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This study presents the successful synthesis of a vibrant blue nanopigment derived from the metastable structure of Na‐heulandite zeolite. Employing ion exchange and coprecipitation methods with cobalt and zinc ions, followed by thermal treatment at 1100°C, resulted Co‐willemite and gahnite phases, confirmed by x‐ray diffraction and Rietveld refinement. Optical analyses verified the blue coloration, with cobalt ion transitions evident. CIE L* a* b* colorimetric analysis placed the pigment in the blue region (L* = 49.19, b* = −22, a* = −11). Application to ceramic tiles, followed by sodium dodecyl sulfate (SDS) modification, produced a nearly superhydrophobic surface (contact angle 140°, sliding angle 8°), attributed to the nano–micro structure and SDS–silica interaction. Field emission‐scanning electron microscopy images confirmed the pattern‐like surface with small patterns. These findings indicate potential self‐cleaning capabilities when exposed to dirt or water, highlighting the research's promise in enhancing ceramic functionality. [ABSTRACT FROM AUTHOR]

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Natural tuff samples in western Anatolia (Türkiye) originating from Miocene rhyolitic–pyroclastic rocks with >80 wt.% heulandite/clinoptilolite zeolites were investigated for their surface characteristics determined according to nitrogen adsorption after degassing at 150°C (specific surface area, pore volume and pore diameter). Additionally, these surface characteristics were correlated with the cationic compositions of the heulandite/clinoptilolite group minerals. The examined samples were characterized by two main pore diameters that were not related to specific surface area and pore volume but were partially related to the types and occupancy of extra-framework cations. One set of samples has a pore diameter of ~24 Å, total cation content (Na + K + Ca + Mg) ranging from 3.46 to 4.40 and a (Na + K)/(Ca + Mg) ratio ranging from 0.34 to 0.92. The total cation contents and (Na + K)/(Ca + Mg) ratios of the remaining samples with a pore diameter of ~37 Å are 4.30–5.08 and 1.48–2.85, respectively. After degassing at 300°C, there is a slight difference in the pore diameters of these two sets of samples (~37 and 38 Å). The pore sizes of the samples with a (Na + K)/(Ca + Mg) ratio < 1 (heulandite composition) increased from 24 to 36–38 Å with increasing degassing temperature, whereas the pore sizes of the samples with a (Na + K)/(Ca + Mg) ratio > 1 (clinoptilolite composition) increased from 37 to only 38–39 Å. However, there is no correlation between the Si/Al ratios and the cation-exchange capacities of the samples and their surface characteristics obtained by degassing at the two temperatures. [ABSTRACT FROM AUTHOR]

Acid treatment of natural zeolites is considered to be an effective method of “improving” their structure and properties, among which thermal stability occupies a special place, especially for catalytic applications of zeolites. The influence of hydrochloric acid solutions with concentrations up to 2 mol/L and calcination at temperatures up to 1100 °C on the structure and properties of heulandite-containing tuff from the Georgian Dzegvi-Tedzami deposit, selected for the creation of new bactericidal zeolite filter materials for purification and desinfection of water from various sources, was studied by the X-ray energy dispersion spectra, diffraction patterns and thermal analysis, as well as by adsorption of water, benzene and nitrogen methods. It has been found that an acidic environment leads to significant dealumination (Si/Al molar ratio increases from 3.6 to 9.5) and decationization (total charge of metal ions per Al atom decreases from 1 to 0.68) of the sample; solutions of hydrochloric acid do not lead to amorphization of the zeolite microporous crystal structure, but gradually dissolve it. As a result of acid treatment, there is also a sharp increase in the volume of micropores available for large molecules (from ≈ 7 to 80–90 mm³ /g) and surface area (from ≈ 13 to 120–175 m² /g), as well as changes in the mesoporous system, leading to the prevalence of pores with a diameter of up to 4 nm. Heulandite heating leads to stepwise dehydration proceeding up to ≈ 800 °C, amorphization starting at ≈ 250 °C, and structural changes: the transition to methastable heulandite B phase at ≈ 340 °C is not fixed, but at ≈ 500 °C wairakite (Ca(Al2Si4O12)∙2H2O) is formed, at temperatures above ≈ 1000 °C, amorphous aluminosilicate contains crystalline inclusions of cristobalite (polymorph of SiO2), α-quartz, albite (Na(AlSi3O8), hematite (Fe2O3) and magnetite (FeO∙Fe2O3); heating-induced changes in micro- and mesopore systems are insignificant. It is also shown that heat treatment increases the acid resistance of heulandite, which is expressed in a decrease in the degree of dealumination after acid treatment of calcined samples. Thus, acid and heat treatment of heulandite make it possible to obtain materials with different sorption and ion-exchange properties. [ABSTRACT FROM AUTHOR]

