Chapter 2 - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/37779/8/08...hardness deactivation....

[56]

Chapter 2

Potential of Alumina in Removal of Anionic Surfactant

Sodium Dodecyl Sulphate (SDS) from Aqueous Solution &

Preparation of Adsorbent - Anionic Surfactant Modified

Alumina

2.1INTRODUCTION:

2.1.1 Surfactants& Its Properties

Surfactants are organic compounds. They have both polar and non-polar characteristics. They

tend to exist at phase boundaries, where they are associated with both polar and non-polar

media. Surfactants are compounds that lower the surface tension of a liquid, the interfacial

tension between two liquids, or that between a liquid and a solid. Surfactants may act as

detergents, wetting agents, emulsifiers, foaming agents, and dispersants [1]

.

2.1.2 Composition and Structure of Surfactant

Surfactants are usually organic compounds that are amphiphilic, meaning they contain both

hydrophobic groups (their tails) and hydrophilic groups (their heads)[2]

. Therefore, a

surfactant contains both a water insoluble (and oil soluble) component and a water soluble

component. Surfactants will diffuse in water and adsorb at interfaces between air and water

or at the interface between oil and water, in the case where water is mixed with oil. The

insoluble hydrophobic group may extend out of the bulk water phase, into the air or into the

oil phase, while the water soluble head group remains in the water phase. This alignment of

surfactants at the surface modifies the surface properties of water at the water/air or water/oil

interface [1]

.

A surfactant is characterized by its tendency to adsorb at surfaces and interfaces. Examples of

interfaces involving a liquid phase include suspension (solid-liquid), emulsion (liquid-liquid)

and foam (liquid-vapour). In many formulated products several types of interfaces are present

at the same time. Adsorption at the interfaces for removing hydrophobic groups from contact

with the water, thereby reducing the free energy of the system. It is an important phenomenon

since surfactant molecules behave very differently depending on whether they are present in

micelles or as free monomers [3]

.

[57]

2.1.3 Structure of Surfactant Phases in Water

A micelle—the lipophilic tails of the

surfactant ions remain on the inside of

the micelle due to unfavorable

interactions. The polar "heads" of the

micelle, due to favorable interactions

with water, form a hydrophilic outer

layer that in effect protects the

hydrophobic core of the micelle. The

compounds that make up a micelle are

typically amphiphilic in nature, meaning

that micelles are soluble not only in

protic solvents such as water but also in

aprotic solvents as a reverse micelle [1]

.

Figure 2.1: Structure of Surfactant Phases in Water

In the bulk aqueous phase, surfactants form aggregates, such as micelles, where the

hydrophobic tails form the core of the aggregate and the hydrophilic heads are in contact with

the surrounding liquid. Other types of aggregates such as spherical or cylindrical micelles or

bilayers can be formed. The shape of the aggregates depends on the chemical structure of the

surfactants, depending on the balance of the sizes of the hydrophobic tail and hydrophilic

head. This is known as the HLB, Hydrophilic-lipophilic balance. Surfactants reduce the

surface tension of water by adsorbing at the liquid-gas interface. The relation that links the

surface tension and the surface excess is known as the Gibbs isotherm.

2.1.4 Different Types of Surfactants

There are four main types of surfactants used in laundry and cleaning products. Depending on

the type of the charge of the head, a surfactant belongs to the anionic, cationic, non-ionic or

amphoteric/zwitterionic family [4]

.

[58]

I. Anionic surfactants:

Anionic surfactants have permanent negative or positive charges, attached to non-

polar (hydrophobic) C-C chains. This is the most widely used type of surfactant for

laundering, dishwashing liquids and shampoos because of its excellent cleaning

properties. The surfactant is particularly good at keeping the dirt away from fabrics,

and removing residues of fabric softener from fabrics. Anionic surfactants are

particularly effective at oily soil cleaning and oil/clay soil suspension. Still, they can

react in the wash water with the positively charged water hardness ions (calcium and

magnesium), which can lead to partial deactivation. Presence of more calcium and

magnesium molecules in the water, anionic surfactant system suffers from more

deactivation. To prevent this, the anionic surfactants need help from other ingredients

such as builders (Ca/Mg sequestrants) and more detergent should be dosed in hard

water.

The most commonly used anionic surfactants are Sodium Dodecyl Sulphate, Alkyl

Sulphates, Alkyl EthoxylateSulphates and soaps [4]

.

II. Cationic surfactants:

Cationic surfactants have permanent negative or positive charges, attached to non-

polar (hydrophobic) C-C chains. In solution, the head is positively charged. There are

3 different categories of cationic surfactant each with their specific application;

a) In fabric softeners and in detergents with built-in fabric softener, cationic

surfactants provide softness. Their main use in laundry products is in rinse added

fabric softeners, such as ester quats, one of the most widely used cationic

surfactants in rinse added fabric softeners.

b) In laundry detergents, cationic surfactants (positive charge) improve the packing of

anionic surfactant molecules (negative charge) at the stain/water interface. This helps

to reduce the dirt/water interfacial tension in a very efficient way, leading to a more

robust dirt removal system. They are especially efficient at removing greasy stains.

c) In household and bathroom cleaners, cationic surfactants contribute to the

disinfecting/sanitizing properties [4]

.

[59]

III. Non-ionic Surfactants:

Unlike anionic & cationic surfactants, non-ionic surfactants have no permanent

charge; instead, they have a number of atoms which are weakly electropositive and

electronegative. This is due to the electron-attracting power of oxygen atoms. These

surfactants do not have an electrical charge, which makes them resistant to water

hardness deactivation. They are excellent grease removers that are used in laundry

products, household cleaners and hand dishwashing liquids. Most laundry detergents

contain both non-ionic and anionic surfactants as they complement each other's

cleaning action. Non-ionic surfactants contribute to make the surfactant system less

hardness sensitive [4]

.

IV. Amphoteric/Zwitterionic Surfactants:

These surfactants are very mild, making them particularly suited for use in personal

care and household cleaning products. They can be anionic (negatively charged),

cationic (positively charged) or non-ionic (no charge) in solution, depending on the

acidity or pH of the water. These surfactants may contain two charged groups of

different sign. Whereas the positive charge is almost always ammonium, the source of

the negative charge may vary (carboxylate, sulphate, sulphonate). These surfactants

have excellent dermatological properties. They are frequently used in shampoos and

other cosmetic products, and also in hand dishwashing liquids because of their high

foaming properties. [4]

Figure 2.2: Surfactant Classification according to the Composition of their Head:

Nonionic, Anionic, Cationic, Amphoteric.[1]

[60]

2.1.5 Anionic Surfactant [Sodium Dodecyl Sulphate]

IUPAC Name: Sodium lauryl sulfate

Figure 2.3: Sodium Dodecyl Sulfate

Other Names

Sodium monododecyl sulfate; Sodium lauryl sulfate; Sodium monolauryl sulfate; Sodium

dodecanesulfate; Sodium coco-sulfate; dodecyl alcohol, hydrogen sulfate, sodium salt; n-

dodecyl sulfate sodium; Sulfuric acid monododecyl ester sodium salt[1]

.

Table 2.1: General Properties of Sodium Dodecyl Sulphate[1]

Molecular Formula NaC12H25SO4

Molar Mass 288.372 g/mol

Appearance White or Cream-Colored Solid

Odor Odorless

Density 1.01 g/cm³

Melting Point 206 °C, 479 K, 403 °F

Hazards

LD50 1288 mg/Kg (rat, oral)

Sodium dodecyl sulfate (SDS or NaDS), sodium lauryl sulfate or sodium lauryl sulfate (SLS)

is an organic compound with the formula CH3(CH2)11OSO3Na. It is an anionic surfactant

used in many cleaning and hygiene products. The salt is of an organ sulfate consisting of a

12-carbon tail attached to a sulfate group, giving the material the amphiphilic properties

required of a detergent. Being derived from inexpensive coconut and palm oils, it is a

common component of many domestic cleaning products [1]

.

http://en.wikipedia.org/wiki/International_Union_of_Pure_and_Applied_Chemistry_nomenclature

[61]

2.1.6 Production of Sodium Dodecyl Sulphate (SDS)

SDS synthesis is a relatively simple process involving the sulfate ion of 1-dodecanol

followed by neutralization with a cation source. It is available commercially in both broad-cut

and purified forms. Although its environmental occurrence arises mainly from its presence in

complex domestic and industrial effluents, SDS is also directly released in some applications

(e.g., oil dispersants and pesticides) [5]

.

SDS is synthesized by treating lauryl alcohol with sulfur trioxide gas, oleum, or

chlorosulfuric acid to produce hydrogen lauryl sulfate. The industrially practiced method

typically uses sulfur trioxide gas. The resulting product is then neutralized through the

addition of sodium hydroxide or sodium carbonate. Lauryl alcohol is in turn usually derived

from either coconut or palm kernel oil by hydrolysis, which liberates their fatty acids,

followed by hydrogenation.

Due to this synthesis method, commercial samples of SDS are often a mixture of other alkyl

sulfates, dodecyl sulfate being the main component [6]

.

SDS is available commercially in powder and pellet forms. It seems that the pellet form

dissolves faster than the powder form in water [7]

.

2.1.7 Application

SDS is mainly used in detergents for laundry with many cleaning applications [8]

. SDS is a

highly effective surfactant and is used in any task requiring the removal of oily stains and

residues. For example, it is found in higher concentrations with industrial products including

engine degreasers, floor cleaners, and car wash soaps. It is found in toothpastes, shampoos,

shaving foams, and bubble bath formulations in part for its thickening effect and its ability to

create lather [9]

.

[62]

2.1.8 Pollution Caused by Surfactants

Pollution is the introduction of contaminants into a natural environment that causes

instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living

organisms [10]

.

Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans, aquifers and

groundwater). Water pollution occurs when pollutants are discharged directly or indirectly

into water bodies without adequate treatment to remove harmful compounds. Water pollution

affects plants and organisms living in these bodies of water. In almost all cases the effect is

damaging not only to individual species and populations, but also to the natural biological

communities.

Surfactants can have poisonous effects in all types of aquatic life if they are present in

sufficient quantities, and this includes the biodegradable detergents. All surfactants destroy

the external mucus layers that protect the fish from bacteria and parasites; as well as they can

cause severe damage to the gills. Surfactant detergents are implicated in decreasing the

breeding ability of aquatic organisms.

