Revista Mexicana

de Ingenierı́a Quı́mica
Academia Mexicana de Investigación y Docencia en Ingenierı́a Quı́mica, A.C.

Revista Mexicana de Ingeniería Química

Volumen 9, Número 3, Diciembre 2010

ISSN 1665-2738

Vol. 9,CONTENIDO
1

No. 3 (2010) 313-322

Volumen 8, número 3, 2009 / Volume 8, number 3, 2009
1

ADSORPTION STUDIES OF METHYLENE BLUE AND PHENOL ONTO

PECAN AND
213 Derivation CASTILE
and application NUTSHELLS
of the Stefan-Maxwell PREPARED BY CHEMICAL
equations
ACTIVATION
(Desarrollo y aplicación de las ecuaciones de Stefan-Maxwell)
ESTUDIOS DE ADSORCIÓN DE AZUL DE METILENO Y FENOL EN
Stephen Whitaker
NUECES DE PECAN Y DE CASTILLA PREPARADAS POR
ACTIVACIÓN QUÍMICA
V. Bello-Huitle, P. Atenco-Fernández and R. Reyes-Mazzoco∗
Biotecnología / Biotechnology

Departamento de Ingenierı́a
245 Modelado Quı́mica,en
de la biodegradación debiorreactores
Alimentos ydeAmbiental Universidad totales
lodos de hidrocarburos de las del
Américas,
petróleo Puebla

intemperizados enReceived 20 of July 2010; Accepted 22 of October 2010

suelos y sedimentos

(Biodegradation modeling of sludge bioreactors of total petroleum hydrocarbons weathering in soil

Abstractand sediments)
The use of agricultural wastes (AWs) as raw materials in the production of granular activated carbon (GAC) is
S.A. Medina-Moreno, S. Huerta-Ochoa, C.A. Lucho-Constantino, L. Aguilera-Vázquez, A. Jiménez-
an important topic worldwide. The abundance of pecan nutshells (PNs) and castile nutshells (CNs) provided the
motivationGonzález y M. Gutiérrez-Rojas
for producing GAC from these materials. Phosphoric acid was used at several activation ratios (Rs),
and the259
adsorption capacity
Crecimiento, of methylene
sobrevivencia blue (MB)
y adaptación and phenol (PH)
de Bifidobacterium by the
infantis products was
a condiciones measured. The highest
ácidas
GAC yields and the maximum adsorption capacities were obtained at R=2. Although the maximum MB adsorption
capacity of(Growth, survival and
GAC produced fromadaptation
CNs wasofrelatively
Bifidobacterium infantis
small, 170 mg tog−1
acidic conditions)
; that of GAC produced from PNs was 400
−1
mg g , which is among the highest reported. The SEM images of GAC from PNs
L. Mayorga-Reyes, P. Bustamante-Camilo, A. Gutiérrez-Nava, E. Barranco-Florido revealed any ordered arrangement
A. Azaola-
of nearly straight and tubular macropores with abundant mesopores inside. The ball-pan hardness number of the
Espinosa
PN GAC is 80, equal to the value reported for bituminous GAC. These characteristics make the GAC obtained
from PNs suitable forapproach
265 Statistical to optimization
packed tower of ethanol fermentation by Saccharomyces cerevisiae in the
applications.
Keywords: agricultural waste, granular activated carbon, activation ratio, pyrolysis.
presence of Valfor® zeolite NaA
Resumen(Optimización estadística de la fermentación etanólica de Saccharomyces cerevisiae en presencia de
El uso de desechos de agricultura como materia prima en la producción de carbón activado granular (CAG) es un
zeolita Valfor® zeolite NaA)
tema importante alrededor del mundo. La abundancia de cáscara de nuez de pecan (NP) y de castilla (NC) fue la
motivaciónG. Inei-Shizukawa,
para la producciónH.deA. CAG
Velasco-Bedrán,
a partir deG.estos
F. Gutiérrez-López
materiales. Seand H. Hernández-Sánchez
utilizó ácido fosfórico a distintas relaciones
de activación (R) y se midió la capacidad de adsorción de azul de metileno (AM) y fenol. Los CAG con más altos
rendimientos y mayores capacidades de adsorción se obtuvieron con R=2. A pesar de que la máxima capacidad
Ingeniería de procesos / Process engineering
de adsorción de AM del CAG producido con NC fue relativamente pequeña, 170 mg g-1; la del CAG producido
con NP271fueLocalización
de 400 mg de una
g-1, queplanta industrial: dentro
se encuentra Revisión
de crítica y adecuación
los valores de los
reportados criterios
más altos. empleados en en SEM
Las imágenes
del CAG de NP revelaron
esta decisión un arreglo ordenado de macroporos tubulares y casi rectos con mesoporos abundantes
dentro. La dureza según el método Ball-pan Hardness Number del CAG de NP es de 80, igual al valor reportado
(Plant site selection: Critical review and adequation criteria used in this decision)
para el CAG bituminoso. Estas caracterı́sticas hacen que el CAG obtenido de NP sea adecuado para su aplicación
J.R. Medina, R.L. Romero y G.A. Pérez
en torres empacadas.
Palabras clave: desechos de agricultura, carbón activado granulas, relación de activación, pirólisis.

