• Bulletin of the Korean Chemical Society
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• v.18 no.3
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• pp.280-286
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• 1997

Potential energy function sets for some ion-exchanged A-type zeolites, K-A and Rb11Na1-A, were determined by introducing the X-ray crystal structures as constraints. The potential functions reproduced well the X-ray crystal structures of the monovalent ion-exchanged zeolites. The activation energies for the en- or de-capsulation of small molecules (H2, O2, N2, and CH4) and inert gases from the α-cage of model zeolites (Na-A, K-A, Rb11Na1-A, and Cs3Na9-A) were obtained by the molecular mechanical calculations. The calculated activation energies agreed well with experimental results.

• Journal of Environmental Science International
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• v.2 no.4
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• pp.347-356
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• 1993

The three natural zeolites collected in Yungil-gun, Kyungsangbuk-do, Korea, were analyzed by means of chemical wet methods and X-ray diffraction. The results indicated that the primary species of those zeolites were clinoptilolite mixed with heulandite, feldspar, montmorillonite, and quartz. These zeolites were chemically treated with NaOH, $\textrm{Ca(OH)}_2$, and HCl solution and their differences were also studied with X-ray diffraction method. The capabilities of removing $Cs^+$ and Sr^{2+}$ ions with chemically untreated zeolites, chemically treated zeolites, and also with synthetic zeolites were compared. The effect of other cations in removing Sr^{2+}$ ions was also studied. The experimental results showed that$Cs^+$ and Sr^{2+}$ ions could be removed up to 98% and 95% respectively out of 5 ppm with chemically untrearted natural zeolites. The treatment of 0.02N-$\textrm{Ca(OH)}_2$ and that of 2N-NaOH were most effective In removing $Cs^+$ and Sr^{2+}$ ions, respectively. It was found that the mountaintop of Sangjung 1-dong natural zeolite treated with 2N-NaOH was most efficient in removing Sr^{2+}$ ions mixed with other cations, compared with any other chemically treated and untreated natural zeolites in this work.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.749-756
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• 2019

Na-X and Na-A zeolites that give high adsorption capacity for heavy metals in an aqueous system were synthesized from the coal fly ash obtained from a thermoelectric power plant using a fusion method. The characteristics and Cu(II) adsorption capacity of the synthetic zeolites were also compared to those of using a commercial zeolite. For the selection of optimum conditions of zeolite synthesis, the effects of major parameters in the fusion method such as a dosage ratio of NaOH, aging time, hydrothermal reaction time, and also the dosage ratio of NaAlO₂ (Na-A) on the characteristics and Cu(II) adsorption capacity of the synthetic zeolites were studied. For the analysis of characteristics of the synthetic zeolites, X-ray diffraction (XRD), cation exchange capacity (CEC), Brunaue-Emmett-Teller (BET) and scanning electron microscopy (SEM) were used. The optimum conditions for the synthesis of zeolites with a high adsorption capacity for cationic heavy metals including Cu(II) were the aging time of 6 h, hydrothermal reaction time of 6 h and NaOH and NaAlO₂ dosage ratio of 1.5 and 0.5 (Na-A), respectively. According to the Langmuir isotherm test, maximum Cu(II) adsorption capacities of the synthetic and commercial Na-X and Na-A zeolites were found to be 90.1, 105.26, 102.05, and 109.89 mg/g, respectively. This indicates that the adsorption capacity of synthetic zeolites was comparable to commercial ones. The results of this study also suggest that the coal fly ash can be potentially used as a raw material for the zeolite synthesis.

• Journal of the Mineralogical Society of Korea
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• v.3 no.1
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• pp.7-17
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• 1990

화산 유리질 암석을 출발 물질로 사용하여 저온 ($80^{\circ}C$)에서 수열 처리하여 Na-P Na-X 및 Na-A 제올라이트를 합성하였다. 합성과정은 (1) 유리질 분말 시료와 알칼리 용액과의 용해.변질 반응에 의한 1차적인 Na-P의 합성 방식과 (2) 여기서 잔류된 규산질 모액에 Al(OH)3나 NaAlO2의 수용액을 공급하여 보다 고순도의 Na-P, Na-X 및 Na-A를 효과적으로 합성할 수 있었다. 원암의 암상과 조성은 제올라이트들의 화학 조성과 순도 및 백색도같은 물리적 특성에는 영향을 주지만, 합성된 제올라이트의 광물종을 규제하는 주된 요인은 아닌 것으로 해석된다. 합성된 제올라이트의 광물상은 반응 용액의 pH, Al(OH)4 및 Na+에 대한 농도 조건에 주로 의존되는 경향을 나타낸다. 또한 화산 유리질 암석을 제올라이트 합성원료로 활용하는 데에 있어서 (2)와 같음 합성 방안이 보완적으로 시행되면 그 생산성과 효율성을 제고시킬 수 있을 것으로 여겨진다.

• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.488-496
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• 1993

Natural zeolites have recently been the subject of intensive research due to their versatilities in possible industrial applications. Among several different types of domestic natural zeolites, clinoptilolite, is one of the highly prospective domestic natural zeolites. However, it is always possible for heulandite, the isostructure of clinoptilolite, to coexist with clinoptilolite. Unfortunately, heulandite is thermally very unstable restricting its application to industrial process. In this paper, the effects of ion exchanges and heat-treatments on the thermal stability for domestic natural zeolite, heulandite are described. Two different ion-exchanging experiments were carried out followed by heat-treatments at different temperatures. X-ray, IR and AA spectroscopic analyses showed the enhancements in thermal stabilities of heulandite by $Na^+$ cation exchanges.

