Kinetic and isothermal studies of lead ion adsorption onto bentonite

The use of bentonite for the removal of Pb(II) from aqueous solutions for different contact times, pH of suspension, and initial concentration of Pb and particle sizes of absorbent was investigated. Batch adsorption kinetic experiments revealed that the adsorption of Pb(II) onto bentonite involved fast and slow processes. The adsorption mechanisms in the lead/bentonite system followed pseudo-second-order kinetics with a significant contribution of film diffusion. The adsorption isotherms were described by means of the Langmuir and Freundlich isotherms and the Langmuir model represented the adsorption process better than the Freundlich model. The maximum adsorption capacity of Pb(II) onto natural bentonite was 78.82 mg g^− 1.     

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.     

ADSORPTION OF TOLUENE ON BENTONITES MODIFIED BY DODECYLTRIMETHYLAMMONIUM BROMIDE

The adsorption of toluene was studied by using various types of adsorbents (Na⁺- and Al³⁺-bentonite) modified by dodecyltrimethylammonium bromide (DTAB). The characterization of these new sorbing matrices by XRD and IR indicates that DTAB tallow interacted with bentonite and increased the interlayer spacing of the clay with double-layered formation. Adsorption of toluene on modified bentonites was characterized by linear isotherms with no limitation of adsorption within the concentration range studied, thus indicating a mechanism of adsorption due to partition. Adsorption was fast and favored by a slightly acid medium. Pseudo-first-order, pseudo-second-order, the Elovich equation, and intra-particle diffusion models were used to fit the experimental data. The adsorption kinetic of toluene was described by the pseudo-first order onto DTAB-Na-bent, and pseudo-second order onto DTAB-Al-bent. The intra-particle diffusion process was identified as the main mechanism controlling the rate of toluene adsorption. Thermodynamic parameters such as standard free energy change (ΔG ⁰), the standard enthalpy change (ΔH ⁰), and the standard entropy (ΔS ⁰) were also evaluated. The variation of adsorption energy versus the types of adsorbent suggested a physical adsorption mechanism.     

Investigations on the kinetics and mechanisms of sorptive removal of fluoride from water using alumina cement granules

This paper examines the kinetics of fluoride removal from water by the adsorbent alumina cement granules (ALC), exploring the mechanisms involved. ALC exhibited a biphasic kinetic profile of sorption with an initial rapid uptake phase followed by a slow and gradual phase. The kinetic profile has been modeled using pseudo-first-order model, pseudo-second-order model, intraparticle diffusion model and Elovich model. The kinetic sorption profiles offered excellent fit with pseudo-second-order model with a high R² value of 0.9987. The value of activation energy of the system (17.67 kJ mol⁻¹) indicates the significance of diffusion in the sorption process. The rate-limiting step of sorption was evaluated by analyzing the response of the system to pH, inert electrolyte concentration, and desorption pattern of the adsorbent, instead of assigning it to a single kinetic model. Accordingly, the surface reactions involving the heterogeneity of the surface site bonding energy or other reactions occurring on the surface of ALC were found predominant in defining the rate-limiting step. The dominant mechanism of fluoride removal appeared to be a chemisorptive ligand exchange reaction involving the formation of inner-sphere complexation of fluoride with ALC.     

Equilibria,Kinetics, and Mechanisms for the Adsorption of Four Classes of Phenolic Compounds onto Synthetic Resins

The adsorption of five phenolic compounds of four different classes from aqueous batch solutions onto four styrene-divinylbenzene and acrylic resins (EXA 90, EXA 118, XAD 7, and XAD 16) was investigated regarding their equilibria, kinetics and surface-energy heterogeneity, and mechanisms of adsorption. The experimental equilibrium data were very well fitted to Langmuir and Freundlich models (R ² > 0.900). Three kinetic models (pseudo-first-order, pseudo-second-order, and an intra-particle diffusion model) were suitable for describing the experimental data, the pseudo-second-order kinetic model being the best one (p < 0.001). The adsorption energy values were low (<19.00 kJ/mol), suggesting a physical adsorption process. Driving forces involved in the adsorption of the phenolic compounds onto the resins were hydrogen bonding, π ? π stacking and hydrophobic interactions.     

