Zeolite-rich Rocks Research Articles

Mineral Composition and Structural Characterization of the Clinoptilolite Powders Obtained from Zeolite-Rich Tuffs

Clinoptilolite is a precious zeolite mineral that has the most comprehensive physicochemical properties among all the zeolite group minerals. Due to these unique properties, clinoptilolite has a wide range of applications in many different industries. In Poland, the clinoptilolite occurs only as an accompanying mineral in the sedimentary rocks nearby Rzeszów. In Europe, the abundant clinoptilolite-bearing deposits are located in Slovakia and Ukraine, where clinoptilolite mineralization occurs in the volcanic tuffs. Due to clinoptilolite’s rare performance, it is extremely crucial to manage its deposits in a complementary manner. In this paper, the mineralogical and structural characterization of the clinoptilolite powders obtained by mineral processing of the clinoptilolite-rich tuffs from Slovakia and Ukraine deposits were discussed. The scope of research covered determination of the mineral composition of the tuffs, structural analysis of the clinoptilolite crystals, as well as textural and physical properties of the powders obtained by mineral processing of the tuffs. In addition, this paper includes the comparative study of the most significant zeolite deposits in the world and investigated clinoptilolite-rich tuffs. A wide spectrum of methods was used: X-ray powder diffraction (XRD), thermal analysis (DSC, TG), X-ray fluorescence (XRF), optical microscopy, Scanning Electron Microscopy (SEM-EDS), the laser diffraction technique, and low-temperature nitrogen adsorption/desorption. The test results indicated that the major component of the tuffs is clinoptilolite, which crystallized in the form of very fine-crystalline thin plates. The clinoptilolite mineralization in the Ukrainian and Slovakian tuffs exhibited a strong resemblance to the clinoptilolite crystals in Yemeni and Turkish tuffs. With respect to the mineral composition, the investigated tuffs showed excellent conformity with the Miocene white tuffs from Romania. The Ukrainian and Slovakian tuffs do not reveal the presence of the clay minerals, which is quite common for naturally occurring zeolite-rich rocks in various deposits in the world. The textural features together with mineral composition of the investigated samples incline that they are potentially suitable raw materials for the sorbent of petroleum compounds. Moreover, the obtained results can be useful indicators with respect to the crushing and compaction susceptibility of the Ukrainian and Slovakian clinoptilolite-rich tuffs.

Removal of non-steroidal anti-inflammatory drugs from water by zeolite-rich composites: The interference of inorganic anions on the ibuprofen and naproxen adsorption

Composites of two natural zeolites – clinoptilolite and phillipsite, and cationic surfactants (cetylpyridinium chloride and Arquad® 2HT-75) were tested for the removal of two emerging contaminants – ibuprofen and naproxen. For each zeolite-rich rock, two different modifications of the zeolitic surfaces were prepared (monolayer and bilayer surfactant coverage). The influence of the initial drug concentrations and contact time on adsorption of these drugs was followed in buffer solution. The Langmuir model showed the highest adsorption capacity for the composite characterized by a bilayered surfactant at the clinoptilolite surface: 19.7 mg/g and 16.1 mg/g for ibuprofen and naproxen, respectively. Also, to simulate real systems, drug adsorption isotherms were conducted in natural water (Grindstone creek water – Columbia, Missouri, USA) by using the best performing adsorbent; in this case, a slight decrease of drug adsorption was recorded. Kinetic runs were performed in distilled water as well as in the presence of ions such as sulfates and bicarbonates; also, in this case, the interfering agents defined an adsorption decrease for bilayer composites.

Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs

Clinoptilolite is a natural zeolite used for the abatement of ammonium in the treatment of urban wastewater. By considering that mullite was obtained through thermal treatment of NH4-exchanged synthetic zeolites, this work aimed to evaluate if this phase can be obtained from NH4-clinoptilolite. A material containing about 90 wt % of clinoptilolite, prepared using a Sardinian zeolite-rich rock, was NH4-exchanged and subjected to treatments up to 1200 °C. After dehydration, de-ammoniation, and dehydroxylation processes, the clinoptilolite structure collapsed at 600 °C. An association of mullite, silica polymorphs, and glass, whitish in color, was obtained for treatments between 1000 and 1200 °C. The higher degree of crystallinity was reached after a 32 h heating at 1100 °C: mullite 22 wt %, cristobalite 59 wt %, tridymite 10 wt %, glass 9 wt %. It is possible to speed up the kinetics of the transformation by increasing the temperature to 1200 °C, obtaining the same amount of mullite in 2 h, but increasing the residual amorphous fraction (16 wt %). These results indicate that NH4-clinoptilolite could represent a raw material of potential interest in the ceramic field, in particular in the production of acid refractory, opening scenarios for a possible reuse of clinoptilolite-based exchangers employed in ammonium decontamination.

