Adsorption of Uranium(VI) and Zirconium(IV) from Acid Solutions on Silica Gel

Abstract

Adsorption of uranium(VI) and zirconium(IV) from aqueous solutions on silica gel was investigated by the batch equilibration method. The influence of shaking time and concentrations of nitric acid (i.e., pH of solution) and metal ions in solution were studied. Adsorption of uranium(VI) and zirconium(IV) increases with an increase of pH (decrease of nitric acid concentration) and ion concentrations. The adsorption mechanism of uranium(VI) and zirconium(IV) from aqueous solutions on silica gel is proposed. It is shown that zirconium(IV) and uranium(VI) can be separated if the concentration of nitric acid in solution is higher than 0.01 mol/dm³.     

Adsorption of Acetaldehyde,Propionaldehyde, and Butyraldehyde on Silica Gel

Abstract

Adsorption isotherms of acetaldehyde, propionaldehyde, and butyraldehyde on Davison silica gel were determined gravimetrically at three temperatures. The isoteric heat of adsorption initially increased at low loading and then decreased monotonically with an increase in loading. The equilibrium adsorption data were successfully correlated by Polanyi's potential theory. The equilibrium data were also correlated with the Langmuir, BET, Freundlich, and the Hines et al. models. The Freundlich and the Hines et al. models provided the best fit to the data, while the BET equation was found to be applicable only for a relative pressure range of 0.05 to 0.2. The monolayer surface coverages of silica gel by all of the aldehydes estimated by the Langmuir equation were found to be consistently higher than those calculated from the BET equation, except for acetaldehyde at 306.5 K.     

Adsorption and Thermal Desorption of Volatile Organic Compounds in a Fixed Bed – Experimental and Modeling

Adsorption and thermal desorption dynamics of acetone in fixed-bed silica gel were studied experimentally and theoretically. The effect of process factors on adsorption and desorption performances was established. Acetone adsorption from air stream was performed by the dynamic (flowing gas) method in a laboratory setup at two levels of air superficial velocity (0.7 and 1.7 cm s^?1), temperature (30 and 40°C), and adsorbent particle diameter (0.21 and 0.54 cm). The values of saturation adsorption capacity (0.147–0.270 g g^?1) increased up to 78% and 36%, respectively, with a decrease in air velocity and adsorption temperature. Acetone thermal desorption from spent silica gel was studied in a thermobalance at three levels of process temperature (60, 70, and 80°C) and two values of particle size (0.21 and 0.54 cm). Equilibrium desorption efficiency (63–81%) was up to 14% larger for finer particles and increased with the desorption temperature. Kinetic models with relevant parameters adjusted based on experimental data were adopted to predict the dynamics of acetone adsorption and thermal desorption. The models simulated well the real conditions and could be applied to scale up and operate the adsorption columns used for air remediation.     

Impulse Response Analysis for Adsorption of Ethyl Acetate on Activated Carbon in Supercritical Carbon Dioxide

Abstract

Adsorption equilibria and mass transport properties for ethyl acetate on activated carbon have been evaluated in the presence of supercritical carbon dioxide by means of the impulse response technique. A two-column system, one for dissolving solute and one for adsorption, was used to evaluate the phenomena purely in the adsorption column. The adsorption equilibrium constant was larger for higher temperature and lower pressure. The apparent heat of adsorption calculated from the temperature dependence of the adsorption equilibrium constant was 30–40 kJ/mol. The intraparticle effective diffusivity was larger for higher temperature and lower pressure. The Peclet number that relates to the axial dispersion coefficient was 0.08–0.39. These estimated parameters are in good agreement with those obtained from desorption measurements reported in the literature.     

Adsorption of 2-phenylethyl alcohol on silica aerogel from saturated solution in supercritical CO2

Adsorption of 2-phenylethyl alcohol (PEA) from supercritical CO₂ onto silica aerogel was investigated. A monolayer to multilayer adsorption isotherm was observed, measured at 15.0 MPa and 323.2 K, from the PEA-unsaturated to PEA-saturated supercritical CO₂, indicating the potential utility of the solute-saturated supercritical adsorption (SSA)_. The amount of PEA adsorbed on the silica aerogel with SSA at different temperatures and pressures was measured, and the release of PEA from the aerogel at 303.2 K was also evaluated. A theoretical model for the SSA equilibrium was developed with the assistance of the adsorption isotherms of pure CO₂ onto the silica and considering a three-phase binary system, where the two-dimensional van der Waals equation of state and the three-dimensional Stryjek–Vera modification of the Peng–Robinson equation of state were used respectively to describe the adsorbed phase and the bulk phases (vapor phase and liquid phase). Results showed that the model was capable of describing the adsorption behavior of the system with an average absolute relative deviation of 3.3%.     

