ARTICLE IN PRESS
Water Research 38 (2004) 3043–3050
Removal of water pollutants with activated carbons prepared
from H3PO4 activation of lignin from kraft black liquors
E. Gonzalez-Serranoa, T. Corderoa, J. Rodriguez-Mirasola, L. Cotorueloa,
J.J. Rodriguezb,*
a
Department of Chemical Engineering, University of Malaga, Spain
b
Chemical Engineering, University Autonoma of Madrid, Spain
Received 12 February 2003; received in revised form 4 February 2004; accepted 19 April 2004
Abstract
Activated carbons with a high BET surface area and a well-developed porosity have been prepared from pyrolysis of
H3PO4-impregnated lignin precipitated from kraft black liquors. Impregnation ratios within the range of 1–3 and
activation temperatures of 623–873 K have been used, giving rise to carbons with different porous and surface chemical
structure. Increasing the activation temperature and the impregnation ratio leads to a widening of the porous structure
with a higher relative contribution of mesoporosity. The potential application of these carbons for the removal of water
pollutants has been investigated by measuring their adsorption capacities for phenol, 2,4,5-trichlorophenol and Cr (VI)
as representative of toxic contaminants found in industrial wastewaters. The results obtained compare well and even
favorably with those reported in the literature for other activated carbons. An impregnation ratio and an activation
temperature around 2 g H3PO4/g lignin and 700 K, respectively, are recommended as the best combination of operating
conditions to prepare activated carbons for aqueous phase applications although at lower values of these two variables
carbons with good adsorption capacities are also obtained.
r 2004 Elsevier Ltd. All rights reserved.
Keywords: Activated carbon; Lignin; Adsorption; Water pollutants; Phenol; 2,4,5-trichlorophenol; Cr (VI)
1. Introduction
Activated carbons are the most important commercial
adsorbents. Their high surface area together with their
surface chemical structure allows them to be used in a
wide variety of industrial applications, some of the most
important dealing with the environmental field and
particularly with water purification and industrial
wastewater cleaning [1,2]. In these applications adsorption with activated carbon is most commonly oriented
toward the removal of species which are recognized as
*Corresponding author. Ingenieria Quimica, Facultad de
Ciencias, Universidad Autonoma de Madrid, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain..
E-mail address: [email protected] (J.J. Rodriguez).
toxic pollutants, like phenols, halogenated organic compounds and chromium (VI), among others, whose presence
in aqueous effluents is legally restricted to very low limits.
Phenol and its derivatives represent an important
group of refractory organic compounds present in a
variety of industrial wastewaters because they are used
as intermediates in the synthesis of dyes, pesticides,
explosives, insecticides, etc. Chlorophenols are among
the most toxic pollutants found in industrial wastewaters. Work on adsorption of phenol and phenol
derivatives with activated carbons has been reported in
the literature [3–8].
Chromium is one of the most important heavy metals
because of its relative frecuency and high toxicity. It is
present commonly as Cr(VI) and Cr(III). The former is
considered as a powerful carcinogenic agent that
0043-1354/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.watres.2004.04.048
ARTICLE IN PRESS
3044
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
modifies the DNA transcription process causing important chromosomic aberrations. The removal of both
forms of chromium from aqueous phase with activated
carbons has been also reported by different authors [9–
12,7,13,14].
A wide diversity of carbonaceous materials have been
used as precursors for activated carbon. Lignin has
demonstrated its potential application in that respect
from both physical (CO2) and chemical activation with
ZnCl2 [15–17]. In this work we present our results on the
preparation of activated carbons from H3PO4 activation
of lignin precipitated from kraft black liquors and the
application of these carbons as adsorbents to remove
different water pollutants. Phenol, 2,4,5-trichlorophenol
and Cr(VI) have been chosen as representative target
contaminants. Previous work on H3PO4 activation of
other precursors, including lignocellulosic materials and
coals, has been reported in the literature [18–24].
2. Materials and methods
The lignin used in this work as a starting material was
isolated from Eucalyptus Grandis kraft black liquors by
acid precipitation. A complete typical analysis of this
starting material has been reported in previous works
[16,17]. After precipitation the lignin was centrifuged
and dried in a fluidized bed. Prior to impregnation with
H3PO4, the lignin was washed with 1% (w/w) H2SO4
aqueous solution followed by distilled water at 333 K
and dried at 60 C in a vacuum dryer. After this the
lignin had less than 0.1% ash content. It was impregnated by incipient wetting with 85% (w/w) aqueous
H3PO4 at room temperature and dried during 24 h at
333 K in a vacuum dryer. The impregnation ratio
(r ¼weight of H3PO4 relative to that of dry lignin) was
varied from 1 to 3.
