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Andrea R. Gerson - One of the best experts on this subject based on the ideXlab platform.
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the kinetics of desilication of synthetic spent bayer liquor seeded with cancrinite and cancrinite Sodalite mixed phase crystals
Journal of Crystal Growth, 1999Co-Authors: Mark C. Barnes, Jonas Addaimensah, Andrea R. GersonAbstract:Isothermal, batch desilication kinetics of synthetic, sodium aluminate solution (spent Bayer liquor) via cancrinite and cancrinite/Sodalite mixed-phase crystal growth, have been studied under conditions at which sodium aluminosilicate scale forms at the surfaces of steel heat exchangers of alumina plant. Seeding with the pure cancrinite and mixed-phase crystals results in the suppression of scale formation and a faster rate of liquor desilication in comparison with its Sodalite dimorph. Cancrinite seed crystals prepared from NO−3-rich solutions exhibited crystal growth mechanism and kinetic behaviour different from dimorphic mixed-phase crystals prepared from CO2−3-rich solutions, when both were used to desilicate CO2−3-rich spent Bayer liquor. The rate of desilication due to crystal growth on CO2−3-cancrinite/Sodalite mixed phase crystals followed a second-order dependence on the relative supersaturation of SiO2. An activation energy of 52 kJ mol−1 was estimated for the crystal growth process. For desilication kinetics involving NO−3-cancrinite seed crystal growth, a third-order dependence on relative supersaturation of SiO2 and an activation energy of 63 kJ mol−1 were obtained.
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the kinetics of desilication of synthetic spent bayer liquor and Sodalite crystal growth
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999Co-Authors: Mark C. Barnes, Jonas Addaimensah, Andrea R. GersonAbstract:The kinetics of desilication of synthetic, sodium aluminosilicate solution (spent Bayer liquor) and growth of Sodalite crystals have been studied under isothermal, batch crystallization conditions close to those prevailing in Bayer process heat exchangers. The desilication rate of the liquor via the formation and growth of Sodalite scale on steel substrates was found to be independent of agitation rate. With Sodalite seeding, the desilication rate was observed to increase dramatically due to seed crystal growth with the suppression of scale formation. An activation energy of 30 kJ mol−1 and a second order dependence of the desilication rate on relative supersaturation of SiO2 were obtained for Sodalite crystal growth.
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The mechanism of the Sodalite-to-cancrinite phase transformation in synthetic spent Bayer liquor
Microporous and Mesoporous Materials, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:Abstract The precipitation of zeolite, Sodalite and cancrinite and subsequent phase transformations were investigated under a variety of conditions in sodium aluminate liquor. At sufficiently high SiO 2 relative supersaturation, amorphous sodium aluminosilicate and zeolite precipitated at temperatures as high as 160°C. They subsequently transformed to Sodalite and finally to cancrinite. Thus the sequence of the transformation of phases is: [Aluminosilicate species]→Amorphous phase→Zeolite (Linde A)→Sodalite→Cancrinite. It was found that Sodalite did not transform to cancrinite in the absence of a liquid medium. The transformation of Sodalite to cancrinite was demonstrated to involve a solution-mediated mechanism with Sodalite dissolution and subsequent cancrinite precipitation. Neither the amorphous phase nor the zeolite phase precipitates at typical spent Bayer liquor SiO 2 supersaturation.
