ironoxidizing

Ironoxidizing, or iron oxidation, describes chemical and biological processes that convert ferrous iron (Fe2+) to ferric iron (Fe3+). This redox transformation is a central step in the biogeochemical iron cycle and results in the formation of iron oxyhydroxide minerals such as ferrihydrite, goethite, and hematite.

Abiotic iron oxidation occurs when dissolved Fe2+ encounters an oxidant such as molecular oxygen. The rate depends on pH, temperature, and the presence of complexing ligands; at neutral to alkaline pH, Fe3+ rapidly hydrolyzes to Fe(OH)3 and precipitates as ferric oxides.

Biological iron oxidation is performed by specialized microorganisms that gain energy from the transfer of electrons from Fe2+ to an electron acceptor, typically O2 or nitrate. Well-studied iron-oxidizing prokaryotes include Acidithiobacillus ferrooxidans, Leptospirillum spp., and Gallionella ferruginea; marine forms include Mariprofundus ferrooxidans. These organisms often inhabit acidic waters, iron-rich streams, or hydrothermal vent systems, and may form microaerophilic iron-oxide biomineral coatings as a byproduct of metabolism.

Ecological and geochemical significance: iron oxidation affects water chemistry, redox conditions, and mineral precipitation, influencing metal mobility through adsorption and coprecipitation. In natural and engineered settings, it can contribute to corrosion and sedimentation, but it is also harnessed in processes such as bioleaching and bioremediation. The interaction of abiotic and biotic pathways shapes the distribution and characteristics of iron-oxide minerals in diverse environments.