Adsorption Isotherm Models Research Papers (original) (raw)

The adsorption of phenol, and halogenated phenols on granular activated carbon (AC) modified with metal oxide catalyst, followed by catalytic oxidative regeneration, was studied as an efficient technology for the treatment of dilute wastewaters. The advantages of the combination of these technologies are as follows: (1) the process will be accelerated by the high concentrations of pollutants eluted from the adsorbent; (2) a large number of adsorption-regeneration cycles are expected without loss in capacity; and (3) the low-temperature regeneration will be conducted in situ, even in small units, thus improving the economy of the process. Oxidative catalytic regeneration of spent carbons, performed at 240-300°C with air, completely restored the adsorption capacity of phenol on the ACs modified with catalyst, even after 10 cycles of regeneration. Under similar conditions, only partial recovery of the adsorption capacity was obtained for carbons loaded with p-chlorophenol and p-bromophenol. The adsorption capacity and the surface area of the AC (Filtrasorb-400) diminished somewhat with the impregnation of oxides (Fe 2 O 3 , CuO, and additivities of Cr 2 O 3 or inert silica), but that did not affect the shape of the adsorption isotherms.

- by
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- Engineering, Environmental Science, Energy Conservation, Water Treatment

An attempt to alleviate the problem caused by the presence of reactive dyes in textile effluents was undertaken. Since alunite is a very abundant and inexpensive, we decided to experiment with it as a potential adsorbent for a certain type of the supracited pollutants used in cellulose fibers dyeing. The adsorption of Reactive Blue 114 (RB114), Reactive Yellow 64 (RY64) and Reactive Red 124 (RR124) by calcined alunite was studied by varying parameters such as the calcination temperature and time, particle size, pH, agitation time and dye concentration. Acidic pH was favorable for the adsorption of RB114 and alkaline pH was favorable to both RY64 and RR124. The equilibrium data fit the Langmuir isotherm. The adsorption capacities were found to be 170.7, 236 and 153 mg dye per gram of calcined alunite for RB114, RY64 and RR124, respectively. The pseudo first-and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The experimental data were fitted by the second-order kinetic model, which indicates that chemicalsorption is the rate limiting step, inside of mass transfer.

- by Nour Moukhtar
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- Engineering, Mass Transfer, Kinetics, Water Purification

The removal of fluoride from aqueous solution by using the original and activated red mud forms was studied in batch equilibration technique. Influence of pH, adsorbent dose and contact time on the adsorption were investigated. The fluoride adsorption capacity of activated form was found to be higher than that of the original form. The maximum removal of fluoride ion was obtained at pH 5.5. The removal of fluoride was expressed with Langmuir and Freundlich isotherms. Langmuir adsorption isotherm curve was found to be significant. It was found that the sufficient time for adsorption equilibrium of fluoride ions is 2 h. The possibility of removal of fluoride ion by using red mud is explained on the basis of the chemical nature and specific interaction with metal oxide surfaces and the results are interpreted in terms of pH variations.

- by Mustafa Ersoz
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- Chemical Engineering, Analytical Chemistry, Red Mud, Adsorption Isotherm Models

The investigation of adsorption of nitrate onto chitosan beads modified by cross-linking with epichlorohydrin (ECH) and surface conditioning with sodium bisulfate was performed. The results indicated that both cross-linking and conditioning increased adsorption capacity compared to normal chitosan beads. The maximum adsorption capacity was found at a cross-linking ratio of 0.4 and conditioning concentration of 0.1 mM NaHSO 4 . The maximum adsorption capacity was 104.0 mg g −1 for the conditioned cross-linked chitosan beads at pH 5, while it was 90.7 mg g −1 for normal chitosan beads. The Langmuir isotherm model fit the equilibrium data better than the Freundlich model. The mean adsorption energies obtained from the Dubinin-Radushkevich isotherm model for all adsorption systems were in the range of 9.55-9.71 kJ mol −1 , indicating that physical electrostatic force was potentially involved in the adsorption process.

- by Sudipta Chatterjee
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- Engineering, Thermodynamics, Modeling, Water Purification
- by M. Hubinger
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- Chemical Engineering, Food Science, Food Science and Technology, Food Sciences

Talc samples in both sheet and powder form are studied by adsorption calorimetry and adsorption isotherm techniques. A model is used to determine the solid surface energy, the solid surface tension and the dispersive, acidic, and basic components of these terms. These results are introduced in an approximate equation relating adsorption to contact angle data. Experimental contact angles are in correct agreement with this approach. The Neumann equation of state is used to fit the data and discussed. It appears as a numerical form of the general equation taking into account gas adsorption and film pressure. Behaviors of talc in contact with liquids do not appear very different whether the solid is in sheet or powder form. C 2002 Elsevier Science (USA)

- by Harold Malandrini
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- Engineering, Modeling, Immersion, Enthalpy

N2 adsorption isotherms of various pillared montmorillonites (PILCs) were analyzed for evaluation of their porosities. The quantitative data of the total and micropore volumes were calculated using the B.J.H. method and the t-plot, respectively. The volume of mesopores is the difference between the total volume and the micropore volume. The linear branch above the P/Po of 0.5 should be used for the calculations of the micropore volume and external surface area.

