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Materials Chemistry

NANOMODIFICATION OF A NATURAL CLINOPTILOLITE ZEOLITE

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Abstract

Clinoptilolite, a common natural zeolite was chemically modified with HCl and Si to enable the sequestration of Cs and Sr isotopes, in both water and some types of solid waste (nuclear industry residues, for instance). The method reported allows to preserve the crystalline structure of the zeolite, thus maintaining its advantageous textural characteristics, while incorporating the adequate surface moieties for various applications, including trapping of polluting ions in water.

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Evidence for controlled insertion of Fe ions in the framework of clinoptilolite natural zeolites
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The effect of HCl treatment on water vapor adsorption characteristics of clinoptilolite rich natural zeolite
Fehime Özkan

Microporous and Mesoporous Materials, 2005

In this study, water vapor adsorption properties of the clinoptilolite rich zeolite tuff, from Bigadic (Turkey), and its modified forms were examined. The modified forms were obtained by treating the tuff with HCl solutions (0.032, 0.16, 0.32, 1.6 or 5 M) at 25, 40, 75 and 100°C for 3 h. Infrared spectroscopy and water vapor adsorption were used for the characterization of the zeolites. Langmuir, BET and Dubinin-Raduschevich methods were applied in the analysis of water vapor adsorption data. Applications of Dubinin Raduschevich equation to the water adsorption data displayed that the super-micropore volume was not very sensitive to acid treatment. It was found out that the Langmuir surface area and ultra-micropore volume depend on the degree of the removal of aluminum from the structure.

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Selective Removal of Radioactive Cesium from Nuclear Waste by Zeolites: On the Origin of Cesium Selectivity Revealed by Systematic Crystallographic Studies
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Characteristics of the synthetic heulandite-clinoptilolite family of zeolites
Deborah A Cook

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Heulandite-clinoptilolite zeolites can be synthesized over the complete range of Si/Al ratio (2.5 to 6) found for the natural minerals. The unit cell parameters, framework infrared vibrational characteristics and thermal properties are similar to those of their natural counterparts. Results of environmental studies involving the removal of toxic metal ions such as lead, strontium and cesium from solution show that though natural clinoptilolite efficiently removes these ions from solution, the higher aluminum content of heulandite results in an improvement in the capacity of this topology for divalent cations. The ability to readily prepare synthetic heulandite and clinoptilolite using environmentally benign methods is expected to lead to improvements in the use of this family of zeolites for similar environmental applications.

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Natural Zeolites as Potential Materials for Decontamination of Radioactive Cesium
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Adsorption experiments of Cs + were carried out by using two natural zeolites, namely mordenite and clinoptilolite. The same experiments were also conducted by using synthetic zeolite A, synthetic zeolite X, and artificial zeolite Na-P1 as references. The purpose of this study was to investigate the potential of natural zeolites on the adsorption of radioactive Cs + . The results indicated that although cation exchange capacity of the natural zeolites was much lower compared to the synthetic and artificial zeolites, the adsorption capacity of Cs + was much greater than the synthetic and artificial zeolites. The order of the adsorption capacity of Cs + was mordenite>clinoptilolite> Na-P1 >> zeolite A > zeolite X. It indicates that natural zeolites are promising materials in the removal of radioactive Cs + .

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ION EXCHANGE BEHAVIOR OF ZEOLITES A AND P SYNTHESIZED BY NATURAL CLINOPTILOLITE
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Clinoptilolite with surface-enhanced functionality for radionuclide and inorganic pollutants removal
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Aqueous pollutants of cesium, iodide, lead, zinc and chromate ions adsorbed on natural and Ag + (Pb 2+)-or NH 4 +-exchanged clinoptilolite together with surfactant hydrophobized, Ca-alginate pelletized as well as MnOx-and FeO(OH)-clinoptilolites compared with the inland montmorillonite were assessed. The investigations of zeolites (clinoptilolite type) for the removal of various kinds of aqueous pollutants incl. radioactive ones lead to the conclusion that this natural resource can be considered for an alternative cost-effective adsorption material, either with or without surface treatment, depending on the type of water to be purified.

