Über die Hydrolyse von Eisen(III)-Salz-Lösungen. II Die Alterung der Hydrolyseprodukte

On the Hydrolysis of Iron (III) Salt Solutions. II. Ageing of Hydrolysis Products The long time ageing up to 15 years of the products obtained by alkalifying iron(III) chloride solutions to different neutralisation degrees has been studied. The concentration of the Fe³⁺ and the Cl- ions, the strength of the alkali, and the rate of its addition influence the results. Slow alkalifying produced up to 90% neutralisation β-FeOOH. The transformation of the amorphous iron(III) oxidehydroxide to β-FeOOH was promoted by a high concentration of the Cl- ions. When a large amount of amorphous iron(III) oxidehydroxide was formed, intimately intergrown crystals of α- and β-FeOOH resulted. On further ageing β-FeOOH transformed into α-FeOOH. At a degree of neutralisation of 95 and 100% transformation of the amorphous iron(III) oxidehydroxide into α-Fe₂O₃ occurred. The 100% neutralized precipitate, however, remained partly amorphous. Authors discuss the factors that determine very slow reactions leading to these results.