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Background Natural zeolite heulandite (ZH) has been functionalized with 4-(3-triethoxysilylpropyl)- thiosemicarbazide (TSC) to increase the adsorption capacity of Cu(II), Co(II), and Ni(II) ions. Methods The functionalization is confirmed by nitrogen adsorption/desorption (BET), XRD, 1H, 13C NMR, FT-IR, and SEM-EDX techniques. The thermal stability of the modified zeolite is investigated by the TGA-DSC method. The adsorption of Cu(II), Co(II), and Ni(II) ions with the modified zeolite (ZH-TSC) is studied in one- and multi-ionic aqueous solutions with pH = 5.0. Significant findings The functionalization is accompanied by the significant structural changes in the surface of the zeolite. Grafting of TSC onto the zeolite decreases specific surface area and specific volume of pores and micropores of the material, the zeolite surface becoming more uniform and less porous. The adsorption capacity of ZH-TSC is found to be 0.46 mmol/g (29.5 mg/g), 0.42 mmol/g (24.9 mg/g) and 0.28 mmol/g (16.6 mg/g) for Cu(II), Co(II) and Ni(II), respectively. The adsorption of heavy metal ions on the surface of the modified zeolite ZH-TSC is mainly contributed by the formation of chelate complexes due to the donor-acceptor interaction of metal ions with nitrogen and sulfur atoms of the thiosemicarbazide fragment. Localization of Ni, Co, Cu coincides with the position of the coordination centers. Modified zeolite ZH-TSC can be used in environmental science, engineering, or medicine as an effective adsorbent/entero(hemo) adsorbent of heavy or toxic metals.

Elucidating the underlying structure-performance relationship of Fe3O4-containing catalysts for the aquathermolysis of crude oil is essential for the design of efficient heterogeneous catalysts. Therefore, recyclable Fe3O4 nanoparticles (NPs) with different morphology and particle size were first prepared and tested for catalytic aquathermolysis. The easily prepared Fe3O4 NPs with irregular morphology (L-Fe3O4) have larger intercrystalline mesopores than oleic acid-modified Fe3O4 NPs. This leads to enhanced mass transfer ability, more accessible active sites and thus better aquathermolysis performance. Moreover, these L-Fe3O4 NPs were loaded on a heulandite support by a scalable co-precipitation method, and this L-Fe3O4/heulandite catalyst showed very good performance in catalytic aquathermolysis, with a viscosity decrease of extra-heavy crude oil of 85.0%. The underlying structure-performance relationship was systematically investigated by XRD, HRTEM, EDX-mapping, FT-IR, elemental analysis, SARA (saturate, aromatic, resin and asphaltene) analysis and 1H NMR. The Fe3O4/heulandite catalyst broke C–S bonds and reduced the resin and asphaltene content of the oil. This work is important for the design of Fe3O4-containing catalysts in catalytic aquathermolysis.

Heulandite/polyaniline (HU/PANI) composite was prepared by mechanical mixing from natural heulandite and synthesized polyaniline. HU/PANI was characterized by XRD, SEM, TEM, FT-IR, and UV–Vis spectroscopy. The product is of polycrystalline nature with an average crystallite size of 25.7 nm and optical band gap of 1.69 eV. HU/PANI shows higher efficiency in the removal of light green SF dye than natural HU or PANI in the dark and under artificial illumination. The equilibrium time was attained after 360 and 480 min in the dark and under illumination, respectively. The results fitted well with pseudo second order and Elovich kinetic models. The adsorption isotherm in the dark fitted well with Langmuir isotherm model and the calculated qmax was 44.6 mg/g. Using illumination, the data fitted better with the Freundlich and Temkin model than with the Langmuir model. Based on response surface analysis, the predicted conditions for maximum removal of light green SF dye in the dark (70.9%) were 5.5 mg/L, 24 mg, 3, and 430 min for dye concentration, HU/PANI dose, pH, and contact time, respectively. Whereas, under light illumination (97%) at operating conditions of 15 mg/L, 15 mg, 3, and 589 min, respectively. The composite also shows high efficiencies in the removal of other types of acidic and basic dyes.

The sorption characteristics of Cs and competitive ion exchange with other alkali cations and Sr on three natural zeolites, chabazite, stilbite, and heulandite, were investigated. Chabazite showed the most rapid sorption of Cs, followed by heulandite and then stilbite, and this was closely related to its high cation exchange capacity (CEC) and low Si/Al ratio. The kinetic data for all zeolites were best explained by a pseudo-second-order rate model. The sorption process involved multiple steps and is influenced by the CEC values of the zeolites. The equilibrium adsorption isotherms of the three zeolites were best fitted by both the Langmuir and Freundlich models. The exchange isotherms of Cs and the other investigated cations clearly showed that chabazite showed higher selectivity for Cs than for the others. At lower equivalent fractions of Cs in solution, the selectivities for the other cations showed the following trend: Na > Li > Sr > K > Rb. However, for stilbite and heulandite, the selectivity for Cs is only higher at lower equivalent fractions, and isotherms show sigmoidal shapes mainly because there are more than two sorption sites for Cs while chabazite has one site. Those trends were confirmed by Kielland plots.

Vibrational spectroscopy can be considered as one of the most important methods used for structural characterization of various porous aluminosilicate materials, including zeolites. On the other hand, vibrational spectra of zeolites are still difficult to interpret, particularly in the pseudolattice region, where bands related to ring oscillations can be observed. Using combination of theoretical and computational approach, a detailed analysis of these regions of spectra is possible; such analysis should be, however, carried out employing models with different level of complexity and simultaneously the same theory level. In this work, an attempt was made to identify ring oscillations in vibrational spectra of selected zeolite structures. A series of ab initio calculations focused on S4R, S6R, and as a novelty, 5–1 isolated clusters, as well as periodic siliceous frameworks built from those building units (ferrierite (FER), mordenite (MOR) and heulandite (HEU) type) have been carried out. Due to the hierarchical structure of zeolite frameworks it can be expected that the total envelope of the zeolite spectra should be with good accuracy a sum of the spectra of structural elements that build each zeolite framework. Based on the results of HF calculations, normal vibrations have been visualized and detailed analysis of pseudolattice range of resulting theoretical spectra have been carried out. Obtained results have been applied for interpretation of experimental spectra of selected zeolites.

