J. Nig. Soc. Phys. Sci. 5 (2023) 1143

Journal of the
Nigerian Society

of Physical
Sciences

Modelling and Simulation for the use of Natural Waste to
Purified Contaminated Heavy Metals

Suha Ibrahim Salih Al-Alia,, Zaidun Naji Abudib, Mohammed Nsaif Abbasb

aDepartment of Mathematics, College of Computer and Mathematical Science, Tikrit University, Tikrit, Iraq
bEnvironmental Engineering Department, College of Engineering, Mustansiriyah University, Baghdad, Iraq

Abstract

The possibility of recovering one of the famous heavy metal ions, divalent copper, from contaminated aqueous solutions (which simulates wastew-
ater) was studied in this study. The removal method was adsorption technique using a laboratory batch-mode unit, while the used tea leaves were
the adsorption media. The adsorption process was performed under various operating conditions and ranges that simulate the natural environ-
mental conditions to determine the ideal values that achieve the maximum removal of copper ions. The acquired results demonstrated that the
maximum remediation efficiency was 85%, which was achieved at treatment time, shaking speed, initial concentration, temperature, acid func-
tion, and adsorption dose of 90 min, 250 rpm, 70 ppm, 25oC, 4, 4.5g, respectively. The values of the thermodynamic properties demonstrated
that adsorption is spontaneous, exothermic and has negative entropy, while adsorption follows Langmuir’s model and the second pseudo-model
according to the isotherm and kinetic studies, respectively. To conduct the Zero Residues Level concept, the loaded used tea leaves were prepared
to study it effect as a simple type of rodenticide by applying it to Sprague Dawley rats. The results of the test show that the effectiveness of
utilizing the residues as rodenticide and the Half lethal dose LD50 of the proposed rodenticide were identical to those mentioned in the literature.
Based on these results, the current study sheds light on the possibility of converting used tea leaves from harmful solid waste to an environmentally
friendly substance using it as an effective adsorbent medium for the treatment of water polluted with heavy metals.

DOI:10.46481/jnsps.2023.1143

Keywords: Adsorption; copper; used tea leaves; kinetic; isothermal and thermodynamic

Article History :
Received: 10 October 2022
Received in revised form: 04 December 2022
Accepted for publication: 06 December 2022
Published: 23 December 2022

c© 2022 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license

(https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Communicated by: B. J. Falaye

1. Introduction

The great growth of the world’s population, industrial and
agricultural progress in the past century led to the pollution of
all elements of the environment (water, air, soil and space) and
the depletion of natural wealth sources [1]. In addition, the
failure to follow appropriate methods in treating the sources of
pollution, and the lack of proper planning have. The problems

Email address: suhaibrahim3@tu.edu.iq (Suha Ibrahim Salih Al-Ali )

of pollutant accumulation and depletion of natural resources
can be considered among the most important major environ-
mental issues at the present time for developed and developing
countries alike [2]. Pollution refers the interference of human
activities with the resources and energies of the environment,
such that this interference endangers human health or natural
resources, or puts them in a situation where they are likely to
be directly or indirectly exposed to danger [3]. Pollution is
defined as the presence of foreign substances in any compo-
nent of the environment, which renders it unsuitable for use