- by Huaiyong Zhu
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- Materials Engineering, Porous Materials, Specific surface area, Surface Area

The water-binding properties of wheat starch films were studied through the determination of water vapour adsorption isotherms at 20°C. Starch films were obtained by casting after mixing native starch at 95°C for 15min with different ratios of plasticizer (glycerol).Unplasticized starch film was found to adsorb less water than native starch granules. The effect of glycerol on water vapour adsorption by

- by Patrice Dole and +1
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- Food Chemistry, Multidisciplinary, Relative Humidity, Phase Separation

Adsorption of crystal violet dye from aqueous solutions applying olive leaves powder (OLP) as a biosorbent has been examined under various experimental circumstances. The influence of contact time, pH, initial concentration of studied dye and adsorbent dose on the adsorption process has been investigated applying batch experiments. The concentration of remaining dye has been determined using molecular absorption spectrometry at wave length of 580 nm. The maximum removal of studied dye has been realized at pH 7.5 with a percent removal of 99.2% after 20 min of agitation time. Langmuir, Freundlich,and Temkin isotherm models exemplify the best fit for the experimental data; while the elevated adsorption capacity was 181.1 mg.g1. Adsorption kinetics of crystal violet was expected sufficiently with the empirical pseudo-second-order model. Corresponding to the adsorption capacity, olive leaves powder thought as a low cost, effective, and environmentally friendly biosorbent for the removal of crystal violet dye from aqueous solutions.

In this work the adsorption features of activated carbon and the magnetic properties of iron oxides were combined in a composite to produce magnetic adsorbents. These magnetic particles can be used as adsorbent for a wide range of contaminants in water and can subsequently be removed from the medium by a simple magnetic procedure. Activated carbon / iron oxide magnetic composites were prepared with weight ratios of 2:1, 1.5:1 and 1:1 and characterized by powder XRD, TG, magnetization measurements, chemical analyses, TPR, N adsorption-desorption isotherms, Mossbauer 2 spectroscopy and SEM. The results suggest that the main magnetic phase present is maghemite (g-Fe O ) with small 2 3 amounts of magnetite (Fe O ). Magnetization enhancement can be produced by treatment with H at 600 8C to reduce 3 4 2 maghemite to magnetite. N adsorption measurements showed that the presence of iron oxides did not significantly affect the 2 surface area or the pore structure of the activated carbon. The adsorption isotherms of volatile organic compounds such as chloroform, phenol, chlorobenzene and drimaren red dye from aqueous solution onto the composites also showed that the presence of iron oxide did not affect the adsorption capacity of the activated carbon. 

- by Luiz Oliveira
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- Engineering, Carbon, Activated Carbon, Physical sciences

In this work the evolution of the surface concentration, surface potential, and surface tension for adsorption of a charged amphiphile at an interface is studied numerically. While the results are of interest for any amphiphile, the simulations are performed for typical surfactant material parameters. The surface potential is related at each time step to the instantaneous surface charge density determined by the surfactant surface concentration using the Gouy-Chapman model. The sublayer concentration at each time step is a Boltzmann distribution in instantaneous equilibrium with the surface potential. At equilibrium, the surfactant is assumed to obey the Davies adsorption isotherm.

- by Sammy Datwani
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- Engineering, Mass Transfer, Kinetics, Electrostatics

Rubber wood (Hevea brasiliensis) esteri®ed with acetic anhydride, maleic anhydride and phthalic anhydride was studied for moisture adsorption behaviour. FTIR spectroscopic technique was used to analyse the chemical changes in the wood through the correspondent reactions. Spectra indicated increasing intensity of the C@O and C-O stretching bands, and reduction in O-H stretching vibrations that re¯ects formation of less hygroscopic ester bonds with hydroxyl groups of cell wall polymers. Moisture adsorption isotherms show low equilibrium moisture content in esteri®ed wood at all relative humidity values as compared to a control. The adsorption data was analysed by applying Hailwood-Horrobin theory which separated the adsorbed water into hydrated water and dissolved water corresponding to mono-layer and multi-layer adsorption. Curve for M h and M s were similar in pattern for esteri®ed wood and control with different magnitude. Low M h and M s in esteri®ed wood indicate reduction in moisture adsorption sites. Inaccessible fraction of wood for water vapour was increased by 43%, 32% and 26% in acetic, maleic and phthalic anhydride treated wood, respectively, compared to the control. Acetic anhydride treatment was found most effective in reducing hygroscopicity of wood.

- by Shakti Chauhan
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- Building, Hevea brasiliensis, Maleic Anhydride, Relative Humidity

Adsorption of phenolic compounds from aqueous solution to a macroporous polymeric adsorbent (CHA-111), its animated derivative (MCH-111) and a reference weakly anion exchanger (ND-900) was studied. Experimental results indicated that amino functional groups on the polymeric matrix play an important role in phenol adsorption by MCH-111 and ND-900, which was attributed to the formation of hydrogen bonding between the phenol molecule and the amino group on the polymeric matrix. The semi-empirical Freundlich isotherm equation and its reduced form were employed to interpret the adsorption behavior. A site energy distribution model based on the Polanyi adsorption potential theory can elucidate the adsorption mechanism reasonably.

