogan et al., 2006

Starch Basic Green 4 Pseudo-second-order model fits the experimental data better.

Shimei et a'., 2006

Slica Styryl Pyridinium Silica surface involving hydrogen bonding.

Parida et al., 2006

Bentonite Acid Dye Follow Lagergren first order kinetic.

Baskaralingam et al., 2006

Activated Carbon

Malachite green Kinetic data of malachite green onto activated carbon by non-linear and linear method.

Kumar et al.,2006

Chitosan Remacryl Red Adsorbents desorbed over 80% of the adsorbed dye.

Lazaridis et al., 2006

25

Adsorbent Dyes Remark References

Bentonite Methylene Blue The time needed to reach equilibrium was less than 30 min.

Banat et al., 2007

Activated Bentonite

Methylene Blue Bentonite shows >83 % adsorption.

Akimbaeva et al.,2007

Activated Carbon and Graphitic Thermal Carbon Black

Methylene Blue Acidic dye (Acid Orange;

Addition of an electrolyte does not affect the adsorption of dyes. It is suggested that hydrophobic interactions.

Khokhlova et al., 2007

Activated Carbon

Methylene Blue, Acid Blue 25 and AcidRedlSl, Reactive Red 23

The rate coefficients (k) followed an order of: RR < AR <AB < MB.

Tsang et al., 2007

PolyN-vinyl pyrrolidone/2(me thacryloyloxyeth yl) trimethyl ammonium chloride

Orange-II, Reactive Orange -13 , Reactive Orange-14

The binding ratio of the hydrogel/dye system increases in the following order: 0R-II>R0-14>R0-13.

Dadhaniya et al., 2007

Zeolite Red-40, Yellow-5 The external cation exchange capacities for the clinoptilolite rich tuff and the sodium form were 0.0940 and 0.0852 meq/g.

Perez et al., 2007

BDTDA treated sawdust

Disperse Blue 56 Optimum pH for adsoiption of disperse dyes is found to be in the range of 2-3

Rai et al., 2007

Carbonized Water Weeds

Methylene Blue Maximum adsorption capacities based on the Langmuir model for pure and carbonized water hyacinth were 7.05 and 2.07(mg/g).

Tarawou et al., 2007

Chitosan/montm orillonite nanocomposite

Congo Red Adsorption processes follow the pseudo-second-order and the Langmuir isotherm.

Wang et al., 2007

Pumpkin seed hull

Methylene blue The equilibrium process was described well by the multilayer adsorption isotherm.

Hameed et al, 2007

26

Adsorbent Dyes Remark References

White-rot fungus and Chitosan

Acid Blue 161 Sorption capacity of each sorbent increased with increasing initial dye concentration up to SOOrngf'.

Aksu et al., 2007

Chitosan Methyl Orange Data were well fitted to a hybrid Langmuir-Freundlich isotherm

Morals et al., 2007

Olive pomace and Charcoal

Methylene Blue Charcoal showed higher sorption capacity than that of olive pomace.

Banat et al., 2007

Broad bean peels Methylene Blue The monolayer adsorption capacity was found to be 192.7 mg/g

Hameed etal., 2007

Beer brewery waste

Methylene Blue Pseudo-second-order model were in accordance with their pore properties

Tsai et al., 2007

Activated Carbon

Acid Red 97, Acid Orange 61 and Acid Brown 425

The rates of adsorption were found to conform to the pseudo-second-order kinetics.

Gomez et al., 2007

Zeolite Malachite Green The adsorption capacities of malachite green at 30°C,pH6is5xlO"Vol/g

Wang et al., 2007

Activated palm ash

Acid Green 25 The adsorption capacities were found to be 123.4, 156.3 and 181.8 mg/g at 30, 40, and 50 °C. was calculated as 70 mg/g

Hameed et al., 2007

Wheat bran Astrazon Yellow 7GL

The adsorption capacity (Qo) calculated from the Langmuir isotherm was 69.06 mg/g for at pH 5.6.

Sulak et al., 2007

Colemanite Acid Blue 062 Adsorption follows a pseudo-second order equation.

Atar et al., 2007

Diatomite Methj'lene Blue, Cibacron Reactive black, Cibacron Reactive Yellow

A rapid decrease in the column adsorption capacity with an increase in particle size.

Ghouti et al, 2007

1

Wheat bran Reactive Blue 19, Reactive Red 195 and Reactive Yellow 145)

The monolayer covarage capacities for RB 19, RR 195 and RY 145 dyes were obtained as 117.6, 119.1 and 196.1 mg/g at 60 °C.

Ciceketal., j 2007 j

Adsorbent Dyes Remark References

Fungi and yeast, C.I. Reactive Black 8, C.I. Reactive Brown 9, C.I. Reactive Green 19, C.I. Reactive Blue 38, and C.I. Reactive Blue 3.