The interaction between methanol and the Heulandite-type zeolite has been unveiled to give an atomic scale detail regarding the catalytic activity of this zeolite for methanol conversion. The study was carried out by first principle molecular dynamics to get an insight into the structure and electronic behaviour of methanol inside the zeolite structure at different temperatures. The behaviour of methanol was studied when the location of the proton of Bronsted acid sites was varied to give both possible direct and less interaction with methanol. The results show that methanol interacts with the proton from zeolite to give a cationic species of [CH3OH2]+ both in 300K and 573K conditions. However, when the proton is located at different location far from possible interaction with methanol, the formation of a cationic species is hindered. This study provides an insight into the design of Heulandite type zeolite to give a catalytic activity toward methanol transformation.

The results of an investigation of the structure and adsorption properties of a Mo/zeolite composite obtained by enrichment of zeolite from the Chuguevskoe deposit in Primorskii Krai with Mo nanoparticles followed by sintering are presented. Its phase and elemental compositions were determined. The adsorption-structural characteristics of the composite were investigated by means of the BET method. The specific surface area, total pore volume, and mesopore size distribution were determined. The results obtained are of interest for the production of catalytically active materials based on zeolite raw materials. [ABSTRACT FROM AUTHOR]

Clinoptilolite is one of the most common, widespread and abundant zeolites in nature. Its availability, low cost, and outstanding ion exchange properties make clinoptilolite an excellent candidate for both direct use and various modifications to create new low-cost functional materials for sustainable development. Specific applications in which clinoptilolite is already being used include water treatment and heavy metal ion removal, agricultural purposes, storage and conversion of unwanted gaseous emissions into the atmosphere, production of catalysts and photocatalysts, bioactive materials, and a number of others. Unlike some other zeolites, clinoptilolite is difficult to synthesize, which is why most publications refer to this zeolite in its natural form, either directly from the deposit or after applying various processes to this mineral to improve its properties. Among the modification methods used, ion exchange stands out. This review is devoted to the study of ion exchange processes in natural clinoptilolite with two goals: first, as its strategic property for use in processes in which cation exchange is fundamentally necessary; second, as a way to modify it to create composite materials with predetermined desired properties. [ABSTRACT FROM AUTHOR]

Isomerization of α-pinene epoxide was carried out over a Colombian natural zeolite as potential geocatalyst with heulandite, chabazite and clipnotilolite as main crystallographic phases; the heulandite was identified as the active phase. Over synthetic zeolites, isomerization of α-pinene epoxide depended on Si/Al ratio, unit cell and the kind of structure. The best solvent was toluene and not isomerization activity was observed in presence of solvents with carboxyl groups. Complete α-pinene epoxide conversion and 45% selectivity to campholenic aldehyde were obtained at 70 °C, with fencholenic aldehyde, carveol, and p-cymene as main by-products. Decrease of activity of natural zeolite was associated with loss of acid sites. A reaction mechanism based on experimental and computational data was proposed including adsorption of α-pinene epoxide on Fe or Al sites of the natural zeolite; a reaction rate constant of 4.02 × 10–4 mol g−1 min−1 was estimated from a pseudo homogeneous kinetic model. [ABSTRACT FROM AUTHOR]

