Koble-Corrigan Isotherm Models Research Articles

Removal of malachite green by in-situ N-doped biochar derived from wheat bran: kinetics, isotherms, and adsorption mechanism study

The biomass-based adsorbents offer a promising solution for wastewater decolorization owing to their superior specific surface area, low-budget, high adsorption capacities, and environmental sustainability. In this work, wheat bran (WB) was used as raw material for the production of in situ N-doped biochar through a molten salt template method, and the adsorption characteristics of Malachite Green (MG) onto biochars prepared from WB by immersing and non-immersing (BC–NaK and BC–NaK-n) in the mixed salt solution (NaCl and KCl) were investigated. The experimental results indicated that the adsorption capacity of MG onto the BC–NaK was significantly better than BC–NaK-n, which was attributed to the rich functional groups and well-developed pore structure of BC–NaK. The adsorption equilibrium data of MG onto the BC–NaK was fitted well to Sips and Koble-Corrigan isotherm models and adsorption process of MG was spontaneous and endothermic. Meanwhile, the pseudo-second-order model was successfully applied to depict the adsorption process of MG. Furthermore, the adsorption of MG onto BC–NaK was primarily regulated by H-bonding, π–π interaction, hydrophobic interaction, electrostatic interaction. The maximum saturated adsorption capacity of the BC–NaK was 880.14 ± 9.35 mg g−1 at 298 K, further demonstrating that biochar prepared from wheat bran provided a long-term development strategy for dye wastewater treatment.

Adsorptive removal of Safranine T dye from aqueous solutions using sodium alginate–Festuca arundinacea seeds bio–composite microbeads

In this study, composite microbeads were prepared using Festuca arundinacea seeds and sodium alginate biopolymer at different ratios and utilized as sorbents for the sorption of Safranine T from wastewater. The sorbents were characterized by FTIR, SEM, XRD, and BET analysis. According to BET analysis, the specific surface area of the adsorbents was calculated to be 10.99 m2/g and the surface was found to be mesoporous. The optimum conditions for adsorption studies including initial pH (2−12), concentration (10–50 mg/L), contact time (0–150 min), and adsorbent mass (0.05 g/50 mL-0.25 g/50 mL) were determined at 25 °C. The raw data obtained from sorption tests were applied to Freundlich, Langmuir-1, Langmuir-2, Langmuir-3, Langmuir-4, Temkin, Toth, and Koble-Corrigan isotherm models. The best results were obtained from the Langmuir-2 and accordingly the qm values were calculated as 454.54, 833.33, and 625.00 mg/g for FA, FA-SA-20, and FA-SA-30 at 25 °C, respectively. Adsorption kinetic data illustrated that the process followed the PSO model. Reusability and desorption studies were performed for composite microbeads. Additionally, the thermodynamic studies were performed at 25, 35 and 45 °C. Considering all these results, it was seen that the FA-SA-20 composite had the highest adsorption capacity and the best desorption efficiency.

Assessment of β-cyclodextrin-immobilizing hydrolyzed polyacrylonitrile membrane for enhanced remediation of bisphenol A and tetracyclines: Adsorption and antibacterial studies

A citric acid-crosslinked β-cyclodextrin modifying hydrolyzed polyacrylonitrile membrane (β-CD-HPAN) was designed for bisphenol A (BPA), tetracycline (TC), and oxytetracycline (OTC) uptake. β-CD-HPAN was successfully prepared with several characterizations and optimized synthesis conditions. In batch mode, there was a good removal capacity toward BPA in a broad pH range, the uptake of TC and OTC (TCs) possessed a relatively high adsorption effect at pH of 3.0–4.0. The addition of salinity had a negative result on adsorption. The isotherm behaviors exhibited a monolayer equilibrium removal capacity (qe) of 45.3 mg/g for BPA, with heterogeneous qe of 124 mg/g and 98.4 mg/g for TC and OTC, respectively. These processes were accorded with Koble-Corrigan isotherm model, and the kinetic behaviors followed Elovich equation. The binary experiment elucidated that BPA and TC/OTC removal onto β-CD-HPAN was independent from each other. β-CD-HPAN also elucidated good regeneration performances. Adsorption mechanisms were proposed that β-CD cavities on β-CD-HPAN mainly contributed to entrap molecules of non-polar BPA, carboxyl and hydroxyl groups provided binding sites for polar TCs. The membrane owned antibacterial capacity against gram-positive S. aureus. Overall, β-CD-HPAN membrane has great potentials in wastewater purification to adsorb BPA and TCs due to its green synthetic procedure, easy separation, bifunctional groups, and low cost.

