HEU-type Zeolite Research Articles

Insight into the structure of the heulandite-type zeolite containing aromatic compounds using periodic density functional theory

The heulandite-type zeolite (HEU) is an important class of naturally occurring zeolite materials. The recent development of a synthetic HEU zeolite with a high Si/Al ratio opens new possibilities for various applications. Herein, a periodic density functional theory with dispersion correction scheme (DFT-D3) was performed on the HEU-type zeolite. Various aspects of zeolite properties, such as the distribution of Al atoms within the zeolite framework, the prediction of the non-Löwenstein structure, and the presence of aromatic compounds within the cavity, were investigated. Calculation of the initial HEU framework shows that the Al atoms occupy the T2 and T3 sites in the most stable structure. Additionally, a non-Löwenstein structure was predicted for the first time to give a relatively stable HEU structure containing the Al–O–Al configuration. The preferred location of various aromatic compounds, namely, benzene, toluene and naphthalene, could be modeled in the 10-member ring channel to represent a host-guest system in this zeolite with a Si/Al ratio of 10. The results exemplify the importance of understanding the crystal structure of zeolites and the effect it has because of the presence of Al atoms and adsorbate molecules within the zeolite frameworks.

COMPARATIVE STUDY OF THE CESIUM UPTAKE ABILITY BETWEEN HEU-TYPE (CLINOPTILOLITE-HEULANDITE) ZEOLITIC TUFF AND PURE HEULANDITE

Specific continuous layers of zeolitic tuff in Ntrista stream location of Petrota area of Evros region (NA11) and pure natural crystals of heulandite (HEU1) from the collection of the Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, have been investigated. The X-Ray Diffraction analyses showed that the sample NA11 consists of 86 wt% HEU-type zeolite, 4 wt% micas+ clay-minerals, 4 wt% quartz, 2 wt% christobalite and 4 wt% feldspars, while the sample HEU1 is pure heulandite crystal. The mineral-chemistry was determined by SEM-EDS microanalyses. The zeolite of the NA11 sample is Ca-rich clinoptilolite and its chemical formulae is Ca1.8K1.0Mg0.7Na0.5Al6.4 Si29.5O72·21H2O, while the zeolite of the sample HEU1 is heulandite and its chemical formulae is Ca3.6Na1.0Κ0.2Sr0.2Ba0.1Al8.1Si27.6O72·21H2O. The uptake ability of the samples was measured by the AMAS method (Ammonium Acetate Saturation). The two examined materials show high uptake ability. The measured value for the zeolitic tuff NA11 is 231 meq/100g, while for the heulandite crystal (HEU1) is 296 meq/100g. For the determination of the cesium sorption a CsNO3 solution (concentration 500 mg/L), labelled with small activity of 137Cs, and pH 2-12 was used. The sorption of the cesium by the two materials, was determined by measuring the gamma radiation emitted by the 137Cs tracer. The zeolitic tuff presents higher uptake ability of radioactive cesium than the pure heulandite crystal, whereas the sorption of radioactive cesium is not significantly affected by the pH values of the initial solutions in the range pH 2-12.The clinoptilolitic zeolitic tuff NA11 is suitable material for various environmental, agricultural and industrial applications.

UPTAKE ABILITY OF ZEOLITIC ROCK FROM SOUTH XEROVOUNI, AVDELLA, EVROS, HELLAS

Zeolitic rock samples from South Xerovouni contain on average, 57 wt.% HEU type zeolite, 6 wt.% clay minerals, 3 wt.% mica (total of 66 wt.% microporous minerals), 19 wt.% feldspars, 10 wt.% cristobalite and 5 wt.% quartz (total of 34 wt.% non-microporous minerals). Chemically the zeolitic rock consists mainly of 69.9 wt.% SiO2, 13.2 wt.% Al2O3, 1.2 wt.% Fe2O3t, 1.0 wt.% MgO, 3.0 wt.% CaO, 1.5 wt.% Na2O and 2.2 wt.% K2O. The zeolitic rock shows an average ammonia ion exchange capacity of 150 meq/100g. HEU-type zeolite accounts for the most of the uptake ability, while clay minerals and mica contribute to a relative small extent only. The uptake ability of the five zeolitic rock samples showed positive correlations with the content of HEU-type zeolite as well as with the total content of microporous minerals (zeolite + mica + clay minerals). Such materials could be used in a wide range and scale of agricultural, aquacultural, and environmental applications.

