Cementation is a type of precipitation, a heterogeneous process in which ions are reduced to zero valence at a solid metallic interface.
The iron oxidizes, and the copper ions are reduced through the transfer of electrons.
The reaction is spontaneous because copper is higher on the galvanic series than iron.
This 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.
[1] Cementation is used industrially to recover a variety of heavy metals including cadmium,[2] and the cementation of gold by zinc in the Merrill-Crowe process accounts for a substantial fraction of world gold production.