Sorption of dissolved organics from aqueous solution by polystyrene resins—II. External and internal mass transfer

External and internal mass transfer were characterized for the sorption of 2,4-dichlorophenol and p-nitrophenol on polystyrene resins. An evaluation method is presented which estimated the external mass-transfer coefficient, κ_L, from the concentration uptake in an integral fixed-bed reactor. The experimental κ_L values are compared with values predicted using four different empirical correlations. The effect of axial dispersion on the values of κ_L was shown to be small under the given conditions.To quantify the intraparticle mass transfer, an effective diffusion coefficient, D_eff, was estimated using the pore diffusion model interpretation of data from a differential column reactor within a recirculated batch system. The D_eff values depend on both resin structure and solute properties. Values of D_eff between 0.3 × 10⁻⁹ and 1.8 × 10⁻⁹ m²/s were observed for macroporous resins, which exceed values that are characteristic of pore diffusion, and a value of 0.6 × 10⁻¹¹ m²/s was estimated for a microporous resin.     

Preparation,characterization, and performance evaluation of LTA zeolite–ceramic composite membrane by separation of BSA from aqueous solution

Using low-cost clay supports as substrates, ceramic–LTA zeolite composite membranes (Z1–Z4) were fabricated with hydrothermal crystallization. The composite membranes were achieved with variations in the sequential zeolite depositional steps. For Z1–Z4 membranes, various characterization techniques such as thermogravimetric (TG), particle size distribution (PSD), X-ray diffraction (XRD), and field emission scanning electron microscopic (FE-SEM) analysis were applied. For the Z1–Z4 membranes, the pure water permeability, porosity, and average pore size varied from 1.22 × 10^?7 to 1.19 × 10^?8 m³/m²s kPa, 30–23%, and 215–76 nm, respectively. For the Z4 membrane, ultrafiltration experiments were conducted at a pH of 2.5 and transmembrane pressure differential of 207 kPa using aqueous bovine serum albumin (BSA) solutions. The optimal flux and rejection correspond to 4.54 × 10^?7 m³/m²s and 80%, respectively.     

Kinetics and thermodynamics of U(Ⅵ) adsorption from aqueous solution by modified corncob

The corncob was microwave-assistedly modified by KMnO₄ and used for adsorption of U(Ⅵ)ions from aqueous solution.The kinetics and thermodynamics of their adsorption were measured using batch experiments.The results show that the kinetics of adsorption follows well the pseudo-second order equation,indicating that the uranium adsorption by the modified corncob is mainly chemisorption. The Langmuir,Freundlich and D-R isothermal adsorption models were used to relate the equilibrium data,finding that Langmuir isotherm of monolayer adsorption is better fitting them,pointing out that the adsorption mainly occurs on surface active sites of modified corncob.The values of apparent activation energy E_a and average adsorption energy E_s support also the suggestion that adsorption of U(Ⅵ) on modified corncob is mainly chemisorption,although some physical adsorption can not be got rid of.The thermodynamic parameters(ΔH,ΔS and ΔG)calculated from the adsorption isotherms at various temperatures indicated that the adsorption of U(Ⅵ)on modified corncob is an endothermic,spontaneous process and more favorable at higher temperature.     

Sorption in zeolites—I: Sorption of single component and binary sorbate systems

Sorption in zeolites with parallel and non-intersecting channels is described by a molecular model. The experiments usually conducted to measure diffusivities at different sorbate concentrations are simulated using a Monte-Carlo type of approach. Simulations depict increase in diffusivity with sorbate concentration which is in quantitative agreement with Darken's equation. The approach permits interpretation of the increase in diffusivity from the kinetic consideration. The model is further extended to simultaneous sorption of two sorbates and the dependence of apparent diffusivities in the binary system on sorbate concentration and intrinsic diffusivities of the sorbates is examined.     

Boron separation by adsorption and flotation with Mg–Al-LDHs and SDBS from aqueous solution

Layered double hydroxides(LDHs) have been shown to be effective adsorbents for boron. However, solid–liquid separation is still a problem when separating boron from industrial radioactive waste liquid. In this research, three types of Mg–Al-LDHs including Mg–Al-LDH(NO₃^–), Mg–Al-LDH(Cl^–) and Mg–Al-LDH(SO₄^2–)were applied to adsorb boron, and moreover sodium dodecylbenzenesulfonate(SDBS) was used to float the LDH particles from aqueous solution...     

