Clinoptilotite-heulandite: applications and basic research

Natural Zeolite Clinoptilolite Application in Wastewater Treatment: Methylene Blue, Zinc and Cadmium Abatement Tests and Kinetic Studies

In recent decades, several abatement techniques have been proposed for organic dyes and metal cations. In this scenario, adsorption is the most known and studied. Clinoptilolite was considered, since it is a zeolite with a relatively low cost (200-600 $ tons^-1) compared to the most well-known adsorbent used in wastewater treatment. In this work, Clinoptilolite was used for the adsorption of Methylene Blue (MB) at three different concentrations, namely, 100, 200, and 250 ppm. Furthermore, the adsorption capacity of the natural zeolite was compared with that of Activated Charcoal (250 ppm of MB). The two adsorbents were characterized by complementary techniques, such as N₂ physisorption at -196 °C, X-ray diffraction, and field emission scanning electron microscopy. During the adsorption tests, Clinoptilolite exhibited the best adsorption capacities at 100 ppm: the abatement reached 98% (t = 15 min). Both Clinoptilolite and Activated Charcoal, at 250 ppm, exhibited the same adsorption capacities, namely, 96%. Finally, at 250 ppm MB, the adsorption capacity of Clinoptilolite was analyzed with the copresence of Zn²⁺ and Cd²⁺ (10 ppm), and the adsorption capacities were compared with those of Activated Charcoal. The results showed that both adsorbents achieved 100% MB abatement (t = 40 min). However, cation adsorption reached a plateau after 120 min (Zn²⁺ = 86% and 57%; Cd²⁺ = 53% and 50%, for Activated Charcoal and Clinoptilolite, respectively) due to the preferential adsorption of MB molecules. Furthermore, kinetic studies were performed to fully investigate the adsorption mechanism. It was evidenced that the pseudo-second-order kinetic model is effective in describing the adsorption mechanism of both adsorbents, highlighting the chemical interaction between the adsorbent and adsorbate.

Effect and mechanism of modification treatment on ammonium and phosphate removal by ferric-modified zeolite

In this study, the reason for the decline of ammonium sorption capacity by zeolite after ferric modification and the effect of modification treatment on ammonium and phosphate removal by ferric-modified zeolite were studied. Modification treatment media (Na salt and HCl) and Na concentration (0.1 and 0.9 mol/L) have been investigated. Zeolites have been characterized by SEM, XRD, BET and XRF; meanwhile, CEC and pHpzc have been also determined. Equilibrium batch sorption for ammonium and phosphate individually and kinetics batch sorption for ammonium were conducted. The results showed a decline in sorption capacity or diffusion coefficients for ammonium but an increase for phosphate after ferric modification. The decrease of surface negative charge was the main contributor for the former, but iron loading did not well account for the latter. The performance of 0.1 mol/L Na modification treatment was better than other treatments for ammonium sorption and equal to HCl modification treatment for phosphate sorption, and the enhancement extent increased for ammonium but declined for phosphate when Na concentration increased. The advantage of Na modification treatment for ammonium was due to the enhancement of textural properties and high exchange rate with ammonium.

Influence of Butyrate Loaded Clinoptilolite Dietary Supplementation on Growth Performance, Development of Intestine and Antioxidant Capacity in Broiler Chickens

The study was conducted to evaluate the effects of dietary butyrate loaded clinoptilolite (CLI-B) on growth performance, pancreatic digestive enzymes, intestinal development and histomorphology, as well as antioxidant capacity of serum and intestinal mucosal in chickens. Two hundred forty 1-day-old commercial Arbor Acres broilers were randomly assigned to 4 groups: CON group (fed basal diets), SB group (fed basal diet with 0.05% sodium butyrate), CLI group (fed basal diet with 1% clinoptilolite), and CLI-B group (fed basal diet with 1% CLI-B). The results showed that supplementation of CLI-B significantly decreased (P < 0.05) feed conservation ratio at both 21 and 42 days of age, improved the pancreatic digestive enzymes activities (P < 0.05), increased the villus length and villus/crypt ratio (P < 0.05), and decreased the crypt depth of intestine (P < 0.05) as compared to the other experimental groups. Furthermore, the CLI-B environment improved the antioxidant capacity by increasing the antioxidant enzyme activities (P < 0.05) in intestine mucosal, and decreasing the NO content and iNOS activity (P < 0.05) in serum. In addition, CLI-B supplementation had improved the development of intestine and antioxidant capacity of broilers than supplementation with either clinoptilolite or butyrate sodium alone. In conclusion, 1% CLI-B supplementation improved the health status, intestine development and antioxidant capacity in broiler chickens, thus appearing as an important feed additive for the poultry industry.