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The solubility of Sodalite and cancrinite in synthetic spent Bayer liquor
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:The equilibrium SiO2 solubility of Sodalite and cancrinite crystals in sodium aluminate solutions containing low concentrations of aluminium (synthetic spent Bayer liquor) has been determined over a range of temperatures (90–220°C) and as a function of solution NaOH and Al(OH)3 concentration for cancrinite. The same SiO2 solubilities, within experimental error, were measured when equilibrium was approached from both above and below SiO2 solubility for spent Bayer liquors in contact with either Sodalite or cancrinite crystals. The solubility of Sodalite and cancrinite (expressed in terms of SiO2 concentration) increased linearly with increasing temperature. The equilibrium SiO2 solubility of Sodalite was higher than that of cancrinite at all temperatures. The solubility of cancrinite increased with increasing concentration of NaOH (3.87–5.42 M) and Al(OH)3 (1.39–2.23 M) in solution. The SiO2 solubilities of four types of dimorphic Sodalite/cancrinite mixed phase seed crystals synthesised from Bayer plant spent liquor and synthetic Na2CO3, Na2SO4 or NaNO3 rich NaOH solutions containing dissolved kaolinite were investigated. The solubility of the four types of mixed phase seed crystals was found to be substantially the same as the solubility for pure cancrinite
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A methodology for quantifying Sodalite and cancrinite phase mixtures and the kinetics of the Sodalite to cancrinite phase transformation
Microporous and Mesoporous Materials, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:A simple methodology for determining the cancrinite proportion of a Sodalite and cancrinite phase mixture was developed using powder X-ray diffraction. Using this methodology to quantify phase mixtures, the kinetics of the Sodalite to cancrinite phase transformation were determined. The transformation reaction leading to cancrinite formation was found to be first order with respect to the relative concentration of Sodalite. Over the temperature range 160–240°C, an activation energy for this process was estimated to be 133 kJ mol−1. The techniques of 29Si MAS NMR and FTIR were both found to be unsuitable for quantifying dimorphic phase mixtures due to the ambiguity of the results they produced.
Mark C. Barnes - One of the best experts on this subject based on the ideXlab platform.
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the kinetics of desilication of synthetic spent bayer liquor seeded with cancrinite and cancrinite Sodalite mixed phase crystals
Journal of Crystal Growth, 1999Co-Authors: Mark C. Barnes, Jonas Addaimensah, Andrea R. GersonAbstract:Isothermal, batch desilication kinetics of synthetic, sodium aluminate solution (spent Bayer liquor) via cancrinite and cancrinite/Sodalite mixed-phase crystal growth, have been studied under conditions at which sodium aluminosilicate scale forms at the surfaces of steel heat exchangers of alumina plant. Seeding with the pure cancrinite and mixed-phase crystals results in the suppression of scale formation and a faster rate of liquor desilication in comparison with its Sodalite dimorph. Cancrinite seed crystals prepared from NO−3-rich solutions exhibited crystal growth mechanism and kinetic behaviour different from dimorphic mixed-phase crystals prepared from CO2−3-rich solutions, when both were used to desilicate CO2−3-rich spent Bayer liquor. The rate of desilication due to crystal growth on CO2−3-cancrinite/Sodalite mixed phase crystals followed a second-order dependence on the relative supersaturation of SiO2. An activation energy of 52 kJ mol−1 was estimated for the crystal growth process. For desilication kinetics involving NO−3-cancrinite seed crystal growth, a third-order dependence on relative supersaturation of SiO2 and an activation energy of 63 kJ mol−1 were obtained.
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the kinetics of desilication of synthetic spent bayer liquor and Sodalite crystal growth
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999Co-Authors: Mark C. Barnes, Jonas Addaimensah, Andrea R. GersonAbstract:The kinetics of desilication of synthetic, sodium aluminosilicate solution (spent Bayer liquor) and growth of Sodalite crystals have been studied under isothermal, batch crystallization conditions close to those prevailing in Bayer process heat exchangers. The desilication rate of the liquor via the formation and growth of Sodalite scale on steel substrates was found to be independent of agitation rate. With Sodalite seeding, the desilication rate was observed to increase dramatically due to seed crystal growth with the suppression of scale formation. An activation energy of 30 kJ mol−1 and a second order dependence of the desilication rate on relative supersaturation of SiO2 were obtained for Sodalite crystal growth.
