Description Of Adsorption Process Research Articles

Removal of ionic liquid by engineered bentonite from aqueous solution

The removal of ionic liquid (1-butyl-3-methyl imidazolium chloride: BMImCl) was studied from aqueous solution by raw bentonite, acid-activated bentonite and organic-modified bentonite. These types of bentonite sample were characterized by FT-IR, TGA and XRD. The effects of contact time, BMImCl initial concentration, pH, ionic strength, and humic acid on the removal of BMImCl were investigated via batch adsorption experiments. The adsorption kinetics models were applied to predict the adsorption constants, and the kinetic data indicated that the pseudo-second-order model gave a better fit. Furthermore, the Langmuir, Freundlich and Temkin isotherms models were also introduced to describe adsorption process in order to obtain possible mechanism of the removal. The applied isotherms models demonstrated that the adsorption data of acid-activated bentonite samples were well described by Temkin adsorption isotherm, and the isotherm model of organic-modified bentonite was Langmuir adsorption isotherm. The adsorption experiments indicated that these bentonite samples might be applied in repair of soil and water contaminated by ionic liquids.

ChemInform Abstract: Nonexponential Kinetics of Surface Chemical Reactions

AbstractReview: 222 refs.

Conversion of waste FGD gypsum into hydroxyapatite for removal of Pb2+ and Cd2+ from wastewater

Flue gas desulfurization (FGD) gypsum, a familiar waste generated from coal-fired power plants, was successfully transformed to hydroxyapatite (FGD-HAP) by hydrothermal method. The obtained FGD-HAP was characterized by XRD, FTIR, TEM and BET methods and investigated as adsorbent for removal of Pb2+ and Cd2+ from wastewater. Batch experiments were performed by varying the pH values, contact time and initial metal concentration. The result of pH impact showed that the adsorption of two ions was pH dependent process, and the pH 5.0–6.0 was found to be the optimum condition. The achieved experimental data were analyzed with various kinetic and isotherm models. The kinetic studies displayed that the pseudo-second order kinetic model could describe adsorption processes well with high correlation coefficient, and the Langmuir isotherm model provided the best fit to the equilibrium experimental data. The maximum adsorption capacities calculated from Langmuir equation were 277.8 and 43.10mg/g for Pb2+ and Cd2+, respectively, which can compete with other adsorbents. The thermodynamic parameters revealed the adsorption processes were endothermic and spontaneous in nature. In binary adsorption, the amount of Cd2+ adsorbed on FGD-HAP decreased by 46.0% with increasing concentration of Pb2+, which was higher than that of Pb2+(21.7%), demonstrating the stronger affinity between FGD-HAP and Pb2+. The highest amount of Pb2+ and Cd2+ desorbed from saturated FGD-HAP by EDTA solution confirmed the FGD-HAP was a promising alternative adsorbent in treatment of toxic Pb2+ and Cd2+ wastewater.

Nonexponential Kinetics of Surface Chemical Reactions

On the basis of current trends in the description of adsorption processes in complex media a conceptual analysis was made of the mechanisms of the appearance of nonexponential kinetics (stretched exponential function) in chemical reactions on a surface. A review of approaches ranging from a phenomenological description to a generalized fractal formalism is presented, and it was used to develop a model of adsorption in nonuniform media in terms of the concepts of the reaction space as a topological subject. By “geometric description” of the evolution of the surface reactions it is possible to unify the various types of effect in terms of a reaction space of required dimensionality and to establish a relationship between the parameters of macroscopic kinetics and features of the trajectory of the analyte in the nonuniform environment during its movement toward the receptor center.

A geometrical model of random porous structures to adsorption calculations

This paper describes a new approach to identification of random porous structures (e.g. present in cheap natural adsorbents, active carbons). It comes from a clustering based description of adsorption process assuming an exponential distribution of adsorbate stack size (the LBET model), combined with the new consistent mathematical relationships between the pore geometry, adsorption isotherm parameters and physical properties of adsorptive. The newly derived formulae are discussed, and results of their application to analysis of an active carbon structure are shown.

