removal of cr (iii) and pb (ii) from solution by

ISSN: 1579-4377
REMOVAL OF CR (III) AND PB (II) FROM SOLUTION BY
ADSORPTION ONTO CASUARINA GLAUCA TREE LEAVES.
N. T. Abdel-Ghani , R.M. El-Nashar and G. A. El-Chaghaby *
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt.
*Central Laboratory for food and feed, Agriculture Research Center, Giza, Egypt.
ghadiraly@yahoo.com
ABSTRACT
This paper reported the research of the removal of Cr (III) and Pb (II) from wastewater by
using tree leaves. One kind of road side tree leaves was tested at room temperature. Effects
of contact time and pH on the adsorption process were investigated. The isothermal studies
were carried out with 1 g of leaves in 50 ml synthetic wastewater at different metal ions
concentrations. The initial pH of the synthetic wastewater was about 5. The experimental
results were examined using the Langmuir, Freundlich and Temkin isotherms to obtain the
appropriate model. The Temkin isotherm was found to well represent the measured sorption
data. The goal for this research is to develop inexpensive, highly available, effective metal
ion adsorbents from nature as alternative to existing conventional adsorbents.
KEYWORDS
tree leaves; adsorption; chromium; lead; isotherm.
El-Chaghaby et al. EJEAFChe, 7 (7), 2008. [3126-3133]
INTRODUCTION
Heavy metal ions are toxic pollutants. Some of these are cumulative poisons capable of
being assimilated, stored, and concentrated by organisms that are exposed to low
concentration of these substances for long periods or repeatedly for short periods [1]. Many
authors [2- 4], addressed the fact that, chromium toxicity to mammalians and aquatic
organisms appears to be lower compared to other heavy metals, due to general low solubility
of Cr(III) compounds, low mobility in the environmental compartments and limited
availability to living organisms.
Lead in the environment is strongly absorbed by
sediments and soil particles, and is therefore largely unavailable to plants and animals. Many
of the inorganic salts of lead (lead oxides and sulfides) are not readily soluble in water and
are sequestered in sediments. In aquatic system, uptake is influenced by various
environmental factors such as temperature, salinity, pH, and the presence of organic matter
[5&6]. Lead can pass through the placenta and thus affect a growing fetus. Organic lead
compounds are fat-soluble and are more toxic than other forms [7].
Industrial and municipal wastewaters frequently contain metal ions. Current methods
for such wastewater treatment include precipitation, coagulation/flotation, sedimentation,
flotation, filtration, membrane process, electrochemical techniques, ion exchange, biological
process, and chemical reaction. [8]. In recent years, the application of low-cost sorbents has
been widely studied for metal removal from water. Natural materials that are available in
large quantities or certain waste from agricultural operations may have potential to be used
as low cost adsorbents, as they represent unused resources, widely available and are
environmentally friendly[9].
This work's goal was to study the possibility of the utilization of one kind of tree
leaves: Casuarina Glauca for the sorption of chromium and lead ions from mixed solutions.
The system variables studied include contact time pH and initial ion concentration.
Isothermal studies were achieved to find the appropriate model describing the adsorption
over the studied concentration range.
MATERIALS AND METHODS
The major interest of this study was to investigate sorption of chromium and lead by using
roadside tree leaves present in Egypt. The leaves of widely present roadside trees: Casuarina
Glauca was chosen for this study.
The raw tree leaves were gathered from twigs into clean plastic bags. Washed with
DI water and laid flat on a clean table to dry. Dry leaves were grounded with electrical
grinder.
Analytical grade reagents were used in all cases. The stock solutions of chromium
(III) and lead (II) (1000mg/L) were obtained from Merck. All working solutions were
prepared by diluting the stock solution with deionized water.
Batch sorption experiments were performed at room temperature on a reciprocating
lab-line shaker. In all sets of experiments, 1.0 g of tree leaves was thoroughly mixed into 50
ml cation solution. After shaking for 120 min, the reaction mixtures were separated by
filtration and the filtrate was analyzed with an inductively coupled plasma optical emission
spectroscopy (ICP-OES) for the concentration of cation.
The removal % was calculated as :
Removal % = [( C0 - Cf )/ C0] X 100
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Where: Co and Cf are the initial and equilibrium concentration (ppm) of metal ions in
solution, respectively.
Effect of contact time
Batch sorption tests were done at different time intervals: 30, 60 ,90,180 and 240 minutes.
Each used a mixture metal ion solutions of 25ppm concentrations and 1 gm of adsorbent.
Effect of pH
Batch sorption experiments were carried out at the desired pH (2.5 , 4.5 ,6.5 and 8.5) and
each used a mixture metal ion solutions of 25ppm concentrations and 1 gm of adsorbent.
Isothermal studies
Three of the most common adsorption isotherms were used to predict the best model
describing metal ions adsorption onto tree leaves. The Langumuir, Freundlich and Temkin
models were used to fit the adsorption data over the studied metal ions concentration range
from 5 to 50ppm.
