The chloride process is used to separate

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

from its ores. The goal of the process is to win high purity

titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insoluble ...

from ores such as

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

(FeTiO₃) and rutile (TiO₂). The strategy exploits the volatility of TiCl₄, which is readily purified and converted to the dioxide. Millions of tons of TiO₂ are produced annually by this process, mainly for use as white pigments. The chloride process has largely displaced the older sulfate process, which relies on hot sulfuric acid to extract iron and other impurities from ores..

Process chemistry

In this process, the feedstock is treated at 1000 °C with

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

and

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...

gas, giving

titanium tetrachloride Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds ...

. Typical is the conversion starting from the ore

: :2 FeTiO₃ + 7 Cl₂ + 6 C → 2 TiCl₄ + 2 FeCl₃ + 6 CO The process is a variant of a

carbothermic reaction Carbothermic reactions involve the reduction of substances, often metal oxides (O^2-), using carbon as the reducing agent. These chemical reactions are usually conducted at temperatures of several hundred degrees Celsius. Such processes are applie ...

, which exploits the reducing power of carbon. Other impurities are converted to the respective chlorides as well, but most are less volatile than TiCl₄. Vanadium tetrachloride and vanadium oxytrichloride codistill with TiCl₄, but these impurities can be removed by chemical reduction. The titanium tetrachloride is purified by

distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...

. It can be subsequently oxidized in an

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

flame or plasma to give the pure titanium dioxide. :TiCl₄ + O₂ + heat → TiO₂ + 2Cl₂ In this way, chlorine is recovered for recycling.

Process engineering

The standard chloride process for titanium dioxide base material consists of the following main production units: *Oxidation *Chlorination *Condensation *Purification The following auxiliary production units are necessary: *Ore/coke storage *Off-Gas Treatment *Dust treatment Under steady state conditions the chloride process is a continuous cycle in which chlorine changes from the oxidized state to the reduced state and reverse. The oxidized form of the chlorine is molecular chlorine Cl₂, the reduced form is titanium tetrachloride (TiCl₄). The oxidizing agent is molecular oxygen (O₂), the reducing agent is coke. Both must be fed into the process. The titanium is fed into the process in form of ore together with the coke. Titanium ore is a mixture of oxides. The added O₂ leaves the process with the product TiO₂, the added coke leaves the process together with the added oxygen from the titanium ore in form of CO and CO₂. The other fed metals leave the process in form of metal chlorides.

References

External links

* *{{cite web , title= The Chloride Process from Ti-Cons , publisher= Ti-Cons Jendro, Weiland und Partner , url= http://www.ti-cons.com/TC2/index.php/en/ , access-date= 2010-06-16 Chemical processes Chlorine