吸附制冷用复合吸附剂的吸附性能

固体吸附式制冷因具有环保和节能两大优势,成为国内外竞相开发的热点,尤其是将其用于新型空调系统和太阳能应用产品方面的开发研究备受关注．但从实用化研究成果来看,还远不满足工业化条件,其主要原因之一是受吸附制冷工质对（吸附剂-制冷剂）的性能制约．目前,国内外关于吸附制冷工质对的研究报道比较多,所采用的吸附（工）质仍然以水、甲醇、乙醇和氨为主,对于吸附剂的研究进展比较快,已从当初单一组分吸附剂的选用发展到目前多组分、复合吸附剂的研制．研制性能优良的吸附剂被认为是推动固体吸附式制冷工业化的关键之一．     

Batch Adsorber Rate Analysis of Methylene Blue on Amberlite and Clinoptilolite

Abstract

Adsorption of Methylene Blue on clinoptilolite and on Amberlite XAD‐4 was investigated in a temperature range of 20–50°C, in a batch adsorber. Results of this work showed that clinoptilolite was a better sorbent than Amberlite XAD‐4 for the removal of Methylene Blue. Among the four adsorption rate models tested in the analysis of the adsorption rate data, a simple single parameter diffusion model (Model C) was shown as the best model to be used in practical applications. The diffusivity found from this model was not dependent on the adsorbate concentration. Although the pseudo‐first order adsorption rate model also gave good agreement with the experimental data obtained at the initial periods of the adsorption experiments, the concentration dependence of the rate constant of this model was found as the major disadvantage of this model. Results indicated that dissociative chemisorption and blocking of some of the pores during adsorption caused high tortuosity factors and a decrease in the adsorption rate. Adsorption capacity of these adsorbents were also found to be increased significantly by a decrease of the pH of the solution from 10 to 3.     

Correlation of Methyl Chloride,Methylene Chloride,Chloroform, and Carbon Tetrachloride Adsorption Data on Silica Gel

Abstract

Adsorption data of the homologous series methyl chloride, methylene chloride, chloroform, and carbon tetrachloride on silica gel were measured gravimetrically at 288, 293, and 298 K. For all the chlorinated hydrocarbons examined, the isotherms were Type I, showing no apparent hysteresis between the adsorption and desorption cycles. Experimental data were compared with the calculated equilibrium uptake as predicted by a synthetic heterogeneous isotherm model in which the local isotherm on a site is given by the Jovanovic equation and the distribution of energetically different sites is represented by a Morse-type energy distribution function. The absolute errors between the values calculated by the heterogeneous isotherm model and the experimental data ranged from 1.17 to 2.67%. Energy distribution functions showed that silica gel exhibits the same degree of heterogeneity for all of the adsorbates in the homologous series.     

Iminodiacetic acid‐containing polymer brushes grafted onto silica gel for preconcentration and determination of copper(II) in environmental samples

Silica gel has been modified by silylation with 3‐mercaptopropyltrimethoxysilane followed by graft polymerization of dimethylacrylamide and (N,N‐bis‐carboxymethyl)amino‐3‐allylglycerol‐co‐dimethylacrylamide, synthesized via the reaction of allyl glycidyl ether with iminodiacetic acid. The sorbent, poly(AGE/IDA‐co‐DMAA)‐grafted silica gel, has been characterized by FTIR, elemental analysis, thermogravimetric analysis (TGA), FT‐Raman, and scanning electron microscopy and studied for the preconcentration and determination of trace amounts of Cu(II) ion in environmental water samples. The optimum pH value for quantitative sorption of Cu(II) in batch mode was 5.5 and desorption was achieved, using 0.5 mol L^?1 nitric acid. The sorption capacity of functionalized sorbent is 32.3 mg g^?1. The chelating sorbent was reused for 15 sorption–desorption cycles without any significant change in sorption capacity. The profile of copper uptake by the sorbent reflected good accessibility of the chelating sites in the poly(AGE/IDA‐co‐DMAA)‐grafted silica gel. Scatchard analysis demonstrated homogeneous nature of binding sites. The equilibrium adsorption data of Cu(II) on modified sorbent were analyzed by Langmuir, Freundlich, Temkin, and Redlich–Peterson models. Based on equilibrium adsorption data, the Langmuir, Freundlich, and Temkin constants were determined as 0.0665, 4.26, and 8.34, respectively, at pH 5.5 and 20°C. Adsorption isotherms were analyzed at different temperatures to obtain free energy, enthalpy, and entropy of adsorption. The method was applied for Cu(II) determination in sea water samples. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adsorption of Phenol and Nitrophenol Isomers onto Montmorillonite Modified with Hexadecyltrimethylammonium Cation