Green sulfidated iron oxide nanocomposites for efficient removal of Malachite Green and Rhodamine B from aqueous solution.

A green and facile pathway was described using Viburnum odoratissimum leaf extract in the presence of sodium thiosulfate for the synthesis of sulfidated iron oxide nanocomposites (S-Fe NCs) adsorbents. The prepared S-Fe NCs can be used for the efficient removal of Malachite Green (MG) and Rhodamine B (RhB) from aqueous solution. Analytical techniques by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) were applied to understand the morphologies and compositions of S-Fe NCs. The stability of the adsorption capacity on S-Fe NCs was studied. Results from the characterization studies showed that S-Fe NCs were mainly composed of iron oxides, iron sulfides and biomolecules. The S-Fe NCs displayed high adsorption capacity for a wide range of pH values. The Koble-Corrigan isotherm model and Elovich model well described the adsorption process. The maximum adsorption capacity for MG and RhB was 4.31 mmol g-1 and 2.88 mmol g-1 at 303 K, respectively. The adsorption mechanism may be attributed to the electrostatic interaction, the hydrogen bonding, the π-π stacking interactions, the inner-sphere surface complexation or the cation bridging among the S-Fe NCs and dye molecules.

Optimized preparation of activated carbon from furfural residue using response surface methodology and its application for bisphenol S adsorption.

Furfural residue (FR), a solid waste, was applied as the precursor to prepare activated carbon by steam activation. The Box-Behnken design (BBD) approach-based response surface methodology (RSM) was utilized to optimize the preparation conditions to evaluate their effects on the performance of activated carbon from furfural residue (FRAC). The optimum preparation conditions of FRAC were found as follows: activation temperature of 922 °C, activation time of 62 min, and the mass ratio of char to H2O of 1:4.5, resulting in 1,501.84 mg/g of iodine adsorption capacity and 1,662.41 m2/g of specific surface area. The FRAC was characterized and then the adsorption performance of bisphenol S (BPS) on FRAC was investigated. Langmuir and Koble-Corrigan isotherm models were well fitted to the experimental data, and the adsorption kinetics process was perfectly described by the pseudo-second-order model. Thermodynamic parameters showed that the adsorption of BPS was a spontaneous exothermic process. Besides, the regeneration efficiency of FRAC was over 97% after five consecutive cycles. The maximum monolayer adsorption capacity of FRAC for BPS was 3.2848 mmol/g at 298 K, indicating that the FRAC was an excellent adsorbent for the removal of BPS from aqueous solutions.

Enhanced fluoride adsorption from aqueous solution by zirconium (IV)-impregnated magnetic chitosan graphene oxide

In this study, zirconium (IV)-impregnated magnetic chitosan graphene oxide (Zr-MCGO) was synthesized for removing fluoride from aqueous solution in batch mode. Characterization approaches (pHpzc, FTIR, SEM, XRD, VSM, Raman, BET, and XPS) proved the successful incorporation of Zr into the adsorbent. Zr-MCGO exhibited a relatively favorable and stable capacity of defluoridation at lower pH with a wide range of pH from 4.0 to 8.0, while there was slightly negative effect of ionic strength on adsorption. In addition, Elovich kinetic model and Koble-Corrigan isotherm model could describe the uptake of fluoride well. The adsorption capacity was 8.84 mg/g at 313 K and Zr-MCGO was easily separated from mixtures using external magnet. Based on the experiments and XPS, electrostatic force, ligand exchange, and Lewis acid–base interaction might be potential adsorption mechanisms. Pseudo-second-order model was more compatible with the desorption process by 0.01 mol/L NaHCO3 solution. Therefore, Zr-MCGO was a promising candidate for defluoridation on wastewater pollution remediation.

