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DE LA FACULTAD DE INGENIERÍA
REVISTA TÉCNICAREVISTA TÉCNICA
Patrimonio del Estado Zulia e
interés Cultural desde 2001
Fecha de Construcción:
1954-1958
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Villanueva, con elementos
novedosos de adaptación
climática.
Policromía de la obra: Artista
Zuliano Victor Valera.
VOL.42 ENERO - ABRIL 2019 No.1
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, 10-17
Cu (II) Chemisorption on Calcined Substrates made with an
Oxidic Refractory Variable Charges Lithological Material
Fernando Millán1* , José G. Prato2,3 , Luisa Carolina González4 , Andrés Márquez1
Pablo Djabayan5
1Polythecnic Institute “Santiago Mariño” IUPSM-Mérida, Venezuela, Chemical Engineering School,
2Universidad Nacional de Chimborazo (Unach), Facultad de Ingeniería, Riobamba, Ecuador.
3Los Andes University, (ULA), Chemical Engineering School, Mérida, Venezuela.
4Universidad Nacional de Chimborazo (Unach), Facultad de Ciencias de la Salud, Carrera Laboratorio Clínico e
Histopatológico, Riobamba, Ecuador.
5Universidad Nacional de Chimborazo (Unach), Facultad de Ciencias de la Salud, Medicina, Riobamba, Ecuador
*Autor de Contacto: fcarlosmillan@gmail.com, pratoj@gmail.com
https://doi.org/10.22209/rt.v42n1a02
Recepción: 01/03/2018 | Aceptación: 20/10/2018 | Publicación: 31/12/2018
Abstract
This work presents a complementary study on the nature of copper ions adsorption reaction on calcined substrates
with variable charge surfaces prepared with refractory lithological materials obtained from San Juan de Lagunillas, near the
city of Mérida, Mérida State, Venezuela. The study was performed on activated and non-activated calcined substrate, prepared
with granulometric fraction between 425 mm – 250 mm. The results of the PZC showed that thermal treatment favors the
formation of amphoteric oxides with pH0 6 – 7 similar to those reported in the literature. Although the isotherms obtained
in previous experiments are L
do not represent an absolute proof about a chemosorption reaction. This kind of adsorption reaction should produce H3O+
0.01 and 0.1 M Cu+2 produced 0.11, 0.27 and 1.19 mmol of protons ions respectively. These data complement the information
Keywords: Adsorption; lithological materials; variable charge surface; cupper ion.
Quimioadsorción de Cu (II) sobre un Sustrato Calcinado
preparado con un Material Litológico Refractario de Carga
Variable
Resumen
Este trabajo presenta un estudio complementario sobre la naturaleza de la reacción de adsorción de iones cobre
obtenidos de San Juan de Lagunillas, Mérida, Venezuela. El estudio se realizó sobre sustrato calcinado activado y no activado,
preparado a partir de la fracción granulométrica entre 425 y 250 mm. Los resultados del experimento de PCC mostraron
que el tratamiento térmico favorece la formación de óxidos anfóteros con pH0 entre 6 y 7 similares a los reportados en la
literatura. Aunque las isotermas obtenidas en estudios previos son de tipo L+2
sobre 2 g de sustrato calcinado con soluciones de 0,001, 0,01 y 0,1 M de iones cobre producen 0,11, 0,27 y 1,19 mmol de
protones respectivamente. Estos datos complementan la información de las isotermas a favor de una quimioadsorción de los
Palabras clave
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
11Cu (II) Chemisorption on Calcined Substrates made with an Oxidic Refractory
Introduction
Transitional metal adsorption in variable charge
soils have been well studied by several authors [1, 2] but
has not been treated for the case of calcined substrates
prepared with oxidic refractory lithological materials. In
both cases the Fe and Al, as well as Mn and Ti amphoteric
oxides are the most important source of variable charge;
these amphoteric surfaces can be either protonated or
deprotonated by acid or alkaline treatment to create
positive or negative charges on the oxides surfaces, leading
to cation and anion adsorption reactions respectively,
according to equation (1) [3].
