Lead Plumbate
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25-1-2019
1710
Lead Plumbate
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. Lead plumbate is obtained by heating lead monoxide (PbO) to 450-480°C in air:
3PbO+1/2O2→Pb3O4
or by oxidative annealing of lead white:
3Pb2CO3(OH)2+O2→2Pb3O4+3CO2+3H2O
Lead plumbate decomposes into lead monoxide and oxygen above 550°C. Pb3O4 can be seen formally as a lead(II)plumbate(IV), Pb2[PbO4], or 2PbO⋅PbO2 . In nitric acid the lead(II) oxide reacts forming lead nitrate, while the insoluble lead(IV) oxide is left unchanged:
Pb3O4+4HNO3→2Pb(NO3)2+PbO2+2H2O
Lead plumbate is virtually insoluble in water. However, it dissolves in hydrochloric acid (which is present in the stomach), and is therefore toxic when ingested. Lead plumbate (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.
Lead plumbate 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).
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