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The mechanism of the Sodalite-to-cancrinite phase transformation in synthetic spent Bayer liquor
Microporous and Mesoporous Materials, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:Abstract The precipitation of zeolite, Sodalite and cancrinite and subsequent phase transformations were investigated under a variety of conditions in sodium aluminate liquor. At sufficiently high SiO 2 relative supersaturation, amorphous sodium aluminosilicate and zeolite precipitated at temperatures as high as 160°C. They subsequently transformed to Sodalite and finally to cancrinite. Thus the sequence of the transformation of phases is: [Aluminosilicate species]→Amorphous phase→Zeolite (Linde A)→Sodalite→Cancrinite. It was found that Sodalite did not transform to cancrinite in the absence of a liquid medium. The transformation of Sodalite to cancrinite was demonstrated to involve a solution-mediated mechanism with Sodalite dissolution and subsequent cancrinite precipitation. Neither the amorphous phase nor the zeolite phase precipitates at typical spent Bayer liquor SiO 2 supersaturation.
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The solubility of Sodalite and cancrinite in synthetic spent Bayer liquor
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:The equilibrium SiO2 solubility of Sodalite and cancrinite crystals in sodium aluminate solutions containing low concentrations of aluminium (synthetic spent Bayer liquor) has been determined over a range of temperatures (90–220°C) and as a function of solution NaOH and Al(OH)3 concentration for cancrinite. The same SiO2 solubilities, within experimental error, were measured when equilibrium was approached from both above and below SiO2 solubility for spent Bayer liquors in contact with either Sodalite or cancrinite crystals. The solubility of Sodalite and cancrinite (expressed in terms of SiO2 concentration) increased linearly with increasing temperature. The equilibrium SiO2 solubility of Sodalite was higher than that of cancrinite at all temperatures. The solubility of cancrinite increased with increasing concentration of NaOH (3.87–5.42 M) and Al(OH)3 (1.39–2.23 M) in solution. The SiO2 solubilities of four types of dimorphic Sodalite/cancrinite mixed phase seed crystals synthesised from Bayer plant spent liquor and synthetic Na2CO3, Na2SO4 or NaNO3 rich NaOH solutions containing dissolved kaolinite were investigated. The solubility of the four types of mixed phase seed crystals was found to be substantially the same as the solubility for pure cancrinite
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A methodology for quantifying Sodalite and cancrinite phase mixtures and the kinetics of the Sodalite to cancrinite phase transformation
Microporous and Mesoporous Materials, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:A simple methodology for determining the cancrinite proportion of a Sodalite and cancrinite phase mixture was developed using powder X-ray diffraction. Using this methodology to quantify phase mixtures, the kinetics of the Sodalite to cancrinite phase transformation were determined. The transformation reaction leading to cancrinite formation was found to be first order with respect to the relative concentration of Sodalite. Over the temperature range 160–240°C, an activation energy for this process was estimated to be 133 kJ mol−1. The techniques of 29Si MAS NMR and FTIR were both found to be unsuitable for quantifying dimorphic phase mixtures due to the ambiguity of the results they produced.
B Boddenberg - One of the best experts on this subject based on the ideXlab platform.
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erratum to 23na solid state mas nmr of sodium halides occluded in zeolites
Solid State Nuclear Magnetic Resonance, 1998Co-Authors: A Seidel, B Schimiczek, U Tracht, B BoddenbergAbstract:Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the 23Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the Sodalite cages are shown to have incorporated salt which is concluded to be part of [Na4Hal]3+ clusters as in the case of Sodalite type materials.
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23na solid state mas nmr of sodium halides occluded in zeolites
Solid State Nuclear Magnetic Resonance, 1997Co-Authors: A Seidel, B Schimiczek, U Tracht, B BoddenbergAbstract:Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the 23Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the Sodalite cages are shown to have incorporated salt which is concluded to be part of [Na4Hal]3+ clusters as in the case of Sodalite type materials.
Jonas Addai-mensah - One of the best experts on this subject based on the ideXlab platform.
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The mechanism of the Sodalite-to-cancrinite phase transformation in synthetic spent Bayer liquor
Microporous and Mesoporous Materials, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:Abstract The precipitation of zeolite, Sodalite and cancrinite and subsequent phase transformations were investigated under a variety of conditions in sodium aluminate liquor. At sufficiently high SiO 2 relative supersaturation, amorphous sodium aluminosilicate and zeolite precipitated at temperatures as high as 160°C. They subsequently transformed to Sodalite and finally to cancrinite. Thus the sequence of the transformation of phases is: [Aluminosilicate species]→Amorphous phase→Zeolite (Linde A)→Sodalite→Cancrinite. It was found that Sodalite did not transform to cancrinite in the absence of a liquid medium. The transformation of Sodalite to cancrinite was demonstrated to involve a solution-mediated mechanism with Sodalite dissolution and subsequent cancrinite precipitation. Neither the amorphous phase nor the zeolite phase precipitates at typical spent Bayer liquor SiO 2 supersaturation.
