Unheated and Heated Batch Methods in Ion Exchange of Clinoptilolite (original) (raw)
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Adsorption Science & Technology, 2009
Physicochemical characterization of the natural solid-phase Gördes clinoptilolite and of the Na +-, K +-, Ca 2+-and Mg 2+-modified forms of the mineral (as obtained through ion-exchange) by batch methods, X-ray diffractometry (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR) and scanning electron microscopy (SEM) is described. It was found that the Na +-and Ca 2+-forms exhibit high ion-exchange rates relative to the Mg 2+-and K +-forms. In addition, the high rate of ion selectivity towards Na + and K + ions, together with lower rates for Mg 2+ and Ca 2+ ions, indicate that the rate of ion selectivity is negatively correlated with the ionic potential of the ions. Such ion-exchange and ion selectivity result in a decrease in pore size and an increase in the surface area of the modified clinoptilolite relative to the natural form; this may possibly be related to the entrance of the ions into the mineral structure. It was concluded that clinoptilolite modified with exchangeable ions from aqueous solutions at two different normalities exhibits features which differ from those of natural clinoptilolite. Thus, modification of clinoptilolite by different cationic forms from aqueous solutions at different normalities might prove suitable for applications in other fields of study.
Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff
Journal of Colloid and Interface Science, 2005
The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution of concentration 0.1 mmol cm −3 and ammonium ions solutions of concentrations 0.0071 to 2.6 mmol cm −3. Molal concentrations, x (mmol g −1) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determination of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentrations lower than 0.1 mmol cm −3 , with regard to exchange capacity for particular ions, best exchanged are Na + ions, followed by Mg 2+ and Ca 2+ ions, while exchange of K + ions is the poorest (Na + > Mg 2+ > Ca 2+ > K +). At ammonium concentrations from 0.2 to 1 mmol cm −3 the order is Na + > Ca 2+ > Mg 2+ > K +. At concentrations higher than 1 mmol cm −3 the order is Na + > Ca 2+ > K + > Mg 2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions at concentrations lower than 1 mmol cm −3 and indicate the importance of Mg 2+ (besides Na + ions) for the exchange between clinoptilolite cations and H + ions, in contrast to K + ions, whose participation in the reaction with H + ions is the lowest. During decationization of the clinoptilolite in acid solution, best exchanged are Na + , Mg 2+ , and Ca 2+ ions, while exchange of K + ions is the poorest. Due to poor exchange of K + and H + ions and good exchange of Na + , Mg 2+ , and Ca 2+ ions, it is to be assumed that preservation of stability of the clinoptilolite structure is caused by K + ions present in the channel C. Clinoptilolite is dissolved in the clinoptilolite A and B channels where Na + , Mg 2+ , and Ca 2+ ions are present. On the acidmodified clinoptilolite samples, exchange of ammonium ions is poorer than on natural zeolite. The longer the contact time of the zeolite and acid solution, the worse ammonium ions exchange. It can be assumed that H + ions exchanged with zeolite cations are consumed for solution of aluminum in the clinoptilolite structure; therefore the concentration of H + ions as exchangeable cations decreases. In the ammonium ion solution at a concentration of 0.0065 mmol cm −3 , from the acid-modified zeolite samples, Al 3+ ions are exchanged best, followed by Na + , Mg 2+ , Ca 2+ , and K + ions. Further to the results, it is to be assumed that exchangeable Al 3+ ions available from clinoptilolite dissolution are best exchanged with H + ions in acid solution.
Adsorption Science & Technology, 2009
Physicochemical characterization of the natural solid-phase Gördes clinoptilolite and of the Na +-, K +-, Ca 2+-and Mg 2+-modified forms of the mineral (as obtained through ion-exchange) by batch methods, X-ray diffractometry (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR) and scanning electron microscopy (SEM) is described. It was found that the Na +-and Ca 2+-forms exhibit high ion-exchange rates relative to the Mg 2+-and K +-forms. In addition, the high rate of ion selectivity towards Na + and K + ions, together with lower rates for Mg 2+ and Ca 2+ ions, indicate that the rate of ion selectivity is negatively correlated with the ionic potential of the ions. Such ion-exchange and ion selectivity result in a decrease in pore size and an increase in the surface area of the modified clinoptilolite relative to the natural form; this may possibly be related to the entrance of the ions into the mineral structure. It was concluded that clinoptilolite modified with exchangeable ions from aqueous solutions at two different normalities exhibits features which differ from those of natural clinoptilolite. Thus, modification of clinoptilolite by different cationic forms from aqueous solutions at different normalities might prove suitable for applications in other fields of study.
Pretreatment of natural clinoptilolite in a laboratory-scale ion exchange packed bed
Water Research, 2001
}The impact of the operational and chemical conditions of pretreatment upon the effective capacity of clinoptilolite has been investigated. Pretreatment tests have been performed in an ion exchange packed bed. The parameters examined for the pretreatment solution were the volumetric flow rate, the concentration, the total volume and the pH; and for washing after pretreatment the volume of washing water used. An optimal flow rate and a minimum concentration were determined, for a pretreatment that leads to a high effective capacity of the material, while pH adjustment did not result in a higher effective capacity and one washing (10 bed volumes) after pretreatment was found to be sufficient. Furthermore, the water quality (use of tap water) as well as the surface dust of the original material (about 5% w/w) did not alter its effective capacity.
