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Indian Journal of Chemical Technology
Vol. 13, May 2006, pp. 203-217
Conventional and non-conventional adsorbents for removal of pollutants from
water – A review
Amit Bhatnagara,b* & A K Minochab
aDepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India
bEnvironmental Science & Technology Division, Central Building Research Institute, Roorkee 247 667, India
Email: amit_b10@yahoo.co.in
Received 7 September 2005; revised received 28 February 2006; accepted 10 March 2006
In the present article, the suitability of activated carbon and other alternative adsorbents for wastewater treatment has
been reviewed. It is evident from literature survey of last 20-25 years that researchers have gained success to some extent in
developing inexpensive adsorbents for water pollution control utilizing naturally available and waste materials. However,
still there is a need to find out the practical utility of such developed adsorbents on large-scale and safe and eco-friendly
disposal of spent adsorbents.
Keywords: Water pollution, Wastewater treatment, Adsorption, Activated carbon, Low-cost adsorbents
Among the various known forms of pollution, water
pollution is of great concern since water is the prime
necessity of life and extremely essential for the
survival of all living organisms. Indeed, it is a part of
life itself, since the protoplasm of most living cells
contains about 80% of water. It is worthy noting that
only 0.02% of the total available water on the earth is
immediately available for use in the form of rivers,
lakes and streams.
However, years of increased industrial, agricultural
and domestic activities have resulted in the generation
of large amount of wastewater containing a number of
toxic pollutants, which are polluting the available
fresh water continuously. With the realization that
pollutants present in water adversely affect human
and animal life, domestic and industrial activities,
pollution control and management is now a high
priority area. The availability of clean water for
various activities is becoming the most challenging
task for researchers and practitioners worldwide.
As a result of the serious efforts of researchers all
over the world in the field of pollution control and
management, a number of methodologies with
varying degrees of success have been developed to
manage water pollution. Some of them involve
coagulation, foam flotation, filtration, ion exchange,
sedimentation, solvent extraction, adsorption,
electrolysis, chemical oxidation, disinfection,
chemical precipitation and membrane process1,2.
However, these methods have their own shortcomings
and limitations. For example, the methods based on
chemical/biological oxidation, ion exchange and
solvent extraction have shown low efficiency for the
removal of trace levels of pollutants3. Further,
coagulation4 requires pH control and causes further
problems of sludge disposal, whereas, ozonation5
while removing colour effectively does not minimize
chemical oxygen demand (COD).
Among various available technologies for water
pollution control listed above, ‘adsorption’ process is
considered better as compared to other methods
because of convenience, easy operation and simplicity
of design. Further, this process can remove/minimize
different type of pollutants6 and thus it has a wider
applicability in water pollution control.
Although certain phenomenon associated with
adsorption were known in ancient times, the first
quantitative studies were reported by C.W. Scheele7
in 1773 on the uptake of gases by charcoal and clays.
This was followed by Lowitz observations who used
charcoal for decolorization of tartaric acid solutions.
Larvitz8 in 1792 and Kehl8 in 1793 observed similar
phenomenon with vegetable and animal charcoals,
respectively. However, the term ‘adsorption’ was
proposed by Bois-Reymond but introduced into the
literature by Kayser9. Ever since then, the adsorption
process has been widely used for the removal of
solutes from solutions and gases from air atmosphere.
INDIAN J CHEM. TECHNOL., MAY 2006
204
The extent of adsorption depends on the nature of
adsorbent especially its porosity and surface area. As
such, various adsorbents showing higher and
sometimes selective adsorption have been developed.
A fundamentally important characteristic of good
adsorbents10,11 is their high porosity and consequent
larger surface area with more specific adsorption
sites. Most adsorbents which have been used in
pollution control have porous structure. The porous
structure not only increases surface area and
consequently adsorption but also the kinetics of the
adsorption. A better adsorbent is the one with large
surface area and which requires less time for
adsorption equilibrium. Hence, one generally looks to
adsorbents with high surface area and faster kinetics
for the removal of pollutants. Some of the important
adsorbents used in pollution control and various
industrial operations are discussed herein.
Silica gel is the most widely used desiccant
(adsorbent for moisture) because of its large
adsorption capacity for water (~ 40% by weight). This
quality is due to its relatively weak bonds with water
as well as larger pore volume and mesoporosity12.
Further, ease in regeneration (~ 150°C) makes silica
gel most widely used desiccant. The gel is considered
a good adsorbent and is used in many industries for
drying of gases and liquids, purification of
hydrocarbons etc.13,14.
Activated alumina and bauxite
Activated alumina comprises partially
hydroxylated alumina oxide, Al2O3. They are porous
solids made by thermal treatment of aluminum
hydroxide precursors and find applications mainly as
adsorbents, catalyst and catalyst support. In general,
as a hydrous alumina precursor is heated, hydroxyl
groups are driven off leaving a porous solid structure
of activated alumina. One of the earliest uses of
activated alumina was removal of water vapour from
gases and this still remains an important application.
Activated alumina having the surface area ranging
from 200-300 m2/g15, is a versatile adsorbent and has
been successfully utilized for the removal of As(V),
PO43-, Cl- and F- from water besides other
applications12. Alumina is particularly effective for
adsorption of As(V) which exists in water as H2AsO4-.
Studies16 have shown that use of fixed bed activated
alumina can reduce the concentrations of arsenic from
50-70 to 5 µg/L in treated waters. Similarly, activated
alumina has also been found a potential adsorbent in
defluoridation of water17, where fluoride contents < 1
mg/L were achieved from a raw water with 3 mg/L
fluoride by using activated alumina as adsorbent.
Activated alumina is receiving renewed attention as
an adsorbent18-20.
On the other hand, bauxite consists of mainly
aluminum hydroxide minerals but also contains
small and variable amounts of silica, iron oxides-
hematite, Fe2O3, and magnetite, Fe3O4, rutile or
titanium oxide and alumina silicate clays. It is
widely used in place of alumina. Its surface area
ranges7 from 25 to 250 m2/g.
