Fly ash as a sorbent for boron removal from aqueous solutions: Equilibrium and thermodynamic studies

ABSTRACT

This study presents the application of fly ash from brown coal and biomass burning power plant as a sorbent for the removal of boron ions from an aqueous solution. The adsorption process efficiency depended on the parameters, such as adsorbent dosage, pH, temperature, agitation time and initial boron concentration. The experimental data fitted well with the Freundlich isotherm model and the maximum capacity was found to be 16.14 mg g^?1. The adsorption kinetics followed the pseudo-second-order model. Also, the intra-particle diffusion model parameters were calculated. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), entropy (ΔS°) revealed on exothermic nature of boron adsorption onto the fly ash.     

Use of a selective extractant-impregnated resin for removal of Pb(II) ion from waters and wastewaters: Kinetics,equilibrium and thermodynamic study

Adsorption of Pb(II) ion by a novel extractant-impregnated resin, EIR, was studied as a function of various experimental parameters using batch adsorption experiments. The new EIR was prepared by impregnating gallocyanine (GCN) onto Amberlite XAD-16 resin beads. The EIR was characterized by nitrogen analysis and SEM micrographs. The new EIR showed excellent selectivity factor values (α) for Pb(II) adsorption respect to other metal ions. The effects of some chemical and physical variables were evaluated and the optimum conditions were found for Pb(II) removal from aqueous solutions. The equilibrium adsorption isotherm was fitted with the Langmuir adsorption model. The maximum adsorption capacity (q_max) of EIR for Pb(II) ions was found to be 367.92 mg g⁻¹. The kinetic studies showed that the intra-particle diffusion is the rate-controlling step. Also, the intra-particle diffusion coefficients, D_ip values, were of the order of 10⁻¹² m² s⁻¹. The values of enthalpy (ΔH°) were positive, which confirms the endothermic nature of adsorption process. Also, the positive entropy changes (ΔS°) were showed that the randomness increased along with the adsorption process. In addition, the obtained negative values of Gibbs free energy (ΔG°) indicated feasible and spontaneous nature of the adsorption process at different temperatures. The new adsorbent was very stable so that it can be successfully used for many consecutive cycles without significant loss in its adsorption capacity.     

Removal of cationic dyes from aqueous solutions by kaolin: Kinetic and equilibrium studies

Experimental investigations were carried out using commercially available kaolin to adsorb two different toxic cationic dyes namely crystal violet and brilliant green from aqueous medium. Kaolin was characterized by performing particle size distribution, BET surface area measurement and XRD analysis. The effects of initial dye concentration, contact time, adsorbent dose, stirring speed, pH, salt concentration and temperature were studied in batch mode. The extent of adsorption was strongly dependent on pH of solution. Free energy of adsorption (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) changes were calculated. Adsorption kinetic was verified by pseudo-first-order, pseudo-second-order and intra-particle-diffusion models. The rate of adsorption of both crystal violet and brilliant green followed the pseudo-second-order model for the dye concentrations studied in the present case. The dye adsorption process was found to be external mass transfer controlled at earlier stage and intra-particle diffusion controlled at later stage. Calculated external mass transfer coefficient showed that crystal violet dye adsorbed faster than brilliant green on kaolin. Adsorption of crystal violet and brilliant green on kaolin followed the Langmuir adsorption isotherm.     

STUDIES ON THE ADSORPTION OF FURFURAL FROM AQUEOUS SOLUTION ONTO LOW-COST BAGASSE FLY ASH

The present study deals with the sorptive removal of furfural from aqueous solution by carbon-rich bagasse fly ash (BFA). Batch studies were performed to evaluate the influence of various experimental parameters, namely, initial pH (p H ₀), adsorbent dose, contact time, initial concentration, and temperature on the removal of furfural. Optimum conditions for furfural removal were found to be p H ₀ ≈ 5.5, adsorbent dose ≈4 g/L of solution, and equilibrium time ≈4 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural is of the order of 10^?13 m²/s. Equilibrium adsorption data on BFA was analyzed by Freundlich, Langmuir, Dubnin-Radushkevich, Redlich-Peterson, and Temkin isotherm equations using regression and error analysis. The Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto BFA. Adsorption of furfural on BFA is favorably influenced by a decrease in the temperature of the operation. Values of the change in entropy (ΔS ⁰) and heat of adsorption (ΔH ⁰) for furfural adsorption on BFA were negative. The high negative value of change in Gibbs free energy (ΔG ⁰) indicates the feasible and spontaneous adsorption of furfural on BFA.     

