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Synthesis of Na-LSX type zeolite from Polish fly ash

Adamczyk Zdzisław, Cempa Magdalena, Białecka Barbara

Gospodarka Surowcami Mineralnymi

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2020

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T. 36, z. 3

145--166

EN

The paper presents the results of hydrothermal zeolitization of fly ash from hard coal combustion in one of the Polish power plants. The synthesis was carried out using various NaOH fly ash mass ratio (3.0, 4.0 and 6.0) and the effect of NaOH concentration in the activating solution on composition of synthesized sample was tested. The process was carried out under the following permanent conditions temperature: 90°C, time – 16 hours, water solution of NaOH (L)/fly ash (g) ratio – 0.025. In the studied fly ash the dominant chemical components were SiO2 and Al2O3, while the main phase components were mullite, quartz and hematite, and a significant share of amorphous substance (glass and unburnt organic substance). After hydrothermal synthesis, the presence of unreacted fly ash phases was found in the products, as well as new phases, the quality and quantity of which depend on the NaOH to fly ash mass ratio used for synthesis: - for ratio 3.0 – Na-LSX type zeolite and hielscherite, - for ratio 4.0 – Na-LSX type zeolite, hielscherite and hydrosodalite, - for ratio 6.0 – hydrosodalite and hielscherite. The grains in all products of synthesis are poly-mineral. However, it was found that the new phases, overgrowing the unreacted phase components of fly ash, crystallize in a certain order. Hielscherite is the first crystallizing phase, on which the Na-LSX type zeolite crystallizes then, and the whole is covered by hydrosodalite. In the products of synthesis, the share of sodium-containing phases (the Na-LSX type zeolite and hydrosodalite) increases with the increasing concentration of NaOH in the solution used for the process.

PL

W pracy przedstawiono wyniki badań hydrotermalnej zeolityzacji popiołu lotnego pochodzącego ze spalania węgla kamiennego w jednej z polskich elektrowni. Syntezę przeprowadzono przy różnych stosunkach wagowych NaOH/popiół lotny (3,0, 4,0 i 6,0) i badano wpływ stężenia NaOH w roztworze aktywującym na skład zsyntetyzowanej próbki. Proces był prowadzony w następujących warunkach: temperatura syntezy – 90°C, czas syntezy – 16 godzin, stosunek roztworu NaOH (L)/popiół lotny (g) – 0,025. W badanym popiele lotnym dominującymi składnikami chemicznymi były SiO2 i Al2O3, natomiast głównymi składnikami fazowymi były mullit, kwarc, hematyt oraz stwierdzono znaczny udział substancji amorficznej (szkliwo i nieprzepalona substancja organiczna). W produktach po hydrotermalnej syntezie stwierdzono obecność nieprzereagowanych faz popiołu lotnego, a także nowe fazy, których jakość i ilość uzależnione są od stosunku masowego NaOH do popiołu lotnego: - dla stosunku 3.0 – zeolit typu Na-LSX i hielscherite, - dla stosunku 4.0 – zeolit typu Na-LSX, hielscherite i hydrosodalit, - dla stosunku 6.0 – hydrosodalit i hielscherite. Ziarna we wszystkich produktach syntezy są polimineralne. Stwierdzono jednak, że nowe fazy, obrastające nieprzereagowane składniki fazowe popiołu lotnego, krystalizują w określonej kolejności. Hielscherite jest pierwszą krystalizującą fazą, na którym krystalizuje zeolit typu Na-LSX i całość oblepia hydrosodalit. W produktach syntezy udział faz zawierających sód (zeolit typu Na-LSX i hydrosodalit) wzrasta wraz ze wzrostem stężenia NaOH w roztworze użytym w procesie.

2

Hydrosodalite ion exchange in saturated Ca(OH)2 solution

Vaičiukyniene D., Baltakys K., Kantautas A.

Materials Science Poland

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2009

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Vol. 27, No. 2

417--426

EN

The possibility of substituting Na+ ions contained in pure hydrosodalite crystal structure with Ca2+ ions in saturated Ca(OH)2 solution has been examined in the temperature range from 25 °C to 95 °C. It was found that temperature strongly influences the hydrosodalite ion exchange: upon increasing temperature only by 5 °C (from 25 to 30 °C) Ca2+ the time required for Ca2+ions to be incorporated within the hydrosodalite crystal structure is reduced by the factor of 3. With the increase of temperature from 45 °C to 65 °C almost all the Ca2+ ions, initially contained in the Ca(OH)2 solution, become incorporated in the hydrosodalite structure after 5 min However, high temperature has an adverse effect on the sorption process (Ca2+ ions will not be incorporated within the hydrosodalite structure before 10 min have elapsed). Partly reversible ion exchange reactions of hydrosodalite are characteristic at temperatures higher than 30 °C). The structure of hydrosodalite crystals remains stable when performing ion exchange reactions at 25-95 °C temperature.

3

Peculiarities of hydration of cement paste with addition of hydrosodalite

Skripkiunas G., Sasnauskas V., Daukšys M., Palubinskaite D.

Materials Science Poland

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2007

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Vol. 25, No. 3

627--635

EN

A synthetic zeolite - hydrosodalite was used as a hydraulic additive for hardened cement paste, and the influence of this additive on the hydration and other properties of the system was determined. Hydraulic activity of zeolite has been examined, X-ray diffraction, DTA and IR analysis of the hardened cement paste with zeolite additive have been carried out. The results have shown that the additive has a high hydraulic activity (the content of bound CaO - 370 mg/g). The addition of hydrosodalite reduces the content of Ca(OH)2 in hardened cement paste which transforms into calcium zeolite - gismundite. The density of the hardened cement paste with the addition of hydrosodalite after 3, 7 and 28 days of curing decreases by about 11%. This predetermines a decrease in the compressive strength of the hardened cement paste. The compressive strength after 3 days of curing decreases by about 70%, after 7 days of curing - by 66%, and after 28 days of curing - by about 65%.

4

The synthesis of hydrosodalite and its use in mortar technology

Sasnauskas V., Palubinskaite D.

Materials Science Poland

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2005

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Vol. 23, No. 3

793--801

EN

The conditions of low-temperature hydrothermal synthesis of zeolites from AlF3 production waste technogenic silicagel polluted with admixtures of fluorides, were analyzed. It was determined that AlF3 admixture encourages the formation of hydrosodalite. When using technogenic silica gel, crystal zeolite hydrosodalite was synthetized. The reaction was conducted under hydrothermal conditions, under atmospheric pressure at 90oC temperature for 0.5, 1 and 2 hours. The best molar ratio of the components Na2O : Al2O3 : SiO2 : H2O was 2 : 0,02 : 1 : 10. Lignosulphonic plasticiser (LST) was modified with synthetized hydrosodalite. The binding duration of cement paste of normal consistence with modified LST plasticiser decreased up to 40/395 min. (at 0.25% content of admixture) and 80/150 min. (0.75%), as compared with that of mortar non-modified with LST plasticiser, where the binding duration was equal to 65/475 min. (0.25 %) and 105/150 min. (0.75%). Larger compression strength of cement grout with modified LST plasticiser after 3, 7 and 28 days of hardening was obtained: 12.61; 21.52; 25.49 MPa (at 0.25 % content of addition), as while that mortar with nonmodified LST plasticiser 6.04; 9.63; 22.69 MPa compression strengths of specimen, respectively.