Titanium is abundant in the Earth's crust, and China ranks first globally in terms of titanium resources, with proven reserves accounting for approximately 38.8% of the world's total. These resources are distributed across more than 100 mining areas in over 20 provinces and regions, primarily concentrated in the southwestern, central-southern, and northern regions of China. In particular, the vanadium-titanium magnetite deposits in the Panxi region are world-renowned for their substantial reserves, accounting for 92% of China's titanium resources, providing a solid foundation for the country's titanium industry. However, the current production process of titanium is characterized by long process cycles, high energy consumption, and severe pollution, leading to high prices and limiting its widespread use. Consequently, developing new low-cost titanium production methods is of paramount importance for accelerating China's transition from a major titanium resource country to a titanium production powerhouse.
Traditional Titanium Metallurgical Process
The traditional titanium smelting process, known as the "Kroll process," involves the reduction of titanium tetrachloride (TiCl4) with metallic sodium or magnesium to obtain metallic titanium. As the titanium is produced below its melting point, it exists in a sponge-like form, hence the name "sponge titanium." The Kroll process consists of three main stages: the preparation of titanium-rich materials, the production of TiCl4, and the reduction and distillation to produce sponge titanium.
New Titanium Metallurgical Processes
To reduce the production cost of metallic titanium, researchers have explored numerous new extraction methods, including TiCl4 electrolysis, ITP (Armstrong) process, FFC process, OS process, Pre-Reduction Process (PRP), QT process, MER process, and USTB process.
TiCl4 Electrolysis for Titanium Production
Titanium oxides and titanium chlorides can serve as raw materials for industrial titanium production. However, only titanium chloride has been used as a precursor for titanium metal production due to its ability to effectively remove oxygen and carbon impurities. Current research focuses on the preparation and purification of TiCl4, with methods such as sodium thermal reduction, oxygen reduction, hydrogen reduction, and direct electrolysis being explored.
Armstrong/ITP (International Titanium Powder) Process
Established in 1997, ITP, based in Chicago, USA, utilizes gaseous sodium to reduce TiCl4, enabling the continuous production of titanium powder. This method involves injecting TiCl4 vapor into a stream of sodium gas, generating titanium powder and NaCl, which are subsequently separated through distillation, filtration, and washing. The process boasts high product purity and environmental friendliness, but challenges remain in reducing production costs and improving product quality.
FFC Process (Cambridge Process)
Proposed in 2000 by Professor D.J. Fray and his collaborators at the University of Cambridge, the FFC process involves electrolyzing a solid titanium oxide as the cathode, graphite as the anode, and an alkaline earth metal chloride melt as the electrolyte. This method is environmentally friendly, with a short production cycle, but faces challenges such as high oxygen content in the product and process discontinuity.
OS Process
Developed by One and Suzuki in Japan, this process utilizes electrolytically obtained calcium to reduce TiO2 to metallic titanium. The process takes place in a Ca/CaO/CaCl2 melt, with titanium oxide powder placed in a cathode basket. The method promises significant cost reductions but produces titanium metal with a relatively high oxygen content.
PRP Process
Proposed by Japanese scholars, this method mixes TiO2 with fluxing agents like CaO or CaCl2, shapes the mixture, sinters it, and exposes it to calcium vapor at high temperatures to produce titanium powder. The resulting powder can achieve a purity of 99% with reduced oxygen content.
QiT Process
Developed by Quebec Iron and Titanium Inc., this process involves electrolyzing titanium slag in a molten salt environment to produce titanium metal. The process can be performed in one or two steps, depending on the titanium content and impurity levels in the slag.
MER Process
Developed by MER Corporation, this process utilizes TiO2 or rutile as the anode and a chloride mixture as the electrolyte. The anode emits a mixture of CO and CO2 gases during electrolysis, while titanium ions are reduced to metallic titanium at the cathode.
USTB Process
In 2005, Professor Zhu Hongmin and his team at University of Science and Technology Beijing proposed a novel method for the extraction of sponge titanium via molten salt electrolysis-the electrolysis of a TiO·mTC anode, a soluble solid solution of TiO2 and TiC, to produce pure titanium.
This method involves mixing carbon and titanium dioxide or titanium carbide and titanium dioxide powders in stoichiometric proportions, pressing them into a shape, and then under certain conditions, forming a TiO·mTC anode with metallic conductivity. Using a molten salt of alkali metal or alkaline earth metal halides as the electrolyte, electrolysis is performed at a specific temperature. During this process, titanium dissolves into the molten salt in the form of low-valent ions and deposits at the cathode, while the carbon and oxygen contained in the anode form gaseous carbon oxides (CO, CO2) or oxygen (O2) that are released. This method can produce high-purity titanium metal powder with oxygen content less than 300×10-6, meeting the national first-grade standard, and achieving a cathode current efficiency of up to 89%.
The notable advantages of this method include the ability to continuously perform the electrolysis process without generating anode slime, simplicity of the process, low cost, and environmental friendliness.
The extraction of metallic titanium is a significant research area in metallurgy, and the molten salt electrolysis process is considered the most promising alternative to the Kroll process for titanium metallurgy. Given the vast reserves and critical importance of titanium resources, the comprehensive utilization of vanadiferous titanomagnetite is of great significance. Examining the current research and development status of titanium extraction processes, processes using TiCl4 as a precursor generally face difficulties in cost reduction, whereas direct preparation of metallic titanium from TiO2 merits further in-depth research. If technical issues can be overcome, industrial-scale application may become feasible.
