Sorption properties of natural clinoptilolite modified by Fe-containing solutions

Sorption properties of clinoptilolite tuff modified by Fe-containing solutions were studied. The absence of sorption of monocharged anions at any pH of the solution and a high sorption capacity (up to 2.0 to 2.5 mg-eq g^–1) for phosphate ions at pH 10 to 11.5 were shown. Desorption of phosphates by solutions of salts and mineral acids was studied.     

Efficient methane/nitrogen separation with low-sodium clinoptilolite

The presence of sodium is shown to have a highly detrimental effect on the gas separation ability of clinoptilolite towards methane and nitrogen.     

Benzalkonium chloride and sulfamethoxazole adsorption onto natural clinoptilolite: effect of time, ionic strength, pH and temperature

The influence of different physical factors on the adsorption of the cationic surfactant benzalkonium chloride (BC) and the model drug sulfamethoxazole by a purified natural clinoptilolite (NZ) has been studied in order to employ zeolite-surfactant-drug composites as drug deliverer. It has been demonstrated that the adsorption of BC and sulfamethoxazole onto NZ depends of the time, the temperature, the ionic strength and the pH of the aqueous medium. The optimal conditions for the preparation of the zeolite-surfactant and zeolite-surfactant-drug composite materials are established. The results of the composite characterization support the presence of BC and sulfamethoxazole, as well as the structural stability of NZ during the treatments performed. The release experiments in acid medium demonstrate that the adsorption of sulfamethoxazole is reversible. It is also confirmed that the drug release profile corresponds to a diffusion or zero-order mechanism as a function of the compression pressure.     

Alumina-supported vanadium nanoparticles: structural characterization and CO adsorption properties

Alumina-supported vanadium particles were prepared under ultrahigh vacuum (UHV) conditions and characterized with respect to their structural and CO adsorption properties. As supporting oxide, we used a thin, well-ordered alumina film grown on NiAl(110). This allows the application of scanning tunneling microscopy (STM), infrared reflection-absorption spectroscopy (IRAS), and X-ray photoelectron spectroscopy (XPS) without charging effects. Vanadium evaporation under UHV conditions leads to the growth of nanometer-sized particles which strongly interact with the alumina support. At very low vanadium coverages, these particles are partially incorporated into the alumina film and get oxidized through the contact to alumina. Low-temperature CO adsorption in this coverage regime permits the preparation of isolated vanadium carbonyls, of which we have identified mono-, di-, and tricarbonyls of the V(CO)(y)() type. A charge-frequency relationship was set up which allows one to quantify the extent of charge transfer from vanadium to alumina. It turns out that this charge transfer depends on the V nucleation site.     

A study of the sorption properties of natural calcium clinoptilolite by using radioactive indicators

The sorption of monovalent ions (cesium, silver, thallium, mercury), bivalent ions (strontium, barium, lead, copper, cobalt, zinc) and polyvalent ions (cerium) on calcium clinoptilolite under dynamic conditions has been studied. Both the dynamic exchange capacities in the different break-through of the ions and the degree of the exchanging ions in sorption of different metal cations have been determined. The good selectivity of calcium clinoptilolite in relation to cesium and strontium is displayed in the presence of sodium. The influence of various factors on the sorption the thermal and radiation treatment of the sorbent, the pH and concentration of solutions, equilibration time, presence of alkali and alkali earth ions deactivating agents—EDTA, citric acid tartaric acid, and boric acid in solution has been studied. The optimum conditions of sorption have been determined. Experiments for the desorption of cesium and strontium have been carried out. The possibility to use calcium clinoptilolite for the purpose of deactivation of radioactive wastes is shown. The better sorption properties of that sorbent, compared to calcium clinoptilolite, can be explained by the higher aluminium content, as well as by a prevalence of calcium and magnesium in its ion exchange complex.     

Iodide adsorption on the surface of chemically pretreated clinoptilolite

The possibility to use the monoionic Ag⁺-form (eventually Hg⁺- and Hg²⁺- forms) of clinoptilolite of domestic origin for radioactive iodide elimination from waters has been studied. The capacity of the monoforms of clinoptilolite towards iodide exceeds many times that of the capacity of clinoptilolite in natural form. Due to the low solubility product of AgI, Hg₂I₂ and HgI₂ iodides generate precipitates on the zeolite surface. Rtg analyses of the silver form of clinoptilolite after sorption of iodide demonstrate the formation of new crystals on the zeolite surface. The influence of interfering anions on the adsorption capacity of silver clinoptilolite towards iodide was investigated, too. Kinetic curves of iodide desorption from the surface of silver and mercury clinoptilolite were compared. Simultaneously, adsorption isotherms for the systems aqueous iodide solution/Ag^–, Hg-clinoptilolite were determined.     

