Occurrence and Behavior of Sulfur‐Bearing Minerals in Metallurgical Coke

Abstract

The behavior of sulfur-bearing minerals is characterized from coking coals to the feed coke and the blast furnace (BF) coke using field emission scanning electron microscope and thermodynamic calculations. In coals, they are represented by sulfides (pyrite, sphalerite, galena, chalcopyrite, and arsenopyrite) and sulfates (anhydrite and barite). During coking process, the minerals undergo phase transformations, but sulfur will be retained in the coke in mineral form for most of the minerals until the end of the coking process. Depending on the initial mineral in the coal, sulfur-bearing minerals will be transformed at the end of coking process into the following phases: pyrrhotite, wurtzite, Cu-Fe-S melt, CaS, and BaS. The amount of sulfur that will be kept in the coke in mineral form increases in the following order:gas flow under BF conditions facilitates liberation of sulfur from mineral phases in the Fe-S and Zn-S system. CaS and BaS are the most stable sulfur-bearing phases formed after sulfur-bearings minerals. The coals with elevated amounts of anhydrite and barite, or with high concentrations of Ca and Ba combined with S should be avoided for coking purposes. Complete elimination of mineral-related sulfur from coke under BF conditions occurs above 2000 C. Tools and MethodsThe samples of coals, feed coke, and BF coke we obtained from SSAB Europe Ltd., Raahe, Finland. The coals are represented by Jas Mos coal from Poland, Willow Creek coal from Canada, Riverside coal from Australia, and Severnaya-Vorkuta coal from Russia. The samples of BF coke were obtained by tuyere drilling. The length of the drill core (depth of drilling to the BF) was about 2 m. The supplied coals have, in general, relatively low content of sulfur, which usually do not exceed 0.5-0.6% (O. Kerkkonen, personal communication).Figure 4. Transformations of sulfur-bearing mineral phases (left column), and concentration of sulfur (right column) in mineral-carbon-gas (BF) system at 1000-2000 C. a) pyrhhotite, b) sphalerite-wurtzite, c) molten sulphide (Cu-Fe-S melt), d) CaS, e) BaS. www.advancedsciencenews.com www.steel-research.de steel research int. 2018, 89, 1700470

Occurrence and Behavior of Phosphorus‐Bearing Minerals in Metallurgical Coke

“…EDS analyses (Table , analyses 1 and 2) give a low total due to properties of the surface, so the phases cannot be identified with certainty. However, atomic proportions of phosphorus and iron indicate that the first one is probably Fe 3 P, while the second is likely to be Fe 2 P. The EDS spectrum of the phases also includes trace amounts of sulfur, which is likely related to the presence of sulfur‐bearing minerals, which are common in the original coking coals . The second variety of Fe–P phases is more common, and it often forms spherical inclusions in the matrix of coke (Figure c, d).…”

“…The conditions for the calculations were the same as we used for the investigation of the behavior of alkali-and sulfurbearing minerals in metallurgical coke. [17,18] The compositions of the coke oven and BF gas were taken from Liao et al [19] and Quinn et al, [20] respectively. Stoichiometric compositions of phosphorus-bearing mineral phases were used as initial values for the calculations as they were presented in the FactSage database.…”

“…In addition to that, thermodynamic calculations were done with FactSage software (version 7.2) in order to trace the behavior of mineral‐related phosphorus under elevated temperatures. The conditions for the calculations were the same as we used for the investigation of the behavior of alkali‐ and sulfur‐bearing minerals in metallurgical coke . The compositions of the coke oven and BF gas were taken from Liao et al and Quinn et al, respectively.…”

“…However, atomic proportions of phosphorus and iron indicate that the first one is probably Fe 3 P, while the second is likely to be Fe 2 P. The EDS spectrum of the phases also includes trace amounts of sulfur, which is likely related to the presence of sulfur-bearing minerals, which are common in the original coking coals. [18] The second variety of Fe-P phases is more common, and it often forms spherical inclusions in the matrix of coke (Figure 4c, d). These inclusions are 5-30 μm with a smooth surface and outlines.…”

Microstructure analysis and mineral phase transformation of coke in blast furnace

“…According to Table 2, the sulphur content first decreased and then increased. Gornostayev et al established that intensive gas flow promoted the escape of sulphur from sulphur-bearing minerals in metallurgical coke [27], coupled with high reaction temperature, which led to the lowest sulphur content in S3 coke. Based on the XRD spectra of coke ash shown in Figure 3, there were still inorganic sulphur minerals (CaS, CaSO 4 ) in the tuyere coke ash.…”