B. de Gennaro

Cu2+, Zn2+, Cd2+ and Pb2+ exchange for Na+ in a sedimentary clinoptilolite, North Sardinia, Italy

Abstract Recent findings of clinoptilolite-bearing volcanoclastic deposits in northern Sardinia promoted a study aimed at evaluating the cation exchange properties of this zeolite in view of a possible future utilization of the parent rock. Isotherms of NH + 4 , Cu2+, Zn2+, Cd2+ and Pb2+ exchange for Na+ at 25°C and 0.1 total normality were obtained and the related thermodynamic quantities Ka and ΔG0 computed. The maximal exchange level was in any case less than 100% for each cation investigated. Good selectivities were recorded for NH + 4 and Pb2+, whereas clinoptilolite proved to be unselective for Cu2+, Zn2+ and Cd2+. The cation selectivity sequence NH + 4 >Pb 2+ >Na + >Cd 2+ >Cu 2+ ≅Zn 2+ was obtained. The results are discussed in the light of literature data, and contrasting performances of various clinoptilolites were ascribed to different cationic compositions of the minerals, due to different minerogenetic conditions, which were proved to affect both cation exchange capacity and selectivity. This led to the conclusion that any practical utilization of a clinoptilolite-rich rock as cation exchanger should be preceded by basic studies on representative samples from the deposit under examination.

Ion exchange selectivity of phillipsite for Cs and Sr as a function of framework composition

Abstract Cs and Sr exchange reactions for Na on sedimentary, hydrothermal and synthetic phillipsites are studied by determining their exchange isotherms at 25°C and 0.1 total normality, and computing the related thermodynamic quantities K a and Δ G °. Sedimentary and synthetic phillipsite, characterized by a higher Si/Al ratio, display good selectivity for Cs and moderate selectivity for Sr. The more aluminous hydrothermal phillipsite displays a lower selectivity for Cs and a higher selectivity for Sr than sedimentary and synthetic phillipsite do. These results, perfectly explainable in terms of field strength of the anionic zeolite framework and of ion charge density, demonstrate that the joint removal of Cs and Sr from water by phillipsite would be possible, provided cheap widespread aluminous phillipsite-rich materials were available.

Chromium removal from water by ion exchange using zeolites and solidification of the resulting sludge in a cement matrix

Abstract A method is presented to remove and segregate Cr 3+ present in some industrial wastewaters using zeolites, on the basis of two important properties jointly exhibited by them: cation exchange and pozzolanic activity. Zeolites, namely synthetic species A and X, chosen because of their marked selectivity towards multivalent cations, were beforehand used as cation exchangers in order to remove the pollutant cation from water. Zeolitic sludge containing Cr 3+ was afterwards solidified in a cement matrix, taking advantage of its excellent reactivity towards lime arising from cement hydration. Various amounts of zeolites A and X were explored in reactions with simulated and real Cr 3+ -containing wastewater, demonstrating that 3g of zeolite X or 4g of zeolite A were able to bring Cr 3+ concentration from 45 mg/liter to values lower than the law limit (2 mg/1) in reasonable time. Subsequent safe stabilization of Cr 3+ -bearing sludges was obtained, provided that the amount of Portland clinker in the blend was not lower than about 25%. In fact the resulting materials showed mechanical strengths much higher than those recommended for landfilling (0.44 MPa) and very satisfying leaching properties.

Data processing of cation exchange equilibria in zeolites: a modified approach

After reviewing the fundamental literature concerning the equilibrium of binary cation exchange reactions on zeolites, this paper provides a straightforward procedure of computation of their thermodynamic parameters, Kα and ΔGo, based on a method of evaluation of cations activity coefficients in solution, which is simple and accurate and is equipped with a sufficiently large data-base. The computation procedure was tested on isothermal equilibrium data of Cd2+ and Zn2+ exchange for Na+ in zeolite A at 25.0°C and 0.05, 0.10, and 0.50 total normality, by calculating their Ka and ΔGo and by comparing these results to those obtained evaluating the cations activity coefficients through a reference largely used method and to previous literature data. The results obtained show that the proposed methods give results in good agreement with those obtained with the reference method so that it appears to be a good alternative for the determination of cation activity coefficients in solution.

Effectiveness of clinoptilolite in removing toxic cations from water: a comparative study

In order to evaluate the influence that structural and/or chemical inconsistencies exert over clinoptilolite behavior as an ion exchanger, a study has been performed aiming to compare the cation exchange properties of three different clinoptilolite-rich tuffs. Equilibrium data have been collected on two samples, coming from a Greek site and a Turkish site and having a similar framework chemistry. Exchange isotherms have been determined for some cation pairs of interest for practical applications and the related thermodynamic quantities calculated. The results, which have been compared with previously published data on a clinoptilolite sample from Sardinia (Italy), have shown analogous but not identical behaviors, possibly due to modest but not negligible differences in zeolite structure and/or original chemistry.