Surfactants also add another problem for aquatic life by lowering the surface tension of the

water. Organic chemicals such as pesticides and phenols are then much more easily absorbed

by the fish [11]

. Surfactants presence into surface water, such as rivers or lakes, may lead to a

harmful situation for aquatic flora and fauna, due to the fact that may interact with oxygen

transfer by modifying surface tension. Binding ability of these products with other dangerous

substances (such as pharmaceuticals) is another hazardous property that may damage

environmental equilibrium.

Phosphates in detergents can lead to freshwater algal blooms that release toxins and deplete

oxygen in waterways. When the algae decompose, they use up the oxygen available for

aquatic life.

The main contributors to the toxicity of detergents were the sodium silicate solution and the

surfactants-with the remainder of the components contributing very little to detergent

toxicity. The potential for acute aquatic toxic effects due to the release of secondary or

tertiary sewage effluents containing the breakdown products of laundry detergents may

frequently be low. However, untreated or primary treated effluents containing detergents may

pose a problem. [11]

[63]

The concentration of surfactants measured in water reservoirs reached significant levels.

Surfactants easily form complexes with other compounds & are rapidly adsorbed at the

interfaces, which hampers their determination by analytical methods & can lead to

understanding the determined values compared to the real pollution of the aquatic ecosystem.

[12]

2.1.9 Entry of Surfactant into the Aquatic Environment

Surfactants are very widely used in both industrial and domestic premises like soaps and

detergents to wash vehicles. The major entry point into water is via sewage works into

surface water. They are also used in pesticide formulations and for dispersing oil spills at sea.

Surfactants produce intensive pollution of water reservoirs. [13]

. Waste effluents from textile

& organic synthesis production plants & factories, may contain up to 2.5-10 g/L of anionic

surfactant [14]

. Surfactants (also called surface active agents or wetting agents) are organic

chemicals that reduce surface tension in water and other liquids. The most familiar use for

surfactants are soaps, laundry detergents, dishwashing liquids and shampoos. Other important

uses are in the many industrial applications for surfactants in lubricants, emulsion

polymerization, textile processing, mining flocculates, petroleum recovery, wastewater

treatment and many other products and processes. Surfactants are also used as dispersants

after oil spills [15]

.

There are hundreds of compounds that can be used as surfactants and are usually classified by

their ionic behavior in solutions: anionic, cationic, non-ionic or amphoteric (zwiterionic).

Each surfactant class has its own specific properties [16]

.

There are many sources of surfactants that are discharged into natural waters. Industrial

sources include textile, surfactants and detergent formulation. Surfactants are also used in

laundries and households and are therefore found in discharges from sewage treatment works.

They also have agricultural applications in pesticides, dilutants and dispersants [16]

.

Surfactants are compounds composed of both hydrophilic and hydrophobic groups. In view

of their dual hydrophilic and hydrophobic nature, surfactants tend to concentrate at the

interfaces of aqueous mixtures; the hydrophilic part of the surfactant orients itself towards the

aqueous phase and the hydrophobic parts orient itself away from the aqueous phase into the

second phase [16]

.

[64]

The hydrophobic part of a surfactant molecule is generally derived from a hydrocarbon

containing 8 to 20 carbon atoms (e.g. fatty acids, paraffins, olefins, alkylbenzenes). The

hydrophilic portion may either ionise in aqueous solutions (cationic, anionic) or remain un-

ionise (non-ionic). Surfactants and surfactant mixtures may also be amphoteric or

zwitterionic [16]

.

Table 2.2: Indian Standards for Drinking Water – Specification (BIS 10500: 1991)

Substance or Characteristic Requirement

(Desirable Limit)

Permissible Limit

(In the Absence of Alternate) Anionic Detergents 0.2 mg/L 1.0 mg/L

Table 2.3: Tolerance Limits for Inland Surface Waters Subject To Pollution (IS: 2296-1982)

Substance or Characteristic Tolerance Limit

Anionic Detergents 1.0 mg/L

2.1.10 Fate and Behavior of Surfactant in the Aquatic Environment

In view of their hydrophilic nature, surfactants tend to be water soluble to some degree.

Depending on the specific chemicals, solubility varies from very soluble (e.g. some anionic

surfactants) to insoluble (e.g. some cationic surfactants). Due to the main role in some of the

most important fields of soft chemical technology (cosmetics, pharmaceuticals, personal care

products) surfactants have achieved a relevant position in human activity. More than 15

million tons per year are used, so surfactant-induced pollution is considered a main task to

research on [15]

.

Anionic surfactants are not appreciably sorbed by inorganic solids. On the other hand,

cationic surfactants are strongly sorbed by solids, particularly clays. Significant sorption of

anionic and non-ionic surfactants has been observed in activated sludge and organic river

sediments. Depending on the nature of their hydrophobic moieties, non-ionic surfactants may

be sorbed onto surfaces. Some surfactants have been found to alter the sorption to surfaces of

coexisting chemical species, such as metals.

[65]

In general, surfactants in modern day use are considered to be biodegradable under conditions

of efficient sewage treatment; the rates of degradation depend partially on the chemical

structure. Surfactants containing linear hydrophobes are generally more biodegraded than

those containing branched hydrophobes. Nonylphenol and some of its ethoxylates are not

readily degraded during sewage treatment [15]

.

Some surfactants are known to be toxic to animals, ecosystems and humans, and can increase

the diffusion of other environmental contaminants [17]

. Despite this, they are routinely

deposited in numerous ways on land and into water systems, whether as part of an intended

process or as industrial and household waste. Many standard laundry detergent powders

contain levels of chemicals such as alkali and chelating agents, which can damage the plants

and should not apply to soil. Some can, however, interfere with the life-cycles of some

aquatic organisms also. Anionic surfactants can be found in soils as the result of sludge

application, wastewater irrigation, and remediation processes. At low concentrations,

surfactant application is unlikely to have a significant effect on trace metal mobility [18].

Surfactants are responsible for causing foams in rivers & effluent treatment plants & they

reduce the quality of water. Surfactants cause short-term as well as long term changes in

ecosystem [19]

.

Surfactants are harmful to human beings, fishes & vegetation & they act synergistically with

other toxic chemicals present. Moreover, hydrophobic toxic chemicals are largely

accumulated in water bodies containing surfactant. Thus, many environmental & public

health regulatory authorities have fixed stringent limits for anionic detergents as standard 0.5

mg/L for drinking water & relax able up to 1.0 mg/L for other purposes[13]

.

In very dilute aqueous solution, an anionic surfactant acts much as normal electrolytes, but at

higher concentrations it acts in a very different way. This behavior is explained in terms of

the formation of organized aggregates of large molecules called the micelle, in which the

hydrophobic parts of the surfactant associate in the interior of the aggregates leaving

hydrophilic parts to face the aqueous medium. The surfactant concentration at which micelles

are formed is called the critical micelle concentration (CMC). The micelles have the ability to

preferentially absorb organic solutes from solution. This process is called Solubilization.[19]

http://www.ukmarinesac.org.uk/activities/water-quality/wq8_46.htm

http://en.wikipedia.org/wiki/Surfactant#cite_note-Metcalfe_TL.2C_Dillon_PJ.2C_Metcalfe_CD-6

http://en.wikipedia.org/wiki/Surfactant#cite_note-Metcalfe_TL.2C_Dillon_PJ.2C_Metcalfe_CD-6

http://en.wikipedia.org/wiki/Alkali

http://en.wikipedia.org/wiki/Chelation

http://en.wikipedia.org/wiki/Surfactant#cite_note-11

[66]

2.1.11 Fate and Effects of the Anionic Surfactant – Sodium Dodecyl Sulfate

(SDS)

Sodium Dodecyl Sulfate (SDS) is the most widely used of the anionic alkyl sulfate

surfactants. Its surface-active properties make it important in hundreds of household and

industrial cleaners, personal care products, and cosmetics. It is also used in several types of

industrial manufacturing processes, as a delivery aid in pharmaceuticals, and in biochemical

research involving electrophoresis. As discuss above environmental occurrence of SDS arises

mainly from its presence in complex domestic and industrial effluents, SDS is also directly

released in some applications (e.g., oil dispersants and pesticides)[5]

.

Surfactants are known to significantly contribute to the toxicity of some effluents; no official

water quality standards currently exist. Research has shown SDS to be highly biodegradable

by a large number of naturally occurring bacteria, and degradation is generally reported to be

> or = 90% within 24 hr. The process involves initial enzymatic sulfate liberation and

conversion to dodecanoic acid, followed by either beta-oxidative shortening or elongation

and desaturation. All surfactant properties are lost after initial sulfate hydrolysis [5]

.

SDS can enhance absorption of chemicals through skin, gastrointestinal mucosa, and other

mucous membranes. Thus, it is used in transepidermal, nasal, and ocular drug delivery

systems and to enhance the intestinal absorption of poorly absorbed drugs; enhancement is

concentration dependent. Human exposure is mainly through oral ingestion and dermal

contact, although cases of respiratory exposure are known. The main sources of daily intake

are ingestion of personal care products, residues on insufficiently rinsed utensils, and

contaminated drinking water. Uptake, distribution, and excretion of SDS are all rapid. In fish,

uptake in various tissues plateaus within 24-72 hr, with elimination occurring within < 24-48

hr; selective accumulation occurs in the hepatopancreas and gall bladder. In mammals, it is

readily absorbed via the intestine, colon, and skin. Metabolism is similar in fish and

mammals, proceeding from initial omega-oxidation to a carboxylic acid, then to beta-

oxidation to butyric acid 4-sulfate, which is finally nonenzymatically desulfurated to gamma-

butyrolactone and inorganic sulfate. SDS elicits both physical and biochemical effects on

cells, with the membrane the primary target structure [5]

.

[67]

2.1.12 Alumina& Its Properties

Corundum is the most common naturally occurring crystalline form of aluminum

oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their

characteristic colors to trace impurities. Rubies are given their characteristic deep red color

and their laser qualities by traces of chromium. Sapphires come in different colors given by

various other impurities, such as iron and titanium [1]

.

