Preparation of microporous silica from metakaolinite by selective leaching method

Okada, Kiyoshi; Shimai, Akira; Takei, Takahiro; Hayashi, Shigeo; Yasumori, Atsuo; MacKenzie, Kenneth J.D.

doi:10.1016/s1387-1811(98)00015-8

Cited by 128 publications

(95 citation statements)

References 19 publications

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“…Observa-se que a caulinita pura (Figura 3a) apresenta um pico endotérmico centrado em 51 °C, correspondente à eliminação de moléculas de água de adsorção/absorção e um pico endotérmico centrado em 529 °C, correspondente a seu processo de desidroxilação, o qual transforma a caulinita em metacaulinita 1,34,35 . Um pequeno pico endotérmico foi observado em 275 °C, provavelmente de uma impureza cristalina, apesar de que por difratometria de raios-X, nenhum material cristalino contaminante foi observado.…”

Section: Figura 2 Difratogramas De Raios-x Da Fase Hidratada Seca Aounclassified

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Comportamento térmico da caulinita hidratada

Gardolinski

Filho

2003

Quím. Nova

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Recebido em 23/11/01; aceito em 28/5/02 THERMAL BEHAVIOR OF HYDRATED KAOLINITE. Well-ordered kaolinite from the Brazilian Amazon Region (State of Pará) was initially reacted at 60 °C with a water dimethylsulfoxide mixture. After washing and characterisation, the resulting material was washed several times with methanol and in the final step with water. The water molecules displace the previously dimethylsulfoxide intercalated molecules and two different hydrated kaolinites were obtained. An unstable phase characterized by an interplanar basal distance of 0,996 nm that after drying collapse to the stable 0,844 nm hydrated kaolinite. The dehydration of the sample to disordered kaolinite was accompanied by Powder X-ray Diffractometry, thermal analysis (simultaneous TG and DSC) and FTIR spectroscopy.Keywords: kaolinite; clay minerals; intercalation compounds. INTRODUÇÃOOs argilominerais do grupo da caulinita envolvem quatro variedades politípicas polimórficas, a Nacrita (JCPDS:16-606), Diquita (JCPDS:10-446), Caulinita (JCPDS:14-164 e 29-1488) e Haloisita 0,7 nm ou metahaloisita (JCPDS:29-1487), todos com a fórmula Al 2 Si 2 O 5 (OH) 4 , além da Haloisita 1,0 nm ou endelita (JCPDS:1489) com a fórmula Al 2 Si 2 O 5 (OH) 4 .2H 2 O 1,2 . Tipicamente os argilominerais nacrita, diquita, caulinita e haloisita 0,7 nm ocorrem na forma de cristais tabulares e a haloisita 1,0 nm na forma de tubos ou cilindros, que ocorrem pelo enrolamento das lamelas da caulinita.Dependendo da sua gênese, a caulinita pode se apresentar com elevada, média e alta ordem estrutural ao longo do eixo "b" da estrutura triclínica (ou monoclínica), sendo baixo o teor de substituintes isomórficos (normalmente Fe +3,+2 no sítio do alumínio), sendo considerada eletricamente neutra. Minerais do grupo da caulinita e outros argilominerais são formados pela decomposição de feldspatos por processos geológicos, tendo provavelmente sericita como intermediário (Eq. 1). A formulação da caulinita pode ser descrita como resultante da deposição de 2 moles de gibbsita (variedade polimórfica do Al(OH) 3 ) sobre dois moles de sílica, mantendo-se as estruturas dos dois compostos (tipo 1:1). A Figura 1 apresenta a estrutura da gibbsita (a), sílica (b), o processo de montagem da estrutura ideal da caulinita (c) e a estrutura final da caulinita (d).Na estrutura da gibbsita os átomos de alumínio estão posicionados nos centros dos octaedros e, nos vértices, estão posicionados os grupamentos hidroxila. Somente 2/3 dos octaedros são ocupados e os octaedros são ligados pelas arestas, o que caracteriza a caulinita como dioctaédrica 1,2 . Na estrutura da sílica, os átomos de silício estão posicionados nos centros dos tetraedros, nos quais os vértices são ocupados por átomos de oxigênio. Devido a forma com que os tetraedros são coordenados uns aos outros, cria-se um buraco na lamela que expõe a hidroxila interna para eventuais reações (Figura 1b). Exemplos de intercalação de caulinitas envolvem o uso de pequenas moléculas polares (tipicamente dimetilsulfóxido e Nmetilformamida) 3-...