Maximum uptake capacity (Q°) for the selected dyes was in the range 112-204 mg/g biomass.

Kumari et al., 2007

Chitin Reactive Red 141 Total elution of modified chitin and chitin were 92.76% and 55.29%.

Dolphen et al., 2007

Hectorite C.I. Reactive Orange 122.

Kinetic studies were fitted with the pseudo-second-order kinetic model.

Baskaralingam et al.,2007

Egg shell Acid Red 14 (AR14) and Acid Blue 92 (AB92)

Maximum desorption of >89.6% was achieved for AR14 and 82.8% for AB92 in aqueous solution at pH 12.

Arami et al., 2007

Coal fly ash Reactive Black 5 (RB) and Reactive Yellow 176 (RY)

At the final pH of 8.1-8.5, the adsorption capacity of both dyes on the FA-BM was maximum and decreased above or below this pH.

Pengthamkeerati et al.,2007

Activated carbon Basic Blue 3 The monolayer adsorption capacity was 227.27 mg/g.

Hameed etal., 2008

Waste metal hydroxide sludge

Remazol Brilliant Blue

A pseudo-second-order model showed good agreement with experimental data.

Santos et al., 2008

Rice husk Congo Red Thomas model was found suitable for the normal description of breakthrough curve.

Han et al., 2008

! 1

Marine seaweed Methylene Blue The adsorption reached equilibrium at 90 min.

Cengiz et al., i 2008 i

1

Yellow passion fruit peel

Methylene Blue An alkaline pH was favorable for the adsorption of MB.

Pavan et al, 2008 i

Distiller waste Reactive Red 231 The necessary time to reach the equilibrium was found to be less than 2 min.

§ener, 2008 1

i 1

28

Adsorbent Dyes Remark. References

Activated carbon Methylene Blue The highest bed capacity of 40.86 mg/g was obtained using 100 mg/1 initial dye concentration, 6 cm bed height and 20 ml/min flow rate.

Tan et al., 2008

Chitosan Basic Blue 3 The sorption was dependent on the presence of sulfonate groups.

Crini et al., 2008

Parthenium biomass and Parthenium carbon

Rhodamine-B The adsorption capacities of the studied adsorbents were in the order PWC > WC.

Lata et al., 2008

Luffa cylindrica Methylene Blue Average BET surface area of fibers was calculated as 123 m^/g.

Demir et al., 2008

Polystyrene-graft-copolymer

Green Torquoise Blue, Magenta Red, Rhodamine, Crystal Violet, Congo Red, Methylene Blue

The graft copolymers are observed to possess a high affinity for basic, acid, and reactive dyes.

Vivek et al, 2008

Activated carbon Alkaline Black Adsorption of alkaline-black follows Langmuir adsorption isotherm models.

Fan et al., 2008

Pyrolyzed petrified sediment

Methylene Blue The activation energy of adsorption was found about 8.5kJmor'.

Aroguz et al., 2008

Sand Coomassie Blue, Malachite Green and Safranin Orange

For all the three dyes 1/n < 1, which indicates that adsorption was favorable.

Rauf et al., 2008

Fly ash Methylene Blue The enthalpy (AH") value is positive (5.63 kJ/mol), suggesting an endothemiic nature of the adsorption.

Lin et al., 2008

Ti02-chitosan Methylene Blue and Benzopurpurin

Interaction between adsorbent and adsorbate molecules was not only physical but chemical.

Carolina et al., 2008

Coconut coir pith Direct Red 12Band Rhodamine B

Adsorption capacity of 76.3 mgg~'and 14.9 mg g~' for Direct Red 12B

and Rhodamine B.

Kumar et al., 2008

29

Adsorbent Dyes Remark References

Pomelo peel Methylene Blue The monolayer adsorption capa- city was 344.83 mg/g at 30 °C.

Hameed et al., 2008

Montmorillonite Congo Red Adsorption kinetic was best described by the pseudo-second-order model.

Wang et al., 2008

Chitosan /oil palm ash composite beads

Reactive Blue 19 The thermodynamics of reactive dye adsorption indicates its spontaneous and endothermic nature.

Hasan et al., 2008

Bentonite Direct Red 2 The equilibrium time was reached within 40 min.

Zohra et al, 2008

Activated carbons

Reactive orange Adsorption follows pseudo-second-order reaction with regard to the intraparticle diffusion rate.

Amin, 2008

Activated carbon reactive black 5 Cationic surfactant could enhance sorption capacity of RB5 on activated carbon.

Choi et al., 2008

Bottom ash and deoiled soya

Basic Fuchsin Adsorption follow pseudo-second-order kinetics.

Gupta et al., 2008

Almond shells Direct Red 80 The adsorption studies revealed that the mixture type of almond shells remove about 97% of the DR 80 dye from aqueous phase after 1 h.