Electrodynamics of adsorption processes in condensed media

Electrodynamic approaches to describing adsorption processes on a solid surface in condensed physicochemical systems are presented. Theoretical continuous consideration of the indicated processes showed that the possibilities of direct electrometry of the properties of substances in a condensed state and of adsorbing media can be increased considerably.

Study on Adsorption and Desorption Performance of Direct Dyes on Anionic Exchange Membrane

The adsorption and desorption performance of C.I. Direct Red 13 and C.I. Direct Blue 6 on anionic exchange membrane were studied. The adsorption and desorption performances of anionic exchange membrane under different conditions were compared. The results showed that the adsorption accords with the pseudo-second dynamics model. Langmuir adsorption model could well describe adsorption processes. The addition of inorganic salt Na2SO4 in the dye solution had certain influence on the adsorption. The desorption percentage could reach above 80% using the mixture of ethanol, sodium chloride and water solution as desorbent, and the anionic exchange membrane could be reused.

Adsorption Behavior of Fe(II) and Fe(III) Ions on Thiourea Cross-Linked Chitosan with Fe(III) as Template

A new type of thiourea cross-linked chitosan with Fe(III) as template (TCCTS template) was synthesized. The adsorption of Fe(II) and Fe(III) on this TCCTS template was studied. The factors affecting adsorption such as pH and contact time were considered. The results showed that the optimum pH value for adsorption was pH = 5.0 and the adsorption equilibrium time was about 60 min. The adsorption isotherms and kinetics were investigated, and the equilibrium data agreed very well with the Langmuir model and the pseudo second-order model could describe adsorption process better than the pseudo first-order model. Results also showed that TCCTS template was a favourable adsorbent for Fe(II) and Fe(III) in aqueous solution.

Study on Adsorption and Desorption Performance of Reactive Dyes on Anionic Exchange Membrane

The adsorption and desorption performance of Reactive Brilliant Red K-2BP and Reactive Brilliant Red K-2G on anionic exchange membrane were studied. The adsorption and desorption performances of anionic exchange membrane under different conditions were compared. The results showed that the adsorption accords with the pseudo-second dynamics model. Langmuir adsorption model could well describe adsorption processes. The addition of inorganic salt Na2SO4 in the dye solution had certain influence on the adsorption. The desorption percentage could reach above 80% using the mixture of ethanol, sodium chloride and water solution as desorbent, and the anionic exchange membrane could be reused.

Method of molecular distribution functions in the description of adsorption processes in nanoscale structures

The short-range order during gas adsorption by micropores can be described based on integral equations of statistical mechanics for partial distribution functions. The assumptions necessary for correct analysis of physical sorption are considered, and adsorption characteristics of carbon nanofibers in relation to hydrogen are calculated.

Computer analyses of new numerical methods for the description of adsorption process and the reliability of identification of microporous structure parameters

The aim of this work was the computer analysis of numerical properties of the original mathematical method of the description of adsorption process and the reliability of the identification of structure parameters. The method is based on the theory of multilayer adsorption, the derivation and further theoretical discussion of which was presented in the author's earlier works. The following tasks were given special attention in this paper: the influence of the assumed structure parameters, the influence of the high-pressure section of adsorption isotherms and the influence of the number of simultaneously fitted adsorption isotherms on the quality of identification and the errors of microporous structure parameters. This research provides a basis for the evaluation of the reliability of the parameters calculated for real adsorption systems.

