Preparation and mechanism of formation of hematite particles in the Fe-HNO3 system

► 6-Line ferrihydrite was an important intermediate species in the Fe-HNO3 system. ► Fe(II) ions can catalyze the transformation of 6-line ferrihydrite to hematite. ► Hematite was obtained by the dissolution-recrystallization of 6-line ferrihydrite.