Variation of the NH4+-exchange and CO2-adsorption capacities with zeolite content was investigated in detail to assess the potential use of these capacities for the estimation of the zeolite contents of the samples taken from the Bigadiç clinoptilolite deposit in western Anatolia, as an alternative to the widely used semi-quantitative X-ray diffraction (XRD) technique. Samples with known clinoptilolite contents taken from 2 different zones with fine- and coarse-grained tuffs of the Bigadiç deposit were used for this purpose. Na-enriched forms of the samples were prepared by repeated ion-exchange with NaCl solutions, and NH4+-forms by repeated Na exchange followed by NH4+ exchange with NH4Cl solutions, which in turn were calcined to obtain the H-forms. NH4+-exchange capacities by Kjeldahl analyses of the NH4+-forms and CO2 adsorption isotherms in the 0 to 100 kPa range of Na- and H-forms of the samples were determined. Dubinin-Astakhov model parameters were calculated from the isotherm data.

A strong relationship exists between the experimental CO2-adsorption capacities at 100 kPa of the Na-forms and the zeolite contents of the samples. Although the Dubinin-Astakhov model represented the isotherm data quite well, the relationships between the amounts of adsorbate at saturation pressure, calculated from the model, and the zeolite contents of the samples were weaker. The strength of the relationship between NH4+ exchange capacities and zeolite contents was seen to vary with the zone of origin. There is a very strong relationship between the adsorption and ion-exchange capacities of the samples in their Na-forms taken from the fine-grained zone, indicating that either ion-exchange or adsorption capacity measurements can be used to estimate the zeolite contents of the samples taken from this zone, whereas, significant diffusion hindrance was observed against ion-exchange of hydrated cations from aqueous solutions for some samples from the coarse-grained zone. Inspection of the data pointed to systematic errors in the zeolite contents determined by a semi-quantitative XRD technique. When both zones are considered together, CO2-adsorption capacities at 100 kPa of the samples in their Na-forms can be used as a reliable measure of the zeolite content, which in turn is an important index to predict the performance of natural samples in various applications.

Heulandite-group zeolites are abundant in the Miocene pyroclastics from Western Anatolia, Turkey. We investigated the relation between the I(111)/I(3¯11) intensity ratios measured by X-ray diffraction (XRD) and the content of exchangeable cations for 15 samples of natural heulandite-group minerals gathered from the Gördes and Bigadiç regions of Western Anatolia. The intensity ratios range from 0.77 to 0.94 in natural heulandites and from 1.38 to 1.80 in natural clinoptilolites. The data obtained from Na-, K- and Ca-exchanged forms of a heulandite and clinoptilolite show that the intensity ratio increases with Na-, K- and Ca-exchange in heulandite and also with Na- and K-exchange in clinoptilolite, whereas it decreases with Ca-exchange in clinoptilolite. The intensity ratios were calculated using the known structural data of clinoptilolites to understand the effect of positions, amounts and kinds of exchangeable cations and water molecules. An increase in Na and Ca may increase or decrease the intensity ratio, depending on their sites and occupancies. Potassium causes a significant increase in the intensity ratio and an increase in Mg decreases the intensity ratio. There is a strong correlation between the intensity ratio I(111)/I(3¯11) and (Na + K)/(Ca + Mg) ratio and thermal stability, both of which have been used to characterize heulandite-group minerals.

The present work is part of a study focused on the use of organo-zeolite conditioner to remediate soil polluted by toxic elements. The Neapolitan yellow tuff (NYT) was utilized as a component of an organo-mineral sorbent/exchanger soil conditioner with pellet manure (NYT/PM) to reduce the mobility of Cd and Pb and recover plant performance in heavily polluted soils from illegal dumps near Santa Maria La Fossa (Lower Volturno river basin, Campania Region, southern Italy). Pot experiments were performed by adding the NYT/PM mixture (1:1, w/w) to polluted soil at the rates of 0%, 25%, 50% or 75% (w/w). Wheat (Triticum aestivum) was used as the test plant. The addition of organo-zeolite NYT/PM mixture significantly reduced the DTPA (diethylene-triamine-pentaaceti c acid)-extractable Cd and Pb from 1.01 and 97.5 mg kg−1 in the polluted soil, to 0.14 and 11.6 mg kg−1, respectively, in the soil amended with 75% NYT/PM. The best plant response was observed in amended soil systems treated with 25% NYT/PM, whereas larger additions induced plant toxicities due to increased soil salinity.

