2006-4 Recent Studies on Activated Carbons

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Energy Sources, Part A, 28:627–638, 2006
Copyright © Taylor & Francis Group, LLC
ISSN: 1556-7036 print/1556-7230 online
DOI: 10.1080/009083190951401
Recent Studies on Activated Carbons and
Fly Ashes from Turkish Resources
AYHAN DEMIRBA ¸S
GULSIN ARSLAN
EROL PEHLIVAN
Department of Chemical Engineering
Selcuk University
Konya, Turkey
This article deals with adsorptive properties of activated carbons (ACs) and fly ashes
from Turkish coal and biomass resources. ACs because of their high surface area,
microporous character and the chemical nature of their surface have been considered
potential adsorbents for the removal of heavy metals from industrial wastewater.
Pyrolysis is an established process method for preparation of activated carbon from
biomass. The bio-char is can be used as AC. The adsorption properties of ACs were
strictly defined by the physicochemical nature of their surface and their texture, i.e.,
pore volume, pore size distribution, surface area. It is well known that the pH of the
solution-adsorbant mixture is an important variable in the adsorption process. Fly
ash has the highest adsorption capacity (198.2 mg/g) for Cd(II). Almond shell AC
has the lowest adsorption capacity (2.7 mg/g).
Keywords active carbon, fly ash, adsorption, lignite, Turkish resources
Recently, the production of active carbon (AC) from Turkish natural carbon based sources
has received increasing attention. All starting materials used in commercial production
of ACs in Turkey are those with high carbonaceous content such as wood, lignite, peat,
and coal of different ranks or are low-cost and abundantly available such as agricultural
nutshells (hazelnut, almond, walnut shells, apricot stones, cherry stones, grape seeds) and
by-products.
AC is widely used as an effective adsorbent in many applications such as air sepa-
ration and purification, vehicle exhaust emission control, solvent recovery, and catalyst
support because of its high specific pore surface area, adequate pore size distribution, and
relatively high mechanical strength. The development of ACs from agricultural carbona-
ceous wastes will be advantageous for environmental problems. ACs because of their
high surface area, microporous character, and the chemical nature of their surface have
been considered potential adsorbents for the removal of heavy metals from industrial
wastewater (Aggarwal et al., 1999).
The production of ACs mainly includes four sequential stages: drying, preactivation
(physical activation and carbonization), main activation, and desulfurization and purifi-
This study has been supported by Scientific Research Project (BAP in Turkish initials) of
Selcuk University.
Address correspondence to Professor Ayhan Demirbas, Selcuk University, Department of
Chemical Engineering, 42031 Konya, Turkey. E-mail: ayhandemirbas@hotmail.com
627

628 A. Demirba¸setal.
cation (demineralization). In the main activated stage, char can be used in the prepara-
tion of AC when its pore structure and surface area are appropriate. Chemical additives
(AlCl
3
, FeCl
3
,H
3
PO
4
,NH
4
Cl, KOH. and ZnCl
2
) slightly affect the first step by in-
hibiting hemicelluloses decomposition and accelerating cellulose decomposition through
the dehydration reaction. The hemicelluloses undergo thermal decomposition very read-
ily. The hemicelluloses reacted more readily than cellulose during heating. The thermal
degradation of hemicelluloses begins above 373 K during heating for 48 h; hemicellu-
loses and lignin are depolymerized by steaming at high temperature for a short time.
The metoxyl content of wet meals decreased at 493 K (Demirba¸s and Kucuk, 1994). In
the activation process phosphoric acid exhibited the largest influence on the slow pyrol-
ysis. At concentrations higher than 30% H
3
PO
4
, the two weight loss steps ascribed to
hemicelluloses and cellulose decomposition overlapped (Zanzi, 2001).
ACs with high surface area can be produced from carbonaceous materials using
one-step preparation method that is slow pyrolysis and steam activation. Overall reaction
undergoes as following main stage:
Carbonaceous material → Char + Liquids + Gases. (1)
Lignocellulosic materials were extensively used as the starting raw material for
preparing activated carbons. Many reports have appeared on the development of acti-
vated carbon from cheaper and readily available lignocellulosic materials (Omar et al.,
2003; Demirba¸s, 1999; El-Hendawy et al., 2001; Heschel and Klose, 1995; Yenisoy-
Karakas et al., 2004; Yardim et al., 2003; Demirba¸s et al., 2002; Savova et al., 2001;
Yalcin and Sevinc, 2000).
The characterization of a polymeric activated carbon (PAC) was performed by com-
paring its adsorption, porosity, functional groups and some of physical properties with a
commercial well-shaped activated carbon (CAC) (Yenisoy-Karakas et al., 2004).
