Adsorption Studies of Pb2+, Cu2+ and Cr3+ from Aqueous Solution Using Azadirachta Indica (Neem) Seed Husk and Adansonia Digitata (Baobab) Seeds

Nasiru Pindiga Yahaya; Yahaya Aliyu Saad; Adamu Abubakar

doi:doi:10.11648/j.sjc.20241204.12

Research Article |

| Peer-Reviewed

Adsorption Studies of Pb²⁺, Cu²⁺ and Cr³⁺ from Aqueous Solution Using Azadirachta Indica (Neem) Seed Husk and Adansonia Digitata (Baobab) Seeds

Nasiru Pindiga Yahaya^*

, Yahaya Aliyu Saad, Adamu Abubakar

Published in Science Journal of Chemistry (Volume 12, Issue 4)

Received: 12 June 2024 Accepted: 10 July 2024 Published: 27 August 2024

Views: Downloads:

Download PDF

Share This Article

Twitter
Linked In
Facebook

Abstract

The adsorption of Pb²⁺, Cu²⁺ and Cr³⁺ from aqueous solution using Neem seed husk (NSH) and baobab seed (BS) were studied through the use of batch adsorption system. The adsorbents were prepared by drying at 120°C for 24hours and were characterized using FT-IR, XRD, and SEM analysis. The FTIR spectroscopy revealed the presence of O-H, N-H, C-H, C=C, C=O, and C-O stretching; XRD revealed the particle sizes as 44.51nm for NSH and 42.61nm while the morphology of the NSH and BS were revealed by SEM to be porous for NSH and BS. Various parameters such as, initial metal ion concentration, adsorbent dosage, contact time, Temperature and pH of metal ion solution were investigated in a batch-adsorption System. The adsorption uptake was found to increase with increase in adsorbent dose, contact time and temperature but decreases with the initial concentration. The uptake of the metal ions increases and reaches optimum at pH of 4-6. The maximum adsorption capacity was found to be Pb-NSH (15.267mg/g) and Cu-NSH (19.46mg/g). Adsorption of Cu²⁺onto NSH fitted Langmuir isotherm model with (R² > 0.93) while Adsorption of Pb-NSH Fitted Freundlich isotherm Model with (R²> 0.99). Kinetic data fitted pseudo-second-order model (R² > 0.98) which was more suitable in explaining the adsorption rate. Thermodynamic data showed that Gibb’s free energy (ΔG°) values for all metal ions were negative indicating feasibility and favorability of adsorption. Positive enthalpy change (ΔH°) and Entropy change (ΔS°) values indicate endothermic processes and increase in randomness.

Published in	Science Journal of Chemistry (Volume 12, Issue 4)
DOI	10.11648/j.sjc.20241204.12
Page(s)	73-85
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2024. Published by Science Publishing Group

Keywords

Adsorption Studies, Aqueous Solution, Azadirachta Indica (Neem) Seed Husk, Adansonia Digitata (Baobab) Seeds

1. Introduction

Heavy metals are generally referred to those metals which possess a specific density of more than 5 g/cm³ and adversely affect the environment and living organisms

[1]

. These are group of pollutants, which are non-bio-degradable in living organisms.

[1]

. They constitute a very heterogeneous group of elements widely varied in their chemical properties and biological functions The most common heavy metal contaminants are copper, iron, zinc, lead, cadmium, arsenic, manganese, cobalt, chromium, mercury and nickel

[2]

Although it is acknowledged that, heavy metals have many adverse health effects and last for a long period of time, heavy metal exposure continues and is increasing in many parts of the world. Heavy metals are significant environmental pollutants and their toxicity is a problem of increasing significance for environmental reasons Heavy metals enter the surroundings by natural means and through human activities. Various sources of heavy metals include soil erosion, weathering, leaching and volcanic eruption. Anthropogenic source of heavy metals which result from human activities such as mining, agricultural activities, fossil fuel combustion, refineries, textile and paper industries e.t.c.

