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Andrea R. Gerson - One of the best experts on this subject based on the ideXlab platform.
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Desilication of low alumina to caustic liquor seeded with sodalite or Cancrinite
Hydrometallurgy, 2017Co-Authors: Lina Shi, Shuai Ruan, Andrea R. GersonAbstract:Abstract The aim of this study was to improve understanding of scale formation mechanisms and to provide theoretical support for development of scale inhibition strategies. Sodium aluminosilicate scaling on plant surfaces is a critical problem in Bayer refineries, particularly within digesters and heat exchangers. Although numerous studies have been carried out to understand the mechanisms of scale formation and to develop scale inhibition strategies in double-stream circuit Bayer plants, there is still insufficient relevant research on single-stream Bayer plants. We have studied the desilication behavior of a liquor of similar composition to spent cleaning caustic liquor, for which the aluminate concentration and A/C are both less than heat exchanger liquor. These concentration conditions were chosen in order to investigate the early stage of scale formation in single-stream Bayer plants by increasing the component of aluminosilicate bulk precipitate upon seeding and decreasing the relative degree of scaling. Solution desilication experiments were performed using spent cleaning caustic liquor at 140 °C either without seeding or with sodalite (seed loading 1.125 g L −1 ) or Cancrinite seeding (seed loadings 1.125 g L −1 and 2.850 g L −1 ) in the presence of steel substrates. The solution desilication rate showed significant increase in the presence of seeds and was found to be greater in the presence of Cancrinite seeds than sodalite of the same surface area. The desilication kinetics of the synthetic spent cleaning caustic liquor suggests predominant heterogeneous nucleation for unseeded desilication, a mixed secondary-nucleation and growth process for desilication on addition of sodalite seeding, and Cancrinite seeding with both smaller and greater loading. A first layer, possibly amorphous, with high Al and low Si concentrations was observed by SEM and FIB/SEM on the coupon surface after desilication with or without seeds. We note that this layers forms despite the low A/C and high Si supersaturation suggesting that under single-stream heat exchanger conditions this may also be the first layer to form. XRD confirmed that sodalite formed on the coupons in unseeded and sodalite seeded desilication systems while Cancrinite formed on the coupons upon Cancrinite seeded desilication with both smaller and greater seed loading. The coupon from the Cancrinite seeded liquor with high seed loading is least covered by scale amongst the coupons, suggesting that Cancrinite seeding may be a potential strategy for reducing scale formation in single-stream Bayer circuits.
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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 seeded with Cancrinite and Cancrinite/sodalite mixed-phase crystals
Journal of Crystal Growth, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, 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 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
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 seeded with Cancrinite and Cancrinite/sodalite mixed-phase crystals
Journal of Crystal Growth, 1999Co-Authors: Mark C. Barnes, Jonas Addai-mensah, 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 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.
Wolfram Koch - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic properties of se2 2and se 2in Cancrinite
IEEE Journal of Solid-state Circuits, 1996Co-Authors: Gottlieb-georg Lindner, Katrin Hoffmann, Klaus Witke, Dirk Reinen, Christoph Heinemann, Wolfram KochAbstract:Abstract Selenium has been introduced into the Cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 × 1 × 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in Cancrinite—in contrast to post-synthesis loading. UV/VIS and Raman investigations identify Se2−2as the predominating coloring species besides Se−2. Because of the high optical anisotropy of Cancrinite (⊥c, ∥c) strong polarization effects were detected.
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Spectroscopic Properties of Se2−2and Se−2in Cancrinite
Journal of Solid State Chemistry, 1996Co-Authors: Gottlieb-georg Lindner, Katrin Hoffmann, Klaus Witke, Dirk Reinen, Christoph Heinemann, Wolfram KochAbstract:Abstract Selenium has been introduced into the Cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 × 1 × 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in Cancrinite—in contrast to post-synthesis loading. UV/VIS and Raman investigations identify Se2−2as the predominating coloring species besides Se−2. Because of the high optical anisotropy of Cancrinite (⊥c, ∥c) strong polarization effects were detected.