ABSTRACT

Single- and two-component competitive adsorptions were carried out in a batch adsorber to investigate the adsorption behavior of phenol and 2-, 3-, and 4-nitrophen-ols in aqueous solution at 25°C onto hexadecyltrimethylammonium (HDTMA)-treated montmorillonite. HDTMA cation was exchanged for metal cations on the montmorillonite to prepare HDTMA—montmorillonite, changing its surface property from hydrophilic to organophilic. Effective solid diffusivity of HDTMA cation in the montmorillonite particle was estimated to be about 3 × 10^?12 cm²/s by fitting the film-solid diffusion model to a set of HDTMA adsorption kinetic data onto mont-morillonite. Adsorption affinity on HDTMA—montmorillonite was found to be in the order 3-nitrophenol = 4-nitrophenol > 2-nitrophenol > phenol. The Langmuir and the Redlich—Peterson (RP) adsorption models were used to analyze the single component adsorption equilibria. The ideal adsorbed solution theory (IAST) and the Langmuir competitive model (LCM) were used to predict the multicomponent competitive adsorption equilibria. These models yielded favorable representations of both individ-ual and competitive adsorption behaviors.     

Criteria for Selection of an Adsorbent for a Temperature Swing Process: Applied to Purification of an Aliphatic Solvent Contaminated with Aromatic Solutes

Abstract

Temperature swing adsorption (TSA) is different in several respects from conventional adsorption. This paper explores the distinctions from the standpoint of adsorbent characteristics. In particular, a fixed-bed TSA process is considered for separating dilute aromatics from aliphatics (e.g., toluene and/or xylene in heptane). Relevant adsorbent characteristics include thermal-exchange capacity and properties that affect dissipative effects, e.g., intraparticle diffusivity, bed permeability, axial dispersion coefficient, and thermal diffusivity. Many of the dissipative effects can be manipulated by adjusting particle size, though trade-offs exist that have no clear-cut technical resolution. The adsorbents considered were silica gel, activated alumina, activated carbon, zeolite 13X, and a polymeric adsorbent (XAD-7). Silica gel was selected due to its superior thermal-exchange capacity. The other properties did not vary enough among the other adsorbents to compensate for their lesser capacities.     

Production and characterization of a novel hierarchical porous silica adsorbent for removal of methylene blue dye from wastewaters

Adsorption of methylene blue (MB) dye by hierarchical porous silica (HPS) is reported as a means of removing the dye from wastewater. HPS was produced through a sol–gel process by templating on rubber particles in skimmed natural rubber latex. The silica precursor was tetraethyl orthosilicate and the costructure directing agent was 3-aminopropyltriethoxysilane. Based on nitrogen-sorption, the HPS had a total pore volume of 1.0?cm³/g, a specific surface area of 237?m²/g, and a peak pore size of 4?nm. Larger pores (sizes >100?nm to 1?µm) were observed by scanning electron microscopy. The pores had an ink-bottle morphology of narrow necks connected to large cavities. The adsorption obeyed the Langmuir isotherm and was endothermic. Pseudo-second-order adsorption kinetics were observed. The specific adsorption of MB on HPS was 0.225?mmol/g at equilibrium. HPS was superior to many adsorbents reported for removing MB from aqueous media.     

Fluoride Removal from Water with Spent Catalyst

Abstract

The adsorption of fluoride from water with spent catalyst was studied. Adsorption density of fluoride decreased with increasing pH. Linear adsorption isotherm was utilized to describe the adsorption reaction. The adsorption was a first-order reaction, and the rate constant increased with decreasing surface loading. Adsorption reaction of fluoride onto spent catalyst was endothermic, and the reaction rate increased slightly with increasing temperature. Fluoro-alumino complex and free fluoride ion were involved in the adsorption reaction. It is proposed that both the silica and alumina fractions of spent catalyst contribute to the removal of fluoride from aqueous solution. Coulombic interaction is proposed as the major driving force of the adsorption reaction of fluoride onto spent catalyst.     

Adsorption equilibria for m-cresol,quinoline, and 1-naphthol onto silica gel

Adsorption isotherms for m-cresol, quinoline, and 1-naphthol onto silica gel in n-hexane at 30°C were measured in the concentration range of 1–30 mole/m³. The experimental results for m-cresol and quinoline were well represented by the generalized Toth isolherm, and for 1-naphthol by the superimposed two sites Langmuir model. At low concentrations the adsorbed amounts onto silica gel were decreased in sequence of quinoline, 1-naphthol, and m-cresol. However as the concentration increased, the sequence was reversed. For binary systems, the competitive adsorption was quantitatively studied by introducing the competitive adsorption coefficient. The relative affinity of quinoline with respect to silica surface was larger than those of the other two components.     