[1]

This accumulation of the heavy metals is harmful to the environment because these metals generally accumulated in their most stable oxidation states, i.e., As³⁺, Pb²⁺, Hg²⁺, Cd²⁺, Cu²⁺and Cr³⁺ which further react with body bio-molecules to generate extremely stable bio-toxic compounds which are very difficult to dissociate

[3]

The release of heavy metals into the natural environment has resulted in various environmental challenges due to their non-biodegradable and persistent characteristics

[4]

. The toxicity of heavy metals in humans may result in damage to various physiological systems, such as the central nervous, cardiovascular, and gastrointestinal systems, as well as the lungs, kidneys, liver, endocrine glands, and bones, which may increase the prevalence of degenerative illnesses and cancers

[2]

Various methods have been developed for the removal of heavy metals from water, including chemical precipitation, electro dialysis, ultrafiltration, ion exchange, reverse osmosis, phytoremediation, membrane separation, aerobic and anaerobic degradation, chemical oxidation, coagulation, and flocculation. Some of these methods have been shown to be effective, however they have some limitations such as excess amount of chemical usage, accumulation of concentrated sludge that has serious disposal problems, formation of toxic compounds during the process, high cost, and incomplete removal of certain ions and takes long time for heavy metal removal. The adsorption technique, which is based on the transfer of pollutants from the solution to the solid phase, is known as one of the efficient and general wastewater treatment method

[5]

The major advantages of adsorption over these conventional treatment methods are low cost, high efficiency, minimization of chemicals, no additional nutrient requirement, and reuse of adsorbent for further metal uptake and possibility of metal recovery

[2]

Lowcost adsorbent such as rice husk, maize cob, banana peels, orange peels, wheat shell, water hyacinth, hazelnuts shells, orange peel pith, sunflower, coconut husk, groundnut husk, coconut shell, palm fibres, are used for removal of heavy metals from industrial waste water.

This research, explore the potential of Neem seed husk for possible use as adsorbent for removal of Pb²⁺, and Cu²⁺ ions from waste water.

Aim

The aim of this work is to determine the potentials of Azadirachta indica (Neem) seed husk, and Adansonia Digitata (Baobab) husk for the removal of Pb²⁺, Cu²⁺ and Cr³⁺ ions from aqueous solution for possible use as an adsorbent for heavy metals removal from the environment.

Objectives

The objectives of the study are:

i. To characterize the adsorbents using FTIR, SEM and XRD.

ii. To study the effect of initial concentration, adsorbent dose, time, temperature and pH on adsorption of Pb²⁺, Cu²⁺ and Cr³⁺ions.

iii. To study and understand the adsorption equilibrium isotherms for Pb²⁺, Cu²⁺, and Cr³⁺ ions removal by Neem seed husk, Baobab seeds and Mahogany leaves.

iv. To study and understand the kinetics of the adsorption process and the thermodynamic parameters for removal of Cu^2+, Pb²⁺ and Cr³⁺ ions.

2. Materials and Methods

2.1. Reagents

All reagents used were of analytical grade. These include: Pb(NO₃)₂, CuSO₄, Cr(NO₃)₃, NaOH, and HNO₃

2.2. Preparation of Stock Solutions

1000g/L Stock solutions of Pb(NO₃)₂, CuSO₄ and Cr(NO₃)₃were prepared according to standard procedures by dissolving 1.5980g, 2.5117g and 4.5775g each in 1L of deionize water. Serial dilution method from the stock solution to obtain different concentration by using the formula below, equation (1).

C₁V₁=C₂V₂(1)

Where

C₁is the concentration of stock solution, V₁is the volume of the stock solution, C₂is the concentration of the dilute solution and V₂ is the volume of the dilute solution.

2.3. Sample Collection and Preparation

Neem Seed Husks samples and Baobab seeds were collected within Gombe State University Area. The samples were prepared by using slightly modified method of

[6, 7]

. The samples were washed with ordinary water thoroughly and with distill water in order to remove impurities and debris present. The sample was dried in oven at about 120^ᵒC for 24 hrs. These dried samples were then crushed to a fine powder and sieved with 150mm mesh size sieve. The prepared adsorbents were kept in an airtight bottle awaiting subsequent experiments.

2.4. Sample Characterization

Neem Seed Husk and Baobab Seeds samples were characterized using X-ray diffraction analysis (XRD), Scan Electron Microscopy (SEM) and FT-IR spectroscopy.