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Title Page Sorption Properties of Natural Zeolites for the Removal of Ammonium and Chromium Ions in Aqueous Solution Sorption Properties of Natural Zeolites for the Removal of Hazardous Elements Keywords
Guillaume ndayambaje

2011

There are huge amount of natural clinoptilolite available in South Africa which can be utilised for wastewater treatment of ammonia and chromium if their characteristics are properly known. However, these deposits have not been well characterised but in this study, the untreated clinoptilolite materials were fully characterised using techniques such as SEM-EDS, HRTEM-SAED, XRD, XRF, FTIR and BET. After acid pretreatment with several extractions, the pretreated samples were again characterised using the above mentioned techniques. These pretreated materials were used for NH 4 + and Cr 3+ adsorption of wastewater. The three natural South African clinoptilolite samples used in this study were from ECCA Holdings (ESC and EHC samples) and Pratley (PC sample) deposits obtained from Western Cape and KwaZulu-Natal Province respectively. This study revealed that the chemical composition and mineral phases of South African clinoptilolites vary considerably from site to site, even clinoptilolite mined from the same deposit sites. The XRD analyses showed that Pratley clinoptilolite (PC) was the most pure clinoptilolite sample (81.41 %) compared to the purity of EHC (67.88 %) and ESC (44.0 %) sample. The ECCA Holdings untreated clinoptilolite samples contained dense phases such as quartz which was not found in Pratley sample. Quartz was found to be the most dominant impurity in both ECCA Holding sample. The cation exchange capacity (CEC) of ESC, EHC and PC samples were found to be 1.23, 1.81 and 2.90 meq/g respectively and these results were compared to that of XRF analyses. The acid solutions of 0.02 and 1.0 M HCl were used to pretreat natural clinoptilolite to determine the optimum acid concentration and number of extractions required to fully replace the exchangeable cations. The pretreatment results showed that 0.02 M HCl was the optimum acid concentration for acid pretreatment of clinoptilolite samples. Between 7 and 22 extractions were required to remove Na + , K + , Ca 2+ and Mg 2+ without causing much dealumination Abstract iii of the framework. Sodium ion was found to be weakly bound cation in the clinoptilolite framework, since it could be completely exchanged by H + after 7 extractions with 0.02 M HCl acid solution. Potassium ion was found to be strongly bound in the clinoptilolite framework since it could not be completely exchanged during the acid pretreatment process even after 22 extractions. The HRTEM-SAED and BET results showed that ESC, EHC and PC were all polycrystalline and microporous materials respectively. It was found that the adsorption capacity of the treated Pratley clinoptilolite sample was increased by 36 % for NH 4 + removal, compared to that of the untreated PC sample. The adsorption study results showed that the pretreatment of clinoptilolite samples using 150 mL volumes of 0.02 M HCl with 7 acid extractions at 25 °C for ESC pretreated and EHC pretreated. The pretreatment of PC sample at 22 extractions could remove high percentage of NH 4 + (98.11 %) within a short contact time of 10 min. The pretreated Pratley clinoptilolite sample was found to be the best NH 4 + adsorbent (98.11 % NH 4 + removal) compared to EHC treated (93.89 % NH 4 + removal) and ESC treated (75.00 % NH 4 + removal) clinoptilolite samples. However, acid-pretreated Pratley clinoptilolite did not sufficiently remove Cr 3+ (16.10 %) from synthetic wastewater showing that it is not a good adsorbent for this particular metal ion removal. Despite several studies that have been conducted on clinoptilolite, no study has been carried out on the pretreatment and comparison of sorption capacity of different South African clinoptilolites for the removal of NH 4 + from wastewater. This study has been able improve on the acid-pretreatment procedure for clinoptilolite. This study demonstrated that it is not only the acid concentration that is important but also the number of extractions needed to remove all the exchangeable cations from the clinoptilolite framework. This study has also been able to prove that South African clinoptilolite can treated ammonia from wastewater. Declaration iv DECLARATION I declare that "Sorption properties of natural zeolites for the removal of hazardous elements" is my own work, that it has not been submitted for any degree or examination in any other university, and that all the resources I have used or quoted have been indicated and acknowledged by complete references.