∗ Corresponding author. E-mail: rene.reyes@udlap.mx

Tel. 222 2292660, Fax 222 2292727

Publicado por la Academia Mexicana de Investigación y Docencia en Ingenierı́a Quı́mica A.C. 313
 Bello-Huitle et al./ Revista Mexicana de Ingenierı́a Quı́mica Vol. 9, No. 3 (2010) 313-322

1 Introduction uses include fluids deodorization and color removal

(Karim et al., 2005), retention of toxic metallic
Pecan and castile nutshells (PNs and CNs) are substances (Srivastava, et al., 2008; Jusoh et
suitable raw materials for the production of al., 2007) retention of gold from gold bromine
granular and powder activated carbon because the solutions (Pesic and Storhok, 1992), ventilation
nutshells are approximately 50% of the weight of filters, solvent regeneration, and even catalyst
the fruit. The nuts are commonly commercialized support for liquid HgCl2 (Kai et al., 2009).
peeled, and the nutshells are retained at the The use of GAC columns in pre-treating water
packing site, making collection easy. In the State for desalination processes could minimize reverse
of Puebla, Mexico, alone, an estimated 442 tons osmosis costs by adsorbing suspended and soluble
of CNs and 1,768 tons of PNs were generated organic matter (Guy-Reznik et al., 2008).
in 2007. Pecan nuts are an important crop Experimentation and development of GAC
internationally, and the US is the most important from the AW mentioned above has been carried
producer (with more than 100,000 tons produced out using chemical activators such as KOH, ZnCl2 ,
per year), followed by Mexico. On the other H2 SO4 , H3 PO4 and CO2 . Water vapor and
hand, castile nuts are almost exclusively produced other gases have also been used as physical
in the State of Puebla, Mexico, with an annual activators. This treatment of the raw material
production of over 1,000 tons (USDA, 1997). before pyrolysis creates macropore, mesopores,
There are several types of agricultural by- and micropores on and inside the solid’s surface.
products that have been used for granular However, acid treatment improves the final
activated carbon (GAC) production at laboratory quality of the GAC by introducing ions on the
or industrial levels. Coconut shells (Azevedo et surface structure, such as chlorides, sulfates and
al., 2007), palm saw dust (Selvi et al., 2001), phosphates (depending on the acid used), yielding
moss (Subramani, 2002), oregano stems (Timur, a GAC capable of ion exchange (Cañizares et
2002), sunflower seeds (Karagöz et al., 2008), al., 2006). It has been suggested that H3 PO4
olive husks (Michailof et al., 2008), corn husks produces better modification to the botanic
(Tsai et al., 2001), apple pulp (Suárez-Garcı́a et structure than other acids. These modifications
al., 2002), vetiver roots (Altenor et al., 2009), are both physical and chemical and include
grain sorghum (Yulu and Walawenderand, 2002), penetrating, swelling, and partially dissolving the
pistachio nutshells (Lua et al., 2004), and wood available biomass, dividing bonds and reforming
(Heschel and Klose, 1995) are some examples. new thermal resistant polymers (Girgis et al.,
Even waste products such as activated sludge (Al- 2002; El-Qada et al., 2008). This acid also
Qodah and Shawabkah, 2009) and turkey manure acts as a stabilizer to prevent the collapse of
(Lima and Marshall, 2005) have been processed the raw material, restricts the formation of tar
in an effort to produce GAC. The abundance of and guarantees the creation of macropores that
these resources in different places of the world transport the fluid and mesopores and micropores
can transform a by-product into a valuable raw to where the adsorption occurs (Ahmadpour et al.,
material with potentially high profits. Bamboo in 1998).
Malaysia (Hameed et al., 2007), European cherry The quality of the GAC can be measured
stones in Spain (Olivares-Marı́n et al., 2007), and by superficial area, granulometry, dominant
date stones in Saudi Arabia (Alhamed, 2006) are pore type, and adsorption indicators, among
examples of low-cost, accessible raw material for others. The factors that are most important in
the production of high quality activated carbon determining GAC quality are carbonization time,
(AC). In addition to offering economic advantages carbonization temperature and the activation
over mineral or bituminous coal, agricultural ratio (R), which is the mass ratio of activator
waste (AW) can be processed at temperatures to raw material. The activator intervenes in
below 600◦ C, while ordinary coal yields its best the pyrolysis chemistry, mainly as a dehydrating
results at over 800◦ C (Nowicki et al., 2008). agent. The activating ratio determines the
The demand for GAC as a water-purifying product’s porosity while the pyrolysis temperature
agent has dramatically increased, as has its use determines the extent of the carbonization.
in tertiary wastewater treatment. Color and odor Generally, a larger ratio of macropores to
removal are important in these processes. Other micropores is obtained from higher values of R

