Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

Langmuir model application on solid-

liquid adsorption using agricultural

wastes: Environmental application

review

Dalia Khalid Mahmoud1,∗, Mohamad Amran Mohd

Salleh1,2, Wan Azlina Wan Abdul Karim1

1 Department of Chemical and Environmental Engineering,

Faculty of Engineering, Universiti Putra Malaysia, 43300 UPM

Serdang, Selangor, Malaysia

2 Green Engineering and Sustainable Technology Laboratory,

Institute of Advanced Technology, Universiti Putra Malaysia,

43300 UPM Serdang, Selangor, Malaysia

almusaferdalia@yahoo.com

Article Info

Received:10th May 2012

Accepted: 20th May 2012

Published online: 1st June 2012

ISSN: 2232-1179 © 2012 Design for Scientific Renaissance All rights reserved

ABSTRACT

Langmuir isotherm is a model that used intensely at adsorption studies to make comparison between the

adsorption capacities of different adsorbents in order to evaluate the efficiency of these adsorbents.

Langmuir model is concept of the monomolecular adsorption on homogeneous surfaces. Adsorption has

been proved to be a promising technique at wastewater treatment. Recently many researchers have proved

the capability of agricultural solid wastes as alternative adsorbents instead of commercial activated carbon

to remove different classes of pollutants such as dyes, phenols and metals. This review presents the use of

agricultural solid wastes as adsorbents to remove different pollutants and the effect of treatment on their

efficiency. Adsorbent efficiency related to the physical and chemical properties of adsorbent.

Keywords: Adsorption, Langmuir model, Agricultural wastes, Review

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201

1. Introduction

The day-to-day human activities and industrial revolution have influenced the flow and

storage of water and the quality of available fresh water (Mohan et al., 2007). Industries have a

large potential to cause lake, streams and river pollution. The nature of pollution varies from

industry to industry and also from plant to plant (Mohan et al., 2008).

Among all physicochemical methods, adsorption is known to be a promising technique due

to the ease of operation, comparable low cost of application, high-quality of the treated effluents

especially for well-designed sorption processes (Eren and Afsin, 2007; Qadeer, 2007).

Activated carbon is widely used as an adsorbent, but it is expensive and therefore not

economical for wastewater treatment (Chandra et al., 2007), thus researchers interested to

investigate the using of adsorbents based on the agricultural wastes to remove different types of

pollutant, such as using of pomelo peel for adsorption of methylene blue dye (Hameed et al,

2008a), banana stalk for adsorption of methylene blue dye (Hameed et al, 2008b), Lemon peel

for adsorption of malachite green dye (Kumar, 2007), sugarcane bagasse for adsorption of ions

Cu(II), Cd(II) and Pb(II) (Gurgel and Gil, 2009) and palm seed for adsorption of phenol

(Rengaraj et al., 2002).

2. Adsorption technology

Adsorption is the method for separation of mixtures on a laboratory and industrial scale

where it is a surface phenomenon that can be defined as the increase in concentration of a

particular component at the interface between two phases.

Adsorption is very important process due to its technological, environmental and biological

importance. Furthermore the practical applications of adsorption process in industry and

environmental protection are important. Adsorption is a method for separation of mixtures that

based on the change in concentration of components at the interface. The development of

adsorption at surface science is considered as physical science that representing an

interdisciplinary area between chemistry, physics, biology and engineering. Adsorption process

systems can be as: liquid-gas, liquid-liquid, solid-liquid and solid-gas.

Physical adsorption can happened due to the universal van der Waals interactions, while

chemical adsorption or chemisorption can occur when there will be a character of a chemical

process.

The practical applications of adsorption can be at separation and purification of liquid and

gas mixtures, bulk chemicals, drying gases and liquids before loading them into industrial

systems, removal of impurities from liquid and gas media, recovery of chemicals from industrial

and vent gases and water purification. Activated carbon is the most widespread uses of for

liquid-phase adsorption in water treatment and has increased throughout the world. (Dabrowski,

2001; Noll et al., 1992). Adsorption process also used in many industrial wastewaters that

contain substances difficult to remove via conventionally secondary treatment, toxic or

hazardous, volatile and cannot be transferred to the atmosphere, substances have the potential for

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

202

creating noxious vapors or odors or for imparting color to the wastewater and substances present

is very small concentrations that make their removal via other methods difficult (Armenante.,

NJIT).

The change in the concentration of a pollutant (adsorbate) in the surface layer of the material

(adsorbent) in comparison with the bulk phase with respect to unit surface area is termed

adsorption. The term ‘‘biosorption’’ is given to adsorption processes, which use biomaterials as

adsorbents (or biosorbents). The assessment of a solid-liquid adsorption system is usually based

on two types of investigations: batch adsorption tests and dynamic continuous-flow adsorption

studies. When studying adsorption from solutions on materials it is convenient to differentiate

between ‘‘adsorption from dilute solution’’ and ‘‘adsorption from binary and multicomponent

mixtures covering the entire mole fraction scale’’. Batch studies use the fact that the adsorption

phenomenon at the solid/liquid interface leads to a change in the concentration of the solution.