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The use of clinoptilolite and its sodium form for removal of radioactive cesium, and strontium from nuclear wastewater and Pb 2+, Ni 2+, Cd 2+, Ba 2+ from municipal wastewater
H. Faghihian, Hossein Kazemian

Applied Radiation and Isotopes, 1999

Three different samples of Iranian natural zeolites (clinoptilolite) and its sodium exchanged forms have been investigated for uptaking several different cations. Ion-exchange isotherms, have been given and discussed.

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Cleaning of liquid radioactive wastes using natural zeolites
N. Elizondo

Applied Radiation and Isotopes, 2000

Natural zeolite, clinoptilolite, was used to eliminate liquid radioactive wastes (LRW) 137 Cs and 90 Sr. The in¯uence of several factors (pH of solution, grain size of the zeolite, etc.) on the process eectivity was studied. It was shown that clinoptilolite is an eective ®lter of the nuclides above. #

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References (14)

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The use of columns of the zeolite clinoptilolite in the remediation of aqueous nuclear waste streams
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Journal of Radioanalytical and Nuclear Chemistry

Mud Hills clinoptilolite has been used in an effluent treatment plant (SIXEP) at the Sellafield nuclear reprocessing site. This material has been used to remove 134/137 Cs and 90 Sr successfully from effluents for 3 decades. Samples of the zeolite have been tested in column experiments to determine their ability to remove radioactive Cs + and Sr 2+ ions under increasing concentrations of competing ions, Ca 2+ , Mg 2+ , Na + and K +. These ions caused increased elution of Cs + and Sr 2+. Ca 2+ , Mg 2+ and K + were more effective competitors than Na +. For Na + , it was found that if concentration was reduced, then column performance recovered rapidly.

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Radiation-modified natural zeolites for cleaning liquid nuclear waste (irradiation against radioactivity)
Sergey K Nikoghosyan, Yeghis Keheyan

Scientific Reports, 2013

There have been comparatively few investigations reported of radiation effects in zeolites, although it is known that these materials may be modified substantially by exposure to ionizing radiation. Thus, by exposure to c-rays or high-energy particles, the charge states of atoms may be changed so to create, and accumulate, lattice point defects, and to form structurally disordered regions. Such a technique may permit the creation, in a controlled fashion, of additionally useful properties of the material while preserving its essential stoichiometry and structure. Accordingly, we present an application, in which the cation-exchange capacity of a natural zeolite (clinoptilolite) is substantially enhanced, for the treatment/decontamination of water contaminated with radionuclides e.g. 134 Cs, 137 Cs and 90 Sr, by its exposure to high-energy (8 MeV) electrons, and to different total doses. ''R arely in our technological society does the discovery of a new class of inorganic materials result in such a wide scientific interest and kaleidoscopic development of applications as has happened with the zeolite molecular sieves'', Donald W. Breck (1974) 1 . Just some of the manifold applications of zeolites are shown in , the variety and number of which are extended on an annual basis. The study of minerals is a mature science, and a major driving force for investigations of this kind is that, through the understanding of means for their formation, their crystal structure and other salient properties, novel materials may be produced by both a priori and post-synthetic means. Of the broad family of minerals, it is the zeolites which furnish highly effective catalysts, as are used extensively in the petrochemical industry and for other niche applications, e.g. in catalytic convertors, to mitigate local air-pollution from vehicles. The catalytically active sites are located within the internal cavities of a microporous structure, and are associated with cations that are present in sufficient concentration to electrostatically counterbalance the negatively charged, aluminosilicate framework 1,2 . Many physical and chemical properties of zeolites are determined by the nature and concentrations of those cations that are present in the zeolite unit (elementary) cell.

