The crystallization kinetics of sodalites grown by the hydrothermal transformation of kaolinite studied by 29Si MAS NMR

Buhl, Josef‐Christian; Hoffmann, Wolfgang; Buckermann, Wilhelm A.; Müller‐Warmuth, W.

doi:10.1016/s0926-2040(97)00052-0

Cited by 23 publications

(24 citation statements)

References 10 publications

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“…The XRD patterns of potential secondary mineralization were checked against those of MINCRYST (2003) data set and published ones. The XRD analysis (data not shown) confirmed the formation of cancrinite (Buhl et al 1997) and sodalite (Sieger et al 1991).…”

Section: Outflow Solution and Colloid Characterizationmentioning

confidence: 87%

“…3) and alteration of the original clay minerals was evident in all layers. Evidently, at higher temperature the alteration of sediment minerals and precipitation of new phases are more pronounced (Buhl et al 1997;Bauer et al 1998;Barnes et al 1999;De la Villa et al 2001). The top layer of the 50 • C column was dominated by altered layered clay minerals, and spherical particles formed on their surfaces.…”

Section: Mineralogymentioning

confidence: 95%

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Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C

Mashal

Çetiner

2009

Environ Monit Assess

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Formation of secondary minerals and Cs mobility in Hanford sediments were investigated under conditions similar to the Hanford tank leak in a dynamic flow system at 50 degrees C. The objectives were to (1) examine the nature and locations of secondary mineral phases precipitated in the sediments and (2) quantify the amount of Cs retained by the sediment matrix at 50 degrees C. To this end, Hanford sediments were packed into 10-cm long columns and leached with simulated tank waste consisting of 1.4 M NaOH, 0.125 M NaAlO(2), 3.7 M NaNO(3), and 1.3 x 10(-4) M Cs at 50 degrees C. Compositions of outflow solution were monitored with time for up to 25 days, and the columns were then segmented into four 2.5-cm long layers. The colloidal fraction in these segments was characterized in terms of mineralogy, particle morphology, Cs content, and short-range Al and Si structure. It was observed that cancrinite and sodalite precipitated at 50 degrees C. Approximately 53% Cs was retained in the column treated by the simulated tank waste at this temperature. Cesium retention in the column was lowered in the high ionic strength solution due to competition from Na for the exchange sites. This can be explained by alteration of distribution and number of sorption sites which reduces the selectivity of Cs for Na, and through the formation of cancrinite and sodalite. The formation of hydroxide complexes in highly alkaline solutions could also contribute to relatively poor retention of Cs by hindering ion exchange mechanism.

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Section: Outflow Solution and Colloid Characterizationmentioning

confidence: 87%

Section: Mineralogymentioning

confidence: 95%

Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C

Mashal

Çetiner

2009

Environ Monit Assess

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“…A síntese hidrotermal de sodalita básica,Na 8 [AlSiO 4 ] 6 (½CO 3 ,OH) 2 . qH 2 0, 0 < q < 2, foi realizada em autoclave de aço inox com revestimento interno de teflon e capacidade máxima de 50 mL.…”

Section: Processo De Síntese Hidrotermalunclassified

“…No entanto, a utilização desse rejeito como matéria-prima na síntese de zeólitas tem-se mostrado bastante viável, 4,5 isso porque tal material é composto essencialmente por caulinita, argilomineral mais empregado como fonte de Si e Al em síntese de zeólita e de material com estrutura relacionada. [6][7][8][9] A caulinita é o principal constituinte do caulim, quimicamente é um silicato de alumínio hidratado, que normalmente se encontra associada a outros minerais sob a forma de impurezas, de modo geral, quartzo, mica, feldspato, óxidos de ferro e titânio. É formada pelo empilhamento regular de camadas 1:1, isto é, cada camada é constituída de uma folha de tetraedros SiO 4 e uma folha de octaedros de Al 2 (OH) 6 ligadas entre si por oxigênios comuns, dando uma estrutura fortemente polar.…”

Section: Introductionunclassified

“…17 A Structure Commission of the International Zeolite Association classifica as zeólitas segundo um código de três letras maiúsculas para cada tipo de estrutura, exemplos: estilbita = STI, mordenita = MOR, faujazita = FAU, sodalita = SOD. 20 O mineral sodalita, com a composição química Na 8 [AlSiO 4 ] 6 Cl 2 , foi descoberto por Thomson,21 e teve sua estrutura descrita primeiramente por Pauling. 22 Com o desenvolvimento de diferentes métodos de síntese, tem-se chegado a sodalitas com uma vasta variedade na composição.…”

Section: Introductionunclassified

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Síntese hidrotermal de sodalita básica a partir de um rejeito de caulim termicamente ativado