Adsorption isotherms are constructed by measuring the concentration of adsorbate in the medium

before and after adsorption, at a fixed temperature (Crini and Badot, 2008).

3 Adsorption isotherm using Langmuir model

Adsorption is technique suitable for the removal of low concentrations of pollutants from

large volumes of process effluents, potable water, wastewater and aqueous solutions. Adsorption

equilibrium information is important to understand of how much adsorbate can be

accommodated by a solid adsorbent. Adsorption isotherm describes how pollutants interact with

adsorbent materials with relate to adsorption properties and equilibrium data. Mathematical

description of equilibrium adsorption capacity is necessary for efficient prediction of adsorption

parameters and quantitative comparison of adsorption behavior for different adsorbent systems.

For solid–liquid adsorption system, adsorption isotherm is important model in description of

adsorption behavior. At equilibrium, a saturation point is reached where no further adsorption

can occur. Typically, the mathematical correlation, which constitutes an important role towards

the modeling analysis, operational design and applicable practice of the adsorption systems, is

usually depicted by graphically expressing the solid-phase against its residual concentration. The

adsorption isotherm is representing the relationship between the mass of adsorbate adsorbed per

unit weight of adsorbent and the liquid-phase equilibrium concentration of adsorbate.

Giles et al. (1974), proposed a general modeling of sorption isotherms, in which four

particular cases are used as the four main shapes of isotherm commonly observed (Fig. 1).

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Fig. 1. The four main types of isotherms (Limousin et al., 2007).

According to Limousin et al., (2007), at the ‘‘C’’ isotherm (Fig. 1a), the curve is a line of

zero-origin which means that the ratio between the concentration of the compound remaining in

solution (C) and adsorbed on the solid (Q) is the same at any concentration. The ‘‘C’’ isotherm is

often used for a narrow range of concentration or very low concentrations rather than an accurate

description. At the ‘‘L’’ isotherm (Fig. 1b), the ratio between the concentration of the compound

remaining in solution (C) and adsorbed on the solid (Q) decreases when the solute concentration

increases, providing a concave curve suggesting a progressive saturation of the solid.

At the ‘‘H’’ isotherm (Fig. 1c), the initial slope is very high because the compound exhibits

sometimes such a high affinity for the solid (Toth, 1995). At the ‘‘S’’ isotherm (Fig. 1d), the

curve is sigmoidal and thus has got a point of inflection. This type of isotherm is always the

result of at least two opposite mechanisms.

Irving Langmuir was awarded the Nobel Prize in 1932 for his investigations concerning

surface chemistry. The Langmuir model (Langmuir, 1918) is probably the most popular one due

to its simplicity and its good agreement with experimental data (Crini & Badot, 2008; Hamdaoui

and Naffrechoux, 2007; Limousin et al., 2007).

Langmuir model is clear concept of the monomolecular adsorption on energetically

homogeneous surfaces. The statement proposed by Langmuir was applied to chemical adsorption

and with some restrictions to physical adsorption and the constant parameters of the Langmuir

equation have a strictly defined physical meaning. The Langmuir equation and the method of

solid surface area determination based on it can be applied to systems in which the adsorption

process is not complicated by formation of a multilayer (Dabrowski, 2001; Noll et al., 1992).

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204

Most of adsorption isotherm equations were proposed as modification of the classical

Langmuir equation (Rudzinski and Plazinski, 2007). The Langmuir isotherm gives the following

hypotheses (Gimbert et al., 2008):

Monolayer adsorption (the adsorbed layer is one molecule thick).

Adsorption takes place at specific homogeneous sites within the adsorbent.

Once a dye occupies a site, no further adsorption can take place at that site.

Adsorption energy is constant and does not depend on the degree of occupation of an

adsorbent’s active centers.

The strength of the intermolecular attractive forces is believed to fall off rapidly with

distance.

The adsorbent has a finite capacity for the adsorbate (at equilibrium, a saturation point is

reached where no further adsorption can occur).

All sites are identical and energetically equivalent.

The adsorbent is structurally homogeneous.

There is no interaction between molecules adsorbed on neighboring sites.