- by Jessie Chen
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- Engineering, Earth Sciences, Thermodynamics, Kinetics

Expression in transgenic plants is potentially one of the most economical systems for large-scale production of valuable peptide and protein products. However, the downstream processing of recombinant proteins produced in plants has not been extensively studied. In this work, we studied the extraction and purification of recombinant aprotinin, a protease inhibitor used as a therapeutic compound, produced in transgenic corn seed. Conditions for extraction from transgenic corn meal that maximize aprotinin concentration and its fraction of the total soluble protein in the extract were found: pH 3.0 and 200 mM NaCl. Aprotinin, together with a native corn trypsin inhibitor (CTI), was captured using a tryspin-agarose column. These two inhibitors were separated using an agarose-IDA-Cu 2+ column that proved to efficiently absorb the CTI while the recombinant aprotinin was collected in the flowthrough with purity of at least 79%. The high purity of the recombinant aprotinin was verified by SDS-PAGE and N-terminal sequencing. The overall recombinant aprotinin recovery yield and purification factor were 49% and 280, respectively. Because CTI was also purified, the recovery and purification process studied has the advantage of possible CTI co-production. Finally, the work presented here introduces additional information on the recovery and purification of recombinant proteins produced in plants and corroborates with past research on the potential use of plants as biorreactors.

- by Zivko Nikolov
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- Production, Biotechnology, Multidisciplinary, Downstream Processing

This paper describes the adsorption behaviour of three solvents (ethyl acetate, ethanol and acetone) on BASF activated carbon at various temperatures (15-808C). The adsorption isotherms show hysteresis which persists to very low pressures 22 (Low Pressure Hysteresis, LPH). After prolonged outgassing (,10 mbar) at 473-523 K we found that LPH still remains. This LPH is more pronounced for ethyl acetate at higher temperatures. Due to its importance on Pressure Swing Adsorption (PSA) units design and operation we discuss the adsorption behaviour when adsorption / desorption cycles are applied. We concluded that after approximately five cycles the system reaches what we called 'limiting isotherm' where adsorption and desorption branches cannot be distinguished within experimental error. This isotherm is independent of system history if a sufficiently low pressure and / or a sufficiently high pressure is used for cycling and in these conditions the adsorbent has higher capacity than when fresh. Also the Langmuir equation correlates quite well with the limiting isotherms.

- by Carlos Costa
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- Engineering, High Pressure, Carbon, Activated Carbon

The adsorption isotherms between aqueous solutions of sodium dodecylsulphate and gelatin against air, toluene, or diethylphthalate were determined using the spinning drop method. The results qualitatively and quantitatively agreed with those found by surface tension measurements on sodium dodecylsulphate/gelatin solutions using the ring method in the version of Du Noüy. Interaction between gelatin and the surfactant will yield complexes which are more interfacially active than the components by themselves. The saturation of the interfaces occurs at lower concentrations than in solutions of the single components.

The biosorption of nickel(II) and copper(II) ions from aqueous solution by dried Streptomyces coelicolor A3(2) was studied as a function of concentration, pH and temperature. The optimum pH range for nickel and copper uptake was 8.0 and 5.0, respectively. At the optimal conditions, metal ion uptake was increased as the initial metal ion concentration increased up to 250 mg l −1 . At 250 mg l −1 copper(II) ion uptake was 21.8% whereas nickel(II) ion uptake was found to be as high as 7.3% compared to those reported earlier in the literature. Metal ion uptake experiments were carried out at different temperatures where the best ion uptake was found to be at 25 • C. The characteristics of the adsorption process were investigated using Scatchard analysis at 25 • C. Scatchard analysis of the equilibrium binding data for metal ions on S. coelicolor A3(2) gave rise to a linear plot, indicating that the Langmuir model could be applied. However, for nickel(II) ion, divergence from the Scatchard plot was evident, consistent with the participation of secondary equilibrium effects in the adsorption process. Adsorption behaviour of nickel(II) and copper(II) ions on the S. coelicolor A3(2) can be expressed by both the Langmuir and Freundlich isotherms. The adsorption data with respect to both metals provide an excellent fit to the Freundlich isotherm. However, when the Langmuir isotherm model was applied to these data, a good fit was obtained for the copper adsorption only and not for nickel(II) ion.

- by ihsan khan
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- Chemical Engineering, Biomedical Engineering, Kinetics, Adsorption

The contact angle method has been used to characterize Three talc samples have been studied by adsorption and immerthe surface intensive properties of solids. Indeed, the contact sion methods after a classical characterization of their properties. angle between a drop of a liquid probe and the solid surface The combination of adsorption isotherms and of immersion meastudied is linked to solid/liquid, solid/vapor, and liquid/ surements allows the calculation of enthalpies and entropies of vapor interfacial tensions through Young's equation:

- by Harold Malandrini
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- Engineering, Physical sciences, CHEMICAL SCIENCES, Surface Tension

Equilibrium studies were carried out for the sorption of Cr(VI) onto Kraft lignin as an adsorbent. The experimental data were fitted to the Freundlich, Langmuir, Temkin, Dubinin-Radushkevich, Redlich-Peterson, Sips and Toth isotherms by non-linear method. We presented the comparison of two-and threeparameter isotherm. Only non-linear regression method was used in selecting the optimum isotherm for the experimental data. The coefficient of correlation was used to select the best theoretical isotherm. The best two-parameter isotherm is equally Langmuir and Dubinin-Radushkevich isotherm. From threeparameter isotherms Redlich-Peterson isotherm proved to be the best. Generally, Redlich-Peterson isotherm was found to be the best representative for Cr(VI) adsorption on the sorbent.