The removal of cobalt, zinc and manganese from aqueous solutions by natural zeolites has been examined using the batch method.The heavy metal ion concentrations in solution ranging from 50 to 400 mg/l were used. The extraction efficiency of natural zeolites for metal ions observed higher at the lower concentration. The results of extraction efficiency (%R) and the distribution ratio (Kd) increases with decreasing ion concentration in solutions. It is clear from these results that the Mordenite is a potential candidate for removal of Co2+, Zn2+ and Mn2+ ions from wastewater than the Stilbite and Heulandite. The extraction efficiency value for Co2+is observed highest forMordenite at a concentration of 50 mg/l. Present results suggest that natural zeolites can be removed heavy metal ions from wastewater effectively

Hydrothermally affected basaltic flows and volcaniclastic rocks in northwestern Parana (Brazil) display textural features associated with secondary minerals, reflecting the temperature intensity and evolution of the hydrothermal process. Determination of the secondary mineralogy and the geochemical processes associated with their precipitation are addressed in this paper. The lithotypes that comprise the bulk of the Parana Igneous Province have millimetric to centimetric vesicles filled by secondary minerals. Field data, petrographic descriptions, mineral characterization and mineral chemistry were used to analyze these secondary mineral phases. Matrix material in volcaniclastic rocks (e.g. shards, glass pisolites) precedes the precipitation of the secondary minerals. Coalescence and necking features are common in vesicles located on top of basaltic flows. Clay minerals identified as vesicle and/or fracture infillings include celadonite, illite/smectite (I/S) interestratifications, as well as montmorillonite and nontronite, with morphologies typical of authigenic volcanic processes such as cauliflower-like and honeycomb. The occurrence of different zeolites species is primarily controlled by CaO and Na2O activity in the hydrothermal fluid. Heulandite is the most pervasive zeolite, followed by stilbite and analcime. Calcite occurs in the center of vesicles, as the last crystallizing phase, or isolated in monomineralic vesicles. Vesicle formation occurred by magma degassing processes at temperatures of up to 1150 °C. However, infilling of these voids occurred later with the percolation of hydrothermal fluids external to the system. Although random from a geographical perspective, gradual decrease in temperature and fluid evolution were responsible for the systematic change in the mineral phases within individual vesicles. The hydrothermal fluid was marked by a Ca–Na signature, high cation/hydrogen ratio and low to intermediate temperatures, ranging between 50 and 200 °C. The controls for precipitation were mainly temperature and the chemical composition of the fluid, with high alkalinity and low H+ activity.

The aqueous chemistry, isotopic composition (δ18O and δ2H), and geothermometry of the Breitenbush Hot Springs area in the central Oregon Cascades were examined. Water samples were collected from springs (5), wells (8), and the Breitenbush River (2). Geothermometry was interpreted using the Reservoir Temperature Estimator (RTEst) software package and constrained by the reported mineralogy. Reservoir temperature was calculated assuming equilibration with chalcedony, celadonite, laumontite, heulandite, and epidote. Because of its relatively rapid reaction rate, calcite was presumed to remain equilibrated during cooling of the ascending reservoir waters. CO2(g) degassing from the springs was accounted for by adjusting the carbon content and temperature to be consistent with a cooling curve passing through the chemical composition of the deep well waters. The average estimated reservoir temperature of 137.1 ± 2 . 0 ∘ C is lower than the 174 to 180 °C reported in other multicomponent geothermometric studies. However, our new estimate is consistent with mineralogical, aqueous geochemical, and fluid inclusion data, and with geothermal borehole temperature measurements near the site. Stable oxygen and hydrogen isotope data indicate that the thermal waters at Breitenbush and Austin Hot Springs are a mixture of 4 to 8% "andesitic water" (Giggenbach, 1992) and local meteoric waters recharged at elevations of 1750 to 2200 m, along the crest of the Cascade Mountains. Br/Cl ratios, δ18O, and δD, and their correlation with Cl− concentrations from our study combined with data and analyses from other sources, suggests that Cl−, other halogens, and CO2 in the Breitenbush hot springs are primarily derived from degassing fluids rising from the serpentinized forearc mantle. The calculated reservoir temperature and average measured thermal water Cl− concentration were used with previously reported chloride-flux-based measurements by the USGS to estimate a hydrothermal discharge of 13.7 ± 1.6 L/s and an advective heat discharge of 7.1 ± 0.8 MW. This calculated hydrothermal heat loss is slightly less than Ingebritsen et al.'s (1992) previous estimate of 9 MW. However, it still represents a substantial transfer of heat from a relatively small, constant groundwater discharge.

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-Lowenstein 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-Lowenstein 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.

This study developed an approach to synthesise zeolite LTA from three different natural heulandite class zeolite deposits (Escott, Avoca, and NextSand). The challenge was to determine the impact of pre-activation of clinoptilolite or heulandite materials upon the synthesis of zeolite LTA. Heulandite (Escott; Avoca) was thermally less stable (ca. 200 o C) than clinoptilolite (NextSand) (ca. 600 o C); with all samples losing cation exchange capacity as a result of heating at elevated temperature (ca. 120 to 30 meq/100 g). Attempts to synthesise zeolite LTA from as received natural zeolite under typical industry conditions (80 °C; 2 h) were not successful due to the stability of the natural zeolite framework. In agreement with this discovery, the amount of active alumina and silica was relatively small ( 80 % of monomeric silicates and aluminates. Significantly, the zeolite product resultant from hydrothermal synthesis of the activated materials comprised of ca. 85 % crystalline zeolite LTA and non-diffracting material; independent of the activation method or the identity of the natural zeolite. This study revealed that fusion activation of natural zeolites improved the robustness of the synthesis process and opened up new avenues for green zeolite formation. Future studies should focus on reducing the activation costs by lowering activation temperature and sodium hydroxide consumption.

Industrial applications of natural zeolites depend on their mineralogical, physical and chemical characteristics. Over the last 20 years, Australian natural zeolites have been investigated for use in various industrial applications. However, there are few, if any, mineral characterisation studies on Australian natural zeolites since the early 1990s that use modern techniques. In this study, a detailed mineralogical analysis was conducted on zeolite specimens from Avoca and Werris Creek deposits, located in Queensland and New-South-Wales, respectively, in Australia. Their physical properties, thermal behaviour and porosity, as well as mineral compositions were determined by conventional methods, including thermogravimetry, N2 adsorption/desorption, optical microscopy, XRF, in situ XRD, SEM/EDS and EPMA/WDS. High-precision, high-accuracy measurements of the chemical compositions of fine-grained zeolites (

Chlorite, ordered mixed-layer chlorite-smectites, laumontite, quartz and albite are the most widespread alteration assemblage in cone-building and near-vent successions of lavas, autoclastic, pyroclastic and resedimented volcaniclastic deposits of the Oligocene Smrekovec Volcanic Complex, Slovenia. Randomly interstratified corrensite-chlorite with ~ 70–80% of corrensite layers (R0 Cr-Ch) is less common in occurrence and associated either with clinoptilolite and heulandite in fine-grained vitric tuffs, or with prehnite, laumontite, actinolite, analcime and albite in extensively altered and/or fractured host-rocks. The assemblage with clinoptilolite and heulandite indicates the temperatures of formation of

Clinoptilolite-Na, Na 2.55 Ca 1.67 K 0.37 (H 2 O) 21.5 [Al 6.21 Si 29.79 O 72 ], with the space group C 2/ m , a = 17.6229(4), b = 17.9957(3), c = 7.39625(15) A, β = 116.353(3)°, V = 2101.85(7) A 3 , 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 H 2 O over the wide pressure range. This occurs owing to the additional population of partially vacant positions. With further increasing the pressure, H 2 O 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.