The activated carbon from furfural was prepared by polymerization of furfural fol-
lowing carbonization and activation of the obtained polymer material with water vapor
at 800
◦
C (Yardim et al., 2003). The adsorption of Hg(II) from aqueous solution at 293 K
by activated carbons obtained from apricot stones, furfural, and coals was studied (Ekinci
et al., 2002). The activated carbon prepared from hazelnut shell was used as an adsorbent
for the removal of a metal ion from aqueous solution (Demirba¸s et al., 2002).
Carbonaceous adsorbents with alkaline character of the surface products were ob-
tained by steam pyrolysis of agricultural samples (almond shells, nut shells, apricot stones,
cherry stones, grape seeds). The carbonaceous adsorbents obtained have a hydrophilic
surface and were suitable for sorption metal ions from waste water (Savova et al., 2001).
Recognizing the economic drawback of activated carbon, many investigators have
studied the feasibility of less expensive materials such as waste rubber tire (Rowley et al.,
1984; Netzer and Wilkinson, 1974; Knocke and Hemphill, 1981; Meng et al., 1998),
fly ash (Kapoor and Viraraghavan, 1993; Sen and De, 1987), coal (Karthikeyan and
Chaudhuri, 1986; Pandey and Choudhuri, 1982), carbon fibers (Kaneko, 1988), activated
charcoal cloth (Jayson et al., 1984), rice husk (Tewari et al., 1995), saw dust (Raji and
Anirudhan, 1996), clays (Farrah and Pickering, 1978; Filho et al., 1995b), wood (Morita
et al., 1987), peat (Viraraghavan and Kapoor, 1995), human hairs (Tan et al., 1985), soil
(Yin et al., 1997), binata bark (Deshkar et al., 1990), moss (Coupal and Lalancette, 1976),
starch xanthate (Campanella et al., 1986), and chitosan beads (Kawamura et al., 1998)
for the removal of heavy metals from wastewater. For an excellent review, the reader is
referred to an article by Pollard et al. (1992).

Activated Carbons and Fly Ashes 629
The objective of this present study was to develop an industrially viable, cost ef-
fective, and environmentally compatible technology for the removal of Hg (II) from
wastewater. For this purpose, studies were performed to convert the waste slurry from a
fertilizer plant into an inexpensive carbonaceous adsorbent. Some studies for the removal
of metal ions and phenols from such adsorbents have already been reported (Srivastava
et al., 1989; 1997). Nitrogen-based fertilizer plants often generate waste slurry due to
partial combustion of liquid fuel. The costs for disposal of the slurry could be signif-
icantly high. In this investigation, the adsorbent prepared from a fertilizer plant waste
slurry was used to remove Hg (II) (Mohan et al., 2000).
Commercial ACs can be manufactured from various carbonaceous precursors like
lignite and coal (∼42%), peat (∼10%), wood (∼33%), and coconut shell. Since the
price of commercial AC has dropped continually over the last decade or so, interests are
growing in the use of other low-cost and abundantly available lignocellulosic materials
as precursors for the preparation of AC. Some agricultural solid wastes, such as Oil-palm
shell (or called endocarp) have been successfully converted into ACs on a laboratory scale
(Guo and Lua, 2002). AC with a high adsorption capacity for removal of copper ions
from aqueous solution is produced from pecan shells (Dastgheib and Rockstraw, 2001).
Experimental Considerations
Carbon is air-dried, crushed and screened to obtain fractions with geometrical mean sizes
ranging from 0.5 to 2.0 mm. Then, 100 g of the selected fraction was impregnated with
concentrated H
2
SO
4
, and it is activated in a hot air oven at 150
◦
C for 24 h. The carbonized
material is washed with distilled water to remove the free acid, and the activated carbon
is then soaked in 1% NaHCO
3
solution to remove any remaining acid. This is then
washed with distilled water until the pH of the AC reached 6.25, dried at 105
◦
C, and
sieved to the particle size 0.90–1.60 mm (Ekinci et al., 2002). The general procedure of
the activation process for this study is described below and is schematically outlined in
Figure 1.
The ACs were prepared by ZnCl
2
/CO and other salt solutions/CO activation of the
rice husk (Yalcin and Sevinc, 2000). In their study, a certain amount of dried rice husks
were mixed with changing amount of ZnCl
2
and salts such as FeSO
4
.7H
2
O, FeCl
3
.6H
2
O,
KCl, and CaCl
2
.2H
2
O together with CO. The surface area and the nature of the porosity
of the resulting ACs were found to be related to the concentration and type of the
impregnated salt solutions.