- by Tatjana Došenović
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- Chemical Engineering, Adsorption Isotherm Models

This paper presents results on sodium dodecyl sulfate (SDS) enrichment at the surface of pure acrylic or acrylic/laponite composite latex films. Surface concentrations were measured by Confocal Raman Spectroscopy leading to higher values than the nominal concentration of 6 wt%. X-ray Photoelectron Spectroscopy (XPS) analyses showed uppermost surface layers saturated with SDS in most cases. High resolution Atomic Force Microscopy (AFM) revealed a variety of morphologies for these surfactant top layers, highlighting the occurrence of SDS bilayers in different configurations. In an attempt to check for a correlation between the surface concentration of the surfactant in dry films and the concentration of free surfactant in water in the initial latex, this latter concentration was determined from the level of the plateau in adsorption isotherms. Adsorption studies by conductimetry showed an unexpected increase of the amount of adsorbed SDS with pH. The proposed interpretation is that, upon acrylic acid neutralization, the chains at the surface become more hydrophilic and spread out in water, revealing more sites for SDS to adsorb on. No correlation between free surfactant and surface enrichment could be established, indicating that the enrichment process is more complex than expected.

- by Yves Holl
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- Engineering, Raman Spectroscopy, Atomic Force Microscopy, Physical sciences

Physico-chemical investigation on adsorption of congo red, an anionic azo dye by chitosan hydrobeads has been carried out. Adsorption process has been found to be dependant on temperature with optimum activity at 30 °C. Both ionic interaction as well as physical forces is responsible for binding of congo red with chitosan. Theoretical correlation of the experimental equilibrium adsorption data for congo red–chitosan hydrobeads system would be best explained by linearized form of Langmuir isotherm model. The kinetic results follow pseudo second-order rate equation. pH of the experimental solution influenced congo red adsorption inversely, and ∼20.0% of the dye could be desorbed from the loaded beads by changing the pH of the solution to alkaline range (∼pH 12.0). Both sodium chloride and sodium dodecyl sulfate significantly influenced the adsorption process.

- by Sandipan Chatterjee
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- Engineering, Kinetics, Modeling, Nanoparticle

The work described here entails the synthesis and characterization of polyvinyl alcohol mercaptyl fibers, coated on a 31 fiberglass substrate, for the purpose of removing arsenite (As ) from water. Because thiols are chemically the most active functional groups found in cells and are capable of forming very stable complexes with metal ions, this functional group was selected as an excellent candidate for arsenite removal from water. The fibers were characterized through infrared spectroscopy, elemental analysis, analytical titration, scanning electron microscopy, and environmental scanning microscopy. The ability of these systems to chelate arsenite was measured using equilibrium adsorption isotherms at initial concentrations of 10 and 100 ppm. The ability to regenerate these systems is also described. The fibrous mercaptyl system's performance is compared to the commercial product, Duolite's GT-73, a macroreticular polystyrene-divinylbenzene resin with chelating thiol functional groups. 

Adsorption of water vapour on wool provides not only textile comfort, but also convenience in transportation due to increase in its bulk density. The adsorption and desorption isotherms of water vapour for wool were determined by both volumetric technique using a Coulter Omnisorp 100CX instrument and gravimetric method employing a Cahn 2000 electronic microbalance. Adsorption isotherm fitting to B.E.T. model and hysteresis on desorption was observed. The average effective diffusion coefficient of water in wool was found to be 8.4 × 10-14 m2s-1 at 25°C from gravimetric data. The effects of packing height and air velocity on the breakthrough curves were also investigated in the wool packed columns. For pseudo first order model, k values changing between 0.33 × 10-6 − 69 × 10-6 s-1 was obtained for 2.2–6.4 cm s-1 air velocity and 0.05–0.20 m packing height ranges.

- by Semra Ülkü
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- Materials Engineering, Chemical Engineering, Adsorption, First-Order Logic

The present study was conducted to evaluate the feasibility of nano-alumina for nitrate removal from aqueous solutions. The nature and morphology of sorbent was characterized by XRD, FTIR, BET and SEM analysis. Batch adsorption studies were performed as a function of contact time, initial nitrate concentration, temperature, pH and influence of other interfering anions. Nitrate sorption kinetics was well fitted by pseudo-second-order kinetic model. The maximum sorption capacity of nano-alumina for nitrate removal was found to be ca. 4.0 mg g −1 at 25 ± 2 • C. Maximum nitrate removal occurred at equilibrium pH ca. 4.4. The nitrate sorption has been well explained using Langmuir isotherm model. Results from this study demonstrated the potential utility of nano-alumina for nitrate removal from water.

- by Mika Sillanpää
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- Chemical Engineering, Environmental Science, Kinetics, Modeling

The adsorption behavior of horseradish peroxidase (HRP) onto hybrid particles of poly(methylmethacrylate) (PMMA) and carboxymethylcellulose (CMC) was investigated by means of spectrophotometry. Dispersions of PMMA/CMC particles were characterized by light scattering, zeta potential measurements and scanning electron microscopy before and after HRP adsorption. HRP adsorbed irreversibly onto PMMA/CMC particles; the adsorption isotherm showed an initial step and an adsorption plateau. The enzymatic activity of free HRP and immobilized HRP (plateau region) was monitored by means of spectrophotometry as a function of storing time. Upon adsorbing HRP there is little (up to 20%) or no reduction of enzymatic activity in comparison to that observed for free HRP in solution. After storing free HRP and HRP-covered PMMA/CMC particles for 18 days the level of enzymatic activity is kept. HRP-covered PMMA/CMC particles dispersions, which were dried and re-dispersed, retained 50% of their catalytic properties. These interesting findings were discussed in the light of a beneficial effect of a hydrated microenvironment for maintenance of enzyme conformation and activity.