Modeling pedogenization of zeolitized tuffs. II: medium-term weathering of phlegraean yellow tuff and red tuff with black scoriae by water and humic acids

An experimental pedology research program was started aiming at modeling the potential pedogenization of zeolitized tuffs. The present study deals with a medium-term weathering of Phlegraean Yellow Tuff (PYT, with phillipsite>chabazite) and Red Tuff with Black Scoriae (RTBS, with chabazite>phillipsite) under discontinuous treatment by water (W) and by humic acids (HA). Significant amounts of cations, increasing in the sequence Al<Fe<Mg<Ca, were extracted by both water and humic acids. The humic acids showed in all cases the highest extracting efficiency. All cations, especially calcium, were more easily removed from PYT than from RTBS. The only exception was iron which was preferentially removed from RTBS by HA. At the end of the experiment, smectite was not any more detected in the PYT residues. On the whole, the results indicate that PYT is more prone than RTBS to both humic acid and water weathering due to its different mineralogy.

Properties of zeolitized tuff/organic matter aggregates relevant for their use in pedotechnique. III: organic matter stability and exchange properties

Abstract A study was performed to evaluate the suitability of zeolitized tuffs to restore degraded soils. Ca-saturated Neapolitan yellow tuff or clinoptilolite-rich tuff from Turkey were mixed with organic matter either as humic matter (tannic acid, humic acids) or non-humic matter (polygalacturonic acid). Organic matter was strongly stabilized in clinoptilolite-rich tuff aggregates based on humic matter, whereas it was more easily oxidized in models with non-humic matter. Cation exchange capacity (CEC) was determined according to Ba/Mg-TEA method and by ammonium acetate procedure. The former method underestimated the CEC of the zeolitized tuffs, but was able to detect the contribution of organic matter to the CEC of aggregates. The latter method provided consistent CEC values for the zeolitized tuffs, but underestimated the exchange activity of the organic components of aggregates. CEC of aggregates including tannic acid was practically nil. Binding tannic acid to zeolite via Ca-bridges, results evidently in occlusion of zeolite pores.

01-O-05 - Ion-exchange features of intermediate-silica sedimentary phillipsite

Publisher Summary This chapter discusses the ion-exchange features of intermediate-silica sedimentary phillipsite. Equilibrium ion-exchange data for intermediate-silica sodium (Na)-exchanged phillipsite at 25°C, in the presence of cation pairs Na/X, where X is barium (Ba), cobalt (Co), potassium (K), or calcium (Ca), are collected, and the relevant thermodynamic parameters are computed. Phillipsite is found very selective for Ba, K, and ammonium (NH 4 ), unselective for Co, whereas only about 50% Na could be readily replaced by Ca. This behavior is interpreted in terms of phillipsites structural features.

Ion exchange kinetics and thermodynamics of hydrosodalite, a narrow pore zeolite

The ion-exchange properties of a synthetic hydrosodalite (Na-hS) have been investigated by kinetic and thermodynamic analysis of exchange reactions of the original sodium form for lithium, potassium and calcium forms. Kinetic curves, modelled by a Langmuir-type equation, revealed that exchange rate for lithium and for potassium are of the same order, whereas they are two order faster than for calcium. Thermodynamic analysis of the cation exchange isotherms pointed out that sodalite is selective for sodium over the other three cationic forms examined, which is consistent with the preference exhibited by the sodalite type for sodium environments, either in natural or in laboratory crystallization. Na/Li and Na/Ca exchanges are incomplete, whereas unexpectedly Na/K exchange turns out to be complete, even though K+ dimension exceeds the width of the access window to sodalite cages. The obtained results have been discussed in terms of Eisenman–Sherry theory, pointing out agreements and discrepancies.

The combined use of steam-treated bentonites and natural zeolites in the oenological refining process

Abstract Industrial minerals, particularly bentonites, have long been used in treatments to improve the stability and shelf life of white wines. We evaluated a new combination of rocks and minerals, including steam-treated bentonites and natural zeolites (chabazite and phillipsite), to greatly reduce the risk of protein and tartaric instability of wines. Detailed mineralogical, chemical and electrokinetic studies of these materials were conducted using powder X-ray diffraction (PXRD), X-ray fluorescence (XRF), microporosimetry, BET surface-area analysis and zeta-potential measurements. Several model wine solutions containing Bovine Serum Albumin (BSA) were prepared to evaluate the oenological performance of the rock/mineral combinations. UV-VIS spectrophotometry and ion chromatography were used to evaluate the degree of wine stabilization from the protein and tartaric point of view. The experimental results showed that steam treatment modifies both the microporosity and external surface area of the bentonite. These changes in surface area, along with creation of hydrophobic surfaces, significantly modified the behaviour of the steam-treated bentonites, requiring an increase in the amount of material necessary to bring the protein content to required levels. An important benefit derived from the use of steam-treated bentonites is that the pre-mixing with water before addition to wine is not necessary, as the material is readily dispersed. Finally, the addition of natural zeolites effectively decreased the potassium content, thereby improving the tartaric stability of white wines. In addition, this procedure results in minimal waste, as the bentonite-zeolite mixture can be reused as soil amendments in agriculture.