2.5. The Batch Adsorption Experiment

Batch adsorption experiment was carried out in order to study the effect of change in initial metal concentration of metal ions, adsorbent dose, contact time, temperature and pH on the adsorption of the Pb²⁺, Cu²⁺ and Cr³⁺. The effect of each parameter was studied by keeping others parameters constant. The solutions were then filtered and the filtrates were subjected to AAS analysis.

i. Effect of Initial Metal Concentration

The effect of initial metal concentration on adsorption of Pb²⁺, Cu²⁺ and Cr³⁺ ions was determine at different concentration of 50, 100, 150, 200, and 250mg/L at room temperature (~25°C). 0.5 g of adsorbents was added 50ml the metal ion solution in each conical flask. The solutions were shaken for 30min at 150rpm. The solutions were filtered using Whatman filter paper and the filtrates were analyzed with AAS.

ii. Effect of Adsorbent Dose

Effect of adsorbent dose on Pb²⁺, Cu²⁺ and Cr³⁺ ions were determined at different amounts of dosage ranging from 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2g. For each experiment, an accurate quantity of the adsorbents were added to 50 mL of metal ions solution at 100mg/L, at 25°C in 250 ml conical flasks. The solutions were shaken at 150 rpm for 30minutes. The solutions were filtered with Whatman filter paper and the filtrates were analyzed using AAS.

iii. Effect of Contact Time

The effect of contact time on the adsorption process of Pb²⁺, Cu²⁺ and Cr³⁺ was studied at the following time intervals 10, 20, 30, 40 and 60mins at optimum concentration of 100mg/L for the metal ions, adsorbent dose of 0.5g at temperature of 25°C. 50 ml of the metal ions were transferred into 250ml conical flasks. The solutions were shaken at 150 rpm at different time intervals. The solutions were filtered using Whatman filter paper and filtrate was analyzed with AAS.

iv. Effect of Temperature

The effect of temperature on the adsorption process of Pb²⁺, Cu²⁺ and Cr³⁺ ions were examined at the following temperatures 25, 30, 35, 40 and 60°C. Then 50ml of 100mg/L metal ions solutions were transferred into 250ml conical flasks, 0.5g of the adsorbents were added in to the flasks. The solutions were shaken at 150 rpm for different temperatures. The filtrates were then filtered and analyzed using AAS.

v. Effect of pH

The effect of pH on the process of adsorption Pb²⁺, Cu²⁺ and Cr³⁺ ions by the adsorbents was determined at different pH value of 2, 3, 4, 5, and 7 and optimum concentrations of metal ions of at room temperature (~25°C). The pH was adjusted using 0.1M HNO₃ and 0.1M NaOH. 50ml of 100mg/L solutions of metal ions were transferred into 250ml conical flasks, 0.5 g of absorbents samples were added and the solutions were shaken for 30 min at 150rpm. The solutions were filtered whatman No1 filter paper and the filtrate was analyzed with AAS.

2.6. Data Evaluation

The data obtained by AAS was carried out to analyze the amount Pb²⁺, Cu²⁺ and Cr³⁺ ions adsorbed. The equations 2 and 3 were used to calculate the amount of metal ions adsorbed per unit mass of the adsorbent and percentage removal of metal ions.

q_{e} = \frac{(C_{0} {- C}_{e}) V}{M}

(2)

% R = \frac{C_{0} - C_{e}}{C_{0}} \times 100

(3)

Where

𝑞𝑒 is the amount of ions adsorbed (mg/g) at equilibrium, C₀ is the adsorbate initial concentration (mg/l) and Ce is adsorbate final concentration (mg/l) at equilibrium, V is the solution volume (l) and M is the adsorbent dosage (g).

2.7. Adsorption Equilibrium Studies

The experimental data was modeled using Freundlich and Langmuir isotherms (equations 4 and 5) separately to determine maximum adsorption capacity and adsorption mechanism. The model with the highest R² value best fitted the adsorption data.

I Langmuir Isotherm

The Langmuir isotherm model equation is expressed as:

\frac{1}{qe} = (\frac{1}{qmax}) + (\frac{1}{qmaxKL}) \frac{1}{Ce}

(4)

Where

qe is the equilibrium dye concentration on the adsorbent (mg g^-1);

Ce is the equilibrium dye concentration in solution (mg L^-1);

q_max is the monolayer capacity of the adsorbent (mg g^-1);

K_L is the Langmuir constant.

The value of K_L and q_max are determined from the slope and intercept of the plot of 1/qe against 1/Ce.

The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor R_L that is given by equation 5,

R

= \frac{1}{1 + KL c_{0}}

(5)

Where

C₀ (mg/L) is the highest initial concentration of adsorbate. The value of R_L indicates the shape of the isotherm to be either unfavorable (R_L>1), linear (R_L = 1), favorable (0< R_L< 1), or irreversible (R_L =0) (Olgun and Atar, 2012).