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 2

or limits its use [4]. Pollutants are defined as substances, mi-
crobes or energies that harm humans or living organisms in gen-
eral and cause diseases or lead to destruction [5]. In the past,
natural ecosystems were able to assimilation of the pollutants,
whether in the soil, water, or air, because of the small quan-
tities and low concentrations of pollutants, and the absence of
difficult or non-degradable foreign substances [6]. Today, nat-
ural ecosystems are unable to assimilate these pollutants, and
the influence of these contaminants depends on the degree of
their concentration in the environment, their chemical, physical
and biological characteristics, and the nature of their interac-
tion with each other and with the surrounding environment [4].
Water pollution resulting from industrial and human activities
is considered to be one of the main issues in the world, as it
is the main cause of 80% of diseases worldwide [7]. The re-
ports issued by WHO show that the safe drinking water does not
reach more than 109 inhabitants worldwide, and most of them
are from poor and developing third-world countries [8, 9]. It
should be noted that thousands of chemicals are released into
the environment in general and into water sources without any
treatment on a daily basis [10]. These chemicals (even drugs,
medicines or pharmaceutical products in high concentrations)
will be affected the human body [11]. Among these chemicals,
heavy metals are among the most dangerous and harmful, even
if found in small amounts, because they accumulate inside liv-
ing tissues [12]. Some heavy metals such as iron, copper and
zinc are directly related to the vital activities of living organ-
isms, while others such as lead, cadmium and mercury do not
play any role in these activities and are therefore classified as
toxic elements [13]. However at high concentrations (exceed-
ing the permissible or recommended limit), all heavy metals
are toxic to living organisms, regardless of which they are nec-
essary [14]. There are many ways to recover heavy metals from
contaminated water, including membrane separation, electro-
dialysis, ion exchange, precipitation, liquid extraction and ad-
sorption [15]. Adsorption method is an effective and excellent
technique in removing heavy metals and other pollutants. There
are many kinds of pollutants remediate by adsorption such as
dyes [16], radioactive materials, inorganic toxins and others.
The ability may be attributed to the high surface area provided
by various adsorption media such as activated carbon [17], alu-
mina [18] and silica [19]. However, the high cost of these me-
dia and the loss of some of their mass in each regeneration step
prompted researchers to use alternative materials of appropriate
efficiency, available, cheap, and at the same time, without toxic-
ity [20]. Among these materials that meet the above conditions
are agricultural wastes [21]. Agricultural residues are available
in large quantities throughout the year as a result of the human
consumption of agricultural crops and can be utilize by different
methods, such as producing beneficial chemicals [22], fertiliz-
ers [23], and [24], and addition of material to concrete [25] and
synthesis of nano-materials [16] because of its unique proper-
ties, either naturally or gained after treatment [26]. They are
low-cost and not invaluable materials with an appropriate sur-
face area and have proven their efficiency in removing many
pollutants from water [27], soil [28] and petroleum [29], and
non-toxic substances [30]. In addition, its accumulation (from

any source) leads to the pollution of various elements in the en-
vironment by raising the vital requirement of water or being a
medium for the growth of insects harmful to humans [31]. As
a result of the foregoing, researchers studied the ability of this
waste to treat polluted water including rice husks [32], banana
peels [33], and orange peels [34], pomegranate peels [1], wa-
termelon peels [35], lemon peels [36], egg shells [37], algae
[38], water hyacinth [39] among others. Tea leaves are one of
the most common types of agricultural waste. Tea is consumed
worldwide in large quantities daily. As a result of this con-
sumption, very large quantities of tea leaves are accumulated,
which must be disposed of in economical, safe and environ-
mentally friendly ways [40]. This paper studies the adsorption
possibility of copper ions (Cu+2) from polluted water by using
tea leaves as an available, cheap and non-toxic adsorbent me-
dia in a laboratory batch-mode unit. The adsorption procedure
was performed using various design parameters to determine
the optimum values that gave the highest adsorption efficiency.
In addition, we studied a suitable method to dispose the toxic
residues using a beneficial route. Thus, this study presents the
concept of safe, efficient and economical simultaneous disposal
of more than one type of environmental pollutants at the same
time.

2. Material and methods

2.1. Adsorbent media preparation

The raw media of adsorption i.e., the used tea leaves were
collected from the domestic use as a batch. Each collected batch
was washed with two types of water. The first one was per-
formed with excess tap water to remove any dirt or dust that
may be stuck. While the second one was conducted by double
distilled water to neutralize the adsorption media. The washed
leaves were dried for 48 h in a drying oven at 50oC to avert
charred. They were then ground in a domestic mill and sieved to
obtain fine powder. Powder that passed through a 35 mesh sieve
was selected as the adsorption medium. The prepared powder
was stored in opaque glass containers in a cool dry place until
use. The used tea leaves were collected, washed and dried in
continuous batches. After ending all things, the media was first
kept in opaque glass containers (i.e., amber glass jar with tight
lid). These jars are put in a dark drawer at room temperature to
prevent light and humidity.