Langmuir adsorption isotherm plays an important role in the determination of the maximum

capacity of adsorbent. Langmuir’s isotherm describing the adsorption of adsorbate (A) onto the

surface of the adsorbant (S), where the chemical reaction for monolayer adsorption can be

represented as follows (CHEM 331L):

A + S AS (1)

Where AS represents a solute molecule bound to a surface site on S. The equilibrium

constant K for this reaction is given by:

K = (2)

[A] denotes the concentration of A, while the other two terms [S] and [AS] are two-

dimensional analogs of concentration and are expressed in units such as mol/cm2. The principle

of chemical equilibrium holds with these terms. The complete form of the Langmuir isotherm

considers (Eq. 2) in terms of surface coverage q which is defined as the fraction of the adsorption

sites to which a solute molecule has become attached. An expression for the fraction of the

surface with unattached sites is therefore (1 - q). Given these definitions, we can rewrite the term

[AS]/[S] as:

= (3)

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205

Now we express [A] as C and rewrite equation 2 as:

K = (4)

Rearranging, we can obtain the final form of the Langmuir adsorption isotherm:

= (5)

Where =

The Langmuir isotherm model (Langmuir, 1918) assumes that the adsorption occur at

homogeneous sites at adsorbent surface, and saturation happen when the dye molecule fill the

site where no more adsorption can occur at that site. According to the above equations Langmuir

isotherm can represent by the following equation:

C

Cqq

eL

eLe

K

K

1

max (6)

qe - Amount of adsorbate adsorbed at equilibrium (mg/g)

qmax Maximum monolayer adsorption capacity of the adsorbent (mg/g)

Ce---- Equilibrium concentration of adsorbate (mg/L)

KL Langmuir adsorption constant related to the free energy adsorption (L/mg)

Since the estimation of the adsorption isotherms parameters interference by the method of

linearization [Hamdaoui, 2006], therefore five forms of Langmuir isotherm equation used to

determine the constants KL and qmax. Equation 2 can be linearized in to the following five forms

of Langmuir isotherm equations (Hamdaoui and Naffrechoux, 2007):

maxmax

1

qC

qqC e

Le

e

K (7) (7)

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

206

Cqqq

eLe Kmaxmax

111 (8)

max

qC

qq

eLe

K

e (9)

max

qL

KqL

KC

q

ee

e

(10)

L

L

KK

ee q

q

C max1

(11)

The constants values can be evaluated from the intercept and the slop of the linear plot of

experimental data of (Ce/qe) versus Ce or (1/qe) versus (1/ Ce) or qe versus (qe / Ce), (qe / Ce)

versus qe , (1/ Ce) versus(1/qe).

Although non-linear method provides a better result, but the linear least-square method is still

preferred in favor of its simplicity and convenience. (Febrianto et al., 2009). It is clear that

transformations of non-linear model to linear forms implicitly alter their error structure and may

also violate the error variance and normality assumptions of standard least-squares method

(Kinniburgh, 1986; Ho and Wang, 2004). Equations 7 and 8 are the most frequently used by

several researchers because of the minimized deviations from the fitted equation resulting in the

best error distribution (Hamdaoui and Naffrechoux, 2007).

The essential feature of the Langmuir isotherm can be expressed by means of RL, a

dimensionless constant referred to as separation factor or equilibrium parameter RL which is

calculated using the following equation (Hall et al., 1966):

CK

RL

L

1

1 ------- -------------- (12)

KL ---- Langmuir adsorption constant related to the free energy adsorption (L/mg)

Cο---- The highest initial adsorbate concentration (mg/L)

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

207

The value of separation factor RL indicates the adsorption process as given:

Unfavorable (RL >1)

Linear (RL =1)

Favorable (0< RL <1)

Irreversible (RL = 0)

Most of adsorption studies are using the same theories for the adsorption isotherms, which

depend on the comparison between the adsorption capacities of different adsorbents in order to

evaluate the efficiency of these adsorbents (Foo and Hameed, 2010).

4 Agricultural solid wastes

Agricultural “green energy” production is the principal contributor in economic development

of a developing country. Its economy development is based on agricultural production and most

people live in the rural areas. Implementation of integrated community development programs is

therefore very necessary. It is believed that integrated community development contributes to

push up socio-economic development of the country (Demirbas et al., 2006).

Agricultural by-products usually are composed of lignin and cellulose as major constituents and

may also include other polar functional groups of lignin, which includes alcohols, aldehydes,

ketones, carboxylic, phenolic and ether groups (Pagnanelli et al., 2003).

There have been many attempts to find inexpensive and easily available adsorbents to

remove the pollutants. According to the physico-chemical characteristics and low cost of the

agricultural solid wastes, they may be good potential adsorbents (Rafatullah et al., 2010).

Agricultural solid wastes used as adsorbents to remove many types of pollutants, such as dyes,

metals and phenol compounds. Agricultural productions are available in large quantities around

the world; thus big amount of wastes rejected (Mohd Salleh et al., 2011a). Table 1 shows

agricultural production (Ton/year) in some countries (FAO, 2009).