• Journal of the Mineralogical Society of Korea
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• v.5 no.2
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• pp.61-71
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• 1992

Through the low-temperature(60-150${\circ}C$) hydrothermal treatment of perlite with the alkaline solution at various NaOH concentrations, the mode of volcanic glass alteration and resultant zeolite formation were investigated in a closed system. At a temperature of 80${\circ}C$ and alkalinities of pH range 8 to 12, corresponding to the natural environments of diagenetic zeolite formation, only weak dissolution of perlitic glass occurs without zeolite formation despite the residence time of 100 days. Activities of Si and Al increase progressively, as a consequence of increasing pH, whereas activity ratios of Si/Al decrease. Zeolites were synthesized from perlite in the alkaline solution at above 0.1M NaOH concentrations. Below the temperature of 100${\circ}C$ Na-P was mainly formed, whereas analcime was the dominant zeolite at the temperature range of 100-150${\circ}C$. During Na-P synthesis chabazite and Na-X were also formed as by-products in case of lower proportion of solution/sample(<10ml/g) and higher NaOH concentraion (>3M), respectively. The alteration modes of perlite in the zeolite synthesis reflect that the formation of synthetic zeolites occurs as an incongruent dissolution likely with the diagenetic formation of natural zeolites from volcanic glass. Considering much difference in reaction kinetics between natural and synthetic systems, however, the evaluated synthetic conditions in these experiments were not directly applicable to the natural diagenetic system.

• Applied Chemistry for Engineering
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• v.5 no.1
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• pp.24-29
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• 1994

The zeolite X was prepared from the Korean natural clinoptilolite, which contains some mordenite. Thermal treatment removed the clinoptilolite structure from the ore remaining mordenite. The natural clinoptilolites dealuminated with 2N-8N HCI solution and/or thermal treatment were mixed with NaCl, $NaAlO_2$ and NaOH, and reacted to zeolites X at $95^{\circ}C$ for 12~36 hrs. Maximum yield of NaX was obtained for the reactant mixture of 25 gr of natural zeolite acidtreated with 8 N HCI, together with 3.5g NaCl, 8g $NaAlO_2$ and 50 ml of 6N NaOH at $95^{\circ}C$, for 24 hrs.

• Clean Technology
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• v.30 no.3
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• pp.248-257
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• 2024

Carbon dioxide is an undesired component of biogas and landfill gas. As a result, it needs to be removed from these mixtures in order to increase their heating value and reduce corrosion during treatment. Zeolites are a class of microporous materials that can be used as adsorbents for the separation of carbon dioxide from gas mixtures. In this work, the pure gas adsorption isotherms of methane and carbon dioxide and the selectivity of their mixture onto LTA-4A, FAU-13X and FAU-NaY adsorbents at temperatures of 273, 298 and 323 K and pressures up to 30 bars were calculated by the Monte Carlo method. Also, the influence of a flexible framework in a set of zeolites on the separation of methane and carbon dioxide was studied. Carbon dioxide adsorption onto the zeolites used in this work was more favorable than methane adsorption. The FAU-13X adsorbent had the highest adsorption capacity among the studied adsorbents. However, the selectivity of carbon dioxide over methane for LTA-4A was the highest. The adsorption capacities of a rigid framework were higher than those of a flexible framework. The influence of the framework flexibility in FAU on adsorption capacity was small. In contrast, its influence on selectivity seemed to be much larger.

• Journal of the Korean Applied Science and Technology
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• v.32 no.2
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• pp.240-247
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• 2015

Zeolite A was prepared from coal fly ash upon NaOH fusion treatment, followed by hydrothermal treatment. The effects of treatment conditions such as NaOH/ash ratio, fusion temperature, the amount of sodium aluminate added, hydrothermal treatment temperature and time on the type and the crystallinity of zeolites were investigated. The optimal NaOH/ash weight ratio and fusion temperature to produce high crystalline zeolite A were 1.2 and $550^{\circ}C$, respectively. The dissolution of $Si^{4+}$ and $Al^{3+}$ from the fused fly ash was not affected by stirring time. The type of synthetic zeolites was found to be dependent on the amount of sodium aluminate added. The low amount of sodium aluminate favored zeolite X, while a single phase zeolite A was produced by increasing the amount sodium aluminate. Zeolite A was transformed into hydroxysodalite with increasing hydrothermal treatment time and temperature. A high crystalline zeolite A could be obtained by decreasing the temperature increasing time up to the reaction temperature.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.160-168
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• 2014

In the present study, water vapor adsorption was evaluated at 298.15K for 9 different zeolites having LTA, FAU, CHA, and RHO frameworks, and then effect of framework type, Si/Al molar ratio, and alkali ion type on water up-take was investigated. Zeolites showed water up-takes which were increased in an order of $RHO<CHA{\approx}LTA<FAU$ frameworks. NaY zeolite having FAU framework showed a water up-take of 406 mg/g at p/po=0.5. The up-take was a little larger than that of 13X zeolite with the same framework. Among LTA zeolites, Ca-type 5A zeolite showed the highest water adsorption (282 mg/g at p/po=0.5) which could be explained by the large pore volume. Both CHA zeolite with a Si/Al molar ratio of 2.35 and RHO zeolite with a Si/Al molar ratio of 3.56 showed considerable water up-takes, even though the Si/Al molar ratio was much larger than that of LTA zeolite. In the present study, it is announced that in addition to FAU and LTA zeolites, CHA and RHO zeolites can be a promising dehumidification adsorbent.