Dual Functional Composite of Montmorillonite-Rich/Chitosan (MCC) for Decolorizing the Water Used in Joss Paper Process: Thermodynamic, Isotherm, and Kinetic Studies

A hybrid montmorillonite (Mt)-rich/chitosan composite (MCC) with high adsorption performance was synthesized for the decolorization of water used in the joss paper process. The performance was reported in terms of the dye removal. The composite expressed higher performance than chitosan or Mt-rich clay, respectively. The optimum condition for complete dye removal was achieved when using at least 0.6 g of the composite over a wide pH range (3–10) and initial dye concentration (10–100 mg L−1). The composite showed good reusability without the requirement of regeneration, adsorbing the dye completely for up to eight successive cycles of adsorption (>1.33 gdye gMCC−1). Thermodynamic analyses revealed the degree of spontaneity and the endothermic adsorption process. From the isotherm studies, the Koble–Corrigan isotherm model fitted very well to the experimental data, revealing that the composite had a heterogeneous surface with various active sites to adsorb the dye molecules. This also evidenced the synergistic electrostatic attraction and hydrophobic interaction between the dye and the composite. The pseudo-second-order model best explained the kinetic rate of adsorption. From evaluation of the adsorption process using the Webber and Morris equation and Boyd model, the rate-limiting step consisted of film diffusion and intra-particle diffusion.

Hydrothermal synthesis of LaFeO3 nanoparticles adsorbent: Characterization and application of error functions for adsorption of fluoride

The adsorption of fluoride from aqueous solution by lanthanum ferrite nanoparticles (LaFeO3 NPs) synthesized by the hydrothermal method has been investigated. This experimental study was conducted on a laboratory scale. The effects of various operating parameters such as pH (3–11), LaFeO3 NPs dosage (0.1–1.0 g/L), contact time (15–120 min), temperature (303–318 K), and initial concentration of fluoride (15–40 mg/L) on fluoride adsorption were studied. The results showed that under optimal conditions of fluoride concentration of 20 mg/L, pH of 5, LaFeO3 NPs dosage of 0.9 g/L, temperature of 308 K, and contact time of 60 min, maximum percentage removal of 94.75 % was obtained. The process of fluoride adsorption on LaFeO3 NPs was found to depend on the Freundlich adsorption and Koble–Corrigan isotherm models. The monolayer adsorption capacity of LaFeO3 NPs was 2.575 mg/g. The kinetic data fitted best into the pseudo-second-order model considering the values of the regression coefficients (r2) and error functions used. The thermodynamics study indicated that the adsorption process was exothermic (ΔH°< 0) and spontaneous (ΔG°< 0) in nature. It could be concluded that the synthesized LaFeO3NPs can be used as an effective adsorbent for fluoride ions removal from aqueous solutions.

Optimized Preparation of High Value-Added Activated Carbon and Its Adsorption Properties for Methylene Blue

AbstractThe optimal preparation conditions of activated carbon (AC) derived from corncob (CC) by steam activation were investigated using response surface methodology. In response to iodine adsorption capacity, experimental design was established using three synthetic variables based on the Box–Behnken central composite design. The optimum conditions of 892 °C activation temperature, 40 min residence time, and 1:1.6 the mass ratio of char to H2O gave 1216.74 mg/g iodine adsorption value. AC was characterized using instrumental analyses consist of Brunauere-Emmette-Teller (BET), Fourier transform infrared (FT-IR) and Scanning electron microscopy (SEM). The effect of experimental parameters such as adsorption time, adsorbent dosage and pH on the uptake of methylene blue (MB) were studied. Experimental equilibrium data was analyzed by the Langmuir, Freundlich, Sips and Koble–Corrigan isotherm models. The results showed that the Freundlich and Koble–Corrigan models could properly represent the adsorption behavior of MB on AC. In addition, it was known that the adsorption of MB was a spontaneous and endothermic process from the thermodynamic parameters of ΔG, ΔHand ΔS.