DETERMINATION OF THE PHOSPHATE CONTENT ORIGINALLY ADSORBED ON THE SOIL BY FITTING AN ADSORPTION ISOTHERM MODEL

In order to replace the rather complicated physico-chemical method, a mathematical technique related to the binding of phosphate ions was elaborated to determine the labile, and thus plant-available phosphate content of the soil. The technique is based on the analysis of the quantity of phosphate bound to the soil in the equilibrium state when soil samples are suspended in solutions containing various concentrations of phosphate. The majority of soils contain a certain amount of adsorbed phosphate, so negative adsorption is observed if the analysis is carried out with solutions containing little or no phosphate. The isotherm models generally used to describe adsorption processes do not assume the presence of any material originally bound on the adsorbent surface, so their starting point is a state with a zero quantity of adsorbed material on the adsorbent in a solution with an initial equilibrium concentration of zero. In the case of soil phosphate adsorption, however, different results are obtained, as the soil already contains adsorbed phosphate in its original state. For this reason the isotherm model was modified. The modified isotherm model was fitted to the measurement data using non-linear regression. The quantity of phosphate originally adsorbed on the soil can be calculated using a model parameter. The phosphate quantity calculated in this way exhibits a close correlation both with the isotopically exchangeable phosphate content, and with the results obtained with the best chemical extraction methods.

Numerical modelling and laboratory studies on the removal of Direct Red 23 and Direct Red 80 dyes from textile effluents using orange peel, a low-cost adsorbent

Wastewater containing direct dyes discharged from various industries, in particular, textile industry often causes many environmental problems. Considering the possibility of the adsorption process of synthetic dyes and their removal from aqueous solutions using orange peel as an eco-friendly and low-cost adsorbent before discharging to the receiving environment is the most important task. This paper presents a numerical finite element model to simulate the removal of dissolved textile synthetic dyes from wastewater taking into consideration both linear and the Langmuir isotherms to describe adsorption process. The CTRN/W model was integrated with SEEP/W model and modified to solve mathematical equations describing the problem at hand. The modelling accuracy was first verified with an analytical equation for a reactive mass transport problem including advection, dispersion and linear adsorption processes through groundwater flow medium. The modelling results were then compared to those results obtained from experimental tests for the removal of Direct Red 23 and Direct Red 80 dyes from textile wastewater using orange peel adsorbent. The model predictions somewhat agree with the experimental measurements. It was found that the adsorption process by orange peel adsorbent could be well described by the Langmuir isotherm. Furthermore, a pseudo-second order kinetics showed to be well-suited with the rate of sorption. Although the generation of such wastewater by the different industries is nearly unavoidable, the results of model presented here can help to design an appropriate environmental management strategy to minimise the adverse impacts caused by industrial wastewater.

Copper Sorption Mechanisms on Smectites

AbstractDue to the importance of clay minerals in metal sorption, many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. To provide a basis for development of adsorption models it is critical that molecular-level studies be done to characterize sorption processes. In this study we conducted X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength, Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and EPR spectroscopy results provides evidence that multinuclear complexes are forming. Fitting of extended X-ray absorption fine structure spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 Å apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.

Bestimmung der dynamischen Oberflächenspannung mit Hilfe eines automatischen Blasendrucktensiometers / Dynamic surface tension determination using an automated bubble pressure tensiometer

A newly designed fully automated maximum bubble pressure tensiometer has many advantages compared to known instruments developed so far. The most striking feature is the possibility to determine the bubble dead time and to calculate the efficient surface age of a bubble. The state of the art of the theory for describing adsorption processes at the surface of a growing bubble is discussed and useful approximate solutions are given and applied to example experiments. The temperature and viscosity dependence of the adsorption kinetics of a model surfactant, Triton X-100, are discussed in terms of a diffusion controlled adsorption model. Finally, as an example, measurements of human blood and urine samples are presented in order to show the sensitivity of dynamic surface tensions to changes in the composition of such complex liquids. Measurements of river water samples show an additional field of application in water treatment control.

