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Greg Power - One of the best experts on this subject based on the ideXlab platform.
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organic compounds in the Processing of lateritic bauxites to alumina part 2 effects of organics in the Bayer Process
Hydrometallurgy, 2012Co-Authors: Greg Power, Joanne S.c. Loh, Chris VernonAbstract:Abstract This review is the second of a series examining the history and current state of knowledge of the science related to organic compounds in the Bayer Process for the extraction of alumina from lateritic bauxites. The series of reviews provides a compilation of the information available from the public literature, and critical analysis of the research that has been carried out in this area in the past 50 years. It points the way to future opportunities for research to assist in mitigating the high costs that organics impose on the industry globally ($500 Mpa in Australia alone). Part 2 provides unique insights into the effects on the Bayer Process of organic compounds in the liquor.
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Understanding Hydrogen in Bayer Process Emissions. 2. Hydrogen Production during the Degradation of Unsaturated Carboxylic Acids in Sodium Hydroxide Solutions
Industrial & Engineering Chemistry Research, 2011Co-Authors: Allan Costine, Joanne S.c. Loh, Greg PowerAbstract:This is the second in a series of studies of the production of hydrogen from the degradation of organic compounds in sodium hydroxide solutions. Unsaturated carboxylates, which are intermediate products in the wet oxidation of the types of monoaromatic compounds typically present in Bayer Process liquors, have been found to produce significant amounts of hydrogen during alkaline degradation. The alkaline degradation of nine unsaturated carboxylates was investigated under anaerobic conditions in an autoclave, and the effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of acrylate, 2-butenoate, maleate, and 2-hexenoate was studied in detail for reaction times up to 120 min. All of the compounds investigated decompose to produce about 1 mol of hydrogen gas per mole of organic compound consumed, as well as a range of low molecular weight (LMW) carboxylates. The stoichiometries of the formation of hydrogen and LMW carboxylates from the unsaturated carboxylates observed here are...
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A review of the determination of organic compounds in Bayer Process liquors.
Analytica chimica acta, 2011Co-Authors: Greg Power, Joanne S.c. Loh, Johannes E. Wajon, Francesco Busetti, Cynthia JollAbstract:Abstract Bayer Process liquors present a difficult and complex matrix to the analytical chemist, and the history of the application of modern analytical techniques to this problem is a case study in innovation. All Bayer Process liquors contain organic compounds, in amounts varying from traces to several grams per litre. The total organic carbon content of Bayer liquors may be less than 5 g/L up to as much as 40 g/L. The presence of these organic impurities is of concern to Bayer technologists because they can have significant impacts on the economics of the Process and the quality of the product. This review examines the history and current state-of-the-art of the analysis of organics in Bayer Process liquors, and provides guidance on the applicable techniques matched to a comprehensive list of the compounds most likely to be present.
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organic compounds in the Processing of lateritic bauxites to alumina addendum to part 1 origins and chemistry of organics in the Bayer Process
Hydrometallurgy, 2010Co-Authors: Greg Power, Joanne S.c. Loh, Klaus NiemelaAbstract:This review is the first of a series examining the history and current state of knowledge of the science related to organic compounds in the Bayer Process for the extraction of alumina from lateritic bauxites. Part 1 covers the origins, nature and chemistry of organic compounds in Bayer liquors. It provides a compilation of the information available from the public literature, and critical analysis of the research that has been carried out in this area in the past 50 years. It points the way to future opportunities for research to assist in mitigating the high costs that organics impose on the industry globally ($500 Mpa in Australia alone).
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Fundamentals of Wet Oxidation of Bayer-Process Liquor: Reactivity of Malonates
Industrial & Engineering Chemistry Research, 2010Co-Authors: Jackie Dong, Greg Power, Chris Vernon, Joanne Loh, James Tardio, Suresh K BhargavaAbstract:The application of wet oxidation to the removal of organic impurities from Bayer-Process liquors has the potential to deliver major benefits to the alumina industry. Previous work has identified the malonate anion as especially reactive under WO conditions, a property ascribed to its ability to form a carbanion in alkaline conditions. Understanding of the reaction mechanism involved in this effect is of importance to the development of improved WO technology. The current work confirms carbanion formation as the first step in the reaction. Deuterium exchange experiments and 13C NMR spectroscopy are used to demonstrate the weak acidity of the α-hydrogen atoms which leads to carbanion formation. The acidity of the α-hydrogen atoms in malonate is induced by the electron-withdrawing effect of the two adjacent carboxylate groups. Substituting an electron-donating group such as methyl or ethyl at the α-position reduces this effect, resulting in reduced oxidation rates for the substituted malonates. The role of t...