- by Denise Petri
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- Light Scattering, Catalysis, Scanning Electron Microscopy, Polysaccharides

Modified Thevetia peruviana shell activated carbon for sorption of dimethoate from aqueous solution derived with potassium hydroxide (KOH) was studied at different concentrations for its potential application in water treatment. The batch sorption was investigated using dimethoate solution of 10–100mg/L concentrations. Proximate analysis was determined and changes on the surfaces and structure of the TPS were characterized after chemical activation with KOH using XRD, FTIR, SEM–EDAX, pHpzc, BET. The quantum chemical calculation for dimethoate yielded molecule associated energies of –9.8421 (HOMO) and –2.3879 (LUMO) and a total energy of –53,376.2. The kinetic of the sorption was modeled which indicated the sorption equilibrium time as 90min and pseudo-first order kinetics model showing R2=0.994 provided a better description of the process. Analysis of sorption equilibrium revealed that the data fitted well to Freundlich sorption isotherm model (R2=0.966), indicating multi-layer sorption of dimethoate on the surface of sorbent. The sorption of dimethoate onto KOHTPS shows 92.60% removal efficiency.

- by WILLIAMS E ND
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- Kinetics, Adsorption, Pesticides, Adsorption Isotherm Models

The corrosion inhibition of aluminium in HCl solution in the presence of exudate gum from Raphia hookeri at temperature range of 30-608C was studied using weight loss and thermometric techniques. The exudate gum acts as an inhibitor in the acid environment. The inhibition efficiency increases with increase in inhibitor concentration but decreases with an increase in temperature. The inhibitive effect of the Raphia hookeri exudate could be attributed to the presence of some phytochemical constituents in the exudate which is adsorbed on the surface of the aluminium metal. The exudate gum was found to obey Temkin adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady et al. at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous.

- by Saviour Umoren and +1
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- Engineering, Kinetics, Desalination, Weight Loss

The aim of the present study was to investigate the adsorption properties of surface modified chitosans in the aqueous solutions containing Co(II) and/or Ni(II) ions. For this purpose, the ligands of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) were immobilized onto polymer matrices of chitosan. Adsorption of Co(II) and Ni(II) by prepared adsorbents was investigated in batch techniques. The effects of pH, functional group, contact time, and the concentration of metals were studied. Metal uptake by EDTA-chitosan was 63.0 mg g −1 for Co(II) and 71.0 mg g −1 for Ni(II) and by DTPAchitosan 49.1 mg g −1 for Co(II) and 53.1 mg g −1 for Ni(II). The adsorption efficiency of studied adsorbents ranged from 93.6% to 99.5% from 100 mg L −1 Co(II) and/or Ni(II) solution, when the adsorbent dose was 2 g L −1 and solution pH 2.1. The kinetics of Co(II) and Ni(II) on both of the modified chitosans followed the pseudo-second-order model but the adsorption rate was also influenced by intraparticle diffusion. The equilibrium data was best described by the Sips isotherm and its extended form was also well fitted to the two-component data obtained for systems containing different ratios of Co(II) and Ni(II). Nevertheless, the obtained modeling results indicated relatively homogenous system for Co(II) and heterogeneous system for Ni(II) adsorption. (E. Repo). 1 Tel.: +358 15 355 3707; fax: +358 15 355 6363. 1385-8947/$ -see front matter

- by Mika Sillanpää
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- Chemical Engineering, Kinetics, Second Order, Heterogeneous Systems

This paper focuses on the effectiveness of removing ammonium ion and the theoretical aspects of adsorption including adsorption isotherm, kinetics and thermodynamics as well as desorption-regeneration studies. Results have demonstrated that natural zeolite shows good performance with up to 97% for ammonium removal depending on contact time, zeolite loading, initial ammonium concentration and pH. The adsorption kinetics is best approximated by the pseudo-second-order model, whereas the adsorption isotherm results indicated that Freundlich model provides the best fit for the equilibrium data. Furthermore, with regard to thermodynamic parameters, it was found that Gibbs free energy change or adsorption energy (ΔG°), − 19.52 kJ/mol at 25°C, − 20.45 kJ/mol at 35°C and −22.91 kJ/mol at 45°C is negative indicating the spontaneous nature of the adsorption process, whereas the enthalpy change (ΔH°), 30.96 kJ/mol is positive indicating endothermic adsorption process. The entropy change (ΔS°), 0.169 kJ/(mol K) at 25°C is also positive indicating increasing randomness at the solid-solution interface during adsorption. In addition, the desorption-regeneration studies demonstrated that desorption of ammonium on the zeolite is sufficiently high using NaCl solutions.

- by nurul widiastuti
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- Engineering, Thermodynamics, Kinetics, Adsorption

Here we report a separation of a cationic dye, acridine orange (AO), by use of magnetic nanoparticles (␥-Fe 2 O 3 ). The particles were showed to capture 98% of the dye within the first 20 min of contact time. The maximum sorption capacity of the magnetic nanoparticles (MNPs) for AO was 59 mg/g. The sorption isotherms fit well with the Freundlich model. The sorption kinetics fits well the pseudo-second-order rate equation model. 60-90% dye recovery was achieved by rotary evaporating the dye bearing nanoparticles in acetone. The nanoparticles were recycled for additional dye removal.