Ardejani et al., 2008

Zeolite Toluidine Blue 0 The maximum adsorption capacity of clinoptilolite for TBO was 2.1 x lO""* mol g~" at solution pH of 11.0

Alpat et al., 2008

Rattan sawdust Malachite Green The monolayer adsorption capacity of RSD was found to be 62.71 mg/g

Hameed et al.,2008

Activated carbon Astrazon yellow 7GL

Adsorption process was spontaneous and endothermic

Demirbas et al.. 2008

Activated carbon Methylene Blue Adsorption process was attained to the equilibrium within 5 min.

Karaca et al, 2008

Adsorbent Dyes Remark References

Chitosan Basic Blue 3G Thermodynamic analysis showed that the sorption process was spontaneous and endothermic with an increased randomness

Kyzas et al.,2008

Chitosan C. I. Acid Green 25, C. I. Acid Green 12,C. I. Acid GreenlO, C.I. Acid Redl8, C.I. Acid Red 73

The effect of varying the percentage degree of deacetylation showed that from 52% to 97% resulted in decrease in the dye adsorption capacity

Wonget al., 2008

Posidonia oceanica

Solophenyl Brown Redlich-Peterson model provides the best fit for the experimental equilibrium data

Ncibi et al., 2008

Literature survey shows that a lot of new materials have been utilized for the removal of

various dyes from wastewater but still there is a need to explore new materials in order to

remove the dyes from wastewater. Keeping this view in mind, it has been decided to

investigate the adsorption for removal of dyes from wastewater. Remarkable results were

obtained for Ginger waste material as an adsorbent, which has been discussed in chapter-2

of this dissertation.

Cficipter-2

Adsorption ofcrystaCvioCet dye from aqueous

soCution onto ginger waste materiaC(QW94.):

^.valuation of equiCiSrium, isotHerms, ^netics

ancf Brea^tirougH capacity

1. Introduction Water pollution due to discharge of coloured effluents from dyes manufacturing and

textile dyeing industries are one of the major environmental concerns in the world today.

Though dyes impart appealirig colors to textile fibers, foodstuff, etc. however, strong

colours imparted by the dyes pose aesthetic and ecological problems to the aquatic

ecosystem. Dyeing waste discharged into natural water stream may make them

unacceptable for public consumption. Thus, it is desirable to eliminate dyes from textile

water (Inthorn et al., 2004). The total dye consumption of the textile industry alone is in

excess of 10 kg/year and an estimated 90% of this total ends up on fabrics.

Consequently, approximately 10^ kg/year of dyes are discharged into waste streams by

the textile industry (Choy et al., 1999). Among the many available dyes, crystal violet

(CV) is a well-known dye that is used in a variety of ways: as a biological stain,

dermatological agent, veterinary medicine, additive to poultry feed to inhibit propagation

of mold, intestinal parasites, and fungus, etc. It is also extensively used in textile dying

and paper printing. However, crystal violet is also a mutagen and mitotic poison (Au et

al., 1978).

The most widely used methods for removing dyes from wastewater systems include

physicochemical, chemical and biological methods such as flocculation, coagulation,

precipitation, adsorption, membrane filtration, electrochemical techniques (Dabrowski et

al.,2001). Adsorption is widely used in the removal of contaminants from wastewater.

The design and efficient operation of adsorption process require equilibrium adsorption

data. The equilibrium isotherm plays an important role in predicting modeling for

analysis and design of adsorption system (Allenet et al., 2004). Although activateti

carbons are among the most effective adsorbents with high surface area and can be

regenerated by thermal desorption or combustion of the toxicants in air, are siiii

considered expensive (Chakraborty et al., 2005), A variety of agricultural waste biomas-

has been used for adsorption process, namely rice husk, rice straw, coconut husk, bagase;

and tree bark (Gupta et al., 2003). India and Nigeria are the major ginger (Zingiber

Officinale) producing country in the world. Overall ginger (rhizome) production in Indi;:

is greater than 275,000 million tones. The rhizomes of ginger are well known for thei;

medicinal and flavoring properties. Chinese, Japanese and Indian traditional medicine-

(ayurvedic and unani) different formulation of ginger are used for treamient o '

gastrointestinal problem, reduce serum cholesterol, common cold, skin infection and

other ailments. Therefore, due its large availability, it can be used as a potential adsorbent

for the removal of crystal violet dye.

The objective of this study was to evaluate the adsorption potential of ginger waste

material (GWM) for the adsorption of crystal violet. The equilibrium, Isotherms model

and kinetic data of adsorption studies were processed to understand the adsorption

mechanism of crystal violet dye on to GWM. The breakthrough capacity and desorption

studies were also performed in order to find out the maximum possible capacity of the

material.