Adsorption of Furfural from Aqueous Solution onto Activated Carbon: Kinetic,Equilibrium and Thermodynamic Study

Abstract

The present study aims to evaluate the influence of various experimental parameters viz. initial pH (pH ₀), adsorbent dose, contact time, initial concentration and temperature on the adsorptive removal of furfural from aqueous solution by commercial grade activated carbon (ACC). Optimum conditions for furfural removal were found to be pH ₀ ≈ 5.9, adsorbent dose ≈ 10 g/l of solution and equilibrium time ≈ 6.0 h. The adsorption followed pseudo‐second‐order kinetics. The effective diffusion coefficient of furfural was of the order of 10^?13 m²/s. Furfural adsorption onto ACC was found to be best represented by the Redlich‐Peterson isotherm. A decrease in the temperature of the operation favorably influenced the adsorption of furfural onto ACC. The positive values of the change in entropy (ΔS ⁰); and the negatived value of heat of adsorption (ΔH ⁰) and change in Gibbs free energy (ΔG ⁰) indicated feasible, exothermic, and spontaneous nature of furfural adsorption onto ACC.     

Electrochemical removal of boron from water: Adsorption and thermodynamic studies

The present work provides an electrochemical removal of boron from water and its kinetics, thermodynamics, isotherm using mild steel and stainless steel as anode and cathode respectively. The various operating parameters on the removal efficiency of boron were investigated, such as initial boron ion concentration, initial pH, current density and temperature. The results showed that the optimum removal efficiency of 93.2% was achieved at a current density of 0.2 A dm^?2 at pH of 7.0. First‐, second‐order rate equations, Elovich and Intraparticle models were applied to study adsorption kinetics. Adsorption isotherms of boron on Fe(OH)₃ were determined and correlated with isotherm equations such as Langmuir, Freundlich and D‐R models. Thermodynamic parameters, such as standard Gibb's free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°), were also evaluated by Van't Hoff equation. The adsorption process follows second‐order kinetics. The adsorption of boron preferably fits with Langmuir adsorption isotherm suggesting monolayer coverage of adsorbed molecules. The adsorption of boron onto Fe(OH)₃ was found to be spontaneous and endothermic. © 2011 Canadian Society for Chemical Engineering     

Removal of Reactive Orange 12 from aqueous solutions by adsorption on tin sulfide nanoparticle loaded on activated carbon

In the present study, tin sulfide nanoparticle loaded on activated carbon simply was synthesized and characterized using different techniques such as SEM, XRD and UV-analysis. Then, this new efficient adsorbent was used for Reactive Orange 12 (RO-12) adsorption. To improve the efficiency of adsorption effect of variables viz. pH, mass of SnS-NP-AC, initial dye concentration, contact time and temperature were examined and optimized. The adsorption mechanism and rate of processes was investigated by analyzing time dependency data to various conventional kinetic models such as pseudo-first-order and second order, Elovich and intra-particle diffusion models. Among them it was found that adsorption followed the pseudo-second-order kinetic model with good agreement between the equilibrium experimental and expected adsorption data. High fitting with the Langmuir models shows heterogeneous surface and mono-layer nature adsorption of Reactive Orange 12 on the SnS-NP-AC. Thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), activation energy (E_a), of sticking probability (S^*) and Gibb's free energy changes (ΔG) were also calculated. It was seen that the proposed adsorbent has high tendency and adsorption capacity for RO-12 adsorption in a feasible, spontaneous and endothermic fashion.     

Removal of methylene blue from aqueous solutions by adsorption onto chemically activated halloysite nanotubes

This study examines the adsorption behavior of methylene blue (MB) from aqueous solutions onto chemically activated halloysite nanotubes. Adsorption of MB depends greatly on the adsorbent dose, pH, initial concentration, temperature and contact time. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms and the Langmuir model agrees very well with experimental data. The maximum adsorption capacities for MB ranged from 91.32 to 103.63 mg·g⁻¹ between 298 and 318 K. A comparison of kinetic models applied to the adsorption data was evaluated for pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion equation. The results showed the adsorption process was well described by the pseudo-second-order and intra-particle diffusion mode. Thermodynamic parameters suggest that the adsorption is spontaneous and endothermic. The obtained results indicated that the product had the potential to be utilized as low-cost and effective alternative for dye removal in wastewater.     