In-situ characterization of RF field induced reactions by Raman spectroscopy — I. Urethane formation kinetics and mechanisms

The effects of radiofrequency (RF) electromagnetic field on the kinetics and mechanism of a series of secondary alcohol and phenylisocyanate reactions were studied by in-situ Raman spectroscopy. The urethane reaction rates under intense RF fields increased significantly. A 2-propanol and phenylisocyanate reaction under an RF field of 6.3 kV/cm could reach 90 percent conversion in less than 150 seconds, yet it took more than 30 min without the exposure to an RF field. The maximum reaction rate of such a reaction system increased from 0.4 to 1.6 percent per second when the RF field intensity increased from 1.6 to 6.3 kV/cm. Reaction kinetics simulation based on a simple kinetic model was employed to analyze the mechanisms of these reactions. The simulation results suggest that an intense RF field has no direct influence on urethane reaction mechanism and kinetic parameters. The main effect of an RF field on pure urethane reactions is the dielectric heating effect. Although the heat generated during the reaction due to the systems' dielectric loss is small, an intense RF field creates high initial heating rates, which induces high heat generation of these exothermic reaction (urethane) systems, and results in high reaction temperatures (from 20°C to 160°C in about 45 seconds for a 2-propanol and phenylisocyanate reaction under an RF field of 6.3 kV/cm).     

Adsorption of chromium(VI) from aqueous solution by Artist’s Bracket fungi

The objective of this study was to investigate Artist’s Bracket (AB) fungi for the removal of Cr(VI) from aqueous solutions. The effects of pH, adsorbent dosage, temperature, contact time and initial concentration of Cr(VI) were evaluated. The optimal pH value for the removal of Cr(VI) was at pH 2. Moreover, the results showed that the adsorption of Cr(VI) decreased by increasing the initial Cr(VI) concentration and pH. The absorption of Cr(VI) on AB can be described by both Freundlich and Langmuir isotherm models. In addition, both pseudo-first-order and pseudo-second-order kinetic model well described the adsorption of Cr(VI) onto AB.     

Removal of diclofenac from aqueous solution with multi-walled carbon nanotubes modified by nitric acid☆

Modified multi-walled carbon nanotubes (MWCNTs) were used as adsorbents for removal of diclofenac. The re-action conditions were examined. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models were applied to determine appropriate equilibrium expression. The results show that the experimental data fit the Freundlich equation well. Thermodynamic parameters show that the adsorption process is spontaneous and exothermic. The kinetic study indicates that the adsorption of diclofenac can be well described with the pseudo-second-order kinetic model and the process is controlled by multiple steps.     

Modeling of removal of an organophosphorus pesticide from aqueous solution by amagnetic metal–organic framework composite

Today, a variety of pesticides are used to fight plant pests in the world. The entry of these resistant pollutants into water resources can have devastating effects on human health and the environment, hence their removal from the environment is a vital task. In the present work, the magnetic iron-based metal–organic framework (Fe₃O₄/MIL-101 (Fe)) was synthesized by a simple and feasible method and characterized by FT-IR, XRD, BET, FESEM, TEM, TGA, and VSM techniques. The synthesized nanocomposite was successfully applied for the removal of fenitrothion (FEN) pesticide from the aqueous solutions. The isothermal and kinetic models were also investigated. The Langmuir isotherm model (type I) and pseudo-second-order kinetic model were more consistent in the adsorption process. The thermodynamic parameters of fenitrothion sorption were also calculated. The results revealed that the adsorption of fenitrothion onto Fe₃O₄/MIL-101 (Fe) was spontaneous and endothermic under optimized conditions. Moreover, the removal efficiency of FEN was predicted using the developed fuzzy logic model. Four input variables including the initial concentration of FEN (mg·L^-1), pH of the solution, adsorbent dosage (mg), and contact time (min) versus removal efficiency as output were fuzzified by the usage of an artificial intelligence-based method. The fuzzy subsets consisted of Triangular and Trapezoidal membership functions (MFs) with six levels and a total of 23 rules in IF-THEN format which was applied on a Mamdani inference system. The obtained coefficient of determination value (=0.98205) proved the excellent accuracy of the fuzzy logic model as a powerful tool for the prediction of FEN removal efficiency.     

Stable isotope characterization of olive oils. I—Compositional and carbon-13 profiles of fatty acids

Nearly 200 olive oils produced in the Mediterranean basin, mainly in Greece, during 4 yr from 1993 to 1996, were studied by gas chromatography (GC) and on-line GC-isotope ratio mass spectrometry (GC-C-IRMS). The composition of the oils in the more abundant fatty acids (C_16:0, C_16:1, C_18:0, C_18:1, C_18:2, and C_18:3) was obtained by GC after transesterification of the triglycerides into methyl esters. Using the hyphenated GC-C-IRMS technique, the ¹³C contents of the three most abundant acids, C_16:0, C_18:1, and C_18:2, were measured with satisfactory accuracy. The results, analyzed in terms of geographical, temporal, and botanical factors, provide new criteria for the authentication of olive oils.     

