Equilibrium Sorption Studies Research Articles

Organoclay with Soil-Bentonite Admixture as Waste Containment Barriers

Organoclays, clays modified by cationic surfactants, for engineering applications have recently drawn great attention because of their high organic removal capacity. In this study, the potential use of organoclays with soil-bentonite admixtures as waste containment barriers is investigated by experimental tests such as batch equilibrium sorption studies, compaction tests, and hydraulic conductivity tests. Sorption isotherms of total organic carbon (TOC), a gross organic term, by five different types of soil admixtures are nonlinear. The soil specimen with more organoclays exhibits higher organic sorption capacity and a larger retardation factor. The specimens with 20% by dry weight of bentonite have higher optimum water content and plasticity. With the addition of bentonite in the soil material consisting of completely decomposed volcanic rock (CDV) (natural soils) and organoclays, the hydraulic conductivity to leachate decreases from about 10−7 to 10−8 cm/s. This indicates that the presence of bentonite ...

Enhancing the Effect of Surfactants in Dyeing of Aramid Fibres

The results of a study of equilibrium sorption of anion-active SF by SVM fibre indicate the high substantivity of sodium alkyl sulfates. When alkyl sulfates are used in an amount below the saturation concentration, the enhancing effect of the SF is due to loosening of the supermolecular structure of the heteroarylene.

Kinetics of Drying of Fibre Materials

The results of a study of equilibrium sorption of anion-active SF by SVM fibre indicate the high substantivity of sodium alkyl sulfates. When alkyl sulfates are used in an amount below the saturation concentration, the enhancing effect of the SF is due to loosening of the supermolecular structure of the heteroarylene.

Removal of Selected Metal Ions from Aqueous Solutions Using Chitosan Flakes

Commercially available chitosans potential in the adsorption of heavy metals like zinc, copper, cadmium, and lead from aqueous solutions under variable physicochemical conditions was investigated. The results obtained from equilibrium and kinetic studies showed that there was significant uptake of these metal ions by chitosan and that chitosan flakes had a maximum sorption capacity for copper ions. The order of metal ion adsorption by chitosan decreased from Cu2+ to Zn2+ as follows: copper lead cadmium zinc. There was a considerable increase in sorption capacity with an increase in chitosan amount; however, this parallelism diminished when the chitosan mass exceeded 0.24 g in 25 mL of metal solution. The sorption of metal ions from various salt solutions by chitosan flakes was not improved by agitation. The heavy metal uptake by chitosan was found to be pH-dependent, with a maximum at pH 6.0 and 7.0. Sorption equilibrium studies were conducted with a constant sorbent weight and varying initial concentration of metal ions. The experimental data of adsorption from solutions containing metal ions were found to correlate well with the Langmuir isotherm equation.

Equilibrium and spectroscopic studies of lead retention in smectite1

Heavy metal pollution of soils and water is a serious environmental problem. Sorption onto solid surfaces from aqueous solutions is an important process influencing transport and accumulation of heavy metals in the environment. Lead (Pb) sorption in smectite SWy‐2 was investigated by equilibrium sorption studies, coupled with spectroscopic methods. The isotherm and pH‐edge of lead sorption in the smectite were measured in batch experiments. The sorption isotherms under uncontrolled pH were best‐fitted with the Langmuir equation, while those with a fixed pH 5.5 were best‐fitted with the Freundlich equation. The pH‐edge of lead sorption shifted to a higher pH as the Pb concentration increased. The ionic strength only affected Pb sorption in the low pH range. The effects of associated nitrate and perchlorate anions were significant only for the Pb sorption at high Pb concentration (>2 mM). FTIR and XRD spectroscopies were performed with oriented clay samples. In the infrared spectra, apeak with a maximum near 1398 cm‐1 and a shoulder centered near 1470 cm‐1 was significant for the samples treated with >1 mM Pb at pH >5.6. This peak may be composed of several IR bands, including an OH bending band from Pb hydroxides and CO3 2‐ stretching bands from Pb carbonates. The basal spacing of Pb‐treated smectites increased with increasing Pb content in the clay and correlated well with the intensity of OH bending band (around 1621 cm‐1) of adsorbed water. The increase of basal spacing at low pH (pH <3.3) was poorly correlated with the intensity of water OH bending band. The comprehensive studies provided many evidences for revealing the structure of various lead complexes on clay surfaces.