Equilibrium and Kinetic Studies on Lithium Adsorption from Geothermal Water by λ-MnO2

The adsorption equilibria of lithium from geothermal water were investigated by using both powdery and granulated forms of λ-MnO₂ derived from spinel-type lithium manganese dioxide. Optimum amounts of adsorbents were 1.0 g adsorbent/L-geothermal water for powdery λ-MnO₂ and 6.0 g adsorbent/L-geothermal water for granulated λ-MnO₂. The adsorbents exhibited the promising adsorption capacities and their adsorption equilibria of lithium agreed well with the Langmuir adsorption isotherm model. The kinetic data of lithium adsorption have been evaluated using pseudo-first-order, pseudo-second-order kinetics models, as well as Elovich kinetic model. In addition, intra-particle diffusion model has been used for evaluating the kinetic data to evaluate the adsorption mechanism. The adsorption kinetic process was attributed to the gradual adsorption stage where intra-particle diffusion was found as the rate-controlling step.     

Adsorption behavior of methylene blue onto titanate nanotubes

Calcined titanate nanotubes were synthesized with hydrothermal treatment of the commercial TiO₂ (Degussa P25) followed by calcination. The morphology and structures of as-prepared samples were investigated by transmission electron microscopy, X-ray diffraction and N₂ adsorption/desorption. The samples exhibited a tubular structure and a high surface area of 157.9 m²/g. The adsorption of methylene blue onto calcined titanate nanotubes was studied. The adsorption kinetics was evaluated by the pseudo-first-order, pseudo-second-order and Weber's intraparticle diffusion model. The pseudo-second-order model was the best to describe the adsorption kinetics, and intraparticle diffusion was not the rate-limiting step. The equilibrium adsorption data were analyzed with three isotherm models (Langmuir model, Freundlich model and Temkin model). The best agreement was achieved by the Langmuir isotherm with correlation coefficient of 0.993, corresponding to maximum adsorption capacity of 133.33 mg/g. The adsorption mechanism was primarily attributed to chemical sorption involving the formation of methylene blue-calcined titanate nanotubes nanocomposite, associated with electrostatic attraction in the initial bulk diffusion.     

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.     

Polyamine Functionalized Magnetite Nanoparticles as Novel Adsorbents for Cu(II) Removal from Aqueous Solutions

Three novel magnetic adsorbents were synthesized through the immobilization of di-, tri-, and tetraamine onto the surface of silica coated magnetite nanoparticles. The adsorbents were characterized by XRD patterns, FTIR spectroscopy, elemental and thermogravimetric analysis, magnetic measurements, SEM/TEM, EDX spectroscopy, and N₂ adsorption/desorption isotherms. Their capacity to remove copper ions from aqueous solutions was investigated and discussed comparatively. The equilibrium data were analyzed using Langmuir and Freundlich isotherms. The kinetics was evaluated using the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The best interpretation for the equilibrium data was given by the Langmuir isotherm for the tri- and tetraamine functionalized adsorbents, while for the diamine functionalized adsorbent the Freundlich model seemed to be better. The kinetic data were well fitted to the pseudo-second-order model. The overall rate of adsorption was significantly influenced by external mass transfer and intraparticle diffusion. It was observed that the adsorption capacity at room temperature decreased as the length of polyamine chain immobilized on the adsorbent surface increased, the maximum adsorption capacities being 52.3 mg g^?1 for 1,3-diaminopropan functionalized adsorbent, 44.2 mg g^?1 for diethylenetriamine functionalized adsorbent, and 39.2 mg g^?1 for triethylenetetramine functionalized adsorbent. The sorption process proved to be highly dependent of pH. The results of the present work recommend these materials as potential candidates for copper removal from aqueous solutions.     

