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Lead Plumbate

Author: Hans Lohninger

Lead plumbate, also called red lead, minium or Mennige (in German), is a mineral showing colors from light red to brown/yellow tints. As a pure chemical it shows a vivid red. Minium is rare and occurs in lead mineral deposits that have been subjected to severe oxidizing conditions. It also occurs as a result of mine fires. It is most often associated with galena, cerussite, massicot, litharge, native lead, wulfenite and mimetite.

Minium is obtained by heating lead monoxide (PbO) to 450-480C in air:

3 PbO + 1/2 O2 Pb3O4

or by oxidative annealing of lead white:

3 Pb2CO3(OH)2 + O2 2 Pb3O4 + 3 CO2 + 3 H2O

Minium decomposes into lead monoxide and oxygen above 550C.

Pb3O4 can be seen formally as a lead(II)plumbate(IV), Pb2[PbO4], or 2PbOPbO2. In nitric acid the lead(II) oxide reacts forming lead nitrate, while the insoluble lead(IV) oxide is left unchanged:

Pb3O4 + 4 HNO3 2 Pb(NO3)2 + PbO2 + 2 H2O

Minium is virtually insoluble in water. However, it dissolves in hydrochloric acid (which is present in the stomach), and is therefore toxic when ingested. Minium (in a mixture with linseed oil or other organic adhesives) has been used as an anti-corrosion paint for iron. It forms insoluble iron(II) and iron(III) plumbates when brought into contact with iron oxides and with elementary iron. However, its use as a protective undercoat paint is limited due to its toxicity.

Minium was used as a red pigment in ancient and medieval periods for paintings and the production of illuminated manuscripts (the term miniature is connected to the name of the substance).



Last Update: 2011-02-16