Advances in Ma terials Physics and Che mist ry, 2012, 2, 119-125
doi:10.4236/ampc.2012.24B032 Published Online December 2012 (http://www.SciRP.org/journal/ampc)
Adsorption of Cu(II), Ni(II), Zn(II), Cd(II) and Pb(II) onto
Kaolin/Zeolite Based- Geopolymers
Bassam El-Esw ed1, Mazen Alshaaer2, Rush di Ibr ahim Yousef3, Imad Hamadneh4, Fawwaz Khalili4
1Zarka University College, Al-Balqa Applied University, Zarka, Jordan
2Deanship of Academic Research, Uni vers ity of Jordan, Amma n, Jordan
3Chemistry Department, Faculty of Science, Preparatory Year Program, King Faisal University, Al-Ahsaa, Saudi Arabia
4Department of Chemistry, Faculty of Sciences, University of Jordan, Amman, Jordan.
Received 2012
ABSTRACT
This work deals with geopolymers based on local Jordanian resources, namely, kaolin and zeoltitic (phillipsite) tuff. The geopoly-
mers were prepared from these two materials by a reaction with an alkali solution at 80ºC. The research group of the present work
has demonstrated in previous work that addition of zeolitic tuff to kaolin based-geopolymers increases the adsorption capaci ty toward
Cu(II) metal io n compared to zeolite-free geop olymers, while ret aining high mechanical strength. The ai m of the p resent work is to
extend our work and to study the effect of changing geopolymers components (zeolitic tuff and kaolin) on their adsorption properties
toward Cu(II), Ni(II), Zn(II), Cd(II) and Pb(II) metal ions. Both isothermal and kinetic studies revealed that increasing the zeolitic
tuff: kaolin ratio improves the adsorption capacity of geopolymer toward metal ions. The adsorption capacity of the geopolymers of
150: 50 zeolites: kaolin content was found to be higher than that of the raw materials themselves. The rate of adsorption of geopoly-
mers was fou nd to be lower than that of raw materials due to kinetic limitations imposed by the formation of geopolymerization net-
work. The selectivity of geopolymers toward adsorption of metal ions was found to be distinct from raw zeolite and kaolin where
the adsorption onto geopolymers was found to be more preferential for small size metal ions (Cu(II), Ni(II), Zn(II)) than for large
size metal ions (Pb(II), Cd(II)). The adsorption of Cu(II) and Pb(II) onto geopolymers did not decrease with competition with other
metal io ns, which indi cates cooperative adsorption. The adsorption process of metal ions onto geopolymers was found to be reversi-
ble that indicates that metal ions are bound by physical cation exchange to the exchangeable sites of unreacted phillipsite and new
amorphous geopolymer sites. Leaching of metal ions from raw kaolin was much more effective than geopolymers and zeolite be-
cause of compact structur e of geopo lymers.
Keywords: Geopolymers; Kaoli n; Zeolitic Tuff; Adsorption; Heavy Metal Io ns
1. Introduction
Several methods h ave evolved o ver the years on the removal of
heavy metal ions present in industrial wastewaters and soils.
These are chemical precipitations, conventional coagulation,
reverse osmosis, ion exchange, and adsorption. Out of these
methods, adsorption appears to be the most widely used for the
removal of heavy metals [1]. Substances like kaolin and zeo-
lites have assumed a wid e application i n this regard [2-4].
This work deals with geopolymers based on local Jordanian
resources, namely, kaolin and zeoltitic (phillipsite) tuff. The
geopolymers were prepared previously from 1:1 mass ratio of
these two materials b y a reaction with an alkali solution at 80ºC.
The research group of the present work has demonstrated in
previous work that addition of zeolitic tuff to kaolin based-
geopolymers increases the adsorption capacity toward Cu(II)
metal ions compared to zeolite-free geopolymers, while retain-
ing high mechanical strength [5,6]. These geoplymers can be
used as construction materials for water treatment, storage and
transportation. The process used in the present work is of much
lower cost than the most popular metakaolin based geopoly-
mers which, involves calcination of kaolin at 600ºC which re-
quires large amounts of energy and complete dissolution of
metakolin which r equir es large amount of base [7].