Optimization and analysis of nickel adsorption on microwave irradiated rice husk using response surface methodology (RSM)

BACKGROUND: The removal of heavy metals using adsorption techniques with low cost biosorbents is being extensively investigated. The improved adsorption is essentially due to the pores present in the adsorbent. One way of improving the porosity of the material is by irradiation of the precursor using microwaves. In the present study, the adsorption characteristics of nickel onto microwave‐irradiated rice husks were studied and the process variables were optimized through response surface methodology (RSM). RESULT: The adsorption of nickel onto microwave‐irradiated rice husk (MIRH) was found to be better than that of the raw rice husk (RRH). The kinetics of the adsorption of Ni(II) from aqueous solution onto MIRH was found to follow a pseudo‐second‐order model. Thermodynamic parameters such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were also evaluated. The thermodynamics of Ni(II) adsorption onto MIRH indicates that it is spontaneous and endothermic in nature. The response surface methodology (RSM) was employed to optimize the design parameters for the present process. CONCLUSION: Microwave‐irradiated rice husk was found to be a suitable adsorbent for the removal of nickel(II) ions from aqueous solutions. The adsorption capacity of the rice husk was found to be 1.17 mg g^?1. The optimized parameters for the current process were found as follows: adsorbent loading 2.8 g (100 mL)^?1; Initial adsorbate concentration 6 mg L^?1; adsorption time 210 min.; and adsorption temperature 35 °C. Copyright © 2008 Society of Chemical Industry     

Removal of Orange II by Phosphonium-modified Algerian Bentonites

An Algerian montmorillonite was modified with two organic surfactants, methyltriphenyl phosphonium bromide and n-hexyltriphenyl phosphonium bromide. The solids obtained were used as adsorbents to remove Orange II, an anionic dye from aqueous solutions. Batch experiments were conducted to study the effects of temperature (20–60°C), initial concentration of adsorbate (50–150 mg L^?1) and pH of solution 6.5 on dye adsorption. Due to their organophilic nature, exchanged montmorillonites were able to adsorb Orange II at a very high level. Adsorption of Orange II for B-NHTPB and B-MTPB at different pH show that the adsorption capacity clearly decreases with an increase in pH of the initial solution from 2 to 8, this decrease being dramatic for pH > 8. This may be due to hydrophobic interactions of the organic dye with both phosphonium molecules and the remaining non-covered portion of siloxane surface. The kinetics of the adsorption was discussed on the basis of three kinetic models, i.e., the pseudo-first-order, the pseudo-second-order, and the intraparticle diffusion models. Equilibrium is reached after 30 min and 60 min for B-MTPB and B-NHTPB, respectively; the pseudo-second-order kinetic model described very well the adsorption of Orange II on modified bentonites. The non-linear Langmuir model provided the best correlation of experimental data, maximum adsorption of Orange II is 53.78 mg g^?1 for B-NHTPB and 33.79 mg g^?1 for B-MTPB. The thermodynamic parameters, such as free energy of adsorption (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were also determined and evaluated. From thermodynamic studies, it was deduced that the adsorption was spontaneous and exothermic.     

Adsorption of fulvic acids from aqueous solutions by carbon nanotubes

Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g^?1 at 5 °C and equilibrium concentration of 18 mg dm^?3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰), have been obtained. Acidic conditions (pH = 2–5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm^?3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry     

Adsorption of bovine serum albumin onto glass powder surfaces coated with polyvinyl alcohol

The adsorption of bovine serum albumin (BSA) was carried out onto polyvinyl alcohol–coated glass powder surfaces. The adsorbed amount was about four times more than that on uncoated glass. The kinetics of the adsorption process was followed colorimetrically, and kinetic parameters, such as adsorption coefficient, rate constants for adsorption and desorption, diffusion constant, and penetration rate constant, were evaluated. The effects of experimental conditions, such as pH, presence of salts, addition of aliphatic alcohols, and variation in the dielectric constant of the medium, on the amount of adsorbed BSA were investigated. The effect of temperature on adsorption was also studied, and several thermodynamic parameters, such as standard free energy change (ΔG°), heat of reaction (ΔH°), and entropy change (ΔS°), were evaluated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 933–940, 2000     

MODIFIED PLANTAIN PEEL AS CELLULOSE-BASED LOW-COST ADSORBENT FOR THE REMOVAL OF 2,6-DICHLOROPHENOL FROM AQUEOUS SOLUTION: ADSORPTION ISOTHERMS,KINETIC MODELING,AND THERMODYNAMIC STUDIES