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208

Table 1 Agricultural production in some countries (Ton/year) (FAO, 2009)

Agricultural wastes are lignocellulosic materials that consist of three main structural

components which are lignin, cellulose and hemicelluloses. These components contribute mass

and have high molecular weights. Lignocellulosic materials also contain extractive structural

components which have a smaller molecular size (Demirbas, 2009). Agricultural and industrial

sectors dispose of large amounts of untreated waste, which may pollute the land as a result

damage the ecosystem. On the other hand, improper treatment of these wastes causes similar

problems. Therefore legislative control of pollutants should be enacted to prevent or to minimize

the transfer of hazardous material to other areas (Mannan and Ganapathy, 2004). Thus, within

the last few years many ideas have been introduced in order to properly dispose of these wastes,

such as intensive use as adsorbents for pollutant removal especially for dye removal where it

showed high adsorption capacity (Noeline et al., 2005). Agricultural wastes are better than other

adsorbents because the agricultural wastes are usually used without or with a minimum of

processing (washing, drying, grinding) and thus reduce production costs by using a cheap raw

material and eliminating energy costs associated with thermal treatment (Franca et al., 2009).

Researchers also used carbon derived from different agricultural solid wastes to be used as

adsorbents and used different activation treatments in order to improve their physical, chemical

and morphological characteristics. Physical activation involves carbonization of material then

activation at elevated temperature in the presence of suitable oxidizing gases such as air, carbon

dioxide, steam or their mixtures, while the chemical activation involve mixing the precursor with

chemical activating agents such as acid, basic solutions, as dehydrating agents and oxidants.

Steam activation involve heating at moderate temperatures (500-700 °C) under a flow of pure

steam, or heated at (700–800 °C) under a flow of just steam (Ioannidou and Zabaniotou, 2007).

Products Malaysia Indonesia India Mexico Nigeria Philippines

Coconut 459640 21565700 10148000 1004710 236700 15667600

Oil palm 84842000 86000000 - 292499 8500000 516115

Coir 23400 - 507400 - - -

Rice,paddy 2510000 64398900 133700000 263028 3402590 16266400

Sugar cane 700000 26500000 285029000 49492700 1412070 22932800

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5 Dyes removal

Synthetic dyes are an important class of organic compounds and are often found in the

environment as a result of their wide industrial use (Crini and Badot, 2008). Many industries are

involved with water pollution, such as textile companies, food processing companies, dye

manufacturers, electroplating factories, paper and pulp mills usually discharge coulored

wastewaters, where it is aesthetically undesirable and may reduce sunlight penetration.

Furthermore dyes have complex structure and synthetic origin therefore these dyes are difficult

to decolorize (Kuo et al., 2008; Demirbas et al., 2008). The total dye consumption of the textile

industry worldwide is in excess of 10 7

kg/year and 1000 tonnes/year or more of these dyes are

discharged into waste streams by the textile industry worldwide (Marc, 1996). Dyes can affect

aquatic plants because they reduce sunlight transmission through water. Also dyes may impart

toxicity to aquatic life and may be mutagenic, carcinogenic and may cause severe damage to

human beings, such as dysfunction of the kidneys, reproductive system, liver, brain and central

nervous system (Kadirvelu et al., 2003; Dinçer et al., 2007; Shen et al., 2009).

In the dye molecules there are two important components: chromophores which are

responsible for producing the color and auxochromes which enhance the affinity of the dye

toward the fibers (Gupta and Suhas, 2009). Generally, the dyes used in the textile industry are

basic dyes, acid dyes, reactive dyes, direct dyes, azo dyes, mordant dyes, vat dyes, disperse dyes

and sulfur dyes (Demirbas, 2009).

There is higher consumption of synthetic dyes over natural dyes for most types of industrial

applications, due to the low production cost and brighter colors of synthetic dyes, furthermore

better resistance towards environmental factors and easy-to-apply factor (Ngah et al., 2011).

Many researchers had studied the adsorption of Methylene blue dye since it is an important basic

dye and widely used in the textile industry. Acute exposure to Methylene blue may cause

jaundice, quadriplegia, increased heart rate, cyanosis, shock, vomiting, heinz body formation and

tissue necrosis in humans (Vadivelan and Kumar, 2005). Fig.2 shows the chemical structures of

different classes of dyes. Different adsorbents derived from agricultural solid wastes have been

used for dye removal from wastewater and many studies of dye adsorption by agricultural solid

wastes have been published. Table 3 lists previous studies of the adsorption of dyes using

adsorbents based on agricultural solid wastes.

Adsorption capability of adsorbent usually related by the physical and chemical properties of

adsorbent such as BET surface area and functional groups. The carboxyl and hydroxyl groups

are the major functional groups in the adsorption of cationic dyes. Carboxyl group bearing

negative charge inhibited the adsorption of anionic dyes, while hydroxyl group is important

functional group in the adsorption of anionic dyes (Gong et al., 2005).