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(Suárez-Garcı́a et al., 2002). 2.5 Adsorption isotherm determination

This work proposes the use of PNs and CNs for MB (CAS 61-73-4; Sigma-
as raw materials for the GAC production through Aldrich 7220-79-3) and PH (CAS
activation with phosphoric acid to produce the
108-95-2; Sigma-Aldrich 108-95-2).
best adsorption results. The effects of preparation
conditions were studied on the final yield, and A total of 0.100 g of GAC in a 8-18 mesh range
the adsorption capacity was measured through was weighed and mixed with different volumes
adsorption isotherms with methylene blue (MB) (10, 12, 14, 16, 18, 20, 30, 40, and 50-mL) of a
and phenol (PH). 1000 ppm MB solution in 250-mL flasks. For PH
isotherms, 0.15 g of GAC in a 16-30 mesh range
was weighed and mixed with different volumes (5,
2 Experimental procedures 20, 35, 65, 80, and 95-mL) of a 500 ppm PH
solution. All flasks, at pH 7.0, were covered and
2.1 Nutshell preparation left to stir at 125 rpm and 20oC for 72 hours.
It was previously determined that after 48 hours
The nutshells were washed with tap water to dynamic equilibrium in the adsorption process
eliminate any residue or foreign material and was reached for the concentrations used. The
dried for 24 hours in a 110◦ C stove to eliminate remnant or equilibrium concentration, Ce , for each
humidity. The nutshells were partially crushed to substance was determined with a UV/V (HACH
facilitate handling in subsequent processing. DR/4000U) spectrophotometer. The amount
adsorbed at equilibrium, qe , was calculated
2.2 Impregnation and activation through Eq. (1) from Ce , the initial concentration,
Co , the volume of solution, V , and the mass of
The quantity of phosphoric acid (CAS 7664-38- carbon, m.
2; Sigma-Aldrich 7664-38-2) determined by the
R selected for each sample was dissolved in 25- (C0 − Ce ) V
qe = (1)
mL of distilled water. This solution was mixed m
with clean, dry PNs or CNs in 250-mL covered The absorbances were measured at the
flasks. These flasks were heated to 85◦ C and maximum absorption wavelengths, which were 265
stirred at 150 rpm for 4 hours to increase acid nm for PH and 665 nm for MB. The compositions
penetration. After eliminating the excess liquid, were transformed into the calibration lines given
the damp nutshell pieces were heated to 110◦ C for in Eqs. (2) and (3).
24 hours to eliminate humidity.

