Uptake of Zn2+ ions by a fully iron-exchanged clinoptilolite. Case study of heavily contaminated drinking water samples

Clinoptilolite, a natural zeolite, was used for the synthesis of a high surface area clinoptilolite (Clin)-iron (Fe) oxide system, in order to be used for the removal of Zn2+ ions from drinking water samples. The new system was obtained by adding natural Clin in an iron nitrate solution under strongly basic conditions. The Clin-Fe system has specific surface area equal to 151 m(2)/g and is fully iron exchanged (Fe/Al = 1.23). Batch adsorption experiments were carried out to determine the effectiveness of the Clin and the Clin-Fe system in removal of Zn from drinking water. Adsorption experiments were conducted by mixing 1.00 g of each of the substrates with certain volume of water samples contaminated with ten different Zn concentrations (from 7.65 x 10(-5) to 3.82 X 10(-2) M or from 5.00 to 2500 ppm Zn). For our experimental conditions, the maximum adsorbed Zn amount by Clin was 71.3 mg/g, whereas by the Clin-Fe system 94.8 mg/g. The main factors that contribute to different adsorbed Zn amounts by the two solids are due to new surface species and negative charge of the Clin-Fe system. In addition, the release of counterbalanced ions (i.e. Ca2+, Mg2+, Na+ and K+) was examined, as well as the dissolution of framework Si and Al. It was found that for most of the samples the Clin-Fe system releases lower concentrations of Ca, Mg and Na and higher concentrations of K than Clin, while the dissolution of Si/Al was limited. Changes in the composition of water samples, as well as in their pH and conductivities values were reported and explained. (c) 2007 Elsevier Ltd. All rights reserved

Kinetics of phosphate sorption by goethite- and bentonite-goethite (b-g) system

The study of phosphate (PO4) fixation due to reactions which occur to the surface of soil minerals has been limited by a lack of evidence on which a structural model may be based. A structural model should attempt at least to describe the coordination on the absorbed PO43- ion, that is, to indentify the immediate neighbour atoms or ions in contact with it. Many kinetic equations have been used either to deduce the mechanisms or simply to summarise results of this continued removal of PO4 from solution. In this study five kinetics models of first-order, Elovich, parabolic diffusion, modified Freundlich and a new kinetic equation, were evaluated to describe the rate of PO4 sorption from synthetic goethite and bentonite-goethite (b-g) system into 0.01M calcium chloride (CaCl2) solutions of 0.0403-0.4435 mmol P L-1. The rate of PO4 sorption is a dynamic factor that regulates the continuous supply of PO4 and was found initially to be rabid but gradually declined with time. The adsorption of PO4 per gram of goethite was faster and greater than the adsorbed amount of PO4 per gram of bentonite-goethite system. Comparison of the coefficients of determination (r) indicates that Elovich, Freundlich, and the new kinetic models provided better fits for phosphate sorption by goethite while First order, Parabolic, and Freundlich were found to be the best for bentonite goethite (b-g) system

Phosphate adsorption on hematite, kaolinite, and kaolinite-hematite (k-h) systems as described by a constant capacitance model

The constant capacitance model was used to describe phosphate adsorption on hematite, kaolinite, and a kaolinite-hematite system (k-h). The model assumes a ligand exchange mechanism and considers the charge on both adsorbate and adsorbent. The model is shown to provide a quantitative description of phosphate adsorption an these, including the effect of varying pi-I values. The computer program Ma-Za 2, a program that fits equilibrium constants to experimental data using an optimization technique, was used to obtain optimal values for the anion surface complexation constants on hematite, kaolinite, and a kaolinite-hematite system, while the PC program Ma-Za 1 in Q-Basic language was used for the application of the constant capacitance model. The model represented adsorption of phosphate anions well over the entire pH rang studied (3.8-9.0). The main advantage of the model is its ability to represent changes in anion adsorption occurring with changes in pH. Extension of the model to describe phosphate adsorption in a mixed system, such as the kaolinite-hematite system, using the surface protonation-dissociation constant of hematite was qualitatively successful. In mixed system the model reproduced the shape of the adsorption isotherms well over the pH range 3.8-9.0. However, phosphate adsorption was overestimated. The hematite and the kaolinite-hematite system were synthesized and identified by X-ray, NMR, and FT-IR spectroscopy

Potassium sorption by Ca-bentonite - Commonly used isotherms

The sorption of potassium (K) on calcium-bentonite was studied by examined two parameters, the initially added concentration of KCl and the pH. Generally was found that the amount of adsorbed K increased as pH and initial concentration increased although the sorption at pH 7.0 shows a different behaviour. The common and a modified form of Langmuir, the Freundlich, and the Temkin isotherms were fitted to K sorption data for calcium-bentonite (Ca-b) at pH range 4.0 - 9.0. Langmuir isotherm in its commonly used form was found to be unacceptable for pH 4.0, 5.0, 6.0, 8.0 and 9.0. On the other hand modified Langmuir, Freundlich, and Temkin were found to describe K sorption data for all pH values with comparable success, with the modified type of Langmuir being slightly superior (r2 = 0.998). Copyright © 1996 by Marcel Dekker, Inc

Phosphate adsorption from aqueous solutions onto goethite, bentonite, and bentonite-goethite system