AC prepared from coirpith, an agricultural solid waste by-product, has been used for
the adsorption of Cd(II) from aqueous solution. Parameters such as the agitation time,
metal ion concentration, adsorbent dose, and pH are determined. The adsorption data fit
well with the Langmuir and Freundlich isotherm models. The mechanism of adsorption
seems to be ion exchange. As coirpith is discarded as waste from coir processing indus-
tries, the carbon is expected to be an economical product for metal ion remediation from
water and wastewater (Kadirvelu and Namasivayam, 2003).
The activation temperature was varied from 250 to 550
◦
C, and activation time was
controlled as 0.5, 1, 2, 3, and 4 h. The concentration of activating agent was 1, 3, 5, and
7M. The weight ratio of raw material and ZnCl
2
solution was varied as 1:1, 1:3, 1:5, and
1:7. In the derived optimal conditions, an activation experiment was carried out using CaCl
2
as the activating agent to compare the activating ability with ZnCl
2
(Kim et al., 2001).
Commercially available ACs are expensive. A wide variety of ACs have been pre-
pared from agricultural wastes such as peanut hull (Periasamy and Namasivayam, 1996),

630 A. Demirba¸setal.
Figure 1. Schematic flow diagram for activation process.
baggage pith (McKay et al., 1987), tea dust leaves (Balasubramanian and Muralisankar,
1987), paddy straw (Namila and Mungoor, 1993), wood products, (Fung and Miller,
1993), Coir pith (Kadirvelu et al., 2001) and parthenium plant (Kadirvelu et al., 2001,
2002). ACs were prepared from the agricultural solid wastes, silkcotton hull, coconut
tree sawdust, sago waste, maize cob, and banana pith and used to eliminate heavy metals
and dyes from aqueous solution. High-surface-area ACs in granular form were prepared
by chemical activation of pistachio-nut shells with potassium hydroxide (Yang and Lua,
2003). AC was prepared from chickpea husk by chemical activation with K
2
CO
3
(Hayashi
et al., 2002).
Pyrolysis is an established process method for preparation of activated carbon. The
biomass samples are subjected to pyrolize for obtaining biochars at high temperature
(450–1250 K) in a cylindrical reactor batch reactor. When the pyrolysis temperature
increases the biochar yield decreases (Arni, 2004). The biochar can be used as an AC.
The biochar yield increased with increasing particle size of the sample.
Physical, Chemical, and Adsorption Properties of the Materials
Table 1 shows the elemental composition of coal samples from different Turkish re-
sources. The physical properties of fly ashes from Turkish coal resources are given in
Table 2. The adsorption properties of ACs, Afsin-Elbistan and Seyitomer fly ashes for
Ni(II), Cu(II), and Zn(II) are tabulated in Table 3. Table 4 shows the density and silica
content of ash from rice husks.
Low-cost and nonconventional adsorbents include agricultural wastes, such as nat-
ural compost, Irish peat, planer shell, walnut shell, and biomass, such as Aspergillus
tureens and Macular remanniamus (Azab and Peterson, 1989), chitoson (Muzzarelli and

Activated Carbons and Fly Ashes 631
Table 1
Elemental composition of coal samples from different Turkish resources (wt%)
O
Source C H N S (by diff.) Reference
Afsin-Elbistan 68.9 4.6 1.8 5.2 19.5 Kara and Mirzaoglu, 1998
Beypazari 62.5 5.3 2.1 9.1 21.0 Simsek and Olcay, 1995
Beysehir 60.5 5.6 1.8 0.9 31.2 Kara and Ceylan, 1988
Can 72.6 5.2 2.3 3.5 16.3 Vayisoglu et al., 1996
Dadagi 71.3 5.3 1.7 3.3 18.4 Kara and Ceylan, 1988
Ermenek 65.5 5.4 1.8 0.8 26.5 Kara and Ceylan, 1988
Gediz 64.7 5.0 — 4.2 — Yaman and Kucukbayrak,
1996
Goynuk 61.0 5.6 1.7 3.3 28.4 Simsek and Olcay, 1995
Ilgin 62.4 5.7 1.9 0.7 29.3 Kara and Ceylan, 1988
Seyitomer 71.0 5.2 2.1 1.7 20.1 Artok et al., 1994
Soma 71.6 5.2 1.8 3.7 17.7 Vayisoglu et al., 1996
Tuncbilek 71.9 5.4 2.6 3.2 16.9 Simsek and Olcay, 1995
Yatagan 65.3 5.1 1.5 5.5 22.7 Simsek and Olcay, 1995
