Manufacture of .gamma.-iron(III) oxide

In a process for the manufacture of acicular .gamma.-iron(III) oxide by reacting an aqueous solution of iron(II) salt with aqueous solutions of alkali metal hydroxides, oxidizing the resulting suspensions of iron(II) hydroxide with oxygen or oxygen-containing gases to goethite, reducing the resulting goethite to magnetite and oxidizing the magnetite to acicular .gamma.-iron(III) oxide, the improvement comprising:

• carrying out the oxidation of the iron(II) hydroxide suspension in three stages, wherein in the first stage not more than 8% by weight of the iron(II) present is oxidized over a period of from 0.5 to 4 hours in the first stage, in the second stage from 25 to 55% of the iron(II) originally present in the suspension is oxidized over an additional period of 1.5 to 6 hours by introducing 0.1 to 0.4 mole per hour of oxygen/gram atom of the iron contained in the suspension at the beginning of said second stage and gradually increasing the introduction of oxygen during said second stage up to 0.2 to 0.9 mole per hour of O.sub.2 /g atom of iron at the end thereof and in the third stage oxidizing the remaining iron(II) by introducing 1 to 2 moles of oxygen per hour per gram atom of iron contained in the suspension.