Study Of Using Bentonite – Poly Ethylene Glycol Composite for Metal
Removal from Water
NEAMA AHMED SOBHY AHMED
Sanitary & Environmental Engineering Institute
Housing & Building National Research Center
87 Tahrir St., Dokki
EGYPT
Abstract: - Direct polymerization of polyethylene glycol (PEG) in suspensions of Bentonite (Ben) was used for
preparation of Ben-PEG composite. The prepared composite was characterized using field-effect scanning
electron microscopy, surface area measurements, and X-ray diffraction. In the XRD pattern there is a change in
peak intensity. But New peaks appeared. This may be due to high dispersion of particles of polymer in the Ben
matrix or low concentration of the modifying agent. The crystallinity absence after loading the sorbent with
cadmium and lead ions in the SEM measurement indicates that there was no crystalline phase after sorption.
The optimal conditions for adsorption of Cd2+ and Pb2+ ions were found to be a PEG content of 0.2 % and a
contact time of 150 min. The sorption experiments were performed under different operating variables,
including, pH, adsorbent dose and initial concentration of metals. For both Cd2+ and Pb2+, Adsorption
parameters were determined using both Langmuir and Freundlich isotherms, but the experimental data were
better fitted to the Langmuir equation than to Freundlich equation. The adsorption equilibrium was described
by the Langmuir model, which confirmed the presence of saturated mono-layer of adsorbent molecules on the
adsorbent surface, that the energy of adsorption is constant. The potential of Ben-PEG composite for the
removal of cadmium and lead from aqueous solution was substantiated.
Key words: Polymerization; Poly Ethylene Glycol; Bentonite; Cadmium and Lead Ions.
Received: June 29, 2022. Revised: August 17, 2023. Accepted: September 23, 2023. Published: October 5, 2023.
1 Introduction
The amount of toxic pollutants increased as a result
of industrialization as well as the increase in human
activities. Among them, heavy metals, dyes, and
phenolic compounds [1]. In recent years, the
adsorption process has attracted much attention
because of its easy control, reduced operating costs
and outstanding performance [2-3]. Heavy metal ion
contamination exists in aqueous waste streams from
different industries such as, batteries, metal plating
manufacturing besides agricultural sources where
fungal sprays and fertilizers are seriously utilized
[4]. The heavy metal ions released into the
environment represents a risk to the ecosystem,
human health and particularly to people due to its
toxicity for living organisms [5-6]. Clay and
bentonite are adsorbents and have received great
attention due to their environmental suitability, high
mechanical and chemical stability, low cost, and
natural abundance. These materials are
characterized by high surface area and high cation
exchange capacity and are used as adsorbents for
various separation purposes [7-10]. The
improvement of the adsorption ability of natural
adsorbents such as clay and bentonite is essential
[11].
Many clay adsorbents in the natural state do not
have a high capacity for adsorption, so they are
often modified to improve the properties of
adsorption, thermal activation, catalysts and various
complexing agents such as organic materials and
polymers used to activate natural adsorbents with
different methods [12]. The novelty of research
work is preparation of adsorbent with low cost and
is applicable to be used for removal of heavy metal
pollutants with high removal efficiency.
The aim of this work was to study the characteristics
of modified bentonite sorbent and study the removal
of lead and cadmium ions. In this work, the Ben
clay was modified with poly ethylene glycol (PEG)
which is an available reagent and non- toxic,
miscible in water and interacts at the molecular
level. Batch adsorption experiments are carried out
International Journal of Chemical Engineering and Materials
DOI: 10.37394/232031.2023.2.10
Neama Ahmed Sobhy Ahmed
E-ISSN: 2945-0519
70
Volume 2, 2023
and the adsorption kinetics and isotherm were
contemplated.
2 Experimental Setup
2.1. Materials
Bentonite (Ben) (95% purity), purchased from the
local company (Egypt); Poly ethylene glycol (PEG)
produced by Sigma-Aldrich with molecular weight
of 4000 g mol−1; Pb(NO3)2 and CdCl2 · 2H2O
produced by Alpha chemicals.
2.2 Preparation of Adsorbents
The Ben clay was treated with different
concentrations of PEG. For this purpose, 25 gm
natural Ben was mixed with 200 ml of 0.2, 0.5, 1.0,
1.5, 2 and 4 % aqueous solutions of PEG, using
continuous stirring at 25℃ for 2 h and left for 36 h at
ambient temperature. Then the suspension of the
adsorbent was separated from the solution by
filtration. Then washed thoroughly with distilled
water and dried at 130℃ for 5 h. Finally, the
sorbents obtained were ground to a powder of 80
µm in size using a porcelain mortar.