Thin-Layer Chromatography of Metal Ions in Formic Acid Medium on Impregnated and Unimpregnated Silica Gel G: Semiquantitative Determination of Fe3+, Cd2+, Th4+, Al3+, Zn2+, UO2+ 2, VO2+, Ce4+, and Ni2+

Abstract

The adsorption behavior of metal ions in the formic acid-sodium formate system using unimpregnated as well as impregnated silica gel G as thin layers has been studied. A remarkable result of this study is the dramatic selectivity of impregnated silica gel G thin layers when compared to the corresponding unimpregnated silica gel G thin layers. This impregnation effect provides us with a new adsorbent phase which is sufficiently stable in the formic acid-sodium formate medium. Some important ternary separations have been achieved on silica gel G thin layers. Al³⁺, Ni²⁺, Fe³⁺, and Pb²⁺ have been qualitatively separated from mixtures of other ions. Cu²⁺ has been selectively separated on impregnated silica gel G thin layers. The semi-quantitative determination of nine metal ions on impregnated silica gel G layers has also been attempted.     

Synthesis and characterization of a surface imprinting silica gel polymer functionalized with phosphonic acid groups for selective adsorption of Fe(III) from aqueous solution

A Fe(III) ion‐imprinted silica gel polymer functionalized with phosphonic acid groups (IIP‐PA/SiO₂) was prepared with surface imprinting technique by using Fe(III) ion as template ion, grafted silica gel as support, and vinylphosphonic acid as functional monomer. The polymer was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller, and thermogravimetric analysis. The synthesized imprinted silica gel polymer was used as a sorbent for Fe(III) adsorption. The adsorption properties, such as the effect of solution pH, adsorption kinetic, adsorption isotherm, adsorption selectivity as well as the regeneration of sorbent were studied. The results showd that the prepared sorbent (IIP‐PA/SiO₂) had a short adsorption equilibrium time (12 min) and high adsorption capacity (29.92 mg g^?1) for Fe(III) at the optimal pH of 2.0. The selectivity coefficients of the sorbent for Fe(III) in presence of Cr(III), M_n (II), and Zn(II) were 51.76, 27.86, and 207. 76, respectively. Moreover, the adsorption capacity of the prepared sorbent did not decrease significantly after six repeated use. Thus, the prepared ion‐imprinted silica gel polymer was a promising candidate sorbent for the selective adsorption of Fe(III) from aqueous solutions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45165.     

Liquid-phase diffusivity of benzene within mesoporous materials measured by a laser Raman technique

The intracrystalline diffusivities of benzene within a series of porous materials in the liquid phase (cyclohexane was used as solvent) were measured by a constant volumetric method using Raman spectroscopy at a temperature range from 323 to 393 K. Silicalite-1, mono-dispersed mesoporous silica spheres (MMSS), silica gel, γ-Al₂O₃, and SiO₂–Al₂O₃ were used as adsorbents. The intracrystalline diffusivity was calculated by parameter fitting using theoretical equations and the experimental transient change of benzene concentrations with time in response to the adsorption. The intracrystalline diffusivities of benzene within mesoporous silicas were almost the same as that within the micropore of silicalite-1, though the pore diameters of silicalite-1 and mesoporous silicas were different from each other. It is considered that the pore walls as well as the solvent molecules of cyclohexane affect the diffusion of benzene molecules in the mesopore region.     

Adsorption Behavior of Iminodiacetic Acid Type of Chelating Gel Prepared from Waste Paper

Abstract

Adsorption gel was prepared from waste recycled paper by immobilizing iminodiacetic acid (IDA) functional group by chemical modification. The gel exhibited good adsorption behavior for a number of metal ions viz. Cu(II), Pb(II), Fe(III), Ni(II), Cd(II), and Co(II) at acidic pH. The order of selectivity was found to be as follows: Cu(II)>Pb(II)>Fe(III)>Ni(II)～Cd(II)～Co(II). From the adsorption isotherms, the maximum adsorption capacity of the gel for both Cu(II) and Pb(II) was found to be 0.47 mol/kg whereas that for Cd(II) was 0.24 mol/kg. A continuous flow experiment for Cd(II) showed that the gel can be useful for pre‐concentration and complete removal of Cd(II) from aqueous solution.     

Least squares estimation of kinetic parameters in batch adsorption of phenol with confidence interval analysis

Adsorption kinetics of phenol on granular coconut shell activated carbon and granular coal based activated carbon was investigated by the model of homogeneous surface diffusion plus external film mass transfer with the stirred batch adsorber. The model was solved numerically by finite element and the parameter estimation was performed with the nonlinear least squares method. Through the confidence interval analysis and evaluation of the error sum of squares, higher precision of the parameter estimates can be obtained by combining more decay curves; the decay curves with the different initial solution concentrations and adsorbent dosages can be well represented with identical film mass transfer coefficient and surface diffusivity, and the effect of surface adsorption coverage on the surface diffusivity is negligible in the adsorption systems. The values of the film mass transfer coefficient and surface diffusivity are in the order of magnitude 10^?5 and 10^?12, respectively.