Calciothermic reactions are metallothermic reduction reactions (more generally, thermic chemical reactions) which use calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 metal as the reducing agent

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 at high temperature.

Calcium is one of the most potent reducing agents available, usually drawn as the strongest oxidic reductant in Ellingham diagram

Ellingham diagram

An Ellingham diagram is a graph showing the temperature dependence of the stability for compounds. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulphides. These diagrams were first constructed by Harold Ellingham in 1944...

s, though the lanthanides best it in this respect in oxide processes. On the other hand this trend does not continue to other compounds that are non-oxides, and for instance lanthanum

Lanthanum

Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...

 is produced by the calciothermic reduction of the chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

, calcium being a more potent reducing agent than lanthanum involving chlorides.

Calciothermic processes are used in the extraction of metals such as uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

, zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...

, and thorium

Thorium

Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 from oxide ore

Ore

An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

s.

An interesting way of performing calciothermic reductions is by in-situ generated metallic calcium, dissolved in molten calcium chloride, as shown in the FFC Cambridge Process

FFC Cambridge Process

The FFC Cambridge Process is an electrochemical method in which solid metal compounds, particularly oxides, are cathodically reduced to the respective metals or alloys in molten salts. It is thought that this process will eventually be capable of producing metals or alloys more efficiently than...

.