- by Shahnaz M Qadri
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- Engineering, Kinetics, Modeling, Nanoparticle

The surface reactivity of synthetic poorly crystalline apatites, similar to bone mineral, is reported in this study. Considerable changes of crystallinity and chemical composition of the solids occurred with time. The maturation process was expressed as a gradual evolution of the initial precipitate toward a highly crystalline apatitic phase, a relocation of nonapatitic phosphate groups accompanied by an increase of apatitic phosphate and the incorporation of hydroxyl ions in the lattice. The adsorption isotherms obtained for the samples investigated in KCl solutions are Langmuirian. The interaction of bovine serum albumin molecules with the solid was related to the structure, the short-range order, and the composition of the crystals. The evolution of the adsorption parameters with the content of labile phosphate groups indicates that these surface species play a leading role in the adsorption process and could consequently affect their biological functions.

Phosphate removal from an aquatic environment was investigated using La(III)-, Ce(III)-and Fe(III)-loaded orange waste. The adsorption isotherm, the kinetics of adsorption and the effect of pH on the removal of phosphate have been examined. The % removal of phosphate using La(III)-and Ce(III)-loaded orange waste gel increases with increasing pH within the range of 5-7 but decreases when the pH is increased beyond this range. The equilibrium sorption was observed to be in accordance with Langmuir type adsorption and the maximum adsorption capacity was evaluated as 13.94 mg P/g of dry gel for all the three types of gels. Kinetic studies revealed that 15 h is enough to reach equilibrium in batch experiments. Fixed bed sorption experiments confirmed the continuous phosphate adsorption and elution capability of such simply modified gels. Due to their low cost, availability and significantly high adsorption capability, metal-loaded SOW gels can be effectively employed for the removal of phosphate from water.

- by Biplob Biswas
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- Engineering, Kinetics, Adsorption, Physical sciences

Activated carbons were prepared from waste tyres by gasification with steam and carbon dioxide and their characteristics were investigated. A two-stage activation procedure (pyrolysis at 800 8C in N 2 atmosphere, followed by steam or carbon dioxide activation) was used for the production of activated samples. The effect of the activation temperature (750-900 8C) and the activation time (1-3 h) on the surface characteristics of the prepared carbon was investigated. Carbons produced to different degrees of burn-off were characterized by means of their nitrogen adsorption isotherms at 77 K. In both sets of experiments, the mesopore, micropore volume, and BET surface area increased almost linearly with the degree of activation. For burn-off values lower than 53%, the steam activation produced carbons with a narrower and more extensive microporosity and higher BET and external surface area than the carbon dioxide activation. As the activation proceeds (burn-off > 53%), a strong development of the mesoporosity in the carbons was observed and the micropores size distribution revealed broader micropores, that is, a more heterogeneous distribution. #

- by Juan Carlos Gonzalez
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- Carbon Dioxide, Multidisciplinary, Activated Carbon, Porosity

The effect of temperature and pH on the zeta potential of α-Al 2 O 3 and adsorption of fluoride ions at the α-Al 2 O 3 /aqueous solution interface has been investigated through electrophoretic mobility measurements and adsorption studies, to delineate mechanisms involved in the removal of fluoride ions from water using alumina as adsorbent. When the temperature increases from 10 to 40 • C, the pH of the point of zero charge (pH pzc ) shifts to smaller values, indicating proton desorption from the alumina surface. The pH pzc increases linearly with 1/T , which allowed estimation of the standard enthalpy change for the surface-deprotonation process. Fluoride ion adsorption follows a Langmuir-type adsorption isotherm and is affected by the electric charge at the α-Al 2 O 3 /aqueous solution interface and the surface density of hydroxyl groups. Such adsorption occurs through an exchange between fluoride ions and surface-hydroxyl groups and it depends on temperature, pH, and initial fluoride ion concentration. At 25 and 40 • C, maximum fluoride adsorption density takes place between pH 5 and 6. Increasing the temperature from 25 to 40 • C lowers the adsorption density of fluoride.

- by Alejandro López-Valdivieso
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- Engineering, Water Treatment, Adsorption, Electrokinetics

We have found optimised conditions for alkaline synthesis of the large pore molecular sieve, MCM-41, by determining small angle X-ray scattering and adsorption isotherms from materials at various stages of the preparation. The presence of highly curved surfaces, sealed structures, and quasicrystalline hexagonal products coexisting with true MCM-41 are all detected by transmission electron microscopy. Calcination must be carried out with care. The product is most crystalline from unstirred preparations which have been heated at 100°C for no longer than three days. Under these conditions, a maximum BET surface area of 1950 m 2 g-X was attained, with evident crystallinity observed by electron diffraction and transmission electron microscopy. In the stirred system, which appears to be in a nonequilibrium state, materials after calcination exhibiting Bragg d-spacings of 35 A, 37 ~, and 38 A have been identified.