Yeniceltek 74.0 5.8 2.8 2.3 15.2 Simsek and Olcay, 1995
Zonguldak 88.3 5.2 1.0 0.6 4.9 Simsek and Olcay, 1995
Rocchetti, 1986), and peat moss (Chaney and Hundemann, 1979). Oxidized anthracite
(Petrov et al., 1992), silica gel (Filho et al., 1995a), bituminous coal (Singh and Rawat,
1994), goethite (Johonson, 1990), blast furnace sludge (Lopez-Delgado et al., 1998), red
mud (Apak et al., 1998; Lopez et al., 1998), lignin modified with glycerol (Demirba¸s,
2004), modified lignin from pulping waste (Celik and Demirba¸s, 2004), wollastonite
(Sharma et al., 1990), bentonite (Bareket et al., 1997), and peat (McKay and Porter,
1997) have also been tried for the removal of Cd(II) from water and wastewater. Acti-
vated carbon obtained from peanut hull (Periasamy and Namasivayam, 1994), almond
Table 2
Physical properties of fly ashes from Turkish coal resources
Source Coal type
Bulk density
(g/cm
3
)
Specific gravity
(g/cm
3
)
Specific
surface area
(m
2
/g)
Afsin-Elbistan Lignite 1.05 2.70 0.342
Catalagzi Bituminous 1.07 1.95 0.139
Seyitomer Lignite 0.88 1.58 0.115
Soma Lignite 0.95 2.12 0.207
Tuncbilek Lignite 1.11 1.83 0.094
Yatagan Lignite 1.07 1.99 0.334
Yenikoy Lignite 1.44 2.99 0.168
Source: Bayat, 1998.

632 A. Demirba¸setal.
Table 3
Adsorption properties of activated carbon, Afsin-Elbistan and
Seyitomer fly ashes for Ni(II), Cu(II) and Zn(II)
Percentage removal
Equilibrium
Adsorbent period (h) Ni(II) Cu(II) Zn(II)
Activated carbon 1.5 79.9 98.5 97.1
2.0 87.5 99.2 99.1
3.0 85.6 99.2 98.9
Afsin-Elbistan fly ash 1.5 89.6 97.7 91.9
2.0 97.7 98.0 94.4
3.0 96.0 98.0 93.3
Seyitomer fly ash 1.5 88.1 92.1 60.6
2.0 90.0 93.8 85.3
3.0 88.5 94.4 85.8
Source: Bayat, 2002.
shell, olive stones, and peach stones (Ferro-Gracia et al., 1988) and commercial activated
carbons have also been used for Cd(II) removal. Marshall and Johns (1996) have used
agricultural by-products as adsorbents for removal of metal ions from aqueous solution.
The adsorption properties of ACs were strictly defined by the physicochemical nature
of their surface and their texture—pore volume, pore size distribution, surface area.
Activated carbons are characterized by their high adsorption capacities. Although the
highly active surface properties of the ACs are often attributed to the chemical functional
groups, surface morphology plays a significant role in determining the surface availability.
The surface characteristics of the clean and saturated granular activated carbon particles
were analyzed by scanning electron microscope (SEM). Pore size distribution has been
used to describe the internal structures and adsorption capacities of activated carbons
(Davies et al., 1999). The highly active surface properties of the activated carbon are
attributed to the chemical functional groups and the internal surface areas, which typically
range from 500 to 3000 m
2
/g.
The analysis of the images taken by SEM showed that macropores were not accessi-
ble by the large phenolic organic used in the study. Adsorption was more efficient on the
edges of the carbon surface. The rough surfaces had a higher adsorption potential for the
Table 4
Density and silica content of ash from rice husks
Temperature (K) Density (g/cm
3
) SiO
2
(wt%)
773 1.825 83.66
873 1.923 91.50
973 1.938 91.85
1073 1.960 92.90
Source: Yalcın and Sevinc, 2001.

Activated Carbons and Fly Ashes 633
phenolic compound used. As a result, the rough surfaces, which showed a higher per-
centage of edge area, also had a higher adsorption potential. The smooth surface showed
a thin layer of adsorption.
Many techniques have been used for the characterization of activated carbons. This
includes infrared spectroscopy, X-ray diffraction, scanning electron microscopy, trans-
mission electron microscopy, optical microscopy, iodine number, ion-exchange capacity
and apparent surface area estimation by nitrogen adsorption (El-Sheikh et al., 2004).