(1)
The literature also suggest a mechanism for
which the adsorption of transitional metals on these
kind of surfaces, through the formation of a covalent
bond between the metal ion and the oxidic surface, called
chemisorption, according to equation (2) where M could
be any transitional metal.
(2)
Such kind of reaction modifies the surface
charge through more positive values, which allows
anion adsorption, and produces acidification through the
formation of H3O+ ion. This process is defined as specific
adsorption or chemisorption, which has the tendency to
be irreversibility. In previous publications [4, 5] copper
adsorptions on calcined substrates prepared with some
of these refractory lithologic materials which have surface
variable charges were described. This physicochemical
characteristic is due to the presence of amphoteric oxides
in the material, such as Fe, Al, Mn and Ti, previously
described in the literature [6, 7]. As a consequence of these
particular properties, these lithological materials are
versatile for preparing calcined adsorbing substrates and
their applications in water treatment. Furthermore, due
to their capacity for anion/cation exchange, heavy metals,
oxyanions and organic matter are removed by adsorption
processes. In previous publications the application to
water softening [8], cation adsorption reactions [4], anion
adsorption reactions [9, 10] and water treatment [11]
have been described. The objective of this paper is to
complement the information presented by the previous
articles with new findings which support the hypothesis
of the chemisorption of cupper ions on the oxidic surface
of these calcined substrates, in order to continue working
on this project. Moreover, according to the theoretic
model described above, H3O+ ion must be one of the
reaction products, producing acidification in the solution.
Therefore, by following up the pH evolution during the
adsorption reaction it should show this acidification
process.
Experimental Section
lithologic material have been described in the literature
[7]. Being an arid zone, the soils are classified as aridisols
[12], presenting serious limitations for agronomical uses.
However, some of these lithological materials are used by
potters for making kitchen hardware and constructions
materials like bricks and crockery using thermal treatment
due to its refractory properties. Calcined subtrates were
prepare according to the procedure described in the
literature [4 - 6], so by using the granulometric fraction
between 425 – 250 mm for the determination of the
zero charge point, the pH and the electrical conductivity
the BET technique using isothermal N2 adsorption. The
procedure for the deprotonation reaction of the calcined
substrate (substrate activation) is also described in the
same literature were the substrate is chemically treated
excess of alkali is wash out with distillate water until
it reaches pH 7, and later it dries in a furnace at 120oC.
The determination of Point of Zero Charge (PZC) of raw
the material, (RM), calcined non-activated (NAS) and
activated substrates (AS) was performed according to
the method described by the literature [13, 14]. The pH
was measured at different ionic strength against pH in
aqueous extract and pH0 was recorded on a graphic of
pH against pHH2O which gives de pHo at the intersection
of pHH2O axe. The adsorption study was performed by
triplicate, in isothermal conditions at 20 ± 2 oC for 24 h,
using batch equilibration procedure by treating 2 g of
calcined substrate with 5, 10, 15, 20, 25, 30 and 40 mL of
0.001 M Cu+2, in closed vessels. Then the Cu+2 equilibrium
concentration were determined by the complexometric
titration at pH 10 with a 0.001 M EDTA standard solution
and NET as metalochromic indicator. Thus, adsorption
isotherms were obtained by plotting the amount of copper
adsorbed (mmol g-1 substrate) against the equilibrium
Langmuir equation [15-17]. The pH and the EC variations
were measured using the same batch equilibration
procedure, in triplicate samples, by treating 2 g of raw
material, activated and non-activated calcined substrate,
with increasing volume of 0.001 M, 0.01 M and 0.1 M of
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
12 Millán y col.
Cu+2 solutions. Suspensions were periodically shaken at 20
± 2 oC for 24 h in 100 mL glass beakers. pH was measured
with a Hanna 211 pHmeter, calibrated with commercial
buffer solutions of pH 4 and 7. Electrical Conductivity
was measured with a Trans Instrument HC3010
Conductimeter, calibrated with standard reference.