Uranium adsorption characteristic and thermodynamic behavior of clinoptilolite zeolite

Summary Natural zeolite, clinoptilolite was tested for its ability to remove uranium from aqueous solutions. Influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficients of uranium on clinoptilolite were measured by batch technique. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. Values of ΔH and ΔS were found as 0.93 and 56.09 J/mole, respectively. It was observed that the adsorption process is endothermic. Kinetics of uranium sorption was investigated at different time intervals at 30 °C. The reaction rate and diffusion constant were calculated.     

Sorption of radioactive cobalt in natural Mexican clinoptilolite

The ability of a natural Mexican clinoptilolite to sorb radioactive cobalt from aqueous solution was studied. The zeolite was stabilized partially with sodium and the content of Na⁺ in the samples was determined by neutron activation analysis. Ion exchange experiments were performed with solution labeled with radioactive⁶⁰Co at pH 6.5. XRD patterns were used to verify if the crystallinity of the aluminosilicate was affected by ionic exchange. A fast sorption uptake was observed and it was found that 0.408 meq/g of zeolite of Na⁺ ions were replaced by cobalt ions, followed by a desorption process where the uptake decrease to 0.314 meq/g of zeolite. This behavior is a consequence of the partial dehydration of the zeolite.     

Adsorption of nitrogen from natural gas by clinoptilolite

Much of world’s natural gas reserves are impure, one of the principal contaminants being nitrogen which makes it unsuitable for application and, hence, its separation is important. In this research, clinoptilolite, the most abundant natural zeolite with an open aluminosilicate framework structure and high internal surface area, was modified by ion exchange process to highly exchanged forms of cations of Na⁺, K⁺ and H⁺. The adsorption of N₂, CH₄ and C₂H₆ on natural clinoptilolite (Cp) and on its cation-exchanged forms (Na-Cp, K-Cp and H-Cp) was studied at 25 °C. The influence of cation exchange on equilibrium adsorption of N₂ showed that selectivity decreased in the order of Cp > Na-Cp > K-Cp and H-Cp has no affinity to nitrogen.     

Sorption of lanthanum ions by natural clinoptilolite tuff

The equilibrium and kinetics of sorption of lanthanum ions on natural clinoptilolite tuff are studied. It is demonstrated that sorption of lanthanum ions from diluted solutions occurs in micropores of clinoptilolite, and from concentrated solutions in the mesoporous structure of tuff. The main capacity of zeolite tuff is found in the secondary porous structure. The sorption of lanthanum ions is limited by diffusion in tuff grains. Lanthanum ions are regularly distributed in the tuff phase and interact with the Brønsted centers of large clinoptilolite cavities.     

Removal of RuO4 vapors on natural clinoptilolite

Natural clinoptilolite has been used for the retention of RuO₄ vapors and its sorption properties were determined under a dynamic regime. In the course of retention, dissocíation of RuO₄ to RuO₂ and O₂ proceeds, which is probably in the first phase catalyzed by Fe₂O₃ contained in clinoptilolite and in the second phase, after the formation of RuO₂, it is autocatalyzed by this oxide. The autocatalytic reaction, which is promoted by an increase of temperature, can theoretically proceed up to the complete clogging of the intergrain volume, which would give the RuO₄ retaining capacities by several orders of magnitude higher than in the case of mere physical sorption. However, the exploitation of this capacity is, prior to the onset of the autocatalytic reaction, limited by the transient breakthrough of RuO₄. Conditions were found under which this transient breakthrough is completely avoided.     

Study of secondary porosity by SAXS and N2 adsorption in composite materials obtained from a Cuban natural clinoptilolite

In this work, a study of the secondary porosity of two zeolite-based composites is carried out by small angle X-ray scattering (SAXS) and N₂ adsorption at 77 K. The composites were obtained by the inclusion of ZnO nanoparticles in a Cuban natural clinoptilolite by mechanosynthesis and ‘in situ’ methods. It was observed a decrease in the specific surface area as a result of ZnO nanoparticles inclusion from 149 m² g⁻¹ in the started material to 60 m² g⁻¹ in the composite prepared by in situ method, whereas the mesopore diameter remained almost constant. The results confirmed the presence of mesopores with diameter between 3 and 36 nm, with good match by both methodologies. These materials were developed in view of their future application as catalysts and adsorbents, where the presence of secondary porosity is key to favor the diffusion processes.     

Adsorption of toxic metals by natural and modified clinoptilolite

The chromium, cobalt and lead removal from aqueous solution by natural and modified zeolites was examined by using a batch-type method. Clinoptilolite samples used in this study were supplied from Bigadi?, Turkey. All samples were modified with HNO3 or NaOH to improve the adsorption capacity for heavy metals. The removal efficiencies and kinetics of heavy metals such as chromium, cobalt and lead on natural and modified zeolites were determined. The effects of the initial metal concentration on the removal percentage of heavy metal ions were studied. Freundlich and Langmuir isotherm constants and correlation coefficients were found and the equilibrium process was described by the Freundlich isotherm. The adsorption kinetic was tested and then it indicates the process to be diffusion controlled.     