2. Materials and Methods

2.1. Preparation of adsorbent

In the present study, the ginger waste material (GWM) was collected from local mill after

extraction. Initially, GWM was washed with double distilled water to remove the

impurity and was grounded and then it was crushed, sieved to lOOmesh BSS standard

particle size. Fifteen grams GWM was activated by refluxing with 20 ml of (IM) H2SO4

and 20 ml of (1000 mg/1) ZnC^ and was kept for 24 hr at 30 ' C. Then it was again

washed with double distilled water and dried in air oven at 60 ''C and was used as such for

further studies.

2.2. Adsorbate

Crystal violet

Crystal violet dye was purchased from Sigma, India and used without purification. The

characteristics and chemical structure of the dye is listed in Fig.l and Table 2.L

respectively are given below.

A

CH3 C H ,

Fig.l. Structure of Crystal Violet

J J

Table 2.1

The physical and chemical characteristics of crystal violet dye

Generic name C.I. Basic Violet (10 BV 10)

Color Index number 42555

Abbreviation lO(BVlO)

Molecular formula C25H30N3CI

Purity (%) 80

Molecular weight 408

^max (nm) 584

Chemical name (lUPAC) Hexamethylpararosaniline chloride

Solubility in water 16 g/L (25 °C)

2.3. Batch equilibrium and kinetic studies

Adsorption experiments were carried out by adding a fixed amount of adsorbent (0.05g)

into a series of 250 ml conical flasks filled with 50 ml solution of various concentration

ranges from (5-20 mg/1). The conical flasks were then sealed and placed in a water bath

shaker and shaken ai 125 rpm with a required ?dsorr)tion time at 30, 40 and 50 ' C at dye

natural pH. The effect of pH was investigated at temperature 30 ' C and initial

concentration 10 mg/1. pH adjustments have been done using solutions of 0.1 M NaOH

and 0.1 M HNO3. The flasks were then removed from the shaker, and the final

concentration of dye in the solution was measured at maximum wavelengths of crystal

violet (584nm) using double beam UV-vis spectrophotometer model (Elico SL164). The

amount of dye equilibrium qe (mg/g) on GWM was calculated from the following

equation:

(CO-CeW qe = - ^ (1)

W

Where CO and Ce (mg/g) are the liquid phase concentration of dye at initial anci

equilibrium, respectively, V the volume of the solution (L) and W is the mass of

adsorbent used (g).

3. Results and discussion

3.1 Characterization of the adsorbent

Scanning electron micrograph (SEM) was recorded at two different magnifications (Fig. 2

a & b) using a software controlled digital scanning electron microscope - LEO 420. The

SEM clearly reveal the surface texture and porosity of ginger waste material (GWM) and

small opening on the surface before adsorption'while the SEM study after adsorption

clearly shows that these small opening and pores are filled probably because of the

adsorption of crystal violet.

3.2. Effect of contact time

The adsorption of crystal violet dye by GWM increases as the initial dye concentration

increased as shown in the Fig. 3. It indicates that the contact time needed for crystal violet

solution with initial concentration of 5-20 mg/1 to reach the equilibrium is 150 minutes.

However, the experimental data was measured at 180 minutes to make sure that full

equilibrium was attained. The removal of crystal violet (mg/g) increased with increase in

agitation time and concentration remained nearly constant after equilibrium time. The

time required to attain this state of equilibrium is termed equilibrium time, and the

amount of dye adsorbed at the equilibrium time reflects the maximum adsorption capacity

of the adsorbent under those operation condition. At the begirming, the dye ions were

adsorbed by the exterior surface of GWM, the adsorption was fast. When the adsorption

of exterior surface reached saturation, the dye ions entered into the pores of ginger waste

material and were adsorbed by the interior surface of the particles. These results are in

agreement with the finding reported by (Porkodi et al., 2007)

3 .3 . Effect of p H

The effect of solution pH was studied for adsorption of crystal violet on GWM a'

temperature 30 C, initial concentration 10 mg/1, amount of adsorbent (0.5 g). The range

of solution pH was adjusted between 2 and 10. Fig.4 shows the effect of pH on the

adsorption of crystal violet on GWM. It was observed that amount of crystal viole;

adsorbed was found to increase from 5 to 9 mg/g. This behavior can be explained on the

basis of change in surface charge of the GWM. In case of basic dyes (crystal violet) a:

lower pH, the H" ions will compete with the dye cations causing in decrease in qe value.

This can be observed from the higher and lower sorption capacity of crystal violei at

35

higher and lower pH. Similar results were reported for the adsorption of crystal violet

from aqueous solution on to jute fiber carbon (Porkodi et al., 2007) and raw and pre-

treated sepiolite (Eren et al., 2007).

3.4. Effect of temperature

The adsorption studies were carried out at three different temperatures 30, 40 and 50 °C,

and the results of these experiments are shown in Fig. 5. The adsorption capacity increases

with the increasing temperature, indicating that the adsorption is an endothermic process.

