Estimation of the Zeolite Contents of Tuffaceous Samples from the Bigadiç Clinoptilolite Deposit, Western Turkey

Abstract

Abstract--Variation of the NH4+-exchange and CO2-adsorption capacities with zeolite content was investigated in detail to assess the potential use of these capacities for the estimation of the zeolite contents of the samples taken from the Bigadiq clinoptilolite deposit in western Anatolia, as an alternative to the widely used semi-quantitative X-ray diffraction (XRD) technique. Samples with known clinoptilolite contents taken from 2 different zones with fine-and coarse-grained tufts of the Bigadi~ deposit were used for this purpose. Na-enriched forms of the samples were prepared by repeated ion-exchange with NaC1 solutions, and NH4+-forms by repeated Na exchange followed by NH4 § exchange with NH4C1 solutions, which in turn were calcined to obtain the H-forms. NHa+-exchange capacities by Kjeldahl analyses of the NHa+-forms and CO2 adsorption isotherms in the 0 to I00 kPa range of Na-and H-forms of the samples were determined. Dubinin-Astakhov model parameters were calculated from the isotherm data.A strong relationship exists between the experimental CO2-adsorption capacities at 100 kPa of the Na-forms and the zeolite contents of the samples. Although the Dubinin-Astakhov model represented the isotherm data quite well, the relationships between the amounts of adsorbate at saturation pressure, calculated from the model, and the zeolite contents of the samples were weaker. The strength of the relationship between NH4 § exchange capacities and zeolite contents was seen to vary with the zone of origin. There is a very strong relationship between the adsorption and ion-exchange capacities of the samples in their Na-forms taken from the fine-grained zone, indicating that either ion-exchange or adsorption capacity measurements can be used to estimate the zeolite contents of the samples taken from this zone, whereas, significant diffusion hindrance was observed against ion-exchange of hydrated cations from aqueous solutions for some samples from the coarse-grained zone. Inspection of the data pointed to systematic errors in the zeolite contents determined by a semi-quantitative XRD technique. When both zones are considered together, CO2-adsorption capacities at 100 kPa of the samples in their Na-forms can be used as a reliable measure of the zeolite content, which in turn is an important index to predict the performance of natural samples in various applications.

The concept of “capacity” in zeolite ion-exchange systems

“…The most effective is the Rietveld method, which requires a structural model for each major mineral present in the mixture and is therefore limited to minerals having well-defined structures [49,50]. Another method is to use pure mineral species as intensity references [49,51].…”

“…As a result, certain minor constituents cannot be identified by XRD alone. Furthermore, it is known that X-ray line intensities may not always be proportional to the zeolite contents [51]. For these reasons, XRD methods should be used along with other methods for the determination of zeolite capacity.…”

“…This means that the zeolite cations should be exhaustively (totally, fully) exchanged: in other words, the zeolite negative charge should be balanced by an equivalent amount of incoming cations. This total (exhaustive) exchange could be achieved by (a) repeated equilibrations in batch systems with periodical renewal of the solution phase [5,[51][52][53][54]; (b) one simple equilibration in a batch system using a high solution-volume/zeolite-mass ratio [32,55]; (c) under dynamic conditions (in columns): the term "crossexchange method" is used in order to present this procedure [5].…”

“…Conversion of all exchangeable ions to one species (homoionic form) is a common step for cation-exchange capacity determinations [21,44,51,[56][57][58][59]. According to Sirkecioglu and Erdem-Senatalar, zeolites should be converted to near-homoionic form in order to eliminate as much as possible the well-known effects of the variation of the cationic composition with location on capacity [51]. During the homoionic form preparation there are two different ways to determine the REC: by chemical analysis of the solid or liquid phase.…”

Crystallization of Zeolite A Coatings from Natural Zeolite

“…21,22 . The mineralogical composition of the material, originating from a deposit near Bigadiç, Turkey, mainly consisted of clinoptilolite (about 85%).…”