Equilibrium,kinetic and thermodynamic study of removal of reactive orange 12 on platinum nanoparticle loaded on activated carbon as novel adsorbent

The proposed research describes the synthesis and characterization of platinum nanoparticles loaded on activated carbon (Pt-NP-AC) and its efficient application as novel adsorbent for efficient removal of reactive orange 12 (RO-12). The influences of effective parameters following the optimization of variables on removal percentages, their value was set as 0.015 g Pt-NP-AC, pH 1, contact time of 13 min. At optimum values of all variables at 25 and 50 mgL⁻¹ of RO-12 enthalpy (ΔH⁰) and entropy (ΔS⁰) changes was found to be 59.89 and 225.076, respectively, which negative value of ΔG⁰ shows a spontaneous nature, and the positive values of ΔH⁰ and ΔS⁰ indicate the endothermic nature and adsorption organized of dye molecule on the adsorbent surface. Experimental data was fitted to different kinetic models including first-order, pseudo-second-order, Elovich and intra-particle diffusion models, and it was seen that the adsorption process follows pseudo-second-order model in consideration to intra-particle diffusion mechanism. At optimum values of all variables, the adsorption process follows the second-order kinetic and Langmuir isotherm model with adsorption capacity 285.143 mg g⁻¹ at room temperature.     

THERMODYNAMIC AND KINETIC STUDY OF ADSORPTION OF Ni(II) IONS ON CARBON ANODE DUST

In this study the use of carbon anode dust (CAD), which is the solid residue from aluminum production, as a low-cost adsorbent for the removal of Ni(II) ions from wastewater was investigated. A mechanism of adsorption kinetics and thermodynamics was proposed. In order to investigate the adsorption process of nickel ions on CAD three kinetic models were used: Lagergren's pseudo-first-order model, pseudo-second-order model, and the intra-particle diffusion model. Various thermodynamic parameters, such as the energy of activation (E_a), activation enthalpy (ΔH*), activation entropy (ΔS*), and free energy of activation (ΔG*), were evaluated. Observation of the value of the energy of activation suggests that the process uptake of Ni(II) ions can be described as activated chemisorption. The positive values of enthalpy of activation and free energy of activation, as well as negative values of entropy of activation, mean that the process of removal of Ni(II) ions is endothermic, non-spontaneous, and without structural changes in the solid carbon anode dust particles.     

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.     

海藻酸纤维对臧红T的吸附动力学研究

以自制海藻酸纤维为吸附剂,研究它对臧红T的吸附性能。用准一级动力学方程、指数函数方程、准二级动力学方程、粒子扩散方程、Elovich方程和双常数方程对不同染料浓度、吸附时间的曲线进行拟合。结果表明,后四种方程的拟合度较好,这说明此吸附是复杂的非均相扩散吸附过程,存在化学吸附,且膜扩散和颗粒内扩散共同控制吸附速率。     

Influence of pH on the aluminum speciation in freeze-dried poly(hydroxo aluminum) intercalated bentonites

Two freeze-dried poly(hydroxo aluminum) intercalated Wyoming bentonites were prepared starting from two different aluminum pillaring solutions. Their charge versus pH properties were studied by zeta potential measurements, potentiometric titrations and calcium sorption measurements in order to determine the speciation of the intercalated Al-species as a function of pH. The structural changes of the intercalated bentonite induced by the pH increase were studied by XRD analysis and N₂ adsorption/desorption measurements. At pH 5 the permanent charge (0.75 meq/g) of the original Wyoming bentonite is completely neutralized by positively charged Al-hydroxo species. With increasing pH the Al-species deprotonate and aggregate until their complete neutralization at pH 9.4. Above this pH the Al-polymers start to dissolve from the clay as Al(OH)₄⁻.     

Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons

Physical properties of activated carbons prepared from pinewood at different activation times (0.5, 1.5, 2.7, and 4.0 h) in steam at 900 °C were studied. The adsorption equilibria and kinetics of three dyes and three phenols (phenol, 3-chlorophenol, and o-cresol) from aqueous solutions on such carbons were then examined at 30 °C. The adsorption isotherms of phenols could be well fitted by the Freundlich equation, and those of dyes were adequately described by the Langmuir-Freundlich equation. The effect of microporosity of the carbons on adsorption capacity was explored. Four simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, intraparticle diffusion model, and the Elovich equation were selected to follow the adsorption processes. The adsorption of all six adsorbates could be best described by the Elovich equation. The kinetic parameters of this best-fit model were calculated and discussed.     