2.2. Stock Solution

To avoid competition between copper and other elements
may be found in wastewater, adsorption experiments of copper
ions were conducted using laboratory prepared solutions with
predetermined concentrations. Stock solution of divalent cop-
per ions (1000 ppm) was prepared by dissolving 3.81 g of blue-
colored copper (II) nitrate trihydrate salt of Cu(NO3)2.3H2O
chemical formula and 241.6 g/mol molar mass. A 99.5% pu-
rity salt was purchased from IndiaMART.A stock solution was
prepared using a magnetic stirrer under laboratory conditions,
which are atmospheric pressure and temperature of 25−28±1◦C

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 3

2.3. Calibration Curve
By Atomic Absorption Spectroscopy (AAS) device, the con-

centration of Cu+2 ions are detecting. The detection was achieved
by preparing calibration curve for copper ions at a wavelength
of 372.0 nm. The process was carried out by preparing a series
of known concentrations of copper ions and accurately deter-
mining the absorbance for each concentration. The concentra-
tion was plotted against the absorbance so that the calibration
curve was ready in its final form. Calibration curve experiments
were conducted in triplicate for each concentration and the av-
erage between three readings was taken to reduce the error. The
calibration curve of Cu+2 ions is explained via Figure 1.

Figure 1. Calibration curve of Cu+2 ions using AAS

2.4. Adsorption Experiments
Adsorption experiments of divalent copper ions were con-

ducted using used tea leaves in a batch type adsorption unit con-
sisting of a water bath shaker under various operating parame-
ters. The acidity function, initial concentration of Cu+2 ions,
shaking speed, adsorbent dose, treatment time and temperature
represented the operating conditions of the adsorption process
and their values ranged between 1 − 8, 1 − 100 ppm, 100 − 350
rpm, 0.5−5.0 g, 10−120 min, 25−50oC, respectively. The pH
was adjusted using a pH meter with 1 M solutions of HCl and
NaOH. Glass beakers (100 ml capacity glass) of a specific con-
centration and pH were placed in a water bath shaker, and the
device was turned on after setting the temperature and shaking
speed. After the end of the specified time for the experiment,
the sample was purified using filter paper and tested using an
AAS device. The remaining concentration of unadsorbed Cu
was determined from the calibration curve. The percentage of
copper ions adsorption and the adsorption capacity are calcu-
lated using equations 1 and 2 respectively

%R = 1 −
(
C f
Ci

)
, (1)

q =
V
m

(
Ci − C f

)
, (2)

where %R is the percentage of adsorption, C f and Ci are the
final and initial concentrations of divalent copper ions (ppm),
respectively, V is the volume (l), q is the capacity of adsorption
(mg/g), m: the adsorbent dose used (g).

2.5. Isothermal Study

The dispersion of copper ions between the solution and the
adsorption media can be explained by using theoretical mod-
els after the system reaches the equilibrium state. There are
many models that explain this relationship, the most important
of which are the Langmuir and Freundlich models.

2.6. Langmuir Model

This model was introduced by the American chemist Lang-
muir at 1916 and it is assumed that the adsorption occurs on
one layer only, the energy is distributed in it evenly, and that the
number of adsorption sites is specific and identical. When the
layer is saturated, the maximum value of adsorption is achieved,
in addition to the actuality that the density of the adsorption
layer is determined by the same thickness of the particle. Equa-
tion 3 symbolizes the general formula of the Langmuir model,
Equation 4 symbolizes the linear mathematical formula of this
model, and Equation 5 describes the formula for the separation
factor RL by which the type of adsorption is determined.

qe =
qmax KLCe
1 + KLCe

(3)

1
qe

=
1

qmax KL

1
Ce

1
qmax

(4)

Where: qe: equilibrium adsorption capacity (mg/g) ; KL: bind-
ing sites constant of Langmuir equation, (l/mg); qmax: maxi-
mum adsorption capacity (mg/g); and Ce: equilibrium adsorbed
concentration (mg/l)

RL =
1

1 + KLCe
(5)

The value of RL gives a good indication of the nature and form
of adsorption, if the value of the separation factor is higher than
1, the adsorption is not preferred, and linear adsorption if its
value is 1. The adsorption is preferred if 0 < RL < 1 value, and
adsorption is irreversible if RLvalue is 0. By plotting the graph
between 1/qe and 1/Ce, a linear relationship is resulted through
which the Langmuir constants KL and qmax are calculated.

2.7. Freundlich Model

A model presented by the German scientist Freundlich in
1909 assumes that adsorption gets multiple and heterogeneous
layers and adsorption sites can be unsaturated as well as irreg-
ular energy levels. Equations 6 and 7 describe the general and
linear form of the Freundlich model, respectively

qe = KF Ce
1
n (6)

lnqe = lnKF
1
n

lnCe (7)

Where: KF : constant of Freundlich equation [(mg/g).(l/mg)1/n],
n: adsorption intensity (−).