In this study, the feasibility of using modified plantain peel to remove 2,6-dichlorophenol from iaqueous solutions was investigated under batch mode. The effects of physical factors such as initial 2,6-dichlorophenol concentration, contact time, biosorbent particle size, biosorbent dosage and temperature on the removal process were evaluated. The results showed that biosorption of 2,6-dichlorophenol was dependent on these factors. The equilibrium biosorption data were analyzed by the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) adsorption isotherm models. The four tested isotherm models provided good fits to the experimental data obtained at 30°C; however, the Freundlich isotherm model provided the best correlation (R² = 0.9874) of the experimental data. The maximum monolayer biosorption capacity (Q _max ) was found to be 14.25 mg/g. The biosorption kinetics data of 2,6-dichlorophenol were analyzed by pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, and liquid film diffusion models. The five kinetic models fitted well to the biosorption kinetic data; however, the pseudo-second-order kinetic model gave the best fit when the biosorption mechanism was controlled by film diffusion. Thermodynamic quantities such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), standard entropy change of biosorption (ΔS°), and activation energy (E_a) were evaluated, and it was found that the biosorption process was spontaneous, feasible, endothermic in nature and of dual nature, physisorption and chemisorption; however, the physisorption process was dominant. Therefore, modified plantain peel has potential for application as an effective bioadsorbent for removal of 2,6-dichlorophenol from aqueous solution.     

Novel hexamethylene diamine‐functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly[(glycidyl methacrylate)‐co ‐(ethylene glycol dimethacrylate)] (PGME ) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME‐HD ) were tested as potential Cr(VI ) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI ) sorption was investigated in the temperature range 298–343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI ) sorption obeys the pseudo‐second‐order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g^?1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰) and entropy change (ΔS ⁰) and activation energy of sorption (E _a), were calculated. The Cr(VI) adsorption onto PGME‐HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME‐HD sample GMA 60 HD was easily regenerated with 0.1 mol L^?1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed. © 2016 Society of Chemical Industry     

Removal of Cr (VI) from aqueous solution by newspapers

The potential to remove Cr (VI) ions from aqueous solution using newspapers was investigated in the present study. The effects of relevant parameters such as solution pH, adsorbent concentration, and reaction temperature on Cr (VI) adsorption were examined. The adsorption of Cr (VI) ions onto newspapers was found to be highly pH-dependent and the highest uptake occurred at pH 1.0. The sorption equilibrium data were correlated to the Langmuir, Freundlich, Redlich-Peterson and Dubinin-Radushkevich equations. Five different non-linear error functions were examined and the result indicated that the Freundlich and Redlich-Peterson equations better fitted the equilibrium data than Langmuir isotherm. The maximum sorption capacity was found to be 55.06 mg/g at pH 1.0, adsorbent concentration 4 g/L and reaction temperature of 30 °C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) were also evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The kinetic experimental data were well fitted by the pseudo-second order, external film diffusion and diffusion models allowing the corresponding parameters to be evaluated. The sorption capacity increased with the decrease of adsorbent concentration.     

Surface modification of rubber (Hevea brasiliensis) leaves for the adsorption of copper ions: kinetic,thermodynamic and binding mechanisms

BACKGROUND: This research describes the adsorption of copper ions from aqueous solutions following the modification of rubber (Hevea brasiliensis) leaves with formaldehyde solution. The main objectives of this research were to identify the binding mechanisms of copper ions on the chemically modified rubber leaves by spectroscopic techniques and to investigate the effects of several important physicochemical parameters such as pH, copper concentration, contact time, adsorbent dose and temperature on copper removal. RESULTS: Based on a kinetic study, the pseudo‐second‐order model was found to fit the experimental results well, while the Boyd kinetic model indicated that the rate‐determining step was due to film diffusion. Adsorption isotherms were modelled by the Langmuir and Freundlich isotherm equations, with the former providing a better fit for the data. Based on the Langmuir model, the maximum adsorption capacities of Cu(II) ions at 300, 310 and 320 K were 8.36, 8.61 and 8.71 mg g^?1, respectively. Thermodynamic parameters such as the Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy changes (ΔS°) were calculated. The adsorption process was spontaneous as the values of ΔG° were negative, and endothermic as higher adsorption capacities were recorded at higher temperatures. More than 80% of copper ions bound on the adsorbent were able to be desorbed using 0.02 mol L^?1 HCl, HNO₃ and EDTA solutions. Besides ion exchange, surface complexation could also play a major role in copper binding. CONCLUSION: Due to its relative abundance and satisfactory adsorption capacity, the modified rubber leaves can be considered as a good low‐cost adsorbent for removing copper ions from dilute aqueous solutions. Copyright © 2008 Society of Chemical Industry     

