Equilibrium and Kinetic Modelling of Adsorption of Phosphorus on Calcined Alunite

The adsorption of phosphorus onto calcined alunite has been studied. Its equilibrium isotherm has been measured. The isotherm was determined by shaking 1.0 g calcined alunite, particle size range 90–150 m, with 100 mL phosphorus solution of initial concentrations from 0.5 to 2.5 mmol/L. The water bath shaking a constant rate of 200-rpm was used and the temperature maintained at 298 ± 2 K. A contact time of 120 min was required to achieve equilibrium. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich equations. The monolayer adsorption capacity is 1.355 mmol P per g calcined alunite. Three simplified kinetic models including a pseudo first-order equation, pseudo second-order equation and intraparticle diffusion equation were selected to follow the adsorption process. Kinetic parameters, rate constants, equilibrium sorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the adsorption of phosphorus could be described by the pseudo second-order equation.     

Comparative modelling of mono- and dinitrophenols sorption on yellow bentonite from aqueous solutions

Equilibrium removal of three substituted nitrophenols, namely 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP), by adsorption on yellow bentonite was tested. The batch kinetic data are described by the pseudo-first order, pseudo-second order, and intraparticle diffusion models. Results show that chemisorption processes could be rate limiting in the sorption step. The adsorption equilibrium was modelled by the Langmuir and Freundlich equations. The Langmuir model better represents the equilibrium isotherm data for 2-NP, 4-NP, and 2,4-DNP uptake on yellow bentonite. 4-NP is adsorbed in larger amounts than the disubstituted nitrophenol. Uptake of nitrophenols increases in the order 2-NP < 2,4-DNP < 4-NP.     

Adsorption of direct dyes from aqueous solutions by carbon nanotubes: determination of equilibrium, kinetics and thermodynamics parameters

This study examined the feasibility of removing direct dyes C.I. Direct Yellow 86 (DY86) and C.I. Direct Red 224 (DR224) from aqueous solutions using carbon nanotubes (CNTs). The effects of dye concentration, CNT dosage, ionic strength and temperature on adsorption of direct dyes by CNTs were also evaluated. Pseudo second-order, intraparticle diffusion and Bangham models were adopted to evaluate experimental data and thereby elucidate the kinetic adsorption process. Additionally, this study used the Langmuir, Freundlich, Dubinin and Radushkevich (D-R) and Temkin isotherms to describe equilibrium adsorption. The adsorption percentage of direct dyes increased as CNTs dosage, NaCl addition and temperature increased. Conversely, the adsorption percentage of direct dyes decreased as dye concentration increased. The pseudo second-order model best represented adsorption kinetics. Based on the regressions of intraparticle diffusion and Bangham models, experimental data suggest that the adsorption of direct dyes onto CNTs involved intraparticle diffusion, but that was not the only rate-controlling step. The equilibrium adsorption of DR86 is best fitted in the Freundlich isotherm and that of DR224 was best fitted in the D-R isotherm. The capacity of CNTs to adsorb DY86 and DR224 was 56.2 and 61.3 mg/g, respectively. For DY86, enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were 13.69 kJ/mol and 139.51 J/mol K, respectively, and those for DR224 were 24.29 kJ/mol and 172.06 J/mol K, respectively. The values of DeltaH(0), DeltaG(0) and E all indicate that the adsorption of direct dyes onto CNTs was a physisorption process.     

Removal of methylene blue by seed-watermelon pulp-based low-cost adsorbent: Study of adsorption isotherms and kinetic models

Based on the abundance of seed-watermelon pulp (SWP) in Xinjiang, China, SWP was employed to prepare low-cost adsorbent toward the removal of methylene blue (MB). The effects of contact time at different initial concentration were studied. The widely used adsorption isotherm models including Langmuir, Freundlich, and Temkin isotherms were employed to depict the adsorption process. The Langmuir isotherm was best fitted to the experimental data. Batch kinetic studies showed that an equilibrium time of 300 minutes was needed for the adsorption. The adsorption properties can be well described by pseudo-second-order kinetic model and the MB uptake was not controlled by intraparticle diffusion mechanism.     