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 4

2.8. Kinetic Study

2.8.1. Pseudo first order model (PFO)
The assumption of this model represented by the adsorption

time rate is of the first order as a result of obtaining adsorption
on only one layer. Equations 8 and 9 describe the general and
linear form of this model, respectively

dqt
dt

= k1(qe − qt) (8)

Where: k1: first order rate constant (s−1); qe: equilibrium ad-
sorption capacity (mg/g); and qt amount adsorbed onto adsor-
bent at any time t (mg/g)

ln(qe − qt) = lnqe − k1t (9)

The relationship shown in Equation 10 can be represented math-
ematically as a straight line by plotting ln(qe − qt) against t its
slope equilibrium constant k1.

2.8.2. Pseudo second order model (PSO)
The most important hypothesis of this model is that the ad-

sorption rate time is directly proportional to the number of ac-
tive sites on the adsorption surface, and it is the model closest to
describing adsorption kinetics when physical or chemical inter-
actions occur between the adsorbent and the adsorbent. Equa-
tion 10 shows the general form and Equation 11 describes the
linear form of this model.

dqt
dt

= k2(qe − qt)
2 (10)

Where: qe: is the equilibrium adsorption capacity (mg/g), qt:
is the adsorption capacity at any time (mg/g), t : is the time(s)
and (k2): is the second order rate constants (g.mg−1.s−1).

1
qt

=
1

k2qe2
+

1
qe

t (11)

The PSO model constants can be found by plotting the relation-
ship between t/qt with t, which is the equation of a straight line
with intercept and slope 1/(k2qe2) and 1/qe respectively.

3. Results and discussions

A batch-mode unit was used to study the influence of some
design factors, such as pH, shaking speed, temperature, treat-
ment time of the adsorption unit, initial concentration of diva-
lent copper ions, and adsorbent dose (used tea leaves < 700 µm)
on the copper ion removal efficiency. The copper ions concen-
tration in the treated simulated aqueous solution after treatment
was detected using an AAS device and calibration curve, and
then the percentage and the capacity of the adsorption were cal-
culated.

3.1. Influence of treatment time
Treatment time is significant design factors that have been

studied in experiments to remediate heavy metals from polluted
media, owing to the importance of this factor in the unit ac-
cessing the state of equilibrium, in which the time affects the
adsorption process, and any subsequent period does not affect
the adsorption of pollutants. The effect of treatment time was
studied in the current study within a range of 10 − 120 min-
utes, based on similar literature [18].The results of studying of
this operating factor indicated that the maximum recovering ef-
ficiency of copper ions was achieved at 90 minutes, and this is
obviously from Figure 2. At the beginning of the adsorption,
the ability of used tea leaves (the adsorption media) to adsorb
pollutant ions is high because they are virgin and do not contain
any kind of competition for the active sites; therefore, adsorp-
tion is the maximum possible. Over time, the heavy metal ions
begin to accumulate on the adsorbent surface and are linked to
functional groups with diverse bonds, which restricts the arrival
of new ions to the active sites; thus the adsorption decreases
gradually until the system reaches the equilibrium state. After
equilibrium is achieved, any increase in the treatment time on
the adsorption efficiency is not beneficial, and the adsorption
capacity is fixed while other variables remain constant at the
optimum values. These results have been indicated by [40] in
their conclusions.

Figure 2. Influence of treatment time on removal of Cu+2 ions

3.2. Influence of initial concentration
The effect of varying the concentration of Cu+2 ions on the

removal capacity is shown in Figure 3. It is reported -from the
figure- that the highest adsorption efficiency was at the lowest
initial concentration. At the same time, the adsorption concen-
tration increased until its maximum value was reached and then
remained constant. Studying the influence of the initial concen-
tration of Cu+2 ion is significant for its effect on the ability of
the material to be adsorbed; the higher the concentration of the
initial pollutant, the lower the adsorption ability according to
the constant value of the surface area of the adsorption media,
and consequently, the limited effective sites of the adsorption
media. The initial concentration increase indicates an increase
in the mass of a heavy element in the same volume unit, and
this means an increase in competition between a large number
of molecules for the same number of active sites that are filled

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 5

with a specified number of molecules. The higher the initial
concentration, the greater the number of unadsorbed molecules
in the solution that remain free, and thus, the adsorption per-
centage removal decreases. The results of the current study
were confirmed by similar results similar on investigate the ad-
sorption of cadmium by watermelon rinds conducted by [32].

