An EXAFS and XANES Study of V, Ni, and Fe Speciation in Cokes for Anodes Used in Aluminum Production
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Lower-quality petroleum coke with higher levels of sulfur and metal impurities will have to be used for the manufacturing of anodes for aluminum production in the future. The sulfur and metallic impurities affect the anode properties in the aluminum production process, but the chemical identity of the metal species in the coke is not known. In this study, industrial petroleum cokes with high sulfur levels were analyzed by X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) in order to determine the identity of the V, Ni, and Fe impurities. The XANES spectra were compared with pure-phase standards. EXAFS was used to compare the impurity metal structures with known crystal structures. It was found that V is present mainly as hexagonal V3S4. Ni is present mainly as hexagonal NiS, and Fe is present as hexagonal FeS. This knowledge of the chemical states of the metal elements in coke, which are known to affect anode performance, is the first step in understanding the mechanism of the action of these elements on anode reactivity. https://doi.org/10.1007/s11663-019-01676-z Ó The Minerals, Metals & Materials Society and ASM International 2019
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INTRODUCTION
THE Hall–He´roult process of producing aluminum by electrolysis of aluminum oxide using carbon anodes in a cryolite melt is the only commercial method to produce aluminum.[1] The global growth in the production of aluminum results in higher demands for of raw materials. The consumable carbon anodes are made from calcined petroleum coke (ca. 65 mass pct), recycled anode butts (ca. 20 mass pct), and coal tar pitch (ca. 15 mass pct). The formed anodes are stacked and baked in an anode-baking furnace. To achieve a predictable and effective behavior in the cell, there are strict
GØRIL JAHRSENGENE and ANN MARI SVENSSON are with the Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway. HANNAH C. WELLS and RICHARD G. HAVERKAMP are with the School of Engineering and Advanced Technology, Massey University, Palmerston North 4222, New Zealand. Contact e-mail: [email protected] CAMILLA SOMMERSETH and ARNE PETTER RATVIK are with the SINTEF Industry, 7491 Trondheim, Norway. LORENTZ PETTER LOSSIUS is with the Hydro Aluminum AS, Primary Metal Technology, 6884 A˚rdal, Norway. KATIE H. SIZELAND is with the ANSTO, Lucas Heights, NSW 2234, Australia. PETER KAPPEN is with the Australian Synchrotron, ANSTO, Clayton VIC 3168, Australia. Manuscript submitted May 2, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
requirements on the calcined petroleum coke (CPC) quality. However, because of the increase in demand, combined with changes in the petroleum industry from which coke is a byproduct, the availability of high-quality coke is not keeping up with the demand.[2] The aluminum industry now needs to determine the impact on the smelting process of using lower-quality cokes with higher metal and sulfur contents, which are closer to the quality of fuel grade coke. Hi
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