The western Anatolian Miocene volcano-sedimentary basins in the Gördes, Demirci and Şaphane regions host abundant heulandite/clinoptilolite (hul/cpt) bearing widespread zeolitized pyroclastic rocks. Lithostratigraphy of these zeolitic pyroclastic levels show comparable association. Petrography and geochemistry of all the samples show mainly rhyolithic and rhyodacitic character and ash size vitric tuffs. Polarized microscopy and X-ray diffraction determinations of the samples show composition of 55–95 wt % hul/cpt and accessory of smectite, illite/mica, opal–CT, quartz, K–feldspar, plagioclase and opaque minerals. Geochemical results obtained from the studied samples represent hul/cpt–rich facieses formed under the moderate alkaline conditions in these pyroclastic units. Correlation of geochemical results and concentration of hul/cpt in these pyroclastic rocks gives some chemical data on zeolitization process and on adsorption and ion-exchange character of hul/cpt type of zeolites. Depleted and enriched elements by zeolitization have similar ionic radii in general. Ca and H2O clearly increased, Si, Na and Si/Al ratio decreased in hul/cpt bearing Lower-Middle Miocene pyroclastic rocks of western Anatolia. Additionally, Sr, Nb, Th, Ni, Hf, Cs, Pb and Ta increased, and Zr, Co, W and most of the rare earth elements (REE) decreased in highly hul/cpt–rich pyroclastics. [ABSTRACT FROM AUTHOR]

The presented study involved detail investigation for the adsorption properties of three types of natural zeolite (heulandite, clinoptilolite, and phillipsite). The studied zeolite samples were described based on the structural features from the XRD patterns and the surficial morphologies from SEM images. The selected zeolite minerals were applied as adsorbents in the decolorization of safranin-T dye from water. The estimated uptake capacities for safranin revealed the higher capacity of heulandite than clinoptilolite and Phillipsite (heulandite>clinoptilolite>phillipsite). As per the kinetic studies, 240min was detected as the decolorization equilibrium of safranin by heulandite and clinoptilolite; and 480min for phillipsite zeolite. The decolorization mechanisms were classified as chemical processes and represented strongly by Lagergren assumption and Elovich model. Monolayer adsorption form was suggested for the uptake by heulandite and clinoptilolite (Langmuir); and multilayer form was predicted for phillipsite (Freundlich). Neutral to alkaline environment was detected to be the best medium for considerable removal of safranin. Natural zeolite minerals also were applied effectively in safarnin decontamination from raw water and showed effective values in the decolorization of other types of dyes. [ABSTRACT FROM AUTHOR]

Fluorosis, either dental or skeleton, is often due to the high fluoride content of well waters. In this work, using solutions which contain different amounts of fluoride, natural zeolites from Ethiopia and Mexico were tested. It is shown that, although zeolites are known to be cationic exchangers, their extra-framework aluminum and their high calcium contents determine their performance. A mechanism involving adsorption and ion exchange is proposed. DOI: http://dx.doi.org/10.4314/bcse.v29i1.5

Natural zeolite heulandite/polyaniline composite (Hu/PANI) was synthesized for the first time as catalyst support for nickel oxide photocatalyst (Hu/PANI@Ni 2 O 3 ). The structural, chemical, morphological, textural and optical properties were investigated using different techniques. The synthetic Ni 2 O 3 crystals showed well developed flaky habits with diameter range 200–400 nm and length range 1–4 µm. The estimated band gap energies of Hu/PANI composite and Hu/PANI@Ni 2 O 3 composite are 1.8 eV and 1.46 eV, respectively, which are remarkably smaller than the recorded value for pure nickel oxide. The photocatalytic properties of Hu/PANI@Ni 2 O 3 composite for efficient degradation of safranin-T dye were evaluated under sunlight as a function of irradiation time, initial dye concentration, catalyst mass, solution pH, and the catalyst stability. Hu/PANI@Ni 2 O 3 composite exhibits amazing photocatalytic degradation efficiency for safranin dye, whereas 80%, 98%, and ~ 100% of 5 mg/l dye were removed after only 1 min of solar irradiation using 0.025, 0.03, and 0.035 g of Hu/PANI@Ni 2 O 3 , respectively. The higher concentrations of the dye (10–50 mg/L) can be fully removed within minutes by increasing the solution pH or using higher doses from the Hu/PANI@Ni 2 O 3 catalyst. The removal percentage achieved the maximum value at the alkaline conditions. Also, the Hu/PANI@Ni 2 O 3 displayed high stability and remain 84.5% of the initial photocatalytic efficiency after 5 runs. Additionally, the composite can be used effectively in the removal of different types of dyes and mixed dyes within the same time intervals. Thus, loading of nickel oxide onto hybrid Hu/PANI composite as a catalyst support achieved amazing photocatalytic degradation capacity. [ABSTRACT FROM AUTHOR]

