The content of titanium in the earth’s crust is very rich. China’s titanium resources rank first in the world, with proven reserves accounting for about 38.8%, distributed in more than 100 mining areas in more than 20 provinces and regions, mainly concentrated in southwest, central and southern China. The vanadium-titanium magnetite in Panxi area is a world-famous comprehensive deposit with abundant reserves, accounting for 92% of China’s titanium resources, providing a solid resource base for China’s titanium industry. However, the characteristics of the current titanium production process such as long process cycle, high energy consumption, and serious pollution have made titanium expensive, which greatly limits the use of titanium. It can also be seen that the development of new low-cost titanium production methods has accelerated the acceleration of China ’s The transition from a large titanium resource country in the world to a powerful titanium production country is of far-reaching significance.
- Traditional titanium metallurgy process
The traditional titanium smelting process is the “Clauer method”, which uses metallic sodium or metallic magnesium to reduce titanium tetrachloride to obtain metallic titanium. Because titanium is produced below the melting point of titanium, the titanium metal produced is spongy, so it is called “sponge titanium”.
The Crawler process has three main processes: the preparation of titanium-rich materials, the preparation of titanium tetrachloride and the reduction distillation to produce sponge titanium.
Titanium-rich materials are usually prepared from ilmenite to remove iron as much as possible and enrich the titanium component; TiCl4 [i] is prepared from chlorine, which converts the titanium component from oxide to chloride, including chlorination and refining; with metal magnesium Steam reduction distillation of titanium tetrachloride, at about 900 ℃ titanium tetrachloride and magnesium steam mixed
- reaction can get sponge titanium.
But the Crawler process is discontinuous, the process is long, and there are many processes, and TiCl4 is volatile and corrosive at room temperature, which makes the production cost of titanium sponge high, limiting the application of titanium in various industries.
- New technology of titanium metallurgy
In order to reduce the production cost of titanium metal, relevant personnel have explored and studied many new methods for extracting titanium, mainly including TiCl4 electrolysis process, ITP (Armstrong) process, FFC process, OS process, pre-reduction molding process (PRP), QT process, MER Craftsmanship.
- 1. TiCl4 electrolytic metal production
Titanium oxide and titanium chloride can be used as raw materials for industrial production of titanium. But so far, only titanium chloride has been used as a precursor for the industrial production of titanium metal. This is mainly due to the strong affinity of oxygen, carbon, and carbon titanium, and the oxygen content of the product seriously affects the performance of titanium and titanium alloys. In the early days, chlorination was considered the only effective method for removing oxygen and carbon in titanium. Therefore, the industrial production of titanium metal involves the preparation and purification of TiCl4. At present, with TiCl4 as the precursor, a lot of research has been carried out at home and abroad, including sodium thermal reduction, oxygen reduction hydrogen reduction and pyrolysis reduction hydrogen reduction and direct electrolysis.
- 2. Armstrong / ITP (international Titanium Powder) process
The inventor, Armstrong, used gaseous sodium to reduce TiCl4 to achieve continuous production of titanium powder. The core technology of this method is to spray TiCl4 vapor into the sodium gas flow through an internal nozzle. The reaction occurs immediately at the nozzle. The generated NaCl and titanium powder are carried out of the reactor by the excess sodium gas flow and enter the next separation stage. After distillation, filtration and washing, metal titanium powder is obtained. The product in the pilot plant has an oxygen content of less than 0.1% and a chlorine content of (50-100) × 106. At present, ITP is optimizing the process to improve the quality of products, producing qualified titanium powder that can be directly used for rapid processing such as powder metallurgy and injection molding, and is committed to reducing the environmental impact of the titanium powder production process.
The Armstrong process is a gas reaction, and the chemical reaction bursts instantaneously, greatly reducing the reaction time and reducing the unit energy consumption; the production process is continuous, and the product is a coarse-grained powder with high purity, which can be directly used as powder metallurgy; by-product hydrolysis Sodium and chlorine can be circulated through; in addition, the process can directly produce alloys, such as Ti-6A1-4V, Ti-A1 alloy, etc. The current problem to be overcome is to use TiCl4 as the raw material, which cannot prevent the chlorination process. The process needs to be improved to meet the environmental requirements, the product quality assurance during the test is expanded, the service life of the Armstrong reactor is extended, and the number of companies using this process is reduced. The required post-investment costs, etc.
- 3.FFC process
The FFC method is also known as the Cambridge process. It was proposed by Professor D.J. Fray and his collaborators at the University of Cambridge in 2000. It is made of solid TiO? As cathode after certain treatment, graphite as anode, molten chloride of alkaline earth metal as electrolyte for molten salt electrolysis, when the applied voltage is lower than the decomposition voltage of molten salt (the working voltage in the experiment is 28 ~ 32V), the oxygen on the cathode ionizes and then enters the human electrolyte and diffuses to the anode, and generates O? At the anode or combines with carbon to generate CO? [Ii] gas is released, and pure metal titanium precipitates on the cathode. This method has caused great interest from experts and scholars in the world metallurgical industry and industry due to the conversion of the original electrochemical deoxygenation process to the electrolytic production of titanium metal using oxides as raw materials.
The advantages of the FFC method are: it does not produce chlorine gas, does not use TiCl4 and other highly corrosive chemicals that pollute the environment, and is a green process; the production cycle is short, the product is suitable for powder metallurgy forming, and casting, machining and other expensive The processing process can save a lot of production costs. However, the titanium oxide content of the sponge product is high, and the process is not continuous.