高温焙烧改性混凝污泥对氨氮的吸附特性

采用高温焙烧改性混凝污泥,通过SEM、XRD对改性前后的污泥进行了表征。本研究探讨改性污泥对水溶液中氨氮的吸附动力学、吸附热力学和吸附特性。结果表明:改性污泥对氨氮吸附符合Freundlich 吸附等温式;分别采用拟一级反应、拟二级反应和颗粒内扩散反应模型对吸附动力学过程进行了拟合,实验数据遵循拟二级动力学反应模型;并计算吸附热力学参数,在30、40和50℃下,对应的Gibbs自由能(ΔG⁰)分別为-1.915、-1.744和-1.719 kJ ·mol^-1,显示该反应属自发性进行;焓变(ΔH⁰)<0,证实该反应为放热反应;熵变(ΔS⁰)<0,说明该吸附反应是熵值减小的过程;黏附概率S^*=0.0812介于0～1范围内,表明该吸附过程主要为物理吸附。     

Preparation and characterization of aluminum pillared K10 and KSF for adsorption of trimethoprim

Montmorillonite KSF and K10 were used as precursor materials for synthesis of aluminum pillared K10 and KSF (Al-K10 and Al-KSF) which characterized by TGA, XRD, SEM and FT-IR spectroscopic analysis. The sorption of trimethoprim (TMP) which is commonly employed as an antibiotic onto Al-K10 and Al-KSF was also investigated as a function of adsorbent dosage, solution pH, contact time and temperature. The adsorption kinetics was interpreted using pseudo-first-order, pseudo-second-order kinetic models and intraparticle diffusion model. The pseudo-second-order model provided the best correlation. Adsorption isotherm parameters were obtained from Freundlich, Langmuir and Dubinin–Radushkevich (DR) isotherm models. Adsorption of TMP onto Al-K10 and Al-KSF was physical in nature and ion-exchange mechanism for DR equation, respectively. Al-K10 exhibits higher removal capacity at lower adsorbent dosages in comparison with Al-KSF. The removal capacity was increased by increasing pH. ΔH⁰, ΔS⁰ and ΔG⁰ showed that adsorption of trimethoprim was endothermic, increasing randomness and not spontaneous in nature.     

Mercury and lead sorption properties of poly(ethyleneimine) coated onto silica gel

In this article, we studied the sorption properties of poly(ethyleneimine) coated on silica gel for metal ions with impact on the environment, such as Zn(II), Cd(II), Hg(II), and Pb(II). The experiments were carried out by batch procedure and the effects of pH, concentration, and temperature were evaluated. In addition, the selectivity was studied for binary, ternary, and quaternary metal ion mixtures. Mercury and lead showed promising results, achieving higher than 65% of sorption after only 1 h of contact. Under competitive conditions, resin presented high selectivity toward Hg(II) reaching 91 and 87% of retention respect to total amount of ions for binary and quaternary mixtures, respectively. The effect of time on Pb(II) and Hg(II) sorption was studied by batch procedure and the experimental data were adjusted to pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. Pseudo-second-order model presented good agreement for Pb(II) sorption, while pseudo-first-order model fits better to Hg(II) sorption. Intra-particle diffusion model showed that sorption process is controlled mainly by film diffusion.     

Study on adsorption of Cu(II)–Cr(VI) binary system by carbonized Eupatorium adenophorum

We first report a mechanism study on the adsorption of Cu(II)-Cr(VI) binary mixture by a novel low-cost adsorbent, carbonized Eupatorium adenophorum. The influences by pH value, dosage, initial concentration, temperature, and adsorption time on its performance to absorb copper and chromium were investigated. The experimental data were fitted according to the Langmuir and Freundlich adsorption isotherm models, the pseudo-first-order kinetics, the pseudo-second-order kinetics, and the intra-particle diffusion model. The results indicated that when the reaction system was with its pH = 5, the dosage of carbonized Eupatorium adenophorum was 0.1 g, the adsorption time was 30 min, and the temperature was 25°C; the adsorption capacities for Cu(II) and Cr(VI) reached 27.62 mg/g and 9.68 mg/g, respectively. The process of carbonized Eupatorium adenophorum to absorb Cr(VI) is also accompanied by redox reactions. The Langmuir model and the pseudo-second-order model can better ?t the experimental data. Observation by fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) found no significant change of functional groups before and after the adsorption by carbonized Eupatorium adenophorum, and this adsorption process is mainly a physical adsorption.