Results and Discussion
Determination of surface zero charge point
Amphoteric oxides have surface charges that are
pH dependent; they react in alkaline or acid medium to
create negative or positive charges which are responsible
for the cation or anion adsorption reactions. So, the pH
value at which surface positive charge equals to the surface
negative charge is called the point of zero charge, PZC or
pH0 [18]. Figure 1 shows the results of the potentiometric
titration on the raw material as well as on the non-
activated activated substrates. The intersection of the
curves with the pHH2O axis shows the pH value when the
surface diffuses electrical charge equals to zero, indicating
the PZC. All the curves present a single intersection point;
pH value. For the
pH values are
positive indicating that the surface charges are basically
negative. However, in the case of calcined substrates
surface charges varies according to the solution pH,
indicating that the thermal treatment favors the formation
of amphoteric oxides.
Figure 1. Potentiometric titrations for the determination
of zero-point charge (ZPC) in raw material, non-activated
and activated substrates.
The PZC values for the calcined substrates lies
between 6 and 7.2 and the PZC in calcined substrates
shifts from 6.4 to 7 because of the alkaline treatment
which creates a greater negative charge density on
the substrate surface due to the oxides deprotonation
reaction. The range in which the PZC of the raw material
and the calcined substrates lies is similar to the PZC values
for pure a-Fe2O3, goethite and gibbsite [19]. Moreover, the
differences with these experimental values are probably
are due to a mixture of amorphous variable charge oxides
in the material. In reality, minerals and clays are rarely
found in soils as pure mineral because particles can be
clays could also be deeply associated with oxides and the
mixing clays and minerals are very common in many types
of soils [12].
Adsorption isotherm
Adsorption of copper ions takes place on active
sites where amphoteric oxides are deprotonated, creating
negative charges not only on non-activated but also in
activated surface. Figure 2 shows the adsorption isotherm
of Cu+2 on adsorbent substrate activated with 0.10 N NaOH
and non-activated. As it was pointed out in a previous
paper [5], the L
between copper ions and the substrate´s surface with
the formation of a saturated monolayer of copper ions on
the surface bounded probably through an inner sphere
complex, as is predicted by the Langmuir model. The
activated substrate enhances the adsorption reaction due
to the grater negative charge density created after oxides
deprotonation through alkaline treatment. The Isotherm
to those reported from the Cu+2 adsorption on goethite and
g-Al2O3, and TiO2
or chemisorption between Cu+2 ions and oxide surface [20,
solution by the formation of H3O+ ions, which is showed by
the pH measurement in different experimental conditions.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
13Cu (II) Chemisorption on Calcined Substrates made with an Oxidic Refractory
Figure 2. Adsorption isotherms obtained from copper
ions adsorption reaction on calcined substrate prepared
with the granulometric fraction between 425 – 250 mm.
The adjustments to the Langmuir model was
presented in the literature cited above [5] showing a good
linear correlation and little average difference between
experimental and calculated values. Table 1 shows the
reaction on the activated and non-activated substrate
prepared with the granulometric fraction between 425 –
250 m 2
slope is greater for the case of adsorption reaction on the
activated substrate which agrees with the information
given by the isotherm in the Figure 1.
Table 1.K12 values, corresponding to the adsorption isotherm obtained
from copper ions adsorption on calcined substrate
Substrate Fitted equation r K1K2
NAS
AS
Ceq/x/m = 0.4850 + 230.31 Ceq
Ceq/x/m = 0.5703 + 98.21 Ceq
0.9977
0.9868
474.86
172.20
0.0043
0.0102
However, isotherm may show but does not
Cu+2 ions and calcined substrate surface; neither does
the FTIR spectra [5]. Nevertheless, L type isotherm is
calcined substrate surfaces. Likewise, according to
the literature, in a chemisorption reaction transitional
metals should bond to the amphoteric surface through
to the formation of a covalent bonding in an inner-
sphere complex in which the metal becomes part of
the oxide surface structure, according to the reaction
2 in which H3O+ ions are ones of the reaction products
isotherm doesn´t explain the production of H3O+ ion
during the adsorption reaction and cannot explain by
itself the real interaction between copper ions and the
substrate surface.
pH study
The information given by the isotherm
chemisorption reaction between copper ions and
substrate surface. The theoretical model for the
between transitional metals and amphoteric oxides,
described by equation (2), suggests the production of
H3O+ ions during the adsorption reaction. Therefore,
the pH measurement should provide the evidence of
an acidifying process during the adsorption reaction.