Combining Sewage Sludge and Clam Shell Waste to Prepare Adsorbents for Efficient Phosphorous Removal

Effluents containing phosphorous as phosphate ions are frequently discharged in freshwater resources contributing to the eutrophication and directly interfering in the biological equilibrium. Clam shell residues and sewage sludge were combined for preparing efficient adsorbents for phosphate removal from aqueous medium. The adsorbents were characterized before and after adsorption testing, and the adsorption equilibrium and kinetics were investigated. Phosphate removal of 89 ± 1% was attained for samples prepared with 0.1 < X < 1.0, where X corresponds to sewage sludge/clam shell mass ratio. The analyses of the experimental errors indicated that the phosphorous removal followed the Elovich kinetic model, which describes adsorption in very heterogeneous surfaces. On the other hand, the best modelling was achieved using the Koble–Corrigan isotherm model, which incorporate different aspects of both Langmuir and Freundlich isotherms to represent the equilibrium data. The observed adsorption capacity (21.4 mgP g−1) are comparable or greater to that observed for other adsorbents described in the literature.

Sulfate decontamination from groundwater by metal layered double hydroxides functionalized high phosphorus iron ore waste as a new green adsorbent: Experimental and modeling

The reuse of mine wastes is an efficient method to reduce disadvantages of the mining operation. High phosphorous iron ore (HPI) waste as a common waste of iron mine has been modified by Ni-Al and Ni-Fe hydroxide metals and utilized as a sulfate adsorbent. These adsorbents were characterized by XRD, XRF, FTIR, SEM, BET and TGA analyses. According to characterization studies, by loading Metal Layered Double Hydroxides (Ni-Al and Ni-Fe hydroxide metals) onto HPI Ore Waste appropriate adsorptive spaces and pores were emerged on the surface of Ni-Fe and Ni-Al HPI which were shown by enhancement intensity of OH bending vibrations in FTIR analysis, increase of Loss On Ignition (L.O.I) value in XRF analysis and the thermal stability reduction in TGA. The RSM method based on central composite design (CCD) was used to investigate the optimum condition. The amount of adsorption in optimum condition led to 34 and 29.89mg/g for Ni-Al and Ni-Fe HPI, respectively. The equilibrium studies have been carried out by the consideration of Langmuir, Freundlich, Temkin, D-R, Redlich-Peterson, Khan, and Koble–Corrigan isotherm models, which displayed that sulfate adsorption onto both adsorbents were performed favorably and chemically. Sulfate adsorption on to Ni-Al and Ni-Fe HPI occurred by the homogenous and heterogeneous process, respectively. Kinetic studies were performed by applying pseudo-first-order, pseudo-second-order and Boyd models which indicated the chemisorption interaction for all three adsorbents by a controlling step of the film diffusion. The adsorption process was modeled by the extended geometric method by an acceptable estimation fitted well with experimental data. Thermodynamic studies indicate that sulfate adsorption process onto Ni-Al and Ni-Fe HPI were exothermic and associative.

Adsorptive removal of As(III) from aqueous solution by waste litchi pericarps.