Thermodynamics of ion exchange between clinoptilolite and aqueous solutions of and
Geochimica et Cosmochimica Acta, 1994
To provide a the~~ynamic basis for undemanding zeohte-water intemctions in geologic systems, ion-exchange experiments were conducted at 25°C between clinoptilolite, which is the predominant zeolite mineral in altered pyroclastic and volcaniclastic rocks, and aqueous mixtures of Na+/K+ and Na+/Ca2+, Isotherm points were obtained by equilibrating Na-clinoptilolite, which was prepared from clinoptilolite-rich tuff from Death Valley Junction, California, USA, and Na+/K+ and Na+/Ca'+ chloride solutions having different ionic concentration ratios, but constant total normalities of 0.50.05, or 0.005 N. The experimental data were interpreted using a Margules the~~ynami~ fo~ulation for zeolite solid solutions, coupled with the Pitzer model for aqueous activity coefficients. The isotherm data for 0.5 N Na+/K+ and Na+/Ca*+ solutions were used to derive equilibrium constants and Gibbs free energies for the ion-exchange reactions, as well as parameters for the Margules model. Using the same parameters derived from the 0.5 N data, isotherms were calculated for the 0.05 and 0.005 N solutions. The predicted values agree very well with experimental data, including other data at 0.05 N solution concentration with nitrate as the supporting anion. The results of this study indicate that a Margules solid solution model for zeolites, coupled with an activity coefficient model for aqueous solutions (e.g., Pitzer model), can successfully describe and predict binary ion-exchange equilibria between aqueous solutions and the zeolite mineral chnoptilolite over a wide range of solution composition and concentration, and may provide a foundation for quantitative understanding of ion-exchange equilibria in multicomponent geochemical systems. 'Table 1. Results of ICP analysis of clinoptiloiite ShUtlpleS.'
Microporous and Mesoporous Materials, 2012
In the present work a combination of chemically constrained Rietveld refinement and computer simulation is used for the determination of the positions of the extra-framework cations Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ in the channels of clinoptilolite. The analysis of the metal rich clinoptilolites with two different Si/Al ratio (4.7 and 7.8) demonstrates that most of the cations are located in two extra-framework sites, the first one in the center of channel A and the second one in the center of channel B. In the case of the Cu 2+ exchanged zeolite with high Si/Al ratio (4.7), a third site is found. This site is located at 1.65 Å of the center of the A channel and can be considered as a highly disordered first site. All the metal ions are coordinated to water molecules with no coordination to the zeolite framework. The presence of hydronium cations controls the relative occupancy of the transition metals in the observed sites.
Geochim Cosmochim Acta, 1994
To provide a the~~ynamic basis for undemanding zeohte-water intemctions in geologic systems, ion-exchange experiments were conducted at 25°C between clinoptilolite, which is the predominant zeolite mineral in altered pyroclastic and volcaniclastic rocks, and aqueous mixtures of Na+/K+ and Na+/Ca2+, Isotherm points were obtained by equilibrating Na-clinoptilolite, which was prepared from clinoptilolite-rich tuff from Death Valley Junction, California, USA, and Na+/K+ and Na+/Ca'+ chloride solutions having different ionic concentration ratios, but constant total normalities of 0.50.05, or 0.005 N. The experimental data were interpreted using a Margules the~~ynami~ fo~ulation for zeolite solid solutions, coupled with the Pitzer model for aqueous activity coefficients. The isotherm data for 0.5 N Na+/K+ and Na+/Ca*+ solutions were used to derive equilibrium constants and Gibbs free energies for the ion-exchange reactions, as well as parameters for the Margules model. Using the same parameters derived from the 0.5 N data, isotherms were calculated for the 0.05 and 0.005 N solutions. The predicted values agree very well with experimental data, including other data at 0.05 N solution concentration with nitrate as the supporting anion. The results of this study indicate that a Margules solid solution model for zeolites, coupled with an activity coefficient model for aqueous solutions (e.g., Pitzer model), can successfully describe and predict binary ion-exchange equilibria between aqueous solutions and the zeolite mineral chnoptilolite over a wide range of solution composition and concentration, and may provide a foundation for quantitative understanding of ion-exchange equilibria in multicomponent geochemical systems.
Aim of this study was to evaluate the feasibility of the use of clinoptilolite as a barrier material to eliminate heavy metals from roof runoff. The effect of chemical conditioning with 1 M NaCl solution upon the ion exchange capacity and on kinetic of zinc uptake by clinoptilolite has been investigated. According to the batch experiments the modified clinoptilolite has up to 100% higher sorption capacity, regarding Zn than the natural material. The pre-treatment of clinoptilolite results in an acceleration of the ion exchange process up to 40% regarding zinc. In order to define the reasons of this behaviour, both materials, modified and natural, were analysed for: (i) chemical composition, (ii) density, (iii) pore size distribution and (iv) zeta potential. The clogging of the pores, the charge of the grain surface, the pH of the initial metal solution and the ion metal concentration are the factors which are mainly affecting the ion exchange capacity and the rate of zinc uptake by clinoptilolite. r
In the present work, the effect of acid treatments on the structure of a natural and sodium exchanged clinoptilolite was evaluated using experimental and theoretical methods. The results demonstrated the good stability of the samples submitted to HCl treatments, although it was proven that aluminum was extracted from the framework. It was verified that the sodium clinoptilolite (AZ) is more resistant than its natural form (NZ) to the acid treatment since the aluminum extraction is smaller and the percent of estimated crystallinity is higher in AZ. An increase in the micropore volume, as well as the creation of new narrow micropores, was also verified. The simulation results indicated that the aluminum at T2 position is the easiest to remove during the dealumination process, and it was also noted that, during dealumination, different slabs are formed in the structure, creating a framework like a clay. Calculations suggested that the stability of the dealuminated frameworks was related to attractive and repulsive interactions, which take place between the species involved in the dealumination process. Our work demonstrates that sodium modification is an essential step to obtain a structurally stable acidic natural clinoptilolite.