Zeolites and ion exchange resins
Zeolites are aluminosilicates with Si/Al ratios
between 1 and infinity. There are 40 natural and over
100 synthetic zeolites. They are also considered as
selective adsorbents. Zeolites generally show a
surface area15 in the range of 1-20 m2/g. Zeolite-based
materials are used in detergent manufacture, ion-
exchange resins (i.e. water softeners), catalytic
applications in the petroleum industry, separation
process (i.e. molecular sieves) and as an adsorbent for
water, carbon dioxide and hydrogen sulphide. Various
zeolites have been employed for the removal of water
pollutants by various researchers e.g. Handreck et
al.21 employed zeolites for the removal of methylene
blue dye from water, whereas Okolo et al.22 utilized
zeolites for the removal of phenols and chlorophenols.
Besides this, Ellis and Korth23 investigated the use of
zeolites for the removal of geosmin and
methylisoborneol from drinking water.
A number of ion-exchange resins have also been
used for the removal of specific organic compounds.
Weak and strong acid-type resins used for removal of
cations are called cation exchangers whereas base-
type resins that remove anions are called anion
exchangers. The primary applications of ion-exchange
resins are the softening and deionization of water.
Other applications are waste treatment, catalysis,
purification of chemicals and pharmaceutical.
Recently, anion-exchange resins have been used by
Karcher et al.24 for the removal of dyes.
Activated carbon
Activated carbon has undoubtedly been the most
popular and widely used adsorbent in wastewater
treatment throughout the world. Charcoal, the
forerunner of modern activated carbon has been
recognized as the oldest adsorbent known in
wastewater treatment. Its ability to purify water dates
back to 2000 B.C. Lowitz established the first use of
BHATNAGAR & MINOCHA: ADSORBENTS FOR POLLUTANTS REMOVAL FROM WATER⎯REVIEW
205
charcoal for the removal of bad tastes and odours
from water on an experimental basis in 1789-1790.
The credit of developing commercial activated
carbon25 however goes to Raphael von Ostrejko
whose inventions were patented in 1900 and 1901.
Early applications of carbon in water treatment plant
to remove chlorophenolics were reported by Baylis in
U.S. and Sierp in Germany in 1929.
Activated carbon is produced by a process
consisting of raw material dehydration and
carbonization followed by activation. The starting
material is dehydrated and carbonized by slowly
heating in the absence of air. Carbonization converts
this organic material to primary carbon, which is a
mixture of ash, tars, amorphous carbon and crystalline
carbon (elementary graphitic crystallites). During
carbonization, some decomposition products or tars
are deposited in the pores, but are then removed in the
activation step.
Activation is essentially a two phase process
requiring burn off of amorphous decomposition
products (tars), plus enlargement of pores in the
carbonized material. Burn off frees the pore openings,
increasing the number of pores, and activation
enlarges these pore openings. The resulting product
obtained is known as activated carbon and it generally
has a very porous structure with a large surface area
ranging from 600-2000 m2/g.
Activated carbons can be prepared from a variety
of carbon containing materials25,26, such as coke27,
olive stones28, pinewood29, rice hulls30, palm shell31,
Pinus caribaea sawdust32, anthracite33, plum
kernels34, Moringa oleifera seed husks35, peat,
bituminous coal, coconut shell36, palm fruit bunch
particles37 etc. However, the activated carbon used in
wastewater treatment is generally prepared from
coconut shells, peat, sawdust, wood char, lignin,
petroleum coke, bone char, anthracite coal etc.6
The activated carbon generally exists in two forms
(i) powdered activated carbon (PAC) and (ii) granular
activated carbon (GAC). Since granular form is more
adaptable to continuous contacting and there is no
need to separate the carbon from the bulk fluid, most
of the work on the removal of pollutants from water
has been on GAC. On the other hand, the use of PAC
offers some practical problems because of separation
requirement of the adsorbent from the fluid. However,
inspite of these problems, PAC is also used for
wastewater treatment due to low capital cost and
lesser contact time requirements38. Two more specific
forms viz. activated carbon fibrous (ACF) and
activated carbon clothe (ACC) are also in use39,40.
Activated carbon has become the standard
adsorbent for the reclamation of municipal and
industrial wastewaters to potable water quality.
Numerous researchers have studied the applications
of activated carbon in water and wastewater
treatment. It is not possible here to discuss each and
every finding, however, some of the important
findings are being discussed herein illustrating the
role of activated carbon for the removal of different
types of pollutants from water.
Removal of phenolic pollutants by activated carbon
Activated carbon has been successfully employed
for the removal of phenol and substituted phenols
from water by various researchers. The mechanism of
phenol adsorption on carbon surface was explained by
Mattson et al.41. They suggested that the role of
donor-acceptor complex mechanism involving
carbonyl oxygen groups of the carbon surface acting
as electron donor and aromatic ring of the adsorbate
as acceptor is important in the adsorption of phenols
on carbon surface. Zogorski et al.42 studied the
removal of phenols using activated carbon and
suggested that the process is feasible, efficient and
economical to diminish the phenol concentration to
acceptable levels in drinking waters. Paprowicz43
proved that chemical methods based on oxidation of
phenol by chlorine, ozone or chlorine dioxide and
biochemical methods of decompositions of phenols
on biologic beds or activated sludge, do not remove
whole load of phenol from wastewater. It was
suggested that activated carbons are suitable for
phenol containing wastewater treatment and
powdered form may be used in conjunction with
coagulation chemical process.
Adsorption of phenol, p-chlorophenol and p-
nitrophenol on activated carbons was studied by
Wang et al.44 who found that adsorption ability of
granular carbon is better than powdered carbon for
removal of phenols. Colella et al.45 investigated the
adsorption of twelve mono-, di- and trichlorophenols
from aqueous solutions while Jung et al.46 studied the
adsorption of phenol and chlorophenols on four
commercial granular activated carbons. The results of
these investigations46 suggest that the adsorption of
phenol and chlorophenols is controlled by interaction
of π electrons of activated carbon and phenols.