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Section: Figura 2 Difratogramas De Raios-x Da Fase Hidratada Seca Aounclassified

“…A seguir observou-se um pico endotérmico em 518 °C, atribuído ao processo de desidroxilação da matriz, o qual transforma a caulinita em metacaulinita 1,34,35 . O pico exotérmico em 977 °C é idêntico àquele reportado para a caulinita (Figura 3a), relacionado com a nucleação da mulita 33 .…”

Section: Figura 2 Difratogramas De Raios-x Da Fase Hidratada Seca Aounclassified

Comportamento térmico da caulinita hidratada

Gardolinski

Filho

2003

Quím. Nova

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“…The acid-treatment of Na-TSM also led to an increase in specific surface area and pore volume although the values for acid-treated Na-TSM were much smaller those for acid-treated APMs. Several studies have been conducted on the acid leaching of swellable or non-swellable clay minerals to obtain porous solids [13][14][15][16][17][18][19][20][21][22][23][24]. These studies have yielded porous silica having micro-or mesopores depending on both the species of starting clay mineral and the leaching conditions.…”

Section: Methodsmentioning

confidence: 99%

“…Acid-treatment of various clay minerals, such as kaolinite [13,14], phlogopite [15,16], vermiculite [17], montmorillonite [18,19], fluorohectorite [15], talc [20,21], chlorite [22], saponite [23,24], has been reported. The acid-treated products typically show micro-or mesopores, depending on the starting clay mineral species and the acid-treatment conditions.…”

Section: Introductionmentioning

confidence: 99%

Preparation of novel porous solids from alumina-pillared fluorine micas by acid-treatment

Yamaguchi

Yoshimura

Yamakami

et al. 2008

Microporous and Mesoporous Materials

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New porous solids from alumina-pillared fluorine micas (APMs), which were obtained from synthetic Na-tetrasilicic fluorine mica [NaMg 2.5 Si 4 O 10 F 2 ], were prepared by sulfuric acid-treatment under mild conditions at 25˚C. The products were investigated by XRD, ICP, SEM, TEM and N 2 adsorption-desorption isotherm at 77 K. XRD measurements indicated that the interlayer pillared structure having a large basal spacing collapsed during the early stages of the acid-treatment. ICP analyses indicated that Al 3+ and Mg 2+ ions were leached out from the pillared micas during the acid-treatment. The pore properties of the leached products were found to differ from those of the mother pillared micas: the acid leaching of the pillared micas leads to the formation of mesopores around 3.2 nm in diameter. The correlation between the change in pore properties and cation elution behavior suggests that the mesopore formation results from the leaching of Mg 2+ ions from the octahedral sheet of the pillared micas. The leached products thus obtained retained the flaky morphology of the mother pillared micas. These results show that the mild acid-treatment using APMs provides a novel route for obtaining unique mesopore solids having the large particle sizes of the mother micas.

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“…23,24,26,27) The solubility of clay in acids varies with the nature and concentration of the acid, the acid-to-clay ratio, the temperature, and the duration of treatment. 7,23,2628) Most of these investigations have indicated that the clay is more soluble in sulfuric than in hydrochloric acid.…”

Section: )mentioning

confidence: 99%

Synthesis and Characterization of Mesoporous Silica from Anorthite-Clay Mineral: Role of Mechanical Activation

et al. 2014

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Mesoporous silica was prepared from anorthite-clay via mechanical activation (i.e., grinding) and selective acid leaching method. The pore characteristics of the mesoporous silica with different grinding time and acid treatment time were systematically characterized and compared with those prepared via heat treatment followed by acid treatment. Particle size, X-ray diffraction (XRD), BET surface area, thermal gravity (TG), and solubility analyses were carried out to characterize the samples. The XRD results showed that grinding and heat treatment dramatically altered the crystal structure of the samples, resulting in the change in weight loss curves of the corresponding samples from TG analysis. The results for pore size distribution of the prepared samples revealed that acid-treatment led to significant changes in the pore structure of the samples while grinding and heat-treatment without acid-treatment showed negligible influence on the pore structure. More specifically, acidtreatment increased the specific surface area of the ground and heat-treated samples regardless of acid-treatment. Furthermore, solubility tests for anorthite-clay samples showed that there is a positive relationship between the solubility of anorthite-clay and the specific surface area of mesoporous silica, indicating that the increase in the specific surface area of mesoporous silica was attributed to the increase in the solubility of anorthite-clay.

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Preparation of microporous silica from metakaolinite by selective leaching method

Cited by 128 publications

References 19 publications

Comportamento térmico da caulinita hidratada

Comportamento térmico da caulinita hidratada

Preparation of novel porous solids from alumina-pillared fluorine micas by acid-treatment

Synthesis and Characterization of Mesoporous Silica from Anorthite-Clay Mineral: Role of Mechanical Activation

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