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Fly Ash
Published in Ashok K. Rathoure, Zero Waste, 2019
Bhavana Sethi, Saurabh Ahalawat
Despite of the high demand for alumina, bauxite is currently the only commercially viable source of alumina. Researchers have been working to find an alternative, as the Bayer process yields staggering amounts of red mud—another toxic industrial waste that poses a number of problems(Shemi et al., 2015). Fly ash is considered as a potential source of aluminium and other strategic metals. Most fly ash contains between 25% and 30% aluminium oxide (Al2O3). Different extraction processes of alumina from fly ash are studied by researchers; mainly being limestone sintering process (Zhang and Zhou, 2007; Matjie et al., 2005), soda-lime sintering process (Tang and Chen, 2008; Liu et al., 2006) and acid leaching process (Nayak and Panda, 2010; Thamilselvi and Balamurugan, 2018). However, challenges to commercial viability of these processes still exist, and research is still ongoing in this direction.
Leaching with Alkalies
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2019
The Bayer process steps are (1) digestion of dried bauxite ore with NaOH solution under enhanced pressure and temperature conditions to dissolve aluminum as sodium aluminate, (2) separation of the aluminum-laden solution from the residue (it is carried out by running the liquor through filter presses for removing suspended matter), and (3) precipitation of aluminum hydroxide, which is carried out by introducing the clear liquid, obtained after filtration from the previous step, into precipitation tanks made of sheet-iron cylinders provided with agitators. A small amount of freshly prepared Al(OH)3 is added to the tank to act as seeds, and the whole is then agitated. Precipitation of Al(OH)3 takes place over a period of time that may run up to 60 h. About 70% of the aluminum hydroxide precipitates in 36 h and the remainder on further standing. The precipitated Al(OH)3 settles to the bottom of the tank, where it is drawn off, washed, and filtered before calcination to alumina. The NaOH liquor from the tank is evaporated and concentrated for reuse in the treatment of raw bauxite. The flowsheet of the Bayer process depicting these essential steps is shown in Figure 1.
Properties of Engineering Materials
Published in Keith L. Richards, Design Engineer's Sourcebook, 2017
Pure aluminum is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic, and nonsparking. It is easily formed, machined, and cast. Pure aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminum is an abundant element in the earth’s crust, but it is not found free in nature. The Bayer process is used to refine aluminum from bauxite, an aluminum ore. Because of aluminum’s mechanical and physical properties, it is an extremely convenient and widely used metal.
Reclamation of Red Mud for the TiO2 Production by Ilmenite Smelting at Lower Temperature
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Hyun Sik Park, Kyung Sob Choi, Young Jae Kim
Meanwhile, red mud, which is well known as bauxite residue, is discharged waste from the Bayer process. Global production of red mud reached an estimated 2.7 billion tonnes in 2007, and it increases 120 million tonnes annually (Power, Gräfe and Klauber 2011). Nearly 4 billion tons of red mud are stacked in the world according to the previous study (Wang et al. 2019). Fine particle sizes (≤50 μm) and high alkalinity limit the utilization of red mud for construction materials (Klauber, Gräfe and Power 2011). However, utilization of red mud through versatile methods was studied and reviewed due to the values contained in red muds (Archambo and Kawatra 2021; Paramguru, Rath and Misra 2004). Previous researchers to investigated the extraction of Sc (Ding et al. 2022; Wei et al. 2022), Ce (Meshram and Abhilash 2020) from the red mud. Synthesis of inorganic polymeric materials was also studied (Dimas, Giannopoulou and Panias 2009). Rare earths recovery in from red mud was also investigated by forming iron nugget (Akcil et al. 2018; Archambo and Kawatra 2022). Metallurgical consumption as a feeding material for ironmaking has been attempted (Anameric and Kawatra 2008; Wei et al. 2021) (M. S. Archambo and Kawatra 2021); however, concerns regarding alkaline constituents, heavy metals, and concentrated radioactive elements have prohibited their active use. In addition, a significant amount of Al2O3 contained in the red mud is known to deteriorate the physicochemical properties of slag at high temperatures (Kim et al. 2013).
Bauxite residue sinter leach process – phases formation, reaction pathways and kinetics
Published in Mineral Processing and Extractive Metallurgy, 2021
Harrison Hodge, Matthew R. Rowles, Peter C. Hayes, William Hawker, James Vaughan
The Bayer process is the most commonly used industrial method for transforming bauxite ore into alumina. One of the major issues facing the alumina industry is the rising level of reactive silica concentrations present in the bauxite. Reactive silica refers to any silica-containing mineral that dissolves under Bayer process conditions. After initially dissolving, the silica subsequently precipitates from aqueous solution as a sodium aluminium silicate, which is referred to as the desilication product (DSP). DSP incorporates silicate, as well as a number of other impurities, from the liquor but its formation also removes sodium hydroxide and alumina, the principle reagent and product of the Bayer process respectively. DSP then reports, with other undissolved minerals, to the solid waste stream, bauxite residue (BR). The recovery of this lost sodium and aluminium from the bauxite residue would provide significant benefit to many Bayer alumina operations and potentially allow for the processing of higher silica bauxite ores.
Utilization of Bauxite Residue: Recovering Iron Values Using the Iron Nugget Process
Published in Mineral Processing and Extractive Metallurgy Review, 2021
The Bayer Process treats bauxite ore to produces alumina. Red mud is a byproduct created as a result of the process. Following the digestion of bauxite in sodium hydroxide (NaOH), the green liquor containing dissolved aluminates is removed so that it can be further processed. The remaining solids are dosed with flocculants in a series of thickener tanks in order to increase the solid content before discharge to the red mud containment reservoirs. Red mud disposal is not a negligible part of the process for alumina production, removal of red mud accounts for 30–50% of operations in any given alumina facility (Paramguru, Rath and Misra 2004). Studies have been done to optimize the Bayer process using a technique called mechanical activation which increases the reactivity of aluminum oxide particles through milling by increasing surface area. Increasing reactivity could reduce a large amount of caustic needed in the Bayer process, but this work has only been done at the laboratory scale (Alex et al. 2016).