The impregnated lignin was thermally treated under
continuous N2 flow in an electrically heated horizontal
tube furnace. In each experiment the activation temperature was reached at a 10 K/min heating rate and
then maintained for 2 h. Different activation temperatures within the 623–873 K range were investigated. The
activated samples were cooled inside the furnace,
maintaining the N2 flow, and then washed with distilled
water at 333 K until neutral pH and negative phosphate
analysis in the eluate. The resulting activated carbons
were dried at 373 K and weighted to determine the yield
of the activation process. The yield values (weight of
activated carbon relative to lignin, dry basis) fall always
within a relatively narrow range of 44–52%. The carbon
samples are identified with a P followed by two numbers
indicating the impregnation ratio and the activation
temperature (K). Thus, the sample P2/698 corresponds
to the activated carbon prepared at r ¼ 2 and 698 K
activation temperature.
The porous structure of the activated carbons was
characterized from N2 adsorption–desorption at 77 K
and mercury porosimetry. The N2 isotherms were
obtained in a Quantachrome Autosorb-1 apparatus
after outgassing the samples at 453 K and 103 Torr. A
porosimeter 4000 of Carlo Erba was used for mercury
porsimetry. The apparent surface area was obtained
from the BET equation within the 0.05–0.15 relative
pressure range. The micropore volume and the external
or non-microporous surface area were obtained from
the as method [25]. The mesopore volume was obtained
by combining the information derived from the BET
isotherms (2–4 nm diameter range) and the mercury
porosimetry (4–50 nm diameter range) [17]. The pH of
the activated carbon samples in CO2-free distilled water
has been determined by mixing 1 g of activated carbon
with 35 cm3 of water. The suspensions were shaken and
thermostated at 298 K for 2 days.
Evaluation of surface carbon–oxygen groups was
accomplished by Thermal Programmed Desorption
(TPD) of activated carbon samples. These were performed under a continuous He flow at 10 K/min with
heating rate up to a final temperature of 1173 K. The
evolution of CO and CO2 was analyzed by mass
spectrometry using an MSC 200 Balzers apparatus with
a tungsten filament.
The liquid phase adsorption experiments were performed by contacting 100 ml of aqueous solution of
adsorptive at different starting concentrations with a
weight of activated carbon adjusted close to 10 mg in
150 ml stoppered bottles placed in a thermostated shaker
at 298 K. Several samples were prepared to obtain each
experimental point of the isotherm so that we could
analyze the residual concentration in the aqueous phase
at different contact times up to equilibration. Phenol
and 2,4,5-trichlorophenol were determined by UV
spectrophotometry at 279 and 203 nm wavelength,
respectively. Chromium was analyzed by atomic absorption spectrometry. The equilibrium values have been
fitted to the Langmuir (q ¼ ðKe qm Ce Þ=ð1 þ Ke Ce Þ) and
Freundlich (q ¼ KCen ) equations. From the Langmuir
equation the monolayer adsorption capacity, qm ; and the
equilibrium constant, Ke ; were calculated. In the Freundlich equation, K is a constant related to the adsorption
capacity and n is an empirical parameter representative of
the magnitude of the adsorption driving force.
3. Results and discussion
3.1. Characterization of the activated carbons
3.1.1. Porous structure
Figs. 1 and 2 show the N2 adsorption–desorption
isotherms of the activated carbons obtained at different
temperatures and impregnation ratios, respectively.
ARTICLE IN PRESS
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
V (cm3(STP)/g AC)
Table 1 summarizes the structural characteristics of
these carbons.
All the carbons show a modified type I isotherm
corresponding to a predominantly microporous structure with a contribution of mesoporosity whose
magnitude and distribution depends on the two aforementioned variables.
As can be seen, activation proceeds at relatively low
values of temperature, giving rise to a considerable
development of BET surface area. At an impregnation
ratio of 2 more than 1000 m2/g are reached at 623 K. The
surface reaches a maximum value close to 1500 m2/g at
around 700 K and then decreases moderately up to the
highest temperature investigated (873 K). This trend is
quite similar to that reported by other authors for
H3PO4 activation of different precursors but the values
of surface area reached reveal a fairly good behavior of
lignin as compared with most of those precursors
[19,20,26,22,24].