Remediation of Metal-Contaminated Leachate using Chitosan Flakes

The objective of this study was to study, under various physicochemical conditions, the ability of chitosan to trap heavy metals leached during remedial washing of contaminated soils with organic extractants. The contaminated soil was washed with 0.1M citric acid, pH 5.5, for 24 h, producing a metal-rich leachate containing 0.06, 0.02, 0.003, and 5.87 μmoles ml−1 of Zn, Cu, Cd, and Pb, respectively. Equilibrium and kinetic sorption studies revealed that chitosan significantly reduced the levels of these metal ions in the leachate. A 12 h mixing of the leachate with chitosan flakes resulted in about 50% reduction in metal ion contents of the leachate. However, the adsorption of metal ions by the chitosan was found to depend on the relative concentrations of metal ions present in the leachate. The mass of chitosan required for achieving adsorption equilibrium was consequently dependent on the initial concentrations of metal ions. Reduction in metal ion contents of the leachate by chitosan flakes did not appear to be significantly improved by agitation. In addition, heavy metal removal by chitosan was found to be highest at pH 6.0. Results from the experiments involving replacement of metal-laden chitosan with fresh chitosan suggested that at least four replacements of chitosan would be required for absolute remediation of the leachate.

Humic Acid-Sensitized Photoreduction of Cr(VI) on ZnO Particles

The possibility that humic acids act as sensitizers in the photoinduced reduction of Cr(VI) to Cr(III) in aqueous suspensions containing ZnO particles was verified. Equilibrium sorption studies showed that Cr(III) is totally adsorbed on ZnO, while Cr(VI) adsorption on ZnO is very low. Solar irradiation of the ZnO suspensions induced the photoreduction of Cr(VI), leading to a marked increase of the amount of chromium adsorbed on the mineral oxide. The yield of the reaction is enhanced both in the presence of humic acids and under anoxic conditions. Humic acids adsorbed onto the oxide surface sensitize Cr(VI) photoreduction and the competitive photoreduction of molecular oxygen leading to hydrogen peroxide.

Comparative sorption equilibrium studies of toxic phenols on flyash and impregnated flyash

AbstractIn the present study, the sorption of toxic phenols, which include phenol, o‐cresol, m‐cresol, p‐cresol, o‐nitrophenol, m‐nitrophenol and p‐nitrophenol, has been investigated. The influences of various factors, such as particle size, impregnation of flyash (IFA), pH and temperature on the sorption capacity have been studied. Equilibrium modelling has been carried out using Langmuir and Freundlich isotherm equations and constants have been calculated under different conditions. Thermodynamic studies have also been carried out and values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) calculated.

Thermal and hydrothermal stabilities of zeolite EU-1

The thermal and hydrothermal stabilities of EU-1 (EUO) framework zeolites were investigated as a function of their aluminium content in both the sodium and protonated forms. A course of decomposition patterns and other thermal effects were followed systematically using thermoanalytical (TG/DTA) methods. The results are discussed with the help of data from XRD, IR, XPS, TPD, 27Al MAS-NMR and equilibrium sorption studies. Samples subject to different calcination and steam treatments were examined. It was found that on increasing framework aluminium in EU-1 zeolites the thermal stability decreased and was less stable in its sodium form. The presence of water vapour during the thermal treatment tended to dealuminate the zeolites, changing their acidity pattern with a decrease in the surface Si/Al ratio. The catalytic activity and the product distribution for m-xylene isomerisation over steamed H/EU-1 catalysts were examined.

Removal of Total Phosphorus and Phosphate by Peat Soils of the Florida Everglades

Traditional estimates of soil and sediment phosphorus retention are based on orthophosphate (PO4) removal from water by soil or sediment columns under saturated water flow. These techniques may not reflect the P uptake of in situ soils accurately because the PO4 concentration of through-flowing water is often below detection limits in nonpolluted wetlands during the growing season. We used peat soils from the Florida Everglades in saturated flow and equilibrium sorption experiments to show that the uptake of PO4 reaches saturation quickly, potentially underestimating soil P binding capacity when compared with total phosphorus (TP) retention. The rate of TP uptake was constant for 2 d, while the rate of PO4 uptake slowed and followed saturation kinetics. The majority of the TP removed was associated with particles within a 1–20 μm size range. Experiments using both NaCl and nonionic detergent (Triton X–100) as well as batch equilibrium sorption studies indicate that the primary mechanism for TP removal by these soils is not straining. Removal of TP by these soils appears to involve abiotic mechanisms that include both hydrophobic and ionic interactions.

