What Is Iron Hydroxide?
Iron hydroxide refers to hydroxides of iron and is classified into iron(II) hydroxide (Fe(OH)2) and iron(III) hydroxide (Fe(OH)3) based on the oxidation state of iron.
Iron Hydroxide (II)
Iron(II) hydroxide, or ferrous hydroxide, is an inorganic compound with the formula Fe(OH)2. It forms as a white solid but readily oxidizes in the presence of oxygen to form a light green compound commonly known as “green rust,” seen on water taps. Upon heating in the air, it transforms into iron(III) oxide.
Iron Hydroxide (III)
Iron(III) hydroxide, or ferric hydroxide, has the formula Fe(OH)3. However, the compound often found is iron hydroxide(III) oxide hydrate, with a composition of FeO(OH)-H2O. This compound forms as a reddish-brown solid and occurs naturally in various ores like goethite, akaganeite, lepidocrocite, and limonite, or as the familiar red rust. It can form colloidal particles in alkaline solutions.
Iron Hydroxide Manufacturing Process
Iron(II) hydroxide can be prepared by reacting an aqueous solution of iron(II) sulfate with sodium hydroxide, resulting in the precipitation of Fe(OH)2.
Iron(III) hydroxide is typically precipitated by adjusting the pH of an aqueous iron(III) salt solution. For example, it can be obtained by reacting ferric chloride or ferric nitrate with sodium hydroxide. Iron(III) hydroxide can also be prepared by oxidizing iron(II) hydroxide with hydrogen peroxide in an acidic environment.
Uses of Iron Hydroxide
Iron Hydroxide (II)
Iron(II) hydroxide is used in the manufacturing of enamels, catalysts, heat-absorbing glass, water quality improvement agents, and in the negative electrodes of nickel-iron batteries.
Iron Hydroxide (III)
Iron(III) hydroxide serves as a pigment in paints, inks, paper, rubber, and plastics, and as an abrasive for glass, precious metals, and diamonds. Its high-purity form is used in semiconductors, magnetic tapes, and magnets. It is FDA-approved for cosmetics, including some tattoo inks, and is utilized for lead removal, as a phosphate binder, and in water quality improvement.