II Freundlich Isotherm

The Freundlich isotherm model equation is expressed as in equation 6:

Lnq e = Ln

K_F

+ \frac{1}{n} LnC e

(6)

Where

K_F (mg/g) and n are the Freundlich constants related to adsorption capacity and intensity, respectively. A linear plot of Lnq_e against Ln C_e gives K_F and n values.

2.8. Adsorption Kinetics Studies

In order to obtain a suitable rate equation and investigate the controlling mechanism of adsorption process, two main types of adsorption kinetic models, pseudo-first order and pseudo-second order models were considered.

I The Pseudo First-Order Kinetic Model

The first-order rate expression is given in equation 7:

Ln(qe−qt)=Lnqe−k₁t(7)

where

qt (mg/g) is the amount of the metal ion absorbed at time t. The value of k₁ is the pseudo-first-order rate constant and can be obtained from the slope of the plot of ln(qe−qt) versus t.

II The Pseudo Second-Order Kinetic Model

The pseudo second-order rate expression is given in equation 8:

\frac{t}{qt} = \frac{1}{K_{2} q_{e}^{2}} + \frac{1}{q_{e}} t

(8)

where

qe is the maximum adsorption capacity (mg g^-1), qt is the amount of metal ion adsorbed at time t (mg g^-1) and k₂ is the pseudo-second order kinetic rate constant (g mg^-1 min^-1).

2.9. Thermodynamic Parameters of Adsorption

Thermodynamic parameters for the adsorption process, such as Gibbs-free energy (∆G°), change in enthalpy and (∆H°) change in entropy (∆S°) were obtained from the experiments carried out at different temperatures in equations 9 - 10.

The free energy change

∆

G, enthalpy changes

∆

H and entropy changes

∆

S are determined using fallowing equations 9 - 10.

∆ G = - RTlnKd

(9)

∆ G = ∆ H - T ∆ S

(10)

Where

Kd is the distribution coefficient of the adsorbate, (Kd = Ce/ qe), R is the universal gas constant (8.314 J K^-1 mol^-1), T is the absolute temperature (K). The plot of ln Kd as a function of 1/T yields a straight line from which

∆

H and

∆

S are obtained.

3. Result and Discussion

3.1. FTIR Analysis

[6]	Yahaya, N. P., Aliyu, A. D., David, Y. M. & Abubakar, A. (2022). Kinetic, Equilibrium and Thermodynamics Study of the Adsorption of Pb(II), Cu(II) and Ni(II) from Aqueous Solution using Mangnifera Indica Leaves. Online Journal of Materials Science, 1(1), 16-29.
[7]	Yahaya, N. P., Ali, I., Kolo, A. M., Shehu, A. (2023) “Adsorption Study of Methylene Blue on to Powder Activated Carbon Prepared from Ananas comosus Peels”, Nanochem. Res., 8(4): 231-242.

[11]	Taha, A. A., & AbdelGhani, S. A. A. (2016). Adsorption Kinetics, Equilibrium, and Thermodynamics of Copper from Aqueous Solutions using Silicon Carbide Derived from Rice Waste. Journal of Dispersion Science and Technology, 37(2), 173-182.
[12]	Buhari, M, Nasiru. Y. P., & Ibrahim, M. B. (2024) Synthesis of TiO2 Impregnated Ribes nigrum Stem Nanoactivated Carbon and their Application to Remove Heavy Metals. Asian Journal of Chemical Science., 14(2), 149-160.
[13]	Wilson, L, D., Nasiru, Y. P., & Markus L. (2023) “Green Synthesis and Characterization of Silver – Cadmium (Ag-Cd Bimetallic) Nanoparticles from Ocimum Gratissimum Leaves Extract and Evaluation of its Antimicrobial Activities” Bima Journal of Science and Technology” 7(3) 29-35.

Isotherm Model	Adsorbates
Isotherm Model	Pb²⁺	Cu²⁺	Cr³⁺
Langmuir
q_max	15.267	19.46	14.75
K_L	0.152	0.0498	0.253
R_L	0.294	0.167	0.038
R²	0.9512	0.9921	0.9400
Freundlich
K_F	3.0549	1.867	3.769
1/n	0.7192	0.381	0.547
R²	0.9912	0.9261	0.9922

