A XANES Study of Sulfur Speciation and Reactivity in Cokes for Anodes Used in Aluminum Production

Abstract

Availability of anode raw materials in the growing aluminum industry results in a wider range of petroleum cokes being used to produce carbon anodes. The boundary between anode grade cokes and what previously was considered non-anode grades are no longer as distinct as before, leading to introduction of cokes with higher sulfur and higher trace metal impurity content in anode manufacturing. In this work, the chemical nature of sulfur in five industrial cokes, ranging from 1.42 to 5.54 wt pct S, was investigated with K-edge XANES, while the reactivity of the cokes towards CO2 was measured by a standard mass loss test. XANES identified most of the sulfur as organic sulfur compounds. In addition, a significant amount is identified (16 to 53 pct) as S-S bound sulfur. A strong inverse correlation is observed between CO2-reactivity and S-S bound sulfur in the cokes, indicating that the reduction in reactivity is more dependent on the amount of this type of sulfur compound rather than the total amount of sulfur or the amount of organic sulfur.

An EXAFS and XANES Study of V, Ni, and Fe Speciation in Cokes for Anodes Used in Aluminum Production

“…In CPC in some cases sulfur has been observed as a thiophene-containing polycyclic aromatic hydrocarbons [12][13][14][15]. In the high sulfur cokes studied here for metal impurities, a previous study has shown that the sulfur is present as elemental sulfur or at least contains S-S bonds [16]. These cokes did not follow the normally accepted trend of decreasing CO2 reactivity with increasing sulfur content.…”

“…1% of the total sulfur in the coke. The dominant form of the S in coke is not sulfide, but appears to be organic or S-S bound sulfur [16].…”

“…From the cokes available a selection of six coke samples were chosen for this work based on sulfur and vanadium content to give a range of V and S content. Cokes A-E are the same as those used in a recent XANES study by the same authors of the sulfur speciation in these cokes [16], where sulfur speciation using XANES were accomplished, and evaluated to CO2 reactivity and structure.…”

First‐principles study of the adsorption mechanism of SO2 and CF4 on the α‐Al2O3 (0001) surface

“…Meanwhile, the sulfur content of the carbon anode is increasing day by day, so S emission is very difficult to control. [ 10–13 ] These factors cause the workshop to release more PFC gas and SO 2 gas. [ 14 ] According to international standards, as the main component of PFC gas, CF 4 has a greenhouse effect 6500 times that of CO 2 , while SO 2 damages the environment and endangers human health.…”

Reactivity of Coke in Relation to Sulfur Level and Microstructure

“…This will not necessary represent industrially produced anodes, as doped anodes may not have the same chemical state properly incorporated within the coke structure, which may give misleading results compared to the industrial cokes. Sulfur speciation of selected cokes was previously performed by the authors by the X-ray absorption near-edge structure (XANES) technique [7]. Five cokes were investigated, which varied significantly with respect to content of sulfur (1.4 to 5.5 wt%) and content of metal impurities.…”