Hydrous ferric oxides

Hydrous ferric oxides, also called hydrous iron oxides and iron(III) oxide-hydroxides, are a class of minerals that form from the weathering of minerals that contain iron (Fe) and hydroxides (OH⁻), and weakly bound water. They are poorly crystalline, highly porous and have large surface areas. They usually occur as very small particles and tend to become more crystalline as they age because they are thermodynamically unstable. They have an affinity for organic and inorganic pollutants, which has led to an interest in using them as sorbents for the treatment of effluents and polluted water. Hydrous iron oxides include ferrihydrite, akaganéite, feroxyhyte, goethite, lepidocrocite and limonite.