Kinetic Model	Parameters	Adsorbates
Kinetic Model	Parameters	Pb²⁺	Cu²⁺	Cr³⁺
Pseudo-First order
	q _exp (mg/g)	8.524	8.917	8.7660
	K₁ (min^-1)	0.0438	0.0246	1.7615
	q _cal (mg/g)	4.772	36.509	0.8270
	R²	0.9021	0.9856	0.9908
Pseudo-Second order
	K₂ (min^-1)	0.0164	1.0299	1.5893
	q_cal (mg/g)	8.945	8.7873	8.4817
	R²	0.9895	0.9939	0.9942

[10]	Aderibigbe, A. D., Ogunlalu, O. U., Oluwasina, O. O. & Amoo, I. A. (2017). Adsorption Studies of Pb2+ from Aqueous Solutions Using Unmodified and Citric Acid – Modified Plantain (Musa paradisiaca) Peels. IOSR Journal of Applied Chemistry, 10(2): 30-39.
[15]	Pindiga, N. Y., Walid, A. H., Abdullahi, A. O. & Mohammad, A. B. (2022). Kinetic, Equilibrium and Thermodynamic Study of the Adsorption of Pb (II) and Cd (II) Ions from Aqueous Solution by the Leaves Biomass of Guava and Cashew Plants. Online Journal of Chemistry, 2(1), 23-38.
[19]	Mustapha, S., Shuaib, D., Ndamitso, M., Etsuyankpa, M., Sumaila, A., Mohammed, U. & Nasirudeen, M. (2019). Adsorption isotherm, kinetic and thermodynamic studies for the removal of Pb (II), Cd (II), Zn (II) & Cu (II) ions from aqueous solutions using Albizia lebbeck pods. Applied Water Science, 9(6), 142-152.
[20]	Taşar, Ş., Kaya, F., & Özer, A. (2014). Biosorption of lead(II) ions from aqueous solution by peanut shells: Equilibrium, thermodynamic and kinetic studies. Journal of Environmental Chemical Engineering, 2(2): 1018-1026.

Model	Metal ion
Model	Pb²⁺	Cu²⁺	Cr³⁺
ΔG° (KJ.mol^-1)
25 $℃$	-0.4665	-0.9655	-0.0153
30 $℃$	-0.8994	-2.0486	-0.32143
35 $℃$	-1.2289	-2.9288	-0.59872
40 $℃$	-2.1354	-3.9544	-0.97635
60 $℃$	-2.7753	-4.7526	-1.02944
ΔH° (KJ.mol^-1)
	+18.8528	+29.8389	+8.7131
ΔS° (KJ.mol^-1.K^-1)
	+0.05487	+0.08717	+0.02962

