Adsorption kinetics of naphthalene onto organo-sepiolite from aqueous solutions

In this study, the adsorption kinetics of naphthalene onto organically modified-sepiolite was investigated by means of the effects of pH, contact time, adsorbent dosage and temperature. The modification of natural sepiolite was accomplished with a cationic surfactant, which is namely dodecyltrimethylammonium (DTMA) bromide. The surface characterization both natural- and modified-sepiolite were carried out by using FTIR method to observe the intercalation of DTMA between the sepiolite layers. The elemental and thermal analyses were also performed to understand the modification. The optimum pH values and the equilibrium contact time for the adsorption of naphthalene onto DTMA–sepiolite were found as 6 and 75 min, respectively. The kinetic parameters of the adsorption process were calculated from experimental data. According to these parameters, adsorption process follows the pseudo-second-order kinetic model with the high correlation coefficients (r² = 0.999). The obtained results show that modified-sepiolite is reasonably effective adsorbent for the removal of organic contaminants, which are an important source for the environmental pollutants.     

Adsorption of cationic dye on N,O-carboxymethyl-chitosan from aqueous solutions: equilibrium, kinetics, and adsorption mechanism

In order to improve the adsorption capacity of chitosan (CTS) for methylene blue (MB) cationic dye, a series of N,O-carboxymethyl-chitosans (N,O-CMCTS) were prepared under heterogeneous conditions by controlling the reaction time. The adsorption of MB from aqueous solution onto N,O-CMCTS was studied. The effects of degree of substitution (DS) of N,O-CMCTS, initial pH of the dye solution and adsorption temperature were investigated in detail. The results showed that the adsorption capacities of N,O-CMCTS increased with the increase of DS and N,O-CMCTS with DS of 0.72 exhibited the highest adsorption capacity (349 mg/g). The adsorption kinetics of N,O-CMCTS was found to follow the pseudo-second-order model. The adsorption equilibrium of N,O-CMCTS fitted very well with the Langmuir isotherm model, showing maximum monolayer adsorption capacity of 351 mg/g. The adsorption mechanism of N,O-CMCTS was also discussed by means of FTIR spectra and XPS. The results revealed that the –OH, –NH₂, and –COOH groups of N,O-CMCTS were involved in the adsorption process. The desorption studies showed that N,O-CMCTS could be regenerated and used for the adsorption of MB repeatedly.     

Adsorption of glycine on montmorillonite in aqueous solutions

Glycine was adsorbed on the surface of montmorillonite from aqueous solutions of variable glycine concentrations (0.001–0.3 mol L^− 1) and pHs (2–12) at room temperature. The reaction products were characterized using X-ray diffraction and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy. The results indicate that adsorption is highly pH dependent, increasing at acidic pHs. Glycine adsorption is dominated by complexation of the carboxylate group of zwitterionic glycine onto the edge surface at low concentrations of glycine. When the edge surface is saturated, the adsorption occurs by cation exchange in the interlayer space. ATR-FTIR results point to an adsorption by hydrogen bonding between the NH₃⁺ group and the basal oxygen of the interlayer surface. The dependence of glycine adsorption with its aqueous concentration fits for a Freundlich equation. The measure of the desorbed interlayer cations shows that the 68% of the K⁺ was exchanged with glycine. The K⁺–glycine exchange reaction produces a decrease of the smectite interlayer space from 14.5 to 12 Å and an arrangement of the smectite layers. Intercalated glycine is present as both glycinium and zwitterionic forms. Since only glycinium contribute to structural charge balance, total adsorbed glycine can exceed K⁺ released. These findings are of relevance for the evaluation of distribution and reactions of free amino acids in natural environments.     

Adsorption of cationic dye from aqueous solutions by activated carbon

Batch sorption experiments were carried out to remove a cationic dye, methylene blue (MB), from its aqueous solutions using a commercial activated carbon as an adsorbent. Operating variables studied were pH, stirring speed, initial methylene blue concentration and temperature. Adsorption process was attained to the equilibrium within 5 min. The adsorbed amount MB dye on activated carbon slightly changed with increasing pH, and temperature, indicating an endothermic process. The adsorption capacity of methylene blue did not significantly change with increasing stirring speed. The experimental data were analyzed by various isotherm models, and found that the isotherm data were reasonably well correlated by Langmuir isotherm. Adsorption measurements showed that the process was very fast and physical in nature. Thermodynamic parameters such as the adsorption entropy (ΔS^o) and adsorption enthalpy (ΔH^o) were also calculated as 0.165 kJ mol⁻¹ K⁻¹ and 49.195 kJ mol⁻¹, respectively. The ΔG^o values varied in range with the mean values showing a gradual increase from −0.256 to −0.780 to −2.764 and −7.914 kJ mol⁻¹ for 293, 313, 323 and 333 K, respectively, in accordance with the positive adsorption entropy value of the adsorption process.     