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The solubility of Sodalite and cancrinite in synthetic spent Bayer liquor
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:The equilibrium SiO2 solubility of Sodalite and cancrinite crystals in sodium aluminate solutions containing low concentrations of aluminium (synthetic spent Bayer liquor) has been determined over a range of temperatures (90–220°C) and as a function of solution NaOH and Al(OH)3 concentration for cancrinite. The same SiO2 solubilities, within experimental error, were measured when equilibrium was approached from both above and below SiO2 solubility for spent Bayer liquors in contact with either Sodalite or cancrinite crystals. The solubility of Sodalite and cancrinite (expressed in terms of SiO2 concentration) increased linearly with increasing temperature. The equilibrium SiO2 solubility of Sodalite was higher than that of cancrinite at all temperatures. The solubility of cancrinite increased with increasing concentration of NaOH (3.87–5.42 M) and Al(OH)3 (1.39–2.23 M) in solution. The SiO2 solubilities of four types of dimorphic Sodalite/cancrinite mixed phase seed crystals synthesised from Bayer plant spent liquor and synthetic Na2CO3, Na2SO4 or NaNO3 rich NaOH solutions containing dissolved kaolinite were investigated. The solubility of the four types of mixed phase seed crystals was found to be substantially the same as the solubility for pure cancrinite
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A methodology for quantifying Sodalite and cancrinite phase mixtures and the kinetics of the Sodalite to cancrinite phase transformation
Microporous and Mesoporous Materials, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, Andrea R. GersonAbstract:A simple methodology for determining the cancrinite proportion of a Sodalite and cancrinite phase mixture was developed using powder X-ray diffraction. Using this methodology to quantify phase mixtures, the kinetics of the Sodalite to cancrinite phase transformation were determined. The transformation reaction leading to cancrinite formation was found to be first order with respect to the relative concentration of Sodalite. Over the temperature range 160–240°C, an activation energy for this process was estimated to be 133 kJ mol−1. The techniques of 29Si MAS NMR and FTIR were both found to be unsuitable for quantifying dimorphic phase mixtures due to the ambiguity of the results they produced.
Michael Fechtelkord - One of the best experts on this subject based on the ideXlab platform.
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influence of sodium ion dynamics on the 23na quadrupolar interaction in Sodalite a high temperature 23na mas nmr study
Solid State Nuclear Magnetic Resonance, 2000Co-Authors: Michael FechtelkordAbstract:Abstract High-temperature 23 Na MAS NMR experiments up to 873 K for a number of different Sodalites (Na 8 [AlSiO 4 ] 6 (NO 3 ) 2 , Na 8 [AlSiO 4 ] 6 (NO 2 ) 2 , Na 8 [AlSiO 4 ] 6 I 2 , Na 7.9 [AlSiO 4 ] 6 (SCN) 7.9 · 0.5H 2 O, Na 8 [AlGeO 4 ] 6 (NO 3 ) 2 , and Na 7 [AlSiO 4 ] 6 (H 3 O 2 ) · 4H 2 O) were carried out. The spectra of the first five Sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate Sodalite, the nitrate aluminosilicate, and germanate Sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydroSodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the Sodalite β-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites.
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synthesis and crystal structure of carbonate cancrinite na8 alsio4 6co3 h2o 3 4 grown under low temperature hydrothermal conditions
Microporous and Mesoporous Materials, 1999Co-Authors: Karsten Hackbarth, Michael Fechtelkord, Th M Gesing, Frank Stief, Ch J BuhlAbstract:The synthesis of cancrinite in the system Na2O–SiO2–Al2O3–Na2CO3–H2O was studied under low-temperature hydrothermal conditions in the 353 K
