Phase Transformations and Deoxidation Kinetics during the Electrochemical Reduction of TiO₂ in Molten CaCl₂

Abstract

There are still some different understandings about deoxidization process from TiO 2 to Ti by FFC Cambridge process. Herein, an investigation was carried out on the phase transformations and deoxidation kinetics of the electrochemical reduction of TiO 2 to Ti in molten CaCl 2. The reaction goes through four different stages involving several phase transformations. The first stage is the deoxidation of TiO 2 with the formation of CaO and CaTiO 3. At this stage, Cl 2 is forcibly released from the anode because of the consumption of Ca 2+ on the cathode, balanced with Cl ¹ at the anode. The second stage is the deoxidation of CaTiO 3 and titanium suboxides. These two stages take 45% of the entire deoxidation time from TiO 2 to Ti [O]. The third stage is the deoxidation of titanium suboxides. This stage takes about 55% of the total time. The final stage is further deoxidation of TiO solid solution by electrochemical reduction or by calcium thermal reduction. There are no obvious kinetic barriers in the formation of CaTiO 3 , but the rate of deoxidation of titanium suboxides and CaTiO 3 is relatively slow. Therefore, the limiting step from TiO 2 to Ti by the FFC process in molten CaCl 2 is deoxidation of titanium oxides and the interphase of CaTiO 3 .

The Electrolytic Reduction of MoO3 in CaCl2-NaCl Molten Salt

“…Because of its environmental friendliness and adaptability to a variety of metals, the process has been widely concerned once it was proposed, and has gradually developed into the preparation of various metals and alloys. 5,[10][11][12][13][14][15][16] At present, the research of electro-deoxidation in molten salt mainly focused on transition metal oxides such as TiO 2 , 12,17 ZrO 2 , 18 HfO 2 , 19 Nb 2 O 5 , 20 Ta 2 O 5 , 21 Cr 2 O 3 22 and NiO 23 and so on. Rare earth oxides, including CeO 2 , 24 Gd 2 O 3 , 25 Tb 4 O 7 26 and Dy 2 O 3 27 etc., were also investigated.…”

Electrolytic Reduction of ZnO in the CaCl2-NaCl Molten Salt

“…[1][2][3][4][5][6][7][8] Direct reduction of metal oxides, a novel technology proposed by Chen 9 et al named as FFC Cambridge process, has been adopted to prepare varied metals from oxides. [10][11][12][13] Compared with conventional metallurgical routes, this technology is relatively simple and easy to operate. Besides, the process involved is more economical and environmentally friendly.…”

“…1,4,14 Therefore, the research on developing and optimizing direct reduction of metal oxides technology for metal preparation is essential. At present, many metal oxides, such as TiO 2 , 11,15 ZrO 2 , 16 HfO 2 , 17 Nb 2 O 5 , 18 Ta 2 O 5 , 4 Cr 2 O 3 , 19 MoO 3 , 20 and NiO, 21 etc., have been used as raw materials by this method. Meanwhile, various molten salt systems, such as LiCl, LiCl-Li 2 O, CaCl 2 , CaCl 2 -NaCl, and LiCl-KCl-CaCl 2 , have been used as the electrolytes for the electrolytic reduction process.…”

Electrolytic Reduction of U3O8 and U3O8-MoO3 in CaCl2-NaCl Molten Salt

“…Since the direct reduction of TiO 2 to titanium metal in an electrolysis cell was reported by Chen et al, 1 the preparation of varied metals and alloys by electro-deoxidation of oxides (FFC-Cambridge process) has been extensively studied in the past two decades. [2][3][4][5][6][7][8] Compared with the conventional metallurgical routes, this technology is a much easier, more economical and more environmentally friendly process. 2,9 At present, the reprocessing of spent nuclear fuel (SNF) is still one of the great challenges to the nuclear industry.…”