The present study report the presence of natural zeolites, which were found in the andesitic basalts from the Combia geological formation, municipality of La Pintada, Antioquia department (Colombia). The collected samples were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with detector X-ray energy dispersive (SEM/EDX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM). The results shown the presence of an associated zeolites heulandite group with predominance of heulandite phase rich in calcium and potassium, with prevalence of platy habit and in a lesser extent the habit coffin type, tabular and block were also evidenced. The presence of chabazite, phillipsite and mordenite, were evidenced as minority zeolites phases. Based on the zeolites properties, the phases founded in Combia formation could be an interest materials for technological applications in areas such agriculture, catalysis or gas separation applications. Especially in Colombia this kind of mineral can be important because much of the current consumption is imported from other territories.

Bentonite is an important source of montmorillonite, but has a complex surface chemistry that results from its unique combination of properties, including thixotropic gel formation with water, high water absorption, high surface area, layered structure and high cation exchange capability, and may contain other crystalline or amorphous substances, such as quartz, cristobalite and feldspar. Montmorillonite is 2:1 layer in which surface charge development caused by isomorphous substitution results in inserting interlayer cations between its layers. The cations are easily exchanged with other cationic species, a property known as the cation exchange capacity (CEC). CEC values of various commercially available bentonites were determined by three different analytical methods to investigate the effect of the mineralogical composition on CEC value. The first CEC analytical method, termed the BaCl 2 /MgSO 4 method, is to substitute interlayer cations with Ba which is subsequently substituted with Mg and then titrated with EDTA in the presence of ammonia buffer. The second method is an ammonia electrode technique in which after ammoniating bentonites, an ammonia electrode is used to detect dissolved ammonia in the presence of NaOH, and the third is an equilibrium pH method in which all exchangeable metallic cations within the bentonite structure are replaced with acetic acid. Both CEC values obtained by the BaCl 2 /MgSO 4 method for two different masses of each bentonite were all within ± 10% of each other with several exceptions. CEC values obtained by the second and third methods were larger than by the first method, for bentonites that contained heulandite of the zeolite group. Additionally, CEC values found by the equilibrium pH method were higher than those determined by the ammonia electrode method for bentonites containing calcite which can be dissolved in acetic acid solution. Although the equilibrium pH method was the simplest to perform, it may be the least accurate, as the presence of calcite and zeolite-type minerals in bentonite samples can result in artificially high CEC values.

Spherical carbonate concretions are present in sedimentary strata of varying geological ages worldwide. Recent studies reveal that calcium carbonate concretions form very rapidly around dead organisms after burial in the seabed. However, the formation mechanism of spherical dolomite concretions in marine sediments, particularly the carbon source and the reason for their spherical shape, are still moderately known. This study aims to elucidate their formation process and diagenetic evolution through the characterization of the structure, mineralogical composition, and geochemistry in and around a concretion. Here, detailed studies were conducted on a gigantic dolomite concretion approximately 170 cm in diameter, which formed in tuffaceous fine sandstone of the Morozaki Group in Chita Peninsula, Japan. The Ca and Mg distributions in and around the concretion show that it rapidly formed by outward diffusion of bicarbonate from the carbon source in its center. The δ13C values ranging from +4.4‰ to +7.5‰ and large volume of dolomite cement indicate that the dolomite concretion formed at shallow depth from methanogenic organic matter decomposition during rapid sedimentation. Heulandite occurred only in the surrounding rock matrix comprising altered volcanic glasses because of high temperature during deep burial up to 2–4 km depth. This gigantic dolomite concretion properly preserves its evolution and changes in the superimposed post-depositional environment. This study shows that gaining a better understanding of spherical dolomite concretions can potentially help reveal the burial process of sediments during early diagenesis.

A magnetic composite material composed of nano-magnetite (NMT), heulandite (HE), and cross-linked chitosan was prepared and used as an adsorbent for methylene blue (MB) and methyl orange (MO). The composite was characterized for the morphology, magnetic and surface properties. The optimal mass ratio of chitosan:HE:NMT for the best removal of both dyes was determined to be 1:1:0.33. The adsorption of MB and MO followed the pseudo-second order kinetics, and the maximum adsorption capacities were 45.1 and 149.2 mg g −1 at pH 5.5, respectively. The adsorption of MB increased with the pH increase, while MO adsorption showed an opposite trend.

The present investigation deals with the synthesis of sodium rich heulandite (Na-HEU) zeolite and its applicability as a sorbent for the removal of Th(IV) and Eu(III) from aqueous waste. The diffraction and spectroscopic studies confirm that the as-synthesized material have crystalline heulandite phase. The electron microscopic study reveals the synthesis of nanosize Na-HEU zeolite particles. The sorption of Th(IV) and Eu(III) on as-synthesized Na-HEU zeolite in a single component system under batch process has also been investigated as a function of solution pH, contact times, sorbent dose, initial metal ion concentration and temperature. Based on the Langmuir sorption isotherm model, the predicted maximum monolayer sorption capacities of the as-synthesized Na-HEU for Th(IV) and Eu(III) at 323 K are found to be 0.62 mequiv./g and 0.66 mequiv./g, respectively. Thermodynamic parameters demonstrate the spontaneous and endothermic nature of the studied sorption systems.

A composite adsorbent was prepared by entrapping cross-linked chitosan and nano-magnetite (NMT) on heulandite (HE) surface to remove Cu(II) and As(V) in aqueous solution. The optimized mass ratio among chitosan, HE, and NMT was determined to be 1:1:2. Kinetics studies indicated the removal of both ions followed pseudo-second order kinetics, suggesting specific interaction with surface functional groups was the major route of the removal process. The composite gave the maximum equilibrium uptakes of Cu(II) and As(V) of 17.2 and 5.9 mg g −1 in initial concentration ranges of 16–656 and 17–336 mg L −1 , respectively. The thermodynamic data showed that both adsorption processes were thermodynamically favorable, spontaneous, and endothermic nature. The adsorption capacity for Cu(II) increased continuously with an increase in initial solution pH (3–9), but adsorption of As(V) showed an opposite trend. The overall results demonstrated the potential utility of the composite for Cu(II) and As(V) removal from aqueous solutions.