Selective Adsorption of Co(Ⅱ)by Mesoporous Silica SBA-15-Supported Surface Ion Imprinted Polymer:Kinetics,Isotherms,and Thermodynamics Studies

A novel surface ion imprinted adsorbent [Co(II)‐IIP] using polyethyleneimine (PEI) as function monomer and ordered mesoporous silica SBA‐15 as support matrix was prepared for Co(II) analysis with high selectivity. The prepared polymer was characterized by Fourier transmission infrared spectrometry, scanning electron microscopy, X‐ray diffraction and nitrogen adsorption‐desorption isotherm. Bath experiments of Co(II) adsorption onto Co(II)‐IIP were performed under the optimum conditions. The experimental data were analyzed by pseudo‐first‐order and pseudo‐second‐order kinetic models. It was found that the pseudo‐second‐order model best correlated the kinetic data. The intraparticle diffusion and liquid film diffusion were applied to discuss the adsorption mechanism. The results showed that Co(II) adsorption onto IIP was controlled by the intraparticle diffusion mechanism, along with a considerable film diffusion contribution. Langmuir, Freundlich and Dubinin‐Radushke‐ vich adsorption models were applied to determine the isotherm parameters. Langmuir model fitted the experiment data well and the maximum calculated capacity of Co(II) reached 39.26 mg/g under room temperature. The thermodynamic data were indicative of the spontaneousness of the endothermic sorption process of Co(II) onto Co(II)‐IIP. Co(II)‐IIP showed high affinity and selectivity for template ion compared with non imprinted polymer (NIP).     

Preparation of magnetic composite adsorbents from laterite nickel ore for organic amine removal

Magnetic composite adsorbent (MCA) was prepared successfully using laterite nickel ore. The effectiveness of MCA as an adsorbent was evaluated for removal trimethylamine from aqueous environment. In this technological route, the utilization of solid wastes, wastewater treatment and adsorbent recovery were considered comprehensively. The MCA was characterized by techniques, including XRD, SEM, TEM, EDS, VSM and adsorption-desorption of nitrogen at 77 K. The adsorption processes were best described by pseudo-second-order kinetic model and controlled by intraparticle and surface diffusion processes. Langmuir and Freundlich isotherm models were used to match the adsorption equilibrium data. Freundlich isotherm was the best fitting curve for the sorption equilibrium data. The adsorption mechanism was further interpreted by Gibbs free energy, entropy and enthalpy calculated by thermodynamic equation. The negative values of Gibbs free energy changes (ΔG) manifest that the adsorbing process is spontaneous. The results show that laterite nickel ore can be made into MCA for organic amine removal from polluted water.     

Uranium removal from nitric acid raffinate solution by solvent immobilized PVC cement

The present work deals with uranium removal from a nitric acid raffinate (waste) solution using prepared solvent (tri-butyl phosphate, TBP) immobilizing PVC cement (SIC) as a suitable adsorbent. The studied relevant factors affecting uranium adsorption onto SIC adsorbent involved; contact time, solution molarity, initial uranium concentration and temperature. The obtained adsorption isotherm of uranium onto the SIC adsorbent was fitted to Langmuir, Freundlich and Dubinin–Radushkviech (D–R) adsorption models. The results showed that the obtained equilibrium data fitted well the Langmuir isotherm. Additionally, it was found that the adsorption process obeys the pseudo second-order kinetic model. On the other hand, the calculated theoretical capacity of our prepared SIC adsorbent reached about 17 g U/kg SIC. Uranium adsorption from the studied raffinate solution was carried out applying the attained optimum conditions. The obtained data showed that 58.4 mg U/5 g SIC were adsorbed. However, using of 2 M HNO₃ solution as an eluent, 93 (54.3 mg U) from the adsorbed amount were eluted.     

Removal of copper from aqueous solution by aminated and protonated mesoporous aluminas: kinetics and equilibrium

A novel adsorbent, aminated and protonated mesoporous alumina, was prepared and employed for the removal of copper from aqueous solution at concentrations between 5 and 30 mg/l, in batch equilibrium experiments, in order to determine its adsorption properties. The removal of copper by the adsorbents increases with increasing adsorbent dosages. The adsorption mechanism is assumed to be an ion exchange between copper and the hydrogen ions present on the surface of the mesoporous alumina. The adsorbent was characterized by XRD, TEM, SEM, and BET methods. The sorption data have been analyzed and fitted to linearized adsorption isotherm of the Freundlich, Langmuir, and Redlich-Peterson models. The batch sorption kinetics have been tested for first-order, pseudo-first-order, and pseudo-second-order kinetic reaction models. The rate constants of adsorption for all these kinetic models have been calculated. Results also showed that the intraparticle diffusion of Cu(II) on the mesoporous catalyst was the main rate-limiting step.     