PURIFICATION OF URBAN WASTEWATERS BY HELLENIC NATURAL ZEOLITE

Treatment of urban wastewaters (pHinitial 8.2), with 6 g of Hellenic Natural Zeolite (HENAZE) of an grain-size < 1.5 mm, gave overflowed clear water of pH 7.5, free of odors and improved quality parameters by 87% for the suspended particles, 88% for the color, 91% for the P2O5 content, 93% for the chemical oxygen demand (COD) and 97% for the NH4 content. Compared to previous experiment, the decrease of the amount of HENAZE by 1.5 g (20%) resulted to the purification worsening only by 1-2%. The HENAZE comes from Ntrista stream of Petrota village of Trigono Municipality of Evros Prefecture, Northeastern Greece. HENAZE contains 89 wt.% HEU-type zeolite and exhibit an ammonia ion exchange capacity (sorption ability) of 226 meq/100g. The mineralogical composition and the unique physico-chemical properties, make the HENAZE suitable material for numerous environmental, industrial, agricultural and aquacultural applications, such as: Animal nutrition, soil amendment for agriculture, pH soil regulation, greenhouse and flowers substrates, durability and health improvement of lawn, purification of industrial and urban wastewaters, treatment of sewage sludge, odor control, fishery and fish breeding, gas purification and drying systems, oxygen enrichment of aquatic ecosystems, improvement of drinking water quality, constructed wetlands and wastewater treatment units. The treatment gave as precipitate an odorless and cohesive zeo-sewage sludge, suitable for safe deposition and also for the reclamation of agricultural soils. The zeo-sewage sludge, produced either from the urban wastewater treatment or from the mixing of HENAZE and sewage sludge, can be used for the reclamation of agricultural soils. The presence of HENAZE in the agricultural soils, increases the crops yield by 29 57% and improves the quality of agricultural products by 4-46%, reduces the use of fertilizers by 55-100%, reduces the usage of irrigation water by 33-67%, prevents the seepage of dangerous species into the water environment (e.g., NO3 - by 55-57%), protecting thus the quality of surface and underground waters. The usage of HENAZE in vivarium units and in the animal nutrition, increases the production and improves the quality of the relevant products.

THE MINERALOGICAL COMPOSITION OF THRACE ZEOLITIC ROCKS AND THEIR POTENTIAL USE AS FEED ADDITIVES AND NUTRITION SUPPLEMENTS

Thirty two (32) locations of zeolitic rocks from Thrace (29 from Evros prefecture and 3 from Rhodope prefecture) were investigated for their mineralogical composition by X-Ray Diffraction (XRD) method. According to EU Regulation No 651/2013, clinoptilolite of sedimentary origin (zeolitic tuffs) with ≥80 wt% clinoptilolite, ≤20 wt% clay minerals, free of fibres and quartz, can be used as feed additive for all animal species. The zeolitic rocks of Thrace on average contain, 23-89 wt% HEUtype zeolite (clinoptilolite-heulandite), 8-45 wt% mordenite (ten locations), 24 wt% analcime (one location), 1-11 wt% mica, 1 11 wt% clay minerals, 3-37 wt% quartz, 2-29 wt% cristobalite, 3-34 wt% feldspars and 0-22 wt% amorphous materials. Only one location contains 89 wt% HEU-type zeolite (clinoptilolite-heulandite), 2 wt% clay minerals, is free of fibres, but unfortunately it contains 3 wt% quartz and 2 wt% cristobalite. Considering the mineralogical composition, the zeolitic rocks of Thrace do not meet the requirements of the EU Regulation No 651/2013, and thus cannot be used as feed additives for all animal species and consequently as nutrition supplements, since the zeolitic rocks in all locations, contain on average 3-37 wt% quartz, 2-29 wt% cristobalite, 8-45 wt% mordenite (fibrous zeolite) in 10 locations, 24-65 wt% zeolites (HEU-type ± mordenite ± analcime) in 28 locations, 74 wt% HEUtype zeolite in 2 locations and 77 wt% HEU-type zeolite in 1 location.

