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AssigneeMontedison S.p.A.
InventorsAngelo Garberi, Agostino Geddo, Gian Lorenzo Marziano
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A process is disclosed for preparing magnetite having an equiaxial morphology and a narrow particle size dispersion by precipitation from a ferrous sulphate solution, characterized in that: A. during a first step, at a temperature between 15.degree. and 40.degree. C, alkali is added to the ferrous sulphate solution, in a stoichiometric amount adapted to precipitate, in the form of ferrous hydroxide, 2/3 of the Fe.sup.+.sup.+ ion, and then, at the conclusion of said precipitation, air is blown thereinto thus oxidizing ferrous hydroxide to goethite .alpha.FeO(OH); and B. during a second step, alkali is added to the slurry obtained in the first step, the remaining Fe.sup.+.sup.+ is precipitated in the form of ferrous hydroxide, and the slurry is heated to a temperature between 70.degree. and 100.degree. C, thus causing the formation of magnetite which is then separated from the solution.
A process for preparing magnetite having an equiaxial morphology and a narrow particle size dispersion, starting from a ferrous sulphate solution containing magnesium, wherein in a first step about two-thirds of the Fe.sup.+.sup.+ ion is precipitated by means of an alkali in the form of ferrous hydroxide, which is then oxidized by means of air to goethite .alpha.-FeOOH, and in a second step the remaining Fe.sup.+.sup.+ is precipitated by means of an alkali in the form of ferrous hydroxide and the slurry is heated thus causing the formation of magnetite, said process being characterized in that, in order to prevent the co-precipitation of magnesium in the magnetite, at the conclusion of the oxidation reaction, a predetermined amount of ferrous sulphate solution is added to or removed from the slurry, so as to have an excess of Fe.sup.+.sup.+ equal to 0.2-1 g/liter with respect to the stoichiometric amount necessary for the formation of magnetite.
Dependencies are inferred from the claim text.