Characteristics of Calcium-Aluminate Slags and Pig Iron Produced from Smelting-Reduction of Low-Grade Bauxites
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CKGROUND
DATA from alumina processing industry show an estimated global average production of bauxite residue (red mud) to be 1 to 1.5 ton per ton of alumina, or about 150 million ton of red mud is produced annually.[1] A large number of efforts have been made to valorize this most-abundant industrial byproduct in the world in building materials,[2] using it as the rare earth element’s source,[3] producing green direct-reduced iron (DRI),[4] consuming inorganic polymers and pozzolanic material,[5] and so on. However, none of these fields has moved to a large-scale commercial production due to economic reasons and particular challenges in processing the red mud. Thus, this caustic material is a prominent environmental issue and is a major concern on most of alumina refineries in the world, and obviously, increasingly lower grade of bauxite (high
FABIAN IMANASA AZOF, LEIV KOLBEINSEN, and JAFAR SAFARIAN are with the Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway. Contact e-mail: [email protected] Manuscript submitted February 12, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
iron and silica content) makes the situation even more challenging. In the Bayer process, the iron present in the ore is the main component involved in the production of red mud, while silica causes loss of caustic soda to the solvent due to the high reactivity of the compound. The compositions of the bauxite are important in determining the amount of lime that should be added in the mixtures and, eventually, the ratios of CaO/Al2O3 (C/A) in the slags. In 1927, Harald Pedersen[6] patented a method to extract alumina from bauxite without yielding any red mud; an overall illustration of the process is shown in Figure 1. This process was run commercially in Høyanger, Norway, during 1928 to 1969 with 17,000 ton of annual production before closing down.[7] During that period, other researchers had adapted the patent for utilizing ferruginous bauxite in Albany,[8] and a pilot-plant of alumina production from non-bauxitic source (clay) in Tennessee.[9] Years later, Miller and Irgens[10] also made preliminary studies on alumina refinery plant with 200,000 tons of annual production, based on the same process. The Pedersen process shows a promising potential for the prevention of red mud production, however, as per to date this process has been abandoned more than four decades. Lack of
literature and scientific evidence, especially in smelting-reduction part, has led the current authors to investigate the process thoroughly.
II.
EXPERIMENTAL PROCEDURE
This section describes the applied experimental activities about the pyrometallurgical part of the Pedersen process for treating selected low-grade bauxites. Sequentially, the procedure consists of materials preparation and characterization, and the details of smelting-reduction treatment.
0.01 deg step size, and 2.5 deg for both primary and secondary soller slits. The slag and pig iron samples were mounted in epoxy, pol
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