Application of the Dubinin–Radushkevich Equation for Describing Adsorption from Solutions on to Various Carbons

Dozens of papers have been published recently describing adsorption processes from solutions on to solid surfaces, but a certain lack of understanding of this problem is still observed. This article deals with the description of adsorption from binary solutions of non-electrolytes on to solids. This description covers adsorption both on homogeneous and heterogeneous surfaces from ideal and non-ideal liquid mixtures. Some important factors determining the adsorption process, i.e. the heterogeneity of the solid surface, interactions between the species in the bulk and surface phases, differences in molecular sizes of the adsorbate molecules, etc., have been discussed. The main attention has been focused on the Dubinin–Radushkevich equation and its application in the description of adsorption from solutions on to energetically, heterogeneous adsorbents. Numerous model calculations have been reported for this equation and several experimental systems have been analyzed. The application of the Dubinin–Radushkevich equation in characterizing liquid adsorption on to various carbons has been demonstrated.

General approach to adsorption and absorption

An equation has been proposed to describe adsorption processes in different systems from a common standpoint. The equations of Henry, Langmuir, Fowler-Guggenheim, and Temkin represent specific examples of it.

THERMODYNAMICS OF CONSTANT-PRESSURE AND CONSTANT-VOLUME SORPTION PROCESSES IN CLOSED-CYCLE SOLIDDESICCANT SYSTEMS

A relationship for adsorption equilibrium is proposed and compared to known potential theories. Using this newly proposed relationship, formulas are derived that thermodynamically describe adsorption processes encountered in closed-cycle, adsorption heating and cooling systems.

Thermodynamics of physical adsorption processes of gases on solid adsorbents

A thermodynamic formalism describing adsorption processes of a multi-component gas on a porous and inert solid adsorbent is developed. The formalism is based on the entropy-free thermodynamics of J. Meixner. It includes mass- and heat-exchange between the gaseous adsorptive and the adsorbed phase. Besides, the internal spreading process of the adsorbate in the porous adsorbent is taken into account, this process being treated as internal process of the adsorbent/adsorbate system. General criteria restricting the mathematical structure of the process equations are given. The formalism delivers a set of coupled algebraic equations and ordinary differential equations the numerical solution procedure of which is outlined to a certain extent.

Adsorption kinetics and compositional surface elasticity of multicomponent surfactant solutions

Adsorption kinetics of multicomponent surfactant solutions from a finite volume onto interfaces undergoing uniform nonsteady deformation was analyzed theoretically. General bulk and surface phase transport equations were formulated together with nonlinear kinetic boundary conditions describing adsorption processes governed by various isotherms. By applying the small perturbation technique these equations were linearized around the equilibrium reference state and general expressions for adsorption fluxes in terms of adsorption and desorption constants and the perturbing variables were derived. By introducing the matrix notation and applying the Laplace transformation the set of linearized equations was solved analytically for an arbitrary number of surfactants for spherical and planar interface geometry. The Laplace transformation enabled generalization of the common Fourier elasticity concept to arbitrary periodic and nonperiodic (impulsive) surface deformations. Thus, for characterizing the compositional part of surface elasticity we introduced the operator surface elasticity E( s) (a square matrix of the dimension equal to the number of surfactants considered) analogous to the complex transmittance of an electrical circuit. In the Laplace transformation space, E( s) is the proportionality coefficient between arbitrary surface deformations A ̃ (s) and the resulting surface concentrations θ(s) . Based on the E( s) definition and using the equation of state of the monolayer, the mechanical surface elasticity complex vector ϵ( s) (of the dimension equal to the number of surfactants) and the total mechanical elasticity ϵ t( s) (a scalar quantity) were defined. A previously used restricted definition of the Fourier elasticity modulus was obtained from our equations by substituting s = i ω . Explicit expressions for E( s) and E(i ω) were derived for one- and two-component surfactant solutions in the case of spherical and planar interfaces. The inversion of the transformed equations was also performed, giving analytical expressions for surface concentrations as a function of the time for impulsive and harmonic deformations. Based on these solutions, the range of validity of Fourier elasticity concept was determined.