All the activated carbons prepared within the thermal
range investigated show fairly high values of micropore
volume and its evolution with activation temperature
becomes parallel to that of the BET surface area. A
800
P2/698
700
P2/773
600
P2/873
500
similar situation is observed with regard to the total
mesopore volume and to the external or non-microporous surface area. The relative contribution of external to
the total (or BET) surface area reaches a maximum
value close to 20% at around 700 K and then decreases
slowly up to a 15% at 873 K. The activation temperature
does not show a significant effect on the distribution of
mesopore size, falling in all the cases the ratio between
the volume of mesopores wider than 8 nm and the total
volume of mesopores within a 55–60%. A moderately
wider distribution of microporosity, as obtained from
the MP method [27], has been observed at increasing
activation temperature.
The impregnation ratio r does not show a remarkable
effect on the BET surface area within the range tested
but it affects significantly to the distribution of porosity.
At 698 K activation temperature, at the lowest r value
(r ¼ 1) more than 98% of the surface area is associated
to the micrporosity whereas at r ¼ 2 the non-microporous surface area represents 20% of total BET surface
area and at r ¼ 3 this relative contribution reaches
almost a 50% which corresponds to a fairly mesoporous
structure. Thus, an increase of the impregnation ratio
gives raise to a considerable widening of the porous
structure of the resulting carbons with a substantially
higher contribution of mesoporosity. Nevertheless, that
widening effect does not appear so clear and systematic
when looking at the pore size distribution within the
mesopore range itself.
P2/623
400
300
200
100
0
0.0
0.2
0.6
0.4
0.8
1.0
P/Po
Fig. 1. N2 adsorption–desorption isotherms (77 K) of activated
carbons obtained at different temperatures with r=2.
800
P2/698
700
V (cm3(STP)/g AC)
3045
P3/698
600
500
400
P1/698
300
200
100
0
0.0
0.2
0.4
0.6
0.8
1.0
P/Po
Fig. 2. N2 adsorption–desorption isotherms (77 K) of activated
carbons obtained at different impregnation ratios (activation
temperature, 698 K).
3.1.2. Surface chemical structure
Activated carbons bear different oxygen surface
groups whose nature and amount depend on the starting
material and the activation treatment [1]. The carbon–
oxygen groups of acidic character (carboxylic, lactonic)
evolve as CO2 upon thermal desorption whereas the
non-acidic (carbonyl, ether, quinone) and phenol groups
give rise to CO. Anhydride evolve as both CO and CO2
[28].
Table 2 reports the amounts of CO and CO2 evolved
from TPD of some of the activated carbons up to a final
temperature of 900 C. According to these results,
increasing the activation temperature and the impregnation ratio decreases the presence of oxygen acidic
groups on the surface of the resulting carbons, although
the relative amount of these type of groups is in all the
cases fairly low and even, no CO2 was detected from the
TPD of the activated carbon prepared at the highest
activation temperature investigated (873 K). On the
contrary, the amount of carbon–oxygen surface groups
evolving as CO compares well and even favorably with
that reported for many other activated carbons including surface modified carbons, by oxidation [9,28]). An
increase of the activation temperature increases the total
amount of carbon–oxygen surface groups and the same
can be said with regard to the impregnation ratio
ARTICLE IN PRESS
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
3046
Table 1
Characterization of porous structure of activated carbons
Ativated
carbon
ABET
(m2/g)
External
area (m2/g)
Micropore
volume, Vs
(cm3/g)
Mesopore
volume
(20 ÅoDo80 Å)
(cm3/g)
Mesopore
volume
(80 ÅoDo500 Å)
(cm3/g)
Total
mesopore
volume
(cm3/g)
P2/623
P2/698
P2/773
P2/873
P1/698
P3/698
1031
1459
1372
1244
1336
1363
45
281
146
195
18
662
0.57
0.82
0.74
0.70
0.62
0.36
0.08
0.27
0.25
0.23
0.03
0.26
0.10
0.26
0.37
0.34
0.13
0.46
0.18
0.53
0.62
0.57
0.16
0.72
Table 2
CO and CO2 evolved from TPD of activated carbons
P2/698
P2/773
P2/873
P1/698
P3/698
CO2 (mg/g)
7.1
5.8
E0
7.7
6.7
CO (mg/g)
63
79.6
110.4
59.9
75.5
Total
equivalent O
(mg/g)
41.2
49.7
63.1
39.8
48.0
P2/773
180
160
P2/873
140
q (mg/g AC)
Carbon
sample
200
P2/698
120
P2/623
100
80
P2/698(pH=3)
60
40
20
0
0
although in this case the effect seems to be less
significant.