Statistical thermodynamics models for polyatomic adsorbates: application to adsorption of n-paraffins in 5A zeolite

Experimental adsorption isotherms of five n-paraffins (ethane, propane, butane, pentane, and hexane) in 5A zeolite were described by means of a statistical thermodynamics model for linear adsorbates (MLA) developed by Ramirez-Pastor et al. (1999) and compared with the well-known multisite Langmuir model (MSL) of Nitta et al. (1984). The experimental data, obtained by different authors in a wide range of temperatures and pressures, were correlated by using an algorithm of multiple fitting. Two main conclusions were drawn from the analysis of experimental data: (i) for small molecules (ethane, propane), MLA is the more accurate model, validating the hypothesis of the linear rigid character of the adsorbate and reinforcing previous results obtained from the analysis of computational experiments developed for dimers and linear trimers; (ii) for large molecules (n-butane, n-pentane, n-hexane), the better performance of the MSL model suggests that the admolecules adsorb in a nonlinear structure. The isosteric heat of adsorption dependence on the number of carbons obtained from our study, ranging between 23.84 kJ/mol for ethane and 59.26 kJ/mol for hexane, showed a very good agreement with previous results reported in the literature, confirming the consistency of our analysis.     

Effect of the acidic treatment on the adsorption and structural properties of the natural mineral sorbent M45C20

Adsorption and structural properties of the initial natural mineral sorbent M₄₅C₂₀ and the sorbent treated with 2.33 M H₂SO₄ were studied. The sorbent mainly consists of montmorillonite and clinoptilolite. Aluminum, calcium, magnesium, sodium, and potassium ions are removed from the structure under the action of the acid. The specific surface, porosity of the sorbent, and pore size increase during this process. The sorption of ammonium ions in the natural samples predominantly follows the ion-exchange mechanism (exchange to calcium, magnesium, sodium, and potassium ions). The acid treatment changes the composition of the cation-exchange complex and results in an increase in the sorption capacity to ammonium ions by a factor of ??1.3.     

Study of adsorption phenomena ongoing onto clinoptilolite with the immobilized interfaces

The development of innovative clean-up technologies remains a challenge as current procedures have many limitations, such as being expensive, concentration or pollutant specific, and many others. Natural zeolite of clinoptilolite type was beneficiated with surfactant octadecylammonium and alginate biopolymers using the sol-gel method. Carbonization process in pyrolysis chamber combusted organic waste materials and reaching the maximum temperature of 700°C was used for the surface carbonization, respectively. Resulted zeolite based products were analyzed by FTIR, TG, DTA and examined on the selected aqueous pollutants removal using the conventional laboratory adsorption experiments. The ability of ODA and alginate linked zeolite of clinoptilolite type to form complexes with anions (such as nitrate, sulphate, chloride and phosphate) and to remove them from contaminated waters was validated. Carbon deposition onto clinoptilolite surface originated from the pyrolytic carbon-rich waste combustion simulated the new zeolite based hybrid to active coke, adsorption efficiency of which towards phenol was approved. Thermogravimetric analyses of the advanced zeolite-based adsorbents were accomplished to find out how temperature resistant are the novel zeolite based materials in respect to the original, untreated one. While the native clinoptilolite indicated according to DTA analysis one broad endothermic response around 100–130°C, resulted from the loss of adsorbed water, by the ODA-modified clinoptilolite was except this DTA peak, the broad exothermic response started from 370 up to 560°C observed. This DTA profile is assumed to record a slowly breakdown of attached ODA surfactant and sequential loss of mass due to continual heating of sample under elevated temperature.     

Atomistic model of micelle-templated mesoporous silicas: structural, morphological, and adsorption properties

The structural, morphological, and adsorption properties of MCM-41 porous silicas are investigated using a realistic numerical model obtained by means of ab initio calculations [Ugliengo, P.; et al. Adv. Mater.2008, 20, 1]. Simulated X-ray diffraction, small angle neutron scattering, and electronic microscopy for the atomistic model are in good agreement with experimental data. The morphological features are also assessed from chord length distributions and porous volume and specific geometrical surface calculations, etc. The N(2), CO(2), and H(2)O adsorption isotherms in the atomistic model of MCM-41 are also in reasonable agreement with their experimental counterpart. An important finding of the present work is that water forms a film adsorbed on specific hydrophilic regions of the surface while the rest of the surface is depleted in water molecules. This result suggests that the surface of MCM-41 materials is heterogeneous, as it is made up of both hydrophilic and hydrophobic patches. While adsorption and irreversible capillary condensation can be described using the thermodynamical approach by Derjaguin (also known as the Derjaguin-Broekhoff-De Boer model), the Freundlich equation fits nicely the data for reversible and continuous filling in small pores.