Recently, the influence of carbon-oxygen surface
groups on the adsorption of phenols by activated
INDIAN J CHEM. TECHNOL., MAY 2006
206
Table 1 ⎯ Adsorption capacities of some conventional and non-conventional adsorbents for the removal of phenols from water
S. No. Adsorbent Phenols Adsorption capacity (mg/g) References
1 Activated carbon Phenol
p-Chlorophenol
213
434
50
2 Activated carbon Phenol 256.97 51
3 Activated carbon Phenol
2,3,4-Trichlorophenol
140
500
52
4 (ACF-307)
(ACF-310)
(GAC-S)
(GAC-E)
Phenol 239.2
263.1
142.8
10.44
47
5 Activated carbon from bituminous coal Phenol 93-213 53
6 Activated carbon from apricot stone shells Phenol
m-Cresol
p-Cresol
2-Chlorophenol
4-Nitrophenol
2,4-Dichlorophenol
2,4-Dinitrophenol
27.5-120
28-113
48-120
54-125
48-248
125-595
162-333
54
7 Activated carbons from used tea leaves Phenol,
o-, m-Cresol,
4-Chlorophenol,
4-Nitrophenol,
2,4-Dichlorophenol,
2,4-Dinitrophenol
80-438 48
8 Biological activated carbon Phenol
2,4-Dichlorophenol
25
43.7
55
9 Burnt wood charcoal Phenol 1-7 56
10 Bentonite p-Chlorophenol 10.63 57
11 Bentonite Phenol 0.43-1.71 58
12 Perlite p-Chlorophenol 5.84 57
13 Lake sediments Phenols 28-67 59
14 Na and
K- montmorillonite
Phenol, m-Cresol,
m-Nitrophenol,
p-Bromophenol
29-109
60
15 Chemically treated saw dust Pyrogallol, Pyrocatechol 28-52 61
16 Sawdust
Polymerized sawdust
Sawdust carbon
Phenol 146.25
185.18
138.88
62
17 Iron(III) hydroxide loaded marble Pyrogallol, Pyrocatechol 9-10 63
18 Palm seed coat o-Cresol 19.58 64
19 Bituminous shale 2-Chlorophenol
2,4-Dichlorophenol
3.1
4.2
65
20 Fly ash Phenol
3-Chlorophenol
2,4-Dichlorophenol
67
20
22
66
21 Fly ash Phenol
4-Chlorophenol
2,4-Dichlorophenol
5.58-6.48
8.62-10.0
8.16-8.72
67
22 Fly ash Phenol 0.23 68
23 Fly ash and impregnated fly ash Phenol,
o-Cresol,
m-Cresol,
p-Cresol,
o-Nitrophenol,
m-Nitrophenol,
p-Nitrophenol
3.8-6.3
3.1-4.7
3.5-5.5
4.6-6.7
5.8-6.9
6.5-8.3
7.8-9.6
69
24 Coal fly ash Phenol 549.99 51
BHATNAGAR & MINOCHA: ADSORBENTS FOR POLLUTANTS REMOVAL FROM WATER⎯REVIEW
207
Table 2 ⎯ Adsorption capacities of some conventional and non-conventional adsorbents for the removal of dyes from water
S. No. Adsorbent Dyes Adsorption capacity (mg/g) References
1 Activated carbon
Filtrasorb 400
Deorlene yellow
Talon blue
200
175
70
2 Activated carbon Indigo carmine dye 16.3 – 77.7 78
3 Carbon prepared from waste jack fruit peel Malachite green 166.37 79
4 Buffing dust based activated carbon Acid brown dye 6.24 80
5 Charfins
Lignite coal
Bituminous coal
Activated carbon
Direct brown dye 6.4
4.1
2.04
7.66
81
6 Carbonaceous adsorbent prepared from pearl millet husk Methylene blue 82.37 82
7 Activated carbon
Activated carbon from Hazelnut
Raw kaolinite
Montmorillonite
Acid red 1495
111
29
19
83
8 Rice husk carbon Safranine
Methylene blue
236–310
182–274
84
9 Rice husk ash Acid violet 49
Acid blue 15
Acid violet 17
Acid violet 54
Acid red 119
99.4–155 85
10 Coal Chrome dye 0.62–0.74 86
11 Sagaun sawdust Crystal violet
Methylene blue
Malachite green
Rhodamine b
2.1–3.5
2.0–3.3
1.9–3.3
1.4–2.3
87
12 Activated clay Basic blue 69
Basic red 62
Acid blue 25
Disperse blue 183
Direct red 227
Reactive red 123
394
406.3
256.1
49.64
37.88
36.63
88
13 Neem leaf powder Brilliant green 133.69 89
14 Chitin R 222 100 90
15 Eucalyptus bark Remazol B.B 90 91
16 Dead fungus Aspergillus niger Congo red 14.72 92
17 Maize cob Atrazon blue 160.0 93
18 Orange peel Acid violet 17 19.88 94
19 Banana peel Methyl orange
Methylene blue
Rhodamine B
Congo red
Methyl violet
Amido black 10 B
17.2
15.9
13.2
11.2
7.9
7.9
95
20 Orange peel Methyl orange
Methylene blue
Rhodamine B
Congo red
Methyl violet
Amido black 10 B
15.8
13.9
9.1
7.9
6.1
3.8
95
21 Peat, bentonite, slag, fly ash Disperse red I 23-50 96
22 Metal hydroxide- Sludge Azo reactive dyes 48-62 97
23 Chrome sludge Acid blue 69
Acid blue 25
Reactive yellow 2
Basic blue 3
Methylene blue
58.8
32.3
41.7
0.18
0.51
98
Contd.
INDIAN J CHEM. TECHNOL., MAY 2006
208
carbons was studied by Bansal et al.47. The results of
these studies indicated that while the presence of
acidic carbon-oxygen surface groups which were
evolved as CO2 suppressed the adsorption of phenol,
the presence of non-acidic surface groups which were
evolved as CO tends to enhance the adsorption of
phenol.