The exact mechanism of the geopolymerization is not known
precisely. It was suggested that Na+ or K+ from alkaline solu-
tion to exchange the hydrogen ions on the broken edges of the
clay. Because of this ion exchange, repulsion between the Na+
ions will dissolute some clay particles [8]. The breakdown of
the solid aluminosilicate into smaller ‘monomers’ where Al is
already tetrahedrally coordinated is followed by polycondensa-
tion of these monomers into the geopolymer [9,10]. Because o f
these reactions, solid, hard, and stable materials with hydrox-
ysodali te, feldspatiod, or zeolit e like structure are formed [11].
When aluminum is four coordinated to oxygen atoms, a neg-
ative charge is created and therefore the presence of cations
such as Na+ is essential to maintain electric neutrality in the
geopolymeric matrix (hydroxysodalite). Hydroxysodalite, which
ranges fro m amorphous to microcr ystalline materi al, consists o f
SiO4 and AlO4 tetrahedral linked alternately by sharing all the
oxygen atoms [11]. Positive ions (Na+, K+, Li+, Ca2+, Ba2+,
NH4+, and H3O+) must be present in the framework cavities to
balan ce the negative charge of Al in the fo ur-fold coordination.

B. EL-ESWED ET AL.
120
Little work was found in the literature on the adsorption be-
havior of geopolymers. Li et al. [12] studied the adsorption of
methylene blue (MB) dye onto geopolymeric adsorbent based
on fly ash. The synthesized geopolymer was found to have
much higher adsorption capacity towards MB (0.12 mmol
MB/g adsorbent) than fly ash itself (5.6 x 10-3 mmol MB/g
adsorbent). Wan g et al. [13] reported an amorphous aluminosi-
licate geopolymer resulting from solid-state conversion of fly
ash. The synthesized geopolymer was found to have a higher
adsorption capacity towards Cu2+ ion (1.4 mmol Cu/g adsorbent)
than the fly ash it self (1.6x10-3 mmol Cu/g adsorbent). A
Geopolymer of Jordanian kaolin and zeolitic tuff prepared by
the research group of the present article was found in previous
works to have adsorption capacity of 8.06 mmol MB/g adsor-
bent and 0.83 mmol Cu/ g adsorbent [6] and 0.36 mmol Pb/ g
adsorbent (at pH 6) [14]. Cheng et al. [15] demonstrates that at
pH 4, the adsorption capacity of meta-kaolin based geopolymer
toward Pb(II), Cu(II), Cr(III) and Cd(II) was 0.71, 0.77, 0.38,
0.60 mmol/g adsorbent. The aim of the present work is to ex-
tend previous studies and to study different kaolin: zeolitic tuff
geopolymeric samples in order determine the best ratio of the
geopolymer that gives the highest adsorption capacity toward
Cu(II), Ni(II), Zn(II), Cd(II) and Pb(II). The main concern is
determining the optimum zeolitic content in the geopolymer
that will provide a material with high efficiency for water puri-
fication.
2. Materials and Methods
2.1. Materials
Preparation and characterization of Jordanian kaolinite and zeo-
litic (phillipsite) tuff were discussed in our previous works
[6,14, 16].
2.2. Fabrication of Geopolymeric Samples
Seven geopolymeric samples with different zeolitic content
were prepared from kaolinitic Jordanian soil (K), functional
reactive filler (zeolitic tuff, Z), and alkali solution as shown in
Table 1.
The zeolitic tuff and kaolinitic soil were mixed in different
ratios (Table 1), and then the sodium hydroxide solution was
Table 1. Composition of synthesized geopolymers in grams.
Geopolymer K Z NaOH Water
G1 200 0 14 44
G2 175 25 14 40
G3 150 50 14 36
G4 125 75 14 32
G5 100 100 14 28
G6 75 125 14 24
G7 50 150 14 20
added. After mixing, a semi-dry mixture was formed. After
molding, compacting, curing at 80ºC, the samples were ground
and sieved into aggregate size between 250-500 μm. Then the
product was washed with excess amount of distilled water (to
remove unr e ac te d a lk a li) , dr ied a t 100ºC a nd k e pt i n a de s ic cator.