Acid–base properties of ion exchangers. I. Optimising of potentiometric titration of ion exchangers exemplified by carboxylic acid resins

The aim of this work was to determined conditions for fast titration the ion exchanger in the one-sample experiment allowing obtaining its equilibrium titration curve. Carboxylic acid ion exchangers KB-4 and Dowex MAC-3 were taken as examples. They were titrated under different conditions with NaOH, KOH and Ba(OH)₂. The forward and backward titration of concentrated immersions of finely ground ion exchanger in the electrolyte solutions with 20-min intervals between additions of the titrants of high concentration gave close results, identical to the results of the batch experiment if concentration of the supporting electrolyte was sufficiently high (1 M). It appeared possible to obtain equilibrium potentiometric titration curves in one working day and use this method for express control of properties of ion exchangers.     

Adsorption of thiourea at the polycrystalline silver electrode from aqueous KF solutions—I

Differential capacity of polycrystalline silver electrode in aqueous KF solutions containing thiourea (TU) of concentrations from 0.001 to 0.25 mol dm⁻³ has been measured by the previously described potentiostatic method [M. Brzowstowska-Smolska et al., J. electroanal. Chem.89, 389 (1978)]. The TU adsorption is discussed on the basis of differential capacity results and the potential shift caused by TU concentration changes. Furthermore, the surface pressure has been obtained by integration of the ΔE_σM vs σ_M curves for a number of TU concentrations.     

Equilibrium theory revisited. Isothermal fixed-bed sorption of binary systems—I. Solutes obeying the binary langmuir isotherm

We consider, in Part I of this series, the isothermal equilibrium sorption of two solutes obeying the binary Langmuir isotherm in convective flow of a fluid through a particulate sorptive medium. The pioneering treatment of Glueckauf [Proc. R. Soc.A186, 35 (1946); Discuss. Faraday Soc.7, 12 (1949)] is reexamined and extended by means of simple geometric concepts which allow for a rapid analysis and prediction of solute behaviour in such systems. Most of these carry over to broad classes of non-Langmuir solutes as well (cf. Parts II and III). Conventional adsorption and desorption operations are considered, as well as mutual displacement of the individual solutes. We formulate the I → F rule which relates solute trajectories to the slopes of the characteristics linking initial state I and feed state F. Simple methods are described for deriving breakthrough and desorption times, bed and purge requirements, and the degree of enrichment (“roll-up”) and recovery of pure solute. The significance of the watershed point is discussed in terms of its role in displacement operations. It is shown that below the watershed concentration, a strongly sorbed (“heavy”) displacement agent is no more effective than clean carrier fluid, and less so than a weakly held (“light”) solute. A particularly simple geometric construction is proposed which allows the prediction of the degree of solute enrichment in the displacement of a light or heavy component by its partner. Much of this information is derived directly from pure component isotherms, q = f (Y). Indeed, the entire q-Y hodograph space emerges as a powerful tool for the analysis particularly of non-Langmuir solutes. These are taken up in Parts II and III.     

Removal of 4-nitrophenol from binary aqueous solution with aniline by granular activated carbon using Taguchi’s design of experimental methodology

This paper reports the studies on the simultaneous removal of aniline and 4-nitrophenol from aqueous solutions of the binaries using granular activated carbon as an adsorbent. The effect of operating parameters such as initial component concentrations, temperature, adsorbent dosage and contact time on the adsorption of the above said mixtures of solutes in the binary aqueous solution was studied. Taguchi’s method of design of experiments was used to study the effect of each parameter at three levels on the selected response characteristic (total amount of solutes adsorbed on granular activated carbon (q _tot , mmol/g)).The analysis of variance shows that the adsorbent dosage is the most significant parameter affecting the adsorption process with 22.42 and 37.62% contribution to q _tot and signal-to-noise ratio data. The contribution of interactions between initial concentration of binary components is also significant. Confirmation experiments were carried out to check the effectiveness of the Taguchi’s methodology at the optimum levels of process parameters.     

Application of ZnO–NiO greenly synthesized nanocomposite adsorbent on the elimination of organic dye from aqueous solutions: Kinetics and equilibrium