2.1.12 (A) Production of Alumina

Aluminum hydroxide minerals are the main component of bauxite, the

principal ore of aluminum. A mixture of the minerals comprise bauxite ore,

including gibbsite (Al(OH)3), boehmite (γ-AlO(OH)), and diaspore (α-AlO(OH)), along with

impurities of iron oxides and hydroxides, quartz and clay minerals.[9]

Bauxites are found

in laterites. Bauxite is purified by the Bayer process:

Al2O3 + 3 H2O → 2 Al(OH)3

Except for SiO2, the other components of bauxite do not dissolve in base. Upon filtering the

basic mixture, Fe2O3 is removed. When the Bayer liquor is cooled, Al(OH)3 precipitates,

leaving the silicates in solution. The solid is then calcined (heated strongly) to give aluminum

oxide [20]

.

2 Al(OH)3 → Al2O3 + 3 H2O[1]

2.1.13 Removal of SDS by Alumina:

Surfactant dumping into the environment has become one of the main concerns in water

treatment. Natural ecosystems are capable of removal of polluting substances from water

through a variety of physical, chemical and biological processes. The complex network of

these processes is vital to upgrade and maintain the quality of water compatible with

providing habitats for a number of aquatic species. Another group of important processes are

those which remove excess biogenic elements (primarily N, P) from water or prevent them

from being accumulated in water at concentrations above certain levels. The entire system of

all these processes is important to maintain a certain level of purity of water, which is an

extremely significant condition for making natural water of many water bodies a resource for

[68]

human consumption. The role of surface water bodies as a resource (vs. groundwater) varies

in different regions but it is in general significant [21]

.

Alumina was found to be an efficient adsorbent for SDS and could be used for the removal of

anionic surfactant (AS) from wastewater when it is present in high concentration (several

thousand ppm) [22].

Aluminum oxide is a whitish colored powder which is used for chromatography and is highly

porous and water adsorbing. With a bulk density of 800-920 gms per liter and a surface area

of 180-240 square meters per gram, these adsorbents are suited for various applications like

column chromatographic separations, Food Colours, Dyes & Spectroscopic solvents, Herbal

extractions of Natural products, isolation and antibiotics purification [23].

Aluminium oxide is an amphoteric oxide with the chemical formula Al2O3. It is commonly

referred to as alumina, or corundum in its crystalline form, as well as many other names,

reflecting its widespread occurrence in nature and industry [1]

. In present study 70-290 mesh

(50-200 mm); most are "approximately 150 mesh" particle size of Alumina was used.

Reactivation of Alumina:

Alumina can be reactivated by dehydration at 360°C for five hours or overnight, then

allowing the desired moisture content to be readsorbed [24]

.

2.1.14 Adsolubilization Principle

The adsorption of ionic surfactants on oppositely charged surface is generally different from

ordinary adsorption process. At low surfactant concentration the monolayer & bilayer

structures are formed. These structures act as micelles, & have the potential to solubilize the

organics into the three dimensional structures. The process is called Adsolubilization. Hence,

Adsolubilization is the surface analog to solubilization, with adsorbed surfactant bilayers

playing the role of the micelles. The monolayer structure is called the hemimicelle& the

bilayer structure, the admicelle. Adsolubilization process can efficiently be used for the

removal of different organic pollutants like dyes, phenolic compounds, etc. from water

environment.

[69]

The characteristics of adsolubilization have been studied in the past two decades for many

reasons. Based on their purposes, the studies on adsolubilization can be classified into four

different categories as below;

1) The use of adsolubilized molecules to help characterizing the adsorbed surfactant

layer

2) The use of adsolubilization in separation process

3) The use of adsolubilization in the formation of ultrathin films

4) The use of adsolubilization in admicellar catalysis.[18]

Recycling is a key component of modern waste reduction and is the third component of the

"Reduce, Reuse and Recycle" waste hierarchy. Although many government programs are

concentrated on recycling at home, a large portion of waste is generated by industry. The

focus of many recycling programs done by industry is the cost-effectiveness of recycling [19]

.

2.2Materials & Methodology

2.2.1Materials

a) Reagents:

Acridine Orange (ACO) [3,6-bis(dimethylaminoacridine)]

Sodium Dodecyl Sulphate (SDS - An Anionic Surfactant)

Glacial Acetic Acid

Toluene

Note: All the reagents were of LR grade.

b) Instruments:

Semi Micro Digital Weighing Balance ( RADWAG-LCGC Make, 308552 Model)

Visible spectrophotometer ( SystronicMake, 1854 Model)

In batch experiments adsorption studies were carried out at room temperature. [26]

[70]

2.2.2Determination of Anionic Surfactant in Water / Waste Water

a) Principle:

Acridine Orange Dye has the potential for being used as an ion-pairing agent with Anionic

Surfactant (AS). This method can either be used for the qualitative or yes/no type detection of

AS using a colour chart, or for the quantitative determination of AS using a

spectrophotometer. The method does not involve any toxic/carcinogenic chemical like

chloroform; which is used in the standard method of AS determination. The method is

suitable for field & real sample analysis.

b) Reagents:

i. AcridineOragne (0.01 M): Weigh 0.925 gmAcridine Orange dye & dilutein 250 ml

double distilled water. Prepare reagent as per requirement.

ii. Glacial Acetic Acid(LR Grade)

iii. Toluene(LR Grade)

c) Experiment to Determine SDS by Calibration Curve Method

Prepare 20 mg/L SDS stock solution.

Take 4 ml, 8 ml, 12 ml, 16 ml, and 20 ml from stock solution to prepare 20 ml of 4

mg/L, 8 mg/L. 12 mg/L, 16 mg/L & 20 mg/L standards respectively.

Arrange separating funnel for the test.

Take 10 ml of sample in the separating funnel.

Add 0.1 ml Acridine Orange stock solution, 0.2 ml Glacial Acetic Acid &10 or 15 ml

(as per requirement) Toluene to the sample.

Shake the funnel for 1 minute. After shaking allow the separation of water layer &

organic layer.

Discard the water layer & then collect organic layer i.e. toluene layer.

Measure the absorbance at 467 nm.

Prepare blank by taking toluene directly as a blank or follow the same procedure by

taking 10 ml distilled water.

Note down the absorbance & plot the calibration curve.

[71]

Table 2.4: Experimental Results of Calibration Curve to Determine SDS

Standard Conc.

(mg/L) Abs

Blank 0.000

2 0.114

4 0.209

6 0.270

8 0.360

10 0.450

12 0.557

Figure 2.4: Calibration Curve for Anionic Surfactant – SDS

y = 0.046x

R² = 0.99

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0 2 4 6 8 10 12 14

Ab

s

Std. Conc. (mg/L)

Calibration Curve for SDS - Anionic Surfactant

Calculation:

y = 0.046 x * Sample Vol. (ml)

Where,

y = Absorbance

&

x = Concentration in mg/L

[72]

2.2.3 Experimental Procedure for the Determination of SDS

Arrange separating funnel for the test.

Take 10 ml of sample in the separating funnel.

Add 0.1 ml Acridine Orange stock solution, 0.2 ml Glacial Acetic Acid & 10 or 15 ml

(as per requirement) Toluene to the sample.

Shake the funnel for 1 minute. After shaking allow the separation of water layer &

organic layer.

Discard the water layer & then collect organic layer i.e. toluene layer.

Measure the absorbance at 467 nm.

Note down the absorbance.

Find out concentration of SDS from calibration curve by extrapolating the

Absorbance onto Concentration profile.

[73]

2.2.4 Factors Affecting Removal of SDS by Alumina from Aqueous

Solution

2.2.4(A) Experimental Set Up to Study Effects of pH

Prepare stock solution of 2000 mg/L SDS.

100 ml quantity solution of high initial concentration i.e. 2000 mg/L was taken in 250

ml beaker.

Such 5 numbers of sets were prepared.

Dosage of the adsorbent was adjusted to 100 gm/L & added it to previously prepared

SDS solution. As here quantity is 100 ml add just 10 gm of alumina to the previously

prepared 2000 mg/L SDS solution.

pH of the 5 beakers were adjusted 2, 4, 6, 8, 10 respectively by adding the required

amount of 1N HCl and 1N NaOH.

Beakers were kept on the magnetic stirrer for 2 Hrs.

After shaking contents; in the beaker; were allowed to settle down for 5 minutes.

Supernatant was filtered through ordinary filter paper & filtrate was collected to check

the final concentration of SDS by using above mentioned solvent extraction method.

Readings were recorded & Graph was plotted to get equilibrium pH value.

Figure 2.5: Experimental Set up to Study Effects of pH on Removal of SDS by Alumina

pH 2

2000ppm SDS

+ 100 gm/L

Alumina

Contact Time 2 Hr

pH 4

2000ppm SDS

+ 100 gm/L

Alumina

Contact Time 2 Hr

pH 6

2000ppm SDS

+ 100 gm/L

Alumina

Contact Time 2 Hr

pH 8

2000ppm SDS

+ 100 gm/L

Alumina

Contact Time 2 Hr

pH 10

2000ppm SDS

+ 100 gm/L

Alumina

Contact Time 2 Hr

[74]

2.2.4(B) Experimental Set up to Study Effects of Contact Time

100 ml solution of high initial concentration i.e. 2000 mg/L was taken in 250 ml

beaker.


Dosage of the adsorbent was kept 100 gm/L & added it to previously prepared SDS

solution.

PH 4 (i.e. equilibrium pH resulted from above experiment-2.2.4(A)) kept constant of

the 8 beakers by adding the required amount of 1N HCl& 1N NaOH.

Beakers were kept on the magnetic stirrer for 1hr, 2hrs, 3hrs, 4hrs, 5hrs, 6hrs, 7hrs &

8hrs.

Beakers were allowed to stay for 5 minutes after shaking time.



Readings were recorded & Graph was plotted to get equilibrium contact time.

Figure 2.6: Experimental Set Up to Study Effects of Contact Time on Removal of SDS by

Alumina

1 Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

2Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

3Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

4Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

5 Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

6 Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

7 Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

8 Hr

2000ppm SDS

+ 100 gm/L

Alumina

pH 4

[75]

2.2.4(C)Experimental Set up to Study Effects of Adsorbent i.e. Alumina Dosage


beaker.


Dosage of the adsorbent varied 50gm/L, 100gm/L, 150gm/L, 200gm/L & added to

previously prepared SDS solution.

PH 4 (i.e. equilibrium pH resulted from above experiment-2.2.4(A)) kept constant of

the 8 beakers by adding the required amount of 1N HCl& 1N NaOH.