Singh and Srivastava48 reported that the adsorption
on activated carbon increases up to pH 6 and then
decreases with further increase in pH. Favourable
adsorption of phenol at low pH on activated carbon
was also observed by Mahesh et al.49. Several other
reports50-69 are also available dealing with the
removal/adsorption of phenols with activated carbons
and other low cost adsorbents. Table 1 shows some of
the conventional and non-conventional adsorbents
used in removing phenols from water along with their
respective adsorption capacities.
Removal of dyes by activated carbon
Activated carbon has also been investigated
extensively for the removal of different classes of
dyes and colouring materials from water. McKay70
investigated the ability of one activated carbon
Filtrasorb type (size 1.4-2.8 mm) to remove a range of
dyestuffs (acidic, basic, disperse and direct dyes) from
water. For the basic, acidic and disperse dyes, carbon
was found to be an excellent adsorbent, but direct dye
showed less affinity for adsorption. The author
reported high adsorption capacities for deorlene
yellow (200 mg/g) and telon blue
(175 mg/g). In another report the same author also
provided an evidence71 of high adsorption capacities
(985 mg/g) for basic dyes on carbon (150-200 μm).
Al-Degs et al.72 used different types of activated
carbons for the removal of cationic dye, methylene
blue and an anionic dye, reactive black and reported
that adsorption of dyes is higher on activated carbons
having higher surface area. In another study, Al-Degs
et al.73 investigated the effect of carbon surface
chemistry using Filtrasorb 400 activated carbon on the
adsorption of three anionic reactive dyes in water. The
adsorption followed the following order: Remazol
yellow > Remazol black > Remazol red. Porter74
demonstrated that adsorption by activated carbon is an
effective and complete treatment for the textile
wastewater. Granular activated carbon Filtrasorb 400
was used by Walker and Weatherley75 to treat a
ternary solution of acid dyes and the process plant
effluents containing the dyes in a fixed-bed column
system. The breakthrough data obtained by column
studies correlated with equilibrium adsorption
capacities of 537, 535 and 852 mg/g for tectilon blue
4R (TB 4R), tectilon red 2B (TR 2B) and tectilon
orange 3G (TO 3G), respectively. The authors
suggested that a dye possessing a higher adsorption
capacity will show a long breakthrough time and
relatively efficient use of carbon in column systems.
Meshko et al.76 studied the adsorption of two basic
dyes, Maxilon Schwarz FBL-01 (MS-300) and
Maxilon Goldgelb GL EC (MG 400) from water by
granular activated carbon alongwith zeolite in a batch
system. The results showed that activated carbon
showed stronger affinity compared to zeolite for dyes
removal. It was also obsereved that saturation
capacities for both adsorbents for MG-400 were lower
than the MS-300. It was argued that the molecules of
MS-400 are probably unable to penetrate easily into
the pores of the adsorbents whereas the molecules of
MS-300 have less hindrance. Competitive adsorption
of three basic dyes was studied by Allen et al.77 who
found that the adsorption potential of an individual
dye decreased in the presence of second or third dye.
Several other reports78-102 are also available dealing
with the removal/adsorption of dyes with activated
carbons and other low cost adsorbents. Table 2 shows
some of the conventional and non-conventional
adsorbents used with their respective adsorption
capacities in removing dyes from water.
Table 2 ⎯ Adsorption capacities of some conventional and non-conventional adsorbents for the removal of dyes from water
⎯
Contd
S. No. Adsorbent Dyes Adsorption capacity (mg/g) References
24 Refused derived fuel Methylene blue 83 99
25 Bagasse
Wood charcoal
Methyl violet ~ 5
~ 1.6
100
26 Activated carbon
Chitin
Radish leaves
Remazol brilliant-
Violet 5 R
13.6
38.2
40.0
101
27 Calcium alunite Reactive blue 114
Reactive yellow 64
Reactive red 124
170.7
236
153
102
BHATNAGAR & MINOCHA: ADSORBENTS FOR POLLUTANTS REMOVAL FROM WATER⎯REVIEW
209
Removal of metal ions by activated carbon
Activated carbon has also been employed for the
removal of many toxic metal ions from water. McKay
et al.50 investigated the ability of Filtrasorb 400 for
the removal of Hg(II) and Cr(III) ions besides other
pollutants. The saturation capacity of the activated
carbon was found to be 35 and 138 mg/g for Cr(III)
and Hg(II) ions, respectively. Lead removal studies
with activated carbon were performed by Reed and
Arunachalan103. The adsorption capacity of activated
carbon was found to be 30 mg/g for lead removal by
the authors. The adsorption of mercury, cadmium and
lead on heat treated and sulphurized activated carbon
was investigated by Gomez-Serrano et al.104. They
pointed out that adsorption was very much higher for
mercury than for Cd(II) and Pb(II) for all the
adsorbents. Adsorption of Cr(VI) from water using
activated carbon was also investigated105. Maximum
adsorption capacity of activated carbon105 was found
to be 145 mg/g for Cr(VI) within a pH range of
2.5–3.0. Activated carbon was also used for the
removal of Cd(II) from water106. The maximum
adsorption potential of activated carbon was reported
to be 8 mg/g at pH 8 for Cd(II).