20
40
60
80
100 120
Ce (mg/l)
140
160
180
200
Fig. 3. Adsorption isotherms of phenol (298 K) on the
activated carbons obtained at different activation temperatures
(pH=6, unless indicated).
3.2. Adsorption results
As indicated before the potential application of these
activated carbons as adsorbents for removal of water
pollutants have been checked for three target species
chosen as representative of toxic organic (phenol and
2,4,5-trichlorophenol) and inorganic (Cr(VI)) contaminants.
3.2.1. Phenol
Fig. 3 shows the adsorption isotherms obtained for
phenol at 298 K with the activated carbons prepared at
different activation temperatures and constant r ¼ 2:
The figure includes also information on the effect of pH
on the adsorption of phenol.
As a first conclusion the adsorption capacities
compare fairly well and even favorably with those
reported in the literature for other activated carbons
[18,29,30,4,7,8].
The differences observed on the adsorption capacities
of these carbons cannot be explained from their different
BET surface area. In fact, a reliable correlation between
this and the Langmuir monolayer capacity was not
obtained. Using the micropore volume instead of the
surface area provides a much better correlation with the
relative adsorption capacities of these carbons as can be
seen in Fig. 4. The values reported in that figure can be
fitted to a linear equation given by the following
expression:
qm ¼ 260:8Vs þ 20:8;
where qm represents the Langmuir monolayer adsorption capacity (mg Phenol/g activated carbon) and Vs is
the micropore volume of each carbon (cm3/g). Nevertheless, looking at the correlation coefficient (0.92) and
the deviations of the slope and intercept values (738
and 724, respectively), this equation has to be taken
only as an approximate representation on the trend of
qm versus Vs :
Nevertheless, the micropore volume alone does not
appear sufficient to understand the trend observed on
the adsorption capacities of the different carbons. In
fact, the P2/698 sample, which presents the highest
micropore volume, yields a somewhat lower capacity
than the two other carbons obtained at the same
impregnation ratio but at higher activation temperatures. As indicated before, an increase of the activation
temperature increases the presence of carbon–oxygen
surface groups of the non-acidic character (CO evolving
ARTICLE IN PRESS
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
250
3047
500
P2/773
P2/873
P2/698
450
400
200
q (mg/gAC)
qm (mg/g AC)
350
150
100
P2/623
300
250
200
150
100
50
50
0
0
0
0
0.1
0.2
0.3
0.4
0.5
Vs (cm3/g AC)
0.6
0.7
0.8
0.9
Fig. 4. Langmuir monolayer adsorption capacities of phenol
versus the micropore volume of activated carbons.
groups) and this may compensate the effect of a lower
micropore volume. The influence of basic surface oxygen
groups on the adsortion of phenol by activated carbons
has been reported in the literature [6,31,7].
3.2.2. 2,4,5-trichlorophenol
The adsorption isotherms obtained at 298 K for 2,4,5trichlorophenol with the activated carbons prepared at
different activation temperatures are depicted in Fig. 5.
Again, as a first conclusion, a comparison of the
adsorption capacities obtained with those reported in
the literature [30,4] reveal the feasibility of these carbons
for this potential application.
In spite of the differences in water solubility and
molecular weight between 2,4,5-trichlorophenol and
phenol, the amounts adsorbed become quite comparable
and even similar in terms of mmol of adsorbate/g
activated carbon. Nevertheless, the so-called relative
affinity toward the adsorbent, namely the product of the
equilibrium constant and the monolayer capacity from
the Langmuir equation, qm Ke (see Table 3), becomes
substantially higher for 2,4,5-trichlorophenol as expected from its less hydrophilic character and the
presence in this molecule of electron-withdrawing –Cl.
Electron withdrawal or deactivation of the benzenic ring
favors the formation of electron donor–acceptor complexes between these ring and basic groups on the
surface of activated carbons, increasing in that way the
qm Ke value.
Again, as in the case of phenol, there is no systematically consistent dependence of the adsorption capacity of the different carbons with the BET surface area.