This may be as a result of increase in the mobility of the dye molecule with increasing

temperature (Alkan et al., 2003). An increasing number of molecules may also acquire

sufficient energy to undergo an interaction with active sites at the surface. Furthermore,

increasing temperature may produce a swelling effect within the internal structure of the

ginger waste material enabling large dye to penetrate further (Asfour et al., 1985)

Thermodynamic parameters such as standard free energy change (AG^), enthalpy change

(AH*') and entropy change (AS°) were calculated using the following equations (Catena et

al., 1989, Frajietal., 1992).

Kc = — (2)

Ce '

Where, Kc is the equilibrium constant. Cac and Ce are the equilibrium constants (mg/L)

of the dye on the adsorbent and in the solution respectively. AG° was calculated from the

equation

AG°=-RTlnKc (3)

Where, T is the temperature in Kelvin and R is gas constant (8.314 J/mol K). AH" was

calculated from the following equation

log Kc = (4) 2.303/? 2303RT

AH° and AS' were obtained from the slope and intercept of Van't Hoff plot of log Kc

versus 1/T (Fig.6). Positive value of AH° (Table 2.2) shows the endothermic nature of

adsorption. The negative values of AG*' indicate the spontaneous nature of adsorption of

CV on GWM. The positive value of AS*' shows the increased randomness at the

solid/solution interface during the adsorption of CV on GWM. The increase in adsorption

capacity of GWM at higher temperature may be attributed to the enlargement of pore size

or activation of the adsorbent surface (Vishwakarma et al , 1989). The values of Kc also

increase with rise in temperature (Table 2.2) showing endothermic process.

3.5. Effect of adsorbent mass

Fig.7 shows the plot of equilibrium uptake capacity, qe (mg/g) and % adsorption against

the GWM dose (g) for the sorption of crystal violet. From the figure it was obser\'ed that

the amount of dye adsorbed onto unit weight of adsorbent gets decreased with increasing

GWM concentration. The dye uptake decreased from 8 mg/g to 2.3 mg/g for an increase

in adsorbent mass from 25 to 200mg.Whereas, the % adsorption increases with increasing

adsorbent dose. The % adsorption increased 40-95 % for an increase in adsorbent mass

from 25 to 200 mg. The decrease in qe value may be due to the splitting effect of flux

(concentration gradient) between sorbate and sorbent with increasing GWM

concentration causing a decrease in amount of dye adsorbed on to unit weight of ginger

material. The increase in % adsorption is because, at higher material concentration, there

is a very fast superficial adsorption onto the material surface that produces a lower solute

concentration in the solution than when material concentration is lower (Porkodi et al.,

2007).

3.6. Effect of concentration

The adsorption experiments were performed in the concentration of the adsorbate ranging

from 5 to 20 mg/L at pH 6.2 and temperature 30 °C. The percentage and amounts of

adsorbed CV on GWM are shown in the Fig.8. From the figure, it is observed that the

percent adsorption decreases (80-60 %) as the concentration is increased (5 to 20 mg/L)

while the amount adsorbed increases from 4 mg/g to 12 mg/g. At a fixed adsorbent dose,

the amount adsorbed increased with increasing concentration of solution, but the

percentage of adsorption decreased. In other words, the residual concentration of d\ e

molecules will be higher for higher initial dye concentrations. In the case of lower

concentrations, the ratio of initial number of dye moles to the available adsorption sites is

low and subsequently the fractional adsorption becomes independent of initial

concentration (Chiou et al., 2004). Recently, (Gaffar et al., 2005) reported lliat the

adsorption percentage decreases on increasing the dye concentration. Thi: could be

.w

ascribed to the accompanying increase in dye aggregation and/or depletion of accessible

active sites on the material.

3.7. Adsorption Isotherm

The Langmuir equation is given in the following equation (Langmuir, 1918)

Umax S\L v^c , _ ,

qe = -J (5) 1 + K L C

Where qe is the solid phase adsorbate concentration in equilibrium (mg/g), qmax the

maximum adsorption capacity corresponding to complete monolayer coverage on the

surface (mg/g), Ce the concentration of adsorbate at equilibrium (mg/L) and KL is the

Langmuir constant (L/mg). Eq. (5) can be rearranged to a linear form:

1 1 1 — = + (6) tfe U max Cy ina\

The constant can be evaluated from the intercepts and slopes of the linear plots of 1/qe

versus 1/Ce (Fig.9). It was observed that the equilibrium adsorption data followed

Langmuir isotherm. Conformation of the experimental data to Langmuir isotherm model

indicates the homogeneous nature of the GWM surface, i.e. each dye molecule / GWM

adsorption has equal adsorption activation energy and demonstrates the formation of

monolayer coverage of the dye molecule on the outer surface of GWM. Langmuir

parameters calculated from Eq. (6) are listed in Table 2.3.