Organic dyes are discharged into aquatic systems from several industries causing severe environmental problems and toxicity to aquatic life. Therefore, it should be removed from water with a suitable process. Among several treatment processes, adsorption is one of the most attractive because of its simplicity, efficiency, and low operating cost. Moreover, adsorption supports environmental sustainability if a suitable adsorbent is used. In this work, a green route was followed to prepare ZnO: NiO nanocomposites using the Neem leaf extract as a stabilizing agent instead of harmful chemicals. Four different samples with three different ZnO:NiO ratios were prepared, namely: 3Z:1 N, 1Z:1 N, 1Z:3 N and 1Z:1 N without extract. The samples were characterized by XRD, TEM, SEM, IR, and UV, which all confirmed the successful synthesis of the nanocomposites. The nanocomposites were used for the adsorption of methyl orange (MO) from aqueous solutions. The four nanocomposites prepared with the aid of the extract showed a high sensitivity with 100% removal of MO from 6.25 ppm solutions. Furthermore, all the samples have a relatively fast kinetic with an equilibrium time less than 1 h. Also, the three samples maintained 100% removal efficiency after 5 adsorption-desorption cycles. The difference in particle size distribution obtained for the 1Z:1 N prepared with and without the extract confirms the important rule of the extract as a capping agent with an average size of 18 nm for the sample with the extract and 88 nm for the sample prepared without the extract. This difference in the particle sizes has been reflected on the adsorption performance of the two samples with a maximum adsorption capacity of 33 mg/g for the sample prepared with the extract compared to 6 mg/g for the sample without the extract.     

Separation and Recovery of Silver(I) Ions from Base Metal Ions by Melamine‐formaldehyde‐thiourea (MFT) Chelating Resin

Abstract

Melamine‐formaldehyde‐thiourea (MFT) chelating resin were prepared using melamine (2,4,6‐triamino‐1,3,5‐triazine), formaldehyde, and thiourea and this resin has been used for separation and recovery of silver(I) ions from copper(II) and zinc(II) base metals and calcium(II) alkaline‐earth metal in aqueous solution. The MFT chelating resin was characterized by elemental analysis and FT‐IR spectra. The effect of pH, adsorption capacity, and equilibrium time by batch method and adsorption, elution, flow rate, column capacity, and recovery by column method were studied. The maximum uptake values of MFT resin were found as 60.05 mg Ag⁺/g by batch method and 11.08 mg Ag⁺/g, 0.052 mg Zn²⁺/g, 0.083 mg Cu²⁺/g and 0.020 mg Ca²⁺/g by column method. It was seen that MFT resin showed higher uptake behavior for silver(I) ions than base and earth metals due to chelation.     

Removal of tylosin from aqueous solution by UV/nano Ag/S2O 8 2− process : Influence of operational parameters and kinetic study

The present work deals with the photooxidative degradation of tylosin antibiotic (TYL) in the presence of potassium peroxydisulfate (K₂S₂O₈) irradiated by UV-C in the presence of immobilized nano silver. Effects of pH, temperature, peroxydisulfate concentration and immobilized nano silver dosage on the degradation efficiency of TYL were examined. Degradation efficiency was small when the oxidation was carried out in the absence of UV irradiation. Results showed that degradation of TYL increases with temperature, nano Ag and peroxydisulfate initial concentration and decreases with pH. Due to UV/nano Ag/S₂O ₈ ^2? processes, more than 90% of TYL can be degraded at room temperature in 35 min at an initial concentration of 50 mgl^?. Degradation reaction order of TYL by UV/nano Ag/S₂O ₈ ^2? process is 1.89. Meanwhile, the initial rates of degradation in UV/nano Ag/S₂O ₈ ^2? processes can be described well by the Langmuir-Hinshelwood kinetic model.     

Synthesis and mechanical and tribological characterization of alumina–yttria stabilized zirconia (YSZ) nanocomposites with YSZ synthesized by means of an aqueous solution–gel method or a hydrothermal route

In the present study, yttria stabilized zirconia (YSZ) nanoparticles, prepared by means of an aqueous solution–gel method or a hydrothermal route, are incorporated in a matrix of submicron alumina particles by wet mechanical milling. The microstructural characteristics and the mechanical and tribological properties of the obtained alumina–YSZ nanocomposites are evaluated as a function of different processing conditions like milling time, YSZ amount, sintering procedure and synthesis method of YSZ.     

Passivation of zinc in concentrated alkaline solution—I. Characteristics of active dissolution prior to passivation

As a preliminary stage in the study of the active—passive transition on zinc in concentrated (6.8 mol dm⁻³ solutions of KOH the reported mechanisms have been reviewed and the characteristics of active dissolution prior to passivation have been investigated. The theory of Armstrong and Bulman has been extended in order to relate all the experimentally important parameters. These include electrode potential, current, angular electrode rotation speed and surface concentrations of Zn(OH)²⁻₄ and OH⁻ ions. In common with other observations, it is demonstrated that zinc dissolves quasi-reversibly over a considerable range of potentials. The relationship of this behaviour to other metal/metal-ion systems is discussed. At high current densities (> 100 mA cm⁻²) depletion of hydroxide ions occurs at the zinc surface causing a severe deviation in the exponential dependence of the active dissolution current on potential.