2.3. Characterization of Geopolymers
XRD pattern and SEM pictures were obtained for geopoply-
mers G5 and G7 in order to determine the fate of kaolinite and
phillipsite in the geopolymers sample.
2.4. Kinetics of A dsorption of Meta l Ions onto
Geopolymers and Raw Materials
A 0.5000 g sample of geopolymers (G1-G7) and raw materials
(Z and K) were independently placed in a 500 mL-conical flas k,
to which 250 mL of 100 ppm of a standard solution of a metal
ion (Cu(II), Ni(II), Zn(II), Cd(II), Pb(II)) prepared in 0.1 M
NaCl was added . The solution was adjusted to pH 4 and sha-
ken in the shaker water bath at 25°C and 320 rpm. A 1.0 mL
sample of the solution was withdrawn at different contact times
(0 - 72 h) and diluted to 5 mL with distilled water, then filtered
by microfilter and centrifuged. The concentrations of metal ions
were measured using the atomic absorption spectrometer (Va-
ria n, AA-250 plus).
2.5. Adsorption Isotherms of Metal Ions onto
Geopolymers and Raw Materials
Adsorption of single metal ions: Standard solutions (10–100
ppm) of metal (Cu (II), Ni(II), Zn(II), Cd(II, Pb(II)) in 0.1M
NaCl at pH 4 were prepared (pH adjustment using NaOH/HCl).
Conical flasks were filled with 50 ml of the prepared standard
solutions of metal ions and 0.05 g of geopolymer (G1- G7) or
raw materials (K, Z). A 10.0 mL portions from each conical
flask were withdrawn after 24 h of shaking in water bath at
25ºC and 320 rpm and filtered by microfilters (0.45μm Nylon).
The concentrations of metal ions were determined using the
atomic absorption spect rometer.
Adsorption of multiple metal ions: The same procedure
above was followed, but using standards prepared from combi-
nation of metal ions (Cu(II), Ni(II), Zn(II), Cd(II, Pb(II)).
Analysis using atomic absorption was made for the four ele-
ments in each sample.
2.6. Desorption of Metal Ions
A 0.5 g of geoplymers or raw materials was shaken with 250
mL of 1000-ppm solution of metal ions at pH 4 and 0.1 M
NaCl ionic strength for 24 h. The solution was then filtered and
dried in an o ven at 100 C. The solid was then leached with 250
mL of 0.1 M NaCl solution at different contact times ranging
from 0.25-72 h, where 1.00 mL was pipetted at each time, and
diluted to 5.00 ml and analyzed for metal ions concentration
using atomic absorption spectrometer.

B. EL-ESWED ET AL.
121
3. Results and Discussion
3.1. Characterization of Geopolymers
The XRD patterns of geopolymers G5, G7, raw materials zeo-
lite, and kaolin are presented in Fig ure 1.
The phi llipsite peaks were more noticeable in the patt erns of
G7, which is of higher zeolitic content. The kaolin peaks were
observed in the case of G5 and G7, indicating incomplete dis-
solution of kaolin. The new phase of geopolymer was not de-
tected because this new phase is amorphous.
The SEM graphs (Figure 2) of geopolymers G5 and G7 in-
dicates the presence of crystalline phillipsite immersed in
amorphous geopolymeric material.