Figure 3 shows the pH variation, by triplicating the
measurement, during the adsorption process as a
function of mmol of Cu+2 ions, added from a solution
0.001 M, to the raw material, and calcined activated and
non-activated substrate. In all cases, copper adsorption
of H3O+
solution is more accentuated in the non-activated and
raw material has to be related to the smaller density of
negative charges in the surface material.
Figure 3. pH variation, of the triplicated measurement, as
a function of mmol of Cu+2 ions added to the raw material,
and calcined activated and non-activated substrate.
Dotted, dashed and continued lines represent the three
replicates measurements.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
14 Millán y col.
Figure 4 shows the pH variation, by triplicated
measurements, as a function of mmol of Cu+2 added to the
activated calcined substrate. The three graphics correspond
to the adsorption reaction with the 0.001 M, 0.01 M, and 0.1
M Cu+2 solutions used for the experiment. All curves show
again the production of H3O+ ions during the adsorption
reaction. Consequently, solutions become more acidic as
the copper ion concentration increase. Table 2 shows the
mmol of H+ ions produced at the beginning and at the end
of the adsorption experiment for the conditions described
of H+ ions is at least 10 times greater in relation to the
initial concentration, but also the greater the copper
concentration is, the more acidic the solution become.
described in the Figure 4 are equivalent to 0.11, 0.27 and
1.19 mmol of H+ ions, respectively.
Figure 4. pH variation, of the triplicate measurement, as a
function of mmol of Cu+2 ion added to the calcined
substrate, activated in alkaline medium. Dotted, dashed
and continued lines represent the three replicates
measurements.
Table 2.- mmol of H3O+ ions produced during the adsorption reaction
Cu+2 M mmol H+ 10 mL soln. mmol H+ 50 mL soln. Net mmol H+RED
0.001/RM 6.71x10-7±2.39x10-8 4.60x10-5±9.50x10-6 4.59x10-5±9.03x10-6 19.7
0.001/NAS 1.04x10-5±3.60x10-7 2.23x10-4±1.05x10-5 2.13x10-4±1.05x10-5 4.9
0.001/AS 1.02x10-5±2.84x10-7 1.16x10-4±2.30x10-5 1.06x10-4±2.20x10-5 20
0.01/AS 4.31x10-5±3.00x10-6 3.11x10-4±2.87x10-5 2.68x10-4±2.84x10-5 10
0.1/AS 2.78x10-4±2.89x10-5 1.47x10-3±2.31x10-5 1.192x10-3±3.70x10-5 3
According to the information given by the
isotherm graph and the pH study, it can be suggested
that the interaction between copper ions and the
amphoteric surface of the substrate can be explained by a
chemisorption reaction according to the reaction (3):
(3)
In any case, the interaction between copper
ions and the oxidic surface must be strong enough
because attempts for desorption even with strong
acid solutions were infructuous.
Electrical conductivity study
Figure 5 shows the Electric Conductivity (EC)
variation as a function of mmol of Cu+2 ions added
to the raw material, and calcined activated and non-
activated substrate, using a 0.001 M Cu+2 solution.
In all cases EC of the solution decrease due to the
adsorption reaction. In the case of the raw material,
there is a contribution to the EC from the dissolved
fraction in the solution.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
15Cu (II) Chemisorption on Calcined Substrates made with an Oxidic Refractory
Figure 5. Electric conductivity variation, of the triplicated
measurements, as a function of mmol of Cu+2 ions added,
from a solution 0.001 M, to the raw material, and the
calcined activated and non-activated substrates. Dotted,
dashed and continued lines represent the three replicates
measurements.
However, in the case of calcined substrates, the
EC relay only on copper and sulphate ions, due to their
greater concentration, other ionic species coming from
the calcined substrate has minor contribution because
calcined substrate is slightly soluble, so the dissolved
fraction is negligible. On the other hand, the adsorption
reaction on activate and non-activated substrates seems
to take place by the same mechanism, but it is produced
in a greater extend on activated material due to the
creation of new activated sites through the deprotonation
reaction. This aspect was also evidenced by the isotherms
and Langmuir constants. The lowest EC values during
adsorption reaction on activated substrate in relation to
non-activated substrate shows that adsorption reaction
actually takes place more extensively on this substrate.