Now the micropore volume does not allow either to
obtain such a dependence most probably because the
accessibility to the whole microporosity of the carbons is
more restricted in the case of trichlorophenol than for
phenol. A complete explanation of the relative adsorption capacity of these carbons based only on the porous
structure has not been found because the uptake of
5
10
15
20
25
30
Ce (mg/l)
35
40
45
50
Fig. 5. Adsorption isotherms of 2,4,5-trichlorophenol (298 K)
on activated carbons obtained at different activation temperatures (r=2).
trichlorophenol from aqueous phase is the result of a
combined effect of porosity and surface oxygen groups.
Looking at this last there is a reasonably good
dependence of the aforementioned relative affinity and
the amount of those surface groups. Anyway, the
differences found among the adsorption capacities of
these carbons are relatively low, with the highest and
lowest values of the Langmuir monolayer capacity
differing slightly more than a 10% of the average value.
3.2.3. Chromium (VI)
Fig. 6 reports the adsorption isotherms obtained for
Cr (VI). According to the adsorption capacities of these
carbons their feasibility for Cr (VI) removal from
aqueous solution compares fairly well, and in many
cases favorably, with that of many other activated
carbons reported in the literature [9,11,32].
The relative adsorption capacity of the different
carbons increases with the activation temperature and
with the impregnation ratio both of which are related
with a widening of the porous structure. Although the
size of Cr (VI) should allow a relatively easy access to
the microporosity, that access may be partly hindered by
the existence of negative surface oxygen groups of basic
character at the entrance of micropores [33]. In fact, the
differences observed among the adsorption capacities of
these activated carbons cannot be explained consistently
with the micropore volume values. At lower pH (3) the
adsorption capacity increases significantly as can be seen
in Fig. 6. These results can be explained if Cr(VI) in the
presence of activated carbons is partially reduced to
Cr(III); this reduction takes place at acid pH on the
surface of the carbon and has been described in the
literature [1,11] ), besides, chromium is now adsorbed as
anion, Cr(VI), and as cation, Cr(III). In our case, the pH
of carbons used in this study is between 2.4 and 2.8, and
in the case of the adsorption of Cr(VI) at pH=3, the
reduction of Cr(VI)–Cr(III), in the carbon surface, is
ARTICLE IN PRESS
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
3048
Table 3
Isotherms fitting parameters (298 K)
Adsorbate
Activated carbon
Langmuir
Freundlich
qm (mg/g)
Ke (l/mg)
R
2
n
Ka
Phenol
(pH=6)
P2/623
P2/698
P2/773
P2/873
P1/698
P3/698
169.5
200.0
227.3
212.8
188.7
107.5
0.11
0.11
0.18
0.16
0.15
0.65
0.96
0.97
0.99
0.91
0.88
0.99
0.56
0.58
0.45
0.35
0.36
0.20
TCPhb
(pH=6)
P2/623
P2/698
P2/773
P2/873
P1/698
P3/698
416.7
454.5
476.2
434.8
384.6
400.0
0.13
0.15
0.25
0.26
0.33
0.19
0.96
0.93
0.97
0.99
0.98
0.97
0.47
0.36
0.34
0.41
0.35
0.38
65.2
103.1
129.4
100.5
107.9
90.6
0.98
0.99
0.99
0.99
0.96
0.99
Cr(VI)
(pH=7)
P2/698
P2/773
P2/873
P1/698
P3/698
39.7
42.6
49.3
34.0
55.9
0.10
0.08
0.06
0.06
0.01
0.99
0.99
0.97
0.98
0.91
0.29
0.29
0.31
0.39
0.76
10.2
10.3
10.3
5.3
1.1
0.97
0.99
0.96
0.96
0.96
Cr(VI)
(pH=3)
P2/698
P2/773
P2/873
P1/698
P3/698
84.0
84.7
84.0
81.3
92.6
0.14
0.10
0.27
0.07
0.22
0.99
0.99
0.99
0.98
0.99
0.35
0.37
0.30
0.40
0.31
18.7
15.9
24.5
13.1
25.2
0.86
0.99
0.79
0.88
0.85
a
b
0.99
0.99
0.97
0.89
0.89
0.94
Ce in mg/l and q in mg/g.
TCPh=2,4,5-trichlorophenol.