Adsorption of trivalent chromium from aqueous solutions onto activated carbon

The adsorption of chromium (III) onto activated carbon was investigated as a possible alternative method for its removal from aqueous solutions. The adsorption data were obtained in a batch adsorber and fitted the Langmuir adsorption isotherm well. The effect of pH on the adsorption isotherm was investigated at pH values of 2, 4, 5 and 6. It was found that at pH values below 2 the Cr(III) was not adsorbed and at pH values above 6.4 the Cr(III) was precipitated as Cr(OH)₃. Maximum adsorption occurred at pH 5. The pH plays a very important role in the adsorption of Cr(III) since Cr(III) can form different complexes in aqueous solutions. The adsorption capacity was increased by about 20% as the temperature was raised from 25 to 40°C. It was concluded that Cr(III) is adsorbed to an appreciable extent on activated carbon and that the adsorption is highly dependent upon pH.     

The Adsorption of basic dye onto silica from aqueous solution-solid diffusion model

The adsorption of Basic Blue 69 dye onto silica in a batch adsorption system has been studied. A two resistance mass transfer model has been developed based on film resistance and homogeneous solid phase diffusion. An analytical solution is presented and experimental results and theoretical data are in good agreement, for a wide range of operating conditions, using a single external mass transfer coefficient and a single effective solid diffusivity. The variables investigated are: initial dye concentration, solid/liquid ratios and adsorbent particle size range. Under constant agitation conditions almost all data can be correlated using a film mass transfer coefficient of 2.0 x 10^?4 cm sec^?1 and a diffusion coefficient of 1.2 x 10^?9 cm² sec^?1.     

Adsorption of chromate from aqueous solutions by HDTMA-modified clinoptilolite,glauconite and montmorillonite

Adsorption of chromate on natural clinoptilolite (Cp), glauconite (Gl), and montmorillonite (Mt) treated with hexadecyl trimethylammonium (HDTMA) bromide at amounts equivalent to 1.0 and 2.0 of their cation-exchange capacities (CEC) was investigated by batch study. In the case of the Cp and Gl, adsorption of HDTMA took place on the zeolite and clay mineral surfaces only and thus relates to the external CEC (ECEC). The amount of chromate removed from the solution by the organo-silicates continuously decreased with increasing pH in the range 1.3–10. The highest values were obtained at pH between 1.3 and 6, and decreased rapidly above pH 6. At an initial chromate concentration of 6.25 mmol/L, its amounts bound to the Cp, Gl and Mt modified using 1.0 CEC loadings of the surfactant were 47, 102, and 168 mmol/kg, respectively. When amount of HDTMA used was equivalent to 2.0 CEC of the silicate, these values increased to 182, 240, and 285 mmol/kg, respectively. The results obtained suggest that the surfactant molecules, bound beyond the CEC to the external surfaces of the Cp and Gl, show a greater chromate adsorption ability in comparison with such molecules located in the interlayer spaces of the Mt. It is also evident that an excess of the surfactant, not adsorbed on the silicate surfaces, participated in the removal of chromate from the solution by formation of a precipitate of alkylammonium chromate.     

Adsorption of acid orange 7 dye in aqueous solutions by spent brewery grains

Spent brewery grains (SBG), a by-product of the brewing process, were tested as an adsorbent of acid orange 7 dye (AO7), a monoazo acid dye currently used in paper and textile industries. The presence of AO7 in these effluents causes obvious environmental problems.

Kinetics studies of adsorption of AO₇ to SBG (3.75%, m/v) were carried out at 20 °C, using aqueous solutions with different AO7 concentrations (30–834 mg/L). For every situations tested, no significant variation in residual AO7 concentration in solution was detected after 1 h contact between the dye and the adsorbent. The adsorption process followed a pseudo-first order model.

The equilibrium process showed to be well described by both Freundlich and Langmuir isotherm models, at 20 and 30 °C. The maximum adsorption capacity was estimated to be 30.5 mg AO7/g SBG, at 30 °C.

