Cementation is a method for obtaining metals from solutions of the metal ion. It is a type of
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
, in which
ion
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s are reduced to zero
valence at a solid metallic interface. A cementation step often follows
leaching.
Cementation of
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
is a common example. Copper ions in solution, often from an ore leaching process, convert to metallic copper in the presence of solid
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
. The iron oxidizes, and the copper ions are reduced through the
electron transfer
Electron transfer (ET) occurs when an electron relocates from an atom, ion, or molecule, to another such chemical entity. ET describes the mechanism by which electrons are transferred in redox reactions.
Electrochemical processes are ET reactio ...
s. The reaction is spontaneous because copper is higher on the
galvanic series
The galvanic series (or electropotential series) determines the nobility of metals and semi-metals. When two metals are submerged in an electrolyte, while also electrically connected by some external conductor, the less noble (base) will experien ...
than iron.
: Cu
2+(aq) + Fe(s) → Cu(s) + Fe
2+(aq)
Cementation was a historically useful process for the
production of copper, where the precipitated solid copper metal was recovered as flakes or powder on the surface of scrap iron.
Cementation is used industrially to recover a variety of heavy metals including
cadmium
Cadmium is a chemical element; it has chemical symbol, symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Like z ...
, and the cementation of gold by zinc in the
Merrill–Crowe process The Merrill–Crowe Process is a separation technique for removing gold from the solution obtained by the cyanide leaching of gold ores. It is an improvement of the MacArthur-Forrest process, where an additional vacuum is managed to remove air in ...
accounts for a substantial fraction of world gold production.
["Zinc cementation," R. Walton, ''Developments in Mineral Processing'', volume 15, 2005, pages 589–60]
/ref>
See also
* Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is steelmaking, removal of impurities and undesired eleme ...
* Methods of crucible steel production
* Open-hearth furnace process
References
{{DEFAULTSORT:Cementation (Metallurgy)
Metallurgical processes