The essential characteristics of the Langmuir equation can be expressed in term of a

dimensionless separation factor, RL, defined as (Hall et al., 1966):

Ri. = ^- (7) 1 + KLCO

Where, Co is the highest initial solute concentration and KL is the Langmuir's adsorptioi

constant (L/mg). Table 2.3 shows the values of RL (0.938 to 0.936) are in the range of 0-1

at all temperatures studied, which confirms the favorable uptake of the CV dye.

38

The Freundlich equation is an empirical equation employed to describe heterogeneous

system, in which it is characterized by the heterogeneity factor 1/n. Hence, the empirical

equation can be written (Freundlich, 1906):

qe = KFCe''" (8)

Where qe is the solid phase adsorbate concentration in equilibrium (mg/g), Ce the

equilibrium liquid phase concentration (mg/L), Kp the Freundlich constant (mg/g) and 1/n

is the heterogeneity factor. A linear form of the Freundlich expression can be obtained by

taking logarithms of Eq. (8):

logqc = IcgK.-f-IogCe (9) n

Therefore, a plot of log qe versus log Ce (Fig. 10) enables the constant Kp and exponent

1/n.The values of Friendlich constant are listed in table 2.3. It clear that values of

Freundlich exponent (n) are greater than 1 represent favorable adsorption at all the

temperature studies (Namasivayam et al., 1994). The result suggests that CV is favorably

absorbed by GWM. Langmuir isotherm fits well with the experimental data (correlation

coefficient R^>0.995) 31 til 1 temperature than Freundlich isotherm.

4. Adsorption Kinetics The pseudo- first-order, pseudo second order and intra-particle diffusion equation were

used to find out the adsorption mechanism of CV dye on GWM.

4.1. Pseudo-first-order kinetic model

A simple kinetic analysis of adsorption is the pseudo-first-order equation in the fomi

(Lagergren, 1898):

^ = kiq.-q,) (1G: dt

Where ki is the rate constant of pseudo first order adsorption and qe represents adsorption

capacity (i.e. the amount of adsorption corresponding to monolayer coverage). After

TQ

definite integration by applying the initial conditions t = 0 to t and qt = 0 to qt, Eq. (10)

becomes;

log(qc-q,) = l o g q e - y ^ r (11)

Where qe and qt are the amount of dye adsorbed (mg/g) at equilibrium and at any time t,

ki is the rate constant (min "'). The plot of log (qe-qO versus t gives a straight line for the

pseudo first order adsorption kinetics (Fig. 11). The values of the pseudo first order rate

constant ki were obtained from the slopes of the straight lines. The ki values, the

correlation coefficients, R , and the predicted and experimental qe values are given in

Table 2.4.

4.2. Pseudo- second- order model

The Pseudo- second- order model can be represented in the following form (McKay et al.,

1999):

^^k.{q.2-q,)2 (12)

Where k2 is the rate constant of Pseudo- second- order adsorption, Integration of Eq. (12)

and applying the initial conditions (McKay et al., 1999), we have:

^ + - / (13) q, kzq,2 q.

Where, k2 (min g/mg) is the rate constant for the Pseudo- second- order adsorptioii

kinetics. The slopes of the plots t/qt versus t give the value of qe, and from the intercept k?

can be calculated. Fig. 12 shows the Pseudo- second- order plots for CV onto GWM at 30

°C. The Pseudo- second- order rate constants k2, the calculated qe values and the

corresponding linear regression correlation coefficients value R^ are given in Table 2.4.

The calculated qe values agree with experimental qe,exp values, and also, the correlation

coefficients for the Pseudo- second- order kinetic plots at all the studied concentrations

were higher R" > 0.98. Similar kinetic results have also been reported for the adsor]Dtion

of crystal violet onto jute fiber carbon (Porkodi et al., 2007).

40

4.3. Diffusion rate constant study

The adsoiption of organic dyes from aqueous solution by GWM can be described by three

consecutive steps:

• The transport of adsorbate from bulk solution to the outer surface of the adsorbent

by molecular diffusion, known as external or film diffusion.

• Internal diffusion, i.e. the transport of adsorbate from the particle surface into

interior sites.

• The adsorption of solute molecules from the active sites into the interior surfaces of

pores.

The overall rate of the adsorption process will be controlled by the slowest, i.e. the rate -

limiting step. The nature of the rate - limiting step in batch system can be determined

from the properties of the solute and adsorbent. Rate of adsorption is usually measured by

determining the change in concentration of adsorbate with the adsorbent as a function of

time. Linearization of the data is obtained by plotting (Fig. 13). The amount adsorbed per

unit weight of adsorbent (q) versus Vt , as described by Weber and Morris (Weber et al.,

1963)

q = Kd,rVr + C (14)

Where, Kdif is the intra-particle diffusion rate constant. The adsorption rates for intra-

particle diffusion (Kjif) under different conditions were calculated from the slopes of the

linear portions of the respective plots with units of mgg"' min'' ^ (Singh et al., 1988).The

double nature of these plots may be explained by the fact that the initial curved portions

are boundary layer diffusion effect while final linear portion are a result of intra-particle

diffusion. (Mcay et al.,1987). The values obtained from the slope of the linear portion of

the curves for each concentration are given in Table 2.5.

