Die Ermittlung der Löslichkeit von Eisen(III)‐hydroxiden mit ⁵⁹Fe I Fällungs‐ und Auflösungsversuche

The total solubility of amorphous Fe III ‐hydroxide and α‐FeOOH in 3 M NaClO 4 has been determined using 59 Fe as tracer. The solubility determination of the amorphous hydroxide extended over the pH‐range 3–14. At pH < 3.5 the results agree satisfactorily with the value calculated using the solubility‐product and the constants of hydrolysis. At pH 5–12 an average solubility of ∼ 10 −7 M has been measured but the results show considerable fluctuations. Therefore a colloidal solubility has been assumed. In the alkaline range pH > 12 it could be shown that the equilibrium Fe(OH) 3 + OH − ⇆Fe(OH) is established, the following pK S4 being found to be after 2 h ageing 4.50 ± 0.15 and after 96 h ageing 5.00 ± 0.15.