Formation Process of Magnetite by Reaction between Iron(III) Hydroxide Oxide and Iron(II) Sulfate

Abstract

Magnetite was synthesized by heating of 8-Fe0OH suspension containing urea and iron(II)sulfate at 98°C. Brownish-yellow β-Fe0OH gradually changed to black Fe₃O₄ by heating. In this initial process, β-FeOOH decreased, and at the same time Fe₃O₄ and α-Fe0OH increased. But during further heating α-FeOOH decreased as well as β-FeOOH and finally disappeared. The final product was only Fe3O4. The dissolution of β-FeOOH was promoted in the presence of iron(II) ion. Some part of the produced iron(III) ions dissolved were converted to Fe₃O₄ by the reaction with iron(II)ion, and the others formed α-FeOOH by hydrolysis in the presence of sulfate ion. This α-FeOOH was dissolved in the presence of iron(II) ion, and then Fe₃O₄ was formed. The formation of Fe₃O₄ from the reaction between β-FeOOH and iron(II) sulfate required the longer reaction time as compared to the reaction with iron(II) chloride because of the side reaction through an intermediate α-FeOOH.