Adsorption of Basic Magenta II onto H2SO4 activated immature Gossypium hirsutum seeds: Kinetics,isotherms, mass transfer,thermodynamics and process design

The adsorption of Basic Magenta II onto H₂SO₄ activated immature Gossypium hirsutum seeds was analysed using Ho, modified Freundlich, Sobkowsk–Czerwi, Blanchard, Elovich, Avrami, and modified Ritchie kinetic models by nonlinear regression-sum of normalized errors analysis. The goodness of fit was evaluated with coefficient of determination and root mean square error. The good agreement of experimental data to Avrami second-order model indicated that the mechanism of adsorption followed multiple kinetic orders. The Avrami second-order mechanism was applied to predict the rate constant of sorption and the equilibrium capacity and subsequently the obtained equilibrium adsorption capacities were utilized to find the equilibrium concentrations. Langmuir, Freundlich, Temkin, Sips and Hill isotherms were investigated to understand the nature of adsorption with the help of nonlinear regression analysis. Both Sips and Hill isotherms were best fit to the adsorption equilibrium data showing the homogeneous adsorption on the heterogeneous surface of carbon and the positive co-operative manifestations of the Basic Magenta II molecules. The mass transfer study depicted the details such as mass transfer coefficient, intra-particle diffusion rate, pore diffusion coefficient, and film diffusion coefficient. The adsorption process was found to be controlled by film diffusion. The thermodynamic parameters like, Gibbs free energy change, enthalpy change, entropy change and isosteric heat of adsorption confirmed the endothermic, feasible and spontaneous nature of adsorption. A single stage batch adsorber was designed using Sips isotherm constants to estimate the amount of carbon required for desired purification.     

Removal of uranium(VI) from aqueous solution using citric acid modified pine sawdust: batch and column studies

This study described adsorption of uranium(VI) by citric acid modified pine sawdust (CAMPS) in batch and fixed-bed column modes at 295 K. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Koble–Corrigan and Dubinin–Radushkevich isotherm models. The results indicated that the Langmuir and Koble–Corrigan models provided the best correlation of the experimental data. The Elovish model was better to fit the kinetic process, which suggested that ion exchange was one of main mechanism. The effective diffusion parameter D _i values indicated that the intraparticle diffusion was not the rate-controlling step. In fixed-bed column adsorption, the effects of bed height, feed flow rate, and inlet uranium (VI) concentration were studied by assessing breakthrough curve. The Thomas, the Yan and the bed-depth/service time (BDST) models were applied to the column experimental data to determine the characteristic parameters of the column adsorption. The results were implied that CAMPS may be suitable as an adsorbent material for adsorption of uranium (VI) from an aqueous solution.     

Adsorption of acid dyes from aqueous solutions onto acid-activated bentonite

The adsorption of two dyes, namely, Acid Red 57 (AR57) and Acid Blue 294 (AB294), onto acid-activated bentonite in aqueous solution was studied in a batch system with respect to contact time, pH, and temperature. Acidic pH was favorable for the adsorption of these dyes. The surface characterization of acid-activated bentonite was performed using the FTIR technique. The pseudo-first-order and pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The dynamic data fitted the pseudo-second-order kinetic model well and also followed the intraparticle diffusion model up to 90 min, but diffusion is not the only rate controlling step. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were determined. The Freundlich model agrees very well with experimental data. The activation energies of adsorption were also evaluated for the adsorption of AR57 and AB294 onto activated bentonite.     

PREPARATION AND CHARACTERIZATION OF NOVEL CHITOSAN DERIVATIVES: ADSORPTION EQUILIBRIUM OF IRON(Ⅲ) ION

The adsorption of Fe(Ⅲ)ions from aqueous solution by chitosan alpha-ketoglutaric acid(KCTS)and hydroxamated chitosan alpha-ketoglutaric acid(HKCTS)was studied in a batch adsorption system.Experiments were carried out as function of pH,temperature,agitation rate and concentration of Fe(Ⅲ)ions.The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and isotherm constants were determined.The Langmuir model agrees very well with experimental data.The pseudo-first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated.The dynamical data fit well with the second-order kinetic model.The pseudo second-order kinetic model was indicated with the activation energy of 19.61 and 7.98 kJ/mol for KCTS and HKCTS,respectively.It is suggested that the overall rate of Fe(Ⅲ)adsorption is likely to be controlled by the chemical process.Results also showed that novel chitosan derivatives(KCTS and HKCTS)were favorable adsorbents.     