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 q max 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pollution of groundwater and surface water compartments is one of the major concerns related to the use of glyphosate in plant-protection products, and is attributed to the postulated endocrine-disrupting activity of the compound. There is a consensus that glyphosate cannot be inactivated in water by the addition of other substances that may also be foreign to that compartment. Therefore, a good, environment-friendly solution would involve use of natural zeolite-bearing rock to remove glyphosate from water. The main purpose of this study was to demonstrate that the content of glyphosate in water can be reduced by 50% through its adsorption on natural zeolites. An additional purpose was to identify the mechanism underlying the process – demonstrated to be adequately characterized by Freundlich and Langmuir isotherms. In natural zeolite-bearing rock with grain diameter <0.02 mm, the maximum monolayer adsorption capacity was 3.66 mg glyphosate/g sorbent. Glyphosate was shown to be adsorbed inside medium-sized heulandite channels with internal diameters of 0.4–0.6 nm; moreover, the adsorption of glyphosate onto heulandite crystal was shown to be a physisorption, unaccompanied by the formation of chemical bonds. [ABSTRACT FROM AUTHOR]

Benzodiazepines and their derivatives are a very important class of nitrogen-containing heterocyclic compounds with biological activity that are widely used in medicine. In this study, we demonstrated synthesis of 1,5-benzodiazepines from 1,2-phenylenediamine and ketones (acetone, cyclohexanone, acetophenone, methyl ethyl ketone) in the presence of isostructural porous metal-benzenetricarboxylates of the families MIL-100(M) (M: V 3+ , Al 3+ , Fe 3+ and Cr 3+ ) and three porous aluminium trimesates Al-BTCs (MIL-96(Al), MIL-100(Al) and MIL-110(Al)). A combination of catalytic, theoretical and physicochemical methods showed that reaction rates and yields of 1,5-benzodiazepines were adjusted by the type of metal ions and accessibility of active sites. The yield of 1,5-benzodiazepines in the presence of MIL-100(M) was comparable with zeolites, such as HY, H-ZSM−5, β-zeolite and heulandite. [ABSTRACT FROM AUTHOR]

This study focused on the mineralogical and physico-chemical properties of heulandite/clinoptilolite (Heu/Cpt)-rich zeolitic tuffs SE of Ankara (Turkey) and evaluated their potential for use as adsorbents. The main Heu/Cpt minerals correspond to the intermediate type and the Cpt-type of the heulandite series. Minor chabazite, erionite and rarely analcime and accessory feldspars, mica, smectite, and quartz were also detected. Three types of Heu were recognized according to their thermal behaviour. Cpt (type-III Heu) was thermally stable at 600°C, whereas type-I Heu collapsed and type-II Heu partially collapsed. The Si/Al ratios of the Hul/Cpt ranged from 3.54 to 5.03, the Γ parameter (Γ = Ca/Al + 0.115*Al) varied between 0.78 and 1.85 and Al + Fe3+ varied between 6.27 and 8.00. The Na, K and Ca contents of Heu/Cpt varied widely and the Heu had an intermediate composition between types II and III. The Mg + Ca content is greater than the Na + K content in Heu-type II and smaller in Heu-type III zeolites. The BET surface area and the pore-size of the samples varied between 10.15 and 194.27 m²/g, and between 1.41 and 12.42 nm, respectively. The N2 adsorption and desorption isotherms were comparable, but the adsorption/desorption capacity is greater in type III than in type II Heu zeolites. The cation exchange capacities of the Heu/Cpt-rich samples ranged from 185 to 280 meq/100 g. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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) Å, β = 116.353(3)°, V = 2101.85(7) Å 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, the structural characteristic and the adsorption properties of heavy metals on Mongolian natural minerals were investigated. The natural samples were confirmed as Heulandite group of Clinoptilolite type zeolite and clay sample that contains albite and quartz by X-ray diffraction analysis. According to BET surface analysis, natural zeolites have mesoporous type of pore. The results of adsorption study showed that adsorption ability of natural zeolite is high effective for lead ion in acidic aqueous solution and the order of heavy metal selectivity was Pb2+>>Zn2+>Cd2+. The adsorption performance of Arsenic(V) is significantly increased by modification with magnesium oxide on natural zeolite. [ABSTRACT FROM AUTHOR]

