FeOOH05H2O

FeOOH05H2O, commonly written as FeOOH·5H2O, refers to a hydrated form of iron oxyhydroxide in which five molecules of water are associated with the solid. In standard mineralogy and solid-state chemistry, this compound is described as a pentahydrate of iron oxyhydroxide, though its exact stoichiometry and structure can vary with synthesis conditions. The term is sometimes encountered in literature as a poorly crystalline or amorphous ferric oxyhydroxide phase.

Formation and occurrence

FeOOH·5H2O is typically produced by the oxidation and hydrolysis of ferrous iron in aqueous environments, such as soils, sediments, aquatic systems, and industrial precipitation settings. In natural settings it often appears as a transient or precursor phase that can transform over time into more crystalline iron oxides and oxyhydroxides, such as goethite (FeO(OH)) or ferrihydrite.

Structure and properties

As a hydrated and often poorly crystalline material, FeOOH·5H2O has a high specific surface area and numerous surface hydroxyl groups, which confer high reactivity with dissolved ions. Its water of hydration can be lost upon drying or heating, leading to formation of less hydrated iron oxyhydroxide phases. The material’s stability, dissolution behavior, and phase transformations are strongly influenced by pH, temperature, and the presence of ligands or competing ions.

Applications and relevance

In geochemistry and environmental science, FeOOH·5H2O is used as a model or precursor material for studying mineral transformations, adsorption of contaminants, and nutrient cycling. It also serves as a reference state for understanding the formation pathways and aging processes of iron oxides in natural and engineered systems.

Safety

Iron oxyhydroxide hydrates are generally considered of low acute toxicity, but handling fine powders can pose inhalation and irritation risks. Standard laboratory safety practices apply.

See also

Ferrihydrite, Goethite, Lepidocrocite, Hematite, Iron oxide hydrates.