Innickel hydrometallurgical operations, the removal of iron from process liquorswas critical, with the method of choice commonly being crystallization(precipitation). In this paper special attention was given to the magnetiteprecipitate. Potential/pH diagram for Fe–H2O system was derived at 100 °C,and indicated that the iron ion may precipitate as magnetite at the loweroxidation potential. And the crystallization experiments proved that the ironion partly precipitate as magnetite by slow oxidation at pH 2.0–2.2 andtemperature 90–100 °C. The precipitates could be efficiently separatedfrom the solutions by magnetic flocculation and separation. Further, analyseswith Environmental scanning electron microscopy (ESEM) and X-ray Diffraction(XRD) provided a fundamental understanding of the magnetite precipitationprocess.