Vetiver roots have been utilized for the preparation of activated carbon (AC) by chemical activation with different impregnation ratios of phosphoric acid, X P (g H 3 PO 4 /g precursor): 0.5:1; 1:1 and 1.5:1. Textural characterization, determined by nitrogen adsorption at 77 K shows that mixed microporous and mesoporous structures activated carbons (ACs) with high surface area (>1000 m 2 /g) and high pore volume (up to 1.19 cm 3 /g) can be obtained. The surface chemical properties of these ACs were investigated by X-ray photoelectron spectroscopy (XPS) and Boehm titration. Their textural and chemical characteristics were compared to those of an AC sample obtained by steam activation of vetiver roots. Classical molecules used for characterizing liquid phase adsorption, phenol and methylene blue (MB), were used. Adsorption kinetics of MB and phenol have been studied using commonly used kinetic models, i.e., the pseudo-first-order model, the pseudo-second-order model, the intraparticle diffusion model and as well the fractal, BWS (Brouers, Weron and Sotolongo) kinetic equation. The correlation coefficients (R 2 ) and the normalized standard deviation q (%) were determined showing globally, that the recently derived fractal kinetic equation could best describe the adsorption kinetics for the adsorbates tested here, indicating a complex adsorption mechanism. The experimental adsorption isotherms of these molecules on the activated carbon were as well analysed using four isotherms: the classical Freundlich, Langmuir, Redlich-Peterson equations, but as well the newly published deformed Weibull Brouers-Sotolongo isotherm. The results obtained from the application of the equations show that the best fits were achieved with the Brouers-Sotolongo equation and with the Redlich-Peterson equation. Influence of surface functional groups towards MB adsorption is as well studied using various ACs prepared from vetiver roots and sugar cane bagasse. Opposite effects governing MB and phenol adsorption mechanism on ACs are demonstrated. The various effects involved in adsorption mechanisms of each molecule are demonstrated. (S. Gaspard).

- by Sarra Gaspard
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- Engineering, Kinetics, Adsorption, Activated Carbon

The barium oxide impregnated iron(III) oxide (BaO/Fe2O3) adsorbent was synthesized by an ultrasonic-assisted method. The adsorbent was calcined at 200-500 °C and its adsorption capacity was measured. The ultrasonic-assisted synthesis generated well-dispersed of BaO on Fe2O3 by giving none of the BaO peaks were observed through the XRD pattern. The most efficient adsorbent of BaO/Fe2O3200 was calcined at 200 °C with adsorption capacity for physisorption and chemisorption of 5.01 and 88.81 mg/g respectively. Besides other carbonate species, it was believed the presence of the hydroxyl group could enhance the sorption by forming bicarbonate upon CO2 chemisorption. It is also possessed a lower desorption range compared to BaO and Fe2O3 alone. The experimental CO2 adsorption isotherm at 25 °C fit better with the Freundlich isotherm model. It implies a favorable adsorption process with multilayer adsorption occurs onto the heterogeneous surface.

- by Azizul Hakim Lahuri
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- Adsorption, CO2 capture and storage, CO2 Capturing Processes, Iron Oxide

BACKGROUND: The performance and mechanism of the biosorptive removal of Ni 2+ and Zn 2+ from aqueous solution using grapefruit peel (GFP) as a new biosorbent was investigated by using different experimental approaches, such as potentiometric titration, Fourier transform infrared (FTIR) and energy-dispersive X-ray spectroscopy (EDX) analysis, chemical blocking of functional groups and concomitant release of cations (Ca 2+ , Mg 2+ , Na + , K + ) from GFP with metal (Ni 2+ , Zn 2+ ) uptake. RESULTS: GFP removed Ni 2+ and Zn 2+ rapidly, with 84.73% and 92.46% of the equilibrium sorption being reached in 30 min for Ni 2+ and Zn 2+ , respectively. The equilibrium process was described well by the Langmuir isotherm model, with maximum sorption capacity of 1.33 and 1.51 meq g −1 for Ni 2+ and Zn 2+ , respectively. Release of cations (Ca 2+ , Mg 2+ , Na + , K + ) and protons H + from GFP during uptake of Ni 2+ and Zn 2+ and EDX analysis of GFP before and after metal sorption revealed that the main mechanism of sorption was ion exchange. FTIR spectroscopy showed that carboxyl and hydroxyl groups were involved in the sorption of Ni 2+ and Zn 2+ . Blocking of these groups revealed that carboxylic group was responsible for 78.57% and 73.31% of Ni 2+ and Zn 2+ removal, respectively whereas 22.63% and 28.54% was due to the hydroxyl group. The GFP could be regenerated using 0.1 mol L −1 HCl, with more than 98% metal recovery and reused for five cycles without any significant loss in its initial sorption capacity.

- by Muhammad Iqbal
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- Kinetics, Modeling, FTIR spectroscopy, Multidisciplinary

The empirical linear relationship between the BET surface area S BET and the Freundlich constant K F , calculated from nitrogen adsorption isotherms of activated carbons, S BET = a 0 K F is mathematically demonstrated. This correlation exists in the relative pressure domain in which the BET equation is valid, whatever the value of c for the BET equation and for values of the Freundlich exponent, a, between 0 and 0.2. This study allows to determine the correlation factor a 0 = 1/a with a ¼ 1

- by Nady Passe-Coutrin
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- Engineering, Activated Carbon, Nitrogen, Specific surface area

Hydrothermal conversion of biomass into biofuel could produce a special type of biochar as byproduct. This biochar is quite different from biochar derived from high temperature pyrolysis. In the present study, two biochars, prepared from hydrothermal liquefaction of pinewood (P300) and rice husk (R300), were characterized and investigated for lead removal from aqueous solution. The results indicated that the biochars contained a large amount of oxygen-containing groups on the surface, which were quite effective for lead removal with capacities of 4.25 and 2.40 mg/g for P300 and R300, respectively. The adsorption equilibrium was achieved around 5 h. Higher temperature favored the removal capacity implying that the adsorption was an endothermic process. The adsorption data at optimum solution pH 5 could be well described by Langmuir model and the adsorption process was well fitted by pseudo-second-order model. Moreover, it was found that the adsorption was mainly controlled by film diffusion. Thermodynamics analysis suggested that lead adsorption onto the biochars was physical endothermic process.