Cazetta et al., (2011) activated the coconut shell carbon using NaOH at three NaOH:char

ratio of 1:1 (AC-1), 2:1 (AC-2) and 3:1 (AC-3). They found that the surface area were 783, 1842

and 2825 (m2/ g) while the carboxylic groups were 0.37, 0.62 and 0.75 (mmol/g) for (AC-1),

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

210

(AC-2) and (AC-3) respectively. Therefore the adsorption capacity of AC-3 for adsorption of

Methylene blue was high (916 mg/g).

Wu and Tseng, (2008), studied the adsorption of basic brown1 (BB1) using fir wood char

that treated with NaOH solution (4 NaOH/char weight ratio). They found that the surface area of

activated fir wood char was 2406 m2/g and its adsorption capacity was 2226 g/kg, which

consider high value comparing with other studies.

Wang and Zhu, (2007), studied the adsorption of Methylene blue and Rhodamine B using

commercial activated carbon (Calgon, USA) as original form with BET surface area 972 m2/g

and another form that treated with HCl at BET surface area1015 m2/g. For the adsorption of

Methylene blue, the adsorption shows an order of AC > AC-HCl, while for the adsorption of

Rhodamine B, the adsorption order was AC-HCl > AC. The difference in adsorption capacity

depends on the surface chemistry, where, there are two parallel adsorption mechanisms in the

adsorption, the first involving electrostatic interactions between dye molecules and carbon

surface groups and the second involving dispersive interactions between dye molecules and

carbon surface layers. For adsorption of Methylene blue cationic dye, the electrostatic

interactions between dye molecules and carbon surface groups could play a role but the

predominant effect is the interaction between the delocalised π -electron of the carbon surface

and the free electrons of the dye molecule (aromatic rings and –N=N– or –N=C–C=C– bonds).

Therefore, a carbon with the highest acidity shows a lower adsorption for methylene blue dye

[Pereira et al., 2003]. The basic original carbons exhibited higher adsorption to cationic

Methylene blue dye suggesting that dispersive interaction plays a dominant role in the adsorption

mechanism.

Batzias et al., (2009) studied the adsorption of Methylene blue onto fine grinded wheat straw

where they found that BET surface area was 3.1 (m2/ g) corresponding to adsorption capacity of

2.23 mg/g. After acid treatment, the BET surface area (m2/ g) increased from 3.1 to 9, thus the

adsorption capacity increased from 2.23 to 16.21(mg/ g).

Tseng, (2007) studied the activation of plum kernels by NaOH and he found that the BET

surface area increased from 1478 to 1887 (m2/ g) when the NaOH/char ratio increased from 2 to

4, thus adsorption capacity for Basic brown 1 increased from 1453 to 1845 mg/g.

Foo and Hameed, (2011) used activated carbon prepared from date stones char (DSAC) for

adsorption of Methylene blue. The BET surface area, Langmuir surface area and total pore

volume were 856 m2/g, 1276 m

2/g and 0.4680 cm

3/g, respectively (compared with 66 m

2/g, 99

m2/g and 0.0385cm

3/g for char without activation). The adsorption capacity of DSAC was

316.11 mg/g. The FTIR spectrum of char revealed the peaks at 3233, 2361, 1992, 1424 and 1054

cm−1

, corresponds to the presence of –OH (hydroxyl), alkynes, –COOH (carboxylic acids), OH,

and C–O–C (esters, ether or phenol) functional groups. Meanwhile, the surface chemistry of

DSAC illustrated intensive peaks, at 3233, 1424 and 1054 cm−1

, corresponds to the presence of–

OH (hydroxyl), –OH bending vibrations, and C–O–C (esters, ether or phenol) derivatives.

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

211

Tan, et al., (2008) used acid treated oil palm shell carbon to remove Methylene blue dye.

Activated carbon was prepared by immersing the original activated carbon in 5% hydrochloric

acid (HCl) and left for 4 h. The sample was then filtered, rinsed and dried in an oven. After

activation, the surface chemistry of the activated carbon underwent some changes and the bands

displayed by the FTIR spectra were: 3572 cm−1

(O–H stretching vibrations in carboxylic acid),

2278 cm−1

(C C stretching vibrations), 1236 cm−1

(C–O–C stretching vibrations in ether) and 664

cm−1

(C–Cl stretching vibrations in chloro). That is why the adsorption capacity increased from

243.90 to 303.03 (mg/g) for oil palm shell-based and HCl-treated oil palm shell-based,

respectively.

