REDUCTION OF HEMATITE TO MAGNETITE UNDER CONTROLLED HYDROTHERMAL CONDITIONS WITH HYDROGEN GAS

Haematite (alpha-Fe2O3) was reduced to magnetite (Fe3O4) under hydrothermal conditions, by the use of an autoclave into which hydrogen gas was able to be admitted. The stable reduced conditions for magnetite precipitation were produced even at 100-degrees-C. In acid and neutral mineralizers, the rate of haematite reduction was small below 300-degrees-C and increased with an increase in reaction temperature above 300-degrees-C. Magnetite crystals obtained in these solutions were large and faceted octahedrons in shape. Alkaline mineralizers except NaOH solution accelerated the reduction at low temperatures below 300-degrees-C and gave small magnetite crystals. The reduction of haematite to magnetite was completed even at 150-degrees-C in concentrated CsOH solution (1.0 mol l-1).