Beakers were kept on the magnetic stirrer for 1hr (i.e. equilibrium Contact Time

resulted from above experiment- 2.2.4(B))

Beakers were allowed to stay for 5 minutes after shaking time was completed.



Readings were recorded & Graph was plotted to get equilibrium adsorbent dosage.

Figure 2.7: Experimental Set Up to Study Effects of Adsorbent Dosage on Removal of SDS by

Alumina

50 gm/L Alumina

2000ppm SDS

Contact Time 2 Hr

pH 4

100gm/L Alumina

2000ppm SDS

Contact Time 2 Hr

pH 4

150gm/L Alumina

2000ppm SDS

Contact Time 2 Hr

pH 4

200gm/L Alumina

2000ppm SDS

Contact Time 2 Hr

pH 4

[76]

2.2.4(D) Experimental Set up to Study Effects of Adsorbate i.e. SDS

Concentration

100 ml solution of variable SDS conc. Vz. 2 mg/L, 4 mg/L, 6 mg/L, 8 mg/L, 10 mg/L,

30 mg/L, 50 mg/L, 100 mg/L, 500 mg/L, 800 mg/L, 2000 mg/L, 4000 mg/L, 6000

mg/L, 8000 mg/L, 10,000 mg/L, 20,000 mg/L, 30,000 mg/L & 40,000 mg/L were

prepared from 20 mg/L, 1000 mg/L, 10,000 mg/L, 20,000 mg/L, 30,000 mg/L &

40,000 mg/L stock solution of SDS in 250 ml beakers.

Dosage of the adsorbent was kept 100 gm/L(Equilibrium Dosage confirmed

from2.2.4(C))& added it to previously prepared SDS solution.

PH 4 (i.e. equilibrium pHresulted from above experiment2.2.4(A)) kept constant of all

the beakers by adding the required amount of 1N HCl& 1N NaOH.

Beakers were kept on the magnetic stirrer for 1hr (i.e. equilibrium Contact

Timeresulted from above experiment- 2.2.4(B))

Beakers were allowed to stay for 5 minutes after shaking time.

Supernatant was filtered through ordinary filter paper& filtrate was collected to check


Readings were recorded & Graph was plotted to get equilibrium adsorbate dosage.

[77]

2.2.4(E) Effect of Temperature


beaker.

Such 3 numbers of sets were prepared to study the effect of temperature (30°C, 40°C

& 50°C) in removal of surfactant by alumina.


solution.

PH 4 (i.e. equilibrium Contact Time resulted from above experiment- 2.2.4(A)) kept

constant of all the beakers by adding the required amount of 1N HCl& 1N NaOH.

30°C, 40°C & 50°C temperature set on the magnetic stirrers.

Beakers were kept on them for 1Hr.(i.e. equilibrium contact time resulted from

experiment- 2.2.4(B))

Beakers were allowed to stay for 5 minutes after shaking time was completed.



Readings were recorded & Graph was plotted to get equilibrium temperature.

Same experiment was carried out for 20,000 mg/L initial conc. of SDS & 1 Hrcontact

time also.

Figure 2.8: Experimental Set Up to Study Effects of Temperature on Removal of SDS by

Alumina When Initial Conc. of SDS is 2000 ppm & Contact Time is 1 Hr.

Figure 2.9: Experimental Set Up to Study Effects of Temperature on Removal of SDS by

Alumina When Initial Conc. of SDS is 20,000 ppm & Contact Time is 1 Hr.

30 °C

2000ppm SDS + 100

gm/L Alumina

Contact Time 1 Hr

pH 4

40 °C

2000ppm SDS + 100

gm/L Alumina

Contact Time 1 Hr

pH 4

50 °C

2000ppm SDS +

100 gm/L Alumina

Contact Time 1 Hr

pH 4

30 °C

20,000ppm SDS +

100 gm/L Alumina

Contact Time 1 Hr

pH 4

40 °C

20,000ppm SDS +

100 gm/L Alumina

Contact Time 1 Hr

pH 4

50 °C

20,000ppm SDS +

100 gm/L Alumina

Contact Time 1 Hr

pH 4

[78]

2.2.5Chemical Kinetic study


beaker.

Prepare a single set of 100 ml quantity for the study.


solution.

PH 4 (i.e. equilibrium Contact Time resulted from above experiment- 2.2.4(A))kept

constant of all the beakers by adding the required amount of 1N HCl& 1N NaOH.

Beakers were kept on the magnetic stirrer & take 5 ml supernatant after every 10

minute interval for 2 Hrs.



Readings were recorded & Graphs were plotted.

Following three models were studied of Chemical Kinetics.

1) Pseudo First Order Model

The pseudo-first order kinetic model based on the adsorbent for sorption analysis is of the

form:

Log (qe - qt) = log qe – (k1/2.303) t

Where,

qe(mg/gm)is the mass of Monocrotophos adsorbed at equilibrium

qt(mg/gm) the mass of Monocrotophos at any time (t) & K1 (min-1

) is the equilibrium rate

constant of pseudo-first order adsorption.

The values of k1 &qe are determined from the slope & intercept of the plot of Log (qe- qt)

versus t, respectively [25]

.

[79]

2) Pseudo Second Order Model

A pseudo-second order rate expression based on the sorption equilibrium capacity may be

represented as:

t / qt = 1/ k2qe2 + (1/ qe) t

Where,

k2 is the pseudo-second order rate constant (g mg-1

min-1

) [25]

.

The value of qe is determined from the slope of the plot of t/ qt versus t.

3) Intraparticle Diffusion

In order to understand the mechanism involved in the sorption process the kinetics

experimental results were fitted to the Weber’s intraparticle diffusion model. It is reported

that if intraparticle diffusion is involved in the process then a plot of adsorbate uptake vs. the

square root of time would result in a linear relationship and the intraparticle diffusion would

be the rate limiting step if this line passes through the origin. Thus the kinetics results were

analyzed by the Intraparticle diffusion model which is expressed as

qt = kid t1/2

+ C

Where,

C is the intercept

Kid is the intra-particle diffusion rate constant.

The intra-particle diffusion rate constant was determined from the slope of linear gradients of

the plot qtversus t1/2 [25]

.

2.2.6 Batch Isotherm Studies

Isotherm experiments were conducted to investigate the relationship between the solid phase

concentration of an adsorbate & the solution phase concentration of the adsorbate at an

equilibrium condition. The removal percentage (R %) of SDS was calculated for each run by

following equation:

[80]

R (%) = [(Ci-Ce)/Ci]*100

Where, Ci and Ce are the initial & final concentration of SDS (mg/L) in the solution. The

adsorption capacity of the adsorbent for each concentration of SDS at equilibrium was

calculated using following equation:

qe (mg/g) = [(Ci-Ce)/M]*V

Where, Ci & Ce were the initial & final concentration of SDS (mg/L) in the test solution

respectively. V is the volume of solution (in Liter) & M is the mass of adsorbent (gm) [26]

.

2.2.7 Adsorption Isotherm Studies

In the present study, various adsorption isotherm models have been used to study the

adsorption capacity and equilibrium coefficients for adsorption. Four commonly used

isotherms (viz. Langmuir, BET, Freundlich and Temkin isotherm) were studied.

1. The Langmuir Adsorption Isotherm

In the years 1916-1918 Langmuir developed the adsorption theory in its modern form.

Langmuir isotherm equation is derived from simple mass kinetics, assuming chemisorption.

The derivation of the Langmuir adsorption isotherm involves four implicit assumption: a) the

adsorption is at a fixed number of definite, localized sites; b) monolayer adsorption is formed

on the surface of adsorbent; c) the surface is homogenous, that is, the affinity of each binding

site for gas molecules is the same; d) there is no lateral interaction between adsorbate

molecules. Alternatively at higher concentrations, it predicts a monolayer sorption capacity. It

assumes that the uptake of adsorbate occurs on a homogenous surface by monolayer

adsorption without any interaction between adsorbed ions. The commonly expressed form is:

Ce/qe= [1/Q0b + 1/Q0 × Ce]

Where, Ce is the equilibrium concentration of adsorbate (mg/L) and qe is the amount of

adsorbate adsorbed per gram at equilibrium (mg/g), Q0 (mg/g) and b (L/mg) are Langmuir

constants related to adsorption capacity and rate adsorption, respectively. The values of Q0

and b were calculated from the slop and intercept of the Langmuir plot of Ce versus Ce/qe [27]

.

[81]

The Langmuir adsorption isotherm has the simplest form and shows reasonable agreements

with a large number of experimental isotherms. Therefore, the Langmuir adsorption model is

probably the most useful one among all isotherms describing adsorption, and often serves as

a basis for more detailed developments [28]

.

2. Freundlich Isotherm

Boedecker proposed in 1895 an empirical adsorption equation known as Freundlich isotherm,

because Freundlich assigned great importance to it and popularized its use. It is frequently

found that data on adsorption from a liquid phase are fitted better by the Freundlich isotherm

equation, provided that the adsorption sites are not identical, and the total adsorbed amount is

the same over all types of sites. The Freundlich isotherm is expressed as:

Log 10qe = log 10(Kf) + (1/n) log10 (Ce)

Where, qe is the amount of adsorbate adsorbed at equilibrium (mg/g), and Ce is the

equilibrium concentration of adsorbate in solution (mg/L). Kf and n are the constants

incorporating all factors affecting the adsorption process [27]

.

The Freundlich equation is an empirical expression that encompasses the heterogeneity of the

surface and the exponential distribution of sites and their energies. According to Freundlich

equation, the amount adsorbed increases infinitely with increasing concentration or pressure.

This equation is, therefore, unsatisfactory for high coverage. At low concentration, this

equation does not reduce to the linear isotherm. In general, a large number of the

experimental results in the field of van der Walls adsorption can be expressed by means of

the Freundlich equation in the middle concentration range [27]

.

[82]

3. Temkin Isotherm

Temkin isotherm model is given by following equation:

X= a + b ln C

Where, C is the equilibrium concentration of solution (mg/L), X is amount of adsorbate

adsorbed per gram weight of adsorbent (mg/g), a and b are constants related to adsorption

capacity and intensity of adsorption and related to the intercept and slope of the plots of ln C

versus X [29].