Neutralization of sludge and purification of wastewater from Sindos industrial area of Thessaloniki (Greece) using natural zeolite

The commixture of sludge from Sindos industrial area of Thessaloniki with high quality HEU-type natural zeolite (tuff with 86 wt.% clinoptilolite-heulandite) in equal proportions, resulted in odourless and cohesive zeosludge. Also, the treatment of wastewater of pH 7.8 from the same area with high quality HEU-type natural zeolite (88 wt.% clinoptilolite-heulandite) resulted in production of clear water of pH 7.3, free of odours and improved quality parameters by 60% for the NO3 - content, 76% for the chemical oxygen demand (COD), 100% for P2O5 and Cr contents. Simultaneously, a precipitate of odourless and cohesive zeosludge was produced. The odourless and cohesive zeosludge produced either by the commixture of sludge with the natural zeolite or as precipitate from the treatment of industrial wastewater with the natural zeolite and coagulants, is suitable for safe deposition, since the fixation of the hazardous components in the micro/nano-pores of the HEU-type zeolite, as well as the meso- and macro-porous of natural zeolite, prevents their leaching by the rain water, protecting thus the quality of soils, surface and ground waters.

High-pressure behavior of HEU-type zeolites: X-ray diffraction study of clinoptilolite-Na

Clinoptilolite-Na, Na2.55Ca1.67K0.37(H2O)21.5[Al6.21Si29.79O72], with the space group C2/m, a = 17.6229(4), b = 17.9957(3), c = 7.39625(15) Å, β = 116.353(3)°, V = 2101.85(7) Å3, and Z = 1 has been studied by single-crystal X-ray diffraction method in normal conditions as well as under compression in penetrating (water-containing) and non-penetrating (paraffin) media. When compressing in water medium, clinoptilolite is subjected to the additional hydration at the starting stage unlike the structurally similar heulandite with persistent increasing the content of H2O over the wide pressure range. This occurs owing to the additional population of partially vacant positions. With further increasing the pressure, H2O molecules are redistributed in the extraframework subsystem saving the total number. Both literature and our data on compression of zeolites of the isomorphous heulandite-clinoptilolite series in non-penetrating media evidence that the compressibility along the coordinate directions noticeably differs from sample to sample including differences in the direction of the largest compression. This is evidently associated with variations in the zeolite composition.

Application of Hellenic Natural Zeolite in Thessaloniki industrial area wastewater treatment

The treatment of wastewater (initial pH 7.7) from Sindos industrial area of Thessaloniki (Greece) with different proportions (0.1, 0.2, 0.4, 0.8, 1.6, 3.2, and 6.4 g) of Hellenic natural zeolite (HENAZE), resulted in overflowed clear water of pH 7.4–7.3, free of odours and improved by 69–76% for the chemical oxygen demand, 54–70% for nitrate (NO3-), over than 97% for the P2O5 content, 33% to over than 50% for Pb and 77% to over than 88% for Cr. The treatment process gave also as precipitate an odourless and cohesive zeosludge which is suitable for safe disposal. The HENAZE comprises very high-quality HEU-type zeolitic tuff, containing 86 wt.% HEU-type zeolite (clinoptilolite-heulandite), 4 wt.% mica + clay minerals, 5 wt.% quartz + cristobalite + tridymite, and 5 wt.% feldspars. The HENAZE cannot be used as feed additive for animals and consequently as nutrition supplements, since it contains SiO2 minerals (quartz, cristobalite, tridymite), while chemically, is suitable for use as soil conditioner, since the concentration of trace elements (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) are lower than the maximum allowable concentrations for agricultural soils.