Figure 3. initial concentration influence on Cu+2 removal

3.3. Influence of pH
pH is one of the significant factors affecting the adsorption

process of any kind of material in general, and heavy metals in
particular, as the positive hydrogen ions (H+) are considered a
competition for the heavy metal ions on the adsorption site ow-
ing to the similarity of the charge. On the other hand, hydrox-
ide ions (OH−) with a negative charge can precipitate positive
heavy metal ions in the form of sparingly soluble hydroxide
salts if their concentration is high in the solution. The influ-
ence of acidity on the efficiency of Cu+2 ions adsorption was
studied within a range of 1 to 8, while other factors remained
constant at their optimum values. The relationship between ad-
sorption efficiency and pH is illustrated in Figure 4. It is noted
from the figure that the highest adsorption efficiency for copper
ions was achieved at a pH value of 4, which was 85%. At low
pH values, the adsorption capacity decreases due to the rivalry
of H+ with Cu+2 ions on the adsorption sites, which decreases
with increasing pH value. As the value of the acid function
increases, the hydroxide ions increase and the hydrogen ions
decrease, which reduces competition for active sites. This situa-
tion continues until the maximum value of efficiency is reached.
Subsequently, the removal efficiency will increase, but due to
precipitation in the form of metal hydroxide and not through
adsorption on the active sites. This was observed from the pre-
cipitation of a bluish-green solid at the bottom of the flask after
the acidity function exceeded the value of 4. Although the re-
moval percentage reached its ultimate value, 4 was considered
to be the optimal value of the acidity function for the adsorp-
tion of copper ions. Both [21, 38] indicated results similar to
the acidity function set results obtained in this study.

3.4. Influence of shaking speed
The effect of changing the adsorption removal due to vary-

ing the shaking speed of the polluted solution by keeping the

Figure 4. Effect of pH on Cu+2 removal

remaining operational factors at the optimum values is shown
in Figure 5. It is noted from the above figure that increas-
ing the shaking speed leads to an increase in the ability of the
used tea leaves to steadily remove heavy metal steadily between
100 − 250 rpm. Increasing the shaking speed increases the
chance of ions arriving at active sites by increasing the mass
transfer rate or destroying the film layer growing on the surface
of the used tea leaves, which reduces the resistance that occurs
to the transfer of copper ions. After reaching the maximum
value at 250 rpm, the adsorption efficiency did not change. This
is because the adsorbent reaches the equilibrium state or the rate
of collisions between the used tea leaves increases. Thus, the
Cu+2 ions are adsorbed and then return to the solution after their
liberation from the surface of the adsorbent owing to collisions
by a process called desorption. In general, the results showed
that the best adsorption efficiency for copper ions was recorded
at a shaking speed of 250 rpm. These results that we got are
compatible with the conclusion of Ghulam et. al. [17].

3.5. Influence of Adsorbent Dose

Within a range of 0.5 − 5.0 g, the ability of used tea leaves
as an adsorbent media to remove copper ions was investigated,
and the effect recorded from practical experiments to study this
operating factor was represented in Figure 6. The obtained re-
sults indicate that there is a clear direct relationship between the
amount of adsorbent material and the adsorption capacity be-
tween 0.5 − 4.5 g. The reason for this result is that an increase
in the amount of adsorbent means the increase in the surface
area and, in turn, provides more active sites. Thus, the chance
of adsorption of a larger number of heavy metal molecules will
increase and thus reduce their concentration in the solution, thus
increasing the adsorption efficiency. The removal continued to
increase from 0.5 g of used tea leaves to 4.5 g, and then the
removal efficiency remained unchanged. This stability can be
explained by the fact that an rising of the amount of material
leads to the formation of layers of the material on top of each
other, even if there is a sufficient surface area and additional ef-
fective sites will remain vacant because there is an obstacle that
prevents the arrival of heavy metal ions to the adsorption sites.
Therefore, the optimal adsorbent dose for the adsorption of cop-
per is 4.5 g, the rest of the variables remaining constant at the

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 6

optimum values. Comparable conclusions have been reported
by [35].