Paz¹,

Angélica²,

Neves³

2010

Quím. Nova

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Recebido em 8/3/09; aceito em 1/9/09; publicado na web em 23/2/10 HYDROTHERMAL SYNTHESIS OF BASIC SODALITE FROM A THERMICALLY ACTIVATED KAOLIN WASTE. Basic sodalite was successfully synthesized by hydrothermal method using kaolin waste as source of Aluminum and Silicon. This waste is mainly composed by kaolinite and is produced in large amount by kaolin processing industries for paper coating from the Amazon region. Initially, the waste has been calcined at 700 ºC for 2 h and then reacted with the following solutions: Na 2 CO 3 and mixture of Na 2 CO 3 + NaOH to 150 ºC with autogenous pressure for 24 h. The raw materials and transformed materials were characterized by XRD, FTIR and SEM. In both studied media, well-crystallized, basic sodalite was the only phase synthesized, while in the literature usually a mixture of zeolites is obtained.Keywords: synthesis; basic sodalite; kaolin waste. INTRODUÇÃOA região amazônica dispõe de grandes e valiosos depósitos de caulim que, por sua natureza geológica, são adequados ao seu uso mais nobre, a cobertura de papel. Só no Estado do Pará estão localizadas três grandes indústrias de beneficiamento de caulim do País, que geram de rejeito, somente nas etapas de separação granulométrica e branqueamento, mais de 1 milhão de toneladas por ano e, em função deste elevado volume, faz-se necessária a construção de onerosas lagoas de sedimentação para sua deposição.1-3 O rejeito depositado nas lagoas não apresenta consistência adequada que permita o recobrimento convencional para a recuperação da área, o que o torna um problema ambiental. No entanto, a utilização desse rejeito como matéria-prima na síntese de zeólitas tem-se mostrado bastante viável, 4,5 isso porque tal material é composto essencialmente por caulinita, argilomineral mais empregado como fonte de Si e Al em síntese de zeólita e de material com estrutura relacionada. [6][7][8][9] A caulinita é o principal constituinte do caulim, quimicamente é um silicato de alumínio hidratado, que normalmente se encontra associada a outros minerais sob a forma de impurezas, de modo geral, quartzo, mica, feldspato, óxidos de ferro e titânio. É formada pelo empilhamento regular de camadas 1:1, isto é, cada camada é constituída de uma folha de tetraedros SiO 4 e uma folha de octaedros de Al 2 (OH) 6 ligadas entre si por oxigênios comuns, dando uma estrutura fortemente polar. As ligações entre as camadas são feitas por ligações de hidrogênio, OH-O, uma vez que existe um plano de íons hidroxila numa das faces da camada e um plano de íons oxigênio na outra camada adjacente. A energia de ligação costuma variar para cada espécie, mas no geral é preciso temperaturas entre 500 e 700 ºC para que todas as OH -sejam eliminadas. A fórmula estrutural da cela unitária da caulinita é Al 2 Si 4 O 10 (OH) 8 e a composição percentual: SiO 2 -46,54%, Al 2 O 3 -39,50% e H 2 O -13,96%. 10-13As zeólitas são aluminossilicatos hidratados com uma estrutura cristalina de geometria precisa e nanoporos de tamanho uniforme, formando canais de dimensões moleculares, c...

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A new process for Al₂O₃ production from low‐grade diasporic bauxite based on reactive silica dissolution and stabilization in NaOH‐NaAl(OH)₄ media

Xiao

2011

AIChE Journal

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A new process of Al 2 O 3 production from low-grade diasporic bauxite based on the reactive silica dissolution and stabilization in concentrated NaOH-NaAl(OH) 4 solutions is proposed and proved feasible. NaOH and Al 2 O 3 concentrations and leaching temperature were found to be the main factors affecting the leaching process of reactive silica. The A/S (mass ratio of Al 2 O 3 /SiO 2 ) of diasporic bauxite was enhanced from 5.4 to 15 by reactive silica removal under the optimum operation conditions. Two obvious steps control the whole leaching process of reactive silica in NaOH-NaAl(OH) 4 media: reactive silica dissolution and desilication products (DSPs) precipitation. The kinetics data of two controlling steps fit a shrinking core model based on the calculation of OH À activity with the aid of OLI platform and an empirical kinetic model well, respectively. Apparent activation energies of reactive silica leaching in the temperature range from 80 to 110 C are 101.91 and 58.65 kJ mol À1 for the two steps, respectively. The stabilization mechanism of reactive silica in concentrated NaOH-NaAl(OH) 4 solution was also elucidated based on the complexation of aluminum-bearing species and the calculation of supersaturation to DSP. It was found that the concentration of OH À sharply decreases due to the formation of Al(OH) 4 À species with increasing aluminum concentration, suppressing greatly DSP precipitation. This proposed process paves the way for Al 2 O 3 production from low-grade diasporic bauxite with high-reactive silica content.A/S ¼ mass ratio of Al 2 O 3 /SiO 2 DSP ¼ desilication products S ¼ supersaturation K sp ¼ the solubility product constant of DSP k ¼ the kinetic rate constant (refer to Eq. 10) k 1 ¼ the dissolution kinetic rate constant of reactive silica, kg L À1 min À1 Figure 16. SEM morphologies of Al 2 O 3 obtained in this study.

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The crystallization kinetics of sodalites grown by the hydrothermal transformation of kaolinite studied by 29Si MAS NMR

Cited by 23 publications

References 10 publications

Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C

Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C

Síntese hidrotermal de sodalita básica a partir de um rejeito de caulim termicamente ativado

A new process for Al₂O₃ production from low‐grade diasporic bauxite based on reactive silica dissolution and stabilization in NaOH‐NaAl(OH)₄ media

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The crystallization kinetics of sodalites grown by the hydrothermal transformation of kaolinite studied by 29Si MAS NMR

Cited by 23 publications

References 10 publications

Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C

Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C

Síntese hidrotermal de sodalita básica a partir de um rejeito de caulim termicamente ativado

A new process for Al2O3 production from low‐grade diasporic bauxite based on reactive silica dissolution and stabilization in NaOH‐NaAl(OH)4 media

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A new process for Al₂O₃ production from low‐grade diasporic bauxite based on reactive silica dissolution and stabilization in NaOH‐NaAl(OH)₄ media