Die Ermittlung der Löslichkeit von Eisen(III)‐hydroxiden mit ⁵⁹Fe II Der Zustand kleinster Mengen Eisen(III)‐hydroxid in wässeriger Lösung

Abstract

The state of iron(III)‐hydroxide in aqueous solutions of very low concentrations has been investigated using 59 Fe as tracer. From very dilute solutions (10 −5 M , 10 −7 M and 10 −9 M ) brought to a pH between ∼ 5–12 practically all the iron hydroxide can be sedimented by ultracentrifugation. The particle size varies with the pH, being biggest at a pH ∼ 6.5 and showing a rather wide range of distribution at a higher pH. In the acid (pH 3–5) and the alkaline region (pH 12–14) the dissolved amount of Fe III ‐hydroxide agrees satisfactorily with the values calculated using the solubility‐product and the constants of hydrolysis. In the precipitate two kinds of colloidal particles, spindel shaped α‐FeOOH and irregular aggregations of amorphous hydroxide particles, can be distinguished under the electron microscope.