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Iranian natural clinoptilolite and its synthetic zeolite P for removal of cerium and thorium from nuclear wastewaters
Hamid Modarres

Journal of Radioanalytical and Nuclear Chemistry, 2003

The ion-exchange behaviors of an Iranian natural clinoptilolite and its modified forms as well as a relevant synthetic zeolite P were investigated toward cerium and thorium from nuclear wastewaters. Column experiments were performed on different exchangers in various conditions and the effect of parameters such as particle size, pH, temperature, and time were considered. The distribution coefficient, cation exchange capacity and some thermodynamic parameters were calculated. Ion-exchange isotherms and breakthrough curves were plotted. As a result, the selectivity of synthetic zeolite P from Iranian natural clinoptilolite toward cerium and thorium was compared with that of natural and cationic forms of clinoptilolite.

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Removal of 137Cs from aqueous solutions using different cationic forms of a natural zeolite: clinoptilolite
Hayrettin Yucel

Separation and Purification Technology, 2002

Distribution coefficients of cesium on natural and cation-enriched (Na + , K + , NH 4 + and Ca + 2 ) forms of clinoptilolite were measured by batch, radioactive tracer technique. The measurements were carried out for an initial cesium concentration range of 10 − 6 -10 − 1 mol/dm 3 and at temperatures of 25, 40, 60 and 80°C. Experimental isotherms evaluated from distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R)models. Of the models tested, D-R model was found to represent the isotherms better in a wider range of concentrations than either Langmuir or Freundlich model. Breakthrough behavior of cesium on natural and cation-enriched forms of clinoptilolite for a particular set of conditions were also determined in a small size column. Column parameters were evaluated using mass transfer zone concept.

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Synthesis of lta type zeolites from georgian clinoptilolite
Nato Mirdzveli

Himia, Fizika ta Tehnologia Poverhni, 2017

Generally, the microporous structure of synthetic zeolite is affected by the nature of used reactants and their pretreatments, as well as by composition of the reaction mixture. Our recent investigation of hydrothermal transformation of natural Georgian clinoptilolite demonstrated possibility of preparation of zeolites with high silicon content (mordenite-like materials) without organic template, directly from aged gels having suitable chemical composition and prepared by acid treatment of raw material. The aim of present work was preparation of zeolites with high aluminium content on the same basis without organic templates. The study tested possibility of synthesis of the LTA type zeolites in following steps: treatment of the natural clinoptilolite ((Na 3.3 K 1.15 Ca 0.75 Mg 0.25 [Me] 0.55)(Al 7.0 Si 29.3 O 72). 22.5H 2 O, where Me = Cu, Zn, Ba, etc.) in HCl water solution; gel preparation by suspension in NaOH solution; its hydrothermal crystallization to the sodalite structure (SOD) with Si/Al=1, and then re-crystallization of the sodalite into the NaA zeolite (LTA). Chemical elemental analyses confirm a good accordance with the UPAC SOD and LTA chemical formulas for prepared materials having nearly monocationic composition (Na-78 % SOD and 89 % LTA). In XRD patterns there are no additional peaks from zeolitic or other impurities, prepared materials have high crystallinity, their FTIR spectra are typical for SOD and LTA structures, developed zeolitic crystal microporous structure is confirmed by comparatively high averaged value of water adsorption capacity (0.08 cm 3 /g for SOD, and of 0.24 cm 3 /g for LTA at p/p S = 0.4). SEM images show uniform LTA micrometric crystallites (average diameter 4 μm) with fairly narrow distribution of sizes produced by lasting (> 10 h) low temperature crystallization, as well as nanoscale spherical zeolites (0.2 μm) and fibrous aggregates (0.08 μm) produced at low temperature, that can be used for preparation of composite and hierarchical structures for various catalytic and adsorptive applications.

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