A 33 metre thick pyroclastic-rich zone of the Mezardere formationof Oligocene age is exposed in the Keşan region of Thrace, Turkey.In this zone, vitreous tuffs of dacitic composition have altered primarilyto zeolites, including mordenite, heulandite–clinoptilolite andanalcime. Silicification and alteration to clay minerals are common.Zeolite minerals have developed from volcanic glass, whereas somemordenites have formed from dissolution of heulandite-group zeolites.Although authigenic mineral paragenesis does not vary laterally,there is a marked vertical variation, particularly in zeolites. Mordenite(+heulandite–clinoptilolite) and analcime do not coexist and haveformed in different stratigraphic levels. This suggests that their chemicalenvironment is controlled by different hydrologic systems.Whole rock composition shows the relationship between chemistryand secondary mineralogy. For example, whole rock trace elementgeochemistry indicates the natural selectivities of zeolites. There isalso stratigraphic control on the chemistry and texture of mordenites.Specifically, (Na+K)/(Ca+Mg) ratios of mordenites decrease fromthe lower to the upper levels. Mordenites of the lower level show afibrous habit while the upper level mordenites are needle-like inshape. The average Si/Al ratio in mordenites is 3.90, in heulanditegroupminerals 3.95, and in analcimes 2.34.

The structural evolution of natural heulandite Ca 2.90 Na 2.07 Sr 0.25 K 0.16 Ba 0.06 (H 2 O) n [Al 8.65 Si 27.35 O 72 ] was studied upon compression in penetrating (water-containing) and non-penetrating (paraffin) media using single-crystal X-ray diffraction data in a diamond-anvil cell. Compression in a water-containing medium results in an additional hydration of heulandite from 23 molecules per unit cell at ambient conditions to ≈27 at 3.27 GPa. Water molecules enter both initially vacant and partly occupied positions. Additional hydration stabilizes the crystal structure decreasing its compressibility. [ABSTRACT FROM AUTHOR]

The sorption isotherms of copper(II) ions on natural calcium heulandite at a pH of 1.7 and temperature of 298-318 K have been obtained. The exchange sorption capacity with respect to Cu(II) ions at 298 K was 0.47 mg-eqv/g. The equilibrium constants of the ion exchange and thermodynamic functions including Gibbs energy and entropy and enthalpy of sorption have been calculated. The possibility of using calcium heulandite for purification of the wastewaters of the electroplating industry from ions of heavy metals has been assessed. [ABSTRACT FROM AUTHOR]

By cation exchange for clinoptilolite tuff from the Khonguruu deposit (Yakutia) the Mg-, Ca-, Sr-, Bamodified heulandite-clinoptilolite zeolites are obtained. Based on the data of powder X-ray diffraction and thermal analyses, the properties of these modifications are characterized. Using nitrogen cryosorption, the specific surface areas are determined. Found that the specific surface areas of the cationic modifications obtained increase with the ion charge. [ABSTRACT FROM AUTHOR]

Fluorosis, either dental or skeleton, is often due to the high fluoride content of well waters. In this work, using solutions which contain different amounts of fluoride, natural zeolites from Ethiopia and Mexico were tested. It is shown that, although zeolites are known to be cationic exchangers, their extra-framework aluminum and their high calcium contents determine their performance. A mechanism involving adsorption and ion exchange is proposed. [ABSTRACT FROM AUTHOR]