Absorbance = 0.0141[P H] R2 = 0.998 (2)

2.3 Pyrolysis 2
Absorbance = 0.1682[M B] R = 0.994 (3)
The dried solids were introduced into porcelain
crucibles and set in a furnace to carbonize at Langmuir’s empirical model supported on
500oC. The carbonization time was kept constant kinetics was developed to describe adsorption onto
at 3 hours at maximum temperature for all tests, activated carbon Eq. (4). The processes of
with heating and cooling ramps of 10◦ C/min. At adsorption and desorption are dynamic and a rate
the end of the pyrolysis process, the samples were law can be written for each process, and when the
cooled to 100◦ C and placed in a desiccator. rates become equal an equilibrium state will exist
characterized by a constant fractional coverage
of the original adsorption sites. Langmuir
2.4 Washing and packing isotherm assumes homogenous adsorption with no
The acid activator was completely removed from transmigrations of the adsorbate in the surface.
the GAC using distilled water. The samples were qmax KL Ce
washed with boiling water, followed by cold water, qe = (4)
1 + KL Ce
until pH 6.0 was reached. The GAC was set to dry
for 12 hours at 110◦ C and then packed in sealed where qe is the adsorption of the adsorbate per
bags for the following measurements. unit mass of the adsorbent at equilibrium in

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units of mg g−1 ; KL is the rate adsorption 2007).

constant (ratio of adsorption over desorption rate 1
RL = (8)
constants) in units of L mg−1 ; Ce is the solute 1 + KL C0
concentration at equilibrium in units of mg L−1 ;
and qmax is the maximum solute adsorption 2.6 Ball-pan hardness number (BPHN)
capacity per unit mass of adsorbent in units of
mg g−1 , and also the maximum adsorption site The GAC sample with the highest qmax was tested
density. to obtain its BPHN, also called the mechanical
Freundlich isotherm, Eq. (5), is the abrasion factor, according to D3802-79 ASTM
earliest known relationship describing the non- standard and procedure with sieve numbers 8, 16
ideal and reversible adsorption, not restricted and 100 (ASTM Standards on Activated Carbon,
to the formation of monolayer. This empirical 2006).
model can be applied to multilayer adsorption,
with non-uniform distribution of adsorption
heat and affinities over the heterogeneous 3 Results and discussion
surface. Freundlich isotherm is widely used in
heterogeneous systems for organic compounds in 3.1 Pyrolysis yield
activated carbon.
The pyrolysis yield is defined as the mass of GAC
qe = KF Ce1/n (5) obtained per mass of raw material. Table 1 shows
the yields calculated at different activation ratios
The value 1/n between 0 and 1 is a measure for PNs and CNs. In all cases, the original mass
of adsorption intensity or surface heterogeneity, of the nutshells was 25 g. The yield increased
becoming more heterogeneous as it gets closer at higher activation ratios and was higher for
to zero. Whereas, a value below unity implies PNs, though the results did not follow a linear
chemisorptions process where 1/n above one is an relationship. Yields above 50% are acceptable for
indicative of cooperative adsorption. GAC production and were obtained from both
The experimental data were fitted to the nutshells.
original and the linear transformation of the Table 1 Yields obtained at different
Langmuir isotherms using Eqs. (4) and (6) impregnation ratios.
and the original and linear transformation of
Freundlich isotherms using Eqs. (5) and (7) to R g GAC Y from g GAC Y from
determine which of the two displayed the best from CN CN, % from PN PN, %
goodness-of-fit value (R2 ), and the adsorption 0.5 10.33 29.2 7.29 41.3
constants were calculated from these isotherms. 1 10.89 41.3 10.33 43.6
This is the conventional approach for modeling 1.5 12.70 47.4 11.84 50.8
adsorption isotherm systems presented by Foo and 2 17.62 52.3 13.07 70.5
Hameed (2010) in their review on the topic.