Adsorption of polycyclic aromatic hydrocarbons from aqueous solutions by modified periodic mesoporous organosilica

A novel procedure was developed for the synthesis of a periodic mesoporous organosilica (PMO), which was used to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. Adsorption equilibrium isotherms and adsorption kinetics experiments were carried out in solutions of PAHs (2-60 mg L(-1)), using the PMO as adsorbent. Adsorption models were used to predict the mechanisms involved. The adsorption kinetics data best fitted the pseudo-first-order kinetic model for naphthalene, and to the pseudo-second-order model for fluorene, fluoranthene, pyrene, and acenaphtene. The intraparticle model was also tested and pointed to the occurrence of such processes in all cases. The isotherm models which best represented the data obtained were the Freundlich model for fluoranthene, pyrene, and fluorene, the Temkin model for naphthalene, and the Redlich-Peterson model for acenaphtene. PAHs showed similar behavior regarding kinetics after 24 h of contact between adsorbent and PAHs. FTIR, XRD, BET, and SEM techniques were used for the characterization of the adsorbent material.     

一种球形木质素吸附剂对L-天门冬氨酸的吸附行为研究

以硫酸盐木质素为原料,利用反相悬浮技术制备出球形木质素吸附剂.通过静态吸附试验,研究了球形木质素吸附剂对L-天门冬氨酸的吸附动力学和热力学特性,探讨了pH对吸附过程的影响.结果表明,当溶液pH值为3.0时,SLA的平衡吸附容量为518.0mg/g,球形木质素吸附剂对L-天门冬氨酸的吸附速率同时受液膜扩散和颗粒内扩散过程控制.吸附符合Langmuir和Freundlich等温吸附方程.且焓△H-16.81kJ/mol,表明该吸附反应是以吸热的化学吸附过程为主,活化能Ea=3.3406kJ/mol,说明球形木质素吸附剂的吸附过程是以颗粒内扩散为主.     

Synthesis of propyl aminopyridine modified magnetite nanoparticles for cadmium (II) adsorption in aqueous solutions

In this study, 2‐aminopyridine functionalized magnetite nanoparticles were chemically synthesized and used for removing Cd²⁺ ions from aqueous solutions. The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X‐rays (EDX), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). The SEM results showed the synthesized magnetite nanoparticles have particle size around 26 nm. The effects of several variables including solution pH and volume, adsorbent mass, ionic strength and contact time on the Cd²⁺ adsorption were studied in batch experiments and finally the optimum conditions for adsorption were obtained. The kinetic data were investigated by pseudo‐ first‐order, pseudo‐ second‐order, intraparticle diffusion and Elovich kinetic models and data were described reasonably by pseudo‐ second‐order model (R² = 0.9996) with q_e = 2.31 mg g^?1. Adsorption data were analyzed using Langmuir, Freundlich and Temkin isotherm models. The results indicated that the data were well fitted to the Freundlich isotherm model (R² = 0.9907). After study the possible interference effect of foreign ions on Cd²⁺ removal, the applicability of the proposed nanoparticles for adsorption from real samples confirmed the successfully removal of Cd²⁺ ions with removal efficiency higher than 92%. The obtained results showed that the synthesized nanoparticles as a reusable adsorbent can act as a good choice for Cd²⁺ removal with an easy procedure.     

Optimization of adsorption parameters for Fe (III) ions removal from aqueous solutions by transition metal oxide nanocomposite

Manganese oxide nanocomposite (Mn₂O₃/Mn₃O₄) was prepared by sol-gel technique and used as an adsorbent. Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FE-SEM) were used to characterize the adsorbent. The response surface methodology (RSM) was employed to evaluate the effects of solution pH, initial Fe (III) ions concentration, adsorbent weight, and contact time on the removal ratio of the Fe (III) ions. A total of 27 adsorption experimental runs were carried out employing the detailed conditions designed based on the Box-Behnken design (BBD). Results showed that the pH of the solution and initial Fe (III) ions concentration were the most significant parameters for Fe (III) ions removal. In process optimization, the maximal value of the removal ratio of Fe (III) was achieved as 95.80%. Moreover, the corresponding optimal parameters of adsorption process were as: contact time?=?62.5?min, initial Fe (III) concentration?=?50?mg/L, adsorbent weight?=?0.5?g, and pH?=?5. The experimental confirmation tests showed a strong correlation between the predicted and experimental responses (R²?=?0.9803). The fitness of equilibrium data to common isotherm equations such as Langmuir, Freundlich, and Temkin were also tested. The sorption isotherm of adsorbent was best described by the Langmuir model. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models. The adsorption kinetics of Fe (III) ions were well fitted with the pseudo-second-order kinetic model.     