Release of lead from Pb-clinoptilolite: managing the fate of an exhausted exchanger

The selectivity of clinoptilolite toward Pb2+ has stimulated many studies aimed to evaluate the metal uptake. Conversely, the management of a Pb-bearing clinoptilolite has not received the same attention, although it can release a harmful metal. This work aims to evaluate the possibility to control, through thermal treatments, the release of lead from a Pb-clinoptilolite, prepared to simulate the condition of highest dangerousness of an exhausted exchanger. A zeolite-rich rock from Sardinia (Italy) has been processed, obtaining a powder with almost 90 % (wt.) of clinoptilolite. This material has been initially Na- and then Pb-exchanged, reaching a Pb2+ content of 2.28 meq/g. The lead release has been tested before and after 2-h heating at eight different temperatures from 200 to 900 °C. The unheated material releases 64 % of the lead. Heating weakly affects lead release up to 400 °C (54 %), but higher temperatures determine an abrupt reduction from 44 % at 500 °C to 1 % at 700 °C, when the zeolite breakdown occurs. At 800 °C the nucleation of Pb-feldspar and silica polymorphs begins. Basically, the material heated at 900 °C does not release lead (0.03 %), because the metal is trapped in the lead feldspar, whose content attains 42 % (wt.). This solid-state transformation does not involve the emission of lead vapors, another significant environmental aspect.

A comprehensive evaluation of sedimentary zeolites from Turkey as pozzolanic addition of cement- and lime-based binders

The pozzolanic action played by five natural zeolite-rich materials (three clinoptilolite- and one each mordenite- and analcime-bearing rocks) coming from Turkey, has been examined, evaluating also the influence of various chemical–physical parameters, such as grain size of the zeolitic materials and nature of the cation present as extra-framework component of the structure. Pozzolan activity has been estimated by the official test of the European Standards and by thermogravimetry, finding a good accordance between the two procedures. Clinoptilolite-rich rocks gave the best results, but performance turned out to depend on the specific surface area and pre-enrichment in a potassium form. Experimental data analysis demonstrated that the pozzolanic reaction is kinetically controlled by the diffusion of reactants through a layer of dense reaction products. Experimental blended cements with the five zeolite-rich rocks were also prepared and the compressive strengths measured as a function of the curing time. The effectiveness of the pozzolanic action was monitored by XRD and FTIR analyses. An accurate microstructural study of the hardened pastes was also carried out and point analysis performed, pointing out that the zeolite-lime interaction is characterized by two stages: initially zeolite subtracts calcium from the environment by cation exchange, then it acts as a true pozzolan as soon as its structure breaks down.

The effect of digestive activity of pig gastro-intestinal tract on zeolite-rich rocks: An in vitro study

Two zeolite-rich rock samples extracted from Campanian Ignimbrite tuff quarries, southern Italy, usually used as binding and anticaking agents in animal feeding, were characterized and tested in terms of their resistance in stomach, small and large intestine of pig, using a three step in vitro digestibility trial. The mineralogical composition and major and trace-elements analysis were performed after each digestion step using XRPD and ICP-OES techniques. The main zeolite phases identified are phillipsite and chabazite. Results showed that in vitro physical-chemical conditions (pH 2–3 and T 39 °C) the release of Pb and other elements from the zeolite structure is extremely low and due to the limited breakdown of the zeolite framework and glass/amorphous matter hydrolysis, by the gastric liquids. This aspect also suggests that zeolites, after the total permanence in the animal body digestive tract, can further perform their important function of cation exchanger, with also relevant relapses on the growth and health of the animal species, as well as on the environment. Moreover, the contact of zeolite material with liquids of small and large intestine leads to negligible release of undesirable elements, which are far less than those envisaged by the European Regulations.

Use of surface modified natural zeolite (SMNZ) in pharmaceutical preparations Part 1. Mineralogical and technological characterization of some industrial zeolite-rich rocks

The present research accounted for an accurate selection of representative samples from zeolitized deposits of different world geographical areas commonly mined and marketed by American and European mining companies. These geomaterials displayed high contents of clinoptilolite, phillipsite, and chabazite and were deeply characterized from mineralogical, chemical, and technological points of view. A preliminary quality control of the selected materials allowed us to determine the presence of undesired minerals and/or elements. A thermodynamic investigation of the surface exchange reactions between the selected zeolite-rich rocks and the surfactant agents (HDTMA-Br/Cl, hexadecyltrimethylammonium bromide/chloride, BC-Cl, benzalkonium-chloride, CP-Cl, cetylpiridinum-chloride) enabled us to verify the extent and the compactness of the formed micelle and to foresee their future behavior through interaction with molecules of anti-inflammatory drugs (drug delivery). The encouraging results pave the way towards good perspectives on the possible use of zeolite-rich rocks in the pharmaceutical sector through a preliminary basic protocol for the characterization and monitoring of the batches to be employed.