Adsorption kinetic and thermodynamic tests were conducted using non-irradiated and γ-irradiated (400 kGy) NaOH-modified Philippine natural zeolites for the removal of Cu2+ ions in aqueous solution. The effects of γ-radiation on zeolites were investigated. Samples were equilibrated with binary systems of Cu2+ ↔ 2Na+ at room temperature. There were no significant changes in the elemental composition of the irradiated zeolite. Irradiation primarily results in the shrinking of the zeolite framework and improvements in the crystallinity. The γ-irradiation increases the sorption uptake according to the kinetic study in which the adsorption kinetics followed a pseudo-second-order model. Thermodynamic tests show that the adsorption isotherms of the two samples are best described by the Langmuir model. The maximum adsorption capacities of the non-irradiated and γ-irradiated NaOH-modified zeolites are 33.00 and 43.22 mg Cu2+ g–1, respectively, suggesting that γ-irradiation might enhance the maximum adsorption capacity by up to 30.8%.

Natural zeolites in the Aksitero sedimentary formation of the western Luzon area of the Philippines were evaluated. The natural washed zeolite (NW-Z) was preconditioned with acid to purify it and increase its surface area. Acid treatment with 3 M HCl for 12 h yielded optimum acid treatment of the NW-Z, causing increases in the Si/Al ratio, the specific surface area by 32.5% and the porosity of the acid-treated zeolite (HC-Z). The HC-Z was washed with 4 M NaCl for 3, 6, 12, 18, 24, 48 and 72 h to improve its cation-exchange capacity for copper. The sodium-treated zeolite (Na-Z) was immersed in 100 ppm CuSO4 solution to test the copper-uptake capacity. Pretreatment of HC-Z with 4 M NaCl for 24 h is optimal for sodium treatment of the preconditioned HC-Z. The preconditioning techniques did not significantly alter the structure and morphology of the zeolite samples. It is suggested that the preconditioned Philippine natural zeolite samples are readily available for further functionalization that will enhance their antibacterial, catalytic and adsorption properties, with various useful applications in the field of catalysis, biomedicine, environmental mitigation and wastewater treatment.

Iran has significant deposits of high-purity natural zeolites. Many Iranian scholars conduct scientific research on porous materials, from natural and synthetic zeolites to metal organic framework materials. Iranian zeolite deposits and associated research are reviewed here. Various industrial applications of natural zeolites, from agriculture to animal husbandry to the construction industry and beyond are discussed here.

Two zeolitized tuffs (ZTs), viz. a Neapolitan yellow tuff (NYT) and a clinoptilolite-bearing tuff (ZCL), were tested as pedotechnical materials to improve soil resilience against the impact of treatment by a ‘dirty’ municipal sewage system (DSW). Soils (surface horizon) were a sandy, alkaline Entisol (Typic Xeropsamment), and a sandy-loam, sub-acidic Alfisol (Ultic Palexeralf). Results showed that the presence of ZTs resulted in several favourable effects. Electrical conductivity (EC) decreased and pH was buffered. Ammonium was selectively taken up from the DSW, making the zeolitized tuffs almost saturated by NH4+, by exchanging both beneficial cations, such as K+ and Ca2+, thus improving their potential availability to plants, and undesirable cations such as Na+, thereby hindering the exchangeable sodium percentage (ESP) increase and concurrent soil salinization-alkalinization. At the same time, NH4+ was stored as a potentially slow-release nitrogen fertilizer. The mobility of Pb, Cu and Zn dropped off to a large extent. NYT produced the best effects, and the Entisol gained the greatest benefit from treatments.