Free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were calculated to predict the nature of adsorption. The estimated values for ΔG° were −22.78 and −24.53 kJ/mol, respectively, at 293.3 K (20 °C) and 303.3 K (30 °C), which are rather low indicating that a spontaneous process occurred. The enthalpy changes and entropy of adsorption were 28.66 and 175.36 J/mol K, respectively. The positive value for ΔH° indicates that the adsorption of AO7 dye to SBG is an endothermic process. The positive value of entropy reflects the affinity of the adsorbent for AO7 dye.

The obtained results are very promising since: (i) high levels of colour removal (>90%) were achieved with low contact times adsorbent/dye (less than 1 h contact); and (ii) the whole SBG can be successfully used as adsorbent of AO7 dye in aqueous solution without needing any previous treatments such as milling and/or sieving. Spent grains, being a cheap, and easily available material, can be an alternative for more costly adsorbents used for dye removal in wastewater treatment processes.     

Adsorption studies of aqueous basic dye solutions using sepiolite

Sepiolite, low cost, locally available and natural mineral was studied as an adsorbent for the removal of Basic Astrazon yellow 7GL from aqueous solutions and batch contact tests. The kinetics of the adsorption process was tested for the pseudo-first order, pseudo-second order reaction and intra-particle diffusion models. The rate constants of adsorption for all these kinetic models were calculated. Good correlation coefficients were obtained for the pseudo-second order kinetic model. Langmuir, Freundlich and Dubinin-Radushkevich isotherm models were applied to the experimental equilibrium data by changing temperature. The isotherm constants were determined by using the linear regression of these models. The monolayer coverage capacities of sepiolite for basic dye were found to be in the range of 62.5-88.5 mg/g at different temperatures. Thermodynamic studies showed that the reaction for dye uptake by sepiolite is endothermic in nature. Based on the optimum parameters sepiolite was also used as adsorbent for raw wastewater treatment and found as efficient as dye color removal.     

Adsorption of an acid dye onto coal fly ash

In this study, we found the raw coal fly ash (CFA) that had not been subjected to any pretreatment process had superior adsorbing ability for the anionic dye Acid Red 1 (AR1) than did two modified coal fly ashes (CFA-600 and CFA-NaOH). The adsorption capacities followed the order CFA > CFA-600 > CFA-NaOH, and they each increased upon increasing the temperature (60 °C > 45 °C > 30 °C). The adsorptions of AR1 onto CFA, CFA-600, and CFA-NaOH all followed pseudo-second-order kinetics. The isotherms for the adsorption of AR1 onto the raw and modified coal fly ashes fit the Langmuir isotherm quite well; the adsorption capacities of CFA, CFA-600, and CFA-NaOH for AR1 were 92.59–103.09, 32.79–52.63, and 12.66–25.12 mg g^?1, respectively. According to the positive values of ΔH° and ΔS°, these adsorptions were endothermic processes. The ARE and EABS error function methods provided the best parameters for the Langmuir isotherms and pseudo-second-order equations, respectively, in the AR1–CFA adsorption system.     

Kinetic studies and grafting mechanism for methyl aniline derivatives onto chitosan: Highly adsorptive copolymers for dye removal from aqueous solutions

A polysaccharide, chitosan received vast attention because of its non-toxic, low cost and biodegradable properties. In this study, three promise grafted chitosan copolymers using methyl polyaniline conducting polymeric isomers were successfully synthesized through oxidative-radical copolymerization using ammonium persulphate as initiator in acidic medium. The kinetic behaviors of graft copolymerization were extensively studied under various parameters. Moreover, the rate of grafting copolymerization is affected by concentrations of monomer, initiator, and HCl in addition to temperature. The activation energy (Ea), enthalpy of activation (∆ H*) and negative value of entropy (∆ S*) support the progress of copolymerization. Environmental impacts of the grafted polymers in water detoxification were manifested. A comparison study for adsorption of remazol red dye from aqueous solutions onto Ch–g-PMeANIs was investigated.     

Adsorption of basic dyes from model aqueous solutions onto novel spherical silica support

Removal of CI Basic Blue 9 or CI Basic Red 5 from model aqueous solutions has been studied with spherical silica precipitated in an emulsion system used as an adsorbent. The process of removal of the dye impurities has been studied for the dyes in a wide range of concentrations (50–2000 mg dm⁻³) in model systems. The degree of dye adsorption, chemical stability of the pigments obtained and their detailed physicochemical and morphological characterisation have been ascertained. In particular, the dye removal method proposed has been found to be highly effective in removing CI Basic Blue 9 (99.9%). The degree of dye extraction from the silica (SiO₂) surface at the dye concentration in the model solutions in the range 1000–2000 mg dm⁻³ did not exceed 1.0%. The pigment composites produced are characterised by high uniformity of the particles (polydispersity index = 0.005) with the diameters ranging from 360 to 510 nm. The pigment particles are spherical in shape and of intense blue or red colour.     

