Patent Application
20240240344
The present application belongs to the field of titanium metallurgy, and specifically relates to a method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide.
Metallic titanium has a high specific strength and corrosion resistance, and is widely used in fields such as aerospace, chemicals, energy, and medical care.
Minerals containing titanium mainly include rutile (TiO2) and ilmenite (FeTiO3). Due to a strong affinity of titanium with oxygen, carbon, and other elements, it is very difficult to extract titanium. Ilmenite needs to be treated first to obtain a high-titanium slag (a main component of the slag is titanium dioxide TiO2). Titanium in rutile or high-titanium slag is then converted into titanium tetrachloride TiCl4 through carbochlorination, then impurities are removed through rectification to obtain pure TiCl4, and the pure TiCl4 is then thermally reduced by a metal to obtain titanium sponge. Currently, there are mainly two thermal reduction methods: Kroll method (magnesium reduction) and Hunter method (sodium reduction), where the Kroll method is the mainstream industrially.
The Kroll method involves a long process flow, a large number of procedures, discontinuous production, and a long cycle, which makes a cost remain high. Therefore, the inventor Kroll himself believed that the magnesium thermal reduction method would soon be replaced by electrolysis.
In fact, researchers have been putting a lot of effort into investigation of electrolysis. However, the electrolysis of any of TiO2, K2TiF4, and TiCl4 encounters insurmountable problems. Due to a factor such as high impurity content in a product, low current efficiency, heavy corrosion, complicated device structure, deposition of titanium dendrites and difficult separation of titanium dendrites from a molten salt, or high environmental cost, the electrolysis has so far not been industrially used.
In 2000, the University of Cambridge introduced the Fray-Farthing-Chen (FFC) method. Unlike the idea of the traditional electrolysis method, a medium used in the FFC method is a calcium chloride molten salt, rather than a fluoride molten salt; and thus the FFC method is more eco-friendly than the traditional electrolysis method. The FFC method does not pursue the dissolution of a titanium compound in the molten salt, but adopts a titanium dioxide pellet as a cathode. The FFC method also has a different working principle from the traditional electrolysis method. In the FFC method, titanium is not precipitated from the molten salt, but based on the characteristics of valve metal oxides (unilateral conductivity: these valve metal oxides cannot conduct electricity as an anode, but can conduct electricity as a cathode) and the cathodic polarization, titanium ions in the cathode are reduced into metallic titanium in situ. In the FFC method, during reduction, oxygen anions leave the cathode and enter a melt, migrate to the anode under an action of a Coulomb force, and are oxidized into oxygen (when a carbon anode is used, oxygen further reacts with carbon to produce CO and CO2). However, the titanium dioxide pellet cathode is gradually reduced from outside to inside, and during this process, the diffusion of oxygen ions are increasingly difficult, resulting in small cathode current density and high overvoltage. The preparation of titanium with a low oxygen content requires severe overelectrolysis, resulting in low current efficiency. Moreover, impurities such as iron and carbon can easily enter a product.
The OS method of the Kyoto University in Japan also adopts a calcium chloride electrolyte. In the OS method, calcium ions are reduced into calcium on a cathode titanium mesh; and titanium dioxide is no longer pressed or sintered, but is continuously added in molten salt as the form of powder, which is reduced into a titanium powder by calcium near the cathode. Compared with the FFC method, the dispersed granular cathode titanium dioxide is more conducive to the diffusion and migration of oxygen ions than the solid titanium dioxide pellet. However, metallic calcium dissolved in CaCl2 increases the electronic conductivity of the molten salt and causes the reduction of current efficiency. Moreover, a produced metal is mixed with a molten salt and can hardly be separated; a large amount of the molten salt is required; and impurities such as iron and carbon can also easily enter the product.
In the EMR/MSE method proposed by Japan, the reduction of TiO2 is conducted in stages. In the EMR/MSE method, a Ca—Ni alloy is first prepared through molten salt electrolysis, and then the Ca—Ni alloy is used as a reducing agent to reduce TiO2 into metallic titanium. Given that titanium is easily contaminated due to alloying with nickel, TiO2 is immersed in a molten salt in a hanging basket to avoid direct contact with the Ca—Ni alloy. The EMR/MSE method can operate semi-continuously, but the metallic titanium, the Ca—Ni alloy, and the molten salt coexist, resulting in difficult product separation and complicated equipment and process.
A liquid metal such as bismuth and zinc is also used as a cathode for molten salt electrolysis of titanium dioxide, where a Bi—Ti or Zn—Ti alloy is first produced. However, it is reported that the obtained bismuth alloy includes only 0.6 at % to 2.2 at % of titanium, but includes 17.9 at % to 34.9 at % of calcium. When liquid zinc is used, it is reported that the titanium content at the cathode can reach about 20%. However, the obtained alloys also need to be treated by electrolysis or distillation to obtain metallic titanium.