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Acid blue 92

Amido Black 10B

Methylene blue

Fig. 2. Chemical structures of different dyes

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213

Table 2 previous studies of adsorption of dyes using adsorbents based on agricultural solid

wastes. Adsorbents Dyes qmax

.(mg/g)

References

Kenaf fibre char Methylene blue 18.18 Dalia et al., 2012

Mixture of Agricultural Solid Wastes Methylene blue 93.458 Mohd Salleh et al., 2011b

Cashew nut shell Congo red 5.184 Kumar et al., (2010)

Waste apricot Malachite green 116.27 Başar (2006)

Waste apricot Crystal violet 57.80 Başar (2006)

Wheat bran Malachite green 66.57 Wang et al., (2008)

Yellow passion fruit waste Methylene blue 44.70 Pavan et al., (2008)

Apricot stone activated carbon Astrazon yellow 209.64 Demirbas et al., (2008)

Sunflower oil cake Methylene blue 10.21-

16.43

Karagöz et al., (2008)

Almond shell activated carbon at750 °C Methylene blue 1.33 Aygün et al., 2003

Banana pith Acid brilliant

blue

4.42 Namasivayam et al., (1998)

Peanut hull Sunset yellow 13.99 Gong et al., (2005)

Hazelnut shell carbon at 750 °C Methylene blue 8.82 Aygün et al., (2003)

Coir pith carbon Methylene blue 5.87 Kavitha and Namasivayam, (2007)

Activated date pits at 500 °C Methylene blue 12.94 Banat et al., (2003)

Corncob hull char immersed in KOH Methylene blue 5.53 Wu et al., (2011)

Coconut coir pith

Direct Red 12B 76.3 Sureshkumar and Namasivayam ,

(2008)

Waste apricot activated carbon Methylene blue 102.04 [Basar, 2006

Rice husk Indigo carmine 29.2799 Lakshmi et al., (2009)

neem sawdust malachite green 4.35 Khattri and Singh, (2009)

Acid treated wood-shaving bottom ash Red Reactive 29.9 Leechart et al., (2009)

Thespesia populnea pods activated

carbon

Orange G dye 9.129 Arulkumar et al., (2011)

Coconut bunch Methylene blue 70.92 Hameed et al., (2008c)

Coconut coir pith Direct Red 12B 76.3 Sureshkumar and Namasivayam

,(2008)

Treated Coconut male flowers carbons Crystal violet 60.42 Senthilkumaar et al., (2006)

Jute fiber Eosin yellow 31.489 Porkodi and Kumar,( 2007)

Banana pith Acid brilliant

blue

4.42 Namasivayam et al., (1998)

Peanut hull Sunset yellow 13.99 Gong et al., (2005)

Polygonum orientale Linn activated

carbon

Malachite green 476 Wang et al., (2010)

Mild acid hydrolyzed wheat straw Methylene Blue 16.21 Batzias et al., (2009)

Husk of the mango seed carbon Acid blue 80 9.2 Dávila-Jiménez et al., (2009)

Oil palm empty fruit bunch Methylene blue 50.76 Rebitanim et al., (2012)

Petai (Parkia speciosa) seed Methylene blue 91.74-

100.03

Ahmad et al., (2011)

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

214

6 Phenols removal

Phenols are natural components of many substances like wine, smoked foods and tea.

Phenols are present in animal wastes and decomposing organic material. Phenols can be

generated from the industrial sources of contaminants such as oil refineries, coal gasification

sites and petrochemical units. Phenols also released from the combustion of tobacco and fossil

fuels. Furthermore, phenols are introduced into surface water from industrial effluents such as

those from the coal tar, gasoline, plastic, rubber proofing, disinfectant, pharmaceutical and steel

industries and domestic wastewaters, agricultural run-off and chemical spills. In the refinery and

lubricant production, phenols used as an extracting solvent. Due to their germicidal and local

anesthetic properties, phenols used at preparation of shaving soaps and creams. Phenols also

used as a reagent in chemical analysis and as a primary petrochemical intermediate. Phenols are

biodegradable and at high concentrations can be toxic and mutagenic. Fig.3 shows phenol and

phenol derivatives that commonly found in industrial wastewaters. Table 3 shows molecular

weight of phenol compounds. Phenol is rapidly absorbed through the skin and can cause skin and

eye burns upon contact. Comas, convulsions, cyanosis and death can result from overexposure to

it. Phenols can cause unpleasant taste and odor of drinking water also can cause negative effects

on different biological processes internally, phenol affects the liver, kidneys, lungs and vascular

system (Ahmaruzzaman, 2008; Dąbrowski, 2005; Busca et al., 2008; Lin and Juang, 2009).

Therefore, it is important to remove these compounds from the effluents before it disposed into

the wastewaters. Table 4 lists previous studies of the adsorption of phenols using adsorbents

based on agricultural solid wastes.

Aygün et al., (2003), studied the adsorption of phenol using carbon obtained from several

agricultural wastes (almond shell, hazelnut shell, walnut shell and apricot stone). Although some

properties like surface area and carbon content of all activated carbons are not very much

different from each other, phenol adsorption capacities differ. The BET surface area of hazelnut

shell carbon and apricot stone carbon were 793 and 783 (m2/ g), and their adsorption capacities

for phenol were 145 and 126 (mg/g), that are higher than other adsorbents. Oxygen containing

surface functional groups strongly influence adsorption capacity of for phenolic compounds.