Biosorption of nickel from aqueous solutions by Acacia leucocephala bark: Kinetics and equilibrium studies

The biosorption of nickel(II) ions from aqueous solution by Acacia leucocephala bark was studied in a batch adsorption system as a function of pH, initial metal ion concentration, adsorbent dosage, contact time and temperature. The maximum Ni(II) adsorption was obtained at pH 5. Further, the biosorbents were characterized by Fourier Transformer Infrared Spectroscopy (FTIR). The experimental data were analysed using three sorption kinetic models viz., the pseudo-first- and second-order equations and the intraparticle diffusion model. Results show that the pseudo-second-order equation provides the best correlation for the biosorption process. The equilibrium nature of Ni(II) adsorption at different temperatures of 30, 40 and 50 °C have been described by the Langmuir and Freundlich isotherm models. The equilibrium data fit well Langmuir isotherm. The monolayer adsorption capacity of A. leucocephala bark as obtained from Langmuir isotherm at 30 °C was found to be 294.1 mg/g. The Chi-square (χ²) and Sum of the square errors (SSE) tests were also carried out to find the best fit adsorption isotherm and kinetic model. Isotherms have been used to determine thermodynamic parameters of the process, viz., free energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were calculated indicating that this system was a spontaneous and endothermic process. Present investigation emphasized that A. leucocephala bark may be utilized as a low cost adsorbent for nickel removal.     

Efficient Removal of Cobalt(II) and Strontium(II) Metals from Water using Ethylene Diamine Tetra‐acetic Acid Functionalized Graphene Oxide

Graphene oxide (GO) with high specific surface area was prepared and functionalized with ethylene diamine tetra‐acetic acid (EDTA). The as‐prepared GO and the functionalized one (GO‐EDTA) were characterized using high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), and Raman spectroscopy. The as‐prepared and EDTA funcationalized GO were applied as adsorbent to remove strontium(II) and cobalt(II) from water. The results indicated that the prepared materials are efficient adsorbents for strontium(II) and cobalt(II) removal. The adsorption of Co^II and Sr^II under effects of contact time, temperature, and pH was investigated It is concluded that the maximum adsorption capacities of GO for Co^II and Sr^II were about 168 and 140 mg · g^–1, whereas of GO‐EDTA the values were about 197 and 158 mg · g^–1, respectively. It is indicated that pH 6 and temperature 40 °C are the best condition for Co^II and Sr^II removal from water. The application of Langmuir and Freundlich isotherms indicated that Langmuir isotherm is best fit for Co^II and Sr^II equilibrium adsorption. Adsorption kinetics were studied by applying pseudo first‐order, pseudo second‐order, and intraparticle diffusion models on the experimental data. The results proved that pseudo second‐order model is the best represented adsorption kinetics. Appling the intraparticle diffusion regressions on the experimental data indicated that intraparticle diffusion involved in adsorption process, which was not the only rate‐controlling step.     

An easily organic–inorganic hybrid optical sensor based on dithizone impregnation on mesoporous SBA‐15 for simultaneous detection and removal of Pb(II) ions from water samples: Response‐surface methodology

In this study, a novel organic–inorganic hybrid adsorbent for single‐step detection and removal of Pb(II) ions based on dithizone (DZ) anchored on mesoporous SBA‐15 was fabricated. The designed solid optical sensor revealed rapid colorimetric responses and high selectivity. Central composite design (CCD) combined with desirability function (DF) was applied to evaluate the interactive effects and optimization of important variables such as pH value, mesoporous SBA‐15 dosage, contact time and initial concentration of Pb(II) ions and optimum conditions for each of the factors were obtained 6.0, 25 mg, 30 min and 20 μg ml^{− 1}, respectively. This adsorbent or solid optical chemo sensor exhibited a linear range of 1.0 to 100.0 μg ml⁻¹ of Pb(II) ion concentration with a detection limit of 0.07 μg ml⁻¹. This adsorbent was applied to determine and remove the Pb(II) in spiked samples. Various isotherm models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich were studied for fitting the experimental equilibrium data. Langmuir model was chosen as an efficient model. Various kinetic models such as pseudo‐first, second order intraparticle, diffusion models were studied for analysis of experimental adsorption data and the pseudo second order model was chosen as an efficient model.