The present study investigated the removal of arsenite anions (AsO33-, referred to as As(III)) from aqueous solutions by waste litchi pericarps (LPs). Influential factors such as the adsorbent dose, contact time, solution pH, and initial As(III) concentration were investigated. The optimum conditions for As(III) adsorption by the LPs occurred at a contact time of 60 min, adsorbent dose of 10.0 g/L, solution pH of 5.0, and initial As(III) concentration of 1 mg/L. A Box-Behnken design with three variables (adsorbent dose, contact time, and solution pH) at three different levels was studied to identify the correlations between the influential factors and the As(III) adsorption; the results showed a significant interaction between the adsorbent dosage and pH. Additionally, adsorption isotherms, kinetics, and thermodynamics were investigated to explore the As(III) adsorption mechanism. Adsorption by the LPs conformed to the Langmuir, Redlich-Peterson, and Koble-Corrigan isotherm models, suggesting that the process proceeds via monolayer, homogeneous adsorption. In addition, the As(III) adsorption could be characterized by a pseudo-second-order mechanism, revealing that the rate-limiting step might be chemisorption. The thermodynamic studies showed that As(III) adsorption by the LPs was spontaneous and endothermic, and disorder at the solid-liquid interface increased in the adsorption process.

Adsorption of reactive dye from aqueous solution and synthetic dye bath wastewater by Eucalyptus bark/magnetite composite.

In the present study, Eucalyptus camaldulensis bark/magnetite composite (EBMC) was used for a potential application as a low-cost adsorbent for the removal of Reactive Black 5 (RB5). The adsorption experiments were performed with aqueous solution (RB5 + distilled water) and synthetic dye bath wastewater (SDBW) in order to investigate the potential application of EBMC in the textile industry. The effects of the various parameters, the initial dye concentration, the temperature, the pH, and the EBMC dosage on the adsorption were investigated. It was found that the adsorption capacity of EBMC increases by increasing the RB5 concentration and temperature and by decreasing the dosage of EBMC. 0.8 g EBMC was found to be sufficient for the removal of 250 mg/L RB5 from 150 mL SDBW with ∼85% removal efficiency. The Koble-Corrigan isotherm model described the adsorption process more effectively (R2 = 0.997) than the Langmuir, Freundlich, the Dubinin-Radushkevich and the Jovanovic isotherm models. The Langmuir isotherm predicted a 370.7 mg/g maximum adsorption capacity. The thermodynamic analysis showed that the adsorption of RB5 onto the EBMC was an endothermic process. The multiple linear regression analysis was used in order to determine the cumulative effects of independent variables on the adsorption capacity.

Adsorption of Brilliant Yellow onto Sepiolite: Evaluation of Thermodynamics and Kinetics and the Application of Nonlinear Isotherm Models

We studied the adsorption of Brilliant Yellow (BY) from aqueous solutions onto sepiolite and determined the adsorption equilibrium isotherms. We applied pseudo-first-order and pseudo-second-order kinetic models; the adsorption of BY onto sepiolite was best described by the pseudo-second-order kinetic model. The experimental data obtained at different temperatures were analyzed using various isotherm models; the Koble–Corrigan isotherm model provided the best fits for the BY adsorption data at all temperatures. The thermodynamic parameters of the BY adsorption onto sepiolite indicated that the adsorption process is spontaneous and exothermic in nature.

A comparative adsorption study of sulfamethoxazole onto graphene and graphene oxide nanosheets through equilibrium, kinetic and thermodynamic modeling

Adsorption properties of sulfamethoxazole (SMX) as an antibiotic were promoted by graphene nanosheet (GNS) and Graphene oxide nanosheet (GOS). The five factors influencing the adsorption of SMX (initial SMX concentration, initial solution pH, amount of adsorbent, temperature and contact time) were studied. The results showed that adsorbent dosage of 0.010mg, initial pH∼6 and contact time ∼110min are optimum for both systems. The monolayer adsorption capacity (qm) decreased with the increase of the temperature from 25°C to 45°C. Non-linear regressions were carried out in order to determine the best fit model for each system. To do this, 8 error functions were applied to predict the optimum model. Among various models, Redlich–Peterson and Koble–Corrigan isotherm models represented the equilibrium adsorption data of SMX while kinetic experimental data were well fitted by pseudo second-order model on both adsorbents. The study showed that GOS can be used as a more efficient adsorbent for the adsorption of SMX from water solution.