5. Column studies

5.1. Effect of bed height on breakthrough capacity

The effect of adsorbent doses on the breakthrough curves was studied using GWM

packing material of column (1cm diameter and length 30 cm) at a fixed flow rate of

Iml/min, temperature 30 ^ C, pH 6.2 and initial concentration 10 mg/L. The breakthrough

curve plotted in Fig. 14 reveals that 920, 2180 and 3010 ml of crystal violet solution can

be passed through the column filled with 0.2, 0.3 and 0.5 g of the adsorbent respectively

without any trace being detected in the effluent. The breakthrough capacity and

exhaustive capacity with the adsorbent (0.2 g) for crystal violet have been calculated as

46 mg/g, 91 mg/g respectively. While the break through capacity and exhaustive capacity

was found to be 72.6 and 98 mg/g with (0.3 g) adsorbent and 60.2 and 71 mg/g with (0.5

g) adsorbent. The exhaustive capacity of the sorbent is higher in case of column process

than the batch process. This is because increase in the surface area of adsorbent which

provide more binding sites for the adsorption of dye.

5.2. Desorption studies

Desorption studies help to elucidate the nature of adsorption recycling of the spent

adsorbent. If the adsorbed dye can be desorbed using neutral pH water, then the

attachment of the dye on the adsorbent is by weak bonds and if sulphuric acid or alkaline

water can desorbs the dye, then the adsorption is by ion exchange. If an orgariic acid, like

acetic acid can desorbs the dye, then the dye is held by the adsorbent through

chemisorptions. NaOH and H2O did not show any desorption but weak acid, like acetic

acid (O.IM and IM) solubilized about 35 and 50% of dye from the spent adsorbent,

respectively. The desorption of dye in acetic acid indicates that crystal violet dye is

adsorbed onto GWM through chemisorptions mechanism and very little desorption of dye

in acid confirms the strong affinity of dye on the GWM.

6. Comparison of various low-cost adsorbents

The data presented in (table 2.6) compares the adsorption capacity of different types c

adsorbents used for removal of crystal violet. The most important parameter to compare i

the Langmuir (qmax) value since it is a measure of adsorj^tion capacity of the adsorbcni.

The value of (qmax) in this study is larger than those in most of previous work. Ihi,

suggests that CV could be easily adsorbed on GWM.

42

7. Conclusion The results of this study show that ginger waste material (GWM) can be successfully used

for the adsorption of crystal violet dye from aqueous solution. The adsorption capacity

increases with temperature indicating the endothermic and spontaneous nature of

adsorption which was further confirmed by the positive value of AH* and negative values

of AG . Based on the Langmuir isotherm analysis, the monolayer adsorption capacity was

determined to 64.9, 227.2, 277.7 mg/g at 30, 40 and 50 °C, respectively. The RL values

showed that GWM was favorable for the adsorption of crystal violet dye. Three

simplified kinetic models, pseudo-first-order, pseudo-second-order and intra-particle

diffusion were applied to investigate the adsorption mechanism. The pseudo-second-order

kinetic model fits very well with the dynamical adsorption behavior of CV dye. The

maximum breakthrough capacity was calculated 72.6 mg/g.

43

Table 2.2

Thermodynamic parameters of crystal violet adsorption on GWM

Temp. ("O Kc logKc

(KJ/mol) (J/mol K)

AH'

(KJ/mol)

30 4 0.602 -3.4011

40 10 1 -5.8556 0.22455 64.43

50 20 1.301 7.8555

Table 2.3

Langmuir and Freundlich Isotherm model for adsorption of crystal violet on GWM

Langmuir Isotherm model Freundlich Isotherm model

Temp

(°C)

qmax

(mg/g)

KL

(L/Mg)

R^ RL KF

(mg/g)

n

(L/mg)

R

30 64.93 0.832 0.9951 0.9389 1.12 1.16 0.982(

40 227.27 0.908 0.9986 0.9615 1.14 1.07 0.993

50 277.77 0.944 0.9995 0.9363 1.18 1.09 0.999

44

Table 2.4

Comparison of the pseudo-first-order and pseudo-second-order models for different

initial concentration of crystal violet at 30 C

Pseudo-first-order kinetic model Pseudo-second-order kinetic model

Co qe(exp)

(mg/1) (mg/g)

qe,(cal) ki R^

(mg/g) (min-1)

qe,(cal)

(mg/g)

k2

(g/mg min)

R

5 4.1 2 1.56x10-^ 0.990 4.45 0.01 0.9947

10 8 3.2 1.54x10"^ 0.982 8.59 0.008 0.9979

20 15 13.5 2.16x10-^ 0.99J 18.58 0.0013 0.998'