- by zhengang liu
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- Engineering, Thermodynamics, Water, Biomass

Adsorption, exchange and retention phenomena at the solid-aqueous solution interface. 1. Influence of structural, textural and superficial properties of solids. A crucial step, leading to a proper understanding of adsorption mechanisms at the solid-aqueous solution interface, lies in the precise determination of the structural, textural and energetic properties of the solid phases under study. The various conventional techniques for characterizing the textural properties (specific surface area and porosity) are first reviewed. The use of a new adsorption volumetric technique in quasiequilibrium conditions is then detailed. Using such a technique, the gas adsorption isotherm can be obtained precisely on the whole domain of monolayer filling. The DIS (Derivative Isotherm Summation) method applied to the experimental results then allows a study of the surface energetic heterogeneity, which was difficult to assess using conventional techniques. Two examples are then used to illustrate the potentialities of the technique. Through a judicious choice of the adsorbate, such analysis can be used to characterize the exchange properties of solids and to assign precisely the crystallographic origin of the Cationic Exchange Capacity (CEC) of kaolinite. It can also be utilized to understand the retention mechanisms of organic pollutants such as phenol on activated carbons. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS

- by L. Michot and +1
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- Activated Carbon, Specific surface area, Cation Exchange Capacity, Adsorption Isotherm Models

Gravimetric method was used to study the inhibitory properties of indigo dye during corrosion of mild steel in aerated sulphuric acid solutions at 30-50 • C. The effect of addition of halide salts KCl, KBr and KI was also investigated. The corrosion rates in all systems studied increased with rise in temperature. The inhibition efficiency of indigo dye increased with concentration and synergistically increased on addition of halide salts. Temperature studies revealed increased inhibition efficiency at higher temperatures, which is suggestive of chemisorption mechanism. The inhibitor adsorption characteristics were approximated by Frumkins isotherm and Flory-Huggins isotherm. Activation energy for Fe dissolution in sulphuric acid was observed to reduce from 54.6 kJ mol −1 in the uninhibited system to 34.9 kJ mol −1 in the inhibited system.

- by Emeka Oguzie
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- Materials Engineering, Chemistry, Physical Chemistry, Materials Chemistry

h i g h l i g h t s " Lignosulfonate (LS) is the important pollutant in pulp and paper mill wastewater. " The kinetic and equilibrium studies on LS adsorption by fly ash were conducted. " LS could be adsorbed onto fly ash with good removal efficiency. " The adsorption process could be influenced by the solution chemistry. " Fly ash as low-cost adsorbents showed the potential for the removal of LS.

- by Zahide S Yavuzatmaca and +1
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- Environmental Engineering, Chemical Engineering, Thermodynamics, Analytical Chemistry

The water vapor sorption behavior of a range of natural fibers (jute, flax, coir, cotton, hemp, Sitka spruce) has been studied. The data were analyzed using the Hailwood Horrobin model for isotherm fitting and determination of monolayer moisture content. The Hailwood Horrobin model was found to provide good fits to the experimental data. The extent of hysteresis exhibited between the adsorption and desorption isotherms was dependent on fiber type studied and was larger with high lignin compared with low lignin content fibers. The area bounded by the hysteresis loop decreased as the isotherms were performed at progressively higher temperatures. This behavior is consistent with sorption interactions occurring with a glassy solid below the glass transition temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

- by CALLUM HILL
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- Engineering, Modeling, Adsorption, Hysteresis

The adsorption of heavy metals onto biomaterial derived from the marine alga Ecklonia maxima was investigated via batch experiments. The adsorption equilibria of Cu, Pb and Cd could be represented by Langmuir isotherms and the capacity of fresh alga for Cu, Pb and Cd was approximately 85 -94, 227 -243 and 83.5 mg/g dry alga, respectively. The rate of adsorption onto the marine alga was high. The alga particle size played an important role in the adsorption behaviour. The coarse alga particles had a higher adsorption capacity and slower adsorption kinetics and could be regenerated without significant loss of capacity. In contrast, the fine alga particles had a lower adsorption capacity and faster adsorption kinetics and could not be regenerated without significant loss of capacity. Comparison with a commercial resin indicated that the activated biomass derived from E. maxima could be used as an efficient biosorbent for the treatment of waste waters containing heavy metals. D

- by Chris Aldrich
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- Regeneration, Biomass, Hydrometallurgy, Water Treatment

This study investigated the potential use of a low-cost inorganic powder (Persian Kaolin) for removal of Basic Yellow 28 (BY28), Methylene Blue (MB) and Malachite Green (MG) from aqueous solution. Kaolin was characterized via a laser particle size analyzer (PSA), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. The effect of adsorbent dosage, dye concentration, initial pH and the presence of various electrolytes was studied. The isotherm data of dyes were correlated reasonably well by the Langmuir adsorption isotherm. The values of the adsorption capacity of kaolin towards the cationic dyes ranged from 16 mg/g to 52 mg/g, being probably dependent on the geometry of the dye molecules. The resulting degrees of dye removal were 65-99% for initial dye concentration of 10 mg/L and for kaolin loadings of 0.8-2.5 g/L. It was found that the adsorption of dyes on kaolin followed a pseudo-second order equation. The recovery and reuse of kaolin for a second and third time have also been studied. The thermodynamic studies showed that the dye adsorption onto kaolin is a spontaneous, endothermic and a physical reaction.

- by Niyaz Mohammad Mahmoodi
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- Engineering, Thermodynamics, Kinetics, Desalination
- by Uday Ghosh
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- Chemical Engineering, Thermodynamics, Kinetics, Image Analysis