The present paper examines the phosphate adsorption from aqueous solutions onto goethite, bentonite, and bentonite-goethite system. The properties of the materials were studied by X-ray diffraction (XRD), attenuated total reflectance (ATR), and NMR spectra and by the measurement of the specific surface area, the point of zero charge (p.z.c.) and the pore-specific volume. ATR and NMR spectra of bentonite and bentonite-goethite system show peaks which correspond to tetrahedrally and octahedrally coordinated Al. The specific surface area of the system differs according to the appropriate method used, while system's p.z.c. is higher than bentonite and lower than goethite. The pore-specific volume of bentonite-goethite system is higher than that of bentonite or goethite. According to XRD spectrum of bentonite-goethite system, goethite coats the (001) spacing of bentonite while the coating of (010) plane of bentonite is limited. The crystallinity of the system decreases and the negative permanent charge increases. Phosphate adsorption experiments took place at different pH (3.8-9.0) and concentrations (40.3-443.5 μmol L-1) and constant capacitance model was applied to describe adsorption. A ligand exchange mechanism characterizes the model because the charge is divided among adsorbate and adsorbent. The constant capacitance model describes the adsorption mechanism in all examined pH. This model can be utilized in such systems using the surface protonation-dissociation constant of goethite and showing the exact shape of the adsorption isotherms for different pH values. Τhe produced low-cost bentonite-goethite system presents the highest adsorption of P per kilogram of goethite. © 2012 Springer Science+Business Media Dordrecht

Thermodynamics of phosphate adsorption-desorption by alfisols, entisols, vertisols, and inceptisols

Adsorption and desorption of phosphorous (P) by four types of greek soils, Alfisols, Entisols, Vertisols, and Inceptisols, were the subject of the present investigation. These processes were studied under different conditions of initially added P concentration and at different temperatures. Analytical data (for all studied soils) show an increasing adsorption due to initially added P concentrations and increasing temperature. The desorption was also increased with the increasing of initially added P concentrations but was decreased with temperature increases, indicating that soil affinity for P was increased as temperature increased. Analytical data and results were explained and compained based on the physical properties of the soils. By using experimental data, equivalent constants, Keq (equivalence was reached between solid sample and P in the liquid phase), were calculated. The thermodynamic constants, ΔG°, ΔH°, and ΔS°, were also estimated and discussed. Copyright ©1996 by Marcei Dekker, Inc

Phosphate sorption by goethite and kaolinite-goethite (k-g) system as described by isotherms

Goethite and kaolinite are active sorbents in soils and sediments. Unfortunately measuring their phosphate sorption capacity is difficult, because of the relatively low proportion of these clay minerals in many natural mixtures and the difficulties involved in concentrating and separating them from accompanying minerals. Under these circumstances, synthetic samples are commonly used to study phosphate sorption. In this study, the objectives were to elucidate the Langmuir, Freundlich, Temkin, Gouy-Chapman, and Sposito isotherms. The sorption of phosphate ions by goethite (a-FeOH) and kaolinite-goethite (k-g) system depends on several factors including pH, specific surface, cation exchange capacity, time of sorption, surface charge, temperature and concentration. We investigated the effects of pH, time of sorption and concentration on the adsorption of phosphate on goethite and the k-g system. Batch equilibrium phosphate adsorption experiments were conducted with pH, and initial concentration as changeable parameter in order to produce adsorption envelops. The Langmuir, Freundlich, Temkin, Gouy Chapman and Sposito isotherms were fitted to P sorption data. Each was found to describe phosphorus (P) sorption by goethite and k-g system with comparable success, with the Sposito, Freundlich and Langmuir being slightly superior for kaolinite-goethite (k-g) system and Langmuir for goethite. The total amount of P sorbed by k-g system and goethite after 103 days in equilibrium concentrations 0.0403-0.4435 mmol P L-1 and pH 4.0-9.0 was found to range between 2.74-37.00 mmol kg-1 and 22.97-106.93 mmol kg-1, respectively

Synthesis-identification of hematite and bentonite-hematite (b-h) system

Iron and aluminium are common in soils as the weathering product of soil-forming minerals. Iron occurs as coating on silicate clay minerals and significantly influence the physico-chemical properties of clay mineral. In this study hydrogen saturated bentonite was coated with 16 mequivalents of iron as hematite/g of clay in suspension of pH 6.0. The influence of hematite on the physico-chemical properties of bentonite was studied on the synthetic hematite-bentonite (h-b) system, by X-ray, NMR, FT-IR spectroscopy, specific surface area, magnesium exchange capacity (Mg.E.C.) of hematite, hydrogen-saturated bentonite and bentonite-hematite (b-h) system. Copyright © 1996 by Marcel Dekker, Inc

Phosphate sorption by hematite and kaolinite-hematite (k-h) system as described by isotherms

Journal URL: http://www.informaworld.com/smpp/title~content=t71359724

Kinetics of phosphate sorption by goethite- and bentonite-goethite (b-g) system

The study of phosphate (PO4) fixation due to reactions which occur to the surface of soil minerals has been limited by a lack of evidence on which a structural model may be based. A structural model should attempt at least to describe the coordination on the absorbed PO43- ion, that is, to indentify the immediate neighbour atoms or ions in contact with it. Many kinetic equations have been used either to deduce the mechanisms or simply to summarise results of this continued removal of PO4 from solution. In this study five kinetics models of first-order, Elovich, parabolic diffusion, modified Freundlich and a new kinetic equation, were evaluated to describe the rate of PO4 sorption from synthetic goethite and bentonite-goethite (b-g) system into 0.01M calcium chloride (CaCl2) solutions of 0.0403-0.4435 mmol P L-1. The rate of PO4 sorption is a dynamic factor that regulates the continuous supply of PO4 and was found initially to be rabid but gradually declined with time. The adsorption of PO4 per gram of goethite was faster and greater than the adsorbed amount of PO4 per gram of bentonite-goethite system. Comparison of the coefficients of determination (r) indicates that Elovich, Freundlich, and the new kinetic models provided better fits for phosphate sorption by goethite while First order, Parabolic, and Freundlich were found to be the best for bentonite goethite (b-g) system