Table 2.5

Intra-particle diffusion for different initial concentration of crystal violet at 30 "C

Co (mg/L) Kdif C R^

5 0.1713 2.336 0.9661

10 0.32 4.02 0.8833

15 1.0336 1.914 0.9427

Table 2.6

Comparison of adsorption capacities of various adsorbents for crystal violet

Adsorbent q«,ax(mg/g) Reference

Ginger waste material (GWM) 277.7

Jute fiber carbon (JFC) 23.4

Sepiolite 18.1

Banana peel 20.6

Orange peel 14.3

Coir pith 2.56

Treated Coir pith 94.7

This work

( Porkodi et al., 2007)

(Eren et al., 2007).

(Annadurai et al., 1999)

(Annadurai et al., 2002)

(Namsivayam et al.. 2001a)

(Namsivayam et al., 2001b)

45

i 1 M ^^^^^f^^

™HV 1 IVlag"l DeFT'wD 112/13/2007 • — 200Mm— 1

25 0 kvisSOOxlETDlg 0 mm 13:44 22 PM IIT ROORKEE

Fig.2 (a). Scanning electron micrograph (SEM) image of

ginger waste material before adsorption

Fig.2(b). Scanning electron micrograph (SEM) imagr of

ginger waste material after adsorption

46

u ni Q. 15 .

•2 E e-o (A

•a <

16

14

12

10

8

6

4

2

o 5 ppm ! o tc- IOppm , ^ A—20 ppm ^

A

-x >^ ^

A A

-X X

' O

X ><

0^_o-o- — o — -0

0 a ' : •

0 50 100 150 contact t ime (mint.)

Rg.3. Effect of contact time on adsorpt ion capacity ( T= 30 OC, adsorbent dose

=0.05g/50ml, pH = 6.2)

200>

-_J

0 5 pH 10

Fig.4.Effect of pH on adsorption capacity (T= 30 OC, adsorbent dose = 0.05g/50ml, cone. =

10 mg/L)

15

47

u n Q. n> ,

•2 E B-o in

•a <

2U -18 16 -O 30 0Ci 14 12

X' 40 OCJ ; -A- 50 OCl ^ O

10 8 0 6 4 ? 2 n

0 5 10 15 20 concentration (ppm)

Fig.5. Bfect of temperature on adsorption capacity (Adsorbent dose =0.05g/50ml, pH =

6.2)

25

0.0030 0.0031 0.0031 0.0032 0.0032 0.0033 0.0033; 5 5 ^ ^ 5 5

Fig.6. Plot of logKc versus 1/T '

48

o V) •o <

100

90

80

70

60

50

40

30

20

10

0

25

- % Adsorption

- Adsorption

50 100 150 200

9

8

4 7

Dose (mg) Rg.7. Bfect of adsorbent dose on

adsorption capacity (T= 30 OC, Cone. = 10 mg/L, pH = 6.2)

6c .2 ^

5S.O AO O. ^ M CO ,

• o 34

2

1

0

c o

o v> •a <

90

80

70

60

50

40

30

20

10

0

- % Adsorption - Adsorption capacity

5 10, ,. 15 ^ 20 concentration (ppm)

14

12

Itt: .2 3-CL O

6S «i •u o

4 <

2

0

Fig.8. Effect of concentration on adsorption capacity (T = 30 OC, adsorbent dose =

0.05g/50ml, pH = 6.2)

d<)

0.05 0.1 0.15 0.2

1/Ce

Rg.9. Langmuir Isotherm

0.25

1.4

1.2

1

0) 0.8

O)

2 0.6

0.4

0.2

0

O30 0C D40 0C A50 0C

0.5 1

log Ce

Fig.10. Freundllch isotherm

1.5

3 0

time (mints.)

Fig. 11. Pseudo-first-order Itinetics for adsorption of crystal violet on GWM at 30 OC

5 i

50

45

40

35

30

25

20

15

10

x5ppm D 10 ppmi A 20 ppm

0 50 150 200 100 time (mints.

Fig. 12 . Pseudo-second- order kinetics for adsorption of crystal violet onto GWM at 30

OC

51

14 1 ' o 5ppm A ,A -A

12

10

8

6

- D — lOppm -A 20 ppmi

A A'

A

^ D - ^a—a 5

12

10

8

6

A

D

A A'

A

^ D - ^a—a

4

2

n

6 o ^^ O 0- o o

5 10 15i t1/2(mjn.)

Fig. 13. Intra-particle diffusion kinetics at 30i OC

1.2

1

~o~ 0.2 gm - O - 0.3 gm -A - 0 . 5 g m

1000 2000 Volume (ml)

Fig.14. Hfect of bed height on Breakthrough capacity (T = 30 OC, Cone. = 10 mg/L, pH = 6.2,

Row rate=1ml/min)

4000

52

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