- 4.OS process
This method was proposed by One and Suzuki of Japan. Its main feature is the reduction of TiO? To metallic titanium with calcium obtained by electrolysis. In Ca / CaO / CaCl? Molten salt, the graphite crucible is used as the anode, and the cathode is made of stainless steel mesh. The TiO? Powder is directly placed in the cathode basket and voltage is applied between the two poles for constant current electrolysis. The voltage used is higher than that of CaO. The decomposition voltage is lower than the decomposition voltage of CaCl ?, Ca2 + is reduced to calcium on the cathode, and oxygen generates CO or CO2 on the anode with carbon. Due to the difference in density between TiO? And calcium, the two are not in direct contact, and TiO? Is reduced to metallic titanium by the calcium dissolved in the molten salt.
It is said that this method can greatly reduce the production cost and can be used to produce titanium powder [iii], which has similar advantages and disadvantages as the FFC process, and the titanium metal produced has a higher oxygen content.
- 5. PRP process
This method was proposed by Japanese scholar Okabe et al. It is to mix TiO? And flux CaO or CaCl? Into a desired shape and sinter it at 800 ℃. The sintered solid sample is placed in a stainless steel container and placed in molten Ca Above the metal, Ca vapor reacts with TiO? To form Ti and CaO in the range of 800 ~ 1000 ℃. After the product is pickled, titanium powder with a purity of 99% can be obtained, and the oxygen content can be reduced to 2800 × 106.
- 6.QiT process
Canada’s Quebec Ferrotitanium Company is a world-famous titanium slag production company. The company applied for the patent of titanium slag electrolysis to reduce metal titanium in 2003. The product of this process is melt titanium, which can be cast into ingots and billets. With different electrolytes, anodes and operating methods, there are several different conceptual designs. But the basic conceptual design includes molten salt electrolyte, such as CaF? [Iv] into the reaction chamber, the molten titanium slag is introduced into the reaction chamber and the subsequent electrolysis process.
The solid electrolyte, slag and metal form a lining layer to protect the interior and bottom of the electrolytic cell. The design of the lining layer is the key, which solves the problem of product pollution. This technology has been used for smelting ilmenite in large electric arc furnaces. Electrolysis adopts one-step method or two-step method. In the two-step method, the first step of electrolysis is to purify titanium slag to remove impurities such as Fe, Cr, Mn, and V. The droplets generated on the electrolyte / slag cathode interface settle to the bottom of the reaction chamber due to gravity. The metal mixture accumulates to a certain degree and is discharged through the liquid discharge port at the bottom, and then enters the second step. At a higher temperature, the slag produced in the first step is electrolytically reduced to obtain metallic titanium.
If the reaction is only one step, titanium slag needs to use Sorel [v] slag with high Ti grade or higher grade USG slag, and the total Fe content must be less than 14% (calculated as FeO), otherwise the two-step method must be used . Since many low-cost alloys used in automobiles and other markets contain a certain amount of iron, the inclusion of iron is not a problem. If other metal oxides are added to the melt, the alloy can be obtained.
For example, Ti-6Al-4V alloy can be obtained by adding alumina and vanadium pentoxide. As with other extraction methods, the problems to be solved by this process are product composition control, product quality testing, and cost analysis.
- 7. MER process
This is a brand-new electrolytic reduction process developed by MER. This process uses TiO? Or rutile and carbon as the anode, and a mixture of chlorides as the electrolyte. The anode technology was used for the electrolytic extraction of magnesium and aluminum. TiO? Or rutile powder and carbon-containing raw materials and binders are stirred evenly, then molded into electrodes, and then heat-treated to form composite anodes. During electrolysis, CO / CO? Mixed gas is released on the anode, and the dissolved Ti3 + ions are discharged on the cathode to be reduced to metallic titanium. The method can use ilmenite as raw material to produce ilmenite alloy.
- 8.USTB process
A method of anode electrolysis of TiO and TiC soluble solid solution to produce pure titanium.
It is made by mixing carbon and titanium dioxide or titanium carbide and titanium dioxide powder according to the chemical reaction metering and compression. Under certain conditions, a metal conductive TiO · mTC anode is made, and then the halide molten salt of alkali metal or alkaline earth metal is used for electrolysis Liquid, electrolyzed at a certain temperature, titanium is dissolved into molten salt in the form of low-valent ions, and deposited at the cathode, the carbon and oxygen contained in the anode form carbon oxide gas CO, CO Or O Is released, this method can be obtained High-purity metal titanium powder, which contains oxygen <300 × 106 and carbon <700 × 10, reaching the national first-class standard, and the cathode current efficiency can reach 89%.
The outstanding advantage of this method is that the electrolysis process can be carried out continuously, and no anode slime is produced, the process is simple, the cost is low, and there is no pollution.
The extraction of titanium metal is an important research field in the metallurgical industry. The molten salt electrolysis process is considered to be the most promising titanium metallurgy process to replace Crower. As a huge and very important titanium resource, the comprehensive utilization of vanadium-titanium magnetite is of great significance. Throughout the current research and development status of titanium extraction process, the extraction process using TiCl4 as a precursor is generally difficult to reduce costs, and the direct preparation of titanium metal using TiO? As a raw material is worthy of further in-depth research. If the technical problems can be broken, there is hope to achieve Industrial application.