Evaluation of physicochemical methods in enhancing the adsorption performance of natural zeolite as low-cost adsorbent of methylene blue dye from wastewater

The main aim of this study was to evaluate different facile and cost-effective physicochemical methods in enhancing the adsorption capacity of natural zeolite and subsequently demonstrate the removal of methylene blue (MB). Four different physicochemical methods, namely: acid treatment (AT), base treatment (BT), combined acid-thermal (ATT) and base-thermal treatments (BTT) were investigated. This was followed by understanding the impact of the physicochemical methods on the surface characteristics and properties of modified zeolite through advanced characterisations using field emission-scanning electron microscopy, Fourier-transformed infrared spectroscopy and Brunauer–Emmett–Teller specific surface area and porosity measurements. Batch adsorption studies were carried out using the modified zeolite adsorbents, in order to evaluate the highest removal efficiency of MB under varying adsorption conditions of: pH, initial MB concentration and modified zeolite loading. Results showed that both the physicochemical methods of AT (using 0.4 M HCl) and BT (using 4.0 M NaOH) are able to enhance the adsorption capacity of natural zeolite from 41% to 98.8% and 52.2%, respectively. Surprisingly, the combined physicochemical methods of ATT and BTT showed a reduction in adsorption performance when benchmarked to AT and BT alone. The adsorption data were analysed and modelled using Langmuir, Freundlich, Redlich-Peterson and Koble-Corrigan isotherm models, also the adsorption kinetics were evaluated using pseudo-first and pseudo-second order models. It was found that the adsorption data and kinetics were best represented using the Koble-Corrigan and pseudo-second order models. The improvements yielded through both the AT and BT modified zeolites were found to be promising and have the potential to be used as low-cost adsorbents for wastewater treatment.

Bio-adsorption properties of Rhodamine B from aqueous solution onto natural camphor tree leaf powder

The potential of camphor tree leaf powder (CALP) to remove Rhodamine B (RhB) from aqueous solution was evaluated. The CALP was characterized by the scanning electron microscope and Fourier transform infrared technique, respectively. The effects of contact time, initial RhB concentrations, solution pH, and strength of the coexisting cations and anions upon the RhB adsorption were evaluated. The CALP had buffering action on the RhB/CALP system to maintain the solution pH in the range of 7. The Langmuir, Freundlich, and Koble–Corrigan isotherm models were used to analyze the adsorption behavior and the Koble–Corrigan isotherm fits the equilibrium data best (R2 > 0.99). The kinetic studies indicated that the adsorption process was fitted well with the pseudo-second-order model with rate constants (k2) in the range of 0.2586–3.0489 g/mg/min, suggesting that the adsorption might be a chemisorption process. The thermodynamic parameters indicated that adsorption process was feasible and spontaneous.

Removal of Zn(II) ions from aqueous solutions by ethyl xanthate impregnated activated carbons

A coconut shell based granular activated carbon (AC) was aged in solutions containing different amount of potassium ethyl xanthate (PEX) for 24h and then separated from the solutions, rinsed with distilled several times and used for Zn(II) ion removal. It was shown that the loading capacity of PEX impregnated AC at an initial Zn(II) concentration of 112mg/L slightly increased by increasing PEX preloading, so that it increases from 1.56 to 1.88mg/g by increasing the PEX concentration in the aging solution from zero to 200mg/L.Aging of AC in 0.1N sodium hydroxide solutions containing different amounts of PEX was also performed for 24h and it was shown that the loading capacity of the resultant AC samples for Zn(II) ions at an initial Zn(II) concentration of 112mg/L slightly increased by increasing PEX loading, so that it increases from 7.18 to 8.06mg/g by increasing PEX concentration in aging solution from zero to 600mg/L.Aging of nitric acid oxidized AC in 0.1N sodium hydroxide solutions containing different amounts of PEX also performed for 24h. It was shown that the loading capacity of these modified AC samples for Zn(II) ions at an initial Zn(II) concentration of 112mg/L increased by increasing PEX loading, so that it increases from 15.11 to 16.43mg/g by increasing PEX concentration in aging solution from zero to 1000mg/L.It was revealed that the impregnation of AC samples with PEX results in the decreasing of adsorption kinetics of Zn(II) ions, since the hydrophobic nature of PEX molecules retards solution diffusion onto PEX impregnated AC samples.In order to get the highest Zn(II) loading capacity, the optimum condition for surface modification was determined to be oxidizing of AC with 4M nitric acid solution and then aging in 0.1M sodium hydroxide solution containing 661mg/L PEX for 24h. These surface modified activated carbons were named ACABPEX. The effect of Zn(II) initial concentration in the range of 59 to 165mg/L on its adsorption kinetics and loading capacity onto ACABPEX was investigated. The equilibrium and kinetic data were best represented by the Koble–Corrigan isotherm model and the pseudo second order kinetic model, respectively. It was understood that three mechanisms play main roles in the adsorption of Zn(II) onto ACABPEX.