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Spectroscopic properties of Se22− and Se2− in Cancrinite
Journal of Solid State Chemistry, 1996Co-Authors: Gottlieb-georg Lindner, Katrin Hoffmann, Klaus Witke, Dirk Reinen, Christoph Heinemann, Wolfram KochAbstract:Selenium has been introduced into the Cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 x 1 x 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in Cancrinite-in contrast to post-synthesis loading. UVIVIS and Raman investigations identify Se 2 2- as the predominating coloring species besides Se 2 - . Because of the high optical anisotropy of Cancrinite (⊥c, ∥c) strong polarization effects were detected.
Gottlieb-georg Lindner - One of the best experts on this subject based on the ideXlab platform.
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Selenium dimers and linear chains in one-dimensional Cancrinite nanochannels: Structure, dynamics, and optical properties
The Journal of Chemical Physics, 2002Co-Authors: V.v. Poborchii, Gottlieb-georg Lindner, M. SatoAbstract:Cancrinite crystals possessing parallel nanochannels are attractive for incorporation of guest materials and preparation of one-dimensional structures. In this work, we study variety of Cancrinite crystals synthesized with Se inside their channels. Single crystal x-ray diffraction, polarized Raman, optical absorption, and luminescence spectra are investigated. It is shown that Se is stabilized in the form of Se22− and Se2− dimers located in the center of the channel and oriented along the channel. Different absolute and relative concentrations of Se22− and Se2− are obtained for different samples. The Se22− dimers at high concentration show tendency to organize linear chains. At low temperatures, quite strong interdimer bonding for both Se22− and Se2− is observed. Another important low-temperature effect is appearance of additional Raman bands, which are attributed to the vibrations of linear Se22− chains distorted by the incommensurate potential of Cancrinite. Strong near-infrared polarized luminescence i...
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spectroscopic properties of se2 2and se 2in Cancrinite
IEEE Journal of Solid-state Circuits, 1996Co-Authors: Gottlieb-georg Lindner, Katrin Hoffmann, Klaus Witke, Dirk Reinen, Christoph Heinemann, Wolfram KochAbstract:Abstract Selenium has been introduced into the Cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 × 1 × 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in Cancrinite—in contrast to post-synthesis loading. UV/VIS and Raman investigations identify Se2−2as the predominating coloring species besides Se−2. Because of the high optical anisotropy of Cancrinite (⊥c, ∥c) strong polarization effects were detected.
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Spectroscopic Properties of Se2−2and Se−2in Cancrinite
Journal of Solid State Chemistry, 1996Co-Authors: Gottlieb-georg Lindner, Katrin Hoffmann, Klaus Witke, Dirk Reinen, Christoph Heinemann, Wolfram KochAbstract:Abstract Selenium has been introduced into the Cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 × 1 × 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in Cancrinite—in contrast to post-synthesis loading. UV/VIS and Raman investigations identify Se2−2as the predominating coloring species besides Se−2. Because of the high optical anisotropy of Cancrinite (⊥c, ∥c) strong polarization effects were detected.
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Spectroscopic properties of Se22− and Se2− in Cancrinite
Journal of Solid State Chemistry, 1996Co-Authors: Gottlieb-georg Lindner, Katrin Hoffmann, Klaus Witke, Dirk Reinen, Christoph Heinemann, Wolfram KochAbstract:Selenium has been introduced into the Cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 x 1 x 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in Cancrinite-in contrast to post-synthesis loading. UVIVIS and Raman investigations identify Se 2 2- as the predominating coloring species besides Se 2 - . Because of the high optical anisotropy of Cancrinite (⊥c, ∥c) strong polarization effects were detected.
Jonas Addai-mensah - 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 Addai-mensah, 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 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.
