Cementation is a heterogeneous process in which ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s are reduced to zero valence

Valence (chemistry)

In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...

 at a solid metallic interface. The process is often used to refine leach

Leaching (metallurgy)

Leaching is a widely used extractive metallurgy technique which converts metals into soluble salts in aqueous media. Compared to pyrometallurgical operations, leaching is easier to perform and much less harmful, because no gaseous pollution occurs...

solutions.

Cementation of copper is a common example. Copper ions in solution, often from a ore leaching process, are precipitated out of solution in the presence on solid iron. The iron oxidizes, and the copper ions are reduced through the transfer of electrons.