Electric fields in zeolites: fundamental features and environmental implications‡

A critical review of zeolites and their use in practical applications is presented. Specifically-considered are their role as media for selective light-induced oxidations using molecular O

Radiation Effects on Zeolite Nanomaterials - Some Potential Implications for Cleaning Liquid Nuclear Waste and for Enhanced Radioactive Decontamination

A series of group 1 and group 2 element cation-exchanged samples of zeolite X were prepared and exposed to a beam of spin-polarised, positive muons (of energy 28MeV/c) from a particle accelerator. Longitudinal field repolarisation measurements were made which identified, in each case, both diamagnetic and paramagnetic muon fractions. One of the paramagnetic components revealed a hyperfine field compatible with values reported previously for free muonium atoms (1585 G), while a secondary component was detected showing roughly half the hyperfine coupling measured for atomic muonium, leading to the conclusion that the muonium had become chemically-bound within the zeolite structure, probably via a single-electron bond to a coordinatively unsaturated aluminium atom. A significant “lost fraction” was also indicated along with superhyperfine and anisotropic components that repolarised in weaker magnetic fields (0-100G). As a general trend, the muonium atom yield was found to increase in order of the increasing radius/charge (riz) ratio, though it is constant within the experimental errors, while the chemically bound muonium was formed in similar proportion in all samples (14.1 + 1.9% of the total muonium polarisation), with the exception of HX and the parent NaX (from which the other zeolite samples were prepared by cation-exchange), in which it was absent. Along with data from zero-field experiments which were also undertaken, this is interpreted in terms of an entrapment or effective “scavenging” of radiolytic electrons by the cations (in the order Na+>K+; Mg2+>Ca2+>Sr2+>Ba2+) whose combination with positive muons is therefore impeded, thus reducing the yield of muonium atoms. Results for LiX are anomalous since the muonium yield is greater than expected, possibly due to a greater degree of covalency in the Li-0 bonding than pertains for the other cations. These results may have some implications for zeolites that suffer longterm radiation exposure/damage when they are used to clean radioactive cations (e.g. Cs +, Sr2+) from the waters of nuclear power stations and as materials whose cation-exchange capacity has been deliberately enhanced by prior exposure to ionising radiation.

Requirement of Acinetobacter junii for magnesium, calcium and potassium ions

The goal of this study was to determine the concentrations of Mg, Ca and K ions required for the formation of metabolically active population of phosphate (P)-accumulating bacterium Acinetobacter junii. The availability of Mg, Ca and K originating from natural minerals in the conditions of severe shortage of these cations was tested. In the case of shortage of Mg, Ca and K ions in wastewater the P removal was absent due to the decay of A. junii. In the cases of Mg or K shortage in wastewater the P removal was negligible due to the decay of A. junii, while Ca was not essential for the examined bacterium. The minimal required concentrations of Mg and K in synthetic wastewater were 0.64 mg Mg/mg P and 0.50 mg K/mg P. The natural zeolitized tuffs and bentonite, either in Mg, Ca or K form, successfully replaced the lack of Mg, Ca, K and trace metals in wastewater. The requirement of A. junii for examined cations was in the order: Mg>K>Ca.