Ce 1 Ce 3.2 Testing the adsorption isotherm

= + (6)
qe qmax KL qmax models
1
ln qe = ln KF + ln Ce (7) The experimental data obtained from the
n
adsorption isotherm determination shows that
The essential characteristics of Langmuir both types of GAC lead to a Type I isotherm
isotherms were expressed in terms of the according to Brunauer classification, as it can be
dimensionless separation factor, RL , in Eq. seen in Figs. 1 and 2.
(8), that includes Co, the maximum initial These data were adjusted by linear
concentration, and the rate constant. This transformation and are shown in Figs. 3 and
parameter indicates that adsorption is not 4. For these two samples, the best adjustment
favorable for RL > 1, is linear for RL = 1, favors was obtained using the Langmuir model, Eq. (4).
GAC for 0 < RL < 1; and is irreversible for Adjustment to the Freundlich model, Eq. (5), was
RL = 0 (Karagöz et al., 2008; Hameed et al., also tested.

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Fig. 1 Adsorption isotherms for MB on GAC

Fig. 1 Adsorption isotherms for MB on GAC prepared with R= 2 from CNs
prepared with R= 2 from CNs Fig. 4. Linear transformation of the adsorption
Fig. 4. Linear transformation of the adsorption isotherm for PH on GAC
isotherm for PH on GAC prepared with R= 2 from
prepared
CNswithusing
R= 2 from
theCNs using the Langmuir
Langmuir model.model.

Fig. 2 Adsorption isotherm for PH on GAC

prepared isotherm
Fig. 2 Adsorption with R=for2PH
from CNsprepared with R= 2 from CNs
on GAC
Fig. 5. Linear transformation of the adsorption
isotherm
Fig. 5. Linear for MB
transformation on
of the GAC isotherm
adsorption prepared
2 with
for MB R=
on GAC
from CNs using Freundlich’s model.
prepared with R= 2 from CNs using Freundlich’s model.

The fact that Langmuir’s isotherm model had

a better adjustment indicates that this GAC
will not abruptly desorb substrate molecules
if the surrounding fluid concentration suddenly
changes. The asymptotic nature of the Langmuir
model gives stable adsorption at the maximum
adsorptive capacity; therefore, it will perform
better when used in industrial applications.
Fig. 3. Linear transformation of the adsorption Values of KL > 0 in Table 2 confirm the type
Fig. 3. Linear transformation of the adsorption isotherm for MB on GAC
isotherm for MB on GAC prepared with R= 2 I isotherm favorable to adsorption.
prepared
fromwith
CNsR= 2 using
from CNs using
the the Langmuir
Langmuir model.
model.
An example of such an application is toxic
metal removal and adsorption, in which the
The MB isotherms shown closely conform to metal’s concentration in the stream could change
Langmuir behavior for the entire range of tested slightly, disturbing the GAC’s mass transfer
concentrations. The adsorption data of MB on CN equilibrium. If the AC follows the Freundlich
GAC prepared with R = 2 displayed a R2 of 0.995 model, for example, with weaker molecular
fitting with this model. In comparison, fitting to interactions between adsorbate and adsorbent,
Freundlich’s model yielded a R2 of 0.937 and is then the metal desorption could be prejudicial
shown in Fig. 5. A similar result was obtained to the downstream process. However, if the AC
with data from the other adsorption experiments. follows the Langmuir model, this disturbance-