4. BET Isotherm

BET isotherm was developed by Brunauer, Emmett and Teller as an extension of Langmuir

isotherm, which assumes that first layer of molecules adhere to the surface with energy

comparable to heat of adsorption for monolayer sorption and subsequent layers have equal

energies. Equation in its linearized form expressed as:

Cf/ (Cf-Cs) q = 1/Bqmax– (B-1/Bqmax) (Cf/Cs)

Where, Cs is the saturation concentration (mg/L) of the solute, Cf is solute equilibrium

concentration. B and qmaxare two constants and can be evaluated from the slope and intercept

[30].

[83]

2.3Results& Discussion

2.3.1(A) Effect of pH

pH is an important factor controlling the process of adsorption as it affects the surface charge

of the adsorbent, the degree of ionization & species of adsorbate [31]

.The effect of pH was

studied in the range 2-10. Lower pH is suitable for SDS adsorption. Here in figure: 2.11, it is

shown that maximum removal of SDS was obtained from experimental data i.e. 99.78 % and

adsorption capacity (qei.e.19.95 mg/gm) at pH 4. The zero point charge (Zpc) of Alumina is

9.15. At this pH the adsorption capacity is almost zero. At low pH, the alumina particles

become more positive & hence there is an increase in adsorption at lower pH [32]

. Adsorption

of SDS at low pH by Alumina may be attributed to the large number of H+ions present which

in turn neutralize the negatively charged adsorbent surface [33]

.

[84]

Table 2.5: Effect of pH on Adsorption of SDS by Alumina from Aqueous Solution

Figure 2.10: Effect of pH on Adsorption of SDS by Alumina from Aqueous Solution

High initial

conc. of SDS

(mg/L)

Adsorbent

Dosage

Gm/L

Contact Time

(Hr)

pH

Range Absorbance

Final Conc. of SDS

(mg/L)

from Calibration

Curve

2000 100 2

2 0.270 5.8

4 0.206 4.3

6 0.920 20.2

8 0.853 18.7

10 0.983 21.6

2, 5.8 4, 4.3

6, 20.2 8, 18.7

10, 21.6

0

5

10

15

20

25

0 2 4 6 8 10 12

Fin

al C

on

c. o

f S

DS

(m

g/L

)

pH Range

Effect of pH on Adsorption of SDS by Alumina

[85]

2, 99.71 4, 99.78

6, 98.99 8, 99.06

10, 98.92

98.4

98.6

98.8

99

99.2

99.4

99.6

99.8

100

2 4 6 8 10

% R

em

ova

l o

f S

DS

pH Range

% Removal of SDS by Alumina at Various pH Range

Table 2.6: % Removal of SDS & Adsorption Capacity of Alumina at Different pH:

High initial

conc. of SDS

(mg/L)

Adsorbent

Dosage

Gm/L

Contact Time

(Hr) pH Range % Removal

Adsorption

Capacity

qe(mg/gm)

2000 100 2

2 99.71 19.42

4 99.78 19.95

6 98.99 19.79

8 99.06 19.81

10 98.92 19.78

Note: % Removal of SDS & adsorption capacity at pH 2 or pH 4 are quite nearer to each

other. Here, for the further study we have chosen pH 4 as equilibrium pH but we can also

take pH 2 as equilibrium pH for the industrial scale treatment process.

Figure 2.11: Effect of pH on% Removal of SDS by Alumina

[86]

2.3.1(B) Effect of Contact Time

Agitation time or contact time is one of the effective factors in batch adsorption. The effect of

agitation time on adsorption of SDS on Alumina was observed 99.27% to 99.32% from 1Hr

to 2 Hrs, 100 gm dosage and 4 pH. After that it was decreasing. This decrease in the

adsorption rate may be due to a distribution of surface sites that causedecrease in adsorbent-

adsorbate interaction with increasing surface density [25]

.

It may be explained by the fact that adsorbatemolecules attain the equilibrium at a particular

pH, dose and time, adsorption got slowed down in later stages, because initially a number of

vacant surface sites may be available for adsorption and after some time, the remaining

vacant surface site may be exhausted due to repulsive forces between the molecules of

adsorbate and counter ion binding at the surface of the adsorbent [34]

.

[87]

Table 2.7: Effect of Contact Time on Adsorption of SDS by Alumina from Aqueous Solution

High initial

conc. of SDS

(mg/L)

Adsorbent

Dosage

Gm/L

Equilibrium

pH

Contact

Time

(Hr)

Absorbance

Final Conc. of SDS

(mg/L)

from Calibration

Curve

2000 100 4

1 0.678 14.6

2 0.629 13.5

3 0.693 15.0

4 0.866 18.8

5 0.663 14.4

6 0.864 18.8

7 0.950 20.8

8 0.965 20.9

Figure 2.12: Effect of Contact Time on Adsorption of SDS by Alumina from Aqueous Solution

1, 14.6

2, 13.5

3, 15 4, 18.8 5, 14.4 6, 18.8

7, 20.8

8, 20.9

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8 9

Fin

al C

on

c. o

f S

DS

(m

g/L

)

Contact Time (Hrs.)

Effect of Contact Time on Adsorption of SDS by Alumina

[88]

Table 2.8: % Removal of SDS & Adsorption Capacity of Alumina at Different Contact Time

High initial

conc. of SDS

(mg/L)

Adsorbent

Dosage

Gm/L

Equilibrium

pH

Contact Time

(Hr) % Removal

Adsorption

Capacity

qe(mg/gm)

2000 100 4

1 99.27 19.85

2 99.32 19.86

3 99.25 19.85

4 99.06 19.81

5 99.28 19.85

6 99.06 19.81

7 98.96 19.79

8 98.95 19.79

Note: In the above case we can observe that reaction time 1-2 hrs does not make much

difference in %removal efficiency or adsorption capacity. Therefore we can take 1 hr as

equilibrium contact time to save time and energy.

Figure 2.13: Effect of Contact Time on% Removal of SDS by Alumina

1, 99.27 2, 99.32 3, 99.25

4, 99.06

5, 99.28

6, 99.06

7, 98.96 8, 98.95

98.7

98.8

98.9

99

99.1

99.2

99.3

99.4

1 2 3 4 5 6 7 8

% R

em

ova

l o

f S

DS

Contact Time (Hrs.)

% Removal of SDS by Alumina at various Contact Time

[89]

2.3.1(C) Effect of Adsorbent Dosages

The effect of adsorbent dose on the adsorption of SDS by Alumina is presented in Figure

2.14. It is evident from the experimental data that the rate of adsorption was increased from

99 to 99.31% with increase in adsorbent dosage from 50 to 100 gm. As the concentration of

the SDS was constant, by increasing the dose of adsorbent the surface area for adsorption was

increased. Since the adsorbent particle size is almost constant, the surface area was directly

proportional to the dose of the adsorbent in the system [35]

. Higher the dose of adsorbent in

the solution, greater is the availability of exchangeable sites for metal ions and greater is the

surface area [36]

.Therefore with increasing Alumina dosage per gm adsorption capacity is

decreasing.

[90]

Table 2.9: Effect of Adsorbent Dosage on Adsorption of SDS by Alumina from Aqueous

Solution

High initial conc.

of SDS (mg/L)

Equilibrium

Contact

Time (Hr)

Equilibrium

pH

Adsorbent

Dosage

Gm/L

Absorbance

Final Conc. of SDS

(mg/L)

from Calibration

Curve

2000 1 4

50 0.915 20.0

100 0.629 13.7

150 0.792 17.4

200 0.822 18.0

Figure 2.14: Effect of Adsorbent Dosage on Removal of SDS by Alumina from Aqueous Solution

50, 20

100, 13.7

150, 17.4

200, 18

0

5

10

15

20

25

0 50 100 150 200 250

Fin

al C

on

c. o

f S

DS

(m

g/L

)

Adsorbent (Alumina) Dosage (gm/L)

Effect of Adsorbent Dosage on Adsorption of SDS by Alumina

[91]

Table 2.10: %Removal of SDS & Adsorption Capacity of Alumina at Different Adsorbent

Dosage

High initial

conc. of SDS

(mg/L)

Equilibrium

Contact Time

(Hr)

Equilibrium

pH

Adsorbent

Dosage

Gm/L

%

Removal

Adsorption

Capacity

qe(mg/gm)

2000 1 4

50 99 39.6

100 99.31 19.86

150 99.13 13.21

200 99.1 9.91

Note: here, in the above case adsorption capacity at 50gm dosage is much higher than 100

gm but % removal is almost same for 50 gm& 100 gm dosage. Therefore, we can also take 50

gm as equilibrium adsorbent dosage. But here for the batch study it was taken 100gm/liter

dosage as % removal capacity is higherat this conc.

Figure 2.15: Effect of Adsorbent Dosages on %Removal of SDS by Alumina

50, 99

100, 99.31

150, 99.13 200, 99.1

98.8

98.85

98.9

98.95

99

99.05

99.1

99.15

99.2

99.25

99.3

99.35

50 100 150 200

%R

em

ova

l o

f S

DS

Adsorbent (Alumina) Dosage (gm/L)

%Removal of SDS at different Adsorbent (Alumina) Dosage

[92]

2.3.1(D) Effect of Initial Adsorbate (SDS) Concentration

The effect of initial SDS concentration on the adsorption was studied. Here, adsorbent dose

was kept 100gm/L, pH 4 was adjusted, contact time was given 2Hrs. Initial concentration of

SDS was varied from 0 to 40000 ppm. The removal efficiency was increasing with the

increase of initial concentration & after certain initial concentration it starts decreasing as

shown in figure 2.17.

Table 2.11: Effect of Initial Adsorbate Concentration on Adsorption of SDS by Alumina from

Aqueous Solution

Equilibrium

Adsorbent

Dosage

(Gm/L)

Equilibrium

Contact

Time

(Hr)

Equilibrium

pH Region

High

initial

conc. of

SDS

(mg/L)

Absorbance

Final Conc. of

SDS

from Calibration

Curve (mg/L)

(y=0.046x/Dil.