[1]	Jaishankar, M., Tseten, T., Anbalagan, N., Mathew, B. B., & Beeregowda, K N. (2014). Toxicity, mechanism & health effects of some heavy metals. Interdisciplinary Toxicology, 7(2), 408-428.
[2]	Joshi, N. C. (2018). A Brief Discussion on Biosorption and Biosorption Technology. Journal of Pharmaceutical Chemistry and Biological Science, 5(4), 330-336.
[3]	Pratush, A. & Ajay Kumar & Zhong Hu (2018). Adverse effect of heavy metals (As, Pb, Hg, and Cr) on health and their bioremediation strategies. International Microbiology, 4(2), 121-129.
[4]	Masindi, V., & Muedi, K. L. (2018). Environmental Contamination by Heavy Metals. Scientific Reports, 5(10), 116-133.
[5]	Renu, A. M. & Singh, K. (2017). Methodologies for removal of heavy metal ions from wastewater: an overview. Interdisciplinary Environmental Review, 18(2), 124–142.
[6]	Yahaya, N. P., Aliyu, A. D., David, Y. M. & Abubakar, A. (2022). Kinetic, Equilibrium and Thermodynamics Study of the Adsorption of Pb(II), Cu(II) and Ni(II) from Aqueous Solution using Mangnifera Indica Leaves. Online Journal of Materials Science, 1(1), 16-29.
[7]	Yahaya, N. P., Ali, I., Kolo, A. M., Shehu, A. (2023) “Adsorption Study of Methylene Blue on to Powder Activated Carbon Prepared from Ananas comosus Peels”, Nanochem. Res., 8(4): 231-242.
[8]	Yahaya, N. P., Umar, A., David, Y. M. & Abubakar, A. (2022). Kinetic, Equilibrium and Thermodynamics Study of the Adsorption of Pb(II), Ni(II) and Cu(II) from Aqueous Solution using Psidium guajava (Guava) Leaves. Chemical Science & Engineering Research, 4(10), 9-10.
[9]	Ullah, M., Nazir, R., Khan, M. Khan, W. Shah, M., Afridi, S. G., & Zada, A. (2020). The effective removal of heavy metals from water by activated carbon adsorbents of Albizia lebbeck and Melia azedarach seed shells. Soil and Water Research, 15(1): 30-37.
[10]	Aderibigbe, A. D., Ogunlalu, O. U., Oluwasina, O. O. & Amoo, I. A. (2017). Adsorption Studies of Pb2+ from Aqueous Solutions Using Unmodified and Citric Acid – Modified Plantain (Musa paradisiaca) Peels. IOSR Journal of Applied Chemistry, 10(2): 30-39.
[11]	Taha, A. A., & AbdelGhani, S. A. A. (2016). Adsorption Kinetics, Equilibrium, and Thermodynamics of Copper from Aqueous Solutions using Silicon Carbide Derived from Rice Waste. Journal of Dispersion Science and Technology, 37(2), 173-182.
[12]	Buhari, M, Nasiru. Y. P., & Ibrahim, M. B. (2024) Synthesis of TiO2 Impregnated Ribes nigrum Stem Nanoactivated Carbon and their Application to Remove Heavy Metals. Asian Journal of Chemical Science., 14(2), 149-160.
[13]	Wilson, L, D., Nasiru, Y. P., & Markus L. (2023) “Green Synthesis and Characterization of Silver – Cadmium (Ag-Cd Bimetallic) Nanoparticles from Ocimum Gratissimum Leaves Extract and Evaluation of its Antimicrobial Activities” Bima Journal of Science and Technology” 7(3) 29-35.
[14]	Siti, N., Mohd, H., Md, L. & Shamsul, I. (2013). Adsorption Process of Heavy Metals by Low-Cost Adsorbent: A Review. World Applied Sciences Journal, 28(11), 1518-1530.
[15]	Pindiga, N. Y., Walid, A. H., Abdullahi, A. O. & Mohammad, A. B. (2022). Kinetic, Equilibrium and Thermodynamic Study of the Adsorption of Pb (II) and Cd (II) Ions from Aqueous Solution by the Leaves Biomass of Guava and Cashew Plants. Online Journal of Chemistry, 2(1), 23-38.
[16]	Lawal, O. S., Sanni, A. R., Ajayi, I. A. & Rabiu, O. O. (2010). Equilibrium, thermodynamic and kinetic studies for the biosorption of aqueous lead (II) ions onto the seed husk of Calophyllum inophyllum. Journal of Hazardous Materials, 177(1-3), 829-835.
[17]	Bhagat, S., Gedam, V. V. & Pathak, P. (2020). Adsorption/desorption, Kinetics and Equilibrium Studies for the Uptake of Cu(II) and Zn(II) onto Banana Peel. International Journal of Chemical Reactor Engineering, 18(1), 1-16.
[18]	Meroufel, B., Benali, O., Benyahia, M., Benmoussa, Y. & Zenasni, M. A. (2013). Adsorptive removal of anionic dye from aqueous solutions by Algerian kaolin: Characteristics, isotherm, kinetic and thermodynamic studies. Journal of Materials and Environmental Science, 4(3), 482-491.
[19]	Mustapha, S., Shuaib, D., Ndamitso, M., Etsuyankpa, M., Sumaila, A., Mohammed, U. & Nasirudeen, M. (2019). Adsorption isotherm, kinetic and thermodynamic studies for the removal of Pb (II), Cd (II), Zn (II) & Cu (II) ions from aqueous solutions using Albizia lebbeck pods. Applied Water Science, 9(6), 142-152.
[20]	Taşar, Ş., Kaya, F., & Özer, A. (2014). Biosorption of lead(II) ions from aqueous solution by peanut shells: Equilibrium, thermodynamic and kinetic studies. Journal of Environmental Chemical Engineering, 2(2): 1018-1026.

Model	Metal ion
Model	Pb²⁺	Cu²⁺	Cr³⁺
ΔG° (KJ.mol-1)
25 $℃$	-0.05396	-0.233	-0.19854
30 $℃$	-0.5959	-0.51166	-0.66506
35 $℃$	-0.84665	-1.05825	-1.12888
40 $℃$	-1.19037	-1.43191	-1.27545
60 $℃$	-1.61301	-1.91713	-1.72442
ΔH° (KJ.mol^-1)
	+11.8832	+13.90683	+11.6133
ΔS° (KJ.mol^-1.K^-1)
	+0.040584	+0.04757	+0.04016