2.3 Batch Experimental System
Batch adsorption experiments were conducted using
Ben/PEG composite by varying the dose (0.5, 1, 1.5,
2, 2.5 and 3 g/L), and contact time (0, 30, 60, 90,
120, 150 and 180 min. agitated with 0.5 g). All
experiments were conducted in a jar test at 150 rpm
at room temperature. After equilibrium, the
concentration of samples was measured by Atomic
Absorption Spectrophotometer, (ICE3000, Thermo
scientific Limited, UK.). The percentage of removal
efficiency (R %), has been calculated from equation
(1)
Absorption (%) = (Co-Ce) / Co *100 (1)
where R % is the removal efficiency, Co is the
initial metal concentration in solution (mg/L), Ce is
metal concentration after adsorption in solution
(mg/L).
The capacity of absorption qe (mg/g) at equilibrium
has been calculated using equation (2)
Qe (mg/l) = (Co-Ce) * V/m (2)
Where Qe is the adsorption capacity at equilibrium,
mg/g.
V is the aqueous solution volume, L.
m is the adsorbent weight, g.
2.4. Sorbent Characterization
XRD model X Pert Pro Philips MPP PW 3050/60
X-Ray diffractometer used for detailed
mineralogical composition of the sorbent material.
On the other hand, Scanning Electron Microscopy
(SEM) was used to determine microstructure and
morphological features of the prepared sorbent by
using SEM Model Quanta 250 FEG (field emission
gun) with accelerating voltage 30 KV, (FEI
Company, Netherlands).
2.5 Adsorption Study Pattern
2.5.1 pH Effect
About 0.5 gm of Ben-PEG composite was added to
30 mg/l of lead nitrate and cadmium chloride
solutions separately at temperature 27 C + 2 ℃ and
the stirring of the solution was mixed at 150 rpm.
The pH effect on adsorption of metal ions onto raw
Ben was studied earlier [13]. The pH was adjusted
using NaOH for alkaline medium and HCL for
acidic medium.
2.5.2 Contact Time Effect
A dosage of 0.5 gm of Ben-PEG composite with
different contact times ranging (30-180 minutes)
added to 30 mg/l of cadmium chloride and lead
nitrate solutions separately, ambient temperature
27 + 2 ℃ and the solution stirring rate was fixed at
150 rpm.
2.5.3 adsorbent Doses Effect
Different adsorbent doses (0.5-3 gm) of Ben-PEG
composite were added to 30 mg/L of lead nitrate
and cadmium chloride solutions separately for 120
minutes at temperature 27 + 2℃ and pH 7.
2.5.4 Initial Metal Ion Concentration Effect
A dosage of 0.5 gm of Ben-PEG composite was
mixed in solutions with initial metal ion
concentrations ranging from (5-30 mg/L) at
temperature 27 + 2℃ and pH 7.
3. Results & Discussion
3.1 Characterization of Adsorbents
The obtained Ben–PEG sorbent was thoroughly
characterized by EDX, FE-SEM and XRD Analysis.
Physico-chemical and textural characterization of
the Ben and modified Ben sorbent is summarized in
table 1. Ben in its dry state has a moisture content of
around 8.1% and ash content of 6.1%. Moreover,
the data show that the initial Ben clay modification
leads to a reduction in the total pore volume of
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DOI: 10.37394/232031.2023.2.10
Neama Ahmed Sobhy Ahmed
E-ISSN: 2945-0519
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Volume 2, 2023
acetone (from 28.2 to 18.12%), which indicates a
reduction in the mesopores number. In addition, the
increase in iodine adsorption (from 28.60 to
39.00%) indicates microporous structure
improvement. Water sorption measurements
indicated that the pore volume decreased by
polymer modification. Hence, we observed that the
modification of Ben by PEG leads to a
predominance of meso and micro-pores in the
structure of the sorbent, which significantly enhance
the adsorption of heavy metal ions.