Factor)

100 1 4

1 2 0.110 1.0

4 0.270 4.0

2

6 0.141 2.0

8 0.190 3.5

10 0.116 1.0

30 0.114 1.0

50 0.066 0.9

100 0.389 7.5

500 0.053 0.85

3

800 0.727 45

2000 0.631 25

4000 1.117 105

6000 1.078 105

8000 0.850 65

4

10,000 0.322 700

20,000 0.680 230

30,000 0.865 18810

40,000 1.339 29100

[93]

Figure 2.16(A): Effect of AdsorbateConc. on Adsorption of SDS by Alumina from Aqueous

Solution

Figure 2.16(B): Effect of Adsorbate Conc. on Adsorption of SDS by Alumina from Aqueous

Solution

0

5000

10000

15000

20000

25000

30000

35000

8000 10,000 20,000 30,000 40,000

Fin

al C

on

c. o

f S

DS

(m

g/L

)

Initial Conc. of SDS (mg/L)

Effect of Initial Adsorbate Conc. on Adsorption of SDS by Alumina

0

20

40

60

80

100

120

2 4 6 8 10 30 50 100 500 800 2000 4000 6000 8000

Fin

al C

on

c. o

f S

DS

(m

g/L

)

Initial Conc. of SDS (mg/L)

Effect of Initial Adsorbate Conc. on Adsorption of SDS by Alumina

[94]

Table 2.12: %Removal of SDS & Adsorption Capacity of Alumina at Different Initial

Adsorbate Conc.

Equilibrium

Adsorbent

Dosage

(Gm/L)

Equilibrium

Contact

Time

(Hr)

Equi.

pH

Ini. Conc.

(mg/L)

Final Conc. of

SDS (mg/L)

from

Calibration

Curve

%

Removal

Adsorption

Capacity

qe(mg/gm)

100 1 4

2 1.0 50 0.01

4 4.0 0 0

6 2.0 66.6 0.04

8 3.5 56.25 0.045

10 1.0 90 0.09

30 1.0 96.6 0.29

50 0.9 98.2 0.49

100 7.5 92.5 0.92

500 0.85 99.8 4.9

800 45 94.37 7.55

2000 25 98.75 19.75

4000 105 97.3 38.95

6000 105 98.25 58.95

8000 65 99.18 79.35

10,000 700 93 93

20,000 230 97.3 197.8

30,000 18810 37 111.9

40,000 29100 27.25 109

[95]

Figure 2.17: Effect of Initial Adsorbate Conc. on %Removal of SDS by Alumina

The adsorption isotherm of SDS on Alumina, as obtained in our study, is shown in figure

2.17. From the isotherm study maximum adsorption capacity was found to be 197.8 mg/gm

and it occurs when initial concentration of SDS is 20000 ppm. Maximum % removal was

found to be at 20,000 ppm.

Figure 2.18: Adsorption Isotherm of SDS on Alumina

0

20

40

60

80

100

120

0 5000 10000 15000 20000 25000 30000 35000 40000 45000

% R

emo

va

l E

ffic

ien

cy

Initial Conc. Of SDS (mg/L)

% Removal of SDS at Various Initial Conc. Of SDS

[96]

Figure 2.18 shows the unique adsorption isotherm for the adsorption of anionic surfactant on

oppositely charged surfaces. These isotherms are commonly divided into four regions.

Region 1 shows very low adsorption density. In this region, the surfactants are adsorbed as

monomers & do not interact with one another. The adsorption in this zone results primarily

from electrostatic forces between surfactant ions & the charged solid surface. In the present

study Region 1 occurs between very low concentrations of 2-5 ppm of SDS. Region 2 is

indicated by the sharp increase in the slope of the isotherm. As shown in the graph Region 2

occurs between 6-500 ppm of SDS. In this region, the adsorption is due to the electrostatic

attraction between the ions & the charged solid surface & hemi micelles association of

hydrocarbon chains. The mono layered structure is called hemi micelle. Micelles like

aggregates are formed on the solid surface. The transition from region 2 to region 3 is marked

by a decrease in the slope of the isotherm compared to the transition from region 1 to 2. In

region 3 the surfactant ions are probably adsorbed by a slightly different mechanism. The

adsorption in this zone is due to the association between the hydrocarbon chains. Region 3

starts from 500 ppm of SDS. Transition from region 3 to 4 occurs at 8000 ppm of SDS.

Transition from region 3 to region 4 occurs at the CMC of the surfactant. Region 4 shows the

plateau adsorption region. In colloidal and surface chemistry, the critical micelle

concentration (CMC) is defined as the concentration of surfactants above which micelles

form and all additional surfactants added to the system go to micelles [37]

.

The CMC is an important characteristic of a surfactant. Before reaching the CMC, the surface

tension changes strongly with the concentration of the surfactant. After reaching the CMC,

the surface tension remains relatively constant or changes with a lower slope. The value of

the CMC for a given dispersant in a given medium depends on temperature, pressure, and

(sometimes strongly) on the presence and concentration of other surface active substances

and electrolytes. Micelles only form above critical micelle temperature.

[97]

When the surface coverage by the surfactants increases, the surface free energy (surface

tension) decreases and the surfactants start aggregating into micelles, thus again decreasing

the system's free energy by decreasing the contact area of hydrophobic parts of the surfactant

with water. Upon reaching CMC, any further addition of surfactants will just increase the

number of micelles

2.3.1(E) Effect of Temperature

Thermodynamics study was also carried out to study the effect of temperature on the %

removal of SDS. For the study purpose, 2 numbers of 3 sets were prepared. First set had 2000

ppm initial conc. of SDS & they were given 2 Hr shaking time while second set had 20,000

ppm initial conc. of SDS. Temperature range viz30₀C, 40₀C & 50₀C were adjusted by knob of

magnetic stirrer. Here adsorbent dosage & pH were kept 100 gm/L& 4 respectively for all the

sets. The result shows that maximum % removal i.e. 98.9% and adsorption capacity i.e. 197.8

mg/gm was obtained at 30 ₀C.

[98]

Table 2.13(A): Effect of Temperature on Adsorption of SDS by Alumina from Aqueous Solution

High initial

conc. of SDS

(mg/L)

Equilibrium

Contact Time

(Hr)

Equi.

pH

Adsorbent

Dosage

Gm/L

Temp

(°C) Absorbance

Final Conc.

of SDS

(mg/L) from

Graph

2000 1 4 100

30 0.630 13.4

40 0.890 19.4

50 0.686 14.8

Figure 2.19(A): Effect of Temperature on Adsorption of SDS by Alumina from Aqueous

Solution

30, 13.4

40, 19.4

50, 14.8

0

5

10

15

20

25

0 10 20 30 40 50 60

Fin

al C

on

c. o

f S

DS

(m

g/L

)

Temp. (°C)

Effect of Temp. on Adsorption of SDS by Alumina

[99]

Table 2.14(A):%Removal of SDS & Adsorption Capacity of Alumina at Different Temperature

High initial

conc. of SDS

(mg/L)

Equilibrium

Contact Time

(Hr)

Equilibrium

pH

Adsorbent

Dosage

Gm/L

Temp

(°C)

%

Removal qe (mg/gm)

2000 1 4 100

30 98.9 197.8

40 98.25 196.5

50 98.15 196.3

Figure 2.20(A): Effect of Temperature on % Removal of SDS by Alumina

30, 98.9

40, 98.25 50, 98.15

97.6

97.8

98

98.2

98.4

98.6

98.8

99

30 40 50

% R

em

ova

l

Temperature (°C)

% Removal of SDS at Different Temperature (°C)

[100]

Table 2.13(B): Effect of Temperature on Adsorption of Alumina from Aqueous Solution

High initial

conc. of SDS

(mg/L)

Equilibrium

Contact Time

(Hr)

Equi.

pH

Adsorbent

Dosage

Gm/L

Temp

(°C) Absorbance

Final Conc.

of SDS

(mg/L)

from

Graph

20,000 1 4 100

30 0.669 220

40 0.929 350

50 0.966 370

Figure 2.19(B): Effect of Temperature on Adsorption of SDS by Alumina

30, 220

40, 350 50, 370

0

50

100

150

200

250

300

350

400

0 10 20 30 40 50 60

Fin

al C

on

c. o

f S

DS

(m

g/L

)

Temp. (°C)

Effect of Temp. on Adsorption of SDS by Alumina

[101]

Table 2.14(B): %Removal of SDS & Adsorption Capacity of Alumina at Different Temperature

High initial

conc. of SDS

(mg/L)

Equilibrium

Contact Time

(Hr)

Equilibrium

pH

Adsorbent

Dosage

Gm/L

Temp

(°C) % Re

qe

(mg/gm)

20,000 1 4 100

30 98.9 197.8

40 98.25 196.5

50 98.15 196.3

Figure 2.20(B): Effect of Temperature on % Removal of SDS by Alumina

30, 98.9

40, 98.25

50, 98.15

97.6

97.8

98

98.2

98.4

98.6

98.8

99

30 40 50

% R

em

ova

l

Temperature (°C)

% Removal of SDS at different Temperature (°C)

[102]

2.4 Chemical Kinetic Study

In the present study, three kinetic models have been tested in order to predict the adsorption

data of SDS as a function of time using a Pseudo-first order, pseudo-second order kinetic

models & intra-particle diffusion model.

Table 2.15: Experimental Results of Kinetic Study for Uptake of SDS by Alumina

High

initial

conc. of

SDS

(mg/L)

Equi.

Contact

Time

(Hr)

Equi.

pH

Adsorbent

Dosage

Gm/L

Temp.

(°C)

Time

Interval

(min.)

Absorbance

Final Conc. of

SDS (mg/L)

from Graph

qt

(mg/gm)

20,000 2 4 100 30

10 0.716 260 197.4

20 0.804 300 197.0

30 0.757 260 197.4

40 0.716 240 197.4

50 0.771 280 197.2

60 0.680 230 197.7

=qe

70 0.788 290 197.1

80 0.726 270 197.3

90 0.975 370 196.3

100 0.720 250 197.5

120 1.293 540 194.6

Where, qe (mg/gm) = Mass of SDS Adsorbed, qt (mg/gm) = Mass of SDS at particular time

qe = [(Initial Conc. of SDS – Final Conc. of SDS)/M) * V

Where, V is the volume of solution (in Liter) & M is the mass of adsorbent (gm) [26]

.

