Sulfur is a common impurity in coal, with concentrations varying between 0.19% and 10%. It mainly exists as pyritic sulfur and organic sulfur in coal. Sulfate sulfur, found in forms like gypsum, is less than 0.1% and not a major concern during coal cleaning. Elemental sulfur is also present in small amounts, generally less than 0.2%. Thiols are more abundant in lignites and high volatile bituminous coals compared to low volatile coals. Higher ranked coals contain more thiophenic sulfur than lower ranked ones.