Electrochemical reduction processes and extraction of titanium with different valence states in molten CaO-CaF2 slags

Abstract

Titanium is an excellent structural and functional material. At present, the production of titanium has long process cycle, high energy consumption, serious pollution and other characteristics, so the development of low-cost titanium production methods has extremely far-reaching significance. In this work, the electrochemical reduction process of Ti(IV) and Ti(II) in the CaF2-CaO melt were investigated by cyclic voltammetry and square wave voltammetry measurements at 1740 K, respectively. In the CaF2-CaO-5 wt% TiO2 melt, Ti(IV) ions were reduced to Ti by one step. One measure was taken to lower the valence state of Ti ions: Ti(IV) ions in the melt was changed to Ti(II) by adding Ti0. Ti(IV) ions were reduced in two steps: in the CaF2-CaO-5 wt% TiO2-Ti0 melt, Ti(IV) → Ti(II) and Ti(II) → Ti, respectively, and in the CaF2-CaO-5 wt% TiO, the Ti(II) ions were reduced in a single step: Ti(II) → Ti. It was found that both migration and mass transfer affected the reduction processes. In contrast to the Ti(IV) reduction to Ti process, the Ti(II) reduction to Ti process showed a higher diffusion rate. Electrolytes and electrodes were analyzed after titanium electrodeposition by XRD. It was found that there were no metal titanium was detected in the electrolyte placed close to the cathode after electrodeposition. It believed that the formed metallic Ti reacted with dissolved O2- in the melt to form TiO. The reduction process of Ti(IV) on the iron electrode was investigated, the metal Ti was reduced by alloying process, the oxidation of Ti was hindered, there was a dense structure layer of CaTiO3 outside the reduced metal Ti that prevented the ions transfer and affected the Ti(IV) ions migration process, which might be the main factor that the Ti(IV) reduction process was controlled by migration. The lower valence state of Ti in the melt promoted the formation of Ca2TiO4, which increased the ion migration rate and decreased the mass transfer rate. It was suggested that titanium or titanium alloys may be prepared by reducing the valence of Ti(IV) in minerals and altering the melt composition. It is feasible to prepare titanium and titanium alloys by MOE short process using ore as raw material.