Different types of granular activated carbons were
used by Leyva-Ramos et al.107 for removal of Zn(II)
and they reported the adsorption capacity of about 18
mg/g at pH= 7.0. Adsorption of Ni(II) from water on
activated carbon (prepared from coirpith) has been
investigated by Kadirvelu et al.108. The adsorption
capacity of activated carbon was found to be 62.5
mg/g at initial pH of 5.0 at 30°C for the particle size
Table 3 ⎯ Adsorption capacities of some conventional and non-conventional adsorbents for the removal of metal ions from water
S. No. Adsorbent Metal ions Adsorption-capacity (mg/g) References
1 Activated carbon Cr(III)
Hg(II)
35
138
50
2 Activated carbon Pb(II) 30 103
3 Activated carbon Cr(VI) 145 105
4 Activated carbon Cd(II) 8 106
5 Activated carbon prepared from coirpith Ni(II) 62.5 108
6 Activated carbon from solvent extracted olive-pulp Zn(II) 4.6-33.6 109
7 Parthenium carbon Hg(II) 10 110
8 Peat Cu(II) 19.56 111
9 Sphagnum peat moss Cr(VI) 132 112
10 Perlite Cd(II) 0.42 113
11 Wollastonite Ni(II) 6.52 114
12 Chitin Cd(II) 14 115
13 Chitosan Cd(II) 5.93 116
14 Chitosan Hg(II)
Cu(II)
Ni(II)
Zn(II)
815
222
164
75
117
15 Saw-dust Cu(II) 13.8 118
16 Treated sawdust
Anion resin
Activated alumina
Cr(VI) 111.6
17.1
9.6
119
17 Rice husk carbon Cr(VI) 45.6 120
18 Orange peel Ni(II) 158 121
19 Red mud Cu(II)
Zn(II)
Cd(II)
Ni(II)
19.72
12.59
10.57
10.95
122
20 Waste Fe(III)/Cr(III)-hydroxide Cr(VI) 1.38-1.5 123
21 Blast furnace sludge Pb(II)
Cu(II)
Cr(III)
Cd(II)
Zn(II)
64.17-79.87
16.07-23.66
9.55-16.05
6.74-10.15
4.25-9.65
124
22 Blast furnace slag Pb(II)
Cr(VI)
40
7.5
125
23 Fly ash Cu(II) 1.39 126
24 Fly ash Hg(II) 2.82 127
INDIAN J CHEM. TECHNOL., MAY 2006
210
of 250-500 μm. The authors further reported that
adsorption of Ni(II) increased with pH from 2-7 and
remained constant upto 10. The removal of Zn(II) by
activated carbons (prepared from solvent extracted
olive pulp) was carried out by Galiatsatou et al.109
who reported adsorption capacity in the range of
4.6-33.6 mg/g for the prepared activated carbon for
Zn(II).
Several other reports110-127 are also available
dealing with the removal/adsorption of metal ions
with activated carbons and other low cost adsorbents.
Table 3 shows some of the conventional and non-
conventional adsorbents used with their respective
adsorption capacities in removing metal ions from
water.
Besides the above pollutants viz. phenols, dyes and
metal ions, activated carbon has also been
successfully utilized for the removal of
detergents128,129, pesticides130,131, humic
substances132,133, chlorinated hydrocarbons134,135 and
many other chemicals and organisms136-138.
Modified activated carbon
It has been observed by various workers that
chemical treatment, at the time of activation during
the manufacture of activated carbons, often enhances
the adsorption properties. Swiatkowski et al.139
modified activated carbons for the adsorption of
selected heavy metal ions. They reported that carbon-
oxygen and carbon-nitrogen surface species were
formed on the activated carbons by treating it with
concentrated HNO3 or NH3. Choma et al.140
investigated the changes in surface and structural
properties of porous carbons modified by different
oxidizing agents such as H2O2, HClO4 and HNO3.
They reported that the surface properties of oxidized
carbons depend on the type of oxidizing agent as well
as oxidation conditions. Activated carbons were also
chemically modified by Park and Jang141 by treating
them with hydrochloric acid and sodium hydroxide.
They observed that the adsorption of Cr(VI) ions was
more in the case of acid treatment on activated
carbons resulting due to the increase of acid values (or
acidic functional groups) of activated carbon surfaces.
However, activated carbons treated with a base was
not significantly effective for the adsorption of Cr(VI)
ions, probably due to the effect of the decrease of
specific surface area and basic nature of Cr(VI).
Regeneration of spent activated carbon
The activated carbons are used to purify water and
this is mostly done with column operations. The
columns are generally made with activated carbons.
After use, the columns get exhausted and are no more
capable of further adsorption of pollutants. Once the
activated carbon has been exhausted, it has to be
regenerated for further use. A number of methods are
used for this purpose. The most common technique
practiced in the regeneration of used activated carbon
is thermal treatment142,143. Besides this, chemical
regeneration of spent activated carbon has also been
tried. Martin and Ng144 used acetic and formic acids to
regenerate carbon exhausted by adsorption of
commercial humic acid and reported high
regeneration efficiencies. Regeneration of exhausted
carbon has been reported using NaOH by Newcombe
and Drikas145, acetone by Kilduff and King146,
methanol by Rollar and co-workers147 and through
oxidation by Notthakum148. Regeneration of
exhausted activated carbon has also been investigated
through electrochemical technique by Narbaitz and
Cen149 and Zhang et al.150. They also reported good
regeneration efficiencies for activated carbons.
Low cost alternative adsorbents
Activated carbon has been found to be a versatile
adsorbent, which can remove diverse types of
pollutants such as metal ions, dyes, phenols and a
number of other organic and inorganic compounds
and bio-organisms. However, its use is sometimes
restricted due to higher cost. Due to the higher cost of
activated carbon, attempts are being made to
regenerate the spent activated carbon. Chemical as
well as thermal regeneration methods are used for this
purpose. However, these procedures are not very
cheap and also produce additional effluents and result
in considerable loss of the adsorbent. Therefore, in
situations where cost factors play a major role,
scientists are looking for low cost adsorbents for
control of water pollution. As such, for quite
sometime, efforts have been directed towards
developing low cost alternative adsorbents. A wide
variety of materials have been investigated151 for this
purpose and they can be classified into three
categories: (i) natural materials (ii) agricultural wastes
and (iii) industrial wastes. These materials are
generally available free of cost or cost little as
compared to activated carbons.
Naturally occurring materials as adsorbents
Various naturally occurring materials having
characteristics of an adsorbent, are available in large
quantities. The abundance of these materials in most
BHATNAGAR & MINOCHA: ADSORBENTS FOR POLLUTANTS REMOVAL FROM WATER⎯REVIEW
211
continents of the world and their low cost make them
suitable as adsorbents for the removal of various
pollutants from wastewaters. Among the naturally
occurring adsorbents, chitin is fairly abundant. It is
found in the exoskeleton of shellfish and crustaceans.