[103]

1. Pseudo-First Order Model

Table 2.16: Data Required for Pseudo First Order Kinetic Model Calculation

Time Interval

(min.) (qe – qt) Log (qe – qt) t/qt

10 0.3 -- i.e. 10/197.4 = 0.0507

20 0.7 2.4771 i.e. 20/197 = 0.1015

30 0.3 2.4149 i.e. 30/197.4 = 0.1519

40 0.3 2.3802 i.e. 40/197.4 = 0.2026

50 0.5 2.4471 i.e. 50/197.2 = 0.2535

60 0.0 2.3617 i.e. 60/197.7 = 0.3034

Log (qe - qt) = log qe – (k1/2.303) t

Where, qe(mg/gm)is the mass of SDS adsorbed at equilibrium, qt(mg/gm) the mass of SDS at

any time (t) & k1 (min-1

) is the equilibrium rate constant of pseudo-first order adsorption. The

values of k1 &qe are determined from the slope & intercept of the plot of Log (qe- qt) versus t,

respectively [27]

.

Table 2.17: Pseudo First Order Kinetic Study

Time Interval (min.) Log (qe – qt)

10 -0.5228

20 -0.1549

30 -0.5228

40 -0.5228

50 -0.3010

60 0.0

[104]

Figure 2.21: Pseudo First Order Kinetic Study

Calculation from Graph

K1/2.303 = Slope

Where, Slope from Graph = 0.0053

i.e. K1 = 0.0053 * 2.303 = 0.0122

qe (calculated) = Antilog (intercept from graph) = Antilog (-0.5129) = 0.3

Table 2.18: Parameters of Pseudo First Order Kinetic

y = 0.0053x - 0.5129

R² = 0.1344

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 10 20 30 40 50 60 70L

og

(q

e -

qt)

Time (minute)

Pseudo First Order Kinetic Study

Adsorbent qe (mg/gm)

(Exp.)

qe (mg/gm)

(Cal.) K1 (min

-1) R

2

Alumina 197.7 0.3 0.0122 0.13

[105]

Table 2.18 shows the parameters of Pseudo First Order Kinetic Model. Figure 2.21 represent

the plot of pseudo first order kinetic model i.e. log (qe – qt) Vs. Time. From table 2.18 qe

(exp.) is 197.7 mg/gm whereas qe (cal.) is 0.3 mg/gm. They are not in good agreement with

each other. More over correlation coefficient value of plot is very poor i.e. 0.13. From all

these evidences it is clear that the adsorption doesn’t follow pseudo first order kinetic model.

2. Pseudo-Second Order

t / qt = 1/ k2qe2 + (1/ qe) t

Where, k2 is the pseudo-second order rate constant (g mg-1

min-1

) [27]

. The value of qe is

determined from the slope of the plot of t/ qt versus t (figure 2.23). The calculated value of

qe(196.07 mg/gm) from the pseudo second order model is in good agreement with

experimental qe value (197.7 mg/gm). The obtained value of R2 = 1 indicates very good

adsorption characteristics. This suggests that the sorption system followed the pseudo second

order model. The value of kinetic constants and qe values of SDS sorption onto Alumina are

given in table 2.20.

Table 2.19: Pseudo-Second Order Kinetic

Time Interval (min.) t/qt

10 i.e. 10/197.4 = 0.0507

20 i.e. 20/197 = 0.1015

30 i.e. 30/197.4 = 0.1519

40 i.e. 40/197.4 = 0.2026

50 i.e. 50/197.2 = 0.2535

60 i.e. 60/197.7 = 0.3034

[106]

Figure 2.22:Pseudo-Second Order Kinetic Study

Calculation from Graph

qe (Calculated) = 1/Slope from graph = 1/0.0051 = 196.07

Intercept = 0.0002 = 1/K2qe2

i.e. K2= 1/ [0.0002*(196.07)2] = 1/7.6886 = 0.13000 gm/mg/minute

Table 2.20: Pseudo-Second Order Kinetic Parameters for SDS Adsorption on Alumina

Adsorbent qe (mg/gm)

(Exp.)

qe (mg/gm)

(Cal.) K2 (g mg

-1 min

-1) R

2

Alumina 197.7 196.07 0.1300 1

3. Intra-Particle Diffusion Model

qt = kid t1/2

+ C

Where, C is the intercept & kid is the intra-particle diffusion rate constant. The intra-particle

diffusion rate constant was determined from the slope of linear gradients of the plot qt versus

t1/2 [27]

as shown in the figure 2.23. The values of rate constant of intra-particle diffusion are

given in table 2.21. The values of the intercept C provide information about the thickness of

y = 0.01x + 0.00

R² = 1.00

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 10 20 30 40 50 60 70

(t/q

t)

Time (minute)

Pseudo Second Order Kinetic Study

[107]

boundary later i.e. larger the intercept, larger is the boundary layer effect. Here, intercept C is

197.0 & experimental value of Adsorption Capacity (qe) is 197.7 mg/g. Both of them are in

good agreement. Value of intercept C supports the practically obtained adsorption capacity.

Here, the plot does not pass through the origin, this is indicative of some degree of boundary

layer control & this further show that intra-particle diffusion is not only rate-limiting step, but

also other kinetic models may control the rate of adsorption, all of which may be operating

simultaneously.

Table 2.21: Parameters of Intra-Particle Diffusion

Time Interval (min.) qt (mg/gm) √Time

10 197.4 3.16

20 197.0 4.47

30 197.4 5.48

40 197.4 6.32

50 197.2 7.07

60 197.7 7.75

Figure 2.23: Intra-Particle Diffusion Study

y = 0.06x + 197.02 R² = 0.17

196.8

197

197.2

197.4

197.6

197.8

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00

qt

(mg

/gm

)

Square Root of Time

Intraparticle Diffusion Study

[108]

Table 2.22: Intra-Particle Diffusion Parameters from Graph

Adsorbent Kid C (graph) qe (Exp.)

(mg/gm) R

2

Alumina 0.057 197.0 197.7 0.174

2.5 Adsorption Isotherm

The adsorption isotherm is an equation that shows the transmission of adsorbate from

solution phase to the adsorbent phase at equilibrium condition [38]

. Langmuir, Freundlich,

Temkin & BET adsorption isotherm models were studied Region 4 of Surfactant adsorption

isotherm as shown in figure 2.18.

1. Langmuir Isotherm

The experimental result of Langmuir isotherm for uptake of anionic surfactant SDS on

Alumina from aqueous solution is shown in table 2.23 & Langmuir constant calculated from

graph is shown in table 2.24. Graphical representation of the same is shown in figure 2.24.

Table 2.23: Langmuir Isotherm Data for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

Adsorbate

Conc.

(mg/L)

Langmuir Isotherm

Ce

(Final Conc. of Adsorbate)

(mg/L)

qe

(Adsorption Capacity)

(mg/gm)

Ce/qe

Region 4

10000 700 93 7.53

20000 230 197.8 43.98

30000 8810 111.9 168.10

40000 29100 109 266.97

[109]

Figure 2.24: Langmuir Isotherm Plot for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

Table 2.24: Langmuir Constants for Uptake of SDS on Alumina from Aqueous Solution in

Region 4

Q0 (mg/gm) b (L/mg) R2

100 -1540 0.98

The experimental data of Alumina have best fit for Langmuir isotherms. The value of R2

obtained for Alumina is 0.98 in Region 4 for Langmuir isotherm indicates the adsorption

process follows Langmuir isotherm. It indicates first layer of molecules adhere to the surface

with energy comparable to heat of adsorption for monolayer sorption and subsequent layers

have equal energies [30, 38]

. Here we can say that Langmuir isotherm applies to each layer [38,

39]. The higher values of Q0 i.e. 100 mg/gm obtained for Alumina for Langmuir isotherm

suggest better applicability of it.

y = 0.01x - 15.04

R² = 0.98

-50.00

0.00

50.00

100.00

150.00

200.00

250.00

300.00

0 5000 10000 15000 20000 25000 30000 35000

Ce/

qe

Ce

Langmuir Isotherm for Uptake of SDS on Alumina in

Region 4

Calculation from Graph:

Langmuir Equation:

Ce/qe = [1/Qo b + 1 / Qo× Ce]

Q0 = 1/Slope = 1/0.01 = 100 mg/gm

b = Intercept * Q0 = -15.4 * 100 = - 1540 (L/mg)

[110]

2. Freundlich Isotherm

Results of modeling of the isotherms of SDS adsorption by Alumina according to Freundlich

isotherm model is summarized in table 2.25. Graphical presentation of the Freundlich

isotherm is represented in figure 2.25. Table 2.26 shows the Freundlich constants calculated

from graph.

Table 2.25: Freundlich Isotherm Values for Uptake of SDS on Alumina from Aqueous Solution

in Region 4.

AdsorbateConc.

(mg/L)

Freundlich Isotherm

Ce

(Final Conc. Of Adsorbate) (mg/L) Ce/qe Log Ce Log Ce / qe

Region 4

10000 700 7.5 2.8451 0.8766

20000 230 44.0 2.3617 0.0655

30000 18810 168.1 4.2744 2.2256

40000 29100 267.0 4.4639 2.4265

Figure 2.25: Freundlich Isotherm Plot for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

y = 1.0731x - 2.3427

R² = 0.9883

0.0000

0.5000

1.0000

1.5000

2.0000

2.5000

3.0000

0 1 2 3 4 5

Lo

g C

e/q

e

Log Ce

Freundlich Isotherm for Uptake of SDS on Alumina in

Region 4

[111]

Table 2.26: Freundlich Constants for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

Kf (mg/gm) n (L/mg) R2

0.0045 0.99 0.99

Here, as shown in table 2.26, the value of Kf i.e. adsorption capacity 0.0045 mg/gm for

Region 4. The rate of adsorption or adsorption intensity n is 0.99 L/mg. The value of n fulfills

the condition (0 < n < 1) of Freundlich isotherm [25, 38, 39]

. The value of n in the range 2-10

represent good, 1-2 moderately difficult and less than 1 poor adsorption characteristics [40]

.

The value of coefficient of correlation (R2) for ASMA obtained is in good agreement for

Region 4. The value of R2

is 0.99 indicate good adsorption. It indicates that the adsorption

sites are not identical; the total adsorbed amount is the same over all types of sites. It

encompasses the heterogeneity of the surface, exponential distribution of sites and their

energies. It reflects van der walls adsorption in the middle concentration range [41]

. Thus

Alumina has better fit for Freundlich isotherm.