The outgoing cations of Greek heulandite-rich tuff samples (heulandite type-III, 91wt.%, mica 4wt.%, feldspar 5wt. %, CEC 2.22meq/g) were analysed upon exchange with ammonium acetate using atomic absorption spectrometry (AAS). The kinetic curves of each cation were investigated over a total time of contact of 720h with sampling at frequent intervals. The materials were examined by powder X-ray diffraction, SEM-EDS, and AAS. The sorption ability was measured using the ammonium acetate saturation method. It was found that Ca(2+) presents an unexpected extra-framework release and a surprisingly high degree of exchange (90%). The exchange of Mg (57%) is also worthy of note whereas the behavior of K(+) showed an expected rapid initial release. The behavior of Na(+) must be similar. However, its lower concentration in the zeolitic material minimizes its overall significance somewhat. On the other hand, Ca(2+) and Mg(2+) release is kinetically much slower, compared to that of alkali metal ions, and this phenomenon indicates that different exchange energies are needed till final equilibrium.

A natural zeolite specimen, consisting mainly of heulandite type-II and mordenite, was succumbed to NH 4 + and/or H + -exchange followed by one or two calcination steps and further acid leaching. In an attempt to examine the effect of each treatment on the starting material as well as on pre-modified (intermediate) samples, varied calcination temperatures, contact times and solutions concentrations were applied. On the grounds of the properties and expected behavior of pure substances, a combined XRD, FTIR, XRF, SEM and N 2 -porosimetry analysis enabled the monitoring and comprehension of the phenomena taking place during each treatment, despite the obscurity inherent in each individual analysis when dealing with impure materials. In general, the behavior of the typical counterbalancing ions Na + , K + , Mg 2+ and Ca 2+ , the Fe 3+ content, the extraction of Al 3+ from the lattice and the removal of amorphous Al-substances were found to be crucial factors concerning the properties of the modified samples.

Heulandite and clinoptilolite form the most abundant family of natural zeolite crystals. The topology of both of them is characterized by the framework type HEU. Despite many studies on these crystals, the mineral assignment to a zeolite as heulandite or clinoptilolite is still controversial and unresolved today. Based on a machine learning clustering analysis of crystallographic data of zeolite crystals, we show that zeolites belonging to the HEU framework type are divided into three groups of minerals instead of two. Two of the groups, HEU-h and HEU-c, contain crystals with names heulandite and clinoptilolite, respectively. The third newly proposed group HEU-m is composed of mixed zeolites named under both traditional names. The grouping is based on the EM algorithm and a set of descriptors built from data collected in the NIST/FIZ Inorganic Crystal Structure Database. Verification of the division of the HEU family into three groups is provided based on a battery of machine learning tests.

In this paper the properties and the hydration of cements containing natural zeolite, coming from the Metaxades area, Thrace, Greece, are studied. The experimental part comprises three stages. In the first stage a complete mineralogical characterization of the zeolite was performed. In addition, the pozzolanic reactivity of the zeolite was evaluated on the basis of the Chapelle test. In the second stage, the mechanical and physical properties of blended cements, incorporating 0%, 10% and 20% per weight of fine zeolite were determined. Finally, the hydration rate and products were studied by means of X-ray diffraction and FTIR spectroscopy, in combination with thermoanalytical methods (TG/DTG and DTA). As it is concluded, the examined zeolite consists mainly of heulandite type-II and is a pozzolanic material that contributes to the strength development of zeolite-cement mixtures, the consumption of Ca(OH)2 formed during the hydration of Portland cement and the formation of cement-like hydrated products. Finally, the addition of zeolite up to 20% w/w does not significantly affect the physical and mechanical properties of the blended cements.

The compound 5-amino-1,3,4-thiadiazole-thiol was anchored onto analogue of heulandite by heterogeneous route. The original (HEU) and modified heulandite (HEUATT) samples were characterized through elemental analysis and nuclear magnetic nuclei of carbon-13 and silicon-29. The ability of these materials to remove Mn(II), Zn(II) and Pb(II) from aqueous solution was followed by a series of adsorption isotherms adjusted to a Sips equation. To achieve the best adsorption conditions the influence of pH and contact time were investigated. Based on the capacity of adsorption of HEUATT to interact with metal ions

A study of breakthrough curves for cations usually found in acid mine drainage (Pb(2+), Cu(2+), Zn(2+) and H(+)) and municipal wastewater (NH(4)(+)) have been conducted on some natural zeolitic tuffs. The zeolitic tuffs used in this study are: three zeolitic tuffs from Cayo Formation, Guayaquil (Ecuador), characterized by X-ray diffraction as clinoptilolite (sample CLI-1) and heulandite (samples HEU-1 and HEU-2)-rich tuffs, and two zeolitic tuffs from Parnaiba Basin, Belem do Para (Brazil), characterized as stilbite-rich tuffs (samples STI-1 and STI-2). The clinoptilolite sample CLI-1 shows an exceedingly good exchange capacities for Pb(2+) and NH(4)(+) as received, and also a very high exchange capacity for Cu(2+) and Zn(2+) when conditioned with 2M sodium chloride, with much higher values than those reported in the literature for other clinioptilolite ores. A general order of effective cation exchange capacity could be inferred from breakthrough curves on these zeolitic tuffs: CLI-1 > HEU-2 > HEU-1 > STI-2. Since it is true for most of the cations studied.

Neutron Rietveld refinement of a natural heulandite (Si/Al = 3.1) in its deuterium form was performed in space group C2/m. Two Bronsted acid sites were identified. One was on framework oxygen O1, occupied to 20% and headed toward the center of the 8-membered ring channel running parallel to [1 0 2]; the other was on O6, occupied to 30% and headed toward the 10-membered ring channel running parallel to the c-axis. Three other extraframework sites, located around a distance of 3 A from the framework oxygens, were attributed to reabsorbed H2O molecules. On the whole, about 3.2 Bronsted acid sites were located representing about 37% of the value expected on the basis of the aluminium content. This discrepancy is attributed to proton transfer from the Bronsted site to reabsorbed H2O molecules, forming either a hydroxonium ion (H3O+) or charged clusters such as (H5O2)+ and (H7O3)+.