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related desorption would be minimized, as it is Table 3. Adsorption parameters of Freundlich

shown with the low values of RL in Table 2, which model for the adsorption of MB and PH on
reflect that adsorption is more favorable (Foo and GAC produced from CN and PN.
Hameed, 2010). Solute: MB Kf n R2
CN, R=2 83.9 9.67 0.937
3.3 Effect of R on the GAC adsorption CN, R=1 91.2 15.60 0.860
characteristics PN, R=2 75.3 7.08 0.813
PN, R=1.5 3.14 1.66 0.978
Table 2 shows the results of the adsorption studies Solute: PH
of GAC obtained with the Langmuir model from
CNs and PNs. The comparison of GAC’s based PN, R=1.5 2.85 1.87 0.976
on adsorptive capacity is related to ASTM D PN; R=2 5.99 2.01 0.978
3860-98 “Determination of adsorptive capacity CN, R=2 11.5 4.16 0.908
of activated carbon by aqueous phase isotherm CN, R=1.5 9.25 3.65 0.890
technique” (ASTM Standards on Activated
Carbon, 2006). This practice covers the The adsorption parameters obtained with the
determination of the adsorptive capacity of AC to Freundlich model are shown in Table 3. The
remove undesirable constituents from wastewater Langmuir model yielded a somewhat better fit
as proposed in this work, particularly for the than the Freundlich model. As also illustrated in
removal of color from dye mill and toxicants. Table 3, the values of 1/n are in between 0 and 1,
The GAC derived from PNs had better results which indicates favorable adsorption.
than that from CNs for the activation ratios (Rs) In Table 4, a comparison of the results
tested for activating the carbon. The values of obtained with GAC produced from other AWs
qmax for the MB of the GAC prepared from PNs shows that the GAC produced from PNs equals
are more than twice that of GAC prepared from or surpasses the others. Also shows that the
CN with the same R = 2. The qmax for PH of adsorption data for GAC produced from PNs
the GAC prepared from PNs is three times that with R = 2 had similar values of the adsorption
of GAC prepared from CNs at the same R = 2. parameters for the bamboo-based GAC. The
Table 2 also shows that all GACs produced capacity and strength of adsorption are similar
presented a higher affinity towards MB than and among the highest found in GAC from AW.
PH. This evidence indicates the presence of a The bamboo-based GAC had BET surface area,
greater quantity and density of macropores than total pore volume and average pore diameter of
mesopores or micropores and the capacity of the 1896 m2 /g, 1.109 cm3 /g and 2.34 nm, respectively.
GAC for adsorbing molecules of similar molecular GAC from coconut shells is commercially
weight and size as MB. available and used in several industrial
applications in wastewater tertiary treatment, for
Table 2. Adsorption parameters of Langmuir example. The maximum monolayer adsorption
model for the adsorption of MB and PH on capacity (mg g−1 ) was determined as 277.90,
GAC produced from CN and PN. below the value obtained for the PNs GAC
(Kannan and Sundaram, 2001).
Solute: MB qmax KL RL R2
Table 5 shows the comparison with reported
CN, R=2 169.5 0.045 0.022 0.995 data for the adsorption of PH. The GAC from PNs
CN, R=1 140.8 0.067 0.015 0.988 had the highest qmax value and an intermediate
PN, R=2 400.0 0.625 0.004 0.999 value of RL , implying both high adsorbate and
PN, R=1.5 333.0 0.002 0.398 0.921 reversible retention that make the GAC adequate
Solute: PH for tertiary wastewater treatment.

