Formation of Pure Haematite by Hydrolysis of Iron (III) Salt Solutions under Hydrothermal Conditions

Comparing investigations were carried out of the hydrolysis of iron(III) sulfate, nitrate, and chloride under hydrothermal conditions with an aim to find a new way for the synthesis of pure α‐Fe2O3 (haematite). Rich yields of highly pure haematite can be precipitated from iron(III) nitrate solutions. The strong decrease of the impurity level in the hydrothermal formation of haematite permits to precipitate from impure technical solutions α‐Fe2O3 of adequate purity for many purposes. In contrast, the precipitates from iron(III) sulfate or chloride solutions obtained under comparable conditions are rather uncomplete or the phases formed contain a more or less percentage of the respective anion.