3. Temkin Isotherm

Results of modeling of the isotherms of SDS adsorption by Alumina according to Temkin

isotherm model is summarized in table 2.27. Graphical presentation of the Temkin isotherm

is represented in figure 2.26. Table 2.28 shows the Temkin constants calculated from graph.


Freundlich Equation:

Log10 qe = log 10(Kf) + (1/n) log10 (Ce)

n = 1/Slope = 1/1.0731 = 0.93L/mg

Kf = Antilog (Intercept) = Antilog (-2.3427) = 0.0045

[112]

Table 2.27: Temkin Isotherm Values for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

AdsorbateConc.

(mg/L)

Temkin Isotherm

Ce

(Final Conc. Of Adsorbate) (mg/L) ln C X (mg/gm)

Region 4

10,000 700 6.5511 93

20,000 230 5.4381 197.8

30,000 18810 9.8421 111.9

40,000 29100 10.2785 109

Figure 2.26: Temkin Isotherm Plot for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

Table 2.28: Temkin Constants for Uptake of SDS on Alumina from Aqueous Solution in

Region 4

a (mg/gm) b (L/mg) R2

221.52 -11.659 0.349

The value of a i.e. 221.52 mg/gm is in good agreement with experimental adsorption capacity

i.e. 197.8 mg/gm. But the value of b obtained from Temkin isotherm plot is very low i.e. -

11.659 for Region 4 indicates poor rate of adsorption &correlation coefficient i.e. R2

value is

very low i.e. 0.349.


Temkin Equation: X = a + b lnC

b = Slope = -11.659 L/mg a = Intercept = 221.52 mg/L

y = -11.659x + 221.52

R² = 0.349

0

50

100

150

200

250

0 2 4 6 8 10 12

X

ln C

Temkin Isotherm for Uptake of SDS on Alumina in

Region 4

[113]

4. BET Isotherm

Result of modeling of the isotherms of SDS adsorption by Alumina according to BET

isotherm model is summarized in table 2.29. Graphical presentation of the BET isotherm is

represented in figure 2.27. Table 2.30 shows the BET constants calculated from graph.

Table 2.29: BET Isotherm Values for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

Adsorbate

Conc. (mg/L)

BET Isotherm

Cf

(Final Conc. of

Adsorbate) (mg/L)

q

(mg/gm) Cf/ Cs Cf/(Cs - Cf)*q

Region 4

10,000 700 93 0.07 7.0

20,000 230 197.8 0.0115 2.3012

30,000 18810 111.9 0.63 188.1

40,000 29100 109 0.73 291.0

Figure 2.27: BET Isotherm Plot for Uptake of SDS on Alumina from Aqueous Solution in

Region 4.

y = 375.88x - 12.84

R² = 0.9622

-50.0

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

X

ln C

BET Isotherm for Uptake of SDS on Alumina in

Region 4

[114]

Table 2.30: BET Constants for Uptake of SDS on Alumina from Aqueous Solution in Region 4.

Qmax (mg/gm) B (L/gm) R2

0.0028 -27.94 0.96

The experimental data & value of R2 obtained from figure 2.27 for uptake of SDS on

Alumina in Region 4 is 0.96 shows best fit for BET isotherms. Here we can say that BET

isotherm as an extension of the Langmuir isotherm to account for multilayer adsorption and

Langmuir isotherm applies to each layer [39]

.


BET Equation: Cf/ (Cs-Cf)q = 1/Bqmax – (B – 1/ Bqmax) (Cf/Cs)

1/B*qmax = Intercept i.e. B*qmax= -0.077 i.e. qmax = -0.0077 / -27.94 = 0.0028

((B – 1)/B*qmax) = Slope = 375.88

i.e. B – 1 = -28.94, i.e. B = - 27.94

[115]

2.6 Preparation of Adsorbent – Anionic Surfactant Modified Alumina

(ASMA)

20,000 mg/L SDS in 500 ml standard measuring flask was prepared.

Volume of the solution was 500 ml.

100 gm/L Alumina was added in the flask.

Adjusted pH 4 with 1N HCl & 1N NaOH.

The flask was kept on magnetic stirrer for 24 Hrs to determine reproducibility.

After completion of shaking period, filtered out contents of the flasks through

ordinary filter paper.

Then the filtered solid material (100 gm/L + surfactant), remaining on the filter paper,

was gently washed first with tap water & then with distilled water.

The washed solid material was then dried in hot air oven at 60 °C for 24 Hrs.

This oven dried solid powder is Anionic Surfactant Modified Alumina (ASMA).

ASMA powder was stored in plastic bottle for its further use in the removal of organic

pollutant like Phenol, Crystal Violet Dye etc. from waste water by adsolubilization

method.

Particle size analysis (dry method) was carried out of this adsorbent. From the graph

as shown in figure 2.28 it was observed that the particle size ranges from 1.5 to 800

µm.

[116]

Figure 2.28: Particle Size Analysis (Dry Method) of Adsorbent – Anionic Surfactant Modified

Alumina (ASMA)

[117]

2.7 Conclusion

From the batch experiment studies it was observed that the Alumina can be used as adsorbent

in the waste water treatment for the removal of Anionic Surfactant SDS. The variables for pH

were decided 2, 4, 6, 8 & 10 to find out optimum pH for further treatment. While studying pH

variables; other parameters such as high initial concentration of SDS (2000 ppm), Contact

Time (2 Hr) & Adsorbent Alumina Dosage (100 gm/L) were kept constant. The variables for

contact time were decided as 1 Hr, 2 Hr, 3 Hr, 4 Hr, 5 Hr, 6 Hr, 7 Hr & 8 Hr to find out

optimum contact time for further treatment. While studying Contact Time variables; other

parameters such as high initial concentration of SDS (2000 ppm), pH (4 – optimum pH

obtained from previous study) & Adsorbent Alumina Dosage (100 gm/L) were kept constant.

The variables for Adsorbent Alumina Dosage were decided as 50 gm/L, 100 gm/L, 150 gm/L

& 200 gm/L to find out optimum adsorbent Alumina dosage. While studying Adsorbent

Alumina Dosage variables; other parameters such as high initial concentration of SDS (2000

ppm), pH (4 – optimum pH obtained from previous study) & Contact Time (1 Hr – optimum

contact time obtained from Previous study) were kept constant. The variables for adsorbate

concentration were decided as 2 ppm, 4 ppm, 6 ppm, 8 ppm, 10 ppm, 30 ppm, 50 ppm, 100

ppm, 500 ppm, 800 ppm, 2000 ppm, 4000 ppm, 6000 ppm, 8000 ppm, 10,000 ppm, 20,000

ppm, 30,000 ppm & 40,000 ppm to find out optimum high initial concentration of SDS.

While studying high intial Adsorbate SDS Concentration variables; other parameters such as

pH (4 – optimum pH obtained from previous study) & Contact Time (1 Hr – optimum contact

time obtained from Previous study) & Adsorbent Alumina Dosage (100 gm/L – optimum

contact time obtained from previous study) were kept constant. From the batch study; pH 4

(99.78% removal of SDS), contact time 1Hr (99.27% removal of SDS) & adsorbent (i.e.

Alumina) dosage 100 gm/L (99.31% removal of SDS) was found optimum experimental

conditions for maximum % removal of SDS from aqueous solution. Maximum 197.7 mg/gm

adsorption capacity was observed at 20,000 ppm high initial concentration of SDS. Effect of

temperature was also studied for removal of SDS from aqueous solution. The variables for

temperature were decided as 30 ˚C, 40 ˚C & 50 ˚C to find out optimum temperature range.

The result showed that temperature did not affect SDS removal by ASMA. It was found

almost same i.e. 98% for all the temperature range. Chemical Kinetic study showed that the

whole adsorption process followed Pseudo Second Order Kinetic Model. The calculated

value of qe (196.07 mg/gm) from the Pseudo Second Order Kinetic model is in good

agreement with experimental qe value (197.7 mg/gm). Also the value of correlation

[118]

coefficient R2 = 1 was in good agreement. From the intra-particle diffusion model the value

of intercept C i.e. 197.02 mg/gm was found confirmed the thickness of the SDS layer on

Alumina. The values of coefficient of correlation (R2) for uptake of SDS on adsorbent

Alumina obtained were in good agreement with Langmuir (R2 = 0.98), Freundlich (R

2 = 0.99)

& BET isotherms (R2 = 0.96). The optimum SDS% removal (99.32% at 2000 ppm SDS) and

adsorption capacity (197.7mg/gm at 20,000 ppm SDS) was found at pH 4, contact time 1hr,

adsorbent (i.e. Alumina) dosage 100 gm/L.

2.8 Recommendation

The data may be useful in designing and fabrication of an economic treatment plant for the

removal of anionic surfactant from wastewaters in the detergent/soap manufacturing

industries. By applying this technology we can prevent the introduction of surfactant into

adjacent water resources.

Phenol & dyes are the most dangerous constituents of waste water of many industries. As

they are easily soluble in water, they can damage public health by running to the drinking

water discharge point. Anionic Surfactant Modified Alumina, produced such as above

mentionedway, can adsolubilize toxic dyes & phenol from aqueous media without consuming

much energy.

Here, any industry or mining activity generating Alumina as a waste material can be used as

an adsorbent for the removal of anionic surfactant. It will save the cost of raw material as

well as consumption of fresh raw material. Thus, this technology is being cost effective &

environment friendly.

[119]

Probable plant layout for the treatment of industrial effluent by Alumina & Anionic

Surfactant Modified Alumina is as under:

Figure 2.29: Flow diagram of effluent treatment for anionic surfactant removal &ASMA

preparation.

Waste Water

Containing

Anionic

Surfactant

Equalization

Tank

Agitation Tank,

Where Alumina

Dosage of 100

gm/L can be given

pH 4 should be

Maintained by

Adding 1N HCl or

1N NaOH

1 Hr Retention

Time is Provided

for the Reaction

Recycle &Reuse Treated Water

(supernatant) & Regenerate

exhausted Alumina (sludge) by

NaOH or Spirit to Recycle &

Reuse

Use the Anionic Surfactant Modified

Alumina, produced in such way, for

the adsolubilization of toxic dyes,

phenol, etc.from waste water.

Recycle & Reuse Treated Water

(supernatant) & Regenerate exhausted

ASMA (sludge) by desorption of the

organic pollutants in Acetone to

Recycle & Reuse them

[120]

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