3.2. Adsorption K i ne tics
The effect of contact time on the amount of metal ions (Pb(II),
Cd(II), Cu(II), Ni(II), Zn(II)) adsorbed onto geopolymers and
raw materials was investigated. A sample of this data is given
in Fi gure 3 for Ni(II). Among several kinetic models employed
(first order, pseudo-second order, intraparticle diffusion, film
diffusion) to fit Qt - t data, the pseudo-second order mod el was
selected depending on the correlation coefficient values of the
models. Thus, pseudo-second order kinetics model (eq. 1) [17]
was used to fit the kinetics data of adsorption of metal ions onto
geopo lymers and raw mat erials. Th e linear for m of the pseu do-
second order kinetics model is:
( )
2
1
t ee
tQkQt Q= +
(1)
where Qe is the amount of metal ion adsorbed at equilibrium
(mmol metal ion/g adsorbent); t is the time (min); Qt is the
amount of metal ion adsorbed (mmol metal ion/g adsorbent) at
time t; k is the rate constant of pseudo-second order adsorption
(g adsorbent/ mmol metal ion.min). By plotting t/Qt versus t
(Figure 4, for Ni(II)), the value of the slope 1/Qe and the i nter-
cept 1/(kQe2) can be used for determination of Qe and k.
Figure 1. XRD patterns of geopolymers G5, G7, and raw materials
K and Z.
Figure 2. SEM of geopolymers G5 and G7, respectively.
Figure 3. Plots of Qt (mmol/g adsorbent) versus t (min) for kinetic
study of adsorption of Ni(II) onto geopolymers G1, G3, G5, G7 and
raw materials Z and K.

B. EL-ESWED ET AL.
122
The results of Qe and k obtained for Cu(II), Ni(II), Zn(II),
Cd(II) and Pb(II) are presented in Figure 5. It is clear from
Figure 5, that the amount of adsorption of metal ions onto
geopolymers (Qe) is higher than that of raw mater ials.
Thus, the geopolymerization process that resulted from dis-
solution of aluminosilicate monomers followed by polymeriza-
tion o f theses mon o mers creates new cat io n exch ange si tes. The
amount of equilibrium adsorption capacity (Qe) of metal ions
onto t he geopolymers i ncreases with increasin g zeolitic content
of the geopolymers. This may be due to the increasing phillip-
site content, which increases adsorption efficiency. Neverthe-
less, the rate constant of adsorption (k) of kaolinite is higher
than that of geopolymer and zeolite, which indicates that the
sheet structure of kaolinite imposed less kinetic limitations than
zeolite and geopolymers. It seems that the three dimensional
struct ure of geopolymer is similar to zeolite.
When comparing the amount metal ions adsorbed, the ob-
tained trends of Qe are:
For G1-G7: Ni, Cu, Zn > Cd, Pb
For Z : Cu > Cd > Ni > Zn > Pb
Figure 4. Plots of t/Q (mi n. m mol -1. g adsorbent) vers us t (min) for
kinetic study of adsorption of Ni(II) onto geopolymers G1, G3, G5,
G7 and raw materials Z and K.
Figure 5. Variation of (A) equilibrium adsorption capacity Qe and (B) rate constant k calculated from pseudo-second order kinetic model
with ch a nge of c ompos ition of geopolym er.

B. EL-ESWED ET AL.
123
For K: Cu= Ni > Zn > Pb > Cd
The difference in behavior of zeolite, kaolinite and geopoly-
mers indicates the unique structure of the geopolymers. The
structure of geopolymer may be so condense that it is more
accessible for small size metal ions like Cu, Ni, Zn than large
one like Cd and Pb.
3.3. Adsorption Isotherms
The adsorption isotherms of metal ions (Pb(II), Cd(II), Cu(II),
Ni(II), Zn(II)) onto synthesized geopolymers and raw materials
were investigated. The Langmuir equation (eq. 2) is the most
popular equation for modeling adsorption isotherms [18]:
( )
1
m
QQ KCKC= +
(2)
where, Q is the amount of metal ions adsorbed (mmol metal/g
adsorbent), Qm is the adsorption capacity (mmol metal/g adso r-
bent), K is the affinity constant (L/mmol metal), and C is the
equilibrium concentration of metal ions (mmol metal/L).