It has been used as an adsorbent for the removal of
pollutants from effluents115. Benguella and
Benaissa115 reported the adsorption capacity of 14
mg/g of chitin for Cd(II) ions. However, as compared
to chitin, chitosan, which is produced by alkaline N-
deacetylation of chitin, is considered more important
than chitin for adsorption purposes and has been
investigated intensively. Jha et al.116 studied the
utilization of chitosan for cadmium removal. They
reported an adsorption capacity of 5.93 mg of Cd(II)/g
of chitosan at a pH range of 4.0-8.3 and further
observed that the presence of ethylene diamine tetra
acetic acid (EDTA) significantly decreased the
cadmium removal. The adsorption of some other
metal ions on chitosan was also investigated by
McKay et al.117. It was found that the adsorption
capacity of chitosan for Hg(II), Cu(II), Ni(II) and
Zn(II) were 815, 222, 164 and 75 mg/g, respectively.
Chitosan was also investigated for dyes removal by
various researchers152-154.
Peat is another naturally occurring material
containing lignin and cellulose as major constituents
and has been studied as an adsorbent by various
workers. Poots et al.155 studied the utilization of peat
without any treatment for the removal of Talon blue.
The adsorbent was found to possess adsorption
capacity of 16.3 mg/g on particles of size 150-200
μm. These workers suggested that in spite of its low
adsorption capacity, peat could be used as a low cost
adsorbent in place of activated carbon and the spent
material can be disposed off. Sharma and Forster112
investigated the utility of sphagnum peat moss for the
removal of Cr(VI). A good adsorption potential (132
mg/g) of sphagnum peat moss in removing Cr(VI)
was reported112 at pH 1.5-3.0. Viraraghavan and
Maria156 investigated adsorption characteristics of
peat alongwith fly ash and bentonite for the removal
of phenol from wastewater and found that the removal
efficiency is in the order: peat > fly ash > bentonite.
Peat has also been used by a number of other
workers157-159, as an adsorbent for metals and dyes
removal from wastewaters.
Wood is the most widely spread natural material
and its use as adsorbent for the removal of Talon blue
was first investigated by Poots et al.160. Its adsorption
capacity for the dye varied from 6.95 to 11.56 mg/g
for particle size ranging from 710-1000 and 150-250
μm, respectively. The drawback of this adsorbent was
the long equilibration time required for adsorption and
the low adsorption capacity. However, the same
adsorbent when used for the removal of Astrozone
blue161 exhibited a higher adsorption capacity of 100.1
mg/g for the dye for particles of size 150-250 μm and
much lesser equilibration time (2 h).
The natural coal was used as an adsorbent for the
removal of dyes by Mittal et al.162. The coal was
sulphonated, heated in a water bath and was used as
adsorbent. Sorption and desorption of two basic dyes,
rhodamine B and methylene blue and acidic dye
Sandola rhodine was studied. The desorption studies
indicated that methylene blue and rhodomine B
sorption is not governed by physiosorption while the
adsorption of sandola rhodine is physical in nature.
The coal was also used as adsorbent for the removal
of chrome dye from aqueous solutions by Gupta
et al.86 who reported very low adsorption capacity
(0.62–0.74 mg/g). Besides natural coal, other coal-
based adsorbents viz. charfins, lignite coal and
bituminous coal were also examined by Mohan et
al.81 for dye removal and adsorption capacities of
these adsorbents were found between 6.4 and 7.66
mg/g. Bhattacharya and Venkobachar163 investigated
the use of Girdish coal (GC) for the removal of
cadmium and found that it had an adsorption capacity
of 0.91 mg/g.
Bentonite, another naturally occurring material
shows a wide range of industrial applications
including clarification of edible and mineral oils,
paints, cosmetics and pharmaceuticals. The
abundance of bentonite in most countries and its low
cost makes it a suitable adsorbent for the removal of
many pollutants from wastewaters. Studies have
shown its ability to bind and remove pathogenic
viruses, pesticides, herbicides and other toxins164,165.
The potential of bentonite for phenol adsorption from
aqueous solutions was studied by Banat et al.58. They
reported that the adsorption of phenol increases with
increasing phenol concentration and decreases with an
increase in the pH of solution. Bentonite showed
adsorption capacity in the range of 0.43-1.71 mg/g for
phenol removal in this study. Bentonite along with
perlite was also investigated as adsorbent by
Koumanova and Peeva-Antova57 for the removal of p-
chlorophenol. In this case, a higher adsorption
capacity (10.63 mg/g) was observed as compared to
INDIAN J CHEM. TECHNOL., MAY 2006
212
that for perlite (5.84 mg/g). Perlite was also used by
Mathialagan and Viraraghavan113 for cadmium
removal from aqueous solutions. The adsorption
capacity of perlite113 for Cd in column operations
using Thomas model was found to be 0.42 mg/g.
The adsorption potential of Sagaun sawdust
(Tectona grandis), a naturally occurring material in
removing four basic dyes from water was investigated
by Khattri and Singh87. Low adsorption capacities
(1.4-3.55 mg/g) of this adsorbent for dyes removal
were observed by these workers. Eucalyptus bark was
also investigated91 as adsorbent for the removal of
Remazol BB dye. The dried bark showed a good
adsorption potential of 90 mg/g of dye at pH 2.5 and
at 18°C. The ability of wollastonite (an abundantly
naturally occurring clay mineral), to remove Ni(II)
ions from water was investigated by Sharma et al.114.
They reported adsorption capacity of wollastonite as
6.52 mg/g for Ni(II).
