TRANSACTION PAPER

Titanium production via metallothermic reduction of TiCl₄in molten salt: Problems and products

D.S. van Vuuren^I; S.J. Oosthuizen^I; M.D. Heydenrych^II

^IMaterials Science and Manufacturing, CSIR, Pretoria
^IIDepartment of Chemical Engineering, University of Pretoria

SYNOPSIS

Industrial production of titanium occurs via the batch-wise reduction of titanium tetrachloride (TiCl₄) 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 TiCl₄ 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 TiCl₄ and the reducing metal can occur directly, when TiCl₄ 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 TiCl₄ to react at the outlet of the feed port, rapidly causing blockages of the TiCl₄ 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 TiCl₄ feed line, e.g. mechanical removal, sonic velocities, dilution of the TiCl₄ 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.

Keywords: Titanium dioxide, titanium nitride, carbo-thermic reduction, ilmenite, slag, tunnel kiln, residence time

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