Properties and applications of zeolites

Zeolites are aluminosilicate solids bearing a negatively charged honeycomb framework of micropores into which molecules may be adsorbed for environmental decontamination, and to catalyse chemical reactions. They are central to green-chemistry since the necessity for organic solvents is minimised. Proton-exchanged (H) zeolites are extensively employed in the petrochemical industry for cracking crude oil fractions into fuels and chemical feedstocks for other industrial processes. Due to their ability to perform cation-exchange, in which the cations that are originally present to counterbalance the framework negative charge may be exchanged out of the zeolite by cations present in aqueous solution, zeolites are useful as industrial water-softeners, in the removal of radioactive Cs+ and Sr2+ cations from liquid nuclear waste and in the removal of toxic heavy metal cations from groundwaters and run-off waters. Surfactant-modified zeolites (SMZ) find particular application in the co-removal of both toxic anions and organic pollutants. Toxic anions such as arsenite, arsenate, chromate, cyanide and radioactive iodide can also be removed by adsorption into zeolites that have been previously loaded with co-precipitating metal cations such as Ag+ and Pb2+ which form practically insoluble complexes that are contained within the zeolite matrix.

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves

Zeolites are microporous crystalline materials that find wide application in industry, for example, as catalysts and gas separators, and in our daily life, for example, as adsorbents or as ion exchangers in laundry detergents. The tetrahedrally coordinated silicon and aluminium atoms in the zeolite unit cell occupy the so-called crystallographic T-sites. Besides their pore size, the occupation of specific T-sites by the aluminium atoms determines the performance of the zeolites. Despite its importance, the distribution of aluminium over the crystallographic T-sites remains one of the most challenging, unresolved issues in zeolite science. Here, we report how to determine unambiguously and directly the distribution of aluminium in zeolites by means of the X-ray standing wave technique using brilliant, focused X-rays from a third-generation synchrotron source. We report in detail the analysis of the aluminium distribution in scolecite, which demonstrates how the aluminium occupancy in zeolites can systematically be determined.

Zeolite Mediated Reactions: Mechanistic Aspects and Environmental Applications

An overview is presented of basic research and applications for the use of zeolites in environmentally-related topics. The use of these materials to promote oxidation reactions, and other catalytic processes is surveyed along with ship-in-a-bottle synthesis of particular zeolite-encapsulated catalysts. Methods for probing the surfaces of zeolites using spin-probes and ESR detection are mentioned. The ability of some thermally activated zeolites to produce spontaneously radical cations by single-electron oxidation of organic molecules is reviewed. The issue of the degree of acidity of H-zeolites is discussed, which demonstrates them not to be super-acids. Some ESR determinations of the adsorption of NOx species onto selected zeolites are reviewed and the use of zeolites to catalyse desulfurisation of hydrocarbons is considered. Finally, there is mention made of the use of zeolites to catalyse hydrodechlorination of CFC's and other organic chlorine-containing compounds. Surfactant-modified zeolites (SMZ) for use as polyfunctional decontamination agents are further discussed. Theoretical methods, e.g. Density Functional Theory (DFT), are finding their own application to studying the mechanisms of reactions that are mediated by zeolites as is shown throughout.

Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff

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 Mg2+ and Ca2+ ions, while exchange of K+ ions is the poorest (Na+ > Mg2+ > Ca2+ > K+). At ammonium concentrations from 0.2 to 1 mmol cm(-3) the order is Na+ > Ca2+ > Mg2+ > K+. At concentrations higher than 1 mmol cm(-3) the order is Na+ > Ca2+ > K+ > Mg2+. 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 Mg2+ (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+, Mg2+, and Ca2+ ions, while exchange of K+ ions is the poorest. Due to poor exchange of K+ and H+ ions and good exchange of Na+, Mg2+, and Ca2+ 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+, Mg2+, and Ca2+ ions are present. On the acid-modified 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, Al3+ ions are exchanged best, followed by Na+, Mg2+, Ca2+, and K+ ions. Further to the results, it is to be assumed that exchangeable Al3+ ions available from clinoptilolite dissolution are best exchanged with H+ ions in acid solution.