The potential of clinoptilolite-rich tuffs from Croatia and Serbia for the reduction of toxic concentrations of cations and anions in aqueous solutions

Natural zeolites have a great potential as low-cost, non-toxic and highly selective sorbents in pollution control, especially in waste-water management. The potential of Croatian and Serbian clinoptilolite-rich (HEU-type zeolite) tuffs from four different deposits have been evaluated for their use in metal removal from aqueous solutions by the application of adsorption equilibrium studies, structural studies of metal-loaded zeolite tuffs and their regeneration or further treatment, which were performed in our laboratories or were reported by other authors. The results showed that metals like copper could be completely removed from aqueous solutions at low metal concentrations using Serbian and/or Croatian zeolites (up to 120mg Cu/L). At higher concentrations the efficiency of zeolites slowly decreased, also in accordance with the theoretical adsorption capacities. The studies confirmed that a higher content of zeolite in tuffs from Serbia (70–80% vs. 50% for Croatian tuff) resulted in their better adsorption performance for selected metals. Additionally, the pretreatment of zeolites with Na+ significantly enhanced the uptake of all metal cations, while the pretreatment with Fe3+, which resulted in stable iron-oxo-species on the zeolite surface and positive charge of the framework, enabled the adsorption of anions, like arsenites, arsenates and chromates. The reversibility of the metal uptake depended on the type of metal; for example, post-treatment of the samples with HCl, NaCl or NH4Cl solutions revealed irreversible adsorption of chromium and arsenic and mostly reversible adsorption of zinc and copper. The possible strategies for the regeneration or immobilization of the used metal-loaded zeolites, like immobilization in cements or the use as catalysts, were also considered.

Application of model-free kinetic analysis methods to dehydration of a HEU-type zeolite rich tuff from Turkey

AbstractNon-isothermal dehydration kinetics of a heulandite-type zeolite-rich tuff from Turkey was investigated using thermogravimetric data recorded at three different heating rates (5, 10 and 20°C/min) under nitrogen flow. Isoconversional model-free methods gave a constant activation energy over the temperature range 30–200°C suggesting that the dehydration is a single-step process within this temperature range. The apparent activation energy was determined as: 34.54±1.18, 30.99±1.14 and 27.79±1.42 kJ/mol by the Flynn–Wall–Ozawa, the Kissinger–Akahira–Sunose and the Friedman methods, respectively. The activation energy values determined were less than the activation energy for vaporization of bulk water, indicating control of the dehydration rate by diffusion of water within this temperature range.

Direct observation and structural characterization of natural and metal ion-exchanged HEU-type zeolites

The atomic structure of natural HEU-type zeolite and two ion-exchanged variants of the zeolite, Ag+ (Ag-HEU) and Zn2+ (Zn-HEU) ion exchanged HEU-type zeolites, are investigated using advanced transmission electron microscopy techniques in combination with X-ray powder diffraction and X-ray absorption fine structure measurements. In both ion-exchanged materials, loading of the natural HEU zeolite is confirmed.Using low-voltage, aberration-corrected transmission electron microscopy at low-dose conditions, the local crystal structure of natural HEU-type zeolite is determined and the interaction of the ion-exchanged natural zeolites with the Ag+ and Zn2+ ions is studied. In the case of Ag-HEU, the presence of Ag+ ions and clusters at extra-framework sites as well as Ag nanoparticles has been confirmed. The Ag nanoparticles are preferentially positioned at the zeolite surface. For Zn-HEU, no large Zn(O) nanoparticles are present, instead, the HEU channels are evidenced to be decorated by small Zn(O) clusters.

Synthesis and characteristics of novel layered silicate HUS-7 using benzyltrimethylammonium hydroxide and its unique and selective phenol adsorption behavior

A new layered silicate, HUS-7, was synthesized using amorphous silica, sodium hydroxide, biphenyl, and benzyltrimethylammonium hydroxide as a structure-directing agent (SDA). Structural analyses by powder X-ray diffractometry and solid-state magic-angle-spinning (MAS) NMR spectroscopy revealed that HUS-7 had a layered structure, which was composed of four-, five-, and six-membered rings. Its framework topology was partially similar to that of a HEU-type zeolite including the bre (10T)-type composite building unit. Structural refinement by the Rietveld method showed that the benzyltrimethylammonium cations used as the SDAs were incorporated into the interlayers. The presence of hydrogen bonding between adjacent terminal O atoms was clearly revealed by 1H MAS NMR spectroscopy and the electron-density distribution obtained by the maximum entropy method. HUS-7 selectively and effectively adsorbed phenol from acetonitrile solution containing benzene and phenol. The adsorption of phenol occurred through the exchange of water molecules in the interlayers with phenol.