Figure 5. Effect of shaking speed on Cu+2 removal

Figure 6. Influence of adsorbent dose on Cu+2 removal

3.6. Influence of Temperature

It is noted from Figure 7 that the temperature factor owning
an adverse influence on the adsorption removal of Cu+2 ions
using the used tea leaves, and that the highest efficiency was
achieved at 25oC, and then the efficiency begins to decrease
with increasing temperature until it reaches its lowest value at
50oC. Temperature plays a vital role in the results of Cu+2 ions
adsorption, as its increase leads to raise in the kinetic energy of
the Cu+2 ions on the surface of used tea leaves, making it able
to disengage with it and return to the solution again. Mean-
while, when the temperature arises, the material breaks down
into smaller particles after adsorption, which makes the cop-
per ions free to move in the solution again. This is what was
observed when adsorption was tested at 45 and 50OC. Same re-
sults are recorded by [15]. The results of isotherm study demon-
strated that the adsorption of copper ions utilizing the used tea
leaves is subject to the Langmuir model clearly with higher cor-
relation coefficient (0.999), while the results are identical with
the Freundlich model with a correlation coefficient of 0.97. This
congruence with the Langmuir model can be attributed to the
small size of the small adsorption particles (< 700 µm) which
provide approximately one layer for adsorption. Due to this
tiny size, the energy distribution can be homogeneous and the

Figure 7. Influence of temperature on Cu+2 removal

thickness of the layer is the same as the thickness of the parti-
cle. It is also shown that the adsorption is preferred type due to
the RLvalue. Figures 8 and 9 and Table 1 show the values of
the model constants used in describing the isothermal study.

Figure 8. Langmuir

Figure 9. Freundlich

Table 1. The values of the model constants used in describing the isothermal
models used in this study

Langmuir Freundlich
KL qmax RL n KF
0.1295 1.1537 0.1 4.0733 0.388

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 7

Figure 10. PFO model

Figure 11. PSO model

Figures 10 and 11 explain the obtained results of the kinetic
study. It is noted that the adsorption is subject to the PSO model
with a high R2 that is close to 1, while the other model is far
from representing the adsorption results due to the low correla-
tion coefficient. This result can be clarified according the num-
ber of active sites that the PSO model takes into account, as the
optimum dose of material determines the possibility of reach-
ing the adsorption to the maximum efficiency. It is assumed that
adsorption obtains a single homogeneous layer and this is the
same hypothesis of the PSO model. The constants values of the
kinetic study models used in this study show in Table 2.

Table 2. The values of the model constants used in describing the isothermal
models used in this study

PFO model PSO model
k1 qe k2 qe
0.0496 1.2182 0.01712 1.068

3.7. Thermodynamic Study

In any adsorption process, this study is very important as it
detects the thermodynamic functions of the adsorption system
through which the spontaneity is combined through the values
of the free energy of pressure (M G) in addition to the values
of enthalpy (M H) and entropy (M S ) changes that show the

state of heat emission and the randomness of the adsorption
process. These thermodynamic functions can be calculated by
finding the equilibrium constant values via Equation 11, and
then applying the van’t Hoff equation described by

kad =
qe
Ce

(12)

By plotting the relationship between kad and 1/T , it is possible
to calculate M H from the slope and M S from the intercept,
from which the compressive energy M G of the adsorption sys-
tem can be determined through Equations 13 and 14 below

lnkad = −
M H

R
1
T

+
4S
R

(13)

M G =M H − T M S (14)

Where: kad : thermodynamic equilibrium coefficient of adsorp-
tion (dimensionless); 4H: enthalpy variation (J/mol) ; R: uni-
versal gas constant (8.3144J/mol.K) and M S : entropy varia-
tion (J/mol.K); T : absolute temperature (K).
Figure 12 and Table 3 show the numbers of thermodynamic
functions for adsorption of copper ions on the surface of the ad-
sorbed tea leaves that were studied in this study. It is cleared
from the Figure 12 that the values of the equilibrium constant
decrease with increasing temperature and the reason for this is
that the adsorption efficiency decreases with increasing temper-
ature (as shown previously). As a result, the concentration of
copper ions will increase in the solution as a result of the ions
returning to it again, in addition to adsorption capacity decreas-
ing in the substance It is also noted from the enthalpy values