Anion exchange of uranium from aqueous sulphuric acid solutions: Diffusion kinetics

The ion exchange kinetics of uranium sorption from acidic sulphate solutions onto weak and strong base resins has been studied. In order to facilitate experimentation and analysis, isotopic redistribution experiments of uranyl sulphate ions (with U-235 as a tracer) under conditions of particle diffusion control have been performed. Also, self-diffusion experiments for sulphate ions (with S-35 as a tracer) and counter diffusion measurements involving uranyl sulphate-sulphate exchange have been performed. The ion exchange of uranium is a slow reaction and appears to be particle diffusion controlled at all solution conditions of practical interest. For a weak base resin (Relite MG-1), the self-diffusion coefficient of uranyl sulphate ions changes with particle size, increasing from 1.49 to 4.88 × 10^?9 cm²/s as the particle diameter is reduced from 0.146 to 0.054 cm. With a strong base resin (Dowex-1×8), the self-diffusion coefficient of uranyl sulphate ions remains reasonably constant with varying particle diameter at a value of 1.76 × 10^?9 cm²/s. Sulphate ion self-diffusion coefficients were also constant with particle size (2.50 × 10^?7 cm²/s) and the counter exchange diffusivity lies between the values for the individual species; a typical value is 1.53 × 10^?8 cm²/s. It is argued that resin matrix structure has a significant effect on uranium kinetics and that a knowledge of the relevant diffusion coefficients will provide a rational basis for the design of ion exchange processes and plant equipment.     

柱撑蒙脱石对水中砷(Ⅴ)的吸附研究

采用羟基聚合Al-Fe为柱化剂对蒙脱石进行改性,将制得的柱撑蒙脱石作为吸附剂,研究了其对水溶液中砷的去除效果及其影响因素.结果表明:对蒙脱石柱撑改性后能显著提高其吸附性能.平衡吸附量与平衡质量浓度之间的关系符合Freundlich和Langmuir等温吸附方程所描述的规律.用Elovich方程和双常数方程可以较好地拟合柱撑蒙脱石对As(Ⅴ)的动力学吸附过程.     

Adsorption of γ-aminopropyltriethoxysilane onto bulk iron from aqueous solutions

The adsorption of γ-aminopropyltriethoxysilane (γ-APS) onto mechanically polished iron coupons from 1% aqueous solutions has been investigated using reflection–absorption infrared spectroscopy. Thick films were formed on the coupons during 1-hr exposures to the γ-APS solutions. The outermost portion of these films consisted of highly hydrolyzed polysiloxanes that were weakly bound and easily desorbed by cold water. This fraction of the films was characterized by an infrared band near 1575 cm^?1 that was tentatively assigned to the NH₂ deformation of acceptor amine groups in strong hydrogen bonds or to coordination of the amino nitrogen atoms to silicon atoms. Removal of the weakly bound outermost portion of the films with water revealed an incompletely hydrolyzed, strongly bound film approximately 60 Å in thickness characterized by a band near 1510 cm^?1 that was assigned to NH groups. Formation of NH₃⁺ groups indicated that γ-APS may have been adsorbed initially as cyclic, internal zwitterions.     

Adsorption studies on the removal of Malachite Green from aqueous solutions onto halloysite nanotubes

Halloysite nanotubes (HNTs) were used as nano-adsorbents for removal of the cationic dye, Malachite Green (MG), from aqueous solutions. The adsorption of the dye was studied with batch experiments. The natural HNTs used as adsorbent in this work were initially characterized by FT-IR and TEM. The effects of adsorbent dose, initial pH, temperature, initial dye concentration and contact time were investigated. Adsorption increased with increasing adsorbent dose, initial pH, and temperature. Equilibrium was rapidly attained after 30 min of contact time. Pseudofirst-order, pseudo-second-order and intraparticle diffusion models were considered to evaluate the rate parameters. The adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.999. The factors controlling adsorption process were also calculated and discussed. The maximum adsorption capacity of 99.6 mg g⁻¹ of MG was achieved in pH = 9.5. Thermodynamic parameters of ΔG°, ΔH° and ΔS° indicated the adsorption process was spontaneous and endothermic.     