The synthesis of needle/fibrous particles of analogue of heulandite with particle diameter of 0.08 microm, length 4-8 microm and high specific surface area (478 m(2) g(-1)) with cation exchange capacity (3.27 mequiv g(-1)) have been achieved. The heulandite needles were obtained by using inorganic salts as a source for silicon and aluminum in the hydrothermal synthesis of the material. Alkalinity of the medium played an important role in the formation of heulandite fibers, as it affects the nucleation rate of zeolite synthesis. The analogue of heulandite was characterized using spectroscopic, thermal analysis, scanning and adsorption techniques. After mechanical grinding of crystals of heulandite, obtained powder was used for the study of radionuclide recovery from aqueous waste. The adsorption experiments were carried out under batch process with, pH of medium, amount of sorbent, time of contact between sorbate and sorbent, metal ion concentration and temperature as the variables. The adsorption was strongly dependent on pH of the medium and the uptake of all the metal ions increased from pH 1.0 to 9.0 and the maximum sorption was noticed in the pH range of 5.0-7.0. The optimum condition for these metal ions (Th(IV), Eu(III), Sm(II), and Fe(III)) sorption on self synthesized analogue of heulandite was; 0.001 N metal ion concentration, equilibration time of 4 h, 100 mg sorbent dose and 313-323 K temperature. This sorption process is fit to both Langmuir and Freundlich sorption isotherm. Thermodynamic studies predict the endothermic and spontaneous nature of the same.

This work shows the presence of zeolites in the Cretaceous Cayo formation in Coastal Ecuador. In the area of Guayaquil the Cayo formation consist of marine pyroclastic flow deposits, associated fallout tuffs and epiclastic rocks. The main zeolites are Ca-heulandite (mean Si/Al: 3.30) and Ca-clinoptilolite (mean Si/Al: 4.35). Less common are laumontite, mordenite and analcime. Zeolites compose 10–60% of the rocks. The deposit is of great importance for Ecuador, considering its enormous zeolitised outcrop area (more than 10,000 km2).

Data concerning potential solid products of the interaction of cement pore fluids with bentonite have been reviewed with respect to accurate prediction of bentonite alteration in the long-term. Calcium (aluminium) silicate hydrates (C(A)SH), zeolites, feldspars, hydroxides, carbonates, polymorphs of silica, and some sheet silicates (all of varying degrees of crystallinity) are potential products of cement–bentonite interaction. Evidence from natural systems and laboratory studies suggests that most, or all of these phases, may precipitate on timescales of interest to safety assessment of the geological disposal of radioactive wastes. These data indicate that growth kinetics of secondary minerals is equally as important as thermodynamic stability in controlling occurrence. C(A)SH show variable Ca/Si ratio and Al contents. At high pH (>11), the growth of C(A)SH minerals provides a means by which OH− ions from cement pore fluids may be titrated. Although thermodynamic data exist for a number of naturally-occurring crystalline C(A)SH minerals, they are of doubtful quality and should be applied with caution in predictive modelling. Zeolites are likely to form at lower pH than for C(A)SH, with the Si/Al ratio of the zeolite decreasing with increasing pH of the fluid. Zeolite stability is also strongly dependent upon silica activity in the fluid phase. Although silica activity in bentonite pore fluids will be spatially (and temporally) variable as hyperalkaline alteration proceeds, it is likely that minerals which could form would be those stable in quartz-saturated or supersaturated fluids. Currently available thermodynamic data for zeolites tend to overestimate their stability, leading to inaccurate predictions of their occurrence. Notwithstanding this uncertainty, it is considered that the following secondary minerals are the most likely to form in low temperature cement–bentonite systems: calcite, dolomite, chalcedony, C(A)SH of variable Ca/Si ratio, K-feldspar, illite, phillipsite, analcime, clinoptilolite, and heulandite. The relatively more siliceous zeolites (clinoptilolite, phillipsite) are likely to form at lower pH (distal regions of migrating cement pore fluids), whereas C(A)SH, illite, feldspars, and the more aluminous zeolites (analcime, heulandite) are more likely to form at higher pH and hence, the more proximal regions of migrating cement pore fluids. Predominantly Na-, K-bearing solids will be transformed to those dominated by Ca as the composition of cement pore fluids evolves with time.

A chemical, mineralogical and microstructural study was conducted on zeolitic rocks from two different formations in Cuba (Carolinas and Los Congos) to assess their value as pozzolanic components for cement. The samples were characterized using XRD, FTIR, BSE/EDX, optical microscopy 29Si and 27Al MAS NMR and BET-specific surface techniques. The studies showed the Carolinas rock to be hypocrystalline (predominantly glass) and contain subautomorphic and automorphic heulandite and/or clinoptilolite crystals, allotriomorphic calcite crystals–also present around the edges of the vacuoles–, and small, unevenly distributed masses of Fe and Ti oxide. Los Congos sample was found to be a vitreous (holohyaline), perlitic rock whose constituents included albite, small amounts of quartz, tiny veins and unevenly distributed specks of calcite, and Fe and Ti oxide appearing around the edges of cracks, as a cover over the veins and isolated masses, in addition to faujasite. Finally, both rocks were found to have pozzolanic properties. Both rocks exhibited pozzolanic properties, although the reaction rate with portlandite was much higher in the Carolinas than in the Los Congos samples. This result was related not to the particle size distribution of the materials, but to their soluble SiO2 content and mineralogy.

Volcanic pozzolans are vitreous or poorly crystallized materials rich in SiO 2 and Al 2 O 3 that react with the portlandite generated during cement hydration to yield hydrated calcium silicates and aluminates with low solubility and good cementitious properties (pozzolanic reaction). The purpose of the present study was to analyze the reaction between calcium hydroxide and two natural, partially crystalline pozzolans found in Cuba, characterize the C–S–H gels produced and determine the relationship between pozzolan composition and structure and its capacity to fix calcium. The findings of the XRD and FTIR analyses conducted with this aim included a gradual decline of the zeolite (heulandite and faujasite) peaks on the diffractograms with reaction time, and changes in the IR absorption bands attributed to the zeolites, along with the appearance of new bands indicative of the formation of the CSH gel. Although the amount of Ca fixed by the two pozzolans after 90 days was similar, the reaction rate was faster in the Los Congos material. The gel forming in the Carolinas sample had Al in its composition, with Q 3 (1Al) and Q 2 (1Al) units whose content increased with time. The presence of Fe in the Los Congos sample hampered the analysis of the gel formed, although the presence of Al in its composition could be inferred from the 27 Al MAS NMR data. The thermodynamic data showed that C–S–H gel was formed in both cases.

A new method for Biginelli reaction via heterogenous catalyst has been developed. This method uses natural Heulandite type zeolite (HTMA) as a catalyst for the one pot condensation of an aldehyde, urea and a 1,3-dicarbonyl compound under mild conditions in excellent yields.