Shahrokh Shahhosseini - One of the best experts on this subject based on the ideXlab platform.
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Removal of carbonate and oxalate pollutants in the Bayer Process using thermal and chemical techniques
Hydrometallurgy, 2015Co-Authors: Mostafa Mahmoudian, Ahad Ghaemi, Shahrokh ShahhosseiniAbstract:In the Bayer Process, diasporic bauxite is dissolved in a caustic soda solution in the presence of lime at high temperature. During this Process, concentration of carbonate and oxalate gradually increases causing problems in the alumina refining Process. In this work, removal efficiency of the carbonate and oxalate pollutants from sodium aluminate solution has been increased using thermal and chemical techniques. The pollution of sodium aluminate solution has been reduced by heating the bauxite and removing the carbonate and oxalate by applying a chemical method. Bauxite heating leads to the organic compounds and carbonates in magnesite and calcite minerals exit as CO2, preventing addition of these substances into the sodium aluminate solution. In the method of chemical removal of the carbonate and oxalate soluble in sodium aluminate liquor, barium aluminate with structures of Ba2Al2O5, Ba2Al4(OH)16 and BaAl2O4, calcium aluminate (Ca3Al2(OH)12) and sodium phosphate (Na3PO4)-lime were separately used. As a result, these substances were sedimented as carbonate or barium oxalate, calcium and apatite. The results also showed that soda was retrieved as sodium aluminate or sodium hydroxide. Investigating the effect of temperature, time, concentration of caustic soda, Al2O3 and sodium carbonate revealed that using Ba2Al4(OH)16 and the heating methods are the most efficient technique to remove the carbonate and oxalate, respectively.
X. Jin Yang - One of the best experts on this subject based on the ideXlab platform.
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Efficient and Sustainable Production of Alumina by Electrolysis of Sodium Carbonate
Angewandte Chemie (International ed. in English), 2011Co-Authors: Yongmei Chen, Yinjian Niu, Yang Tang, Pingyu Wan, X. Jin YangAbstract:Aluminium is a leading material for the expanding global economy and its precursor alumina has been produced by extraction of bauxite ores using Bayer and sinter Processes for over 100 years. The Bayer Process involves digesting and leaching the ores using a hot alkali solution and precipitating aluminum hydroxide from the supersaturated aluminate leachate (green liquor) using aluminum hydroxide seed particles. The caustic liquor remaining after precipitation (spent green liquor) is concentrated by evaporation and recycled back to the extraction step (Figure 1A). The sinter Process consists of sintering the ores with sodium carbonate and calcium oxide at above 1000 8C, leaching the sinter mass with water (or dilute NaOH solution) and precipitating Al(OH)3 with carbon dioxide, concentrating the spent green liquor by evaporation, and circulating the concentrate to the next sinter step (Figure 1B). The sinter Process is more effective for poor-grade diaspore ores than the Bayer Process, but its high energy consumption makes it uneconomical compared to the Bayer Process and its environmental impact has been a critical issue. The Bayer Process is relatively simple because of the ease of automation and delivers 90% of the world-wide production of alumina. However, the seed precipitation of the Bayer Process is typically very slow (generally it takes 48–70 h) and requires a large quantity of aluminum hydroxide seeds (seed ratios of 1–2) while only up to 50% of sodium aluminate in the green liquor is decomposed into aluminum hydroxide precipitates. Consequently, large tonnages of sodium aluminate remain in the circuit of the Process. The presence of a large amount of aluminate in the Bayer liquor has significant adverse effects on the leaching efficiency of ore digestion. These problems are the major factors for the loss of productivity of the Bayer-based plants. In addition, the Bayer Process becomes uneconomical for Processing diaspore ores of alumina-to-silica (A/ S) mass ratios < 9. Since the 1970s, the world-wide production of minerals and metals from degrading natural resources has increased. The global production of alumina increased at an average rate of 3.3% per year while the Chinese production of alumina grew at an average rate of 25% between 2001 and 2007. The aluminum industry is one of the major high-pollution and energy-intensive industries. With increasing environmental constraints, continuously increasing demand for aluminum and at the same time the depletion of high-grade bauxite ores, the development of efficient and sustainable production Processes for alumina is of great significance. The key to improving the efficiency of the Bayer Process is to increase the efficiency of aluminate decomposition and the precipitation rate of aluminum hydroxide. The strategies include addition of surfactants, glucose or methanol, to the green liquor. However, the improvement is limited because of the inherent equilibrium between Al(OH)4 , Al(OH)3, and OH of the seeded precipitation [Eq. (1)],
Sandra E. Dann - One of the best experts on this subject based on the ideXlab platform.