90
80
P2/698(pH=3)
70
q (mg/g AC)
6.5
7.32
17.6
24.8
21.2
35.7
R2
60
50
P2/873
40
P2/773
P2/698
30
P1/698
20
10
widely used models for liquid phase adsorption. Table 3
summarizes the values of the fitting parameters together
with the corresponding correlation coefficient obtained
for each adsorptive and activated carbon. According to
the fits obtained, none of those two equations can be
postulated as definitely better to reproduce the equilibrium data, particularly in the case of phenol. The
Freundlich model provides, in general, a somewhat
better fit for 2,4,5-trichlorophenol and the Langmuir
equation for Cr(VI).
0
0
10
20
30
40
50
60
Ce (mg/l)
70
80
90
100
Fig. 6. Adsorption isotherms of Cr (VI) (298 K) on activated
carbons (pH=7, unless indicated).
thermodynamically favored, probably by –OH groups
of the carbon surface of the hydroquinone type [11].
3.2.4. Fitting of the isotherms
The isotherms obtained belong to the L-type of the
Giles’ classification [34]. In general they fitted reasonably well, both the Langmuir and the Freundlich
equations, to make reference to two well-known and
4. Conclusion
Chemical activation through thermal treatment of
H3PO4-impregnated lignin from kraft black liquors
allows to obtain activated carbons with a high surface
area and a well-developed micro- and mesoporosity
which make them good candidates as aqueous phase
adsorbents. The adsorption capacity of these carbons
for three important target compounds used as representative of water toxic pollutants (phenol, 2,4,5trichlorophenol and Cr(VI)) compares well and even
favorably with that reported for other activated carbons.
ARTICLE IN PRESS
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
As a general conclusion of a practical meaning with
regard to the preparation of these activated carbons an
impregnation ratio and an activation temperature
around 2 g H3PO4/g lignin and 700 K, respectively,
provide the recommended combination of operating
conditions leading to the best activated carbons,
concerning their potential use as adsorbents for water
pollutants removal, although lower values of these
variables are also sufficient to obtain activated carbons
with good adsorption capacities.
[13]
[14]
[15]
[16]
Acknowledgements
The authors acknowledge the Spanish MCYT for
financial support through the research project PPQ20001763-C01 and CO-3.
References
[1] Bansal RC, Donnet JB, Stoeckli F. Active carbon. New
York: Marcel Dekker; 1988 [Chapter 2].
[2] Jankowska H, Swiatkowski A, Choma J. Active carbon.
Chinchester: Ellis Horwood; 1991.
[3] Coughlin RW, Erza RS, Tan RN. Influence of chemisorbed oxygen in adsorption onto carbon from aqueous
solution. J Colloid Interface Sci 1968;28:386–96.
[4] Lásló K, Szücs A. Surface characterization of polyethyleneterphtalate (PET) based activated carbon and the effect
of pH on its adsorption capacity from aqueous phenol and
2,3,4-trichlorophenol solutions. Carbon 2001;39:1945–53.
[5] Mahajan OP, Moreno-Castilla C, Walker Jr PL. Surface
treated activated carbons for the removal of phenol from
water. Sep Sci Technol 1980;15:1733–52.
[6] Mattson JS, Mark Jr HB, Malbin MD, Weber WJ,
Crittenden JC. Surface chemistry of active carbon: specific
adsorption of phenol. J Colloid Sci 1969;31:116–30.
[7] Moreno-Castilla C, Rivera-Utrilla J, López-Ramón MV,
Carrasco-Mar!ın F. Adsorption of some substituted phenols on activated carbons from a bituminous coal. Carbon
1995;35:845–51.
[8] Streat M, Patrick JW, Camporro-Perez MJ. Sorption of
phenol and para-chlorophenol from water using conventional and novel activated carbons. Water Res
1995;29:467–72.
[9] Aggarwal D, Goyal M, Bansal RC. Adsorption of
chromium by activated carbon from aqueous solution.
Carbon 1999;37:1989–97.
[10] Alaerts GJ, Jitjaturunt V, Kelderman P. Use of coconut
shell-based activated carbon for chromium (VI) removal.
Water Sci Technol 1989;21:1701–4.
[11] Bautista-Toledo I, Rivera-Utrilla J, Ferro-Garc!ıa MA,
Moreno-Castilla C. Influence of the oxygen surface
complexes of activated carbons on the chromium ions
from aqueous solutions: effect of sodium chloride and
humicacid. Carbon 1994;32:92–100.
[12] Cordero T, Rodr!ıguez-Mirasol J, Tancredi N, Piriz J, Vivó
G, Rodr!ıguez JJ. Influence of surface composition and
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
3049
pore structure on Cr(III) adsorption onto activated
carbons. Ind Eng Chem Res 2002;41:6042–9.