Adsorption kinetics and isotherms of a pesticide on polyester fibers by carrier finishing

The effective management and control of mosquitoes in human living environments are crucial to minimize vector‐borne diseases in homes. Pesticides, such as pyrethroids, are considered powerful tools in the control of mosquitoes and are intended to be incorporated into textiles. The adsorptive behavior of the pesticide ZX‐1 [the main component is 1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl) ethane] in aqueous solution on polyesters fibers at different treatment times, temperatures, and concentrations are discussed in this article. The second‐order model was found to be the most suitable for describing the kinetic diffusion process, and the intraparticle diffusion was the rate‐controlling process. The Langmuir, Freundlich, and Dubinin–Radushkevich adsorption models were applied to these approaches. The results show that the Langmuir model appeared to fit the adsorption of ZX‐1 on the polyester fibers better than other adsorption models. In addition, thermodynamic parameters, such as the free energy of adsorption (ΔG⁰), enthalpy (ΔH⁰), and entropy, were calculated. Positive values of ΔH⁰ and ΔG⁰ indicated the endothermic and nonspontaneous nature of ZX‐1 adsorption on the polyester fibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of crosslinked oxidized starch and its adsorption behavior for calcium ion

Cornstarch, after crosslinking with epichlorohydrin (4%, v/w, dry basis of the starch), was oxidized with hydrogen peroxide over the catalyst Cu(II). The newly synthesized products were applied to examine the calcium ion removal activity from water, under various conditions. Removal efficiency of calcium ion from aqueous solution increased proportionally with carboxyl content and the dose of crosslinked oxidized starch in the solution. Ionization of carboxyl groups in starch was necessary for the effective calcium removal. When the pH of the solution was adjusted below 4.0, the starch was no longer an effective calcium‐sequestering agent. Adsorption isotherm models were developed, wherein the best fit was obtained in the Langmuir model. Thermodynamic study indicated that the adsorption process was exothermic, and the enthalpy change (ΔH^θ), the entropy change (ΔS^θ), and free energy change (ΔG^θ) of the adsorption process were calculated with adsorption isotherm data and basic thermodynamic relations. It was assessed that adsorption occurred by strong electrostatic interactions with the negative adsorption enthalpy (ΔH^θ). The regeneration and reusability of oxidized starch were also assessed and were found to retain the adsorption capacity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1539–1546, 2006     

Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite

The use of low-cost and ecofriendly adsorbents was investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. Sepiolite was used as an adsorbent for the removal of methyl violet (MV) and methylene blue (MB) from aqueous solutions. The rate of adsorption was investigated under various parameters such as contact time, stirring speed, ionic strength, pH and temperature for the removal of these dyes. Kinetic study showed that the adsorption of dyes on sepiolite was a gradual process. Quasi-equilibrium reached within 3 h. Adsorption rate increased with the increase in ionic strength, pH and temperature. Pseudo-first-order, the Elvoich equation, pseudo-second-order, mass transfer and intra-particle diffusion models were used to fit the experimental data. The sorption kinetics of MV and MB onto sepiolite was described by the pseudo-second-order kinetic equation. Intra-particle diffusion process was identified as the main mechanism controlling the rate of the dye sorption. The diffusion coefficient, D, was found to increase when the ionic strength, pH and temperature were raised. Thermodynamic activation parameters such as ΔG¹, ΔS¹ and ΔH¹ were also calculated.     

Removal of Neutral Red from aqueous solution by using modified hectorite

The object of this work was to study the modified hectorite as effective adsorbent for Neutral Red (NR) from aqueous solution. The adsorbent capacity of modified hectorite was discussed. The effects of surfactant content, adsorbent content, pH and adsorption temperature on the sorption of NR on modified hectorite were studied. Experimental results showed that the equilibrium adsorption data fitted well with Langmuir isotherm and the adsorption capacity was 393.70 mg/g for the modified cetylpyridinium bromide hectorite (CPB-Hect). Kinetic studies showed that the dynamical data fitted well with the pseudo-second-order kinetic model. For thermodynamic studies, parameters such as the Gibbs free energy (ΔG⁰), the enthalpy (ΔH⁰) and the entropy (ΔS⁰) indicated that the adsorption process was spontaneous and endothermic in nature.