A comparative study of activated carbon with
natural adsorbents (chitin and radish leaves) for the
removal of a reactive dye, remazol brilliant violet 5R
from aqueous solutions was carried out by Sanghi and
Bhattacharya101. They found adsorption capacities of
activated carbon, radish leaves and chitin to be 13.6,
40.0 and 38.2 mg/g, respectively. The ability of a wild
plant material viz. Parthenium for the removal of
Hg(II) was tested by Kadirvelu et al.110. The
adsorption capacity of this material was found to be
10 mg/g at initial pH of 5.0 at 30 ± 2°C for the
particle size of 125–250 μm. Varghese et al.166
investigated the use of aquatic plant, water hyacinth to
prepare a novel activated carbon for the removal of
phenol, p-chlorophenol and p-nitrophenol. The
maximum adsorption capacity of the prepared
activated carbon was reported to be 1.20, 1.28 and
1.35 mmol/g for phenol, p-chlorophenol and p-
nitrophenol, respectively.
Agricultural wastes as adsorbents
The disposal of waste materials is increasingly
becoming a cause for concern52,166,167 because these
wastes represent unused resources. A large amount of
solid wastes are produced in the agricultural sector in
most countries of the world. A major part of this
waste is normally used as a domestic fuel. However,
for better utilization of this cheap and abundant
agricultural waste, it can be explored as a low cost
alternative adsorbent owing to relatively high fixed
carbon content and presence of porous structure.
Rengaraj et al.168 developed activated carbon from
rubber seed coat for removal of phenols using batch
and column operations. It was suggested that the
adsorbed phenol can be desorbed by sodium
hydroxide. The adsorption process was found to
follow first order kinetics and the isotherm fitted to
both Freundlich and Langmuir equations. Rengaraj et
al.64 also examined the suitability of palm seed coat
for the adsorption of o-cresol and found it to have an
adsorption capacity of 19.58 mg/g with film diffusion
as the rate limiting step. Daifullah and Girgis54 used
chemically treated and low activated apricot stone
shells for the removal of substituted phenols and
reported that di-substituted phenols are adsorbed in
larger amounts than mono-substituted ones. Almond
husk was used as a potential adsorbent for the
removal of Ni(II) ions by Hasar169. The activated
carbons were prepared from almond husk by
activating without (MAC-I) and with (MAC-II)
H2SO4 at different temperatures. The studies proved
that MAC-II performed better. Hirata et al.170
investigated the feasibility of carbonaceous material
produced from coffee grounds for the removal of two
basic dyes, methylene blue and gentian violet and
found that the adsorption of dyes depended upon the
surface polar groups present on the carbonaceous
material. The potential of pearl millet husk (PMHC)
as an adsorbent was explored by Inbaraj et al.82 who
reported an adsorption capacity of 82.37 mg/g of this
adsorbent for methylene blue at pH 6.0. They further
reported that methylene blue adsorption on PMHC is
a chemisorption process and formic acid could be
used to remove the adsorbed dye. Peanut hull was
converted into an adsorbent by Namasivayam and
Periasamy171 by treating it with concentrated
sulphuric acid, then carbonizing it in air and further
treating with 1% sodium bicarbonate overnight. The
treated material was used as an adsorbent for the
removal of Hg(II) ions from aqueous solutions and
the adsorption was found to conform to both
Freundlich and Langmuir isotherms. The same
adsorbent was also used172 for Cd(II) removal and it
was observed that the adsorption conforms to
Freundlich model better than Langmuir.
Chamarthy et al.173 also prepared an adsorbent
from peanut shell by heat treatment in presence of
phosphoric acid or citric acid and used it for the
adsorption of Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II).
Their investigations showed that phosphoric acid
modified shells adsorbed metal ions in larger amounts
BHATNAGAR & MINOCHA: ADSORBENTS FOR POLLUTANTS REMOVAL FROM WATER⎯REVIEW
213
compared to citric acid modified shells. Farro-Gracia
et al.174 examined the use of processed almond shell,
olive stones and peach stones, for the removal of
Zn(II), Cd(II) and Cu(II) from aqueous solutions. The
prepared adsorbents were found to have appreciable
surface areas, 876, 1103 and 1316 m2/g, respectively.
Bagasse pith, a waste product from sugarcane
industry has been studied by McKay et al.175 without
any pretreatment for the removal of two basic dyes
and two acidic dyes from aqueous solutions. High
adsorptive capacity was observed for the adsorption
of basic dyes, 158 mg/g for basic blue 69 and 177
mg/g for basic red 22 while lower capacity of 23 mg/g
and 22 mg/g was observed for acid red 114 and acid
blue 25, respectively.
Besides these, several other agricultural wastes viz.
rice husk84,85,120, corncob waste176, coir pith108,177,
plum kernels178 have also been investigated. However
besides few reports, the adsorption potential of these
adsorbents was found low as compared to activated
carbon.
Industrial wastes as adsorbents
Widespread industrial activities are producing large
amount of solid waste materials. Some of these
materials are being put to use while others find no
proper utilization and are dumped elsewhere. The
industrial waste material is available almost free of
cost and causes major disposal problem. If the solid
wastes could be used as low cost adsorbents, it will
provide a two-fold advantage in reducing the
pollution. Firstly, the volume of waste materials could
be partly reduced and secondly the developed low
cost adsorbent can reduce the pollution of
wastewaters at a reasonably cost. In view of the low
cost of such adsorbents, it would not be necessary to
regenerate the spent materials. With this view, a
number of industrial wastes have been investigated
with or without treatment as adsorbents for the
removal of pollutants from wastewaters. The major
solid waste byproduct of thermal power plants based
on coal burning is fly ash. Fly ash is produced as a
fine, non-combustible residue carried off in the flue
gas with relatively uniform particle size distribution in
the 1-10 μm range. The annual production of fly ash
from coal burning power plants has continued to
increase, yet its overall utilization is marginal.
Currently, the main uses of fly ash include
construction of roads, bricks, cement etc. The high
percentage of silica and alumina in fly ash make it a
good material for utilization as an inexpensive
adsorbent for bulk use. Some studies on this aspect
have been carried out. Haribabu et al.67 investigated
the use of fly ash for the removal of phenol and
chlorophenols and found the process to be
endothermic with first order kinetics. In a similar
study Akgerman and Zardkoohi66 investigated the use
of fly ash as an adsorbent for the removal of phenolic
compounds and found that it had the adsorption
capacity of 67, 20 and 22 mg/g for phenol,
3-chlorophenol and 2,4-dichlorophenol, respectively.