Removal of lead from aqueous solutions by using the natural and Fe(III)-modified zeolite

In the present study, the sorption of lead by the natural and Fe(III)-modified zeolite (clinoptilolite) is described. The characterization of the natural zeolite-rich rock and the Fe(III)-modified form was performed by chemical analysis, point of the zero charge (pHpzc), X-ray powder diffraction, applying the Rietveld/RIR method for the quantitative phase analysis, and scanning electron microscopy. The effects of sorbents dose and the initial lead concentrations on its sorption by two sorbents were investigated. For both sorbents, it was determined that at lower initial concentrations of lead, ion exchange of inorganic cations in zeolites with lead, together with uptake of hydrogen dominated, while at higher initial lead concentrations beside these processes, chemisorption of lead occurred. Significantly higher sorption of lead was achieved with Fe(III)-modified zeolite. From sorption isotherms, maximum sorbed amounts of lead, under the applied experimental conditions, were 66mg/g for the natural and 133mg/g for Fe(III)-modified zeolite. The best fit of experimental data was achieved with the Freundlich model (R2≥0.94).

Use of zeolite-rich rocks and waste materials for the production of structural lightweight concretes

This paper aims at testing the use of mixtures constituted by natural zeolitized products and SiC-bearing industrial wastes (sludge deriving from polishing of porcelain stoneware tiles, hereafter DPM) for the production of lightweight expanded aggregates as constituents of structural and/or thermo-insulating lightweight concretes. Two commercial products have been used as zeolite natural source: Cab70 (Yellow facies of Campanian Ignimbrite) and IZclino (Turkish clinoptilolite-rich epiclastite). Different amounts of a calcareous material (Pozzano limestones — hereafter CP) from the Sorrento peninsula (Naples — Italy) were also added to a Cab70–DPM mixture. All raw materials were characterized by means of mineralogical (XRPD) and chemical (XRF) analyses. All the products and mixtures were tested from a technological point of view by means of fusibility and firing tests in order to evaluate the expanding properties. It was evidenced that the expansion of the mixture was deeply depending on the occurrence of SiC in the industrial waste. The addition of CP (10 wt.%) to the mixtures accounts for an even increased expansion, though this is accompanied by a worsening of the mechanical features of the material. These results along with literature data allowed to select 3 mixtures (70% Cab70–30% DPM, 70% IZclino–30% DPM, 60% Cab70–30% DPM–10% CP) and each of them was used for the preparation of 5 l of lightweight aggregates afterward employed for the manufacture of lightweight concretes. It was remarked that natural zeolitized materials mixed with DPM (30 wt.%) can provide lightweight aggregates with densities ranging between 0.8 and 1.0 g/cm 3 suitable for the preparation of structural lightweight concretes. The addition to the mixture of CP (10 wt.%) produces less dense aggregates (0.6–0.7 g/cm 3) potentially useful for the manufacture of thermo insulating lightweight concretes.

Zn 2+-exchanged clinoptilolite-rich rock as active carrier for antibiotics in anti-acne topical therapy : In-vitro characterization and preliminary formulation studies

The combination of erythromycin and zinc in the topical antibiotic therapy of acne has been proved useful to reduce the development of antibiotic-resistant strains. An Italian zeolite-rich rock, containing 66 wt.% of clinoptilolite, has been used to prepare an active carrier for erythromycin. The zeolite has been conditioned in zinc form by a set of cation exchange processes, then erythromycin has been adsorbed onto the micronized rock by vacuum drying. After 6 month ageing, almost 95% of the loaded drug was found, indicating good stability of the Zn-carrier-erythromycin system. Minimum inhibitory concentration (M.I.C.) assay on Propionibacterium acnes showed that the process of adsorption of erythromycin does not affect its antimicrobial activity. Both drug and zinc release were evaluated from the carrier powder: the erythromycin release was more than 80% in the first hour and independent on hydrodynamic conditions (United States Pharmacopoeia dissolution apparatus or Franz cell). The release of zinc was fast, and more dependent on the hydrodynamic conditions. The influence of formulating the carrier by dispersion in two anhydrous bases, an absorption petrolatum base (HP) and a water soluble polyethylenglycol base (PEG), was evaluated. In both cases erythromycin and zinc showed a release quantitatively similar to that of the powder, although the release rate was slightly lower from the more hydrophobic HP base.

Some Physical Property Characteristics of Zeolitic Rock ? Preliminary Results

Clinoptilolite and mordenite and other zeolite bearing altered ignimbritic rocks have been subject to petrophysical laboratory studies in which textural, magnetic, and electrical properties were investigated. Zeolite-poor and barren rocks also were included in the study. Preliminary results indicate that zeolite-rich rocks manifest: temperature dependent apparent porosities, low grain and dry bulk densities, generally low magnetic susceptibilities, a range of electrical resistivities ? possibly reflecting degrees of silicification, and a tendency to low phase angles. The density and porosity data characterise zeolitic rock quite well; magnetic and electrical data are not diagnostic but do provide useful supplementary information on the likely or possible degree of zeolitisation.