Figure 12. Temperature effect on thermodynamic equilibrium coeffi-
cient

that adsorption is of the chemical type due to the number of en-
thalpy, which means that the link between the adsorbent mate-
rial and the surface of the used tea leaves is the result of chemi-
cal adsorption that lead to the generation of a new type of bonds
that require high energy to break. This also corresponds to the
behavior of temperature (referred to above in paragraph ( Influ-
ence of Temperature). As for the entropy function, it is noted
that it is a negative value, which means that the copper ions are
more uniform in the solution compared to their presence on the
adsorbent media surface. This result is also logical due to the

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Al-Ali et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1143 8

Table 3. The values of thermodynamic functions of this study
Temperature, Entropy varying Enthalpy varying Gibbs Free Energy

(OC) M S (J/mol.K) M H (J/mol) M G (kJ/mol)
25 -19.11375145
30 -17.29230212
35 -15.47085279
40 -364.2898652 -127726.775 -13.64940347
45 -11.82795414
50 -10.00650482

actuality that rising the temperature leads to lower the adsorp-
tion efficiency, which means that the greater number of ions will
be in the solution the higher the temperature. The obtained re-
sults indicate that the adsorption is spontaneous under the stud-
ied operational conditions, due to the negative sign of the values
of the free energy of compression, which decreases as the tem-
perature of the adsorption system increases. This proves that
the adsorption process is self-occurring and does not need any
external energy to complete and that low temperature is better
to achieve maximum efficiency.

3.8. Zero Residues Level (ZRL) Concept Application
After the process of treating the contaminated aqueous so-

lutions at different design conditions, the used tea leaves loaded
with the adsorbed divalent copper ions were collected and clas-
sified according to the amount of the adsorbed heavy metal
and an attempt was made to dispose of them in a safe, useful,
low-cost and eco-friendly method. The use of contaminated
leaves residue as a rodenticide was tested by feeding it to white
Sprague Dawley rats of the scientific name Rattus norvegicus
domestica. Use the same procedure used by [35] in preparing
and preamble the animal cages, as well as the same feeding
method. After the end of the laboratory experiments, the half
lethal dose (LD50) was calculated and compared with the dose
mentioned in the literature and it was within the known range.
Table 4 shows the half lethal dose (LD50) for rats feeding nor-
mal and contaminated used tea leaves. Although copper is one
of the moderate toxic heavy metals compared to other elements
such as lead, chromium, mercury, antimony and others, how-
ever, treating laboratory rats with used tea leaves loaded with
this metal showed that it has effects that range in severity with
increasing dose, leading to the death of rats [24]. The descent of

Table 4. LD50 Dose of proposed rodenticide
LD50 (mg/kg)

Group Type of Feeding
Male Female Standard

Control Provender of No- No- -
group Rats (Ordinary) mortality mortality
G1 Provender of No- No- -

Rats +used mortality mortality
tea leaves

G2 Provender of 41.7301 38.0689 37-42
Rats + Cu+2- (ATSDR,

used tea leaves [41]

albumin and protein materials with urine, diarrhea, and gradual

turbulent skin infections were the corporeal changes that oc-
curred in rats during the period of treatment with pomegranate
peels loaded with bismuth metal [14]. As for the anatomical
study of laboratory rat’s samples that died due to feeding the
used tea leaves loaded with copper, it was found that they suf-
fered from kidney atrophy and that the degree of this atrophy
was increasing with increasing the treated dose [11].

4. Conclusion

In this research, the efficiency of natural adsorbent ı.e. used
tea leaves was tested to remove divalent copper ions from con-
taminated simulated solutions in a unit of batch-mode and at
various design parameters. This available and low-cost sub-
stance has proven highly efficient in treating polluted water with
different concentrations ranging from 1 − 100 parts per mil-
lion, with an adsorption rate of 85%. The study showed that
the adsorption efficiency rising with rising pH, adsorbent quan-
tity, shaking speed and treatment time, while it decreases with
rising initial concentration and temperature. The obtained re-
sults showed that the optimal conditions to achieve the highest
removal percentage were pH of 4, adsorbent dose of 4.5g, treat-
ment time of 90 minutes, shaking speed of 350r pm, initial con-
centration of 70 ppm and temperature of 25oC. The isothermal
study showed that the adsorption follows the Langmuir model
with a correlation coefficient very close to 1, while the adsorp-
tion was spontaneous and of the PSO model according to the
correlation coefficient obtained according to the results of the
kinetic and thermodynamic study.

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