There are no acidic groups on hazelnut shell carbon and apricot stone carbon, that is why the

adsorption capacity of phenol was high on these adsorbents.

Tseng et al., (2003) studied the adsorption of acid blue 264, basic blue 69 and phenol onto

activated carbon prepared from pinewood. Physical activation of pinewood was done under

steam at 900 °C. They found that pinewood activated carbon have high adsorption capacities for

these three adsorbates. The adsorption capacities for the adsorption of acid blue 264, basic blue

69 and phenol were 1176, 1119 and 240.6 g/ kg at high surface area of adsorbent (902 m2/ g).

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

215

Fig. 3 Phenol and phenol derivatives (C6) commonly found in industrial wastewaters or fractions

isolated from vegetal sources. Representative examples are indicated under the general chemical

structures (Soto et al., 2011).

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

216

Table 3 Molecular weight of phenol compounds (Liu, et al 2010)

Phenol compounds Molecular weight

(g/mol)

Phenol 94.1

2-chlorophenol (2-CP) 128.6

4-chlorophenol (4-CP) 128.6

DICHLORO PHENOL

(DCP)

163

Trichlorophenylmethyliodosalicyl (TCP) 197.4

4-Nitrophenol (4-NP) 139.1

dinitrophenol (DNP) 184

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217

Table 4 previous studies of the adsorption of phenols using adsorbents based on agricultural solid

wastes.

Adsorbents Pollutants qmax.

(mg/g)

References

Commercial activated

carbon

Phenol 49.72 Özkaya, (2006)

Granular activated carbon

(GAC)

2-chlorophenol 303.03 Hamdaoui and Naffrechoux, (2007)

4-chlorophenol 322.58

2,4-dichlorophenol 370.37

2,4,6-trichlorophenol 526.32

Coconut husk activated

carbon

2,4,6-trichlorophenol 716.10 Hameed et al., (2008d)

Coconut shell activated

carbon

Phenol 205.8

Mohd Din et al., (2009)

Coconut fibers Phenol 12.23 Phan et al., (2006)

Activated coconut fibers 74.63

jute fibers 19.49

Activated jute fibers 181.81

beet pulp carbon Phenol 90.61 Dursun et al., (2005)

Wood particleboard wastes

activated carbons

Phenol 500

Girods et al., (2009)

Carbon-rich black gram

husk

Phenol 109.92 Srihari and Das, (2008)

Black cherry

Stones activated carbon

Phenol 133.33 Arana et al., (2010)

Oil palm empty fruit bunch

activated carbon

2,4-dichlorophenol 232.56 Shaarani and Hameed, (2010)

Punica granatum

(pomegranate) peel

2,4-dichlorophenol 65.7 BhatnagarMinocha, (2009)

Carbonized Corncobs Phenol 37 El-Hendawy, (2005)

o-nitrophenol 13

m-nitrophenol 20

Pnitrophenols 23

Almond shells Pentachlorophenol 9.6 Estevinho et al., (2008)

Charred saw-dust p-nitrophenol 147 Dutta et al., (2001)

NaOH-Modified Palm Oil

Fuel Ash

4-nitrophenol 500 AL-Aoh et al., (2012)

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218

7 Metals removal

Heavy metals are a general collective term applying to the group of metals and metalloids

with an atomic density greater than 6 g cm-3

(O’Connell et al., 2008). The metals of major

environmental concern today are arsenic, cadmium, chromium, cobalt, copper, lead, manganese,

mercury, nickel and zinc (Bhattacharyya and Gupta, 2008). Toxic metal ions in water represent

serious public health problem where the heavy metal ions are not degradable and cannot be

destroyed therefore they persistent environmental contaminants and can be harmful to aquatic

life. Furthermore these metals may have a potentially damaging effect on human physiology and

other biological systems when the tolerance levels are exceeded. The heavy metal ions are stable

and persistent environmental contaminants since they cannot be degraded and destroyed. The

presence of copper, zinc, cadmium, lead, mercury, iron, nickel and others metals, has a

potentially damaging effect on human physiology and other biological systems when the

tolerance levels are exceeded (Demirbas, 2008; Demirbas et al., 2005). The chemical functional

groups such as carboxylic and phenolic groups are responsible for binding between the metal ion

and lignocellulosic adsorbents by a surface complexation mechanism (Pagnanelli et al., 2003).

Although the maximum adsorption capacities of metal adsorption by agricultural adsorbents

are not high compare to dyes and phenols removal, but still good choice as adsorbents for metal

removal. Table 5 lists previous studies of the adsorption of metals using adsorbents based on

agricultural solid wastes.

