Electrochemical production of titanium by using titanium oxycarbide anodes in molten salts
MetadataShow full item record
New production routes for the production of titanium are strongly desired to reduce the costs and thereby increase the utilisation of titanium. In the present work the possibility to directly reduce and purify titanium containing slag into titanium oxycarbide which then is oxidised into titanium ions, and subsequently reduced to metal in an electrochemical process is explored as an alternative to the current Kroll process. The reduction of pure titanium dioxide by carbothermic reduction at 1500°C into titanium oxycarbide was successful. Anodes were pressed from the titanium oxycar-bide powder, and sintered at 1650°C. Studies of the anodes behaviour in molten NaCl-KCl, and NaCl-Na3AlF6 was performed. In the NaCl-KCl the anodes dissolved into Ti(III) and CO-gas, the Ti(III) underwent a two step reduction at the cathode via Ti(II) to form Ti(0). The cathodically formed titanium had poor adherence to the cathode and a very ¯ne grain size which gave it a too high oxygen content after washing. In NaCl-Na3AlF6 Ti(IV) and Ti(III) were stabilised due to formation of hexa°uoro complexes, while Ti(II) was destabilised. The dissolved Ti(III) underwent a direct reduction to Ti(0). The metal did not adhere to the cathode any better than in chloride melt. It was more di±cult to recover reduced metal from the melt due to the fact that it was not soluble in water. The anode underwent the same chemical reaction in molten NaCl-Na3AlF6, but the stability of the Ti(IV) increased, and the oxidation potential for Ti(III) became cathodic of the anode reaction, hence all dissolved Ti(III) will oxidise to Ti(IV). A lot of black precipitates were also found in the melt after electrolysis, it was probably a result of formation of unsoluble titanium(IV) oxy°uorocomplexes. Liquid alloying cathodes of Bi, Sn and Zn were tested in an attempt to omit the difficulties with poor adherence of the deposited metal at the cathode. The liquid titanium was successfully alloyed into liquid Bi and Sn, but was found in concentrated areas after cooling.