Fast transformation of iron oxyhydroxides by the catalytic action of aqueous Fe(II)

摘要: Iron oxides may undergo structural transformations when entering an anoxic environment. These were investigated using the isotopic exchange between aqueous Fe(II) and iron in experiments with 55Fe-labelled oxides. 55Fe was incorporated congruently into a ferrihydrite, two lepidocrocites (#1 #2), synthesised at 10°C 25°C, respectively, goethite hematite. The then submerged Fe2+ solutions (0–1.0 mM) pH of 6.5. In presence Fe2+, immediate very rapid release observed from goethite, whereas absence no observed. not released hematite, even higher concentration. rate is mainly controlled by characteristics oxides, concentration only has minor influence. Ferrihydrite 5-nm-sized lepidocrocite crystals attained complete equilibration within days. Within this timeframe ferrihydrite transformed completely new more stable phases such as goethite. Lepidocrocite #2 having larger particles, did reach equilibrium experiment; however, continuous slow suggests that will ultimately be attained. Our results imply recrystallization solid Fe(III) induced catalytic action Fe(II). Accordingly, should properly considered dynamic change composition exposed to variable redox conditions. necessitate reevaluation current models for trace metals under reducing conditions, sequestration heavy significance isotope signatures.