Green rust

Green rust (SO2−
4) synthesized under anaerobic conditions in the absence of dissolved oxygen.

Green rust is a generic name for various green crystalline chemical compounds containing iron(II) and iron(III) cations, the hydroxide (OH−
) anion, and another anion such as carbonate (CO2−
3), chloride (Cl−
), or sulfate (SO2−
4), in a layered double hydroxide (LDH) structure. The most studied varieties are the following:

  • carbonate green rust – GR (CO2−
    3    ):
    [Fe2+
    4    Fe3+
    2    (OH−
    )12]2+ · [CO2−
    3    ·2H
    2    O    ]2−;
  • chloride green rust – GR (Cl−
    ):
    [Fe2+
    3    Fe3+
    (OH−
    )8]+ · [Cl−
    ·nH
    2    O    ]−;
  • sulfate green rust – GR (SO2−
    4    ):
    [Fe2+
    4    Fe3+
    2    (OH−
    )12]2+ · [SO2−
    4    ·2H
    2    O    ]2−.

Other varieties reported in the literature are bromide Br−
, fluoride F−
, iodide I−
, nitrate NO−
3, and selenate SeO2−4.

Green rust was first recognized as a corrosion crust on iron and steel surfaces. It occurs in nature as the mineral fougerite.

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