Table (1) Textural characterization of Ben
and Ben-PEG
Characterization
Ben
Ben-PEG
Ash Content, %
6.1
21
Moisture, %
8.1
4.6
Adsorption activity on
iodine, %
28.6
39
The total pore volume of
acetone, %
28.2
18.12
The total pore volume of
water, cm3g-1
0.01
0.008
Figure 1A,1B shows typical FE-SEM images of
natural Ben and modified Ben–PEG. natural Ben
(Fig. 1A) has a uniform texture provided by
micropores which have a diameter in the range of 2–
5μm. Needle-shaped appendages of the polymer are
shown in this image (Fig. 1B), which indicates the
PEG impregnation. The crystallinity is absent after
loading the sorbent with Cd2+ and Pb2+ ions (Fig. 1C
and 1D) indicates that there was no crystalline phase
after sorption.
B
D
Fig1: SEM images of sorbents: (A) Ben, (B) Ben–
PEG, (C) Ben–PEG-Cd and (D) Ben–PEG-Pb.
The main mineral of Ben is the Montmorillonite, it
has a 2:1 layer structure, containing octahedral
alumina sheet between tetrahedral silica sheets [14].
The bond between the silica sheets is very weak,
allowing exchangeable ions and water to enter.
Adsorption of PEG can occur on both interlayer
spaces and external surfaces. So, the adsorption
happens according to the ion-exchange mechanism.
The XRD patterns of raw Ben (A) and modified Ben
(B) are shown in Figure (2), the raw Ben contains
diffraction patterns of Montmorillonite, that located
at 2θ = 20.3, 32.3, and 62.4 and quartz, where the
characteristic peaks located at 2θ= 37.2, 39.1 and
50.65, respectively. The other peaks for impurities
due to illite, field spar and cristobalite [15].
However, as can be observed in the diffraction
pattern of Ben-PEG as shown in Fig. (2), there is a
change in peak intensity. No new peaks appeared.
This may be due to high dispersion of particles of
polymer in the Ben matrix or low concentration of
the modifying agent.
Fig. 2. XRD patterns of: (A) Raw Ben and (B)
Ben–PEG.
3.2. Effect of pH
The effect of variation in pH on the removal of
Cadmium and Lead ions has also been studied using
Ben-PEG composite in the range from 3 to 11 using
0.1 % HCl and 0.1 % NaoH solutions that gave the
maximum value of pH for our investigations for
cadmium and lead ions removal. It is apparent from
Fig. (3) that the lead removal shows maxima at pH 7
solution and then decreases with further increase in
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Neama Ahmed Sobhy Ahmed
E-ISSN: 2945-0519
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Volume 2, 2023
pH and the cadmium removal shows maxima at pH
9 solution and then decreases with further increase
in pH.
Fig. 3: Effect of variation in pH on adsorption of
cadmium and lead ions on Ben-PEG Composite
3.3. Effect of contact time
The effect of stirring time on the removal of
cadmium and lead ions using Ben-PEG composite
was studied by varying the time of stirring from 30
to 180 minutes for the optimum equilibrating time,
pH adjusted at 7 and stirring rate 150 rpm. Results
in Fig. (4) show that the equilibrium in adsorption of
cadmium ions is attained at 150 minutes of stirring
time and lead ions are attained at about 150 minutes
of stirring time. Therefore, the optimum stirring
time of 150 minutes has been chosen for all
investigations throughout the study.
Fig. 4: Effect of contact time on adsorption of
cadmium and lead ions on Ben-PEG
3.4. Effect of adsorbent dose
The effect of adsorbent dose of Ben-PEG composite
on the removal of cadmium and lead ions was
studied by varying adsorbent dose from 0.5 to 3 gm
at 27 + 2°C. The pH of solution adjusted at 7 and
time 150 minutes. It is observed that the maximum
adsorption obtained at 2.5 gm for cadmium and lead
ions removal as shown in Fig. (5).
Fig. 5: Effect of adsorbent dose of Ben-PEG
composite on adsorption of cadmium and lead
ions
3.5. Effect of initial metal concentration
Adsorption studies were carried out on a fixed
weight of Ben-PEG Composite 2 g with varying
lead concentrations from 5 to 30 mg/L. It is
observed from our studies that the cadmium and
lead removal efficiency increase with increasing
lead concentrations and rises to maxima up to
around 25 mg/L as shown in Fig. (6). In a previous
study result [16] have shown that such behavior is
anticipated due to the buffering properties of lead
compounds.