Pérez-Candela M, Mart!ın-Mart!ınez JM, Torregrosa-Maciá
R. Chromium (VI) removal with activated carbons. Water
Res 1995;29:2174–80.
Ranganathan K. Chromium removal by activated carbon
prepared from casurina equisetifolia leaves. Bioresource
Technol 2000;73:99–103.
González-Serrano E, Cordero T, Rodr!ıguez-Mirasol J,
Rodr!ıguez JJ. Development of porosity upon chemical
activation of kraft lignin with ZnCl2. Ind Eng Chem Res
1997;36:4832–8.
Rodr!ıguez-Mirasol J, Cordero T, Rodr!ıguez JJ. Preparation and characterization of activated carbons from
eucalyptus kraft lignin. Carbon 1993;31:87.
Rodr!ıguez-Mirasol J, Cordero T, Rodr!ıguez JJ. Activated
carbons from CO2 partial gasification of eucalyptus kraft
lignin. Energy Fuels 1993;7:133–8.
Daifullah AAM, Girgis BS. Removal of some substituted
phenols by activated carbon obtained from agricultural
waste. Water Res 1998;32:1169–77.
Jagtoyen M, Thwaites M, Stencel J, McEnaney B,
Derbyshire F. Adsorbent carbon synthesis from coals by
phosphoric acid activation. Carbon 1992;30:1089–96.
Jagtoyen M, Derbyshire F. Some considerations of the
origins of porosity in carbons from chemically activated
wood. Carbon 1993;31:1185–92.
Jagtoyen M, Derbyshire F. Activated carbons from yellow
poplar and wite oak by H3PO4 activation. Carbon
1998;36:1085–97.
Molina-Sabio M, Rodr!ıguez-Reinoso F, Caturla F, Sellés
MJ. Porosity in granular carbons activated with phosphoric acid. Carbon 1995;33:1105–13.
Molina-Sabio M, Rodr!ıguez-Reinoso F, Caturla F, Sellés
MJ. Development of porosity in combined phosphoric
acid-carbon dioxide activation. Carbon 1996;33:457–62.
Toles C, Rimmer S, Hower JC. Production of activated
carbons from a Washington lignite using phosphoric acid
activation. Carbon 1996;34:1419–26.
Sing KSW. In: Everet DH, Otewill RH, editors. Surface
area determination. London: Butterworths, 1970.
Laine J, Calafat A, Labady M. Preparation and characterization of activated carbons from coconut shell
impregnated with phosphoric acid. Carbon 1989;27:
191–5.
Mikail RH, Brunauer S, Brodor EE. Investigation of a
complete pore structure analysis. I. Analysis of micropores. J Colloid Interface Sci 1968;26:45.
Figueiredo JL, Pereira MFR, Freitas JMM, Orfao JJM.
Modification of the surface chemistry of activated carbons.
Carbon 1999;37:1379–89.
Hu Z, Srivisan MP. Preparation of high-surface activated
carbons from coconut shell. Microporous Mesoporous
Mater 1999;27:11–8.
Jung MW, Ahn KH, Lee Y, Kim KP, Rhee JS, Park JT,
Paeng KJ. Adsorption characteristics of phenol and
chlorophenols on granular activated carbons (GAC).
Microchem J 2001;70:123–31.
Mattson JS, Mark HB. Activated carbon. surface chemistry and adsorption from solution. New York: Marcel
Dekker; 1971.
ARTICLE IN PRESS
3050
E. Gonzalez-Serrano et al. / Water Research 38 (2004) 3043–3050
[32] Jayson GG, Sangster JA, Thompson G, Wilkinson MC.
Adsorption of chromium from aqueous solution onto
activated charcoal cloth. Carbon 1993;31:487–92.
[33] Radovic LR, Moreno-Castilla C, Rivera-Utrilla J. Carbon
materials as adsorbents in aqueous solutions. In: Radovic
LR, editor. Chemistry and physics of carbon, vol. 27. New
York: Marcel Dekker, 2000.
[34] Giles CH, McEwan TH, Nakhwa SN, Smith D. Studies
in adsorption. Part XI. A system of classification of
solution adsorption isotherms and its use in diagnosis
of adsorption mechanisms and in measurement of
specific surface areas of solids. J Chem Soc 1960;786:
3973–93.