Synthesis and characteristics of novel layered silicates HUS-2 and HUS-3 derived from a SiO2–choline hydroxide–NaOH–H2O system

Three kinds of layered silicates, HUS-2, HUS-3, and HUS-4, were synthesized using amorphous silica, sodium hydroxide, and choline hydroxide as a structure-directing agent (SDA). Structural analyses by powder X-ray diffractometry and solid-state magic-angle-spinning (MAS) NMR spectroscopy revealed that HUS-2 had a layered structure, which was composed of four-, five-, and six-membered rings. Its framework topology was partially similar to that of a HEU-type zeolite including bre (10T)-type composite building units. Structural refinement by the Rietveld method showed that the choline cations that were used as an SDA were incorporated into the interlayers. Double silicate layers were included in each unit cell. The interlayer distance was estimated to be ca. 0.36 nm. The presence of hydrogen bonding between adjacent terminal O atoms was clearly revealed by 1H MAS NMR spectroscopy and through the electron-density distribution obtained by the maximum entropy method. Although the crystal structure of the layered silicate HUS-3 could not be analysed, the HUS-3 was transformed into a CDO-type zeolite by calcination, indicating that the structure of HUS-3 was partially similar to that of a CDO-type zeolite precursor. The crystal structure of HUS-4 was similar to that of PLS-1 synthesized using tetramethylammonium hydroxide. We also demonstrated that the layered silicates HUS-2 and HUS-3 exhibited high catalytic activities as base catalysts in a Knoevenagel condensation reaction.

Ammonium exchange capacity of the Xerovouni zeolitic tuffs, Avdella area, Evros Prefecture, Greece

AbstractZeolitic tuffs from the Xerovouni location of the Avdella area (Evros Prefecture, Greece) contain on average 54 wt.% HEU-type zeolite, 6 wt.% smectite, 4 wt.% mica (64 wt.% microporous minerals), 8 wt.% alkali feldspar, 9 wt.% plagioclase, 11 wt.% cristobalite and 8 wt.% quartz (36 wt.% non-microporous minerals). The chemical formula of the HEU-type zeolite is Ca2.4K0.6Na0.4Mg0.3Al6.7Si29.3O72·17H2O and the tuffs contain on average 72.3 wt.% SiO2, 11.9 wt.% Al2O3, 1.2 wt.% Fe2O3, 1.0 wt.% MgO, 2.8 wt.% CaO, 1.3 wt.% Na2O and 1.9 wt.% K2O. The zeolitic tuffs show an average ammonium exchange capacity of 144 meq/100 g. HEU-type zeolite accounts for the most of the ammonium exchange capacity, while smectite and mica contribute to a relatively small extent. The ammonium exchange capacity of the Xerovouni zeolitic tuffs showed positive correlations with (a) the HEU-type zeolite content, (b) the total microporous minerals content, (c) the loss on ignition content and (d) the CaOcontent. Such materials could be used in a large variety of agricultural, aquacultural, industrial and environmental applications.