Therefore, it can be seen that the existing processes for electrolysis of titanium dioxide to produce titanium have various problems to be overcome, and thus the Kroll method is still the main method industrially. In order to obtain qualified metallic titanium, the above methods have very strict purity requirements for a titanium dioxide raw material used.
An objective of the present application is to provide a method for preparing metallic titanium by molten salt electrolysis with titanium dioxide as a raw material. The method has advantages such as low requirements for the titanium dioxide raw material, simple process flow, low energy consumption, environmental friendliness, and direct acquisition of high-purity metallic titanium.
To achieve the above objective, the present application adopts the following technical solutions:
With respect to the method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide according to the specific implementation of the present application, the anodic molten salt electrolyte and the cathodic molten salt electrolyte both are a halide molten salt. Preferably, the anodic molten salt electrolyte includes one or more selected from the group consisting of CaCl2, BaCl2, LiCl, NaCl, KCl, CsCl, LiF, NaF, and KF. The cathodic molten salt electrolyte includes one or more selected from the group consisting of LiCl, NaCl, KCl, CaCl2, and MgCl2, and TiCl2 and/or TiCl3. Electrolytes in the cathode chamber and the anode chamber of the present application both are halides, or common halide, which have specified solubility for low-valent titanium. Given an effect on the precipitation of titanium impurities at the cathode, only chlorides are selected as an electrolyte in the cathode chamber.
With respect to the method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide according to the specific implementation of the present application, the anode is graphite, and the cathode is a stainless steel, tungsten, or molybdenum cathode. Graphite as anode can react with oxygen ions in the anodic molten salt electrolyte to produce CO or CO2; and the cathode is a high-temperature-resistant conductor.
With respect to the method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide according to the specific implementation of the present application, the liquid alloy is an alloy produced from a solute metal Ti and a matrix metal. The matrix metal has a lower metal activity than the titanium, and is mixed with the titanium to produce an alloy with a low melting point of lower than 1,000° C.; and specifically, the matrix metal can be one or more selected from the group consisting of Cu, Sn, Sb, Zn, Pb, Bi, and Ni.
At work, solid titanium dioxide is added to the anode chamber; an area of the cathode is 1 to 20 times of an area of the anode; and under continuous operating conditions, electrolysis is conducted at an anode current density of 0.05 A/cm2 to 2.0 A/cm2 and a temperature of 400° C. to 1,000° C. CO and CO2 gases are precipitated evolve at the anode, and the metallic titanium product is precipitated at the cathode. Further, in order to improve a flatness of titanium precipitated at the cathode, a reverse current accounting for 1% to 5% of a total electrolysis time is increased during the electrolysis to homogenize dense titanium precipitated at the cathode.
During the electrolysis, the titanium dioxide in the anode chamber is reduced into titanium atoms at an interface between the anodic molten salt electrolyte and the liquid alloy, and dissolved in the liquid alloy by contacting the liquid alloy. Oxygen ions originally binding to titanium move to the anode under driving by an electric field, then lose electrons and are oxidized into zero-valent oxygen, and react with the anode to produce CO and CO2, which escape. Moreover, titanium atoms in the liquid alloy at a side of the cathode chamber are oxidized into titanium ions at the interface between the liquid alloy and the cathodic molten salt electrolyte and enter the cathodic molten salt electrolyte, then move to the cathode under driving of an electric field, and acquire electrons and are reduced into titanium atoms to produce the metallic titanium product. During a titanium reduction process in the anode chamber, metals more active than metallic titanium are difficult to enter the liquid alloy; and during a titanium oxidation process in the cathode chamber, metals more inert than metallic titanium are difficult to enter the cathodic molten salt electrolyte, such that a high-purity metallic titanium product is finally obtained at the cathode.
The present application has the following beneficial effects:
To make the objectives, technical solutions, and advantages of the present application clearly, the technical solutions of the present application will be described in detail below. Apparently, the described examples are some rather than all of the examples of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the examples of the present application without creative efforts should fall within the protection scope of the present application.
The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide in the following examples of the present application is implemented with an electrolytic cell shown in
Anodic molten salt electrolyte: 200 g of CaCl2 was weighed. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 7.8 wt % low-valent titanium chloride (TiCl2: TiCl3: 4:1) was added. 400 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 73:16:11.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm2 (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h;
Anodic molten salt electrolyte: CaCl2 and NaCl were mixed according to a mass ratio of 54:46 to obtain 2 kg of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 2 kg of a mixture, and then 8.7 wt % low-valent titanium chloride (TiCl2: TiCl3: 5:1) was added. 4 kg of a metal alloy was prepared from Sn and Ti according to a mass ratio of 90:10.
The metal alloy was placed in the electrolytic cell and heated to 900° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 100 mA/cm2 (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 12 h;
Anodic molten salt electrolyte: CaCl2 and KCl were mixed according to a mass ratio of 54:46 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 11.3 wt % low-valent titanium chloride (TiCl2) was added. 4,000 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 23:74.5:2.5.