Study of the Removal of Pb(II) Using a Weak Acidic Cation Resin: Kinetics, Thermodynamics, Equilibrium, and Breakthrough Curves

This study presents a method for the removal of Pb(II) from aqueous solution in batch and column modes using a commercial weak acidic cation (WAC) resin (Lewatit CNP80). Batch experiments carried out under different conditions yielded optimum conditions of pH = 5, t = 360 min, and m = 0.05 g (1 g L–1). The mechanism of ion exchange was studied using isotherm, kinetic, and thermodynamic models. The good fit of the Koble–Corrigan isotherm model indicates both heterogeneous and homogeneous sorption of Pb(II) on the resin. The concentration of Pb(II) in the solution had a strong influence on both the diffusion kinetics and the mechanism controlling the kinetic coefficient. The fit of the experimental data to the pseudo-second-order model indicated that the reaction is affected fundamentally by Pb(II) concentration, whereas temperature did not result in a significant change. The Gibbs free energy change (ΔG°) values were negative, corresponding to a spontaneous process of Pb(II) ion sorption onto the WAC resin. The S-shaped breakthrough curves from the column studies show that most of the resin capacity was used up to the breakthrough point. Clean and Pb(II)-loaded WAC resins were characterized on the basis of ζ-potential measurements, Fourier transform infrared spectrum (FTIR) spectral study, thermogravimetric analysis (TGA), and environmental scanning electron microscopy (ESEM) images. The O–H and C–O stretching of the carboxylic acid groups and the C–O–C stretching groups were the main functional groups of the WAC resin participating in the Pb(II) binding. A visible change in the surface morphology observed from the ESEM images showed some fouling, an indicator of the 28% irreversible loss of capacity after regeneration. It can be concluded that ion exchange with WAC resin is a satisfactory process for Pb(II) removal especially for low concentrations.

Equilibrium, kinetic, and thermodynamic studies of lead (II) biosorption on sesame leaf

Sesame leaf, an agricultural solid waste, was used as low cost adsorbent for removal of Pb(II) from aqueous solution in batch mode. The biosorbent was characterized by thermo-gravimetric analysis and Fourier transform infrared spectroscopy. The influences of phase contact time, solution pH, adsorbent dosage, and initial concentrations were investigated to optimize the conditions for maximum adsorption. The experimental data were analyzed by Langmuir, Freundlich, and Koble-Corrigan isotherm models. The Koble-Corrigan and Langmuir isotherms best represented the measured biosorption data. According to an evaluation using the Langmuir equation, the adsorption capacity of the biosorbent was found to be 279.86 mg g-1, which was higher or comparable to the adsorption capacity of various adsorbents reported in the literature. The kinetics of adsorption of Pb(II) was evaluated by pseudo-first order, pseudo-second order, and intra-particle diffusion kinetic models. The experimental data fitted very well with the pseudo-second order kinetic model. The intra-particle diffusion model is not a dominant rate controlling mechanism in the sorption of Pb(II). Thermodynamic analysis showed that the adsorption was a spontaneous and endothermic process. The results indicated that sesame leaf can be used as an effective biosorbent for Pb(II) removal from aqueous solutions.