Langmuir equation can be linearized in the form (eq. 3) [18]:
( )()
11
mm
CQQCQK= +
(3)
The values o f adsorp tion capacit y (Qm) and affinity constants
K were determined from the slope and intercepts of the plots of
C/Q versus C. The values of Qm are presented in Figure 6 for
the metal ions investigated. Geopolymer G7, which has the
highest zeolitic content, has higher adsorption capacity toward
metal io ns than r aw materials K and Z. The adso rption capaci ty
of small size metal ions like Cu and Zn is higher than those of
large siz e one li ke Cd and Pb. These r esults ar e simil ar to those
obtained from the kinetic study.
It is obvious from Figure 6 that increasing the zeolitic tuff
content of geopolymers (moving from G1 to G7) leads to an
increase of adsorption capacity of geo polymers to w ar d.
Figure 6. Langmuir adsorption capacity (Qm, mmol metal/g adsorbent) for geopolymers and raw materials at pH 4, (A) single and (B) multiple
metal adsorption.

B. EL-ESWED ET AL.
124
3.4. Mult iple Adsorption
In the case the multiple metal ions adsorption (Figure 6), one
shou ld exp ect a d ecrease o f adso rpt ion capaci ty of geopolymers
compared to single metal ions adsorption due to competition
between metal ions. This was observed in the case of raw zeo-
lite. On the other hand, in the case of kaolinite, a reverse trend
was observed, where adsorption capacity Qm increases with
competition, which indicate cooperative adsorption. The ad-
sorption capacity of Cd(II), Ni(II), Zn(II) onto geopolymers
decreases with competition in a similar manner to the adsorption
of metal ions onto zeolite. However, the adsorption of Cu(II)
onto geopolymers increases with competition like adsorption of
metal ions onto kaolinite. The adsorption of Pb(II) onto geopo-
lymers was no t affected significantly by competition. Thus, the
adsorption sites of geopolymers are unique and different from
that o f zeo lite and kaolinite. The cooperative adsorption is evi-
dent in the case of adsorption of Cu(II) onto geopolymers and
in the case of adsorption of metal ions onto kaolinite.
3.5. Desorption Study
The adsorption process of metal ions onto geopolymers was
found to be reversible. After 24 h leaching with 0.1M NaCl
solution, about 60% of the adsorbed metal ions were desorbed
from geopolymer loaded with metal ions solution. This indi-
cates that metal ions ar e bound by physical cation exchange and
could be exchanges with Na+. The results of leaching geopoly-
mer loaded with Cu(II) ions are shown in Figure 7. Leaching of
metal ions from raw kaolin was much more effective than geo
polymers and zeolite because of compact structure of geopoly-
mers.
Fig ure 7. The %lea ching of Cu(II) from geopolymers and raw ma-
terials loaded with Cu(II) as a function of time. Leaching was car-
ried out using 0.1 M NaCl solution.
4. Conclusion
Both isothermal and kinetic stu dies revealed th at increasin g the
zeolitic tuff: kaolin ratio improves the adsorption capacity of
geopolymer toward metal ions. The adsorption capacity of the
geopolymers of 150:50 zeolites: kaolin content was found to be
higher than that of the raw materials themselves. The rate of
adsorption of geopolymers was found to be lower than that of
raw materials due to kinetic limitations imposed by formation
of geopolymerization network. The selectivity of geopolymers
toward adsorption of metal ions was found to be distinct from
raw zeolite and kaolin where the adsorption onto geopolymers
was found to be more preferential for small size metal ions
(Cu(II), Ni(II), Zn(II)) than for large size metal ions (Pb(II),
Cd(II)). The adsorption of Cu(II) and Pb(II) onto geopolymers
did not decrease with competition with other metal ions that
indicates cooperative adsorption. The adsorption process of
metal ions onto geopolymers was found to be reversible, whi ch
ind icates that metal io ns are bound by physical cat ion exchange
to the exchangeable sites of unreacted phillipsite and new
amorphous geopolymer sites. Leaching of metal ions from raw
kaolin was much more effective than geopolymers and zeolite
because of compact structure of geopolymers.
5. Acknowledgements
The authors would like to express great thanks for the Scientific
Research Support Fund of the Ministry of Higher Education
and Scientific Research, Amman – Jordan, project (number
S1/22/2009).
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