Adsorption of chromium(VI) from aqueous solutions onto amine-functionalized natural and acid-activated sepiolites

Chromium(VI) adsorption onto amine-functionalized sepiolites from aqueous solution at 298 K was investigated. Natural and acid-activated sepiolites were functionalized by covalent grafting [3-(2-aminoethylamino)propyl]trimethoxy-silane to the silanol groups onto the sepiolite surface. Functionalization was proved by differential thermal analysis and the point of zero charge, pH_pzc, determinations. The adsorption isotherms suggested that the adsorption capacity of the functionalized acid-activated sepiolite was higher than that of the functionalized natural sepiolite, for all investigated initial solution pH values. Adsorption efficiency of the functionalized sepiolites was improved by decreasing solution pH value. Due to the high value of pH_pzc and large buffer capacity of adsorbents, a very low initial solution pH value was required to achieve high protonation of the surface amine groups and provide electrostatic attraction of Cr(VI) anionic species. The maximum chromium(VI) removal was achieved at an initial pH of 2.0; ca. 60 mg/g of functionalized acid-activated sepiolite and ca. 37 mg/g of functionalized natural sepiolite. Equilibrium data for both functionalized sepiolites at an initial solution pH value of 2.0 fitted well to the Freundlich model. The adsorption process followed pseudo-second-order kinetics. The values of the thermodynamic parameters indicate a spontaneous adsorption process of a prevalently physical nature.     

Adsorption of acid dye onto woodmeal by solid diffusional mass transfer

The adsorption of Telon Blue (Acid Blue 25) dye onto wood has been studied using an agitated batch adsorber. The variables studied include agitation, initial dye concentration, wood mass, wood particle size and dye solution temperature. Isotherms were measured and the isotherm parameters were determined.

A mathematical model has been developed using the basis of the model proposed by Mathews and Weber Jr. This model is based on external mass transfer and solid-phase diffusion, and has been used to generate theoretical concentration—time decay curves. The results of the model were adjusted to the experimental data using a ‘best fit’ approach. The external mass transfer coefficient was found to vary with the degree of agitation, and consequently all other variables were considered at a constant agitation speed of 400 rev min⁻¹. A good agreement between the theoretical generated and the experimental concentration—time decay curves was achieved using a constant external mass transfer coefficient, 0.30 × 10⁻³ cm ⁻¹, and a constant solid-phase diffusivity, 0.200 × 10⁻⁸ cm² s⁻¹, for varying initial dye concentrations as well as wood mass. In experiments where the particle diameter was varied, a constant external mass transfer coefficient was sufficient to describe the system, but a decreasing diffusivity was required with increasing particle size. To simulate the effect of varying temperature, both external mass transfer coefficient and diffusivity were varied.     

Removal of Astrazone Blue from aqueous solutions onto brown peat. Equilibrium and kinetics studies

The aim of this study is to characterize and assess the sorption potential of brown peat, in relation to colored pollutants from the textile industry wastewater. The objectives of this paper were: the physicochemical, morphological, and mineralogical characterization of brown peat, testing the adsorption capacity of natural and chemically treated peat samples for Astrazone Blue, evaluation of adsorption process from equilibrium isotherm and kinetic point of view. The characteristics of the peat samples were investigated using elemental analysis, scanning electron microscopy and X-ray diffractometry. Experimental data indicated that the brown peat tested confirm a high level of adsorption (removal efficiency >93.00%, adsorption capacity reaching up to 24.27 mg/g) of Astrazone Blue from aqueous solution. The Langmuir and Freundlich adsorption isotherm models were used to find the best equation able to describe the adsorption process. Experimental adsorption data were successfully described by the Langmuir equilibrium isotherm model. This fact is supported by the agreement between the q values obtained using the Langmuir equation (26.32 mg/g), and the ones obtained experimentally (24.27 mg/g). The kinetic studies showed that the pseudo-second-order model described Astrazone Blue sorption kinetics, as confirmed by the high values of R ² , which are over 0.99 for the whole investigated concentration range (200 to 800 mg/L). The use of brown peat adsorbent is more advantageous compared with other materials since it does not require a preliminary treatment, is low-cost and is an eco-friendly adsorbent. Hence, this peat appears to be a viable material for the decontamination of effluents containing dyes.     

Extraction of citric acid from aqueous solutions with Alamine 336: equilibrium and kinetics

Citric acid is one of the organic acids for which the world market is growing every year. This article describes equilibria and kinetic studies for the extraction of citric acid by Alamine 336 with methyl‐iso‐butylketone (MIBK) as diluent. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of extraction of citric acid by Alamine 336 in MIBK. The reaction has been found to be first order in both Alamine 336 and citric acid with a rate constant of 0.013 m³ kmol^?1 s^?1. Copyright © 2004 Society of Chemical Industry