International Journal of Chemical Engineering and Materials
DOI: 10.37394/232031.2023.2.10
Neama Ahmed Sobhy Ahmed
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Fig. 6: Effect of initial concentration of metals on
adsorption of cadmium and lead ions on Ben-
PEG Composite
3.6. Adsorption models
3.6.1. Adsorption isotherm
An adsorption isotherm equation is an expression of
the relation between the amount of solute adsorbed
and the concentration of the solute in the fluid phase
since the adsorption isotherms are important to
describe how adsorbates will interact with the
adsorbents which are important for design purposes;
therefore, the correlation for equilibrium data using
an equation is essential for practical adsorption
operation [17]. Two isotherm equations were
adopted in this study as follows:
3.6.1.1. Langmuir isotherm equation
The Langmuir equation is based on the assumptions
that maximum adsorption corresponds to a mono-
layer of adsorbent molecules on the surface of
adsorbent, so the energy of adsorption is almost
constant [18] The Langmuir equation is defined as:
Qe = (b.Qm.Ce)(1+bCe) (3)
And in linearized form is:
Ce/Qe = (Ce/Qm) + (1/(bQm)) (4)
Where “Qm” is Langmuir constant related to the
adsorption capacity and “b” is Langmuir constant
related to sorption energy. “Ce” is the equilibrium
concentration in mg/l, and “Qe” is the amount of
adsorbate adsorbed per unit weight of adsorbent
(mg/g). The plots Ce/Qe against Ce are shown in Fig.
(7) and Fig. (8). The adsorption of cadmium and
lead ions on Ben-PEG composite give a straight
line. It is clear that the linear fit is fairly good and
enables the applicability of the Langmuir model.
Fig. 7: Langmuir isotherm plot for adsorption of
cadmium ions on Ben-PEG composite
Fig. 8: Langmuir isotherm plot for adsorption of
lead ions on Ben-PEG composite
Table 2: Langmuir constants from Langmuir
isotherm
R2
Qm
b
Cadmium
removal
0.9857
14.42
246.2
Lead removal
0.9946
12.92
210.9
3.6.1.2. Freundlich isotherm equation
The Freundlich sorption isotherm, one of the
frequently used mathematical descriptions, gives an
expression including the surface heterogeneity and
the exponential distribution of active sites and their
energies.
Qe = k. Ce 1/n (5)
and in linearized form is :
Log Qe = log k + (1/n) log Ce (6)
Where” Ce” is the concentration at equilibrium in
mg/l, ”Qe” amount of adsorbate per unit weight of
adsorbent (mg/g), ”k” is a parameter according to
temperature and ”n” is a characteristic constant for
the adsorption system under study. The plots of log
Qe against log Ce are shown in Fig. (9) and Fig. (10),
the adsorption of cadmium and lead ions onto Ben-
PEG composite give a straight line; values of “n”
between 2 and 10 show good adsorption [18].
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Fig. 9: Freundlich isotherm plot for adsorption of
cadmium ions on Ben-PEG composite
Fig.10: Freundlich isotherm plot for adsorption
of lead ions on Ben-PEG composite
Table 3: Freundlich constants from Freundlich
isotherm
R2
k
n
Cadmium
removal
0.963
0.012
0.54
Lead removal
0.9607
0.01
0.53
4. Conclusions
The Ben-PEG composite was successfully prepared
by direct polymerization and used as an adsorbent
for removing Cd2+ and Pb2+ from aqueous solutions.
SEM and XRD analysis indicate intercalation of the
PEG polymer into the initial structure of the Ben.
The adsorption of Cd2+ and Pb2+ was found to be
dependent on pH, adsorbent dose and the metal ion
concentration. The optimal conditions for adsorption
of Cd2+ and Pb2+ ions were found to be a PEG
content of 0.2 %, contact time of 150 min.,
adsorbent dose 2.5 gm, and initial concentration of
metal ions 25 mg/l. The adsorption equilibrium for
both Pb2+ and Cd2+ can be described by both the
Langmuir model and the Freundlich model, but best
fitted to the Langmuir model and therefore it is
more suitable for the analysis of kinetics. The
results show that the Ben–PEG composite is an
effective sorbent for the extraction of cadmium and
lead ions using modified, low-cost sorbent, which
can be used for purification of wastewater at the
industrial level. In future research the bentonite clay
can be treated and used for removal of dyes from
water.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
The author contributed in the present research, at all
stages from the formulation of the problem to the
final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The author has no conflict of interest to declare that
is relevant to the content of this article.
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