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: galena → pyrite → sphalerite → arsenopyrite → chalcopyrite → anhydrite → barite. Intensive 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