Camire and Clydesdale (1981), studied the effect of heat treatment on the binding of calcium,

magnesium, zinc, iron to wheat bran, and they conclude that the lignin and pectin have a high

metal binding capability. They found that the pH had a significant effect on the binding of

metals by lignin and wheat bran and the boiling had a significant effect on the binding of metals

by cellulose, lignin, and wheat bran.

Agarwal et al., (2006), studied adsorption of chromium (VI) by Tamarindus indica seeds.

They found that the particle size of sorbents has a significant effect on Cr (VI) sorption. The

larger sorbent size showed lesser Cr (VI) removal as compared to the smaller sorbent size. This

may be due to that the surface area available for adsorption decreases with the increase of

particle size, providing less active surface sites for adsorption of sorbate. The reduction in Cr

(VI) removal capacity with increase in sorbent size gives an idea about the porosity of sorbent,

where if the sorbent is highly porous then it would not have significant effect on Cr (VI)

removal.

Adsorption of lead (II) using activated carbon prepared from coconut shell has been studied

by Sekar et al., (2004). The Surface area of the adsorbent was found to be 265.96 (m2 g

−1) with

maximum adsorption capacity of 26.50 (mg/g).

A study of Cr (VI) removal from synthetic wastewater using coconut shell charcoal was

done by Babel and Kurniawan, (2004), and they found that the surface area of the adsorbent was

found to be low (5–10 m2 g

−1) with adsorption capacity of 10.88 (mg/g).

Journal of Purity, Utility Reaction and Environment Vol.1 No.4, June 2012, 200-229

219

Ho and McKay, (2000), studied the kinetics of sorption of divalent metal ions onto sphagnum

moss peat and they found that the chemical bonding among divalent metal ions and polar

functional groups on peat, such as aldehydes, ketones, acids, and phenolics are responsible for

the cation-exchange capacity of the peat.

Table 5 previous studies of the adsorption of metals using adsorbents based on agricultural solid

wastes.

Adsorbents Metals qmax. (mg/g)

References

Coconut shell activated carbon Pb 26.50 Sekar et al., (2004)

Treated green coconut (Cocos

nucifera) shells

Pb+2

54.62 Sousa et al., (2010)

Ni+2

16.34

Cd+2

37.78

Zn+2

17.08

Cu+2

41.36

Ethanol treated Agricultural

Wastes (peat soil, cow dung and

digested paddy husk)

Ni+2

2.5

Zhang and Ismail, (2012)

Green coconut shell powder Cd+2

285.7 Pino et al., (2006)

Coconut shell charcoal oxidized

with nitric acid

Cr(VI) 10.88 Babel and Kurniawan, (2004)

Coconut coir pith Cr(VI) 201.47 Suksabye et al., (2008)

Modified coconut coir pith Cr(VI) 76.3 Namasivayam and Sureshkumar(2008)

Modified coir pith Ni(II) 38.9 Ewecharoen et al., (2008)

Apricot stone activated carbon Ni(II) 27.21 Kobya et al., (2005)

Co 30.07

Cd(II) 33.57

Pb(II) 22.85

Cu(II) 24.21

Cr(III) 29.47

Palm Tree Leaves Zn(II), 14.60 Al-Rub, (2006)

Wool Cr(VI) 41.15 Dakiky et al., (2002)

Tea waste Cu(II) 48.00 Amarasinghe and Williams, (2007)

Tamarindus indica seeds Cr(VI) 0.098 Agarwal et al., (2006)

Rose waste biomass Pb(II) 151.51 Javed et al., (2007)

Tea factory waste Ni(II) 15.26 Malkoc and Nuhoglu (2005)

Rice bran Zn(II) 14.17 Wang et al., (2006)

Orange peels Cd(II) 123.65 Schiewer and Patil, (2008)

Olive pits Cd(II) 9.39 Salem and Allia, (2008)

Commercial activated carbon Zn(II) 19.9 Ramos et al., (2002)

Raw activated carbon Cr(VI) 7.614 Liu et al., (2007)

Oxidized in boiling HNO3 13.74

NaOH and NaCl 13.89

Activated carbon CN 47.62 Behnamfard and Salarirad, (2009)

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220

8 Conclusion

During the last few years many articles concerning the adsorption of pollutants by

agricultural solid wastes have been published. This article is an attempt to highlight the use of

Langmuir adsorption isotherm to determine the maximum capacity of adsorbents and effect of

the physical and chemical properties on to adsorption capacity of adsorbent. Furthermore, to

highlight the effect of different activations on the adsorbents, thus improve their physical,

chemical and morphological characteristics. Previous studies showed that the activation with

acidic or basic solutions can increase the BET surface area and carboxylic groups. The more acid

or basic ratio (acid or basic- adsorbent), the more increase in BET surface area, thus increasing

adsorption capacity. The carboxyl and hydroxyl group are major functional groups in the

adsorption of cationic dyes.

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