The metal alloy was placed in the electrolytic cell and heated to 700° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm2 (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h;
Anodic molten salt electrolyte: 200 g of CaCl2 was weighed. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 10.6 wt % low-valent titanium chloride (TiCl3) was added. 400 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 73:16:11.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm2 (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h and then stopped.
The stainless steel cathode was taken out. A corundum tube wrapped with a metal W rod was connected to the liquid metal; tungsten at a top of the corundum tube was allowed to be in contact with the liquid metal, and tungsten at a bottom of the corundum tube was connected to a power supply; the electrode of the anode chamber was connected to an anode of the power supply, and the W rod was connected to a cathode of the power supply; and a current density was controlled at 50 mA/cm2, titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h and then stopped.
With a graphite electrode as an anode and a stainless steel plate as a cathode, while titanium dioxide was added at a uniform rate to the anode chamber, an electric field was applied, a current density was controlled at 50 mA/cm2, and electrolysis was conducted for 24 h and then stopped.
The cathode electrode was taken out and weighed to obtain 84.4 g of metallic titanium.
Anodic molten salt electrolyte: CaCl2 and BaCl2 were mixed according to a mass ratio of 35:65 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: 200 g of NaCl was weighed, and then 9.3 wt % low-valent titanium chloride (TiCl2: TiCl3: 1:1) was added. 400 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 73:16:11.
The metal alloy was placed in the electrolytic cell and heated to 1000° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 2,000 mA/cm2 (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 1 h and then stopped.
The stainless steel cathode was taken out. A corundum tube wrapped with a metal W rod was connected to the liquid metal; tungsten at a top of the corundum tube was allowed to be in contact with the liquid metal, and tungsten at a bottom of the corundum tube was connected to a power supply; the electrode of the anode chamber was connected to an anode of the power supply, and the W rod was connected to a cathode of the power supply; and a current density was controlled at 2,000 mA/cm2, titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 1 h and then stopped.
With a graphite electrode as an anode and a stainless steel plate as a cathode, while titanium dioxide was added slowly to the anode chamber, an electric field was applied, a current density was controlled at 2,000 mA/cm2, and electrolysis was conducted for 1 h and then stopped.
The cathode electrode was taken out and weighed to obtain 60.3 g of metallic titanium.
Anodic molten salt electrolyte: CaCl2, LiCl, and NaCl were mixed according to a mass ratio of 8:1:1 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 8.5 wt % low-valent titanium chloride (TiCl2: TiCl3: 3:1) was added. 400 g of a metal alloy was prepared from Cu and Ti according to a mass ratio of 3:1.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 1,000 mA/cm2 (an area of the cathode was 10 times an area of the anode), and electrolysis was conducted for 2 h;
Anodic molten salt electrolyte: CaCl2, LiCl, and NaCl were mixed according to a mass ratio of 8:1:1 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 8 wt % low-valent titanium chloride (TiCl2) was added. 1,000 g of a metal alloy was prepared from Sb and Ti according to a mass ratio of 96:4.
The metal alloy was placed in the electrolytic cell and heated to 900° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While a high-titanium slag powder (TiO2>94%) was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm2 (an area of the cathode was 20 times an area of the anode), and electrolysis was conducted for 24 h, where during the electrolysis, a reverse current of 1 min was increased every 29 min;
Anodic molten salt electrolyte: CaCl2 and LiCl were mixed according to a mass ratio of 54:46 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 11.3 wt % low-valent titanium chloride (TiCl2) was added. 4,000 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 23:74.5:2.5.
The metal alloy was placed in the electrolytic cell and heated to 700° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm2 (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h;
Anodic molten salt electrolyte: LiCl and KCl were mixed according to a mass ratio of 45:55 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: LiCl and KCl were mixed according to a mass ratio of 45:55 to obtain 200 g of a mixture, and then 2.3 wt % low-valent titanium chloride (TiCl2) was added. 4,000 g of a metal alloy was prepared from Sn and Ti according to a mass ratio of 99.7:0.3.
The metal alloy was placed in the electrolytic cell and heated to 400° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and tungsten was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 0.05 A/cm2 (an area of the cathode was 20 times an area of the anode), and electrolysis was conducted for 24 h;
Anodic molten salt electrolyte: 200 g of CaCl2 was weighed. Cathodic molten salt electrolyte: NaCl, KCl, TiCl2, and TiCl3 were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 7.8 wt % low-valent titanium chloride (TiCl2: TiCl3: 4:1) was added. 400 g of a metal alloy was prepared from Cu and Sn according to a mass ratio of 3:1.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, the same current density as in the examples was controlled (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h.
A metallic titanium with high tin contents was produced at the cathode.
The above are merely specific implementations of the present application, but are not intended to limit the protection scope of the present application. Any variation or replacement readily conceived by a person skilled in the art within the technical scope disclosed in the present application shall fall within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110499876.5 | May 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/088122 | 4/21/2022 | WO |