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Investigation of zeolite scales formed in the Bayer Process
Microporous and Mesoporous Materials, 2000Co-Authors: J.a Armstrong, Sandra E. DannAbstract:Synthetic sodium aluminosilicate Bayer refinery scale has been prepared in 8 and 4.2 M sodium hydroxide solutions at four temperatures in the temperature range 80–240°C. The effect of different anions (CO32−, OH− SO42−, Cl− and C2O42−) and varying anion concentrations (10−2–10−1 M) on the type of aluminosilicate phase formed has also been investigated. These synthetic phases have been compared with industrial scale formed in different parts of low and high temperature Bayer Processing plants. Synthetic and plant scales were both characterised using powder X-ray diffraction, IR spectroscopy and SEM. The plant scale crystallises as two different zeolitic aluminosilicate phases, depending on the temperature in the area of the plant. This behaviour has been shown to closely mirror the formation of synthetic scale in sodium hydroxide solutions containing the carbonate anion. The large concentration of organic ions present in Bayer liquor appear to have little effect on the type of scale formed and are relatively insignificant in promoting scale formation.
Joanne S.c. Loh - One of the best experts on this subject based on the ideXlab platform.
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organic compounds in the Processing of lateritic bauxites to alumina part 2 effects of organics in the Bayer Process
Hydrometallurgy, 2012Co-Authors: Greg Power, Joanne S.c. Loh, Chris VernonAbstract:Abstract This review is the second of a series examining the history and current state of knowledge of the science related to organic compounds in the Bayer Process for the extraction of alumina from lateritic bauxites. The series of reviews provides a compilation of the information available from the public literature, and critical analysis of the research that has been carried out in this area in the past 50 years. It points the way to future opportunities for research to assist in mitigating the high costs that organics impose on the industry globally ($500 Mpa in Australia alone). Part 2 provides unique insights into the effects on the Bayer Process of organic compounds in the liquor.
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Understanding Hydrogen in Bayer Process Emissions. 2. Hydrogen Production during the Degradation of Unsaturated Carboxylic Acids in Sodium Hydroxide Solutions
Industrial & Engineering Chemistry Research, 2011Co-Authors: Allan Costine, Joanne S.c. Loh, Greg PowerAbstract:This is the second in a series of studies of the production of hydrogen from the degradation of organic compounds in sodium hydroxide solutions. Unsaturated carboxylates, which are intermediate products in the wet oxidation of the types of monoaromatic compounds typically present in Bayer Process liquors, have been found to produce significant amounts of hydrogen during alkaline degradation. The alkaline degradation of nine unsaturated carboxylates was investigated under anaerobic conditions in an autoclave, and the effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of acrylate, 2-butenoate, maleate, and 2-hexenoate was studied in detail for reaction times up to 120 min. All of the compounds investigated decompose to produce about 1 mol of hydrogen gas per mole of organic compound consumed, as well as a range of low molecular weight (LMW) carboxylates. The stoichiometries of the formation of hydrogen and LMW carboxylates from the unsaturated carboxylates observed here are...
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A review of the determination of organic compounds in Bayer Process liquors.
Analytica chimica acta, 2011Co-Authors: Greg Power, Joanne S.c. Loh, Johannes E. Wajon, Francesco Busetti, Cynthia JollAbstract:Abstract Bayer Process liquors present a difficult and complex matrix to the analytical chemist, and the history of the application of modern analytical techniques to this problem is a case study in innovation. All Bayer Process liquors contain organic compounds, in amounts varying from traces to several grams per litre. The total organic carbon content of Bayer liquors may be less than 5 g/L up to as much as 40 g/L. The presence of these organic impurities is of concern to Bayer technologists because they can have significant impacts on the economics of the Process and the quality of the product. This review examines the history and current state-of-the-art of the analysis of organics in Bayer Process liquors, and provides guidance on the applicable techniques matched to a comprehensive list of the compounds most likely to be present.
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organic compounds in the Processing of lateritic bauxites to alumina addendum to part 1 origins and chemistry of organics in the Bayer Process
Hydrometallurgy, 2010Co-Authors: Greg Power, Joanne S.c. Loh, Klaus NiemelaAbstract:This review is the first of a series examining the history and current state of knowledge of the science related to organic compounds in the Bayer Process for the extraction of alumina from lateritic bauxites. Part 1 covers the origins, nature and chemistry of organic compounds in Bayer liquors. It provides a compilation of the information available from the public literature, and critical analysis of the research that has been carried out in this area in the past 50 years. It points the way to future opportunities for research to assist in mitigating the high costs that organics impose on the industry globally ($500 Mpa in Australia alone).