Figure 6 shows the average quantities of
copper ions adsorbed on 2 g of raw material and 2 g of
the activated and non-activated calcined substrate. These
quantities are similar to those reported in previous
reaction creates a greater negative charge density on
the surface were the adsorption reaction may occur.
The greater adsorption on the raw material is due to
adsorption on calcined substrates shows that calcination
process affects the net surface available for the adsorption
raw material and calcined substrate; according to these
about 55% in relation with raw material. However, these
values could be underestimated because the limitations of
N2 adsorption method, when applied to charged surfaces
2/g, due to the non-
polarity of N2 molecule [11].
Figure 6. Amount of copper ions, in mg, adsorbed on 2
g of the raw material and the calcined substrate, with
activated and non-activated surface.
Figure 7 shows Electrical Conductivity (EC)
variation, of the triplicated measurements, as a function
of mmol of Cu+2 solutions added to the calcined substrate,
activated in alkaline medium. The three graphics
correspond to the 0.001 M, 0.01 M, and the 0.1 M Cu+2
solutions used for the experiment. The EC decreases
at lower concentration where the EC decreases to 900
mS during the reaction, instead of 700 mS where the Cu+
2 concentration is ten times greater and 150 mS when the
concentration is 100 times greater.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
16 Millán y col.
Table 3
Raw material Calcined substrate
2/g) 56.35 20.51
Pore volumen (mL/g) 85.80 46.30
External Surface (m2/g) 68.17 23.60
2/g) 77.91 21.05
Figure 7. Electrical conductivity variation as a function of
mmol of Cu+2 ions added to the calcined substrate. Dotted,
dashed and continued lines represent the three replicates
measurements.
Conclusions
The objective of this study is to take advantage
of the physicochemical characteristics of the lithologic
material found in the town of San Juan de Lagunillas,
Mérida, Venezuela and uses it for the preparation of a
calcined substrate that can be applied as a granular media
for heavy metal retention in water treatment. Although
more studies are required, the results obtained from
previous works have shown that the lithologic material
is appropriate for the preparation of ionic adsorbent
substrates and their application in copper retention
from aqueous solutions. Some of these results have
calcined surface characterized by an L type isotherm, and
associated to chemisorption reaction between adsorbate
and adsorbent. The mechanism of copper adsorption on
oxidic surface seems to be the same for activated and
non-activated surfaces however, the differences is given
by the greatest density of negative charges created by
the alkaline treatment, which deprotonates amphoteric
oxides, enhancing adsorption reaction. Nevertheless, this
evidence had to be complemented with additional data by
proving the associated production of H3O+ ion to such kind
of reaction. The pH measurements during the adsorption
reaction, which validates the literature about transitional
metals chemisorption on amphoteric surface with variable
the concentration of copper ions in the solution increases;
low concentration. The hypothesis of the chemisorption
reaction is also supported by the resistance of copper ions
to desorption reaction. This fact could be interpreted in
terms of a covalence formation between copper ions and
is expected that other transitional metals can suffer such
kind of reaction on the surface of these kinds of substrates,
and it is possible to separate it from the contaminated
The variable charge properties of the oxidic surface is
evidenced not only by the PZC experiment, but also by the
activation reaction, which creates new negative charges
that can participate in the adsorption phenomena, thus
for ionic retention. The amphoteric metallic oxides
deprotonate in alkaline medium, increasing negative
charge density on calcined adsorbent surface. The thermal
treatment favors the formation of the amphoteric oxides
with PZC similar to the reported values for pure Fe and Al
oxides. The deprotonation reaction of the reactive groups
in the substrate surface have been also proved by the EC
measurements, showing that adsorption phenomenon is
enhanced on activated surfaces with alkaline treatment
just because Copper ions adsorb irreversibly on the
amphoteric surface being unable to participate as mobile
ions in the solution.
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