It is well known that the pH of the solution-adsorbant mixture is an important variable
in the adsorption process. It is reported that metal removal by ACs is a strongly pH-
dependent process within the range of pH 1–6 (Corapcioglu and Huang, 1987). The pH
influence is less important at pH > 6. Metal adsorption increases slightly with an increase
of ionic strength, due to the compression of the electrostatic double layer (EDL) (Chen
and Lin, 2001). Competitive effect can play a significant role for those weakly adsorbed
metal ions; however, it becomes less important for those strongly adsorbed metals. Other
factors include metal and adsorbent concentration and temperature. In order to simulate
the adsorption kinetics, the equilibrium models must be first obtained. The linear, the
Freundlich and Langmuir isotherms, as well as the surface complex formation models
are used to represent the equilibrium relationship (Tien, 1994; Chen and Wang, 2004).
The adsorption of Cr(III) in aqueous solution was investigated on a series of ozonized
activated carbons, analysing the effect of oxygenated surface groups on the adsorption
process. A study was carried out to determine the adsorption isotherms and the influence
of the pH on the adsorption of this metal. The adsorption capacity and affinity of the
adsorbent for Cr(III) increased with the increase in oxygenated acid groups on the surface
of the activated carbon (Rivera-Utrilla and Sánchez-Polo, 2003).
The adsorption of lead(II) and copper(II) on an AC (Filtrasorb 300, Chemviron) was
characterized assuming that it takes place by formation of complexes with functional
groups, present in the AC. The effect of the pH was also examined, in the range 4–6,
obtaining that the adsorption increases at increasing pH (Pesavento et al., 2003).
Previous studies have reported the adsorbing of metals to some organic acids which
contain carboxyl ligands (Korshin et al., 1998). At lower pHs, the carboxyl groups retain
their protons, reducing the probability of them adsorbing to any positively charged ions.
Whereas at higher pHs (above 4.0), the carboxyl groups are deprotonated and as such
are negatively charged. These negatively charged carboxylate (–COO–) ligands attract
the positively charged metal ions and adsorbing occurs.
Table 5 shows the comparison of adsorption capacity for Cd(II) with different ad-
sorbents. In Table 5, among the adsorbants, fly ash has the highest adsorption capacity
(198.2 mg/g) for Cd(II). Almond shell AC has the lowest adsorption capacity (2.7 mg/g).
Conclusion
The aim of this work is to study inexpensive and effective metal ion adsorbents such as
AC, fly ash, chemically modified material from coal and biomass to offer these adsor-
bents as replacements for existing commercial materials. Commercially available ACs
are expensive. A wide variety of ACs have been prepared from agricultural wastes.
The adsorption properties of ACs were strictly defined by the physicochemical nature
of their surface and their texture—pore volume, pore size distribution, surface area.
Activated carbons are characterized by their high adsorption capacities. Metal ion binding
was rapid, indicating that the metals were probably adsorbed to the pores structure of
the adsorbant. Physical and chemical structure, surface area, porosity, and pH of the

634 A. Demirba¸setal.
Table 5
Comparison of adsorption capacity for Cd(II) with different adsorbents
Adsorption
capacity
Adsorbent (mg/g) Reference
Almond shell AC 2.7 Ferro-Gracia et al., 1988
Bituminous coal 6.5 Singh and Rawat, 1994
Fly ash 198.2 Lopez et al., 1998
Fly ash washed with water 195.2 Lopez et al., 1998
Fly ash washed with acid 195.2 Lopez et al., 1998
Fe(III)/Cr(III) hydroxide 40.5 Namasivayam and Ranganathan,
1995
Furnace sludge 7.4 Lopez-Delgado et al., 1998
Goethite 3.1 Johonson, 1990
Granular activated carbon 11.1 Periasamy and Namasivayam,
1996
Lignin modified with glycerol 7.5 Demirba¸s, 2004
Modified lignin from pulping waste 7.7 Celik and Demirba¸s, 2004
Modified silica gel 33.7 Filho et al., 1995a
Moss 46.6 Low and Lee, 1991
Olive stone AC 5.9 Ferro-Gracia et al., 1988
Oxidized anthracite 28.1 Petrov et al., 1992
Peach stone AC 3.3 Ferro-Gracia et al., 1988
Peanut hull AC 89.4 Periasamy and Namasivayam,
1994
Peat 21.1 McKay and Porter, 1997
Red mud acid-treated 46.9 Lopez et al., 1998
Red mud acid-treated at 600
◦
C 66.8 Lopez et al., 1998
Red mud washed with water 66.8 Lopez et al., 1998
solution-adsorbant mixture are important variables in the adsorption process. Parameters
such as the agitation time, metal ion concentration, adsorbent dose are also important.
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