Titanium production via metallothermic reduction of TiCl sub(4) in molten salt: problems and products

Industrial production of titanium occurs via the batch-wise reduction of titanium tetrachloride (TiCl sub(4)) with a reducing metal, being magnesium in the Kroll process, or sodium in the Hunter process. In the search for low cost titanium, the CSIR is developing a continuous process to produce titanium powder directly via metallothermic reduction of TiCl sub(4) in molten salt, dubbed the CSIR-Ti process. The move to a continuous process has been attempted by a number of organizations, but was until now always met with failure, due in no small part to challenges inherent in the process chemistry. The reaction between TiCl sub(4) and the reducing metal can occur directly, when TiCl sub(4) or any titanium sub-chlorides present, comes into contact with suspended or dissolved reducing metal. The reaction can also occur indirectly, without any physical contact between the reacting species, via an electronically mediated mechanism. The reaction mechanism via electronic mediation can cause TiCl sub(4) to react at the outlet of the feed port, rapidly causing blockages of the TiCl sub(4) feed line. The electrical conductivity of the metal reactor can also cause the electronically mediated reaction to favour the formation of titanium sponge on the reactor walls and internals, rather than titanium powder. Various methods were investigated to overcome the problem of blockages in the TiCl sub(4) feed line, e.g. mechanical removal, sonic velocities, dilution of the TiCl sub(4) and the use of ceramic feed lines. This article discusses problems experienced with the continuous feeding of reagents, and various methods attempted are shown and discussed. Information is also given on the morphology, chemical composition and suitability of the final titanium powder for powder metallurgical application as presently produced by the CSIR-Ti process.