Sorption of cadmium and lead ions on modified groundnut (Arachis hypogea) husks

AbstractThe removal of cadmium and lead ions from aqueous solutions by groundnut husks modified by reaction with EDTA (% N = 12.05) was examined by equilibrium sorption studies at 29°C. The maximum metal ion binding capacity of the EDTA‐modified husk determined from the sorption isotherm from solutions of pH 6.8 was found to be 0.36 mmol g−1 and 0.19 mmol g−1 for Cd(II) and Pb(II) ions, respectively. It was found that the rate of sorption was particle‐diffusion controlled, and the particle‐diffusion control rate coefficient was determined to be of the order of 10−2 min−1.

Removal of heavy metal ions from aqueous solutions with melon ( Citrullus vulgaris) seed husks

The removal of cadmium, copper and lead ions from aqueous solutions by melon seed husks was examined by equilibrium and dynamic sorption studies at 29°C. The amounts of the metal ions removed from solution depended on the metal ion type, and were enhanced by EDTA modification of the husks. The distribution coefficient, D, of the metal ions between the adsorbent phase and the bulk aquueous phase showed little variation with the equilibrium concentration of the metal ions, except for Pb(II) ions where the value of D doubled with a five-fold change in the equilibrium concentration. The sorption data fitted the Langmuir isotherm equation and maximum metal-ion binding capacities of 23·3 mg/g husk and 11·4 mg/g husk were predicted for Cd(II) ions and Cu(II) ions respectively. Relatively higher proportions of Pb(II) ions were removed from solution by melon husks in the column experiments. Pb(II) ions sorbed on melon husks can be quantitatively recovered by treatment with dilute acid.

Anion-involvement in electrochemical transformations of polyaniline. A radiotracer study

The sorption of labelled HSO − 4 and SO 2− 4 ions into polyaniline films was studied by a radiotracer method. Simultaneous voltammetric and voltradiometric measurements and equilibrium sorption studies were carried out. It was found that the oxidation/reduction processes are accompanied by simultaneous changes in the anion sorption. Relationship between anion sorption and redox behaviour is discussed.

Sorption of Cadmium, Lead and Zinc Ions on Sulphur-Containing Chemically Modified Cellulosic Materials

Abstract Cellulosic materials containing 1.7% and 3.3% thiol groups were prepared by treating maize cobs meal with thioglycollic acid solution at 29°C. Equilibrium sorption studies of cadmium, lead and zinc ions from aqueous solutions on the unmodified and thiolated cellulosic materials were carried out at 29°C using various concentrations of the dilute metal ions solutions. The metal ion binding capacity of the cellulosic material was significantly improved by the incorporated thiol groups. The influence of pH of the metal ion solutions on the uptake levels of the metal ions by the cellulosic substrate was examined.

Studies on the graft copolymerization of cellulosic materials

Graft copolymers of acrylic acid on cellulosic materials were obtained by use of ceric ion in aqueous medium at various temperatures. The level of incorporation of poly(acrylic acid) grafts and the efficiency of grafting were significantly reduced as the temperature of polymerization was increased from 35° to 60°C. The uptake of cadmium and copperions from aqueous solution by the cellulose-g-poly(acrylic acid) copolymer was examined by equilibrium and dynamic sorption studies. The amount of metal ions removed from solution depended on the metal ion type, initial concentration of the metal ion solution, level of incorporation of poly(acrylic acid) in the graft copolymer and the temperature of the metal ion solution.

Sorption equilibrium and hydration studies of lysozyme: water activity and 360-MHz proton NMR measurements

Sorption equilibrium and hydration studies of lysozyme: water activity and 360-MHz proton NMR measurements

Sorption of dissolved organics from aqueous solution by polystyrene resins—I. Resin characterization and sorption equilibrium

The results of sorption equilibrium studies indicate that adsorption is only one of the three mechanisms involved in removing organics from aqueous solution by polystyrene resins. The other two mechanisms are associated with the resin's capability to incorporate organics into their polymer matrix while swelling. To describe the overall sorption behaviour, it is not sufficient to characterize the resin structure by estimating pore size distribution and internal surface area of the dry polymers. The amount of swelling in different organic solvents must also be evaluated as an important structural parameter of polystyrene resins. The role of the different mechanisms depends on both the resin structure and the physical and chemical properties of the solute. The solute's affinity for the polystyrene surface can be correlated with the solute's benzene-water partition coefficient. A heuristic model is presented which relates the sorption capacity to both the resin and solute properties.

