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.
Crystallography open database
Calcined petroleum coke
Extended X-ray absorption fine structure
Linear combination fit
X-ray absorption fine structure
X-ray absorption near edge structure
X-ray absorption spectroscopy
Financial supports from the Norwegian Research Council and the partners Hydro Aluminum, Alcoa, Elkem Carbon, and Skamol through the project “Reactivity of Carbon and Refractory Materials used in Metal Production Technology” (CaRMa) are duly acknowledged. This research was undertaken on the XAS beamline at the Australian Synchrotron, a part of the Australian Nuclear Science and Technology Organization (ANSTO).
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