Adsorption of tetraamineplatinum(II) hydroxide, a Pt catalyst precursor, from its aqueous solution onto a (0 1 0) surface of a natural zeolite heulandite was observed, in situ, by atomic force microscopy (AFM). The Pt complex exhibited certain adsorption habits on the surface, frequently forming a short chain along the zeolite a-axis, separated by three times the c unit cell length in the c direction. Possible adsorption sites on the surface were identified and discussed. The present work constitutes the first in situ atom-level observation of a liquid-phase preparation process of supported metal catalysts.

The zeolites of the Pentalofos area, Thrace, Greece, were studied by optical microscopy, X-ray diffraction (XRD) and Fourier Transform IR (FTIR) spectroscopy, in combination with thermoanalytical methods (thermogravimetric analysis (TG/DTG) and differential thermal analysis (DTA)). Their main mineral constituent (>90%) is “heulandite type-II”, an intermediate type of the isomorphous series heulandite–clinoptilolite end members. Feldspars, muscovite, biotite, quartz, and cristobalite were also detected. Traces of smectite were found in only few samples. The cation exchange capacity (CEC) of the Pentalofos zeolites (119 to 152 meq/100 g), as well as their low temperature dehydration behavior (during heating up to 350 °C, 15 of ∼22 molecules H2O are removed) are also characteristic for an intermediate member of the heulandite–clinoptilolite zeolite (“heulandite type-II”). These properties make them a powerful tool in the decontamination of waters and soils, in agriculture, in cement industry, etc. Moreover, this zeolite deposit is of a great economic interest, considering that it is the richest among the zeolite formations in Northeastern Greece (4.7×106 tons, with a zeolite content higher than 90%).

Summarization: Three HEU-type zeolites from Armenia, Georgia and Greece formed from alteration of volcanic glass were treated with dilute KOH and subsequently either reacted with 6N HCl or heated at 700 jC. The raw materials and the reaction products were examined with X-ray diffraction (XRD), infrared spectroscopy (FTIR) and N2 gas adsorption. The cation exchange capacity (CEC) of the zeolites was also determined. The Greek zeolite has thermal characteristics typical for heulandite I, while the Armenian and Georgian zeolites have characteristics typical for heulandite III (clinoptilolite). KOH treatment increased slightly specific surface area (SSA) and microporosity due to dissolution of amorphous material. Acid treatment increased significantly both specific surface area and microporosity, as determined by t-plots, and decreased CEC. This is attributed to partial dissolution of both Si-tetrahedra and free linkages, which yielded secondary micropores and destroyed specific exchange sites of the HEU-type zeolites. Heating decreased both specific surface area and microporosity. Presented on: Applied Clay Science

In this work, the effect of zeolite, coming from Pentalofos area, Thrace, Greece, on the hydration of cement is examined. The experimental part comprises three stages: In the first stage a complete mineralogical characterization of the zeolite was performed. In addition, the pozzolanic reactivity of the zeolite was evaluated on the basis of Chapelle test. In the second stage, pastes of Portland cement, incorporating 0%, 10%, 20% and 30% per weight of fine zeolite were prepared. The pastes were water-cured at 20 °C, for 1, 2, 7 and 28 days. Finally, the hydration rate and products were studied by means of X-ray diffraction and Fourier transform infrared spectroscopy, in combination with thermoanalytical methods (TG/DTG and differential thermal analysis). As it is concluded, the examined zeolite consists mainly of “heulandite type II” and shows a good pozzolanic reactivity (0.555 g of Ca(OH) 2 per gram of zeolite, according to the Chapelle test). The incorporation of zeolite in cement contributes to the consumption of Ca(OH) 2 formed during the cement hydration and the formation of cement-like hydrated products.

The in vitro adsorption of ochratoxin A (OCHRA) by clinoptilolite-heulandite rich tuff modified with different amounts—20, 50 and 100 μmol M+/g of octadecyldimethyl benzyl ammonium (ODMBA) ion was investigated. The organo-zeolites were denoted as OZ-2, OZ-5 and OZ-10. The maximal amount of ODMBA in organo-zeolites 100 μmol M+/g was equal to external cation exchange capacity of starting material. Adsorption of OCHRA by unmodified zeolitic tuff was 40% at pH 3 and 3% at pH 7 and 9. OCHRA adsorption on organo-zeolites increased as the levels of ODMBA increased. At low coverage of zeolitic surface with ODMBA–organo-zeolite OZ-2, adsorption of OCHRA was lower at pH 7 and 9 than at pH 3. The decreased adsorption of OCHRA at pH 7 and 9 may be induced by the presence of anionic form of OCHRA which probably led to repulsion between the OCHRA and uncovered negative zeolitic surface. At higher coverage of the zeolitic surface, organo-zeolites OZ-5 and OZ-10, adsorption of OCHRA was pH independent. OCHRA adsorption on OZ-2 and OZ-10 showed non linear type of isotherm at pH 3, 7 and 9. Adsorption of OCHRA by OZ-5 followed a non linear type of isotherm at pH 7 and 9, while at pH 3 the adsorption was best represented by an S-shaped isotherm. Adsorption of OCHRA on organo-zeolites is dependent on the amount of organic cation at the surface, as well as on their surface concentration—arrangement of alkyl chains at the surface. At low surface concentration of ODMBA, adsorption of OCHRA may be dependent on the form of OCHRA in solution.

Fully Cd-exchanged heulandite of Cd 4.00 Na 0.01 K Ca 0.09 [Al 8.70 Si 27.30 O 71.75 ] · 29H 2 O composition was used for stepwise dehydration experiments. The crystal was heated for approximately 12 h in a stream of hot air from 50 to 250 °C in steps of 50 °C. For X-ray single-crystal data collection the heating device was switched off and the crystal was immediately cooled to −173 °C. The crystal structures of the 50–200 °C data sets were refined in space group Cm , the 250 °C data were refined in C 2/ m . The original crystal had 29 H 2 O molecules per formula unit (pfu). Heating at 50, 100, 150, and 200 °C reduced the H 2 O content to 27(2), 25(1), 26(1), and 13(1) molecules pfu. At 250 °C heulandite-Cd became essentially anhydrous. With loss of H 2 O the cell parameters changed: a decreased slightly, b decreased strongly, c remained more or less invariant, and β increased leading to a decrease of the cell volume with dehydration. Due to the loss of the surrounding H 2 O molecules the Cd ions moved from the center of the eight- and ten-membered rings towards the framework walls causing distortion of the heulandite channels at 250 °C. Parts of the structure transformed to a heat collapsed B-phase. This new topology differs from the original A-phase by broken T–O–T bonds and the appearance of new T–O–T connections reducing the free aperture of the 10-membered ring channels. This new structure forms domains (≈28%) coherently intergrown with the heat collapsed (A type) heulandite framework. It is suggested that in absence of H 2 O and within strongly Cd populated domains, the bonding requirements of Cd 2+ extra-framework cations give rise to the altered T–O–T connections.