RESULTS AND DISCUSSION
Effect of contact time
Fig.(1) shows the removal percentages of Cr(III) and Pb(II) on Casuarina Glauca at an initial
concentration of 25ppm and at an initial pH=4.5 using 1gm of the adsorbent/50 ml of the
mixed ions solutions. From this figure, it is clear that the metal removal percentages
increased with an increase in contact time before attaining equilibrium. Equilibrium time
was attained at 120min, for chromium and lead onto Casuarina leaves. To ensure enough
time to reach equilibrium, 120 min. of contact was used throughout the batch experiments.
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Fig.(1): Effect of contact time on the removal of Cr(III) and Pb(II) ions by adsorption on Casuarina Glauca
leaves.
Effect of pH
In order to optimize the pH for maximum removal efficiency, the experiments were
conducted with 25ppm of mixed metal solution containing 1 g of Casuarina leaves in the pH
range 2.5–8.8. The effect of the pH on the removal of Cr(III) and Pb (II) by the tree leaves as
adsorbents was presented in Fig. 2. The percent removal of the studied ions onto the
investigated adsorbent increased in the pH range of 2.5 – 6.5. The sorption of Cr (III) and Pb
(II) ions on both adsorbents was found to be favorable at a pH value of 6.5. At this optimum
pH, maximum Cr (III) and Pb (II) removal onto Casuarina leaves was found to be 89.99
%and 97.37%, respectively.
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100.00%
90.00%
80.00%
Cr (III)
Pb (II)
% Removal
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
0.00%
2.5
4.5
6.5
8.5
pH
Fig.(2): Effect of pH on the removal of Cr(III) and Pb(II) ions by adsorption on Casuarina Glauca leaves.
the adsorption of the studied metal cations increased as pH increases and recorded its
minimum values at pH 2.5.This can be justified on the bases that at lower pH values, the H+
ions compete with the metal cation for the adsorption sites in the system, which in turn leads
to partial releasing the later. The heavy metal cations are completely released under extreme
acidic conditions [10].These results are in agreement with many other found in literature
[11-13].
Isothermal studies
Equilibrium sorption isotherm studies are fundamentally important in the design of sorption
systems [14]. Equilibrium relationships between sorbent and sorbate are described by
sorption isotherms, usually the ratio between the quantity sorbed and that remaining in the
solution at a fixed temperature at equilibrium. Equilibrium studies are described by sorption
isotherm characterized by certain constants whose values express the surface properties and
affinity of the sorbent. The analysis of our results involved the establishment of the proper
isotherm description for the adsorption process. Before hand a brief note on sorption models
is given. These included the Langmuir, the Freundlich and the Temkin isotherms.
The Langmuir sorption isotherm [15] is given by:
C
=
1
+ C
X
K Xm
Xm
Where,
C = the Concentration of adsorbate in solution at equilibrium (mg/L).
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K= Constant related to the energy or net enthalpy of adsorption;
X = Amount of metal adsorbed per unit weight of adsorbent (mg/gm)
Xm= maximum amount of metal adsorbed per unit weight of adsorbent (mg/gm)
Freundlich isotherm equation is expressed as [16]
ln X = lnK + n ln C
Where,
C = the Concentration of adsorbate in solution at equilibrium (mg/L).
X = Amount of metal adsorbed per unit weight of adsorbent (mg/gm)
K = equilibrium constant indicative of adsorption capacity;
n = adsorption equilibrium coefficient.
Analysis of the data over a concentration range from 5 to 50ppm of the metal ions, showed
that the adsorption of Cr(III) and Pb (II) onto Casuarina Glauca tree leaves was best
described by the Temkin isotherm model. The Temkin isotherm [17] can be expressed by
the following equation:
X = a + b ln C
Where,
C = Concentration of adsorbate in solution at equilibrium (mg/L).
X = Amount of metal adsorbed per unit weight of adsorbent (mg/gm)
a & b are constants related to adsorption capacity and intensity of adsorption.
Figures (3 & 4) gives the plots of X against ln C for Cr (III) and Pb (II), the plots give a
straight line with slope b.
Fig.(3): Temkin isotherm of Cr(III) sorbed on
Casuarina Glauca leaves.
Fig.(4): Temkin isotherm of Pb (III) sorbed on Casuarina
Glauca leaves.
As shown from the figures, the Temkin constant b was
8.839 and 9.6048 for the adsorption of Cr (III) and Pb
(II) onto Casuarina leaves, respectively. The values of
constant (b) were used to predict whether a sorption
system is ‘favorable’ or ‘unfavorable’ in batch processes.
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CONCLUSION
Casuarina Glauca tree leaves were able to simultaneously remove chromium and lead ions
from aqueous solutions. Equilibrium was attained after 120min of contact between the
adsorbent and the adsorbate. It was noted that an increase in the pH resulted in a higher
metal removal. Metal/tree leaves isotherms have been developed and analyzed according to
three isotherm equations. The experimental results were analyzed by using the Langmuir,
Freundlich and Temkin equations. The data were best fitted by the Temkin model over the
studied concentration range. The results showed that tree leaves can be used for the sorption
of the Cr3+ and Pb2+ from mixed solution.
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