2022 Volume 101 Issue 3 Pages 36-42
Recently, we have reported that the needle-like crystals appeared under the different heat treatments between Upper Freeport (UF) and Illinoi#6 bituminous coals. In this study, we investigated the change in the behavior of ash components of UF bituminous coal, Wyodak-Anderson (WD) sub-bituminous coal, and Beulah-Zap (BZ) brown coal with treatment temperature and atmosphere by XRD, TG-DTA, and TEM measurements. Anhydrite, quartz, and hematite were observed for WD heat-treated up to 1000 °C under air atmosphere. The peak of anhydrite for WD was stronger than others at all temperatures. This can be attributed to the difference in the SO3 content in the ash. A part of anhydrite in WD and BZ changed to gehlenite by heat treatment up to 1200 °C, while anhydrite was observed for UF heat-treated. It seems that this would be due to the difference in Ca content. Troilite formed by the reduction of pyrite was observed under argon treatment for coals other than WD. The cubic shape crystals observed in the TEM image in WD and BZ heat-treated at 1200 °C under air atmosphere could be gehlenite from the XRD data.