Fly ash was also studied by Viraraghavan and
Ramakrishna179 for the removal of cationic and
anionic dyes. The process was found to follow first
order kinetics and the isotherms conformed to both
Freundlich and Langmuir models. Panday et al.126
used fly ash without any pretreatment for the removal
of Cu(II) and found that the adsorption data conforms
to Langmuir model. The results of all these studies
have revealed that fly ash is not a very good adsorbent
due to its low adsorption efficiency as compared to
activated carbon. Fly ash has also been used in
conjunction with other materials180, but the adsorptive
capacities were found to be on the lower side for these
mixtures also.
The steel industry produces a number of wastes in
large quantities such as blast furnace slag, dust and
sludge etc. and these have also been investigated as
adsorbents. Yamada et al.181 studied phosphate removal
using soft and hard granulated slag and observed that
phosphate adsorbed well on soft granulated slag than the
hard granulated slag and explained this observation on
the basis of porosity of the adsorbent. On the other hand,
Dimitrova182 investigated ungranulated blast furnace
slag for the removal of Cu(II), Ni(II),
and Zn(II) ions from water in the concentration range of
1 × 10-4–1 × 10-3 M and reported that slag alkalizing
activity creates conditions for adsorption through
hydroxo complex formation and colloidal particles of
silicic acid. Recently, slag columns were utilized by the
same workers183 for lead removal. Other waste materials
generated in steel industry are blast furnace sludge and
blast furnace flue dust, which have also been tried as
possible adsorbents. Jallan and Panday184 reported the
use of untreated blast furnace sludge as adsorbent for the
removal of some toxic ions viz. Pb(II), Ni(II), Cd(II),
Cu(II), Zn(II) and CN-. It was found that sludge has a
good adsorptive capacity for metal ions as well as
cyanide but the adsorption (9 mg/g) was poor in the case
of Zn(II). Sludge was also tested as adsorbent for the
removal of some heavy metal ions by López-Delgado
INDIAN J CHEM. TECHNOL., MAY 2006
214
et al.124 who reported that metal ions are adsorbed in the
order, Pb> Cu > Cr > Cd > Zn. Patnaik and Das185
investigated the use of blast furnace flue dust as
adsorbent for the removal of Cr(VI) and found the first
order kinetics for the adsorption process.
Red mud, a solid waste product of aluminium
industry produced during bauxite processing, was
tested as adsorbent by López et al.122 for wastewater
treatment. The maximum adsorption capacities for
Cu(II), Zn(II), Ni(II) and Cd(II) were found to be
19.72, 12.59, 10.95 and 10.57 mg/g, respectively for a
contact time of 48 h. Red mud was also studied by
Çengeloğlu et al.186 for the removal of fluoride from
aqueous solutions. They used both the original and
activated red mud forms in batch equilibration
technique and found that the adsorption capacity of
activated form, for fluoride removal, was higher than
that of original form. The maximum removal of
fluoride occurred at pH 5.5. Chrome sludge, a solid
waste material from electroplating industry, was
used98 as an adsorbent for removal of colour. The
results indicated that the sludge had a better affinity
for acid dyes than basic dyes. Fe(III)/Cr(III)
hydroxide, a waste material from the fertilizer
industry has been used by Namasivayam et al.123 for
the adsorption of Cr(VI) from aqueous solutions. The
adsorption data fitted with both Freundlich and
Langmuir models. The use of another fertilizer
industry waste viz. carbon slurry was also explored by
Srivastava et al.187. Sekaran et al.80 used buffing dust,
waste generated from leather industry, for the removal
of dyes. The adsorption capacity of buffing dust was
found to be 6.24 mg/g at pH 3.5 and at temperature
30°C for acid brown dye. The adsorption of phenols
on papermill sludges was studied by Calce et al.188
who observed its retention capacity in the order: 2-
nitrophenol = 4-nitrophenol << 2-chlorophenol <
phenol <4-chlorophenol ≤ 3-chlorophenol < 2,4-
dichlorophenol < 3,4-dichlorophenol = 2,4,5-
trichlorophenol < 3, 5-dichlorophenol.
The adsorbents developed by utilizing industrial
wastes have shown a tendency to remove inorganic
contaminants (metal ions) more effectively as
compared to organic constituents (dyes, phenols etc.)
Biosorbents
The removal of pollutants from effluents utilizing
biological materials is a relatively recent
advancement. It was only in the 1990s that a new
technology, biosorption developed that could also
help to recover heavy metals from wastewaters. The
first reports described how abundant biological
materials could be used to remove, at very low cost,
even small amounts of toxic heavy metals from
industrial effluents189. Various biosorbents190-195 have
been tested for the removal of pollutant especially
metal ions with very encouraging results.
Conclusions
In spite of prolific use of activated carbon in
wastewater treatment, its use is sometimes restricted
because of its higher cost. To replace the expensive
activated carbon, a wide range of inexpensive
adsorbents have been investigated utilizing naturally
occurring materials and waste products of different
industries. Some of them were found to be quite
satisfactory. However, still, there is a strong need to
conduct extensive research on the following points:
(i) To improve the removal
efficiencies/adsorption capacities of such
prepared adsorbents after chemical
modifications or appropriate treatment.
(ii) Cost factor is also an important point that
should be considered before selecting
such developed adsorbents in water
pollution control.
(iii) Last but not the least, it is very important
to dispose of the spent adsorbents in an
environmental friendly way. Only limited
information is available in literature about
safe disposal of spent adsorbents. More
efforts should be made in this direction.
If it is possible to develop such adsorbents having
all the above-mentioned characteristics, then these
adsorbents may offer significant advantages over
currently available commercially expensive activated
carbons and, in addition contribute to an overall waste
minimization strategy.
Acknowledgements
Amit Bhatnagar is grateful to Prof A K Jain,
Department of Chemistry, IIT, Roorkee for guidaance
and encouragement. The authors wish to thank the
reviewers for their valuable comments and useful
suggestions, which significantly improved the quality
of this paper.
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