PURPOSE:To obtain fine alpha-iron oxyhydroxide with high axial ratio and narrow granular size distribution by oxidation of ferrous hydroxide produced by reaction between an aqueous solution of a ferrous salt and an alkali aqueous solution in the presence of an organic phosphonic acid compound. CONSTITUTION:Firstly, a ferrous hydroxide-contg. suspension is produced by reaction at 30-80 deg.C while keeping the pH of the reaction system at 3-6 between (A) an aqueous solution of a ferrous salt (e.g. ferrous salfate) 30-100g/l in iron ion concentration and (B) an aqueous solution of an alkali (e.g. NaOH) 1.0 in the neutralization equivalent ratio to the ferrous salt in the presence of (C) 0.1-1.0wt.%, based on the final alpha-iron oxyhydroxide to be formed, of an organic phosphonic acid compound (e.g. phenylphosphonic acid) and, if needed, (D) 0.1-10atom wt.%, on a Zn basis, of a zinc compound (e.g. ZnSO4). Thence, this suspension is aerated with an oxygen-contg. gas and oxidized, thus obtaining the objective alpha-iron oxyhydroxide.
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