Cementation

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Formation of cement copper (light red) over iron plates (gray) in the Kilian tunnel ( Marsberg )

Cementation is a metallurgy term that is used for various processes:

  • the electrochemical deposition of metals from solutions,
  • the surface treatment of metals by introducing foreign metals
  • reducing the carbon content of metals,
  • the increase in the fine gold content.

Electrochemical deposition

Cement copper occurs as an intermediate product in the extraction of copper from low-copper ores or waste. By the insertion of iron in a copper sulfate - solution (cement water) elemental copper precipitates:

Cement water occurs several times as pit water in copper mines .

If elemental copper is present in ores or waste, these raw materials are first roasted . By heating in the presence of oxygen, copper (II) compounds are created.

The starting materials with copper (II) ions are now leached in dilute sulfuric acid . The copper ions (Cu 2+ ) dissolve in the sulfuric acid. Solids are removed from this copper sulphate solution and scrap iron is added. This causes elemental copper to precipitate, which is then fused and electrolytically cleaned (see copper refining ).

Copper is also cemented with zinc ores or zinc , which creates a shiny gold surface ( crinkle gold ) .

Surface treatment

The surface of metallic workpieces is first treated with what is known as cement powder , which contains foreign metals or metal compounds. The subsequent heating connects the metal phases without the substances being melted.

Airtight containers are used for this. Smaller objects are treated in clay vessels (cement boxes), large ones in iron or clay-lined boxes (cement boxes). In the containers, the workpiece is surrounded with the cement powder and heated.

Steelmaking

Fine gold

Gold containing silver is made fine by cementation: the silver content is lowered, which increases the relative gold content ( fineness ). The gold is heated in the form of fine grains or thin sheets with iron sulfate , table salt and brick dust. This creates silver chloride , which melts and is absorbed by the brick dust, while the gold is not attacked.

Other uses

Nickel oxide is reduced to hammerable nickel by heating in a crucible lined with coal . In marine geology , cementation is responsible for the formation of sedimentary rocks . This is done with the help of cementing binding agents.

See also

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