THE CATION EXCHANGE CAPACITY OF THE GREEK ZEOLITIC ROCKS

Forty two zeolitic rock samples, from the Prefectures ofEvros, Rhodope, Samos and Cyclades, have been investigated for their cation exchange capacity (CEC, in meq/100g) and the mineralogical composition (wt.%), using the Ammonium Acetate Saturation method and Powder X-ray Diffraction method, respectively. HEU-type zeolite (heulandite-clinoptilolite) was found in Ρ etrota area (43-89 wt.%, CEC 101- 217), Samos island (34-91 wt.%, CEC 93-217), Pentalofos area (68-74 wt.%, CEC 124-202), Metaxades area (47-64 wt.%, CEC 119-140) and Thira island (33 wt.%, CEC 118). Mordenite was found in Samos island (64 wt.%, CEC 150), Polyegos island (61 wt.%, CEC 136), Thira island (56 wt.%, CEC 130), Milos island (45 wt.%, CEC 97), Kimolos island (30 wt.%, CEC 96) and Feres area (5 wt.%, CEC 22). Analcime was found in Samos island (27-71 wt.%, CEC 104-285) and Darmeni area (16 wt.%, CEC 62). Chabazite was found in Samos island (66 wt.%, CEC 243). HEU-type zeolite+mordenite were found in Feres area (45-74 wt.%, CEC 132-209), Samos island (81 wt.%, CEC 184), Thira island (72 wt.%, CEC 177), Polyegos island (66 wt.%, CEC 153) and Skaloma area (51-60 wt.%, CEC 126-143). HEUtype zeolite+phillipsite were found in Samos island (47 wt.%, CEC 170) and HEUtype zeolite+analcime were found in Samos island (55 wt.%, CEC 129). The CEC of the zeolitic rocks show positive correlations with the type of zeolite and the microporous minerals (zeolites+micas+clay minerals) content, mainly affected by the zeolites and to lesser extent by micas and clay minerals.

Thermal distinction of HEU-type mineral phases contained in Greek zeolite-rich volcaniclastic tuffs

Ten zeolite-bearing rocks rich in HEU-type zeolites from Evros District and Samos island were studied. The samples were heated at 450°C for 8 h and the reductions in the intensity and the peak area of the (020) reflection was measured. Electron microscope and thermal analyses were used, as well. The results of the above methods gave an explicit picture for the HEU-type phases that exist in each sample and they led to their regrouping in three different groups: group I where the main phase of deter- mined HEU-type zeolite was clinoptilolite, group II, presenting mediate characteristics between groups I and III, where the contained main phase of HEU-type zeolite is intermediate heulandite, and group III, where heulandite is the main HEU-type zeolite phase. The combined study of the XRD results in initial and thermally treated samples, compared with the SEM-EDS results and the thermal study of the mass recovery during the cooling stage of the thermal analysis constitute a useful tool for the classification of the HEU-type zeolites in their different phases.

Sorption of Cadmium from Aqueous Solutions at Different Temperatures by Mexican HEU-type Zeolite Rich Tuff

Sorption of Cadmium from Aqueous Solutions at Different Temperatures by Mexican HEU-type Zeolite Rich Tuff

Sorption of Cadmium from Aqueous Solutions at Different Temperatures by Mexican HEU-type Zeolite Rich Tuff

Many factors may affect the heavy metals sorption on natural zeolites among them the temperature, for this reason in this paper the cadmium retention behavior on Mexican zeolitic rich tuff as a function of temperature is considered. The kinetic and the isotherms were determined at 303, 318, and 333 K, the remaining cadmium in the solution samples was analyzed by atomic absorption spectrometry. The pseudo-second order rate constant, k, as well as the apparent diffusion coefficients were calculated from the cadmium uptake by the zeolitic rock as a function of the contact time and temperature, the highest amounts were found for the experiments done at 333 K. The maximum cadmium adsorption capacity by the zeolitic material was 12.2 mg Cd2+/g at 318 K corresponding to 20% of the effective ion exchange capacity of the Chihuahua zeolitic rock. In order to explain the cadmium sorption behavior different kinetics and isotherm models were considered.

Physicochemical and structural characteristics of HEU-type zeolitic tuff treated by hydrochloric acid

Samples of natural HEU-type zeolites ? clinoptilolite-Ca, from the Novakovici deposit (near Prijedor, Bosnia and Herzegovina) were treated with the hydrochloric acid of various concentrations (from 10-3Mto 2M). Zeolitic tuffs before and after the acid treatment were examined using IR, XRPD, and chemical analyses. The changes in the crystal structure of acid treated samples showed a significant reduction in the crystallinity of zeolitic tuffs (60?70 %), which were effected by hydrochloric acid with concentrations of 1 M and above.

HEU‐Type Zeolites Modified by Transition Elements and Lead

AbstractFor Abstract see ChemInform Abstract in Full Text.