A successful route to prepare zeolites with controlled crystal size from the millimeter range down to nanometer scale by simulating the natural formation conditions is presented. Water is used as the solution and reaction medium at high temperatures and pressures (T=120–400°C, p=1 kbar); aluminosilicate glasses with identical chemical composition as the zeolite products are used as precursors. The synthesis of heulandite is reported as representative example.

In the work, the results of 27 Al MAS NMR studies carried out for structures of different framework aluminosilicates are presented. The spectra of natural clinoptilolite and its sodium and hydrogen forms were measured. The zeolite spectra were obtained before and after incorporation of heavy metal cations (Pb 2+ , Cd 2+ , Ni 2+ and Cr 3+ ) into the zeolite structure. After decomposition of the spectra into component peaks differences caused by ion exchange were observed. Additionally, NMR spectra of kalsilite (framework aluminosilicate, not belonging to zeolite group) and other zeolites (chabazite, heulandite and analcime) were measured. 27 Al MAS NMR spectra of all the samples studied were compared with the FTIR spectra measured in the middle infrared region. Based on the results obtained it has been proved that the interpretation of spectra obtained using these two different techniques can give some information concerning changes occurring in various framework aluminosilicate structures.

Adsorption of pyridine base molecules (pyridine and α-, β- and γ-picolines) on a surface of a natural zeolite, heulandite (0 1 0), was examined by Monte Carlo simulations. Two types of adsorption areas were identified on heulandite (0 1 0) bound by surface OH arrays, and each area showed different influence on the adsorption and orientation for pyridine base molecules. The presence of methyl group and its position within the adsorbed molecule also influenced its adsorption characteristics. For pyridine adsorption, molecular dynamics simulation was also performed. The results were compared with existing experimental data obtained through atomic force microscopy.

Surface structures of three zeolites, mordenite (MOR), heulandite (HEU), and Linde Type A (LTA), were investigated by using atomic force microscopy (AFM). The arrangement of 12-membered rings on the (0 0 1) surface of MOR was observed for the first time. Direct imaging of the morphological changes in the dissolving surface of HEU in an acidic or alkaline aqueous solution revealed that the aluminosilicate layers of HEU dissolved from terraces by a layer-by-layer process. This unique dissolution process is due to the characteristic pore structure of HEU. The AFM imaging of the (1 0 0) surface of LTA revealed that double four-rings (D4Rs) are stable units in the crystal growth of LTA and that each terrace has different structure depending on where the bulk structure terminates. This study demonstrates the potential use of AFM to provide information at the atomic level about the zeolite's surface structure vital to the further development of this important class of materials in the field of catalysis.

Grand canonical Monte Carlo simulation has been used to study adsorption of single components and mixtures of nitrogen and methane in purely siliceous models of chabazite and heulandite. The adsorbate framework interactions were modelled with both the Kiselev and the PN potentials. The latter predict rather narrower pores than the former, and this has significant effects on the predictions of the two models. In heulandite the differences can be related to the accessibility of 8-ring pores to nitrogen, since these form a large proportion of the pore space. In chabazite the differences are less notable since the framework contains wide cavities. Isotherms, heats of adsorption and selectivity from mixtures are discussed. Selectivity is found to be reversed between the two models. It may be concluded that the presence of cations in a silica-alumina framework is essential for viable selectivity, and that access through the narrow pores of the framework is a crucial factor.

A total of 48 samples, feed (run-of-mine) coals and their combustion residues (fly ash and bottom ash) were systematically collected twice a week over a 4 week period (June 1998) from two boiler units (I and II) of the Cayirhan power plant (630 MW) that burns zeolite-bearing coals of late Miocene age. The feed coals are high in moisture (22.8% as-received) content and ash (44.9%) yield and total S content (5.1%), and low in calorific value (2995 kcal/kg). The mineralogy of the feed coals contains unusually high contents of the zeolites (clinoptilolite/heulandite and analcime), which are distributed within the organic matter of coal. Other minerals determined are gypsum, quartz, feldspar, pyrite, dolomite, calcite, cristobalite and clays. Common minerals in the crystalline phase of the combustion residues are anhydrite, feldspar, quartz, hematite, lime and Ca–Mg silicate. Minor and trace amounts of magnetite, cristobalite, maghemite, gehlenite, calcite and clinoptilolite/heulandite are also present in the combustion residues. Trace element contents of the feed coals, except for W, fall within the estimated range of values for most world coals; however, the mean values of Mn, Ta, Th, U and Zr are near maximum values of most world coals. Elements such as As, Bi, Ge, Mo, Pb, Tl, W and Zn are enriched more in the fly ash compared to the bottom ash.

The antimicrobial effect of the Mexican zeolitic mineral from Taxco, Guerrero exchanged with silver ions was investigated. The zeolitic mineral as well as sodium and silver zeolitic minerals were characterized by using X-ray diffraction, electron microscopy and IR spectroscopy techniques. The elementary composition of the zeolitic mineral was determined by atomic absorption and microanalyses (EDAX). Escherichia coli and Streptococcus faecalis as indicators of fecal contamination of water were chosen to achieve the antibacterial effect of the Mexican silver zeolitic mineral. The amount of silver in water after contact with the Mexican silver zeolitic mineral as a function of both time and initial sodium concentration in liquid media using 110m Ag and 22 Na as radiotracers was analyzed. It was found that the Mexican silver clinoptilolite–heulandite mineral eliminated the pathogenic microorganisms E. coli and S. faecalis from water with the highest amount of silver supported on the mineral after 2 h of contact time. Under these conditions, the silver level in water remained in 50 μg l −1 (NOM-041-SSA1-1993).

Tetramethylammonium (TMA) and hexadecyltrimethylammonium (HDTMA) cations, applied to Na+-saturated zeolites (clinoptilolite, heulandite, chabazite) in doses varying from 0–150% of the mineral cation exchange capacity (CEC), were used to elucidate the mechanisms of adsorption of tailoring cations, as well as to determine the potential of organically-tailored zeolites for removal of approximately 40 mg/l of deprotonated dehydroabietic acid (DHA) dissolved in aqueous solution (pH 7.25). Langmuir-type adsorption isotherms indicated that both TMA and HDTMA cations, applied in doses less than the mineral external CEC (ECEC), were firmly bound by electrostatic forces on only the external surfaces of zeolite. HDTMA cations improved the DHA uptake capacity of heulandite and chabazite by twenty-fold, ensuring 100% removal of DHA with 20 g/l of tailored aggregates. Analysis of factorial experiments indicated that partitioning of DHA into the hydrophobic HDTMA layer was strongly dependent on the mineral concentration (41% of model variability), while the effects of cation loading, initial DHA concentration and aggregate size were marginal (9%). Over the range examined, temperature and time of treatment did not affect DHA removal. These initial promising results provide a rationale for further research aimed at investigating removal of extractives present in pulp and paper waste waters.