Hydrogen forms of natural mordenite and clinoptilolite were used as catalysts for styrene oligomerization and as matrices to hold the resultant oligomers in order to prepare intense and light-resistant pigments. In contrast to synthetic zeolites of similar pore sizes (mainly H-ZSM-5, H-mordenite), the natural zeolites did not form products with an intense (pink) colouration. H-mordenite samples treated with styrene developed some colour due to styrene oligomers (the chromophore) whereas, in treated clinoptilolites, colour formation was negligible due to the lack of access of styrene molecules into the elliptical channels. The results of catalytic tests for cracking of cumene (cumene and styrene have similar molecular sizes) were consistent with the styrene oligomerization results. They indicate a noticeable catalytic activity with natural H-mordenite and a lack of activity with clinoptilolite. On the other hand, catalytic tests for propan-2-ol decomposition indicate a high activity with both natural zeolites, which confirms the presence of acid sites and their accessibility to small alcohol molecules.

The effect of mechanical activation on the ion-exchange selectivity of natural zeolites from Russia, namely clinoptilolite-bearing tuffs and chabazites, was studied. The structural modifications and thermal properties were investigated, and the specific surface area and porosity of mechanically activated zeolites were determined. At activation doses of up to 1.0 kJ g–1 the main processes are the breakdown of the zeolite particles and pore structure changes. At greater activation doses amorphization takes place. It was shown that during the initial stage of activation in most cases the clinoptilolite selectivity for Sr2+ increased slightly and then decreased; the selectivity for Cu2+ increased 100 times; and the selectivity of chabazite-1 for Sr2+ increased 300 times.

Natural zeolites have traditionally been used as supplements in animal nutrition with positive effects in terms of either faster growth or reduced incidence of diseases and death. The discovery that natural zeolites may act as drugs or coadjutants in pharmaceutical preparations has greatly enlarged the field of their applications in many sectors of biology and medicine, opening unexpected horizons for either basic or applied research. This review updates the state of the art of research in this sector, focusing on clinoptilolite-rich materials, with two main purposes: (1) trying to rationalize this subject, which is extremely variable and heterogeneous, and (2) raising doubts about unsuitable uses of natural zeolites in the light of their known properties and expected behaviour.

Pigments similar to the famous Maya Blue were prepared by entrapment of indigo inside the channels of natural zeolites such as clinoptilolite and mordenite. The zeolites were mixed and ground with indigo and then heated at 150°C. Surplus (unbound) dye was removed by solvent extraction or by vacuum sublimation. As is the case when synthetic zeolites are used as matrices, the colouration of the resulting pigments could be modified by the previous cation exchange of the zeolite.

The uptake of inorganic Hg2+ and organometallic CH3Hg+ from aqueous solutions by 11 different natural zeolites has been investigated using a batch distribution coefficient (Kd) method and supported by a preliminary voltammetric study. The effect of mercury concentration on the Kd response is shown over an environmentally appropriate concentration range of 0.1–5 ppm inorganic and organometallic Hg using a batch factor of 100 ml g-1 and 20 h equilibration. Analcime and a Na-chabazite displayed the greatest methylmercury uptakes (Kd values at 1.5 ppm of 4023 and 3456, respectively), with mordenite as the smallest at 578. All uptake responses were greater for methylmercury than for the inorganic mercuric nitrate solutions, suggesting a distinctive sensitivity of zeolites to reaction with different types of solute species. It is likely that this sensitivity is attributable to the precise nature of the resultant Hg-zeolite bonds. Additionally, both the Si-Al ratio and the Na content of the initial natural zeolite samples are shown to influence the Kd responses, with positive correlations between Kd and Na content for all zeolites excluding mordenite.

This contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.