Viscometric and sorption equilibrium studies on n-alkane-butanone-poly-(dimethylsiloxane) systems

Intrinsic viscosities, [η], second virial coefficients, A 2, and preferential solvation coefficients, λ, for the ternary systems n-alkane (l)-butanone (2)-poly(dimethylsiloxane) (PDMS) (3), with n-alkane = n-hexane, n-heptane, n-nonane and n-undecane, have been determined at 20°. The K and a constants of the Mark-Houwink equation have been evaluated over the whole composition range of the binary solvent mixtures. Polymer (mixed solvent) interaction parameters and unperturbed dimensions have been evaluated both from A 2 and [η] data, the feasibility of A 2 evaluation from [η] experimental data or vice versa being discussed. Experimental and calculated (through Dondos and Patterson theory) excess free energies, G E, follow similar trends with composition; large numerical discrepancies, however, arise between both sets of G E . Maxima in [η], in a and in A 2 are accompanied by inversion points in λ. The solvent mixture composition range in which PDMS is preferentially solvated by n-alkane, as well as the extent of solvation, decrease with increasing number of carbon atoms in the n-alkane.

Chromatographic Study of Interactions Between Polyvinylpyrrolidone and Drugs

A chromatographic technique for the study of possible interactions of drugs with soluble or insoluble polymer additives is proposed. Crospovidone was used as a stationary phase. The method allowed the rapid determination of interaction constants in the range of >1 M­1 as relevant for applications in practice. The interaction of 39 drugs and model compounds of diverse chemical structure with povidone and crospovidone was studied. The results closely agreed with data obtained from conventional equilibrium dialysis and sorption studies. The complexation reaction was found to be dominated by hydrogen binding. A close correspondence between the strength of interaction and the nature, number, and position of hydrogen-donating functional groups in the active ingredient was observed. The binding tendency was enhanced when the functional groups were connected with aromatic residues. The car-boxyl group was more effective than the hydroxide or amino groups. The binding can be quantified by the binding constants, Kp and Ks respectively, describing the interaction with polyvinylpyrrolidone via independent binding sites. At pH 1, with the exception of tannic acid, all investigated drugs exhibited Kp and/or Ks values well below an upper limit of 10­1. Hence, with additive-drug ratios commonly used in pharmaceutical preparations, the bound amount of drug after oral administration can hardly exceed 3%. In view of this already low degree of potential binding and considering its reversible character and its decreasing tendency with increasing pH during GI passage, the presence of polyvinylpyrrolidone in pharmaceutical preparations is not expected to interfere with GI drug absorption.

Use of Thermal Gravimetric Analysis, GLC, and Mass Spectrometry in Sorption Studies III: Evaluation of Clustering Functions of Ethanol-water-polyurethane System

An equilibrium sorption study on the ethanol-water-polyurethane system over an extended ethanol concentration range was conducted by means of thermal gravimetric analysis, GLC, and mass spectrometry. From a single dynamic experiment, the equilibrium solubility in and the activation energy of desorption from the polymer matrix were evaluated simultaneously. The equilibrium sorption behavior of ethanol and water in the polymer matrix was interpreted in terms of the modified Zimm-Lundberg clustering theory applied to the liquid phase. The results indicate that the activation energy for desorption of ethanol decreases to a minimum and then increases with an increasing amount of sorption. The clustering function suggests that there is a greater tendency for ethanol molecules to cluster in the polymer matrix at lower ethanol activity but that there is no tendency for water molecules to cluster together. Water molecules show ideal sorption behavior at high water content and localized sorption on specific polymer sites at lower water content. Below 43% by weight or 0.51 activity, ethanol demonstrates ideal behavior; but at higher ethanol compositions, localized sorption takes place. There is also a great tendency for ethanol and water molecules to cluster together in the polymer matrix. The mean cluster size for ethanol is 1.4-2.5 molecules, while that for ethanol-water is 2.5-3.9 molecules.