Sr-87/Sr-86 isotopic ratios, strontium and Rare Earth Element concentrations obtained on volcano-sedimentary rocks and separated clay mineral and zeolite fractions reveal a formation by pore water-volcanic rock interaction for most of the hydrous silicate minerals of the Site 841 ODP collected from the Tonga forearc. Unusual strontium concentrations and isotopic ratios recorded in the Miocene tuffs associated with specific REE patterns indicate that the formation of these hydrous silicates does not follow a simple burial diagenesis model, but was related to the cooling of intruding basaltic sills in the Miocene volcano-sedimentary series. Migration of strontium into the pore water in response to the heat flow induced the formation of Sr-bearing zeolites such as clinoptilolite, heulandite and chabazite. No evidence of any influence of a further thermal pulse in the Eocene rhyolitic tuffs could be found. As recorded by the chemistry of their clay mineral fraction, the rhyolitic tuffs developed a polyphasic diagenetic process, which might have been influenced by a possible circulation of a fluid into structurally weak areas., Les concentrations en strontium et en terres rares, ainsi que les rapports isotopiques 87Sr/86Sr des roches volcano-sédimentaires et des fractions argileuses et zéolitiques indiquent que la plupart des silicates hydratés du site 841 ODP de l'avant-arc Tonga se sont formés par interaction entre les roches volcaniques et les eaux interstitielles. Les concentrations et rapports isotopiques en strontium inhabituels, enregistrés dans les tufs du Miocène associés à des profils de terres rares spécifiques, indiquent que la formation de ces silicates hydratés ne suit pas un modèle de simple diagenèse d'enfouissement Elle est en relation directe avec le refroidissement d'intrusions de sill basaltiques dans les séries volcano-sédimentaires du Miocène. La migration du strontium dans les fluides interstitiels, en réponse au flux de chaleur, a entrainé la formation de zéolites contenant du strontium, telles que les clinoptilolite, heulandite et chabazite. Dans les tufs rhyolitiques de l’Éocène, aucune influence d'un flux thermique n'a été détectée. La chimie de la fraction argileuse de ces tufs indique qu'ils ont subi une diagenèse polyphasée probablement influencée par la circulation d'un fluide à travers leurs failles

Fully Cd-exchanged heulandite was obtained from a Na-exchanged sample by treatment with 1 M Cd acetate solution at 373 K. Subsequent electron microprobe analyses revealed 4.0 Cd2+ per formula unit (pfu), that was in good agreement with 4.11 Cd pfu refined from single-crystal X-ray data collected at 293 K. Crystal structure refinements were performed in the space groups C2/m, C2, Cm, C1:, and C1, of which only the Cm model yielded reasonable agreement with the observed diVraction data. Cadmium preferentially occupied the center of the A channel, where it formed a distorted octahedral Cd2+(H 2 O) 6 complex, and a central position in the B channel that was sevenfold coordinated by oxygen atoms of the framework and channel H 2 O molecules. Seven additional low-populated Cd sites were located in the channels. Cd-exchanged heulandite was refined in Cm symmetry in contrast to most other natural and cation-exchanged heulandites that commonly show C2/m symmetry. Symmetry lowering is attributed to Si,Al ordering in the tetrahedral framework as well as to the asymmetrical distribution of Cd2+ ions due to preferred Cd bonding of oxygen atoms sharing Al-enriched tetrahedra and cation‐cation repulsion. © 2000 Elsevier Science B.V. All rights reserved.

Low-temperature heat capacity of heulandite Na 0.365 K 0.059 Ca 0.861 Al 2.138 Si 6.860 O 18 ·6.17H 2 O was measured in an adiabatic vacuum calorimeter. The results obtained were compared with those for heulandite and clinoptilolite from literature. The errors in measurements of the water content are shown to be the main reason of discrepancies among the data on heat capacities for the zeolites. The random error can be as high as 1.1%. The greatest systematic error of 2.5% was shown to be in the heat capacities of clinoptilolite. Unusual temperature dependence has been recognized in published data on heat capacity of clinoptilolite, as if free electrons are there in a silicate. Heat capacity of four different species of heulandite–clinoptilolite series are known. However, the data published do not enable one to recognize the relationship between heat capacity and a composition.

Detailed analyses of crystalline, hydrated, and precipitated strontium compounds and an aqueous strontium solution by synchrotron extended X-ray absorption fine structure (EXAFS) were used to quantify local thermal and static disorder and to characterize strontium coordination in a variety of oxygen-ligated bonding environments. Analysis of anharmonic vibrational disorder (i.e., significant contribution from a third cumulant term (C(3)) in the EXAFS phase-shift function) in compounds with low and high static disorder around strontium showed that first-shell anharmonic contributions were generally not significant above experimental error in the EXAFS fits (R+/-0.02 Å with and without C(3)). The only case in which a significant apparent decrease in Sr-O distance was observed with increasing temperature, and for which a third cumulant term was significant, was for dilute strontium in aqueous solution. Empirical parameterization of Debye-Waller factor (sigma(2)) for strontium compounds as a function of backscatterer atomic number (Z), interatomic Sr-Z distance, and temperature of spectral data collection showed systematic increases in sigma(2) as a function of increasing temperature and Sr-Z bond length. At values of sigma(2) greater than approximately 0.025 Å(2) (for N12 and R(Sr)-Z3 Å), backscattering was generally not significant above noise levels in spectra of compounds of known crystal structure. Comparison of the EXAFS spectra of freshly precipitated SrCO(3) (spectra collected wet) to that of dry, powdered strontianite (SrCO(3)(s)) indicated no significant differences in the local atomic structure around strontium. Analysis of partially hydrated strontium in natural Ca-zeolite (heulandite) showed that strontium is substituted only in the calcium (Ca2) site. Backscattering from aluminum and silicon atoms in the zeolite framework were apparent in the EXAFS spectra at low and room temperature at distances from central strontium of4.2 Å. Comparison of strontium structural coordination determined in this and previous studies suggests that previous EXAFS determinations of hydrated strontium may have underestimated first-shell interatomic distances and coordination numbers because minor contributions to the EXAFS phase-shift and amplitude functions were not accounted for, either theoretically or empirically. Copyright 2000 Academic Press.