PN, R=1.5 103.1 0.005 0.289 0.933

PN; R=2 158.7 0.006 0.251 0.987
3.4 SEM images of the PN and the GAC
CN, R=2 53.2 0.023 0.080 0.962 The control sample is presented in Image 1. The
CN, R=1.5 53.2 0.018 0.100 0.964 surface of a PN without any thermal or chemical

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Table 4. Langmuir constants for MB adsorption on GAC produced from different AWs.
Reference (Thinakaran et al., 2008) (Hameed et al., 2007) (Timur, 2002) This work
Raw material Sunflower seed hull Bamboo Oregano stems Pecan nutshells,
R=2
qmax (mg g−1 ) 16.43 454.2 285.7 400.0
KL (L mg−1 ) 1.15 0.518 0.686 0.625
RL 0.050 0.004 0.005 0.004

Table 5. Langmuir constants for PH adsorption on GAC produced from different agricultural
by-products.
Reference Ramos-Rodrı́guez and Lam and Zakaria (2010) Timur (2002) This work
Reyes-Mazzoco (2010)
Raw material Black cherry stones Wood saw-dust Oregano stems Pecan nutshells,
R=2
qmax (mg g−1 ) 133.33 149.25 94.34 158.7
KL (L mg−1 ) 0.0086 0.160 0.010 0.006
RL 0.47 0.04 0.51 0.251

Image 1. Control sample of PN raw material. Image

Image 2.2. GAC
GAC surface
surface porosity. porosity. Scale
Scale line equals line equals
50 m.
Image 1. Control sample of PN raw material. Scale line equals 50 m.
Scale line equals 50 µm. 50 µm.

modification is presented. Importantly, a that this GAC sample contains a large amount
concentration of pores appears on the PN surface. of almost straight cylinders macropores. This
The solid is not entirely smooth but instead GAC is recommended for adsorbing molecules
consists of crevices and pores of approximately 10 of high molecular weight, such as multiple-
µm diameter. ring molecules (> 128 amu), and molecules of
intermediate weight, such as PH or single-ring
organic molecules (78-128 amu).
When examining the SEM images of GAC
produced at R = 2, porosity is observed at a scale
of 10 µm, as shown in Image 2. These pores are The PN GAC sample in Image 3 shows a
responsible for reducing mass-transfer resistance graphitic and structured porosity. Conduits of
for the adsorption (Gleisy et al., 2008; Simpson, roughly 10 µm length with very small pores can
2008). On the rough outer surface of the AC, 10 be detected. The pores are aligned, and there is
µm pores can be observed. This evidence confirms almost no space between pores, significantly incre-

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Langmuir’s model. The adsorption capacities

of MB and PH for GAC from pecan nutshells
were among the highest for GAC produced from
agricultural waste.
The pore structure observed through SEM
images permitted greater adsorption of methylene
blue because of the density of macropores and
mesopores on the AC surface with strong bonding.
The BPHN of the pecan nutshell GAC was 80
making it suitable for applications in the removal
of toxicants from water.

Image
Image 3.3. Internal
Internal porosityporosity of GAC
of GAC produced produced
from PN from
with R=2. Scale line
References
PN with
equal to 20 m R=2.
Alhamed Y. (2006). Activated carbon from dates
stones by ZnCl2 activation. Engineering
asing their density. Science 17, 75-100
With the aid of these images and the
adsorption isotherms, it is possible to understand Ahmadpour A., King B. A., Do D. D. (1998).
the adsorptive behavior of GAC produced from Comparison of equilibria and kinetics of
PNs prepared under different conditions. GAC high surface area activated carbon produced
with a high maximum substrate adsorption from different precursors and by different
and homogeneous surface trends has been chemical treatments. Industrial and
manufactured, comparable with those produced Engineering Chemistry 37, 1329-1334.
from other agricultural waste products.
Al-Qodah Z., Shawabkah R. (2009). Production
3.5 Ball-pan hardness number and characterization of granular activated
carbon from activated sludge. Brazilian
The BPHN helps predict the lifespan of activated Journal of Chemical Engineering 26, 10-15.
carbon in a packed tower, in which it may be
susceptible to effects of abrasion, sheer stress and Altenor S., Carene B., Emmanuel E., Lambert
damage inflicted by surrounding fluids. GAC J., Ehrhardt J.J., Gaspard S. (2009).
must have a high BPHN to withstand extensive Adsorption studies of methylene blue and
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